McGraw Hill - 2002 - W-CDMA and cdma2000 for 3G Mobile Networks_6 pdf

General Capabilities and Features of GPRS In circuit-switched data services, when a user wants to transmit orreceive any data, first a physical channel is set up using the normalGSM call

the figure, interfaces GSM to a private or public network such

as a PSTN, ISDN, circuit-switched public data network, switched public data network, and so on Because the datacommunication protocols of a mobile station may be differentfrom those of devices it is in communication with across anetwork, entity IWF may perform protocol conversion, rateadaptation, and so on

packet-■ Short messaging service A mobile station in GSM may transmit

or receive short alphanumeric messages during both idle andactive call states

■ GPRS This is a new service available with GSM Phase 2 thatenables multiple users to transmit packet data over a single slot

In this section, we will present a brief description of GPRS

General Capabilities and Features of GPRS

In circuit-switched data services, when a user wants to transmit orreceive any data, first a physical channel is set up using the normalGSM call control procedures Because data usually comes in burstsseparated by variable periods of inactivity, the channel may remainidle for a considerable length of time, depending upon the type ofdata services being used One could, of course, release the channelduring inactive periods of data and reestablish the connection whenuser data is ready However, this approach is not very efficient orpractical, because delays associated with call control procedures forsetting up a physical channel are relatively long A packet switchingsystem, where multiple users may transmit their data over the

same physical channel using the so-called virtual circuits,

over-comes this problem by taking advantage of the statistical nature ofthe traffic arrival process The virtual circuits may be either perma-nent or switched But even when they are switched, call controldelays for setting up or tearing down a virtual circuit are usuallyvery small

As we mentioned before, GPRS is a new feature of GSM that vides the capability of packet mode transmission of user data andsignaling information using the existing GSM network and radioresources Each physical channel is shared by multiple users The

pro-Chapter 5174

channel access mechanism has been optimized for intermittent,short bursts as well as large volumes of data, allowing data to betransmitted within about 0.5 to 1.0 seconds of a reservation request.

It supports both IP and X.25 protocols and real-time as well as real-time data Both point-to-point and point-to-multipoint commu-nications are possible There is no restriction on the transfer of SMSmessages over GPRS channels

non-In packet switching, it is necessary to use a set of data cation protocols so that the transmission is efficient and error-free.Protocols that are of interest here are usually the lower-layer proto-

communi-cols such as the logical link control (LLC) and medium access control

(MAC)

Users are allowed to request a desired quality of service (QoS)

from the network However, only a limited number of QoS profilesare supported Different modes of operation are possible For exam-ple, in one mode, a mobile station can receive both GSM and GPRSservices simultaneously (that is, a voice call and packet mode datatransfer at the same time) In another mode, it can only receive theGPRS service In the third mode, the mobile station monitors controlchannels of both GSM and GPRS, but can receive services from onlyone of them at a time (that is, either a voice or packet mode data).Four channel-coding schemes, designated CS-1, CS-2, CS-3, and CS-

4, with coding rates of 1/2,2/3,3/4, and 1, respectively, are supported.The throughput depends on the coding scheme used: with CS-1, themaximum throughput is about 9 kb/s, whereas with CS-4, it is 21.4kb/s Because a user may be assigned all eight slots of a frame, theper-user throughput may be in excess of 160 kb/s

GPRS Network Architecture

Figure 5-13 is the architecture of a general GPRS network Theinterface points between different elements of the network have alsobeen indicated To see the difference between a GSM and a GPRSnetwork, compare this figure with Figure 5-2 Notice that in GPRS,there are only two new entities:

■ Serving GPRS Support Node (SGSN) As the name implies, theSGSN provides GPRS services to a mobile station in the serving

area of its associated MSC A PLMN may have more than oneSGSN, in which case, the SGSNs are connected together over anIP-based Gn interface Two different PLMNs, on the other hand,are connected over a Gp interface A serving GSN connects to agateway GSN via a Gn interface and to its BSS over a Gbinterface that uses the Frame Relay protocol at the link layer.

