Umtsrns 101 wcdma basics

WCDMABasics
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Contents
About this Manual.........................................................................i
Purpose........................................................................................ i
Intended Audience ....................................................................... i
Prerequisite Skill and Knowledge .................................................. i
Computer operation abilityWhat is in This Manual ......................... i
Related Documentation ................................................................ii
Conventions .................................................................................ii
How to Get in Touch....................................................................iii
Chapter 1........................................................................................1
WCDMA Overview........................................................................1
Background Introduction .................................................1
WCDMA Technical Standards Development Trends ...............3
3G Technical Requirements .........................................................3
3G Standardisation Organization .................................................4
3GPP Standard Development Status ............................................5
IMT2000 Frequency Band Allocation ..................................5
Composition of WCDMA System........................................6
UE............................................................................................... 7
UTRAN ........................................................................................8
CN .............................................................................................. 8
Chapter 2........................................................................................1
WCDMA Basics..............................................................................1
Concept of WCDMA Realizing Broadband Communic ation ......1
Basic Concepts of CDMA.............................................................. 2
Basic Concepts of Spread Spectrum Communication ....................4
Transmission of Electric Waves in Mobile Environment ..........6
Features of Land Mobile Communication Environment..................6
Signal Fading in Radio Path .........................................................7
Configuration of Radio Transmitter and Receiver..........................8

Fundamentals of the WCDMA Technology ...........................9
Direct Sequence Code Division Multiple Access ............................ 9
Channel Coding/Decoding ......................................................... 10
Interleaving/Deinterleaving....................................................... 11
Modulation and Demodulation ................................................... 11
Spreading and Scrambling......................................................... 13
Spread Spectrum...................................................................... 15
Some Parameters of WCDMA Physical Layer.............................. 16
Chapter 3 ....................................................................................18
Network Structure ...................................................................18
System Architecture ..................................................... 18
R99 .......................................................................................... 18
R4 ............................................................................................ 19
R5 ............................................................................................ 21
R6 ............................................................................................ 22
UTRAN Architecture...................................................... 22
Figures.........................................................................................25
Tables...........................................................................................27

Confidential and Proprietary Information of ZTE CORPORATION i
About this Manual
Purpose
This Manual provides WCDMA basic knowledge.
Readers can get to know the concept 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 WCDMA
Overview
Introduces the WCDMA technical standards
development trends, IMT2000 frequency
band allocation and composition of
WCDMA system.
Chapter 2 WCDMA
Basics
Introduces concept of WCDMA and
fundamentals of WCDMA technology.
Chapter 3 Network
Structure
Introduces WCDMA network structure in
R99, R4, R5 etc.

WCDMA Basics
ii Confidential and Proprietary Information of ZTE CORPORATION
Chapter Summary
Figures Provides figure lists in this manual.
Tables Provides table lists in this manual.
Related Documentation
The following document is related to this manual:
 WCDMA Theory
Conventions
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Typographical
Conventions
Mouse
Operation
Conventions

About this Manual
Confidential and Proprietary Information of ZTE CORPORATION iii
Typeface Meaning
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(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
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WCDMA Basics
iv Confidential and Proprietary Information of ZTE CORPORATION

Confidential and Proprietary Information of ZTE CORPORATION 1
C h a p t e r 1
WCDMAOverview
Background Introduction
The 3rd Generation Mobile Communication System (3G) is put
on agenda when the 2nd generation (2G) digital mobile
communication market is booming. The 2G mobile
communication system has the following disadvantages: limited
frequency spectrum resources, low frequency spectrum
utilization, and weak support for mobile multimedia services
(providing only speech and low-speed data services). Also,
thanks to incompatibility between 2G systems, the 2G mobile
communication system has a low system capacity, hardly
meeting the demand for high-speed bandwidth services and
impossible for the system to implement global roaming.
Therefore, the 3G communication technology is a natural result
in the advancement of the 2G mobile communication.
As the Internet data services become increasingly popular
nowadays, the 3G communication technology opens the door to
a brand new mobile communication world. It brings more fun to
the people. In addition to clearer voice services, it allows users
to conduct multimedia communications with their personal
mobile terminals, for example, Internet browsing, multimedia
database access, real-time stock quotes query, videophone,
mobile e-commerce, interactive games, wireless personal audio
player, video transmission, knowledge acquisition, and
entertainments. What more unique are location related services,
which allow users to know about their surroundings at anytime
anywhere, for example, block map, locations of hotels and super
markets, and weather forecast. The 3G mobile phone is bound to
become a good assistant to people’s life and work.
The 3G mobile communication aims at meeting the future
demand for mobile user capacity and providing mobile data and
multimedia communication services.
Initially, mobile communication technologies were developed
separately, as various counties and technical organizations
continued to develop their own technologies. Thus, the USA has

WCDMA Basics
2 Confidential and Proprietary Information of ZTE CORPORATION
AMPS, D-AMPS, IS-136, and IS-95, Japan has PHS, PDC, and
the EU has GSM. On one hand, this situation helped to meet the
needs of the users at the early stage of mobile communication
and expand the mobile communication market. On another
hand, it created barriers between the regions, and made it
necessary to unify the mobile communication systems globally.
Under such a context, ITU launched the standardization of the
3G mobile communication system in 1985.
The 3G mobile communication system, IMT-2000, is the general
term for the next generation communication system proposed by
ITU in 1985, when it was actually referred to as Future Public
Land Mobile Telecommunications System (FPLMTS). In 1996, it
was officially renamed to IMT-2000. In addition, the 3G mobile
communication technology extends the integrated bandwidth
network service as far as it can to the mobile environment,
transmitting multimedia information including high quality
images at rates up to 10 Mbps.
Compared with the existing 2G system, the 3G system has the
following characteristics as summarized below:
 Support for multimedia services, especially Internet services
 Easy transition and evolution
 High frequency spectrum utilization
Currently, the three typical 3G mobile communication
technology standards in the world are CDMA2000, WCDMA and
TD-SCDMA. CDMA2000 and WCDMA work in the FDD mode,
while TD-SCDMA works in the TDD mode, where the uplink and
downlink of the system work in different timeslots of the same
frequency.
The 3G mobile communication is designed to provide diversified
and high-quality multimedia services. To achieve these
purposes, the wireless transmission technology must meet the
following requirements:
 High-speed transmission to support multimedia services
 Indoor environment: >2 Mbps
 Outdoor walking environment: 384 Mbps
 Outdoor vehicle moving: 144 kbps
 Allocation of transmission rates according to needs
 Accommodation to asymmetrical needs on the uplink and
downlink
In the concept evaluation of the 3G mobile communication
specification proposals, the WCDMA technology is adopted as
one of the mainstream 3G technologies thanks to its own
technical advantages.

