Wcdma radio functionality

UMTS Radio Features Presentation

Praveen Gupta, MobileStack,
pgupta@mobilestack.com

UMTS Presentation - 1

Admission control overview
Guarantees the overall Quality of Service by controlling the
number of users

Interference
Coverage
Planned coverage
Admission New users blocked
threshold above this point
User added

Capacity / Load

Planned load


Admission control purpose & algorithm
description

Purpose:
– This algorithm selectively denies access requests in order to limit the
load.

Algorithm description:
– When new resources are required for a radio connection (Radio Link
set-up or modification), the Radio Connection Coordination algorithm
requests admission.

This requests includes parameters specifying the requested amount of
resources. Admission Control checks if the requested amount of
resources is available.


Characteristics of admission control

The RBS regularly reports measurements values of
transmitted power
By knowing the connections, the RNC keeps track of ASE,
RBS HW and DL code usage
Handover legs have higher priority than new calls
Different thresholds for different services
At high load, interactive users may be offered lower
datarates than under normal load conditions


Congestion control overview

Bitrate

Over load is resolved by:

Delaying packets
Call removal


Congestion control purpose & algorithm
description

Purpose: This algorithm solves overload situations. An
overload situation occurs due to fluctuations in the UL
interference and the used DL power.

Algorithm description : The algorithm is only triggered in
case of (near) overload in a cell. The algorithm acts in case
the transmitted Carrier Power measurement (DL Power)
indicates overload. It is possible to set different thresholds
for different services.


Example 1: Congestion control work flow
DL power or UL interference
exceeded

Restrict access

Order admission to block

No At overload, alter
Yes Interactive users in connection with
system? highest DL power

Move user to common ch Remove user

Set timer
Message: over- Allow admission
Timer expired load resolved
Wait for command and access


Enhanced Capacity control

Admission control checks HW
resources in both UL & DL

Directed retry at call set-up to
GSM in case of admission denial
in WCDMA

Load balancing between
different frequencies


Power control overview

P(SIR-Target,UL)

Closed loop

DL-TPC UL-TPC UL-Outer loop RNC

SIR-Target,UL
P(SIR-Target, DL)
SIR-Error,UL

DL-Outer loop

BLER-Measured,DL Open loop

SIR-Target,DL P(Startvalue)
BLER = Block Error Rate
SIR = Signal to Interference Ratio
TPC = Transmit Power Control


Power control purpose & reason
Purpose:
The purpose is to minimize the transmit power while
maintaining the quality of radio links. There are three
different types power control:
– Inner loop power control
– Outer loop power control
– Open loop power control.
Reason:
Power control
– Maintains the quality of the connections
– Reduces power consumption
– Minimizes interference
– Improves the coverage and capacity of the system

Power control over time
RBS Inner-loop power Control Inner-loop power Control
Receive Power (Initial Receive Power (Updated Receive Power Target
Target) by Outer-loop power Control)

Open-loop Power Control
Access Preambles

time
Access Preambles RACH DPCH
1500 updates/sec

RBS Receive Power Target

The PRACH is “power controlled” by means of preamble ramping


Channel type switching overview

User 1 User 2
Random-Access Random-Access
Request Request

Random-Access Channel
Switch to Switch to
dedicated TTime-out common
Packet Packet Packet

Dedicated Channel
Release dedicated
channel


Channel type switching purpose & reason

Purpose:
To optimize the channel usage for best effort packet switched
users (Interactive users). To determine if it is necessary to
switch UE connected substates e.g. from a common to a
dedicated channel.

Reason:
For best effort traffic for a particular user there is large
variations in time in the offered traffic (bursty nature of traffic).
It is not efficient for the air-interface to keep up resources for a
dedicated channel continuously. This function saves also
battery for connected UEs, which are not transferring data.

Channel rate switching
Change bit rate when moving away
from RBS:

- UL supported by UE
- DL supported in RNC

Bit rate
Advantage: Higher coverage and higher
capacity

Change of bit rate at high load
Distance
- Reduce bitrate for Interactive users from RBS
- Reduce bitrate for voice users by or
changing AMR mode Load in
the cell
Advantage: Lower blocking probability


Adaptive Multi Rate (AMR) Rate Selection

Selection of the AMR mode
at call set up Bit rate for a user
[kbps]
About four combinations of
simultaneous modes 12.2 X
7.95 X
defined by the standard is 4.75 X
supported
The modes range from Distance
around 4.75 kbps up to 12.2 from RBS
or
kbps Load in
the cell


Adaptive Multi Rate (AMR) Rate Control

Possible to change the AMR
mode for coverage and Bit rate for a user
capacity reasons dynamically. [kbps]

The AMR switching and rate 12.2
7.95
control optimises the usage of 4.75
the air-interface by adapting
the AMR rates for coverage Distance
and capacity reasons. from RBS
or
Load in
the cell


Transmit Diversity - Open loop
- Introduced to combat fading with up to 5dB gain in the downlink

On 10 dB
On

Off
15 dB


Open Loop Transmit Diversity
Coverage & capacity gain
– additional diversity effect -> less transmitted power -> less
interference in the system

The same information is transmitted from the two
antennas. For each antenna the information is coded in a
different way.