An SGSN node locates mobile stations subscribing to GPRSservices and adds this information to the HLR Another function

of the SGSN is to control user access to the network byperforming authentication using the same encryption keys andalgorithm as in GSM Optionally, it can also perform signalingand control for non-GPRS services For example, it can supportshort messaging service over a GPRS radio channel and

efficiently process paging messages and mobile locationinformation required in GSM circuit-switched calls

Chapter 5176

HLR MSC

A

SGSN 1 PSTN/ISDN

PDN1 (e.g The Internet) GGSN

Gn

Gi Another

SGSN 2

Gn

To other PDN

o o

To other SGSN

BSS

VLR

GMSC

SMS-Gd D

C E

■ Gateway GPRS Support Node (GGSN) GGSN provides aninterface between a GPRS network and any external network

such as a packet-switched public data network (PSPDN) Thus,

as an example, whenever a PSPDN has a packet to send to aPLMN, it comes first to the GGSN The gateway GSN containsthe routing information of all mobile stations attached to it andforwards an incoming packet appropriately en route to itsdestination It may request information from an HLR or provideinformation to the HLR when necessary Both SGSN and GGSNhave IP routing functionality, and as such may be connectedtogether by an IP router

In the current version of cellular systems (that is, 2G), GPRS issupported by adding packet-handling capabilities to the base station

controller This is done by means of an interface called packet control

unit (PCU) as shown in Figure 5-14 In a fully evolved 3G system, the

interface to a GPRS network would be integrated into the UTRA BSS

GPRS Protocol Stacks

The GPRS protocol stacks required in a mobile station, BSS, SGSN,and GGSN, are shown in Figure 5-15 Although the networking

HLR MSC

SGSN

PSTN/ISDN

The Internet GGSN

BSC VLR BTS

PCU

Figure 5-14

Support of GPRS in

2G networks

protocol is shown in the figure to be either IP or X.25, GPRS is fullycapable of supporting applications based on any standard data pro-tocol.

GPRS protocols at various layers are thoroughly described in erences [14]—[22] Here, we provide only a short description of theprotocol at each layer:

Ref-■ Subnetwork Dependent Convergence Protocol (SNDCP) SNDCP,which, in the protocol hierarchy, lies between the network layer(that is, IP/X.25) and the LLC layer, takes the network layerPDUs (corresponding to different protocols) and converts theminto a format that is suitable for transmission over the

underlying radio interface network For example, if the protocol

at the layer above it is IP, the SNDCP will take the IP packet,compress its header, and pass it to the LLC layer Similarly,when it receives a packet from the LLC layer, it may

decompress the header and pass it to the IP layer User packetsmay have variable lengths and are segmented, if necessary.Both acknowledged and unacknowledged data transfer ispossible Other functions performed at this layer include

■ Data transfer using negotiated QoS profiles

■ Security and encryption of user data and control to provideprotection against eavesdropping

■ Logical Link Control (LLC) The data link layer at the mobilestation (the Um reference point) consists of two sublayers: the

Chapter 5178

Application IP/X.25 SNDCP LLC RLC MAC

GSM Physical

RLC MAC GSM Physical Layer

RLC MAC

RLC MAC

Physical Layer Frame Relay

Relay

BSSGP

Physical Layer Frame Relay

BSSGP LLC SNDCP

L2 IP TCP/UDP GTP

Physical Layer L2 IP TCP/UDP GTP IP/X.25 Relay

Figure 5-15

GPRS protocol

stacks at a few

reference points

upper sublayer known as LLC and the lower sublayer consisting

of a radio link control (RLC) and a MAC sublayer The LLC sublayer is based on the link access procedures of the ISDN D

channel (LAPD) and supports procedures for the following:

■ Unacknowledged data transfer The Frame Relay protocol is asubset of LAPD procedures using the unacknowledged

information transfer mode

■ Acknowledged data transfer

■ RLC The RLC protocol provides a reliable transmission of data

blocks over the air interface using a selective automatic repeat

request (ARQ)-type procedure, where data blocks received in

error are retransmitted by the source

■ MAC The MAC sublayer controls access of the physicalmedium by mobile stations using a slotted Aloha scheme byresolving contention among multiple users or among multipleapplications of an individual user and then granting therequested access in a manner that ensures efficient utilization ofbandwidth

■ GPRS Tunneling Protocol (GTP) In GPRS, address and controlinformation are added to protocol data units so that they can berouted within a PLMN or between two PLMNs The protocol thatdefines this process is known as the GTP.5Simultaneous

header Its use is quite common in packet-switched networks Suppose that an IPv6 packet has to be sent over a network that is using the older IPv4 protocol In this case,

we could take the original IPv6 packet, add the IPv4 header to it, and send the ing packet over the network That would be called tunneling Another example is IP over ATM where an IP packet, when it first enters an ATM device, is encapsulated with an 8-octet header before it is sent out over ATM.

result-operation of two modes is possible—unacknowledged mode forUDP/IP and acknowledged mode for TCP/IP.

