Umtsrns 201 wcdma theory

WCDMATheory
Version1.00
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Date Revision No. Serial No. Reason for Revision
7/30/2009 R1.0 sjzlyyyyxxxx First edition

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Contents
About this Manual.........................................................................i
Purpose........................................................................................ i
Intended Audience ....................................................................... i
Prerequisite Skill and Knowledge .................................................. i
What is in This Manual.................................................................. i
Related Documents ......................................................................ii
Conventions .................................................................................ii
How to Get in Touch....................................................................iii
Chapter 1........................................................................................5
Key Technologies.........................................................................5
RAKE Receiver...............................................................5
Power Control................................................................7
Purpose of Power Control in WCDMA............................................7
Power Control Types in WCDMA...................................................8
Open Loop Power Control ............................................................ 8
Close Loop Power Control............................................................ 9
Handover......................................................................9
Mobility.......................................................................................9
Handover Types in WCDMA .......................................................10
Softer Handover........................................................................10
Soft Handover...........................................................................11
Hard Handover..........................................................................12
Handover Procedure..................................................................12
Admission Control ........................................................ 16
Measurement Related to Admission Control ............................... 17
Load Control/Congestion Control..................................... 18
AMR .......................................................................... 19
Chapter 2.....................................................................................21
Interface and Protocol............................................................21

Overview.................................................................... 21
UTRAN Common Protocol Model ................................................ 21
The Radio Interface Protocol Reference Model............................ 24
UTRAN Protocol Reference Model............................................... 25
Access Layer and Non-access Layer........................................... 26
Main Protocol Function .................................................. 26
Medium Access Control (MAC) Protocol...................................... 26
Radio Link Control (RLC) Protocol.............................................. 27
Signalling Transport (SCCP) ...................................................... 27
IP Transport for User Data (GTP-U)........................................... 28
Radio Access Network Application Protocol(RANAP) ................... 28
Radio Network Subsystem Application Protocol(RNSAP)............. 28
Node B Application Protocol(NBAP)............................................ 28
Radio Resource Control (RRC) Protocol...................................... 29
Packet Data Convergence Protocol(PDCP).................................. 30
Broadcast Multicast Control(BMC).............................................. 30
UTRAN Frame Protocols(FP) ...................................................... 30
Chapter 3 ....................................................................................31
Channel Structure and Function..........................................31
Overview.................................................................... 31
Channel Type............................................................................ 31
Channel Mapping ...................................................................... 32
Logical Channel ........................................................... 35
Transport Channel ....................................................... 35
Physical Channel.......................................................... 37
Uplink Physical Channel............................................................. 37
Downlink Physical Channel ........................................................ 42
Physical Layer Procedure ............................................... 52
Cell search procedure................................................................ 52
Random Access Procedure......................................................... 53
Chapter 4 ....................................................................................57
Network Transport...................................................................57
Overview.................................................................... 57
Asynchronous Transfer Mode in UMTS ............................. 58
Basic Configuration of ATM........................................................ 59
ATM Adaptation Layer (AAL)...................................................... 61

AAL2.........................................................................................63
AAL5.........................................................................................64
QoS Classes Under 3GPP ...........................................................65
ATM Service Class .....................................................................66
IP Transport in UMTS.................................................... 67
Chapter 5.....................................................................................71
Procedure Examples................................................................71
Elementary Procedures ................................................. 71
Paging.......................................................................................73
RRC Connection Setup............................................................... 75
Transaction Reasoning............................................................... 77
Authentication and Security Control...........................................78
Transaction Setup with Radio Access Bearer (RAB) Allocation.....79
Transaction...............................................................................81
Transaction Clearing and RAB Release .......................................82
RRC Connection Release............................................................85
Chapter 6.....................................................................................87
WCDMA Evolved........................................................................87
WCDMA Evolved Overview ............................................. 87
HSDPA ....................................................................... 87
The Concept of HSDPA ..............................................................87
Shared channel transmission.....................................................88
Higher-order modulation ...........................................................89
Short transmission time interval (TTI) .......................................90
Fast link adaptation...................................................................90
Fast scheduling .........................................................................91
Fast hybrid automatic-repeat-request (ARQ)..............................92
Figures .........................................................................................95
Tables...........................................................................................99

Confidential and Proprietary Information of ZTE CORPORATION i
About this Manual
Purpose
This Manual provides WCDMA theory introduction.
Readers can get an overall understanding of WCDMA.
Intended Audience
This document is intended for engineers and technicians who
perform operation activities on the ZXWR RNS(RNC and Node B
family) equipment.
Prerequisite Skill and Knowledge
To use this document effectively, users should have a general
understanding of wireless telecommunications technology.
Familiarity with the following is helpful:
 Mobile communication knowledge
 Computer operation ability
What is in This Manual
This Manual contains the following chapters:
TAB L E 1 CH APTER SU MMAR Y
Chapter Summary
Chapter 1 Key
Technologies
Introduces the key technologies in
WCDMA, including RAKE receiver, power
control, handover, admission control, load
control/congestion control and AMR.
Chapter 2 Interface and
Protocol
Introduces WCDMA interface and protocol,
including protocol model, main protocol
function.
Chapter 3 Channel Introduces channel types, channel

WCDMA Theory
ii Confidential and Proprietary Information of ZTE CORPORATION
Chapter Summary
Structure and Function mapping, channel frame structure and
function.
Chapter 4 Network
Transport
Introduces ATM and IP transport in
WCDMA network.
Chapter 5 Procedure
Examples
Introduces WCDMA elementary procedure.
Chapter 6 WCDMA
Evolved
Introduces HSDPA technologies mainly.
Figures Provides figure list in this manual.
Tables Provides table list in this manual.
Related Documents
The following document is related to this manual:
 WCDMA Basics
Conventions
ZTE documents employ the following typographical conventions.
TAB L E 2 TYPOGR APH I C AL CON VEN TI ON S
Typeface Meaning
Italics References to other Manuals and documents.
“Quotes” Links on screens.
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and company name.
Constant width Text that you type, program code, files and
directory names, and function names.
[ ] Optional parameters.
{ } Mandatory parameters.
| Select one of the parameters that are delimited
by it.
Note: Provides additional information about a
certain topic.
Checkpoint: Indicates that a particular step needs
to be checked before proceeding further.
Tip: Indicates a suggestion or hint to make things
easier or more productive for the reader.
Typographical
Conventions

About this Manual
Confidential and Proprietary Information of ZTE CORPORATION iii
TAB L E 3 M OU SE OPER ATI ON CON VEN TI ON S
Typeface Meaning
Click Refers to clicking the primary mouse button (usually
the left mouse button) once.
Double-click Refers to quickly clicking the primary mouse button
(usually the left mouse button) twice.
Right-click Refers to clicking the secondary mouse button
(usually the right mouse button) once.
Drag Refers to pressing and holding a mouse button and
moving the mouse.
How to Get in Touch
The following sections provide information on how to obtain
support for the documentation and the software.
If you have problems, questions, comments, or suggestions
regarding your product, contact us by e-mail at
support@zte.com.cn. You can also call our customer support
center at (86) 755 26771900 and (86) 800-9830-9830.
ZTE welcomes your comments and suggestions on the quality
and usefulness of this document. For further questions,
comments, or suggestions on the documentation, you can
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browse our website at http://support.zte.com.cn, which contains
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Mouse
Operation
Conventions
Customer
Support
Documentation
Support

WCDMA Theory
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Confidential and Proprietary Information of ZTE CORPORATION 5
C h a p t e r 1
Key Technologies
RAKE Receiver
Since multipath signals contain useful information, CDMA
receivers improve the S/N of the received signals by combining
multipath signals. What a RAKE receiver does is to receive the
various channels of signals from multipath signals through
multiple related detectors, and then combine them. The RAKE
receiver is a classical diversity receiver specially designed for the
CDMA system. Its theoretical basis is that when the propagation
delay exceeds one chip code cycle, multipath signals are actually
seen to be mutually irrelevant.
RAKE reception separates and combines multipath signals.
Different from the IS-95 A, WCDMA has three times of multipath
resolving power. In addition, in a WCDMA system, the pilot
information sent by the user can be used for coherent
combination on the reverse link. The theoretical analysis of
WCDMA shows that if the reverse link uses 8-path RAKE
reception, over 75% signal energies are used. The suppression
of the RAKE reception for multiple access interference depends
on the correlation between the different user characteristic
codes.
Maximal ratio RAKE combining of symbols is shown as Figure 1.

WCDMA Theory
6 Confidential and Proprietary Information of ZTE CORPORATION
FI GU R E 1 M AXI MAL R ATI O “RAKE” C OMB I N I N G OF SYMB OL S
Channel can rotate the signal to any phase and to any
amplitude.
QPSK symbols carry information in phase.
Energy splitted to many finger -> combining.
Maximal ratio combining corrects channel phase rotation and
weights components with channel amplitude estimate.
RAKE diversity receiver is shown as Figure 2.
FI GU R E 2 RAKE DI VER SI TY REC EI VER
A rake receiver is a radio receiver designed to counter the
effects of multipath fading. It does this by using several "sub-
receivers" called fingers, that is, several correlators each
assigned to a different multipath component. Each finger
independently decodes a single multipath component; at a later
stage the contribution of all fingers are combined in order to
make the most use of the different transmission characteristics
of each transmission path.

About this Manual
Power Control
Quality Of Service (QOS) that radio cell network provides for
each subscriber mainly depends on signal-to-interference ratio
(SIR) of subscriber receiving signals. For CDMA cell system, all
subscribers in same cell use same band and timeslot, and
subscribers are isolated with each other only by the (quasi-)
orthogonalization of spreading code. Correlation characteristics
between each subscriber signals are not so good and signals of
other subscribers interfere signals of current subscribers, due to
multipath and delay of the radio channels.
Increasing of subscribers or power of other subscribers may
enhance interference on current subscriber. Therefore, CDMA
system is a strong power-restricted system and strength of
interference influences system capacity directly.
Power control is regarded as one of the key technologies of
CDMA system. Power control adjusts transmission power of each
subscriber, compensates channel attenuation, countervails near-
far effect and maintains all subscribers at lowest standard of
normal communication. It reduces interference on other
subscribers at most, increases system capacity and prolongs
holding time of mobile phones.
To achieve acceptable call quality when the TX power is small,
both the BS and the MS are required to adjust power needed by
the transmitter in real time according to the communication
distance and link quality. This process is called "power control".
Purpose of Power Control in
WCDMA
Power control in uplink must make signal powers from different
users nearly equal in order to maximize the total capacity in the
cell.
In downlink the power control must keep the signal at minimal
required level in order to decrease the interference to users in
other cells.
Purpose of power control in WCDMA aims at
 Removes near-far effect.
 Mitigates fading.
 Compensates changes in propagation conditions.
 In the system level
 decrease interference from other users

WCDMA Theory
 increase capacity of the system
Power Control Types in WCDMA
Power control of WCDMA includes the fellowing types.
 Open loop power control
Open loop power control is for initial power setting of MS.
Open loop power control is based on the assumption that the
uplink and downlink channels are symmetric. It can
counteract path loss and shadow fade.
 Closed loop power control
 Inner loop power control is used to combat channel fade
and loss, so that the SIR or power of the received signals
can reach the specific target value.
 Outer loop power control generates the SIR or power
threshold for inner power control according to the QoS in
the specific environment. .
Open Loop Power Control
Open loop power control mechanisms attempt to make a rough
estimate of path loss by means of a downlink beacon signal.
Such a method would be far too inaccurate. The prime reason
for this is that the fast fading is essentially uncorrelated between
uplink and downlink, due to the large frequency separation of
the uplink and downlink bands of the WCDMA FDD mode. Open
loop power control is, however, used in WCDMA, but only to
provide a coarse initial power setting of the mobile station at the
beginning of a connection.
FI GU R E 3 OPEN LOOP POW ER CON TR OL

About this Manual
Close Loop Power Control
Close loop power control can be divided into inner loop power
control and outer power control.
 Inner loop power control
Inner loop power control is fast closed power control, with
fast speed 1500 times/second, conduting in physical layer
between BS and MS. If SIR measured in physical layer is
lower than target SIR, BS will send increase power
command to MS, and vice versa. Power control command
includes increase power, decrease power and retain power.
Step is 1 dB every time.
 Outer loop power control
Outer power control is slow close loop power control,usually
conduting in one TTI(10ms,20ms,40ms,80ms). Outer power
control is over physical layer, and calculates BLER through
testing CRC correctness or not to determine the value of
target SIR.
 The relationship between inner loop power control and outer
loop power control
The outer loop power control is a kind of slow changing
adjustment between RNC and Node B, while the inner loop
power control is a kind of fast changing adjustment between
NodeB and UE.
Why need both inner loop power control and outer loop
power control? It is hard to get exactly accurate SIR
measurement result during SIR measurement. SIR and
BER(or BLER) is environmental changing and nonlinear. For
instance, in one kind of multipath spreading environment,
BLER 1/100 need SIR 5 dB,while in another kind of multipath
spreading environment same BLER need SIR maybe 5.5 dB.
That means quality of service is directly determined by BLER
not by SIR(SIR only indirectly determined Qos) .
Handover
Mobility
Mobility provides the possibility of being reachable anywhere and
any time for the end-user.
The mobility is provided through:

WCDMA Theory
Handover: gurantees that whenever the mobile is moving from
one BS area/cell to another, the signal is handed over to the
target BS.
When there is no continuous active radio link between mobile
and BS, the mobility is supported by:
 Location update: user registers in the network that it can be
found in given area. Mobile always initiates the location
update procedure.
 Paging: indication to the user about the the need for
transaction. Paging procedure is always initiated by the
network.
Handover Types in WCDMA
1. Intra-system handovers
 Intra-frequency handovers
MS handover within one cell between different sectors:
Softer handover
MS handover between different BS:
 Soft handover
 Hard handover
 Inter-frequency handovers
Hard handover
2. Inter-system handovers
 Handover between WCDMA <-- > GSM900/1800: Hard
handover
 Handower between WCDMA/FDD <--> TDD: Hard handover
Softer Handover
Softer handover refers to handover between cells with same
frequency and in same base station, as shown in Figure 4.