The total transmitted power is split between the two
antennas.


- Space-Time Transmit Diversity (STTD)
A b0 b1 b 2 b3 Antenna A
B
b0 b1 b2 b3

-b2 b3 b0 -b1 Antenna B
Channel bits

STTD encoded channel bits
for antenna A and antenna B.

The signals from the two antennas are spread and scrambled with the
same code and simultaneously transmitted
The two signals experience different fading patterns and the RAKE
receiver observes the sum of the two faded orthogonal signals
The resulting signal has a smoother fading pattern than the two original
signals
Used on all DL channels (except SCH and CPICH).


- Time Switched Transmit Diversity (TSTD)

b0 b2 Antenna A

b0 b1 b2 b3

b1 b3 Antenna B
Channel bits

In TSTD the transmission alternates between the antennas
Used on Synchronization Channel (SCH)
TSTD is implemented as a part of STTD


Transmit diversity - Closed-loop

Closed-loop Transmit Diversity (DPCH, PDSCH only)
– UE sends Feedback Information (FBI) Bits to the RBS over the DPCCH
– FBI bits tell the RBS how to adjust antenna gain (only mode 2) and phase (both
mode 1 and mode 2) for optimal reception at the UE
– Mode 1 supported in P4 CPICH1 Antenna 1

DCH (or PDSCH)

Σ Antenna 2
DPCCH • S/P Demux
• Channelization
MUX • Scrambling
DPDCH
• I/Q Modulation

Σ

CPICH2

Calculate
Decode FBI
Gains, Phases


TX diversity modes mapped on physical channels

Application of Tx diversity modes on downlink physical channel types
"X" – can be applied, "–" – not applied

Physical channel type Open loop mode Closed loop
TSTD STTD Mode
P-CCPCH – X –
SCH X – –
S-CCPCH – X –
DPCH – X X
PICH – X –
PDSCH – X X
AICH – X –
CSICH – X –


Blossoming and wilting
The purpose of the blossoming (at cell addition) and wilting (at cell removal) is
to allow cells to be added or removed from the radio network with minimum
disturbance to the network.
RBS1 RBS2

Wilting
Blossoming

Output power gradually decreased (wilting) Output power gradually increased (blossoming)


Micro cell support overview

Support of micro cells to:
– cover white spots or to
– increase capacity in hot-spot areas

Advanced load sharing to increase
performance by distributing users
between different cells Micro
Macro
The micro cell can be deployed in:
– different frequency as the macro cell
– the same frequency band as the macro cell


Micro cell evolution scenario

At some cell radius macrocell (i.e. roof-top antennas)
f2
capacity growth is limited due to poor RF isolation.

Microcells can be added in same or different
frequency depending on: f2
– rate of traffic increase
– distance macro-hot spot
– UE velocity

Ultimately there will be a complete micro-layer f2


Connection set-up/release description

Connection Setup and Release includes establishment and
release of control plane connections between the UE and
UTRAN, and between the UE and the Core Networks.

It also covers Radio Access Bearer establishment according
to the requested Quality of Service between a Core Network
and a UE with established signalling connection, as well as
release of existing Radio Access Bearers.
The functions consists of two subfunctions
– Signaling Connection Setup and Release
– Radio Access Bearer Setup and Release


Radio connection supervision
Benefit:
– Allows an efficient resource utilization
– Guarantees that users are not charged for time when they did not have network contact.

Description:
This feature continuously monitors the status of the radio connection for all connected UEs
and disconnects those for which a reasonable quality cannot be maintained and/or the contact
has been lost.

The meter for the "unacceptable quality" depends on measurements performed on up-link
physical channels as well as duration of disturbance or loss of contact. Typically the meters
are set such that the quality is considered unacceptable only when there has been no working
contact with the UE for a few seconds for DCH connected and several minutes for cell
connected.

If the quality is considered unacceptable or the UE is considered lost, the radio network will
request the deletion of all connections towards this UE. Thereby all Radio bearers and RAB's
allocated for this UE are disconnected. Logical, HW and SW resources related to these
channels/bearers are also released.