■ Relay function It provides a procedure for forwarding a packet

received at a node to the next node en route to its destination In

the BSS, LLC PDUs are relayed between Um and Gb interfaces

In the SGSN, packet data protocol (that is, IP and X.25) PDUsare relayed between interfaces Gb and Gn

■ Base Station System GPRS protocol (BSSGP) The function ofthis protocol is to provide multiple, connectionless, layer 2 linksand to transfer data, QoS-specifying parameters, and routinginformation between a base station and an SGSN

■ Frame Relay This is the link layer protocol on the Gb interface

Data is transmitted over one or more permanent virtual circuits

(PVCs) Frames received in error are discarded The data linkconnection identifier is two octets long The maximum framesize is 1,600 octets

The physical layer on the Um interface includes the typical,GSM radio link functions such as framing, channel encoding, inter-leaving, modulation, wave-shaping, synchronization, timing recov-ery, and so on

For a description of TCP and IP protocols, see Reference [10].Figure 5-15 also indicates the need for protocol conversion at dif-ferent points in the network For example, consider the servingGSN After receiving a packet from the base station system, it mustterminate the five lower layers—physical, frame relay, BSSGP, LLC,

and SNDCP—and retrieve the network protocol data units (PDUs).

These IP/X.25 PDUs must then be encapsulated in GTP, TCP/UDP,

IP, and L2 in that order and sent out over its physical layer toGGSN

Packet Structures

The packet structure at each layer of the Um interface is shown inFigure 5-16 PDUs received from the IP or X.25 layer for transmis-sion over the air interface are segmented at the SNDCP layer intosmaller packets and passed to the LLC layer where a header and

Chapter 5180

frame check sequence are added to each segment The maximum size

of the LLC data unit is 1,600 octets Each LLC PDU is further mented, if necessary, into smaller blocks before passing it to theRLC/MAC layer To each of these blocks are added an RLC header, aMAC header, and a block check sequence (BCS) The resulting frame,after the usual physical-layer processing, is sent out in normalbursts, each consisting of 156.25 bits, of which 114 bits are from anRLC/MAC PDU

seg-Logical Channels

Broadly speaking, there are three types of logical channels for mitting packets in GPRS They are packet broadcast control channel,

trans-packet common control channel (PCCH), and traffic channels Some

operate only on uplinks, some on downlinks, and the rest on bothuplinks and downlinks (that is, they’re bidirectional)

Uplink Channels Packet Random Access Channel (PRACH) This

is a common control channel and is used by a mobile station to start

a packet transfer process or respond to a paging message

Network Layer PDU Header + User Data + CRC if needed

Segment 1 Segment 2 o o o Segment N

SNDCP Layer

o o o Segmentation

Segmentation

1 o o o n

RLC/MAC Data (or Signaling) BCS RLC/MAC PDU

Coding, Interleaving, etc Physical Layer

Transmitted over Air Interface in Bursts

RLC Header MAC Header

Downlink Channels Packet Broadcast Control Channel (PBCCH)

It broadcasts system-specific parameters to all mobile stations in aGPRS serving cell

The following are common control channels:

■ Packet Paging Channel (PPCH) The GPRS network uses thischannel to transmit paging messages before sending userpackets

■ Packet Access Grant Channel (PAGCH) When a mobile stationwants to initiate a data transfer, it transmits a Packet ChannelRequest message on a PRACH or on a RACH in the absence of aPRACH In reply, the base station sends a Packet ImmediateAssignment message on a PAGCH, reserving one or more packetdata transfer channels for that mobile station Similarly, thenetwork may send on this channel a resource assignmentmessage to a mobile station

■ Packet Notification Channel (PNCH) This channel is used tonotify a group of mobile stations prior to sending packets tothose stations in a point-to-multipoint fashion

Bidirectional Channels A Packet Data Transfer Channel

(PDTCH) is allocated to a mobile station for transferring their datapackets A given user may request, and be granted, more than onePDTCH

A Packet Associated Control Channel (PACCH) carries signaling information, such as an acknowledgment (ACK), in response to a data

block transfer, a resource assignment message in response to aresource request, or power control information Only one PACCH isassigned to each mobile station, and is associated with all packet datatransfer channels that may be allocated to that station

Logical channels are multiplexed at the MAC layer onto physicalchannels on a block-by-block basis Physical channels used for GPRS

packet data transmission are known as packet data channels (PDCH).