About this Manual
FI GU R E 4 SOF TER H AN D OVER
While MS in overlapping cell coverage area of two adjacent
sectors of a BS, communication between MS and BS is via two
air interface channels (one for each separate sector). Different
sectors have different scrambling codes.
MS tunes the RAKE fingers to different sectors and combines the
outputs. BS receives signals with different antennas and decodes
and combines them.
Soft Handover
Soft handover refers to adding a new link (the old and the new
links exist at the same time) and deleting the old one after
stabilization. Services continue in the handover, as shown in
Figure 5.
FI GU R E 5 SOF T HAN D OVER

WCDMA Theory
MS: At Rake Maximal Ratio Combining of signals from different
BS.
BS: Frame selection. Extra transmission across Iub.
Difference of soft handover and softer handover is that
combination of radio links is realized by RNC for soft handover
while is realized in Node B (decided by RNC) for softer handover.
Hard Handover
Hard handover refers to deleting the old link and then building a
new link. Services break off during the handover, as shown in
Figure 6.
FI GU R E 6 HAR D HAN D OVER
Node B
Node B
Cell 1 Cell 2
Handover Procedure
1. The basic process of handover is shown as Figure 7.
i. Measurement (UE); report on measurement results
(report from UE to RNC)
ii. RNC decides whether to perform handover according to
the report and algorithm (RNC sends the command of
handover to UE if it is necessary).
iii. Handover execution

About this Manual
FI GU R E 7 TH E B ASI C PR OC ESS OF H AN D OVER
Figure 8 shows detailed flow of handover.
FI GU R E 8 HAN D OVER FL OW
Active Set: is a set of signal branches (Cells) through which
the MS has simultaneously connection to the UTRAN.
In 3GPP, events correlative to handover are:
 Event correlative to soft handover in the band: 1A ~ 1F
Measured value is usually Ec/N0 of pilot channel, reflecting
the quality of a certain cell. 3GPP defines a series of

WCDMA Theory
measurement events in the band. UE reports corresponding
events when meeting definitions.
FI GU R E 9 EVEN T C OR R EL ATI VE TO SOF T H AN D OVER
Event Description
Event 1A
Quality of target cell improves, entering a report range of relatively
activating set quality
Event 1B
Quality of target cell decreases, depart from a report range of
relatively activating set quality
Event 1C
The quality of a non-activated set cell is better than that of a certain
activated set cell
Event 1D Best cell generates change
Event 1E Quality of target cell improves, better than an absolute threshold
Event 1F Quality of target cell decreases, worse than an absolute threshold
 Event correlative to hard handover between bands: 2A ~ 2F
Ec/N0 is measured value, reflecting quality of operators by
measuring cells at different bands. UE reports corresponding
FI GU R E 10 EVEN T C OR R EL ATI VE TO H AR D H AN D OVER
Event Description
Event 2A Best band generates change
Event 2B
Quality of currently-used band is worse than an absolute threshold
and that of non-used band is better than an absolute threshold
Event 2C Quality of non-used band is better than an absolute threshold
Event 2D Quality of currently-used band is worsethan an absolute threshold
Event 2E Quality of non-used band is worse than an absolute threshold
Event 2F Quality of currently-used band is better than an absolute threshold
 Event correlative to handover between systems: 3A ~ 3D
RSSI is measured value for GSM. UE reports corresponding
FI GU R E 11 EVEN T C OR R EL ATI VE TO H AN D OVER B ETW EEN SYSTEMS
Event Description
Event 3A
Quality of currently-used UTRAN operator is worse than an
absolute threshold and quality of other radio systems is better than
an absolute threshold
Event 3B Quality of other radio systems is worse than an absolute threshold
Event 3C Quality of other radio systems is better than an absolute threshold
Event 3D Best cell in other systems generates change
For example: Adding a radio link in soft handover and Figure
12 shows signaling process of handover.

About this Manual
FI GU R E 12 SOF T HAN D OVER (AD D I N G A LI N K ) SI GN AL I N G FL OW
2. Compression mode
UE has only one RF reception unit and can only decode
signals of one frequency at one time. Therefore, compression
mode is necessary if measuring two cells of different bands
or different cells. Figure 13 shows compression mode
priciple.

WCDMA Theory
FI GU R E 13 COMPR ESSI ON M OD E PR I N C I PL E
Dat a Compressi on1 Frame/ 10 ms
1 f rame
Compressed
I dl e t i me f or
het ero-f requency
measurement
1 f rame
uncompressed
In compression mode, Node B compresses data when sending
some downlink channel frames. UE takes advantage of
remaining time for measurement of different bands.
Compression mode can be realized by drilling and halving
spreading factors, and so on. When measuring between
frequencies, the system negotiates with UE whether to support
and select compression mode.
Admission Control
The idea behind admission control strategies is as follows. When
a user originates a call to the network requesting a desired QoS,
the network must do two things before accepting the call
request.
First, it must make sure that it has sufficient bandwidth to
allocate to that user.
Second, it must determine if, after admitting the user, it can
continue to provide the same QoS for all existing connections.
One QoS objective may be a desired packet loss probability.
Thus, before the network admits the new user, it should
determine whether it can meet that packet loss probability goal
for all connections, old as well as new.
Call admission control decides to accept or refuse a new
subscriber, new Radio Access Bearer (RAB) and new Radio Link
(RL) according to current resource (such as, handover). Call
admission control is applicable to original UE access, RAB
designation, reconfiguration and handover. It may lead to
different results because of PRI and actual situations.

About this Manual
Call admission control meets QOS of new calls as much as
possible premising the stability of the system, based on
interference measurement, to avoid overloading.
Call admission control falls into:
 Uplink call admission control
 Downlink call admission control
WCDMA is a self-interference system and there exists power
climbing. The core is power. Uplink capacity depends on whether
total receiving interference power is beyond linear dynamic
range of LNA or not. Downlink capacity depends on whether the
distribution of transmission power completes or not.
Process of call admission control:
Measure current load of system cell when making calls (new
access calls and handover calls), and forecast and estimate calls,
then judge whether to access calls. Take QOS requirements of
calls. That is, communication rate, communication quality
(signal-to-noise ratio and error code ratio) and delay into
consideration when forecasting calls. Refuse the call when it
approaches some threshold.
Service calls fall into new calls and handover calls. Reserve some
resources for handover calls to ensure high ratio of successful
handovers. PRI of handover calls is distinguished by admission
control threshold. Admission control threshold of new calls is
lower than that of handover calls. New calls are refused when
current load of the cell is higher than admission threshold of new
calls. However, handover calls are accepted. Handover ratio is
better to be at about 35% in soft handover. Handover calls are
also refused when the load of the cell is higher than handover
admission control threshold. Load control threshold is commonly
higher than admission control threshold of handover, to prevent
overloading when radio circumstances change and to ensure the
stable running of the system.
Measurement Related to Admission
Control
 Node B Common Measurement
 DCH measurement
Major factors to influence WCDMA system capacity (DCH)
are uplink interference and downlink operator emission
power. DCH admission control performs admission
decision on these two parameters. Node B reports RTWP
and TCP of Node B common measurement to RNC
periodically, so that RNC can decide whether to access
the new call according to latest load.
 HS-DSCH measurement

WCDMA Theory
HS-DSCH admission control needs Node B common
measurement information related to HSDPA, including
HS-DSCH required power, transmitted operator power of
all codes not used for HS-PDSCH or HS-SCCH
transmission. Therefore, open these common
measurements simultaneously in cells supporting HSDPA.
 RACH measurement
According to policies of ZTE, to estimate the load, RACH
starts up acknowledged PRACH preambles common
measurement during the admission control, to get actual
utilization ratio of PRACH channel.
 UE measurement
When predicting downlink power, RNC needs real-time route
loss of UE. RNC can get route loss of UE by different means
according to admission requests type, such as, reporting
through some events of UE.
Load Control/Congestion
Control
 Process of load control
The system measures the load of the system cell at real time
continually. The system load is high and the load enters
unstable running district of the system when load average
value exceeds some threshold value in a set time. Load
control is necessary at the moment.
 Load control threshold
The core of load control is to access as many services as
possible premising that the system is running stably, to
realize high efficient running. Leave some redundancy,
excluding base line for system breakdown, as threshold value
of load control. Threshold value of load control is larger than
that of admission control.
 Load control mode
Load control works when system load approaches or exceeds
load threshold value. Main modes:
 Reduce the load in a rapid mode, which is mainly realizes
by base station (Node B).
Downlink rapid load control: Refusing the command to
increase the power from the mobile station.
Uplink rapid load control: Reducing SIR destination value
for uplink rapid power control.
 Reduce the load in medium or slow mode, which is
mainly realized by base station controller (RNC).

About this Manual
Commonly, RNC makes judgment and changes max
allowed transmission power, destination SIR value and
TFCS by reconfiguring the RL. In this mode, the system
load can be reduced for a long time.
Make negotiations if hoping to reduce the system load for
a long time, that is, RNC negotiates with CN to reduce
resource occupation of services during the
communications. Or, share loads with adjacent cells in
RNS to reduce the load of those overloading cells. The
taking-in and sending-out of adjacent cells (covering
radius of one cell increases and that of another adjacent
cell decreases) is called cell breathing.
Conclusions:
 Reducing the throughput of grouping (reducing the
transmission rate)
 Handing over to other WCDMA carrier frequency
 Handing over to GSM system
 Reducing the rate of real-time services
 Executing the call drops
AMR
Adaptive Multi Rate (AMR) code is a voice-coding plan. It is
called broadband AMR (AMR-WB or AMR Wideband) in WCDMA.
Current GSM speech coding (FR, HR, EFR and AMR) is applicable
to narrowband speech and audio bandwidth is limited to 3.4 kHz.
Audio bandwidth of AMR-RB extends to 7 kHz, which makes the
voice much clearer and natural, especially in hands-free
situations.
AMR provides eight coding rates of 4.7 k, 5,15 k, 5.9 k, 6.7 k,
7.4 k, 7.95 k, 10.2 k and 12.2 k. Select codes with low rate on
condition that it does not influence communication quality, to
save network resource.

21
C h a p t e r 2
Interface and Protocol
Overview
UTRAN Common Protocol Model
Figure 14 shows the general protocol model for UT RAN
Interfaces, and described in detail in the following subclauses.
The structure is based on the principle that the layers and planes
are logically independent of each other. Therefore, as and when
required, the standardisation body can easily alter protocol
stacks and planes to fit future requirements.
FI GU R E 14 UTRAN COMMON PR OTOC OL M OD EL
Application
Protocol
Data
Stream(s)
ALCAP(s)
Transport
Network
Layer
Physical Layer
Signalling
Bearer(s)
Transport
User
Network
Plane
Control Plane User Plane
Transport
User
Network
Plane
Transport Network
Control Plane
Radio
Network
Layer
Signalling
Bearer(s)
Data
Bearer(s)
Horizontal, The Protocol Structure consists of two main layers:
 Radio Network Layer

WCDMA Theory
 Transport Network Layer.
All UT RAN related issues are visible only in the Radio Network
Layer, and the Transport Network Layer represents standard
transport technology that is selected to be used for UTRAN, but
without any UTRAN specific requirements.
Vertical, UTRAN falls into the following 4 planes:
 Control Plane
Purpose of the control plane:
Control the radio access bearer and the connection
between UE and the network;
Transmit messages of non-access layer transparently.
The Control Plane includes the application protocol and
the Signaling Bearer for transporting the Application
Protocol messages.
The control plane protocols of each interface on RNL
include:
Interface Iu: RANAP protocol
Interface Iur: RANSAP protocol
Interface Iub: NBAP protocol
Interface :Uu: RRC protocol
Among other things, the Application Protocol is used for
setting up bearers for (i.e. Radio Access Bearer or Radio
Link) in the Radio Network Layer. In the three plane
structure the bearer parameters in the Application
Protocol are not directly tied to the User Plane
technology, but are rather general bearer parameters.
The Signalling Bearer for the Application Protocol may or
may not be of the same type as the Signalling Protocol
for the ALCAP. The Signalling Bearer is always set up by
O&M actions.
 User Plane
Purpose of user plane:
Transmit the user data via the access network.
The User Plane Includes the Data Stream(s) and the Data
Bearer(s) for the Data Stream(s). The Data Stream(s)
is/are characterised by one or more frame protocols
specified for that interface.
 TNL Control Plane
TNL control plane protocol is ALCAP, belonging to SAAL
(Signalling AAL) of ATM.
The Transport Network Control Plane does not include
any Radio Network Layer information, and is completely
in the Transport Layer. It includes the ALCAP protocol(s)
that is/are needed to set up the transport bearers (Data

Chapter 2 Interface and Protocol
23
Bearer) for the User Plane. It also includes the
appropriate Signalling Bearer(s) needed for the ALCAP
protocol(s).
The Transport Network Control Plane is a plane that acts
between the Control Plane and the User Plane. The
introduction of Transport Network Control Plane makes it
possible for the Application Protocol in the Radio Network
Control Plane to be completely independent of the
technology selected for Data Bearer in the User Plane.
When Transport Network Control Plane is used, the
transport bearers for the Data Bearer in the User Plane
are set up in the following fashion. First there is a
signalling transaction by the Application Protocol in the
Control Plane, which triggers the set up of the Data
Bearer by the ALCAP protocol that is specific for the User
Plane technology.
The independence of Control Plane and User Plane
assumes that ALCAP signalling transaction takes place. It
should be noted that ALCAP might not be used for all
types Data Bearers. If there is no ALCAP signalling
transaction, the Transport Network Control Plane is not
needed at all. This is the case when pre-configured Data
Bearers are used.
It should also be noted that the ALCAP protocol(s) in the
Transport Network Control Plane is/are not used for
setting up the Signalling Bearer for the Application
Protocol or for the ALCAP during real time operation.
The Signalling Bearer for the ALCAP may or may not be
of the same type as the Signalling Bearer for the
Application Protocol. The Signalling Bearer for ALCAP is
always set up by O&M actions.
 TNL User Plane
The user plane data and control plane data of all RNL
belong to TNL user plane.
The Data Bearer(s) in the User Plane, and the Signalling
Bearer(s) for Application Protocol, belong also to
Transport Network User Plane. As described in the
previous subclause, the Data Bearers in Transport
Network User Plane are directly controlled by Transport
Network Control Plane during real time operation, but the
control actions required for setting up the Signalling
Bearer(s) for Application Protocol are considered O&M
actions.

WCDMA Theory
The Radio Interface Protocol
Reference Model
FI GU R E 15 RAD I O I N TER F AC E PR OTOC OL R EF ER EN C E MOD EL
L1 – radio physical layer
L2 – radio link layer
L3 – radio network layer
 L1:
As shown in Figure 15, the physical layer provides its
services as a set of WCDMA transport channels. This makes
the physical layer responsible for the first multiplexing
function: to map the flows from transport channels to
WCDMA physical channels and vice versa.
 L2:
The radio link layer is another multiplexing layer, one
that makes a major contribution to dynamic sharing of
capacity in the WCDMA radio interface. Instead of the
wide variety of L1 transport channels this layer allows the
upper layer to see only a set of radio bearers, along
which different kinds of traffic can be transmitted over
the radio link.
 The Medium Access Control (MAC) sublayer controls the
use of the transport block capacity by ensuring that
capacity allocation decisions (done at the UTRAN end) are
executed promptly at both ends of the radio interface.