Chapter 1 WCDMA Overview
WCDMA Technical
Standards Development
Trends
WCDMA was originated by standardization organizations and
manufacturers in European countries and Japan. WCDMA inherits
the high standardization and openness of GSM, and its
standardization progresses smoothly. WCDMA is the third
generation mobile communication standard developed by 3GPP,
with the GSM MAP as its core and UTRAN (UMTS Terrestrial
Radio Access Network) as its wireless interfac e. Using the chip
rate of 3.84 Mbps, it provides data transmission rate up to 14.4
Mbps within 5 MHz bandwidth.
The WCDMA technology has the following characteristics:
 Supporting both asynchronous and synchronous BSs, for
easy and flexible networking
 Using QPSK modulation mode (the HSDPA services also use
the 16QAM modulation mode)
 Using pilot assisted coherent demodulation
 Accommodating transmission of multiple rates, and
implementing multi-rate and multimedia services by
changing the spread spectrum ratio and using multi- mode
concurrent transmission
 Rapid and efficient power control of uplink/downlink greatly
reduces multiple access interference of the system, but
increases the system capacity while reducing the
transmission power.
 The core network is evolving based on the GSM/GPRS
network, and maintains compatibility with the GSM/GPRS
network.
 Supporting soft handover and softer handover, with three
handover modes, inter-sector soft handover, inter-cell soft
handover, and inter-carrier hard handover.
3G Technical Requirements
 Bit Rate:
 –Rural outdoor 144 kbps (500 km/h).
 Suburban outdoor 384 kbps (120 km/h) .
 Indoor 2 Mbps (10 km/h).
 Variable bit rate capability: granularity, circuit and packet
bearers.

WCDMA Basics
 Service Multiplexing.
 Varying delay and quality of service requirements. ( priorities
of traffic).
 Handover: seamless between the cells and different
operators. Co-existence
 with and handover to 2G systems (with WCDMA to GSM).
 Support of asymmetric traffic.
 High spectrum efficiency.
 Coexistence of FDD and TDD modes.
3G StandardisationOrganization
Based on the standardisation ITU has the following grouping:
FI GU R E 1 IM T2000 FAMI L Y
IMT2000
ITU provides references to 3GPP specifications and does not
make specifications of its own. 3GPP covers CDMA direct spread
and TDD.
3GPP is an “umbrella” aiming to form compromised standards by
taking into account, political, industrial, and commercial
pressures from local specification bodies:
 ETSI European Telecommunication Standard Institute
/Europe
 ARIB Association of Radio Industries and Business /Japan
 CWTS China Wireless Telecommunication Standard group
/China
 T1 Standardisation Committee T1 Telecommunications /US
 TTA Telecommunication Technology Association /Korea
 TTC Telecommunication Technology Committee /Japan

FI GU R E 2 3GPP AN D L OC AL SPEC I F I C ATI ON B OD I ES
3GPP Standard Development Status
3GPP standard versions include R99, R4, R5, R6 and R7.
 R99 version was frozen formally in Mar, 2000, and refreshes
once every three months. Current commercial version of R99
is based on the version of June, 2001, for in later version,
the number of CR is decreasing rapidly and there are no
larger modifications and non-compatible upgrade.
 R4 version was frozen in Mar, 2001. It passed in Mar, 2002
and is stable currently.
 R5 version was frozen in June, 2002 and is stable currently.
Most R5 versions that providers support are the version of
June, 2004.
 R6 version was frozen in June, 2005 and may be stable in a
year.
 At present, R7/LTE has started up and its functional features
are still in initial phase.
IMT2000 Frequency Band
Allocation
In 1992, World Radio-communication Conference (WRC-92)
allocated the frequency bands for the 3G mobile communication,
with a total bandwidth of 230 MHz, as shown in Figure 3.

WCDMA Basics
FI GU R E 3 FR EQU EN C Y SPEC TR U M AL L OC ATI ON OF 3G M OB I L E
COMMU N I C ATI ON
At WRC92, ITU planned the symmetric frequency spectrum
resources of 120MHz (1920MHz ~ 1980MHz, 2110MHz ~
2170MHz) for use by the FDD, and asymmetric frequency
spectrum resources of 35MHz (1900MHz ~ 1920MHz, 2010MHz
~ 2025MHz) for use by the TDD.
At WRC2000, the 800 MHz band (806MHz ~ 960MHz), 1.7GHz
band (1710MHz ~ 1885MHz), and 2.5GHz band (2500MHz ~
2690MHz) were added for use by the IMT-2000 services. These
two combined make the future spectrum for 3G reach over 500
MHz, reserving enormous resource space for future applications.
Composition of WCDMA
System
The Universal Mobile Telecommunication System (UMTS) is a 3G
mobile communication system adopting WCDMA air interface.
Therefore, the UMTS is usually called a WCDMA system.
In terms of functions, the network units comprise the Radio
Access Network (RAN) and Core Network (CN).
The RAN accomplishes all the functions related to radio
communication.
The CN handles the exchange and routing of all the calls and
data connections within the UMTS with external networks.
The RAN, CN, and the User Equipment (UE) together constitute
the whole UMTS.
The network elements in a PLMN are as shown in Figure 4.