Packet Transmission Protocol

Multiple users may transmit packets on a PDCH on a time-sharedbasis Each PDCH consists of one time slot of a TDMA frame How-

Chapter 5182

ever, a mobile station may be assigned up to eight PDCHs for packetdata transmission.

A cell may permanently set aside a fraction of its available cal channels exclusively for packet data transmission and the restfor the usual voice traffic Alternatively, it may use a dynamic allo-cation scheme whereby one or more channels out of its available pool

physi-of channels are allocated to packet data transmission on a demandbasis, and are deallocated and returned to the pool when there is nolonger any need for them The number of packet data channels active

at any time depends on the number of simultaneous users and thevolume of traffic generated by each user However, there must be atleast one PDCH to enable transfer of control and signaling informa-tion (as well as user data if necessary) It is not necessary that thesame PDCH be used to send packets to/from a given mobile station.Multiple users transmit on a PDCH using a slotted Aloha, multi-ple-access reservation scheme In the event of transmission errors,

an ARQ protocol is used that provides error recovery by selectiveretransmissions of RLC blocks To this end, GPRS employs the con-

cept of a temporary block flow (TBF), which is actually a physical

connection between a mobile station and the network, allowing thetransfer of RLC/MAC blocks.6 Each RLC data block or RLC/MAC

control block includes in its header a temporary flow identifier (TFI)

that indicates the TBF to which the block belongs.7Furthermore, all

downlink RLC/MAC blocks contain in their header an uplink state

flag (USF) that indicates which mobile station (or application) can

use the next uplink RLC block on the same time slot In this way, ferent mobile stations may be multiplexed on the same PDCH whennecessary

dif-A mobile station transfers packets to an SGSN following the statediagram of Figure 5-17 The corresponding state machine represen-tation of an SGSN is similar

In the IDLE state, a mobile station may select or reselect a cell,but its location or routing information is not available to the SGSN

and is removed when it is no longer needed.

Similarly, different PDCHs may use the same TFI.

In other words, it is not attached to the mobility management tion, and therefore cannot receive or originate a call.

func-When the mobile station establishes a logical link to an SGSN, itenters the READY state The mobile is now attached to the mobilitymanagement function and can initiate a mobile-originated call on aPRACH (that is, a packet random access channel) or monitor thepacket-paging channel to see if there is any packet transfer requestfrom the network If there is no PRACH available yet, the GPRS-attached mobile station may use the GSM common control channel.After being allocated appropriate resources from the network, themobile station can begin to transmit and receive packets

The mobile station remains in the READY state as long as there

is any packet to send Even when there is no packet pending in itsbuffer, it may continue in the READY state for a certain length oftime that is marked by starting an associated timer As the timer isrunning, the network has the capability to preempt the timer andforce the mobile station into the STANDBY state When the timerexpires, the mobile station changes to the STANDBY state While inthe READY state, the mobile station may power down by performing

a GPRS-detach procedure It then enters the IDLE state, whereuponthe SGSN deletes the location and routing information of the mobile

In the STANDBY state, the mobile station is still GPRS-attachedand sends the SGSN its location and routing information periodi-

cally and each time it moves into a new routing area (RA) While in

this state, it can transmit a PDU and then transition to the READYstate

The packet transfer procedure when initiated by a mobile station

is shown in Figure 5-18 The mobile station sends a packet channelrequest over a packet random access channel (or in its absence, a

Chapter 5184

random access channel) The network replies by reserving the essary resources required by the MS and sending a packet immedi-ate assignment message In this case, the access method completes

nec-in a snec-ingle phase In a two-phase access procedure, when the work sends a packet immediate assignment, it reserves only theresources required by a mobile station to transmit a packet resourcerequest Consequently, the mobile station sends this request mes-sage indicating resources it needs, whereupon the network makesthe necessary reservation and replies with a packet resource assign-ment message

net-After receiving the packet immediate assignment, the MS canbegin to send data packets The network may withhold acknowledg-ment until after receiving a few packets When it receives a block inerror (say, block 3 in this example), it sends an ACK (4,5), excludingblock 3 from this acknowledgment, as shown in Figure 5-18 In thiscase, the mobile station performs a selective retransmission of block

3 only (and not blocks 3, 4, and 5), transmitting it along with block 6.Alternatively, the network could send a NACK in the event of anerror

The packet transfer procedure initiated by the network (that is, anSGSN) is shown in Figure 5-19 The mobile station monitors the