25
 The Radio Link Control (RLC) sublayer then adds regular
link layer functions onto the logical channels provided by
the MAC sublayer.
 For CS domain data (e.g., transcoded speech) the
convergence function is null, but for the PS domain an
additional convergence sublayer is needed. This Packet
Data Convergence Protocol (PDCP) sublayer makes the
UMTS radio interface applicable to carry Internet Protocol
(IP) data packets.
 BMC has been specified for message broadcast and
multicast domains. The scheduling and delivery of cell
broadcast messages to User Equipment (UEs) is the main
task of this protocol.
 L3:
The L3 control plane protocol is the Radio Resource Control
(RRC) protocol. As shown in Figure 15, an RRC protocol
entity at both the UE and UTRAN ends has control interfaces
with all other protocol entities.
UTRAN Protocol Reference Model

WCDMA Theory
Access Layer and Non-access Layer
The concepts of access layer and non-access layer are related to
the communication of UE and CN. The access layer bears the
upper layer services via the SAP (Service Access Point), as
shown in Figure 16.
FI GU R E 16 AC C ESS LAYER AN D NON -AC C ESS LAYER
UTRANUE CN
Access Stratum
Non-Access Stratum
Radio
(Uu)
Iu
Radio
proto-
cols
(1)
Radio
proto-
cols
(1)
Iu
proto
cols
(2)
Iu
proto
cols
(2)
The UTRAN AP and frame protocols together form the UMTS
access stratum, which covers all those communication aspects
that are dependent on the selected radio access technology.
Within generic UMTS radio access bearers, non-access stratum
protocols are then used for direct transfer of signalling and
transparent flow of user data frames between UEs and the CN.
This is achieved by encapsulation of the higher layer payload
into UTRAN protocol messages.
Main Protocol Function
Medium Access Control (MAC)
Protocol
The Medium Access Control Protocol performs the following
functions:
 Mapping between logical channels and transport channels.
 Selection of appropriate Transport Format for each
Transport Channel depending on instantaneous source
rate.
 Priority handling between data flows of one UE.

27
 Priority handling between UEs by means of dynamic
scheduling.
 Identification of UEs on common transport channels.
 Multiplexing/demultiplexing of upper layer PDUs
into/from transport block sets delivered to/from the
physical layer on dedicated transport channels.
 Traffic volume measurement.
 Transport Channel type switching.
 Ciphering for transparent mode RLC.
 Access Service Class selection for RACH and CPCH
transmission.
The complete specification of the MAC protocol is given in 3GPP
specification TS25.321.
Radio Link Control (RLC) Protocol
The Radio Link Control Protocol performs the following functions:
 Segmentation and reassembly.
 Concatenation.
 Padding.
 Transfer of user data.
 Error correction.
 In-sequence delivery of upper layer PDUs.
 Duplicate detection.
 Flow control.
 Sequence number check.
 Protocol error detection and recovery.
 Ciphering.
 SDU discard.
The complete specification of the RLC protocol is given in 3GPP
specification TS25.322.
Signalling Transport (SCCP)
SCCP is derived from SS7 and provides both a connectionless
and connection-oriented service. The connection-oriented
service is used to support signaling bearers.

WCDMA Theory
IP Transport for User Data (GTP-U)
The main functions of GTP-U are:
 Data packet transfer.
 Encapsulation and tunnelling.
 Data packet sequencing.
 Path alive check.
GTP-U is defined in 3GPP specification TS 29.060.
Radio Access Network Application
Protocol(RANAP)
RANAP is the protocol that controls resources in the Iu interface.
One RANAP entity resides in the RNC and another peer entity
resides in the MSC server or the SGSN.
The detailed specification for RANAP is given by 3GPP
specification TS 25.413.
Radio Network Subsystem
Application Protocol(RNSAP)
RNSAP is responsible for bearer management signalling across
the Iur interface.
RNSAP is used for setting up radio links and allowing the SRNC
to control these
radio links using dedicated resources in a DRNC.
The complete specification of RNSAP is given in 3GPP
specification TS 25.423.
Node B Application Protocol(NBAP)
NBAP is a radio network layer protocol that maintains control-
plane signaling across the Iub interface and, thus, controls
resources in the Iub interface and provides a means for the BS
and RNC to communicate.
The complete specification of NBAP is given in 3GPP specification
TS 25.433.

29
Radio Resource Control (RRC)
Protocol
The RRC protocol is the key radio resource control protocol
within the UTRAN.
The major function of the RRC protocol is to control the radio
bearers, transport channels and physical channels. This is done
by set-up, reconfiguration and release of different kinds of radio
bearers.
The Radio Resource Control Protocol performs the following
functions:
 Cell Broadcast Service (CBS) control.
 Initial cell selection and cell re-selection.
 Paging.
 Broadcast of information:
– related to the non-access stratum (Core Network).
– related to the access stratum.
 Establishment, maintenance and release
– of an RRC connection between the UE and UTRAN.
– of Radio Bearers.
 Assignment, reconfiguration and release of radio
resources for the RRC connection.
 Control of requested QoS.
 UE measurement reporting and control of the reporting.
 RRC message integrity protection.
 Arbitration of radio resources on uplink DCH.
 Slow Dynamic Channel Allocation (DCA) (TDD mode).
 Timing advance (TDD mode).
 RRC connection mobility functions (RNC relocation).
 Outer loop power control.
 Control of ciphering.
The RRC protocol is specified in 3GPP specification TS 25.331.

WCDMA Theory
Packet Data Convergence
Protocol(PDCP)
As its name suggests PDCP is designed to make WCDMA radio
protocols suitable for carrying the most common user-to-user
packet data protocol, TCP/IP.
The Packet Data Convergence Protocol performs the following
functions:
 Header compression and decompression of IP data
streams (e.g., TCP/IP and RTP/UDP/IP headers for IPv4
and IPv6) at the transmitting and receiving entity,
respectively.
 Transfer of user data. This function is used for
conveyance of data between users of PDCP services.
 Maintenance of PDCP sequence numbers for radio bearers
that are configured to support lossless SRNS Relocation.
The complete specification of PDCP is given in 3GPP specification
TS 25.323.
Broadcast Multicast Control(BMC)
The Broadcast Multicast Control Protocol performs the following
functions:
 Storage of Cell Broadcast Messages.
 Traffic volume monitoring and radio resource request for
CBS.
 Scheduling of BMC messages.
 Transmission of BMC messages to UE.
 Delivery of Cell Broadcast messages to upper layer.
UTRAN Frame Protocols(FP)
UTRAN frame protocols are radio network layer user-plane
protocols that carry UMTS user data over the common UT RAN
transport network. They are active across the UTRAN interfaces
Iu, Iur and Iub. The transport network service used by frame
protocols is based on either ATM or the IP protocol stack.

31
C h a p t e r 3
ChannelStructure and
Function
Overview
Channel Type
Three separate channels concepts in the UT RA N: logical,
transport, and physical channels.
 Logical channels define what type of data is transferred. It
can be divided into two large types:
 Control channel
 Service channel.
 Transport channels define how and with which type of
characteristics the data is transferred by the physical layer.
A general classification of transport channels is into two
types:
 Dedicated channel: used by dedicated user.
 Common channel: used by all users within one cell.
 Physical data define the exact physical characteristics of the
radio channel. In WCDMA, each radio frame of the physical
channel has a length of 10 ms, and there are 15 timeslots.
Each timeslot has a length of Tslot = 2560 chips,
corresponding to one power control cycle. In other words,
one power control cycle is 10/15 ms.

WCDMA Theory
FI GU R E 17 CHA NNEL TY P ES IN UTRAN
The three types of channels correspond to the egresses of
different layers of the protocol stack. The logical channel is
between the MAC and RLC, the transport channel is between the
MAC and layer 1, and the physical channel is below layer 1.
Channel Mapping
Channel mapping is shown as Figure 18 and Figure 19.
FI GU R E 18 UPL I N K M APPI N G

Chapter 3 Channel Structure and Function
33
FI GU R E 19 DOW N L I N K M APPI N G
The transport channel to physical channel mapping is illustrated
in Table 4.
TAB L E 4 TR AN SPOR T C H AN N EL TO PH YSI C AL C H AN N EL MAPPI N G
Transport Channel Physical Channel
(UL/DL) Dedicated CHannel
DCH
Dedicated Physical Data CHannel
DPDCH
Dedicated Physical Control CHannel
DPCCH
(UL) Random Access CHannel
RACH
Physical Random Access CHannel
PRACH
(UL) Common Packet CHannel
CPCH
Physical Common Packet CHannel
PCPCH
(DL) Broadcast CHannel BCH
Primary Common Control Physical
CHannel P-CCPCH
(DL) Forward Access CHannel
FACH
Secondary Common Control
Physical Channel S-CCPCH
(DL) Downlink Shared CHannel
DSCH
Physical Downlink Shared CHannel
PDSCH
No mapping transport channels
for these signaling physical
channels
Synchronisation CHannel SCH
Common PIlot CHannel CPICH
Acquisition Indication CHannel
AICH
Paging Indication CHannel PICH
CPCH Status Indication CHannel
CSICH

WCDMA Theory
Transport Channel Physical Channel
Collision Detection/Channel
Assignment Indicator CHannel
CD/CA-ICH
A dedicated channel (DCH) is mapped onto two physical
channels. The Dedicated Physical Data Channel (DPDCH) carries
higher layer information, including user data, while the
Dedicated Physical Control Channel (DPCCH) carries the
necessary physical layer control information. These two
dedicated physical channels are needed to support efficiently the
variable bit rate in the physical layer. The bit rate of the DPCCH
is constant, while the bit rate of DPDCH can change from frame
to frame.
Transport channels contain the data generated at the higher
layers, which is carried over the air and are mapped in the
physical layer to different physical channels.
The data is sent by transport block from MAC layer to physical
layer and generated by MAC layer every 10 ms.
The transport format of each transport channel is identified by
the Transport Format Indicator (TFI), which is used in the
interlayer communication between the MAC layer and physical
layer.
Several transport channels can be multiplexed together by
physical layer to form a single Coded Composite Transport
Channel(CCTrCh).
The physical layer combines several TFI information into the
Transport Format Combination Indicator (TFCI), which indicate
which transport channels are active for the current frame.
Two types of transport channels: dedicated channels and
common channels.
 Dedicated channel –reserved for a single user only.
Support fast power control and soft handover.
 Common channel – can be used by any user at any time.
Don’t support soft handover but some support fast power
control.
Note:
There exist physical channels to carry only information relevant
to physical layer procedures. That means in addition to the
physical channels mapped from the transport channels, there
exist physical channels for signaling purposes to carry only
information between network and the terminals. The
Synchronisation Channel(SCH), the Common Pilot Channel
(CPICH) and the Acquisition Indication Channel (AICH)are not
directly visible to higher layers and are mandatory from the
system function point ofview, to be transmitted from every base
station. The CPCH Status Indication Channel(CSICH) and the

35
Collision Detection/Channel Assignment Indication Channel
(CD/CA-ICH) are needed if CPCH is used.
Logical Channel
Logical channels are divided into control channel and traffic
channel.
FI GU R E 20 LOGI C AL C H AN N EL
Control channels only used to transport control plane
information, including BCCH,PCCH,CCCH,DCCH,SHCCH.
Traffic channels only used to transport user plane information.
Including DTCH,CTCH.
Transport Channel
Transport channels are services offered by Layer 1 to the higher
layers. A transport channel is defined by how and with what
characteristics data is transferred over the air interface. A
general classification of transport channels is into two groups:
 Dedicated channel: used by dedicated user.
 Common channel: used by all users within one cell.

WCDMA Theory
FI GU R E 21 TR AN SPOR T C H AN N EL
BCH
PCH
FACH
DSCH
RACH
CPCH
DCH
DCH
There exists only one type of dedicated transport channel, the
Dedicated Channel (DCH). The Dedicated Channel (DCH) is a
downlink or uplink transport channel. The DCH is transmitted
over the entire cell or over only a part of the cell using e.g.
beam-forming antennas.
There are six types of common transport channels: BCH, FACH,
PCH, RACH, CPCH and DSCH.
 Broadcast Channel -BCH
The Broadcast Channel (BCH) is a downlink transport
channel that is used to broadcast system- and cell-specific
information. The BCH is always transmitted over the entire
cell and has a single transport format.
 Forward Access Channel -FACH
The Forward Access Channel (FACH) is a downlink transport
channel. The FACH is transmitted over the entire cell. It is
used to transmit control information after base station has
received the random access requirement sent by UE. FACH is
also can be used to send packet data.
There is one or several FACH within one cell. One of them
must has low data rate, so all terminals in this cell can
receive it. The others can have high data rate.
 Paging Channel - PCH
The Paging Channel (PCH) is a downlink transport channel.
The PCH is always transmitted over the entire cell. The
transmission of the PCH is associated with the transmission
of physical-layer generated Paging Indicators, to support
efficient sleep-mode procedures.
 Random Access Channel - RACH
The Random Access Channel (RACH) is an uplink transport
channel. The RACH is always received from the entire cell. It
is used to carry control information (such as call setup

37
request) sent by UE. The RACH is characterized by a collision
risk and by being transmitted using open loop power control.
 Common Packet Channel - CPCH
The Common Packet Channel (CPCH) is an uplink transport
channel. CPCH is associated with a dedicated channel on the
downlink which provides power control and CPCH Control
Commands (e.g. Emergency Stop) for the uplink CPCH. The
CPCH is characterized by initial collision risk and by being
transmitted using inner loop power control.
 Downlink Shared Channel - DSCH
The Downlink Shared Channel (DSCH) is a downlink
transport channel shared by several UEs. The DSCH is
associated with one or several downlink DCH. The DSCH is
transmitted over the entire cell or over only a part of the cell
using e.g. beam-forming antennas.
Physical Channel
Physical channels are defined by a specific carrier frequency,
scrambling code, channelization code (optional), time start &
stop (giving a duration) and, on the uplink, relative phase (0 or
/2). There are two types of physical channel:
 Uplink physical channel
 Downlink physical channel
Uplink Physical Channel
There are two types of uplink dedicated physical channels(Uplink
Dedicated Physical Data Channel and Uplink Dedicated Physical
Control Channel) and two types of uplink common physical
channels(Physical Random Access Channel and Physical
Common Packet Channel) as shown in Figure 22.