FI GU R E 4 NETW OR K EL EMEN TS I N A PLM N
The classifications, functions, contained boards of each shelf are
as shown in Table 4.
TAB L E 4 UM TS IN TER F AC E DESC R I PTI ON
Interface
Name
Functional Description
Cu
This is the electrical interface between the USIM
smartcard and the ME.
Uu
This is the WCDMA radio interface. The Uu is the
interface through which the UE accesses the fixed part
of the system.
Iu This connects UTRAN to the CN.
Iur
The open Iur interface allows soft handover between
RNCs from different manufacturers, and therefore
complements the open Iu interface.
Iub The Iub connects a Node B and an RNC.
Note:
The term ‘Node B’ used in 3GPP specifications means Base
Station, the same thing. UMTS is the first commercial mobile
telephony system where the Controller–Base Station interface is
standardised as a fully open interface. Like the other open
interfaces, open Iub is expected to further motivate competition
between manufacturers in this area. It is likely that new
manufacturers concentrating exclusively on Node Bs will enter
the market.
UE
The UE(User Equipment) is an equipment which can be vehicle
installed or hand portable. Through the Uu interface, the UE
exchanges data with network equipment and provides various
CS domain and PS domain services, including common voice
services, broadband voice services, mobile multimedia services,

WCDMA Basics
and Internet applications (such as E- mail, WWW browse, and
FTP).
UTRAN
The UMTS Terrestrial Radio Access Network (UTRAN) comprises
Node B and Radio network Controller (RNC).
 Node B
As the base station (wireless transceiver) in the WCDMA
system, the Node B is composed of the wireless transceiver
and baseband processing part. Connected with the RNC
through standard Iub interface, Node B processes the Un
interface physical layer protocols. It provides the functions of
spectrum spreading/despreading, modulation/demodulation,
channel coding/decoding, and mutual conversion between
baseband signals and radio signaling.
 RNC
The RNC manages various interfaces, establishes and
releases connections, performs handoff and macro
diversity/combination, and manages and controls radio
resources. It connects with the MSC and SGSN through lu
interface. The protocol between UE and UTRAN is terminated
here.
The RNC that controls Node B is called Controlling RNC
(CRNC). The CRNC performs load control and congestion
control of the cells it serves, and implements admission
control and code word allocation for the wireless connections
to be established.
If the connection between a mobile subscriber and the
UTRAN uses many RNS resources, the related RNC has two
independent logical functions:
Serving RNC (SRNC). The SRNC terminates the transmission
of subscriber data and the Iu connection of RANAP signaling
to/from the CN. It also terminates the radio resource
controlling signaling (that is the signaling protocol between
UE and UT RAN). In addition, the SRNC performs L2
processing of the data sent to/from the radio interface and
implements some basic operations related to radio resources
management.
Drift RNC (DRNC) All the other RNCs except the SRNC are
DRNCs. They controls the cells used by the UEs.
CN
The CN is in charge of the connections with other networks as
well as the management and communication with UEs. The CN

can be divided into CS domain and PS domain from the aspect of
logic.
 The CS domain equipment refers to the entities that provide
circuit connection or related signaling connection for
subscriber services. The specific entities in the CS domain
include:
 Mobile switching center (MSC)
 Gateway mobile switching center (GMSC)
 Visitor location register (VLR)
 Interworking function (IWF).
 The PS domain provides packet data services to subscribers.
The specific entities in the PS domain include:
 Serving GPRS support node (SGSN)
 Gateway GPRS support node (GGSN)
 Other equipment such as the home location register (HLR) or
HSS, authentication center (AuC), and equipment identity
register (EIR) are shared by the CS domain and PS domain.
The major functional entities are as follows:
 MSC/VLR
As the functional node in the CS domain of the WCDMA core
network, the MSC/VLR connects with the UTRAN through Iu
CS interface, with external networks (PSTN, ISDN, and other
PLMNs) through PSTN/ISDN interface, with the HLR/AUC
through C/D interface, with the MSC/VLR, GMSC or SMC
through E interface, with the SCP through CAP interface,
and with the SGSN through Gs interface.
The MSC/VLR accomplishes call connection, mobility
management, authentication, and encryption in the CS
domain.
 GMSC
As the gateway node between the CS domain of WCDMA
network and external networks, the GMSC is an optional
entity. It connects with the external networks (PSTN, ISDN,
and other PLMNs) through PSTN/ISDN interface, with the
HLR through C interface, and with the SCP through CAP
interface.
The GMSC accomplishes the incoming and outgoing routing
of the Visited MSC (VMSC).
 SGSN
As the functional node in the PS domain of WCDMA core
network, the SGSN connects with the UTRAN through Iu_PS
interface, with GGSN through Gn/Gp interface, with the
HLR/AUC through Gr interface, with the MSC/VLR through Gs
interface, with the SCP through CAP interface, with the SMC

WCDMA Basics
through Gd interface, with the CG through Ga interface, and
with the SGSN through Gn/Gp interface.
The SGSN accomplishes the routing forward, mobility
management, session management, authentic ation, and
encryption in the PS domain.
 GGSN
The GGSN connects with the SGSN through Gn interface and
with the external data networks (Internet /Intranet) through
Gi interface.
The GGSN provides routes to the data packets between the
WCDMA network and external data networks, and
encapsulates these data packets. The major function of the
GGSN is to provide the interface to the external IP packet -
based network, thus the UEs can access the gateway of the
external packet-based network. To the external networks,
the GGSN seems like the IP router that can be used to
address all the mobile subscribers in the WCDMA network. It
exchanges routing information with external networks.
 HLR
The HLR connects with the VMSC/VLR or GMSC through C
interface, with the SGSN through Gr interface, and with the
GGSN through Gc interface. The HLR stores subscriber
subscription information, supports new services, and
provides enhanced authentication.

C h a p t e r 2
WCDMABasics
Concept of WCDMA
Realizing Broadband
Communication
WCDMA (Wideband CDMA) is CDMA radio communication mode
cased on direct spread-spectrum technology. WCDMA has an
obvious advantage over GSM and IS-95 in subscriber capacity
and radio transmission performance, for it adopts a series of key
technologies.
WCDMA bears following two meanings literally:
 WCDMA adopts CDMA communication technology
CDMA technology is the most advanced communication
technology in the world at present. It takes advantage of
different codes to divide different channel and then
distinguish different subscriber.
 WCDMA adopts wider spectrum
Narrowband power signals are sent out after being spread as
broadband signals (spread-spectrum) with WCDMA
technology. Broadband signals have stronger anti-
interference ability than narrowband signals. Wider
bandwidth realizes RAKE receiving at subscriber end and
increases communication quality.
Figure 5 shows WCDMA communication. Bandwidth of original
signals increases and power density decreases after spread-
spectrum. Signals meet with noise during the transmission.
Power density of the noise decreases after the dispreading, for
spectrum dispreading is the same as spectrum spreading.
However, power density of original signals is much larger than
that of noise (that is, signal-to-noise ratio is high) and it is easy
to resume.