Packet Channel Request on RACH or PRACH

Data Block 1 on PDTCH Packet Immediate Assignment on AGCH or PAGCH

Data Block 2 on PDTCH ACK (1,2) on PACCH Data Block 3 on PDTCH Data Block 4 on PDTCH

GPRS Network

ACK (4,5) on PACCH Data Block 3 on PDTCH Data Block 6 on PDTCH ACK (3,6) on PACCH

packet paging-channel (or in its absence, the paging channel) When

it receives a packet-paging request, it sends a packet channelrequest The network answers by sending a packet immediateassignment This is followed by a packet-paging response from the

MS and a packet resource assignment At this point, the networkmay begin to transmit data blocks to the MS

Summary

In this chapter, we have presented a brief description of the GSM tem Its features and capabilities have been summarized, and sometechnical detail has been provided about the speech encoder, channelencoder, interleaver, modulator, TDMA slot, frame formats, and logi-cal channels One of the important aspects of GSM is its data servicecapability such as the short messaging service and circuit-switched

sys-Chapter 5186

Packet Channel Request on RACH or PRACH

Packet Paging Response on PACCH Packet Immediate Assignment on AGCH or PAGCH

Packet Resource Assignment on AGCH, PAGCH or PACCH

Data Block 1 on PDTCH Data Block 2 on PDTCH ACK (1, 2) on PACCH Data Block 3 on PDTCH Data Block 4 on PDTCH ACK (4) on PACCH Data Block 3 on PDTCH Data Block 5 on PDTCH Packet Paging Request on PCH or PPCH

data In the short messaging service, users can transmit messages ofabout 160 alphanumeric characters in both point-to-point and point-to-multipoint fashion The circuit-switched data rate per slot may be2.4, 4.8, or 9.6 kb/s By bundling multiple channels, a user can be pro-vided much higher data rates, say, up to about 76.8 kb/s The GPRS

is a relatively new feature of GSM Version 2.5 that provides packetmode data services at rates of 8 to 20 kb/s per slot In this chapter, wehave described the general capabilities and features of GPRS, its net-work architecture, protocols at various layers, logical channels,packet structures, and the packet transmission protocol

[3] N.S Jayant, “High-Quality Coding of Telephone Speech and

Wideband Audio,” IEEE Comm Mag., Vol 28, No 1, pp.

10–19, January 1990

[4] P Vary, et al., “Speech Codec for the European Mobile Radio

System,” Proc ICASSP ‘88, pp 227–230, April 1988.

[5] J Makhoul, “Linear Prediction: A Tutorial Review,” Proc.

IEEE, Vol 63, pp 561—580, April 1975.

[6] R.W Lucky, et al., Principles of Data Communications New

York: McGraw Hill, 1968, pp 200–202

[7] J.G Proakis, Digital Communications New York: McGraw

Hill, 1968, pp 172–186

[8] C Sundberg, “Continuous Phase Modulation,” IEEE Comm.

Mag., pp 25–38, April 1986.

[9] J Cai and D.J Goodman, “General Packet Radio Service,”

IEEE Comm Mag., pp 122–131, October 1997.

[10] M Naugle, Network Protocol Handbook New York:

McGraw-Hill, 1994

ETSI Standards

[11] GSM 03.60: GPRS Service Description, Stage 2

[12] GSM 03.64: Overall Description of the GPRS Radio Interface,Stage 2

[13] GSM 04.60: GPRS, Mobile Station—Base Station System(BSS) Interface, Radio Link Control/Medium Access Control(RLC/MAC) Protocol

[14] GSM 04.64: GPRS, Logical Link Control

[15] GSM 04.65: GPRS, Subnetwork Dependent Convergence tocol (SNDCP)

Pro-[16] GSM 07.60: Mobile Station (MS) Supporting GPRS

[17] GSM 08.08: GPRS, Mobile Switching Center—Base StationSubsystem (MSC-BSC) Interface: Layer 3 Specification.[18] GSM 08.14: Base Station Subsystem—Serving GPRS Sup-port Node (BSS-SGSN) Interface; Gb Interface Layer 1.[19] GSM 08.16: Base Station Subsystem—Serving GPRS Sup-port Node (BSS-SGSN) Interface; Network Service

[20] GSM 08.18: Base Station Subsystem—Serving GPRS port Node (BSS-SGSN); Base Station Subsystem GPRS Pro-tocol (BSSGP)

Sup-[21] GSM 09.60: GPRS Tunneling Protocol (GTP) Across the Gnand Gp Interface

[22] GSM 09.61: General Requirements on Interworking Betweenthe Public Land Mobile Network (PLMN) Supporting GPRSand Packet Data Network (PDN)

[23] GSM 2.01, Version 4.2.0, January 1993

[24] ETSI/GSM Section 4.0.2, “European Digital CellularTelecommunication System (Phase 2); Speech ProcessingFunctions: General Description,” April 1993

Chapter 5188

Universal Mobile Telecommunications System (UMTS)

6

Copyright 2002 M.R Karim and Lucent Technologies Click Here for Terms of Use.