WCDMA Theory
FI GU R E 22 U PL I N K PH YSI C AL C H AN N EL
Uplink Dedicated Physical Channel(DPCCH
DPDCH)
There are two types of uplink dedicated physical channels,
the uplink Dedicated Physical Data Channel (uplink DPDCH)
and the uplink Dedicated Physical Control Channel (uplink
DPCCH).The DPDCH and the DPCCH are I/Q code multiplexed
within each radio frame.
The uplink DPDCH is used to carry the DCH transport
channel. There may be zero, one, or several uplink DPDCHs
on each radio link.
The uplink DPCCH is used to carry control information
generated at Layer 1. The Layer 1 control information
consists of known pilot bits to support channel estimation for
coherent detection, transmit power-control (TPC) commands,
feedback information (FBI), and an optional transport-format
combination indicator (TFCI). The transport-format
combination indicator informs the receiver about the
instantaneous transport format combination of the transport
channels mapped to the simultaneously transmitted uplink
DPDCH radio frame. There is one and only one uplink DPCCH
on each radio link.
Figure 23 shows the frame structure of the uplink dedicated
physical channels. Each radio frame of length 10 ms is split
into 15 slots, each of length Tslot = 2560 chips, corresponding
to one power-control period.

39
FI GU R E 23 F R AME STR U C TU R E OF U PL I N K D ED I C ATED PH YSI C AL C H AN N EL
The parameter k in figure determines the number of bits per
uplink DPDCH slot. It is related to the spreading factor SF of the
DPDCH as SF = 256/2k. The DPDCH spreading factor may range
from 256 down to 4. The spreading factor of the uplink DPCCH is
always equal to 256, i.e. there are 10 bits per uplink DPCCH
slot.
The exact number of bits of the uplink DPDCH and the different
uplink DPCCH fields (Npilot, NTFCI, NFBI, and NTPC) is configured by
higher layers and can also be reconfigured by higher layers.
The FBI bits are used to support techniques requiring feedback
from the UE to the UTRAN Access Point, including closed loop
mode transmit diversity and site selection diversity transmission
(SSDT).
There are two types of uplink dedicated physical channels; those
that include TFCI (e.g. for several simultaneous services) and
those that do not include TFCI (e.g. for fixed-rate services). It is
the UTRAN that determines if a TFCI should be transmitted and
it is mandatory for all UEs to support the use of TFCI in the
uplink.
Npilot =3, 4, 5, 6, 7 and 8. The shadowed column part of pilot bit
pattern is defined as FSW and FSWs can be used to confirm
frame synchronization. (The value of the pilot bit pattern other
than FSWs shall be "1".)
TPC is corresponding to power contrl command.
Multi-code operation is possible for the uplink dedicated physical
channels. When multi-code transmission is used, several parallel
DPDCH are transmitted using different channelization codes.
However, there is only one DPCCH per radio link.

WCDMA Theory
Physical Random Access Channel (PRACH)
The random-access transmission is based on a Slotted
ALOHA approach with fast acquisition indication. The UE
can start the random-access transmission at the
beginning of a number of well-defined time intervals,
denoted access slots. There are 15 access slots per two
frames and they are spaced 5120 chips apart Information
on what access slots are available for random-access
transmission is given by higher layers. The random-
access transmission consists of one or several preambles
of length 4096 chips and a message of length 10 ms or
20 ms.
FI GU R E 24 F R AME STR U C TU R E OF R AN D OM AC C ESS C H AN N EL
Pilot
Npilot bits
Data
Ndata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 10*2k
bits (k=0..3)
Message part radio frame TRACH = 10 ms
Data
Control
TFCI
NTFCI bits
Each preamble is of length 4096 chips and consists of
256 repetitions of a signature of length 16 chips. There
are a maximum of 16 available signatures.
The 10 ms message part radio frame is split into 15 slots,
each of length Tslot = 2560 chips. Each slot consists of two
parts, a data part to which the RACH transport channel is
mapped and a control part that carries Layer 1 control
information. The data and control parts are transmitted in
parallel.
A 10 ms message part consists of one message part radio
frame, while a 20 ms message part consists of two

41
consecutive 10 ms message part radio frames. The
message part length is equal to the Transmission Time
Interval of the RACH Transport channel in use. This TTI
length is configured by higher layers.
The data part consists of 10*2k bits, where k=0,1,2,3.
This corresponds to a spreading factor of 256, 128, 64,
and 32 respectively for the message data part.
The control part consists of 8 known pilot bits to support
channel estimation for coherent detection and 2 TFCI
bits. This corresponds to a spreading factor of 256 for the
message control part. The pilot bit pattern is described in
table 8. The total number of TFCI bits in the random-
access message is 15*2 = 30. The TFCI of a radio frame
indicates the transport format of the RACH transport
channel mapped to the simultaneously transmitted
message part radio frame. In case of a 20 ms PRACH
message part, the TFCI is repeated in the second radio
frame.
Physical Common Packet Channel(PCPCH)
The Physical Common Packet Channel (PCPCH) is used to
carry the CPCH CPCH. The CPCH transmission is based on
DSMA-CD approach with fast acquisition indication. The
UE can start transmission at the beginning of a number of
well-defined time-intervals, relative to the frame
boundary of the received BCH of the current cell.
The PCPCH access transmission consists of one or several
Access Preambles [A-P] of length 4096 chips, one
Collision Detection Preamble (CD-P) of length 4096 chips,
a DPCCH Power Control Preamble (PC-P) which is either 0
slots or 8 slots in length, and a message of variable
length Nx10 ms.
FI GU R E 25 F R AME STR U C TU R E OF CPCH

WCDMA Theory
Pilot
Npilot bits
TPC
NTPC bits
Data
Ndata bits
bits (k=0..6)
1 radio frame: Tf = 10 ms
Data
Control
FBI
NFBI bits
TFCI
NTFCI bits
 CPCH access preamble part：
Similar to RACH preamble part. The RACH preamble
signature sequences are used. The number of sequences
used could be less than the ones used in the RACH
preamble. The scrambling code could either be chosen to
be a different code segment of the Gold code used to
form the scrambling code of the RACH preambles or could
be the same scrambling code in case the signature set is
shared.
 CPCH collision detection preamble part：
Similar to RACH preamble part. The RACH preamble
signature sequences are used. The scrambling code is
chosen to be a different code segment of the Gold code
used to form the scrambling code for the RACH and CPCH
preambles
 CPCH power control preamble part：
The power control preamble segment is called the CPCH
Power Control Preamble (PC-P) part. The Power Control
Preamble length is a higher layer parameter, Lpc-preamble,
which shall take the value 0 or 8 slots. The TFCI field is
filled with "1" bits.
 CPCH message part：
Similar to uplink dedicated channel, Each 10 ms frame is
split into 15 slots, each of length Tslot = 2560 chips. Each
slot consists of two parts, a data part that carries higher
layer information and a control part that carries Layer 1
control information. The data and control parts are
transmitted in parallel. The sf of CPCH message part is
256.
Downlink Physical Channel
Downlink physical channels include Dedicated physical channel
one Shared Physical Channel five Common Control Channel:

43
 Downlink Detedicated physical channel -DPCH
 Primary and secondary Commnon Pilot Channel - CPICH
 primary and secondary Common Control Physicl Channel
- CCPCH
 Synchronous Channel - SCH
 Physical Downlink Shared Channel - DSCH
 Acquisition Indication Channel - AICH
 Paging Indication Channel - PICH
Downlink physical channel is shown as Figure 26.
FI GU R E 26 D OW N L I N K PH YSI C AL C H AN N EL
Downlink Dedicated Physical Channel(DPCH)
There is only one type of downlink dedicated physical
channel, the Downlink Dedicated Physical Channel (downlink
DPCH).
Within one downlink DPCH, dedicated data generated at
Layer 2 and above, i.e. the dedicated transport channel
(DCH), is transmitted in time- multiplex with control
information generated at Layer 1 (known pilot bits, TPC
commands, and an optional TFCI). The downlink DPCH can
thus be seen as a time multiplex of a downlink DPDCH and a
downlink DPCCH.
Each frame of length 10 ms is split into 15 slots, each of
length Tslot = 2560 chips, corresponding to one power-control
period.

WCDMA Theory
FI GU R E 27 F R AME STR U C TU R E OF DL DPCH
The parameter k in Figure 27 determines the total number of
bits per downlink DPCH slot. It is related to the spreading
factor SF of the physical channel as SF = 512/2k. The
spreading factor may thus range from 512 down to 4.
The exact number of bits of the different downlink DPCH
fields (Npilot, NTPC, NTFCI, Ndata1 and Ndata2) is given in table 11.
What slot format to use is configured by higher layers and
can also be reconfigured by higher layers.
There are basically two types of downlink Dedicated Physical
Channels; those that include TFCI (e.g. for several
simultaneous services) and those that do not include TFCI
(e.g. for fixed-rate services). It is the UTRAN that determines
if a TFCI should be transmitted and it is mandatory for all
UEs to support the use of TFCI in the downlink.
Npilot＝2，4，8 & 16。
TPC symbol is corresponding to transmission power control
command T “0” or “1”.
Synchronisation Channel(SCH)
The Synchronisation Channel (SCH) is a downlink signal used for
cell search.
The SCH consists of two sub channels, the Primary and
Secondary SCH. The 10 ms radio frames of the Primary and
Secondary SCH are divided into 15 slots, each of length 2560
chips. The frame structure of the SCH is shown in Figure 28.

45
FI GU R E 28 FR AME STR U C TU R E OF SCH
Primary
SCH
Secondary
SCH
256 chips
2560 chips
One 10 ms SCH radio frame
acs
i,0
acp
acs
i,1
acp
acs
i,14
acp
Slot #0 Slot #1 Slot #14
The Primary SCH consists of a modulated code of length 256
chips, the Primary Synchronisation Code (PSC) denoted cp in
figure , transmitted once every slot. The PSC is the same for
every cell in the system.
The Secondary SCH consists of repeatedly transmitting a length
15 sequence of modulated codes of length 256 chips, the
Secondary Synchronisation Codes (SSC), transmitted in parallel
with the Primary SCH. The SSC is denoted cs
i,k in figure , where i
= 0, 1, …, 63 is the number of the scrambling code group, and k
= 0, 1, …, 14 is the slot number. Each SSC is chosen from a set
of 16 different codes of length 256. This sequence on the
Secondary SCH indicates which of the code groups the cell's
downlink scrambling code belongs to.
Common Pilot Channel (CPICH)
The CPICH is a fixed rate (30 kbps, SF=256) downlink physical
channel that carries a pre-defined bit sequence.
The frame structure of CPICH is shown in Figure 29.
FI GU R E 29 F R AME STR U C TU R E OF CPICH
Pre-defined bit sequence
Tslot = 2560 chips , 20 bits
There are two types of Common pilot channels, the Primary and
Secondary CPICH. They differ in their use and the limitations
placed on their physical features.
 Primary CPICH

WCDMA Theory
 An important area for the primary common pilot channel
is the measurements for the handover and cell
selection/reselection. The use of CPICH reception level at
the terminal for handover measurements has the
consequence that, by adjusting the CPICH power level,
the cell load can be balanced between different cells.
Reducing the CPICH power causes part of the terminals
to hand over to other cells, while increasing it invites
more terminals to hand over to the cell, as well as to
make their initial access to the network in that cell.
 The Primary Common Pilot Channel (P-CPICH) has the
following characteristics:
i. The same channelization code is always used for the P-
CPICH.
ii. The P-CPICH is scrambled by the primary scrambling
code.
iii. There is one and only one P-CPICH per cell.
iv. The P-CPICH is broadcast over the entire cell.
 The Primary CPICH is a phase reference for the following
downlink channels: SCH, Primary CCPCH, AICH, PICH AP-
AICH, CD/CA-ICH, CSICH, DL-DPCCH for CPCH and the
S-CCPCH. By default, the Primary CPICH is also a phase
reference for downlink DPCH and any associated PDSCH.
The UE is informed by higher layer signaling if the P-
CPICH is not a phase reference for a downlink DPCH and
any associated PDSCH. The Primary CPICH is always a
phase reference for a downlink physical channel using
closed loop TX diversity.
 Secondary CPICH may be phase reference for the secondary
CCPCH.
 A Secondary Common Pilot Channel (S-CPICH) has the
following characteristics:
i. An arbitrary channelization code of SF=256 is used for
the S-CPICH.
ii. A S-CPICH is scrambled by either the primary or a
secondary scrambling code.
iii. There may be zero, one, or several S-CPICH per cell.
iv. A S-CPICH may be transmitted over the entire cell or only
over a part of the cell.
A Secondary CPICH may be a phase reference for a
downlink DPCH. If this is the case, the UE is informed
about this by higher-layer signaling. The Secondary
CPICH can be a phase reference for a downlink physical
channel using open loop TX diversity, instead of the
Primary CPICH being a phase reference.

47
Paging Indication Channel (PICH)
The Paging Indicator Channel (PICH) is a fixed rate (SF=256)
physical channel used to carry the paging indicators. The
PICH is always associated with an S-CCPCH to which a PCH
transport channel is mapped.
Figure 24 illustrates the frame structure of the PICH. One
PICH radio frame of length 10 ms consists of 300 bits (b0, b1,
…, b299). Of these, 288 bits (b0, b1, …, b287) are used to carry
paging indicators. The remaining 12 bits are not formally
part of the PICH and shall not be transmitted (DTX). The part
of the frame with no transmission is reserved for possible
future use.
FI GU R E 30 FR AME STR U C TU R E OF PICH
b1b0
288 bits for paging indication
12 bits (transmission
off)
One radio frame (10 ms)
b287 b288 b299
In each PICH frame, Np paging indicators {P0, …, PNp-1} are
transmitted, where Np=18, 36, 72, or 144.
The PI calculated by higher layers for use for a certain UE, is
associated to the paging indicator Pq, where q is computed as
a function of the PI computed by higher layers, the SFN of
the P-CCPCH radio frame during which the start of the PICH
radio frame occurs, and the number of paging indicators per
frame
(Np):
         Np
Np
SFNSFNSFNSFNPIq mod
144
144mod512/64/8/18 










Further, the PI calculated by higher layers is associated with
the value of the paging indicator Pq. If a paging indicator in a
certain frame is set to "1" it is an indication that UEs
associated with this paging indicator and PI should read the
corresponding frame of the associated S-CCPCH.
The PI bitmap in the PCH data frames over Iub contains
indication values for all higher layer PI values possible. Each
bit in the bitmap indicates if the paging indicator associated
with that particular PI shall be set to 0 or 1. Hence, the
calculation in the formula above is to be performed in Node B
to make the association between PI and Pq..The mapping
from {P0, …, PNp-1} to the PICH bits {b0, …, b287} are
according to Table 5.