WCDMA Basics
FI GU R E 5 WCDM A COMMU N I C ATI ON PR I N C I PL E
F
Power
Density
F
Power
Density
F
Power
Density
F
Power
Density
(1) Original Signal
(2) Signal after spread
spectrum
(3)Meeting noise during
signal transmission
(4) Signal and noise after spectrum
dispreading
Signal Noise
Besides, WCDMA adopts such advanced technologies as soft
handover, diversity and power control to enlarge system
capacity and increase communication quality greatly.
Basic Concepts of CDMA
Mobile communication systems can be classified in multiple
ways. For example, there are analog and digital by the nature of
the signals; FM, PM, and AM by the modulation mode; and
FDMA, TDMA and CDMA by the multiple access mode. CDMA
(Code Division Multiple Access) is a new while mature wireless
technology developed from the spread spectrum communication
technology, a branch of the digital technology.
Currently, the GSM mobile telephone networks of China Unicom
and China Mobile are built with the combination of FDMA and
TDMA. GSM has tremendous advantages over the analog mobile
telephone system. However, its spectrum efficiency is only three
times of the analog system. With a limited capacity, it has
difficulty in offering voice quality equivalent to wired telephone.
TDMA terminals support an access rate of only 9.6 kbps. The
TDMA system does not support soft handover, so calls may
easily be dropped, affecting the service quality. Therefore, TDMA
is not the best technology for modern cellular mobile

Chapter 2 WCDMA Basics
communication. On the other hand, CDMA fully meets the
requirements of modern mobile communication networks for
large capacity, high quality, and integrated services, so it is well
received by increasingly more operators and users.
CDMA emerges from the needs for wireless communications of
higher quality. In the CDMA communication system, the signals
used by different users for information transmission are
distinguished not by frequencies or timeslots, but by different
code sequences. CDMA allocates one pseudo random binary
sequence for each signal for frequency spreading, and different
signals are allocated with different pseudo random binary
sequences. In the receiver, correlators are used to separate the
signals. The correlator of each user only receives the specified
binary sequences and compresses their frequency spectrums,
while ignoring all the other signals.
The code division multiple access concept of CDMA can be
illustrated with a party of many persons. At the party, many
users talk at the same time in a room, and every conversation in
the room is in a language you do not understand. From your
perspective, all these conversations sound like noise. If you
know these “codes”, that is, relevant languages, you can ignore
the conversations you do not want to hear, and focus on only
these you are interested in. The CDMA system filters the traffic
in a similar way. However, even if you understand all the
languages used, you do not necessarily hear clearly all the
conversations you are interested in. In this case, you can tell the
speakers to speak louder, and/or ask others to lower their
voices. This is similar to the power control in the CDMA system.
In the frequency domain or time domain, multiple CDMA signals
overlap. The receiver can sort out the signals that use the preset
code pattern from multiple CDMA signals by using correlators.
Other signals using different code patterns are not demodulated,
since their code patterns are different from those generated
locally at the receiver.
One of the basic technologies of CDMA is spectrum spreading.
CDMA is a multiple access technology featuring high
confidentiality. It was first developed in the Second World War to
prevent interference from the enemies. CDMA found wide
application in anti-interference military communications during
the war. After 1960’s, it had been used in military satellite
communication. Later, it was developed by Qualcomm into a
commercial mobile communication technology.
After the first CDMA system was put into operation for
commercial purpose in 1995, the technical advantages of the
CDMA in theory were tested in practice, so it has seen rapid
application in North America, South America and Asia. In many
countries and regions in the world, including China, Hong Kong,
South Korea, Japan, and USA, CDMA is the major mobile
communication technology used. CDMA is superior to TDMA in
system capacity, anti-interference, communication quality, and
confidentiality, so IMT-2000 (3G) launched by ITU and
subsequent standards all employ CDMA.

WCDMA Basics
Basic Concepts of Spread Spectrum
Communication
The basic characteristic of spread spectrum communication is
that it uses a bandwidth for information transmission much
wider than that of the information itself. In other words, the
data for transmission with certain signal bandwidth is modulated
with high-speed pseudo random codes having a bandwidth wider
than the signal bandwidth. Thus, the bandwidth of the original
data signals is spread, before the signals are transmitted
following carrier modulation. The receiving end uses exactly the
same pseudo random codes to process the received bandwidth
signals, converting the broadband signals into the original
narrowband signals, that is, despreading, thus achieving
information communication.
In addition, spread spectrum communication also has the
following characteristics:
 It is a digital transmission mode.
 Bandwidth spreading is implemented by modulating the
transmitted information with a function (spread spectrum
function) irrelevant to the transmitted information.
 At the receiving end, the same spread spectrum function is
used to demodulate the spread spectrum signals, restoring
the transmitted information.
C.E. Shannon found the channel capacity formula in his research
in information theory, as below:
C = W × Log2 (1+S/N)
Where:
C – Information transmission rate
S – Available signal power
W – Bandwidth of the line
N – Noise power
As can be seen from the formula:
To increase C, you can either increase W or increase S/N. In
other words, when C is constant, W and S/N are
interchangeable, where the increase of W reduces the
requirement for S/N. When the bandwidth increases to a certain
level, the S/N is allowed to further decrease, making it possible
for the useful signal power to decrease to a level close to the
noise power or even inundated in the noise. Spread spectrum
communication uses the bandwidth transmission technology to
obtain the benefit in S/N, which is the basic idea and theoretical
basis of spread spectrum communication.
Spread spectrum communication has many outstanding
performances insuperable by narrowband communication,