Soft/softer Handover overview

Algorithm
–Relative thresholds minimizes the
number of mobiles in soft handover
B A

C/I

Add
margin
Drop
margin

Add B Delete A Time


Soft Handover
Soft handover essential for power control
Soft handover reception
– combines signals from RBS in the RNC

RNC

RBS 1 RBS 2


Softer Handover
Softer handover reception
– combines signals from two or more sectors in one RBS

RBS


Characteristics of soft/softer handover

RNC controls the UE measurements (i.e. what to
measure, report type, what to report and the monitoring
set)
UE measures on CPICH (Ec/No, RSCP or path loss)
UE evaluates measurements (event driven or periodic)
RNC evaluates which cells to add/replace/remove from
active set (max size is 4)
RNC executes the handover decision and provides UE
with new neighbor list


Paging

Purpose:
Paging enables the CN to page UEs for terminating service
request or for the UTRAN to reach the UE to trigger a UE
state transition. The function will also broadcast modified
system information to all UEs.
The following cases are handled by the paging function:
– CN originated when UE in idle mode
– CN originated when UE in connected mode.
– UTRAN originated to trigger a UE state transition.
– UTRAN originated to trigger a UE to read updated system in-
formation.


Cell Update

Purpose:
Using common or paging channels are important to allow an efficient
management of resources for always connected low intensity packet
traffic. The feature "Cell Update" is used to allow mobility, cell
reselection ("hard handover") and efficient paging of UE's in such
states.

Benefit:
– Support the mobility for UE's on common or paging channels.
– Provide a high success rate and efficient management of
resources for paging to CELL_PCH connected UE's (PCH is
Paging Channel).


URA_PCH State

New state called RRC Connected Mode
WCDMA RAN
Registration Area URA_PCH Cell_PCH
(URA_PCH State)
Benefit:
– Reduce signaling in Cell_FACH Cell_DCH
WCDMA RAN due to
updates of location of
moving mobiles
– Simplified paging Idle
– Lower UE battery Idle Mode
consumption


Intersystem Handover GSM - WCDMA

WCDMA WCDMA

GSM

Dual mode


Why GSM Interoperability - why GSM Handover?

For service and coverage
– Initially to provide “seamless service” to UMTS users

For load sharing between frequencies and Radio
Access Technologies (RAT)
– Increase capacity pool size
– GSM network full used

For fair behavior in shared network solutions

To allow access to unique bearers


GSM Intersystem Handover

Inter frequency measurements are needed to support inter system
handover
Compressed mode supports these measurements
– 3 different types of compressed mode

Compressed mode

Inter system

SF=SF0/2
SF=SF0 SF=SF0
WCDMA
GSM Tf = 10 ms time for measurements


Compressed Mode - 3 different types
Different alternatives with different impacts
Lower spreading factor
+ Same user data rate
- Power increase
- Need to allocate a code with half spreading factor
1) Allocate code in the same code tree - remain code orthogonality
2) Allocate code in another code tree - easy to get codes
Puncturing
+ Same user data rate can be used
+ Remain on the same spreading factor (code)
- Power increase
- Weakens Forward Error Correction (FEC) coding
Higher layer scheduling
+ Power increase can be avoided
- Lower user data rate


Control of Inter Radio Access Technology
Cell Reselection
UMTS to GSM :
Neighbour Cell List
Quality measure
• CPICH (RSCP or CPICH Eb/N0)
For each neighbour Cell Reseletion criteria
• Serving cell quality limit to start neighbor cell measurements
• Minimum required signal level to allow selection
• Minimum required quality of to allow selection
(For FDD cells)
• Offset between serving cell and neighbor cell
• Hysteresis of the serving cell for ranking of cells
• Time to trigger cell reselection


Intersystem Traffic Control
Always Best Connected

Real time changes of Connection & Cell
WC
Link adaptation and control as well as inter-system, service DM
A
based load sharing.

Based on existing and currently standardized, Iur-g,
interfaces.
E
Functionality for: RNC /EDG
M
- Handover Control GS
- Admission Control
- Load Control Core Network
- Service Differentiation
BSC
Ensure full utilization of
spectrum and system at
maximum performance.


Load Balance GSM-UMTS
System Features for Traffic Control and Efficiency as
Function of Time
100%
Achieved Load-balancing Efficincy
• Self Configuring Radio Network with
Dynamic Cell Reselection Control

• Real time load Balancing, Iur-g
• O&M load Management
• Combined Configuration Management, CCM
• Service based Directed Retry
• Load Control

•Congestion triggered Handover WCDMA to GSM
•System preference based Handover from WCDMA to GSM

• Symmetric Handover Algorithms in GSM and WCDMA
• Congestion triggered Handover from GSM to WCDMA Dual-mode Handset
• System preference based Handover from GSM to WCDMA penetration
• Coverage based Handover from WCDMA to GSM (GSM/EDGE-WCDMA)
• Cell Reselection Idle& PS
• Congestion hold-down

Time


Transparent message transfer

Supports the transfer of signaling and other messages between a
UE and the core network nodes, MSC and SGSN.
Basic feature required for UE signaling, e.g. for call set-up
Provides support for SMS

Description
In UMTS, the radio access network need to transfer signaling
messages (Non Access Stratum) transparently between the UE and
either of the core network domains for establishing and releasing
calls.
Such transparently transferred messages are also used for other
purposes, e.g. LA/RA updating and support SMS services.