WCDMA Theory
TAB L E 5 M APPI N G OF PAGI N G I N D I C ATOR S PQ TO PICH B I TS
Number of paging
indicators per frame (Np)
Pq = 1 Pq = 0
Np=18
{b16q, …, b16q+15} = {1,
1,…, 1}
{b16q, …, b16q+15} = {0,
0,…, 0}
Np=36
{b8q, …, b8q+7} = {1, 1,…,
1}
{b8q, …, b8q+7} = {0, 0,…,
0}
Np=72
{b4q, …, b4q+3} = {1, 1,…,
1}
{b4q, …, b4q+3} = {0, 0,…,
0}
Np=144 {b2q, b2q+1} = {1, 1} {b2q, b2q+1} = {0, 0}
Acqusition Indication Channel(AICH)
The Acquisition Indicator channel (AICH) is a fixed rate
(SF=256) physical channel used to carry Acquisition
Indicators (AI). Acquisition Indicator AIs corresponds to
signature s on the PRACH.
Figure illustrates the structure of the AICH. The AICH
consists of a repeated sequence of 15 consecutive access
slots (AS), each of length 5120 chips. Each access slot
consists of two parts, an Acquisition-Indicator (AI) part
consisting of 32 real-valued symbols a0, …, a31 and a part
of duration 1024 chips with no transmission that is not
formally part of the AICH. The part of the slot with no
transmission is reserved for possible use by CSICH or
possible future use by other physical channels.
The spreading factor (SF) used for channelisation of the
AICH is 256.
The phase reference for the AICH is the Primary CPICH.
FI GU R E 31 FR AME STR U C TU R E OF AICH
1024 chips
Transmission Off
AS #14 AS #0 AS #1 AS #i AS #14 AS #0
a1 a2a0 a31a30
AI part = 4096 chips, 32 real-valued symbols
20 ms

49
CPCH Access Preamble Acqusition Indication
Channel (AP-AICH)
The Access Preamble Acquisition Indicator channel (AP-AICH)
is a fixed rate (SF=256) physical channel used to carry AP
acquisition indicators (API) of CPCH. AP acquisition indicator
APIs corresponds to AP signature s transmitted by UE.
AP-AICH and AICH may use the same or different
channelisation codes. The phase reference for the AP-AICH is
the Primary CPICH. Frame structure of AP-AICH is shown as
Figure 32.
FI GU R E 32 FR AME STR U C TU R E OF AP-AICH
1024 chips
Transmission Off
AS #14 AS #0 AS #1 AS #i AS #14 AS #0
a1 a2a0 a31a30
API part = 4096 chips, 32 real-valued symbols
20 ms
The AP-AICH has a part of duration 4096 chips where the AP
acquisition indicator (API) is transmitted, followed by a part
of duration 1024chips with no transmission that is not
formally part of the AP-AICH. The part of the slot with no
transmission is reserved for possible use by CSICH or
possible future use by other physical channels.
CPCH Collision Detection/Channel Assignment
Indicator Channel (CD/CA -ICH)
The Collision Detection Channel Assignment Indicator
channel (CD/CA-ICH) is a fixed rate (SF=256) physical
channel used to carry CD Indicator (CDI) only if the CA is not
active, or CD Indicator/CA Indicator (CDI/CAI) at the same
time if the CA is active. The structure of CD/CA-ICH is shown
in Figure 33.

WCDMA Theory
FI GU R E 33 FR AME STR U C TU R E OF CD/CA-ICH
1024 chips
Transmission Off
AS #14 AS #0 AS #1 AS #i AS #14 AS #0
a1 a2a0 a31a30
CDI/CAI part = 4096 chips, 32 real-valued symbols
20 ms
CD/CA-ICH and AP-AICH may use the same or different
channelisation codes.
The CD/CA-ICH has a part of duration of 4096chips where
the CDI/CAI is transmitted, followed by a part of duration
1024chips with no transmission that is not formally part of
the CD/CA-ICH. The part of the slot with no transmission is
reserved for possible use by CSICH or possible future use by
other physical channels.
The spreading factor (SF) used for channelisation of the
CD/CA-ICH is 256.
Commnon Control Physical Channel
Common control physical channel consists of Primary Common
Control Physical Channel (PCCPCH) and Secondary Common
Control Physical Channel (SCCPCH).
 The Primary CCPCH is a fixed rate (30 kbps, SF=256)
downlink physical channels used to carry the BCH transport
channel.
The frame structure of the Primary CCPCH is shown as Figure
34.
FI GU R E 34 FR AME STR U C TU R E OF P-CCPCH
Data
Ndata1=18 bits
Tslot = 2560 chips , 20 bits
(Tx OFF)
256 chips

51
The frame structure differs from the downlink DPCH in
that no TPC commands, no TFCI and no pilot bits are
transmitted. The Primary CCPCH is not transmitted
during the first 256 chips of each slot. Instead, Primary
SCH and Secondary SCH are transmitted during this
period
 Secondary Commnon Control Physical Channel (S-CCPCH)
The Secondary CCPCH is used to carry the FACH and PCH.
There are two types of Secondary CCPCH: those that include
TFCI and those that do not include TFCI. It is the UTRAN that
determines if a TFCI should be transmitted, hence making it
mandatory for all UEs to support the use of TFCI. The set of
possible rates for the Secondary CCPCH is the same as for
the downlink DPCH. The frame structure of S-CCPCH is
shown in Figure 35.
FI GU R E 35 FR AME STR U C TU R E OF S-CCPCH
bits (k=0..6)
Pilot
Npilot bits
Data
Ndata1 bits
TFCI
NTFCI bits
The parameter k determines the total number of bits per
downlink Secondary CCPCH slot. It is related to the
spreading factor SF of the physical channel as SF = 256/2k.
The spreading factor range is from 256 down to 4. The FACH
and PCH can be mapped to the same or to separate
Secondary CCPCHs.
If FACH and PCH are mapped to the same Secondary CCPCH,
they can be mapped to the same frame. The main difference
between a CCPCH and a downlink dedicated physical channel
is that a CCPCH is not inner-loop power controlled. The main
difference between the Primary and Secondary CCPCH is that
the transport channel mapped to the Primary CCPCH (BCH)
can only have a fixed predefined transport format
combination, while the Secondary CCPCH support multiple
transport format combinations using TFCI.
Physical Downlink Shared Channel (PDSCH)
The Physical Downlink Shared Channel (PDSCH) is used
to carry the Downlink Shared Channel (DSCH).

WCDMA Theory
A PDSCH corresponds to a channelisation code below or
at a PDSCH root channelisation code. A PDSCH is
allocated on a radio frame basis to a single UE. Within
one radio frame, UT RAN may allocate different PDSCHs
under the same PDSCH root channelisation code to
different UEs based on code multiplexing. Within the
same radio frame, multiple parallel PDSCHs, with the
same spreading factor, may be allocated to a single UE.
This is a special case of multi-code transmission. All the
PDSCHs are operated with radio frame synchronisation.
PDSCHs allocated to the same UE on different radio
frames may have different spreading factors.
The frame structure of the PDSCH is shown in Figure 36.
FI GU R E 36 FR AME STR U C TU R E OF PDSCH
bits (k=0..6)
Data
Ndata1 bits
For each radio frame, each PDSCH is associated with one
downlink DPCH. The PDSCH and associated DPCH do not
necessarily have the same spreading factors and are not
necessarily frame aligned.
All relevant Layer 1 control information is transmitted on
the DPCCH part of the associated DPCH, i.e. the PDSCH
does not carry Layer 1 information. To indicate for UE
that there is data to decode on the DSCH, the TFCI field
of the associated DPCH shall be used.
The TFCI informs the UE of the instantaneous transport
format parameters related to the PDSCH as well as the
channelisation code of the PDSCH.
Physical Layer Procedure
Cell search procedure
During the cell search, the UE searches for a cell and determines
the downlink scrambling code and frame synchronisation of that
cell. The cell search is typically carried out in three steps:

53
 Step 1: slot synchronous
During the first step of the cell search procedure the UE uses
the SCH’s primary synchronisation code to acquire slot
synchronisation to a cell. This is typically done with a single
matched filter (or any similar device) matched to the primary
synchronisation code which is common to all cells. The slot
timing of the cell can be obtained by detecting peaks in the
matched filter output.
 Step 2: frame synchronous and code-group identification
During the second step of the cell search procedure, the UE
uses the SCH’s secondary synchronisation code to find frame
synchronisation and identify the code group of the cell found
in the first step. This is done by correlating the received
signal with all possible secondary synchronisation code
sequences, and identifying the maximum correlation value.
Since the cyclic shifts of the sequences are unique the code
group as well as the frame synchronisation is determined.
 Step 3: scrambling-code identification
During the third and last step of the cell search procedure,
the UE determines the exact primary scrambling code used
by the found cell. The primary scrambling code is typically
identified through symbol-by-symbol correlation over the
CPICH with all codes within the code group identified in the
second step. After the primary scrambling code has been
identified, the Primary CCPCH can be detected.And the
system- and cell specific BCH information can be read.
Random Access Procedure
At each initiation of the physical random access procedure, Layer
1 shall receive the following information from the higher layers
(MAC):
 The Transport Format to be used for the PRACH message
part.
 The ASC of the PRACH transmission.
 The data to be transmitted (Transport Block Set).
The physical random-access procedure shall be performed as
follows:
1. Derive the available uplink access slots, in the next full
access slot set, for the set of available RACH sub-channels
within the ASC Randomly select one access slot among the
ones previously determined. If there is no access slot
available in the selected set, randomly select one uplink
access slot corresponding to the set of available RACH sub-
channels within the given ASC from the next access slot set.
The random function shall be such that each of the allowed
selections is chosen with equal probability.

WCDMA Theory
2. Randomly select a signature from the set of available
signatures within the given ASC. The random function shall
be such that each of the allowed selections is chosen with
equal probability.
3. Set the Preamble Retransmission Counter to Preamble
Retrans Max.
4. Set the parameter Commanded Preamble Power to
Preamble_Initial_Power.
5. In the case that the Commanded Preamble Power exceeds
the maximum allowed value, set the preamble transmission
power to the maximum allowed power. In the case that the
Commanded Preamble Power is below the minimum level
required in [7], set the preamble transmission power to a
value, which shall be at or above the Commanded Preamble
Power and at or below the required minimum power specified
in [7]. Otherwise set the preamble transmission power to the
Commanded Preamble Power. Transmit a preamble using the
selected uplink access slot, signature, and preamble
transmission power.
6. If no positive or negative acquisition indicator (AI  +1 nor –
1) corresponding to the selected signature is detected in the
downlink access slot corresponding to the selected uplink
access slot:
i. Select the next available access slot in the set of
available RACH sub-channels within the given ASC.
ii. Randomly select a new signature from the set of available
signatures within the given ASC. The random function
shall be such that each of the allowed selections is
chosen with equal probability.
iii. Increase the Commanded Preamble Power by P0 =
Power Ramp Step [dB]. If the Commanded Preamble
Power exceeds the maximum allowed power by 6dB, the
UE may pass L1 status ("No ack on AICH") to the higher
layers (MAC) and exit the physical random access
procedure.
ivi. Decrease the Preamble Retransmission Counter by one.
vii. If the Preamble Retransmission Counter > 0 then repeat
from step 5. Otherwise pass L1 status ("No ack on AICH")
to the higher layers (MAC) and exit the physical random
access procedure.
7. If a negative acquisition indicator corresponding to the
selected signature is detected in the downlink access slot
corresponding to the selected uplink access slot, pass L1
status ("Nack on AICH received") to the higher layers (MAC)
and exit the physical random access procedure.
8. Transmit the random access message three or four uplink
access slots after the uplink access slot of the last
transmitted preamble depending on the AICH transmission

55
timing parameter. Transmission power of the control part of
the random access message should be P p-m [dB] higher
than the power of the last transmitted preamble.
9. Pass L1 status "RACH message transmitted" to the higher
layers and exit the physical random access procedure.

57
C h a p t e r 4
Network Transport
Overview
ATM(Asynchronous Transfer Mode) is an effective data
transmission technology in IMT-2000. ATM is the transport
technology used in the first release of the UTRAN, 3GPP R99
implementation.
Ever since 3GPP R5, user data can be transported across all
UTRAN interfaces by using the IP protocol stack as well.
Protocol stacks for ATM and IP transport is shown in Figure 37.
FI GU R E 37 PR OTOC OL STAC K S F OR ATM AN D IP TR AN SPOR T
(a) control-plane protocols in the transport network
(b) user-plane protocols in the transport network
From Release 5, ATM transport and IP transport are equally valid
choices for all user-plane and control-plane UTRAN interfaces.