enabling it to find wide application rapidly in various public and
private communication networks. Its advantages are outlined as
below:
 Powerful anti-interference and low bit error rate
The spread spectrum communication system spreads the
signal spectrum at the transmitting end and restores the
original information at the receiving end, producing spread
gains, thus greatly increasing the anti-jamming margin.
Depending on the spread spectrum gains, signals can be
extracted from noise even when the S/N is negative. In the
current commercial communication system, spread spectrum
communication is the only communication mode that can
work in the negative S/N environment.
 Easy same frequency use for higher radio spectrum
utilization
Radio spectrum is very valuable. Although all waves from
long wave and micro wave have been developed and used,
the need of the society is not satisfied. For this reason,
frequency spectrum management authorities were set up all
over the world. Users can only use the frequencies granted,
and divide them into channels to avoid mutual interference.
As spread spectrum communication uses the correlation
reception technology, the signal transmission power is
extremely low (<1 W, usually 1 mW ~ 100 mW), and can
work in channel noise and hot noise background. Therefore,
a frequency can be easily reused in the same area, and the
frequency can also be shared with the now various
narrowband communications.
 Anti multipath interference
In the wireless communication, anti multipath interference is
a persisting problem that is difficult to solve. With the
correlation between spread spectrum codes, the most
powerful useful signals can be extracted from multipath
signals at the receiving end with a related technology. Also,
the same code sequence waveform from multiple paths can
be added for reinforcement, to achieve effective anti
multipath interference.
 Spread spectrum communication is a form of digital
communication, particularly suitable for synchronous
transmission of digital voice and data. Spread spectrum
communication offers the encryption function for good
confidentiality, making it easy to launch various
communication services.
Using multiple new technologies including code division
multiple access, and voice compression, spread spectrum
communication is more suitable for transmission of computer
network and digitized voices and images.
 Spread spectrum communication involves mostly digital
circuitry. Its equipment is highly integrated, easy to install

WCDMA Basics
and maintain, compact, and reliable and easy to
mount/expand, and has a long MTBF.
Transmission of Electric
Waves in Mobile
Environment
The target of mobile communication system is to gradually
realize personal communication using the always existent radio
channel as transmission media. However, the radio channel has
poor transmission features.
Firstly, there is serious and complicated fading, including path
fading, shadow fading, and multipath fading. Secondly, the radio
transmission path may be direct or obstructed by mountains or
buildings.
It is difficult to analyze the unknown and unpredictable elements
in radio channels. Even the relative moving speed may greatly
affect the fading of signal level.
Although the features of electromagnetic waves change a lot
during transmission, the major changes fall into perpendicular
incidence, reflection, diffraction (inflection), and scattering. In
cities, there is no direct path between transmitters and
receivers. The high buildings and large mansions cause serious
diffraction loss. Reflected by objects by many times, the
electromagnetic waves reach the receiver through different
paths. The interaction of these electromagnetic waves cause
multipath fading at specific place. In a word, the strength of
electromagnetic waves decreases with the extension of the
distance between the transmitter and receiver.
Features of Land Mobile
Communication Environment
 Low Antenna of MS
Because the transmission path is always affected by
topography and man- made environment, and the MS moves
in various topographical environment and buildings, it makes
the signal received by the MS become the increment of a
large number of scattered and reflected signals.
 Mobility of MS
The MS is always moving. Even the MS is not moving, the
surroundings always change, for example, people and
vehicles move, and wind blows leaves. The mobility makes

the transmission path between the base station and MS
always change. In addition, the moving direction and speed
of the MS will cause the change of signal level.
 Random Change of Signal Level
Varying with the time and locations, the signal level can be
described by the probability distribution in random process
only.
 Wave Guide Effect in Metropolitan Environment
The wave guide effect caused by the high buildings on both
sides of the street make the signals received in the direction
parallel to the street enhanced and the signals received in
the vertical direction weakened. There is about 10 dB
difference between the two signals. This effect is attenuated
8 km away from the base stations.
 Loud Man-Made Noise
The man- made noise includes noise of vehicles and electric
power lines, as well as industrial noise.
 Strong Interference
The common interferences include co-channel interference,
adjacent-channel interference, intermodulation interference,
and near-far interference.
Signal Fading in Radio Path
As the MS moves further from the base station, the signal
received becomes weaker and weaker. The reason is that path
loss occurs to the signal. The factors causing the path loss
include carrier frequency, transmission speed, and the
topography and physiognomy where the signal is transmitted.
 Shadow effect: The semi-dead zone in the coverage area
caused by the obstruct of high buildings and other objects.
 Near-far effect: Because the mobile subscribers move at free
will, the distance between the subscriber and the base
station changes. If the MSs have the same transmit power,
the signal strength at the base station is different. If the MS
is nearer to the base station, the signal received by the base
station is stronger. The non-linearity of the communication
system will be worsened, making the stronger signal
stronger, the weaker signal weaker, and the stronger signal
suppress the weaker signal.
Tight and fast power control is perhaps the most important
aspect in WCDMA, in particular on the uplink. Without it, a
single overpowered mobile could block a whole cell.
Mobile stations MS1,MS2 and MS3 operate within the same
frequency, separable at the base station only by their
respective spreading codes. If there were no mechanism for

WCDMA Basics
MS to be power-controlled to the same level at the base
station, MS1 could easily overshout the other two MS and
thus block a large part of the cell, giving rise to the so-called
near-far problem of CDMA. The optimum strategy in the
sense of maximizing capacity is to equalise the received
power per bit of all mobile stations at all times.
FI GU R E 6 NEAR -F AR EF F EC T
Uplink: Because of different attenuation signals to/from
users nearer to BS are stronger than signals to/from further
located users.
Downlink: On the downlink there is no near–far problem due
to the one-tomany scenario. Because of the nature of
attenuation at the cell border, the users experience higher
interference that near to the BS. They have high level of
interfering signals from own BS and from other BS.
 Doppler effect: The shift in frequency which results from the
move of the signal received at high rate. The degree of shift
is in direct ratio with the velocity of the mobile subscriber.
Configuration of Radio Transmitter
and Receiver
Figure 7 shows a generic block configuration of radio transmitter
and receiver in WCDMA (DS-CDMA). Layer 1 (physical layer)
adds a Cyclic Redundancy Check (CRC) code, for detecting block
errors, to each Transport Block (TB), which is the basic unit of
data that is subject to processing [unit of data forwarded from
Medium Access Control (MAC) layer to Layer 1]. This is followed
by channel encoding [Forward Error Correction (FEC)] and
interleaving. The interleaved bit sequence is subject to overhead
additions (e.g. pilot bits for channel estimation), followed by
data modulation. In-phase and quadrature components in the
phase plane mapped following data modulation are spread
across the spectrum by two layers of spreading code sequences.
The resulting chip data sequence is restricted to the 5 MHz band
by a square root–raised cosine Nyquist filter (roll-off factor =
0.22) and then converted into analog signals through a D/A
converter so as to undergo orthogonal modulation. The
orthogonally modulated Intermediate Frequency (IF) signals are

further converted into Radio Frequency (RF) signals in the 2 GHz
band and are subject to power amplification thereafter.
FI GU R E 7 CON F I GU R ATI ON OF RAD I O TR AN SMI TTER AN D REC EI VER
Fundamentals of the
WCDMA Technology
Direct Sequence Code Division
Multiple Access
WCDMA is a wideband Direct-Sequence Code Division Multiple
Access (DS-CDMA) system.
DS-CDMA is a radio-access technology that enables multiple
access based on a spread spectrum system.
Figure 8 shows how DS-CDMA works.