System Information distribution

Allows the UE to get access to updated System Information, which in
turn is necessary for correct network behavior.
Description
The system information is regularly broadcast to the UE's on
Broadcast Channel. The information is relates to:
– Power control, both Common and dedicated channels, e.g. UL
interference
– RRC connection parameters e.g. timers and counters
– Adjacent cell configuration parameters.
– UE Measurements e.g. to support handover evaluation
– Location Area and Routing Area
– Common channel configuration
– Cell selection and re-selection


Node and network synchronization

Node synchronization:
The Node Synchronization function contains four sub-functions:
– Holding of and generation of node reference time in the RNC and the
RBSs,
– Measurement of phase difference between the frame reference time in
the RNC and the frame reference time in each RBS.
– A database of measured phase differences to each RBS is held, and an
estimate of the accuracy of each of the measurement.
– Supervision of drifting frame reference times in the nodes.

Generation of node reference time and phase measurement are
handled by a device, the Timing Unit (TU), present in both RNC and
RBS.


Node and network synchronization

Network synchronization:
The RBS and RNC internal clocks can be synchronized either to:
– the transport network or to
– an external high stability clock reference.

RBSs and RNCs both have stable clocks locked to the reference carried
over the transmission network. The clocks, besides synchronizing internal
functions in the node, also generate sync to the outgoing transmission links
and to the radio transmission.
It is possible to cascade up to 5 clocks (Nodes)
One primary and up to seven secondary synchronization reference links
can be configured for each node
The network synchronization (clock) function can be configured to be
redundant or non-redundant.


Integrity protection and ciphering mode control

Integrity protection handles:
– the control of integrity protection of control plane data
– co-ordination of integrity keys between different core
networks (PS and CS).
The integrity protection maintains access link data
integrity between the SRNC and UE.

Ciphering Mode Control handles:
– the control of ciphering of user plane and control
plane data
– co-ordination ciphering keys between different core
networks (PS and CS).
The ciphering is performed for secure data
confidentiality between the SRNC and UE


IOT certification for Iu/Iur

Iu is the most Vendor-A Vendor-B
common 3G multi- 3G system 3G system
vendor interface
3G CN 3G CN
Enables an
operator to choose Iu Iu
(several) RAN Iu Iu
suppliers
RAN RAN


High Speed Downlink Packet Access (HSDPA)

Requirements
– High peak data rates (8-10 Mbps)
– Higher throughput
– Lower delay

Introduction of a new High Speed Downlink Shared Channel
(part of 3GPP Rel.5)
– Exists in downlink only
– Always associated with a dedicated physical channel (DPCH) pair

D PC H

HS-DS
C H


Mulitcode to allow bit rates >384 kbit/s
One user has more than one channelization code
One user can than have several data streams to achieve
bit rates above 384kbit/s

Primary Data 1 TPC TFCI Data 2 Pilot
DPCCH/DPDCH

Additional Data 3 Data 4
DPCCH/DPDCH

Additional Data N-1 Data N
DPCCH/DPDCH


The use of codes in WCDMA
Single cell view:
– all mobiles need to share the same frequency carrier in WCDMA
– orthogonal codes separate between the users and between
different communication channels to one user (multi-code
operation)
Channelization codes

Network view:
– nearly orthogonal codes to distinguish between the
communication channels from different RBS’s
– One scrambling code per sector and per carrier e.g a 3x2 RBS
has 6 scrambling codes
Scrambling codes


Multiple scrambling codes overview
Each sector/carrier (cell) broadcasts a unique cell
ID code -> downlink scrambling code
With multiple scrambling codes -> there is more
than one downlink scrambling code per
sector/carrier (cell)
Cell #1, ID code 1
Cell #1, ID code 2

Cell #2, ID code 1
Cell #2, ID code 2

Cell #3, ID code 1
Cell #3, ID code 2


Multiple scrambling code benefit
Multiple scrambling codes gives more than one channelization code
tree per sector/carrier
The problem with code shortage is removed.

1
1

11
11 10 10

1111
1111 1100
1100 1010
1010 1001
1001

11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110
11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110


Power Scheduling
load
max planned load

Extra capacity
can be given to
packet data users

time

Load sharing in time results in a high capacity
– Continuous update of the transport format for the interactive RABs both in UL and DL
– The aim is to maximize the bit rate for the interactive users
Smooth interference levels in the system
– Optimize the usage of the radio capacity in the system e.g DL power, without exceeding
the maximum planned load


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