WCDMA Theory
Asynchronous Transfer
Mode in UMTS
Third Generation Partnership Project (3GPP) and Number 2
(3GPP2) standards specify that all the elements of the Radio
Access Network should be interconnected by utilising an ATM
transport network. As a result, currently available UMTS Radio
Access Network (RAN) elements from different manufacturers
are equipped with ATM technology. Practically, this means that
RAN elements include an ATM access port and employ ATM
signalling protocols and switching technology. It is also possible
to use IMA (Inverse Multiplexing for ATM) in RAN. This in turn
brings about the possibility of carrying Iub interface traffic over
GSM transmission routes, allowing network operators to reuse
currently available transmission networks.
In addition to flexible resource sharing, the most important
benefit of using ATM in RAN comes from the way data packets
are formed, classified and carried across the network. Because
each ATM connection is uniquely identified with specific classes,
the network is capable of supporting an efficient QoS
mechanism. This fits well with the bearer architecture thinking of
UMTS defined for different classes of QoS, such as Real Time
(RT) and Non-Real Time (NRT) services, to be supported
simultaneously. These also lead to more efficient resource
management, as the Radio Network Controller (RNC) in the RAN
will be able to schedule and optimise traffic load across the
network. Although ATM will remove the main constraints behind
TDM technology, new limitations arise: ATM signalling is too
complicated and causes undesirable delays and loads to the
network. In addition, ATM may lag behind the reach of
economies of scale, an important advantage of such emerging
technologies as IP. Therefore, transition from ATM towards IP
became the focus of attention in 3GPP and in association with
Releases 4 and 5.
In the current architecture of UMTS, the operator’s transport
network may include base stations (BSs) or Node Bs, RNCs,
Base Station Controllers (BSCs), Mobile Switching Centres
(MSCs), Serving GPRS Support Nodes (SGSNs), and Operat ion
and Management Centres (OMCs). Therefore, ATM-based traffic
in the radio access network can travel over E1 User Network
Interface (UNI) ATM or E1 IMA, or over one or multiple E1 lines
and Synchronous Transport Module 1 (STM-1) links. In order to
support different types of traffic ATM Adaptation Layer Type 2
(AAL2) and ATM Adaptation Layer Type 5 (AAL5) for voice and
data are used. Transmission media could include fibre optics,
E1/T1 copper leased lines, microwave or Digital Subscriber Line
(DSL), depending on the economies of scale and the availability
of media types. It is also possible to combine different kinds of
transmission media. While fibre is the best transport option due
to its speed and capacity, E1/T1, microwave, and DSL bring their
own advantages to the transport network and time after time

Chapter 4 Network Transport
59
they are found to be the only options available due to the cost or
lack of backbone infrastructure and the coexistence of 2G and
3G networks.
In spite of the dominant presence of ATM in the early phase of
UMTS networks, 3GPP has prepared the way for a transition to
IP transport. The original design philosophy of ATM was to
provide good bandwidth granularity while guaranteeing the delay
and jitter requirements for voice services. There is inefficiency in
the handling of data packets due to the small size of the
packets, which cannot be optimised for different traffic flows.
When there is no need for good granularity of ATM (e.g., when
the links have a high bit rate and latency is not so critical), the
use of IP can become more efficient and lucrative. For the
purpose of continuity, however, IP can form an overlay on the
existing ATM backbone and, therefore, ATM will keep its role in
the cellular network in the near future as well.
Basic Configuration of ATM
ATM is a technology that divides information to be transmitted
into 53-byte frames called cells for transmission and switching.
The use of ATM in the RAN is specified under 3GPP Release
1999. There are substantial merits in applying ATM in CN,
including the ability to perform traffic management in
coordination with RAN, implement CS and PS functions in the
same architecture and carry out quality control and operations in
an integral manner. ATM has extensive traffic management and
quality-control functions for handling traffic characteristics, and
is an effective technology for forwarding not only CS services but
also PS services.
A cell, which is the data transfer unit in ATM, consists of a 5-
byte header (which includes routing information etc.) and a 48-
byte payload (storing user data).
FI GU R E 38 ATM C EL L STR U C TU R E
The ATM switching equipment achieves fast switching based on
hardware switching with reference to the routing information in
the header, without detecting data errors in each cell. The
routing information in the header consists of the Virtual Path
(VP) and the Virtual Channel (VC).
ATM cell header structure is shown as Figure 39.

WCDMA Theory
FI GU R E 39 ATM CELL HEA DER STRUCTURE
 VPI (Virtual Path Identifier): the identifier for a Virtual
Path (VP) or, more generally, an identifier for a
constantly allocated semi-permanent connection.
 VCI (Virtual Channel Identifier): an identifier for a Virtual
Channel (VC). This field is long because there may be
thousands of channels to be identified within one VP (e.g.,
multimedia applications may require several VCIs
simultaneously, one VC per multimedia component).
 PT (Payload Type): this indicates whether the 48-byte
payload field carries user data or control data.
 CLP (Cell Loss Priority): this is a flag indicating whether
this ATM cell is “important” or “less important”. If CLP 1
(low priority/less important) the system may lose this
ATM cell if it has to.
 HEC (Header Error Control): in ATM, the ATM cell header
is error-protected.
The stratified connection control consisting of VC (which
corresponds to the user channel) and VP (which is a bundle of
VCs) enable highly flexible, extensible operation and
administration. ATM Adaptation Layer type 2 (AAL2) can set
multiple-user connections in VC. Figure 40 illustrates the
structure of ATM connections.

61
FI GU R E 40 ATM C ON N EC TI ON S
Normally, VP is setup on the basis of system data at the time of
building the network. VC connections can be divided into
Permanent Virtual Channel (PVC), which is inflexibly set up at
the time of network construction, and Switched Virtual Channel
(SVC), which is established and released on the basis of
signaling upon call origination and termination. The
establishment and release of the user connection through the
operation of SVC helps efficiently use ATM connection and
bandwidth resources.
ATM Adaptation Layer (AAL)
AAL is a protocol for coordinating the higher layer, which has
various traffic properties including speech, video streaming and
IP packets, and the ATM layer, which is specified regardless of
the higher-layer application.
Four types of AAL are specified, namely, AAL1,AAL2, AAL3/4 and
AAL5 .

WCDMA Theory
FI GU R E 41 ATM ADA P TA TION LA Y ERS (AALS)
 AAL1 is used for forwarding continuous, fixed-rate data,
such as PCM-coded speech.
 AAL2 was originally standardized for the purpose of
efficiently forwarding short frames in ATM; such as
compressed speech data used in mobile communications,
and is applied as the standard for transferring user data
in IMT-2000 RAN.
 AAL3/4 was developed for data communication purposes,
and is distinctive in that it can transfer up to 1024 types
of higher-layer data on one VC connection with a Multiple
Identifier (MID).
 AAL5 is a simpler protocol compared to AAL3/4, and is
widely used for forwarding data packets and control
signals.
AAL2 and AAL5 are applied in IMT-2000 specifications.
As shown in Figure 42, AAL is divided into two sublayers: the
Convergence Sublayer (CS) and the Segmentation And Re-
assembly (SAR) sublayer. The CS adapts AAL to upper protocol
layers and the SAR sublayer splits the data to be transmitted
into suitable payload pieces and, in the receiving direction,
collects payload pieces and assembles them back to the original
dataflow.

63
FI GU R E 42 GEN ER AL STR U C TU R E OF AAL
TAB L E 6 ATM A DA P T AT ION LA Y ERS U S ED I N UTRAN I N T ERFA CES
Iu Iur Iub
AAL5
CS C-plane
PS C/U-plane
- -
- C-plane -
- - C-plane
AAL2
CS U-plane - -
- U-plane -
- - U-plane
C-plane:Control plane; U-plane: User plane
AAL2
Figure 43 shows the frame structure of AAL2.
FI GU R E 43 AAL2 STR U C TU R E

WCDMA Theory
AAL2 has the function to multiplex up to 256 user connections
on one VC connection, and is able to transmit short frames in a
highly efficient manner with limited delay. The Common Part
Sublayer (CPS) packet consists of a 3-byte header and a payload
between 1 and 45 bytes. The header includes a Channel
IDentifier (CID) for user identification. Multiple user connections
can be transmitted by multiplexing them on one VC connection.
CPS packet is carried by CPS-Protocol Data Unit (PDU) to which
a one-byte STart Field (STF) is assigned, and converted into
cells.
Figure 44 illustrates the IMT-2000 interfaces and the AAL type
applied to the user-plane transfer.
FI GU R E 44 RAN I N TER FA C ES
AAL2 is an important protocol applicable from Node B to CN.
Although there are no specifications under 3GPP in regard to
transmissions inside CN, the application of AAL2 in CN enables
the traffic on the interface between Radio Network Contro llers
(RNCs) (Iur Interface) to be physically relayed by CN and
communications between IMT-2000 terminals to be transmitted
by AAL2 between Node Bs, which allows efficient operations.
AAL5
AAL5 is suitable for forwarding signaling data and IP packet
data. Figure 45 illustrates the frame structure of AAL5.

65
FI GU R E 45 AAL5 STR U C TU R E
The higher-layer user data are attached with a trailer (which
includes length information and error detection codes) and
PADding (PAD) for length adjustment, to construct a Common
Part Convergence Sublayer (CPCS)-PDU. The maximum length
of CPCS-PDU payload is 65535 bytes. Under IMT-2000, control
signals in RAN and PS data on the ATM-based Iu interface and
CN are transmitted in AAL5.
QoS Classes Under 3GPP
Under IMT-2000, which offers substantially faster transmission
speeds, Internet access and other data communications traffic is
expected to increase further. Meanwhile, IMT-2000 will also be
used for voice communications. Hence, each type of traffic would
need to assure a certain level of QoS according to the service
application. QoS classes specified by 3GPP are as follows.
 Conversational Class: Interactive communication that
requires low delay (e.g. speech).
 Streaming Class: Unidirectional communication, requiring
streaming service with low delay (e.g. real-time video
distribution).
 Interactive Class: Requires response within a certain
period and low error rate (e.g. Web browsing, server
access).
 Background Class: Requires best-effort services
performed in the background (e.g. e-mail, file download).
These QoS need to be assured end-to-end. The traffic
capabilities of ATM can be used to achieve this in RAN and CN,
as illustrated in Figure 46.

WCDMA Theory
FI GU R E 46 EN D-TO-EN D QOS A N D ATM QOS
In particular, ATM can disperse the processing load associated
with QoS control and execute network quality control with
certain standards by guaranteeing the QoS in the lower layer of
the network, without resorting solely to traffic control of end-to-
end protocols. The traffic management functions of ATM include
efficient use of network resources by statistical multiplexing,
provision of various service classes, assurance of communication
quality by securing bandwidth at the time of connection setup
and function to monitor contract traffic violations.
ATM Service Class
Figure 47 illustrates the transmission image of each service
class.
FI GU R E 47 ATM SER VI C E C L ASSES AN D B AN D W I D TH U SAGE
 Constant Bit Rate (CBR) is suitable for quality assurance
applications with a fixed speed, such as PCM coded
speech and unrestricted bearer services, as it secures
bandwidth based on the Peak Cell Rate (PCR).

67
 Real-time Variable Bit Rate (rt-VBR) and non-realtime
Variable Bit Rate (nrt-VBR) secure bandwidth with the
use of PCR, Sustainable Cell Rate (SCR) and Maximum
Burst Size (MBS). MBS specifies the permissible level of
burstiness in the traffic exceeding SCR, and assures the
speed of SCR in communications.
rt-VBR is suitable for variable bit rate, compressed
speech data, as it guarantees cellforwarding delays,
whereas nrt-VBR is suitable for bursty packet
communications with an assured data loss rate, as it does
not provide for quality in terms of delay. Because nrt-VBR
has a low delay requirement and allows more queuing
delay, its statistical multiplexing effect is greater than rt-
VBR.
 Unspecified Bit Rate (UBR) is a service class of a best-
effort type, for which there are no bandwidth or quality
provisions. As UBR does not normally secure bandwidth,
the inflow of data in excess of transmission capacity
results in data loss.
 Available Bit Rate (ABR) secures bandwidth at the
Minimum Cell Rate (MCR) and enables communications
up to PCR using flow control.
According to the characteristics mentioned in the preceding text,
the QoS classes under 3GPP may be mapped to the ATM service
classed as follows:
 Conversational class → CBR
 Streaming class → rt-VBR
 Interactive class → nrt-VBR
 Background class → UBR
IP Transport in UMTS
With the rapid growth of the global use of IP and the smooth
convergence of telecommunication and IP services, the use of IP
transport in the cellular network has become ever-current. IP-
based transport has already become commonplace in fixed
networks. In this way, it has proven its robustness and ability to
support a more distributed functional architecture coupled with a
more flexible network topology than what is practical in TDM or
ATM networks. IP transport benefits from economies of scale,
openness, simplicity and easy-to-deploy characteristics. While it
satisfactorily meets the requirements of the UMTS network it
also alleviates the limitations of an ATM-based transport
technology, at least for data-centric traffic.

WCDMA Theory
IP refers to a set of protocol stacks, specified by the Internet
Engineering Task Force (IETF), that form the pillars of the
Internet. All services (such as email, web browsing, file
downloads, gaming, etc.) use the IP to carry data throug h the
global network. As each data packet is identified by a unique
global address, user data can be dealt with by simply using
addressing and routing mechanisms when transferring data from
the source to the destination nodes.
A simplified illustration of an IP packet being transferred from
the source to the destination host is shown as Figure 48.
FI GU R E 48 IP TR AN SMI SSI ON
Coupled with other higher level protocol stacks, such as
Transmission Control Protocols (TCPs), IP constitutes a simple
and flexible data delivery mechanism that can convey any type
of digital information between devices connected in a world full
of heterogeneous networks and subnetworks. When an IP host,
such as a PC, mobile or any IP devices equipped with a global IP
address, desires to send a message to a destination IP device
the message body is encapsulated in an IP packet. Once the
packet is provided with the globally unique IP address of the
destination device and the IP routers in the Internet are in place,
delivering the packet to the target destination can be easily
achieved. In principle, the same procedure can be applied for all
services provided by the Internet.
The simplicity, openness and flexibility of IP transport, coupled
with its global acceptance, were found to be valuable assets for
it to be considered for UMTS networks as well. The UMTS packet
CN uses routers when connecting to the Internet. This allows, to
some extent, IP mobility and mobile Internet services to be
offered to mobile users.
Ever since 3GPP R5, user data can be transported across all
UTRAN interfaces by using the IP protocol stack as well (see
Figure 37). The common part of the IP stack used for user data
transport is UDP/IP: on the Iub and Iur interfaces, radio frames
are transported as plain UDP datagrams; on the Iu-PS interface,
the tunnelling protocol (GTP-U) is used to carry user data
packets; and on the Iu-CS interface, the Real Time Protocol
(RTP) is used on top of UDP/IP to carry speech frames.

69
In order to maintain harmonisation between IP transport and
ATM transport of UMTS signalling both stacks should provide the
same transport service. Therefore, it was decided to “surface”
both stacks using the Signalling Connection Control Part (SCCP)
protocol entity, which always delivers a harmonised signalling
transport service.
In the original case of SS7 signalling network the SCCP protocol
is running on top of the Message Transfer Part Layer 3 (MTP3)
protocol, which is responsible for routing signalling messages
between signalling points.
The adaptation of the SCCP protocol on top of the IP protocol
stack was achieved by using two convergence protocols, which
are developed and standardised by the SIGTRAN Working Group
at the IETF. These protocols and the corresponding IETF
documents are:
 Stream Control Transport Protocol (SCTP), RFC 2960.
 MTP3 User Adaptation (M3UA) layer (Internet draft
document).
The purpose of the SCTP is to provide a robust and reliable
signalling bearer. To achieve this, SCTP provides appropriate
congestion control procedures, fast retransmit in the case of
message loss and enhanced reliability. It also provides additional
security against blind attacks and will be used to increase
security in connecting the UMTS networks of different operators.
The purpose of the M3UA protocol is to support SCCP signalling,
so that the SCCP lower interface does not need to be modified.
M3UA needs to manage the use of SCTP streams and to match
the performance of its SS7 counterpart, the Message Transfer
Part-3 Broadband (MTP-3B) protocol, while running on top of an
IP stack. M3UA provides mapping of SS7 addressing to IP
addressing.