WCDMA Basics
FI GU R E 8 PR I N C I PLES OF DS -CDMA
 The transmitted data sequence is spread across the
spectrum after being encoded by spreading codes, each of
which is assigned uniquely to each user at a higher rate than
the symbol rate of the information data. Wideband Code
Division Multiple Access (WCDMA) spreads the information
data over a 5 MHz band per carrier. The spread high-speed
data sequence is referred to as chip and the rate at which the
spread data varies is called chip rate. The ratio of chip rate to
symbol rate is called the Spreading Factor (SF).
 The destination mobile phone uses the same spreading code
as the one used for spreading at the transmission point to
perform correlation detection (a process called despreading), in
order to recover the transmitted data sequence. As signals
received by other users carry different spreading codes, the
signal power is reduced evenly to 1/SF.
 In DS-CDMA, all users share the same frequency band and
time frame to communicate, and each user is identified by a
spreading code uniquely assigned to the user.
Channel Coding/Decoding
A radio channel is an adverse transmission channel. When digital
signals transmitted over a radio channel, bit errors may occur in
the transmission data flow due to various reasons, causing
image jumps and disconnection at the receive end. The step of
channel coding can be used to process the data flow
appropriately, so that the system can have error correction
capability and anti-interference capability to certain extent, thus
greatly avoiding bit errors in the code flow. Therefore, channel
coding aims at increasing data transmission efficiency by
reducing bit error rate.
Ultimately, channel coding intends to increase the reliability of
the channel, but it may reduce the transmission of useful
information data. Channel coding works by inserting some code
elements, usually referred to as overhead, into the source data
code flow, for error detection and correction at the receiving

end. This is like the transport of glasses. To ensure that no
glasses are broken during this process, we usually use foams or
sponge to package them. However, such packaging reduces the
total number of glasses. Similarly, over a channel with fixed
bandwidth, the total transmission code rate is fixed. As channel
coding increases data amount, the useful information code rate
is reduced. This is the cost. The number of useful bits divided by
the total number of bits derives the coding efficiency, which
varies slightly from one coding mode to another.
The coding/decoding technology and interleaving technology can
work together to increase the bit error performance. Compared
with the case without coding, the traditional convolution code
can increase the bit error rate by two orders of magnitude, to
10-3 ~ 10-4, and the Turbo code can further increase the bit error
rate to 10-6. Because the Turbo code has a coding performance
close to the limit of Shannon theorem, it is adopted as the data
coding/decoding technology for 3G. The convolution code is
mainly used for voice and signaling of low data rates.
Interleaving/Deinterleaving
Interleaving/deinterleaving is an important step of the combined
channel error correction system. The actual errors in the channel
are usually burst errors or both burst errors and random errors.
If burst errors are first discretized into random errors, which are
then corrected, the system’s anti-interference performance can
be improved. The interleaver works to discretize long burst
errors or multiple burst errors into random errors, that is,
discretizing the errors.
The interleaving technology rearranges the coded signals by
following certain rules. After deinterleaving, burst errors are
dispersed over time, making them similar to random errors that
occur separately.
Modulation and Demodulation
Modulation is the process to use one signal (know as modulation
signal) to control another signal of carrier (known as carrier
signal), so that a characteristic parameter of the later changes
with the former. At the receiving end, the process to restore the
original signal from the modulated signal is called demodulation.
During signal modulation, a high-frequency sine signal is often
used as the carrier signal. One sine signal involves three
parameters: amplitude, frequency and phase. Modulation of
each of these three parameters is respectively called amplitude
modulation, frequency modulation, and phase modulation.
In the WCDMA system, the modulation is Quaternary Phase Shift
Keying (QPSK). If High Speed Downlink Package Access

WCDMA Basics
(HSDPA) is used, the downlink modulation mode can also be
16QAM.
Modulating rate of WCDMA uplinks/downlinks are both 3.84
Mcps and modulate complex-valued code chip sequence
generated by spread spectrum in QPSK mode.
Figure 9 shows uplink modulation and Figure 10 shows downlink
modulation.
FI GU R E 9 UPL I N K M OD U L ATI ON
S
Im{S}
Re{S}
cos(t)
Complex-valued
chip sequence
from spreading
operations
-sin(t)
Split
real &
imag.
parts
Pulse-
shaping
Pulse-
shaping
FI GU R E 10 DOW N L I N K M OD U L ATI ON
T
Im{T}
Re{T}
cos(t)
Complex-valued
chip sequence
from summing
operations
-sin(t)
Split
real &
imag.
parts
Pulse-
shaping
Pulse-
shaping

Spreading and Scrambling
Spreading means increasing the signal bandwidth. Strickly
speaking, spreading includes two operations:
 Channelisation(Increases signal bandwidth and using
orthogonal codes)
 Scrambling(Does not affect the signal bandwidth and using
pseudonoise codes)
FI GU R E 11 SPR EAD I N G OPER ATI ON
Channelisation codes are orthogonal codes, based on Orthogonal
Variable Spreading Factor (OVSF) technique. The codes are fully
orthogonal, i.e., they do not interfere with each other, only if the
codes are time synchronized. Thus, channelisation codes can
separate the transmissions from a single source.
In the downlink, it can separate different users within one
cell/sector. Limited orthogonal codes must be reused in every
cell. The problem is interference exisits if two cells use the same
code. The solution is using scrambling codes to reduce inter-
base-station interference.
In the uplink, it can only separate the physical channels/services
of one user because the mobiles are not synchronised in time. It
is possible that two mobiles are using the same codes. In order
to separate different users in the uplink, scrambling codes are
used.
The channelisation codes are picked from the code tree as
shown in Figure 12. One code tree is used with one scrambling
code on top of the tree. If c4,4 is used, no codes from its subtree
can be used (c8,7 , c8,8 , …).