71
C h a p t e r 5
ProcedureExamples
Elementary Procedures
In order to get a network-wide view of some of the most
important Universal Mobile Telecommunication System (UMTS)
functionalities discussed in the preceding chapters we present a
few examples of UMTS system procedures.
These procedures illustrate the way in which the actions carried
out by all network entities are coordinated as well as the role of
UMTS protocols in controlling this coordination.
In this chapter a basic model for system-wide procedures is
presented by modelling each system procedure as a kind of
communication-intensive transaction. The concept of transaction
is used to underline the fact that these system-wide procedures
are executed into well-defined completion and that subsequent
procedures represent fairly independent instances of
communication.
The layering and interworking of protocols allows us to identify a
set of elementary procedures that can be used as building blocks
in the design of network transactions. Depending on the
transaction and its type—whether it is Mobile Terminating (MT)
or Mobile Originating (MO)—some parameters and messages are
known to vary within elementary procedures and certain
elementary procedures may or may not be used.
The transport network is used in every procedure: signalling
transport is always required and user data transport is required
by many transactions. Radio network functions are needed
whenever access network services are required within an
elementary procedure.
The overall control of system transactions is carried out by
system network protocols, which invoke the elementary
procedures in a stepwise manner and determine how the
transaction proceeds through the different steps.

WCDMA Theory
Basically, any network transaction can be divided into the eight
steps presented in Figure 49. For each step an elementary
procedure can be distinguished.
FI GU R E 49 BASI C MOD EL OF UM TS N ETW OR K TR AN SAC TI ON S
 Paging is a Mobility Management (MM) procedure that is
used when searching for a given subscriber within the
network coverage area. This procedure is only executed if
the transaction originates from the network side. The
remaining seven steps are the same irrespective of whether
the transaction is originated or terminated by the User
Equipment (UE).

73
 Radio Resource Control (RRC) connection setup is an
elementary procedure containing both activities and a
message flow to establish radio control connection between
the terminal and Radio Access Network (RAN). The details of
this procedure vary depending on the case.
 Transaction reasoning is an elementary procedure in which
the terminal indicates to the Core Network (CN) the kind of
transaction requested. Based on reasoning information the
CN may decide whether to proceed with the transaction or
decide to terminate execution of the transaction.
 After these steps, authentication and security procedures
normally take place. This elementary procedure mutually
authenticates the UMTS subscriber and the network and later
activates the necessary security mechanisms for access
network connection.
 Transaction setup and Radio Access Bearer (RAB) allocation
is an elementary procedure that allocates the actual
communication resources for the transaction. Therefore, the
details of this procedure depend on the type of transaction
(circuit-switched or packet-switched).
 The elementary procedure transaction is the phase when
there exists a user-plane connection (i.e., the UE has a UMTS
bearer connection active across the whole UMTS network).
 Transaction clearing and RAB release is an elementary
procedure used for releasing network resources related to
the transaction.
 RRC connection release is an elementary procedure
containing mechanisms by means of which the radio control
connection between the UE and the access network can be
released.
Paging
The paging procedure is shown as Figure 50 and Figure 51.
FI GU R E 50 PAGI N G TYPE 1

WCDMA Theory
FI GU R E 51 PAGI N G TYPE 2
The paging procedure is needed whenever a UE-terminating
transaction is to be carried out. Unlike the case for the Global
System for Mobile Communications (GSM), the UMTS contains
two types of paging methods, Paging Type 1 and Paging Type 2.
Paging Type 1 is used by CN domains and is the “conventional”
way to use paging. Paging is part of the radio network control
plane and is delivered over the Iu Interface by using a ranap
paging message. The CN domain that initiates paging addresses
it to those Location Areas/Routing Areas (LAs/RAs) to which the
desired UE has last reported its location (i.e., by carrying out
either location update or routing area update).
A ranap paging message contains two mandatory parameters,
the requesting CN domain and an International Mobile
Subscriber Identity (IMSI). From a system security point of
view, the unnecessary transfer of IMSI over the Uu reference
point without encryption is not desired and, because of this, the
Radio Network Controller (RNC) may or may not perform a
number of conversions for the IMSI. For example, the RNC may
issue an rrc paging type 1 message containing a Radio Network
Temporary Identity (RNTI) instead of an IMSI. This value is
assigned when the UE is attached to the network or has carried
out the previous transaction.
In addition to the previously described use, rrc paging type 1
has some RAN-specific uses. When the UE is not in idle mode
and changes in system information parameters need to be made
known to the UE, the RNC may use rrc paging type 1 to
“awaken” the UE and, thus, make it able to read revised system
information or certain parts of it. If the UE has a Packet
Switched (PS) connection in which no activity is taking place the
RNC uses rrc paging type 1 to inform the UE that the PS
connection should be reactivated. In this case there are some
packet data the CN needs to deliver to the UE. This forces the
UE to perform cell update, after which the RNC is able to route
data packets to the correct UE.
UMTS terminals are meant to be able to handle a number of
connections simultaneously (i.e., they can have more than one
connection at a time with CN domains). When the UE already
has a connection with one CN domain and another connection is
established with the same domain the CN sends ranap paging as
in previous cases. The paging sent to the UE by the Serving RNC
(SRNC) is now rrc paging type 2.

75
Separation between Paging Type 1 and Paging Type 2 is done in
the RNC, where RANAP paging always looks the same. The
difference between Paging Type 1 and Paging Type 2 is that the
former is used for paging those UEs that are in idle mode, Cell
Paging Channel (Cell_PCH) state or UMTS Terrestrial Access
Network (UTRAN) Registration Area Paging Channel (URA_PCH)
state and, hence, could either be used for certain UEs or for all
UEs within cell(s). Paging Type 2, on the other hand, is used for
paging those UEs that are in Cell Dedicated Channel (Cell_DCH)
state or Cell Forward Access Channel (Cell_FACH) state and,
therefore, is always dedicated and addressed to just the one UE.
RRC Connection Setup
The RRC connection setup procedure is shown as Figure 52.
FI GU R E 52 RRC CON N EC TI ON SETU P
RRC connection setup always starts at the UE with the message
rrc connection request sent over the Common Control Channel
(CCCH). CCCH in the uplink direction means the Random Access
Channel (RACH) . RRC connection request content actually
comes from the UE over physical RACH as a result of the initial
access procedure. This message reaches the RNC over the Iub
RACH data port. Upon receiving this message the RRC entity at
the RNC end changes its state from IDLE to CONNECTED
Cell_FACH or CONNECTED Cell_DCH. Then the RNC

WCDMA Theory
communicates with the UE over common control channels (of
these, FACH and RACH are respectively used).
The rrc connection request message contains a lot of information
related to requested radio connection, terminal and subscriber
identity; in this message the UE sends to the network such
information as the IMSI or Temporary Mobile Subscription
Identity (TMSI), International Mobile Equipment Identity (IMEI),
Location Area Identity (LAI) and Routing Area Identity (RAI).
The rrc connection request must indicate how many of these
values are inserted in the message and, accordingly, contain
these values as well. In addition to these identities the rrc
connection request contains the reason radio connection is
requested. There are various reasons and the following list
shows some of them:
 Originating conversational call.
 Originating streaming call.
 Originating interactive call.
 Originating background call.
 Terminating conversational call.
 Terminating streaming call.
 Terminating interactive call.
 Terminating background call.
 Emergency call.
 High-priority signalling.
 Low-priority signalling.
 Call re-establishment.
As can be seen from the list, the rrc connection request already
indicates what kind of Quality of Service (QoS) will be requested
when the transaction proceeds. An emergency call is itemised
because it will be treated differently over the network than
under normal transaction conditions. If the subsequent
transaction will just be signalling, this is indicated, too.
Depending on the reason for the request, the RNC makes a
decision about whether to allocate dedicated or common
resources to this transaction. Based on this decision, the SRNC
allocates RNTI and other resources to this transaction. The Iub
interface is “opened” when the RNC sends an nbap radio link
setup message to the BS. This message contains the transport
format description, power control information and code
information, the latter being the uplink scrambling code for
WCDMA-FDD. The Base Station (BS) acknowledges this message
by sending an nbap radio link setup response message. This
message informs the RNC about transport-layer addressing
information (AAL2 address) and provides some referenc e
information for establishment of an Iub bearer in the transport
network.

77
The SRNC starts Iub bearer establishment according to
information received from the BS. This procedure is carried out
by the internal control plane of the transport network at the Iub
interface. The established Iub bearer is bound together with the
DCH assigned to the transaction. Afterwards, the frame protocol
connection over the Iub is synchronised with message exchange.
If we suppose that a dedicated radio connection using DCH is set
up here, then it is the DCH Frame Protocol (DCH-FP) for the Iub.
When Iub communication is ready, the RNC sends the rrc
connection setup message to the UE over common control
channels (FACH in this case). In this message the SRNC informs
the UE of the transport format, power control and codes, which
in the case of Wideband Code Division Multiple Access Frequency
Division Duplex (WCDMA-FDD) is a downlink scrambling code.
The UE confirms RRC connection establishment by sending the
message rrc connection setup complete.
Transaction Reasoning
The transaction reasoning procedure is shown as Figure 53.
FI GU R E 53 TR AN SAC TI ON R EASON I N G
When RRC connection has been established, the UE sends the
message rrc initial direct transfer, which carries in its payload
the first system network message of the transaction from the UE
to the network.
Upon receiving this information the RNC adds some more
parameters to the message and forwards this combination to the
appropriate CN domain as a ranap ue initial message. This
message contains in its payload the contents of the original rrc
initial direct transfer message together with the first system
network message generated by the UE. The contents of the
ranap ue initial message provide the CN with a lot of information
about the transaction initiated by the UE. Among such
information is the (claimed) identity of the UMTS subscriber
(TMSI or IMSI), his or her current location area and the kind of
transaction requested. All this information is used by the CN
node to decide how best to proceed with the transaction request.

WCDMA Theory
Authentication and Security
Control
Figure 54 shows the message flow related to access network
security in the context of a transaction.
FI GU R E 54 AU TH EN TI C ATI ON AN D SEC U R I TY C ON TR OL
During RRC connection establishment the UE has already
informed the RNC, using the UE classmark parameter, about
many of its capabilities, one of which being the security
algorithms it supports.
The UE and the network authenticate each other by sending the
mm authentication request message in the payload of ranap and
rrc direct transfer messages to the UE. After executing the
authentication algorithms on the Universal Subscriber Identity
Module (USIM), the UE responds with an mm authentication
response message, again in the payload of rrc and ranap direct
transfer messages. In this dialogue the RNC acts as a relay that
forwards the contents of ranap direct transfer to rrc direct
transfer and vice versa.
With a ranap security mode command message the related CN
domain indicates to the UTRAN whether the transaction should
be encrypted. This message indicates the selected security
algorithms and delivers the integrity and encryption keys to the
UTRAN.
Based on this information the RNC commands the UE to start
encryption using the corresponding keys and algorithms by
sending the rrc security mode command.
By issuing an rrc security mode complete message the UE
indicates that it has successfully turned on the selected integrity
protection algorithm and the encryption algorithm, thus
protecting further communication in this transaction.

79
The RNC still has to inform the related CN domain about
procedure completion by sending the message ranap security
mode complete.
Transaction Setup with Radio
Access Bearer (RAB) Allocation
 CS Domain
Transaction setup with RAB allocation (CS) is shown as
Figure 55.
FI GU R E 55 TR AN SAC TI ON SETU P W I TH RAB AL L OC ATI ON (CS)
Transaction setup with RAB allocation is the first step where
the different nature of CN domains has to be taken into
account.
In CS transactions the actual setup information is delivered
through rrc/ranap direct transfer messages. These messages
can carry in their payload the cc setup message, as shown in
Figure 55. This message identifies the transaction and
indicates the QoS requirements; in other words, the type of
bearer required for the service and the parameters it should
contain:
 Transaction Identifier (TI)
 Stream identifier
 Traffic class
 Asymmetry indicator

WCDMA Theory
 Maximum bit rate
 Guaranteed bit rate
By means of the TI value the UE and the CN node are able to
separate each other’s calls. Each call has its own TI value.
The stream identifier recognises the bearer used for this call.
If the stream identifier value does not yet exist, this means
that the CC protocol in the UE wants to establish a new
bearer. The stream identifier value could be in use already,
in which case the CC protocol will want to establish a
multicall using an existing bearer (given by the stream
identifier).
Upon receiving the cc setup message the MSC Server bursts
into action. First, it checks whether the UE and current
subscription are allowed to perform the requested operation.
If yes, the MSC server starts RAB allocation by assigning a
unique RAB ID and requesting the setup of an RAB with the
requisite QoS parameters by sending the message ranap rab
assignment request over the Iu interface.
When the RNC receives the ranap rab assignment request it
commences radio bearer allocation by first checking whether
there are enough resources available to satisfy the requested
QoS. If so, the radio bearer is allocated according to the
request. If not, the RNC may select either to continue
allocation with lowered QoS values (e.g., the maximum bit
rate for the bearer could be lowered) or it may choose to
queue the request until radio resources become available.
The RNC informs the UE about bearer allocation by sending
the message rrc radio bearer setup to the UE. When the UE
receives this message, it is then in a position to combine the
information it originally sent to the network in its cc setup
message with the received radio bearer identifier.
Afterwards, the UE can route user data traffic (user plane) to
the correct radio bearer. As soon as the UE is able to receive
data from the new radio bearer it acknowledges this by
sending the rrc radio bearer setup complete message to the
RNC. The RNC must also establish an Iu bearer for the new
transaction. After this the RNC indicates that an RAB has now
been allocated by sending the message ranap rab
assignment response to the MSC server. If the RNC made
any changes to the QoS values requested by the MSC server,
they are indicated in this message. Now, the RAB is
established and the procedure continues at the CC protocol
level.
 PS Domain
Transaction setup with RAB allocation (PS) is shown as
Figure 56.

81
FI GU R E 56 TR AN SAC TI ON SET-U P W I TH RAB AL L OC ATI ON (PS)
When an RAB is to be established for a PS transaction, the
procedure looks pretty much the same (see Figure 56) and
any differences are within the messages. Instead of the CC
protocol the UE now uses the Session Management (SM)
protocol. The UE sends the sm activate pdp context request
message to the network as an rrc direct transfer message
and the RNC relays this as a ranap direct transfer message
to the SGSN in the CN. Radio bearer allocation is similar to
that of CS traffic except that the parameters describing the
QoS properties of the bearer are different. For example,
guaranteed bit rate is an essential parameter for a PS RAB
but is not significant for CS RABs. After an RAB has been
established the CN domain confirms packet session
establishment by sending an sm activate pdp context accept
message. In terms of SM this means that the SM state is
now active and that the UE and the CN domain are able to
exchange PS data.
Transaction
In the most typical cases this phase of the transaction contains
an active user-plane connection.
However, if RRC connection was requested simply for a signaling
purpose, no user-plane bearers are needed.

WCDMA Theory
Transaction Clearing and RAB
Release
 CS Domain
FI GU R E 57 CS TR AN SAC TI ON C L EAR I N G SI GN AL L I N G W I TH RAB R EL EASE
If a transaction has an active user plane, then the user plane
is disconnected first. The disconnect procedure depends on
the transaction type. Figure 57 shows how a CS transaction
is cleared. In this case, clearing is started by the UE, but the
CN can also start user-plane disconnection. More generally,
either party can clear a normal CS call, and this does not
depend on which party initiated the call.
When the user plane has been disconnected, the system
releases the RAB by means of a separate subprocedure.
When this is done using the ranap rab assignment request
and ranap rab assignment response, which indicate release
as shown in Figure 57 , signalling connection still remains.
The UE still has an RRC connection to the UTRAN and any
other RABs for the same UE may still exist. In the general
case, when there is a single RANAP RAB Assignment Request
message, the CN may cause a number of RABs to be
created, deleted or modified.
If all the RABs between the UE and CN domain are released
at the same time and the related radio resources are
deallocated as well, this can be done by using a ranap iu
release command, as shown in Figure 58.

83
FI GU R E 58 CS TR AN SAC TI ON C L EAR I N G SI GN AL L I N G W I TH IU REL EASE
Upon receiving this message the RNC initiates rrc radio
bearer release over the Iub interface. In addition to this, all
possible radio bearers established through Drifting RNCs
(DRNCs) are released.
When the radio bearers are released, RRC connection is also
released. When all the radio bearers and the RRC connection
have been released, the RNC informs the CN domain with a
ranap iu release complete message.
 PS Domain
In PS connections, the user plane and RAB(s) are cleared in
the same way as done for CS connections. Again, any
differences are at the message parameter level. Error!
Reference source not found. illustrates the case where PS
connection is closed by deactivation of the Packet Data
Protocol (PDP) context.

WCDMA Theory
FI GU R E 59 PS TR AN SAC TI ON C L EAR I N G W I TH RAB R EL EASE
The closing of a PS connection is an SM protocol task where
the SM changes its state from active to inactive. The
signalling procedure used for this state transition is called
“PDP context deactivation”. When the UE wants to do this, it
sends an rrc direct transfer message containing an sm
deactivate pdp context request to the SRNC. The SRNC
further relays it as a ranap direct transfer message to the CN
PS domain. A PDP context deactivation request indicates to
the SGSN that the RAB allocated for this PS connection is no
longer needed and, thus, should be released. RAB release is
done in the same manner as for CS connection.
When the RAB has been released, the SGSN indicates that
PS connection is now deactivated by sending the sm
deactivate pdp context accept message to the UE.
After this procedure the UE still has RRC connection with the
network and may have other CS and PS connections open. If
all PS connections are to be terminated and related radio
resources deallocated, the system uses the ranap iu release
command in the same way as it did for CS connections (see
Figure 60).

85
FI GU R E 60 PS TR AN SAC TI ON C L EAR I N G W I TH RANAP IU R EL EASE
RRC Connection Release
The RRC connection release procedure, which is shown in Figure
61, is always started by the RNC.
FI GU R E 61 RRC C ON N EC TI ON R EL EASE
The RNC identifies which RRC connection is to be released and
then sends this information to the UE in the rrc connection
release message.

WCDMA Theory
The UE acknowledges that RRC connection has been released by
sending an rrc connection release complete message.
Afterwards, the RNC starts to clear Iub interface resources. This
is done by exchange of nbap radio link deletion and nbap radio
link deletion response messages.
When radio link deletion is agreed at the NBAP level, the
transport data bearer at the Iub interface is released. Any radio
links established over a Drifting RNC (DRNC) also have to be
released by using Iur subprocedures (not shown in Figure 61).

87
C h a p t e r 6
WCDMAEvolved
WCDMA Evolved Overview
The term “WCDMA Evolved” describes the evolution of
WCDMA addressing both operators need for efficiency and
end-users demand for enhanced experience and simplicity.
The first evolved step of WCDMA is HSDPA – High Speed
Downlink Packet Access.
Later, features to further enhance the uplink with improved
coverage for high data rates, improved uplink capacity and
reduced uplink delay will be part of the second step within
WCDMA Evolved.
The following chapters will focus on the first step of WCDMA
Evolved, HSDPA.
HSDPA
The Concept of HSDPA
In WCDMA 3GPP release 5, WCDMA has been extended with a
new transport channel, the high-speed downlink shared channel
(HS- DSCH), which provides enhanced support for interactive,
background, and to some extent, streaming radio access bearer
(RAB) services in the downlink.
HS-DSCH transmission facilitates several new features. But to
support them with minimum impact on the existing radio
interface protocol architecture, a new MAC sub-layer, MAC-hs,
has been introduced for HS-DSCH transmission. MAC-hs makes
it possible to retain a functional split between layers and nodes
from WCDMA 3GPP release 99.

WCDMA Theory
A minimum of architectural changes allows a smooth upgrade to
HSDPA and ensures HSDPA operation in environments where not
all cells have HSDPA functionality.
HSDPA is based on “fat-pipe”, shared-channel transmission. Its
key features are rapid adaptation to changes in the radio
environment and fast retransmission of erroneous data,
Therefore, the corresponding functionality must be placed close
to the air interface.
The HSDPA concept is based on the following features:
 Shared channel transmission
 Higher-order modulation
 Short transmission time interval (TTI)
 Fast link adaptation
 Fast scheduling
 Fast hybrid automatic-repeat-request (ARQ).
Shared channel transmission
HS-DSCH is based on shared-channel transmission, which
means that some channel codes and the transmission power in a
cell are seen as a common resource that is dynamically shared
between users in the time and code domains.
Shared channel transmission results in more efficient use of
available codes and power resources in WCDMA compared to the
current use of a dedicated channel (WCDMA 3GPP Release 99).
The shared code resource onto which the HS-DSCH is mapped
consists of up to 15 codes. The spreading factor (SF) is fixed at
16 (Figure 1). The actual number employed depends on the
number of codes supported by the terminal/system, operator
settings, and system capacity.

89
FI GU R E 62 HS-DSCH C OD E AN D TI ME STR U C TU R ES
Higher-order modulation
WCDMA 3GPP release 99 uses quadrature phase-shift keying
(QPSK) modulation for downlink transmission. Besides QPSK,
HS-DSCH can also use 16-quadrature amplitude modulation
(16QAM) to provide higher data rates. Because 16QAM has twice
the peak rate capability of QPSK it makes more efficient use of
bandwidth than QPSK. Nevertheless, it also requires better radio
channel conditions than QPSK.
FI GU R E 63 M OD U L ATI ON SC H EMES U SED W I TH HSDPA

WCDMA Theory
Short transmission time interval (TTI)
Channel codes from the shared code resource are dynamically
allocated every 2 ms or 500 times per second. A short TTI
reduces roundtrip time and improves the tracking of channel
variations—a feature that is exploited by link adaptation and
channel-dependent scheduling. Although time is the primary way
of sharing the “fat-pipe” resource among users, it is also
possible to share resources in the code domain by using
different subsets of the total HS-DSCH channel code set.
Fast link adaptation
Radio channel conditions experienced by different downlink
communication links vary significantly both in time and between
different positions in the cell. Fast link adaptation adjust s the
transmission parameters to instantaneous radio conditions and,
when channel conditions permit, enables the use of high-order
modulations.
FI GU R E 64 TR AN SMI SSI ON PAR AMETER S AD JU STED TO I N STAN TAN EOU S
R AD I O C ON D I TI ON S
WCDMA uses power control to compensate for differences and
variations in the instantaneous radio channel conditions of the
downlink. In principle, power control give communication links
with bad channel conditions a proportionally larger part of the
total available cell power. This ensures similar service quality to
all communication links, despite differences in radio channel
conditions. At the same time, radio resources are used more
efficiently when allocated to communication links with good
channel conditions. Thus, when seen in terms of overall system

91
throughput, power control is not the most efficient means of
allocating available resources.
Instead of using power control to compensate for rapidly varying
radio conditions in the downlink, HS-DSCH relies on rate
adjustment. That is, while keeping transmission power constant,
it adjusts the data rate by changing the channel-coding rate.
Commonly known as rate adaptation or link adaptation, this
method is more efficient than power control for services that
tolerate short-term variations in the data rate. What is more, to
further increase peak data rates, HS-DSCH can use spectral-
efficient 16QAM modulation when channel conditions permit.
Fast scheduling
The fast-scheduling feature determines to which user equipment
(UE) the shared channel transmission should be directed at any
given moment. The objective is to transmit to users with
favorable radio conditions.
FI GU R E 65 TR AN SMI TTI N G TO U SER S W I TH F AVOR AB L E R AD I O C ON D I TI ON S
The scheduler determines overall HSDPA performance. For each
TTI, the scheduler decides which users the HS-DSCH should be
transmitted to, and in close cooperation with the link adaptation
mechanism, which modulation and how many codes should be
used. This yields the actual end-user bit rate. Instead of
sequentially allocating radio resources among users (round-robin

WCDMA Theory
scheduling), capacity can be increased significantly using
channel-dependent scheduling. The aim of channel-dependent
scheduling is to transmit to users with favorable instantaneous
channel conditions. The gain obtained by transmitting to users
with favorable conditions is known as multi-user diversity.
Ericsson has chosen to use a proportional fair scheduler to better
exploit the channel conditions and to ensure that all users
receive a guaranteed minimum throughput.
As cell load increases, the number of users queued for
scheduling increases. Therefore, the probability of scheduling
users with good channel quality also increases. This typically
results in a high carrier-to-interference ratio for the scheduled
user. Traffic priorities can also be taken into account—for
example, streaming services can be prioritized ahead of
background users.
A practical scheduling strategy usually exploits short-term
variations while maintaining some degree of long-term fairness
between users. Long-term unfairness results in excess cell
capacity. The differences between various scheduling strategies
are most obvious when system load is heavy.
Fast hybrid automatic-repeat-request
(ARQ)
The UE can rapidly request the retransmission of missing data
and combine information from the original transmission with that
of the later transmission before attempting to decode the
message. This approach, called soft-combining, increases
capacity and provides robustness. A negative acknowledge
(NACK) reply is sent when data is missing at the receiving end.
An acknowledge (ACK) reply is sent when received data is
correct.
FI GU R E 66 RAPI D R EQU EST OF R ETR AN SMI SSI ON OF MI SSI N G D ATA

93

WCDMA Theory

Figures
Figure 1 Maximal ratio “RAKE” combining of symbols ..............6
Figure 2 RAKE Diversity Receiver ........................................6
Figure 3 Open Loop Power Control.......................................8
Figure 4 Softer handover ................................................. 11
Figure 5 Soft Handover ................................................... 11
Figure 6 Hard Handover................................................... 12
Figure 7 The basic process of handover .............................. 13
Figure 8 Handover Flow ................................................... 13
Figure 9 Event correlative to soft handover ......................... 14
Figure 10 Event correlative to hard handover ...................... 14
Figure 11 Event correlative to handover between systems ..... 14
Figure 12 Soft Handover (Adding a Link) Signaling Flow ........ 15
Figure 13 Compression Mode Principle ............................... 16
Figure 14 UTRAN Common Protocol Model .......................... 21
Figure 15 Radio interface protocol reference model............. 24
Figure 16 Access Layer and Non-access Layer ..................... 26
Figure 17 Channel types in UT RAN .................................... 32
Figure 18 Uplink Mapping................................................. 32
Figure 19 Downlink Mapping............................................. 33
Figure 20 Logical channel................................................. 35
Figure 21 transport channel ............................................. 36
Figure 22 uplink physical channel ...................................... 38
Figure 23 frame structure of uplink dedicated physical channel
.................................................................................... 39
Figure 24 frame structure of random access channel ............ 40
Figure 25 frame structure of CPCH .................................... 41
Figure 26 downlink physical channel .................................. 43
Figure 27 frame structure of DL DPCH................................ 44
Figure 28 Frame structure of SCH ..................................... 45
Figure 29 frame structure of CPICH ................................... 45

WCDMA Theory
Figure 30 Frame structure of PICH .................................... 47
Figure 31 Frame structure of AICH .................................... 48
Figure 32 Frame structure of AP-AICH ............................... 49
Figure 33 Frame structure of CD/CA-ICH............................ 50
Figure 34 Frame structure of P-CCPCH............................... 50
Figure 35 Frame structure of S-CCPCH............................... 51
Figure 36 Frame structure of PDSCH.................................. 52
Figure 37 Protocol stacks for ATM and IP transport............... 57
Figure 38 ATM cell structure............................................. 59
Figure 39 ATM cell header structure................................... 60
Figure 40 ATM connections .................................................. 61
Figure 41 ATM Adaptation Layers (AALs) ............................ 62
Figure 42 General structure of AAL.................................... 63
Figure 43 AAL2 structure ............................................... 63
Figure 44 RAN interfaces ..................................................... 64
Figure 45 AAL5 structure..................................................... 65
Figure 46 End-to-end QoS and ATM QoS ................................... 66
Figure 47 ATM service classes and bandwidth usage ............. 66
Figure 48 IP Transmission................................................ 68
Figure 49 Basic model of UMTS network transactions............ 72
Figure 50 Paging Type 1.................................................. 73
Figure 51 Paging Type 2.................................................. 74
Figure 52 RRC Connection Setup..................................... 75
Figure 53 Transaction reasoning ....................................... 77
Figure 54 Authentication and security control...................... 78
Figure 55 Transaction setup with RAB allocation (CS) ........... 79
Figure 56 Transaction set-up with RAB allocation (PS) .......... 81
Figure 57 CS transaction clearing signalling with RAB release .. 82
Figure 58 CS transaction clearing signalling with Iu Release ... 83
Figure 59 PS transaction clearing with RAB release .............. 84
Figure 60 PS transaction clearing with RANAP Iu release ....... 85
Figure 61 RRC connection release ..................................... 85
Figure 62 HS-DSCH code and time structures...................... 89
Figure 63 Modulation schemes used with HSDPA.................. 89
Figure 64 Transmission parameters adjusted to instantaneous
radio conditions .............................................................. 90

97
Figure 65 Transmitting to users with favorable radio conditions
.................................................................................... 91
Figure 66 Rapid request of retransmission of missing data ..... 92

WCDMA Theory

Tables
Table 1 Chapter Summary ..................................................i
Table 2 Typographical Conventions...................................... ii
Table 3 Mouse Operation Conventions ................................. iii
Table 7 Transport channel to physical channel mapping ........ 33
Table 8 Mapping of paging indicators Pq to PICH bits............. 48
Table 9 ATM adaptation layers used in UTRAN interfaces ....... 63

Umtsrns 201 wcdma theory

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