WCDMA Basics
FI GU R E 12 COD E TR EE
In the scrambling process the code sequence is multiplied with a
pseudorandom scrambling code. The scrambling code can be a
long code (a Gold code with 10 ms period) or a short code (S(2)
code).
In the downlink scrambling codes are used to reduce the inter-
basestation interference. Typically, each Node B has only one
scrambling code for UEs to separate base stations. Since a code
tree under one scrambling code is used by all users in its cell,
proper code management is needed.
In the uplink scrambling codes are used to separate the
terminals.
The comparision between channelisation code and scrambling
code is shown in Table 5.
TAB L E 5 TH E C OMPAR I SI ON B ETW EEN C H AN N EL I SATI ON C OD E AN D
SC R AMB L I N G C OD E
Item Channelisation Code Scrambling Code
Usage
UL: Separation of physcial data
and control channels from
same UE
DL: Seperation of different
users
within one cell
UL: Separation of
terminals
DL: Separation of
cells/sectors
Length
UL:4 – 256 chips same as SF
DL:4 – 512 chips same as SF
UL: 10ms=38400
chips
DL: 10ms=38400
chips
No. of
codes
No. of codes under one
scrambling
code = SF
UL: Several millions
DL: 512

Item Channelisation Code Scrambling Code
Code
family
Orthogonal Variable Spreading
Factor
Long 10ms code:
Gold code
Short code:
Extended S(2) code
family
Spreading
Yes, increase transmission
bandwidth
No, does not affect
transmission
bandwidth
Spread Spectrum
Spread spectrum is an information transmission mode. It
modulates information signals with spreading code at sending
end and enables spectrum width of information signals much
wider than bandwidth for information transmission. It dispreads
at receiving end with same spreading code, to resume data of
transmitted information.
Figure 13 shows basic operations of spectrum spread/dispread.
FI GU R E 13 SPEC TR U M SPR EAD I N G/DI SPR EAD I N G I N DS-CDM A
Subscriber data
= -1+1-1-1+1-1
Spread spectrum =
+1-1-1+1-1+1+1-1
Spreading signal =
Subscriber data *
Spread spectrum
Dispreading data
= Subscriber data
* Spread
spectrum
＋1
－1
＋1
－1
＋1
－1
＋1
－1
＋1
－1
Spectrum dispreading
Spectrum spreading
Supposing subscriber data rate is R, subscriber data is 101101,
and according to the rule that 1 is mapped as -1, 0 is mapped as
+1, map subscriber data as -1+1-1-1+1-1 and time it with
spreading code. Spreading code is 01101001 in this example.
Time each subscriber data bit to this code series including 8
code chips. Concluded data rate after spread is 8 × R and is
random, like spreading code. Its spread spectrum factors are 8.
Broadband signals after spread spectrum are transmitted to
receiving end via radio channels. Time code sequence with same
spread spectrum code (dispreading code) when dispreading at
receiving end to resume original subscriber data.
Spreading signal speed by 8 times factor may result in
bandwidth spreading of subscriber data signals (therefore, CDMA

WCDMA Basics
system is often called spread spectrum system). Dispreading
resumes signal rate to original rate.
Distributing different spread spectrum to different subscriber can
distinguish different subscriber, as shown in above sector.
Supposing that there are three subscribers and that signals they
send are b1, b2 and b3, spread their signals with spreading code
of c1, c2 and c3 and final sending signal is y=b1c1 + b2c2 +
b3c3. Supposing that there is no interference in signal
transmission, the receiving end:
 Gets signals after dispread with c1
z1 = y * c1 = c1 * (b1c1 + b2c2 + b3c3) = b1 +
(b2c2c1 + b3c3c1)
z2 = y * c2 = c2 * (b1c1 + b2c2 + b3c3) = b2 +
(b1c1c2 + b3c3c2)
z3 = y * c3 = c3 * (b1c1+b2c2+b3c3) = b3 + (b1c1c3
+ b2c2c3)
All parts in the brackets in above three formulas are interference
of other subscriber signals to this signal. This interference can
be absolutely avoided if using orthogonalized codes.
Orthogonalized code is the code that is 1 after timing itself and
is 0 after timing other codes. So:
z1 = y * c1 = c1 * (b1c1 + b2c2 + b3c3) = b1 + (b2c2c1 +
b3c3c1) = b1 + 0 + 0 = b1
z2 = y * c2 = c2 * (b1c1 + b2c2 + b3c3) = b2 + (b1c1c2 +
b3c3c2) = b2 + 0 + 0 = b2
z3 = y * c3 = c3 * (b1c1 + b2c2 + b3c3) = b3 + (b1c1c3 +
b2c2c3) = b3 + 0 + 0 = b3
Some Parameters of WCDMA
Physical Layer
Some Parameters of WCDMA Physical Layer is show as Table 6.
TAB L E 6 SOME PAR AMETER S OF WCDM A PH YSI C AL LAYER
Parameter Value
Carrier Spacing 5 MHz (nominal)
Chip Rate 3.84 Mcps
Frame Length 10 ms (38400 chips)
No. of slots/frame 15
No. of chips/slot 2560 chips (Max. 2560 bits)

Parameter Value
Downlink SF 4 to 512
Channel Rate 7.5 Kbps to 960 Kbps

C h a p t e r 3
Network Structure
This chapter gives a wide overview of the UMTS system
architecture, including an introduction to the logical network
elements and the interfaces.
System Architecture
R99
The basic configuration structure of the R99 is illustrated in
Figure 14.

Chapter 3 Network Structure
FI GU R E 14 BASI C NETW OR K STR U C TU R E OF R99
To guarantee the investment interests of telecom operators, the
network structure of the R99 is designed with 2G/3G
compatibility fully in mind, for smooth evolution to 3G.
Therefore, the core network in the basic network structure
remains unchanged. To support 3G services, some NEs are
added with appropriate interface protocols, and the original
interface protocols are also improved by different degrees.
R4
The basic configuration structure of the R4 is illustrated in Figure
15.

WCDMA Basics
FI GU R E 15 NETW OR K STR U C TU R E OF TH E R4
BSS
BSC
RNS
RNC
CN
Node B Node B
IuPS
Iur
Iub
USIM
ME
MS
Cu
Uu
MSC server
SGSN
Gs
GGSNGMSC
server
Gn
HSS(HLR)
Gr
Gc
C
D
Nc
H
EIR
F Gf
GiPSTN
IuCS
VLR
B
Gp
VLR
G
BTSBTS
Um
RNC
Abis
SIM
SIM-ME i/f or
MSC server
B
PSTN
cell
CS-MGWCS-MGW
CS-
MGW
AuC
Nb
T-SGW R-SGW
Mc
Mc
Nb
PSTNPSTN
Nc
Mc
Mh
A
Gb
E
Same as the R99 network, the basic structure of the R4 network
consists of the core network and wireless access network, and
there are the CS domain and PS domain on the core network
side. The basic NE entities and the interfaces are largely
inherited from the definitions of entities and interfaces of the
R99 network. The network entities with the same definitions as
the R99 network remain unchanged in basic functionality, and
the related protocols are also similar.
Compared with the R99, the R4 network structure has
tremendous changes in the structure of the CS domain of the
core network, while those of the PS domain of the core network
and of the UTRAN also remain the same.
According to the idea of separation between call control, bearer
and bearer control, the network entity (G) MSC of the CS
domain of the R99 network evolves to the MGW and (G)
MSCServer in the R4 stage, with R-SGW and T-SGW added. In

addition, related interfaces are also changed, with the Mc
interface added between the MGW and MSC Sever, the Nc
interface between the MSC Sever and GMSC Sever, and the Nb
interface between MGWs, and the Mh interface between the MR-
MGW and HLR.
R5
The basic configuration structure of the R5 is illustrated in Figure
16.
FI GU R E 16 NETW OR K STR U C TU R E BASED ON UM TS R5
After 3GPP R4, the aim was to implement the following major
items:
 IP transport over the whole system from the BS up to the
network border gateway. Use of the IP-based transport
as the alternative transport mechanism in UT RAN from
Release 5 onwards.
 To introduce an IP Multimedia Subsystem (IMS) in order
to start wide use of various multimedia services.
 To unify the open interface between the various access
and core networks.
 In this phase it is expected that the majority of services
used are asymmetric in nature(i.e., the downlink
direction carries a heavier load than the uplink direction).
To handle this situation better in UTRAN, a collection of
changes related to the UTRAN radio path are introduced.
This collection is known as High Speed Downlink Packet
Access (HSDPA). This affects the radio path, BS and
transport channel arrangement in UT RAN. The peak
speed of HSDPA is 14.4Mbps theoretically.

WCDMA Basics
 In order to transfer end-user-related radio functionality
within the network as smoothly as possible, UTRAN and
GERAN have a defined interface between themselves
named “Iur-g”. Iurg does not transfer a user plane—this
is provided for signalling purposes only.
R6
The difference between R5 and R6 include the following:
 High Speed Uplink Packet Access(HSUPA) is introduced in
R6. The peak speed of HSUPA is 5.76Mbps theoretically.
 MBMS （ Multimedia Broadcast/Multicast Service ） is
introduced in R6.
UTRAN Architecture
Figure 17 shows the overall architecture of WCDMA UT RAN
(UMTS Terrestrial Radio Access Network) system.
FI GU R E 17 OVER AL L UTRAN AR C H I TEC TU R E
RNS
RNC
RNS
RNC
CoreNetwork
NodeB NodeB NodeB NodeB
Iu Iu
Iur
Iub IubIub Iub
UTRAN
 Interface
 The interface between CN and UTRAN is Interface Iu.
 Inside UTRAN, the interface between RNC and Node B is
Interface Iub.
 Inside UTRAN, the interface between RNCs is Interface
Iur.
 In addition, the interface between UTRAN and UE is
Interface Uu.

 RNS (Radio Network Subsystem): The general name for one
RNC and all Nodes B it manages.
 SRNC (Serving RNC): The RNS connecting with CN is
called SRNS and the RNC of RNS is called SRNC.
 DRNC (Drift RNC): In the case of soft handover of
WCDMA, UE can use several RNSs. Figure 18 shows the
relation of SRNS and DRNS.
FI GU R E 18 SRNS AN D DRNS
SRNS
Core Network
Iu
DRNS
Iur
UE
Cells
Several links can exist inside one UE at the same time. The
user data to access DRNS is sent to SRNS from DRNS via
Interface Iur. DRNC won’t process the data but transmit it
between Interface Iub and Interface Iur transparently. One
UE can access one or several DRNSs.
 CRNC (Control RNC): When UE access one RNS, the RNC
of the RNS is called CRNC. Therefore, in Figure 18, both
SRNC and DRNC are CRNC. CRNC manages the resources
of the whole cell. SRNC schedules data on user DCH and
CRNC schedules data on CCH.
For Source RNC (S-RNC) and Target RNC (T-RNC), refer to
Chapter of Interface Iu.

WCDMA Basics

Figures
Figure 1 IMT2000 Family ...................................................4
Figure 2 3GPP and local specification bodies ..........................5
Figure 3 Frequency Spectrum Allocation of 3G Mobile
Communication.................................................................6
Figure 4 Network Elements in a PLMN .................................7
Figure 5 WCDMA Communication Principle ............................2
Figure 6 Near-far effect .....................................................8
Figure 7 Configuration of Radio Transmitter and Receiver ........9
Figure 8 Principles of DS-CDMA............................................. 10
Figure 9 Uplink Modulation ............................................... 12
Figure 10 Downlink Modulation ......................................... 12
Figure 11 Spreading Operation ......................................... 13
Figure 12 Code Tree ....................................................... 14
Figure 13 Spectrum Spreading/Dispreading in DS-CDMA ....... 15
Figure 14 Basic Network Structure of R99 ........................... 19
Figure 15 Network Structure of the R4 ............................... 20
Figure 16 Network Structure Based on UMTS R5 .................. 21
Figure 17 Overall UTRAN Architecture ................................ 22
Figure 18 SRNS and DRNS ............................................... 23

WCDMA Basics

Tables
Table 1 Chapter Summary ..................................................i
Table 2 Typographical Conventions...................................... ii
Table 3 Mouse Operation Conventions .................................. ii
Table 4 UMTS Interface Description ...................................7
Table 5 The comparision between channelisation code and
scrambling code.............................................................. 14
Table 6 Some Parameters of WCDMA Physical Layer ............. 16

Umtsrns 101 wcdma basics

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