As we indicated in Chapter 1, “Introduction,” the European

Telecom-munications Standards Institute (ETSI)/Special Mobile Group (SMG)

developed two standards for International Mobile Telecommunication

in the year 2000 (IMT-2000) One of them is the Universal Mobile Telecommunications System (UMTS) Wideband Code Division Mul- tiple Access (W-CDMA), which is based upon a direct-sequence CDMA

(DS-CDMA) technology and operates in the frequency division duplex

(FDD) mode The other is the UMTS TDD system, which is based on

time-division CDMA (TD-CDMA) principles The purpose of this

chapter is to present an overview of the W-CDMA UMTS system asspecified in the ETSI standards documents [1]—[40]

The chapter is organized as follows We begin with a synopsis of

the UMTS system features and follow it up with the third-generation

(3G) wireless network architecture The UMTS uses a layered col architecture at different interface points, each layer performing aset of specific functions We present an overview of the radio inter-face protocol stack The next few sections describe each of the con-stituent protocols of this stack, namely the physical layer, themedium access control, radio link control, the packet data conver-gence protocol, the broadcast multicast protocol, and the radioresource control protocol Topics, such as the synchronization proce-dure, power controls, and handovers, are also described The mater-ial of this chapter has been drawn from a series of standardsdocuments In many instances, our descriptions have been necessar-ily brief and comprehensive However, we have included relevant ref-erences at the end of the chapter so that the interested reader mayconsult them for greater detail

proto-System Features

The UMTS operates in two modes—FDD and Time Division Duplex

(TDD) In both modes of operation, the information is transmittedusually in 10 ms frames In FDD, two distinct frequency bands, sep-arated by a guard band, are used—one for the uplink and the otherfor the downlink transmission In TDD, on the other hand, the samefrequency band is used for transmissions in both directions More

Chapter 6190

specifically, in this mode, each frame consists of a number of chronized time slots, some of which are dedicated to uplink and therest to downlink transmissions The difference between the twomodes is illustrated in Figure 6-1.

syn-The UMTS has been allocated a bandwidth of 120 MHz in theFDD mode and 35 MHz in the TDD mode in the 2000 MHz spectrumrange When operating as paired bands as shown in Figure 6-1(a),

the transmitter and receiver frequencies in all user equipment (UE)

must be spaced apart by 190 MHz As we mentioned earlier in the

book, CDMA uses Direct Sequence Spread Spectrum (DSSS).

Because one of the goals of 3G systems is to provide multimedia andhigh-speed data services at rates up to 2 Mb/s, the nominal channelbandwidth is 5 MHz A service provider may, however, adjust thechannel bandwidth if necessary to optimize the spectrum utilization.The center frequency must be an integer multiple of 200 kHz.1Thechip rate for spectrum spreading is 3.84 Mc/s

Uplink

Frequency (MHz)

Guard Bandwidth

Time Uplink Downlink

The two modes of

UMTS: (a) The FDD

mode and (b) The

TDD mode

W-CDMA is an asynchronous system where base stations do nothave to maintain a system-wide reference time scale However, eachcell or each sector of a cell must now use a different scrambling code.Because there is no global timing reference, the time offsets betweensignals received from multiple users by a base station in such a sys-tem may be quite significant Since the cross-correlation betweenscrambling codes assigned to different users is no longer zero, thereceived signal from any user depends not only on the signal fromthat user but also on the signals received from all other users over anumber of consecutive symbol periods Thus, multiuser detectionwould be useful in such a system.2In contrast, cdmaOne is synchro-nous because all base stations in the system use a reference time

that is based on the Global Positioning System (GPS) time derived

from the Universal Coordinated time More specifically, the I and Qchannels at any base station in cdmaOne are spread by two maxi-mal-length pilot pseudonoise sequences with an offset that is uniquefor that base station This simplifies and accelerates cell searching at

a mobile station

The following specifications apply to the radio transmission andreception in the UMTS FDD mode The separation between theuplink and downlink frequency bands must be in the range of 134.8

to 245.2 MHz The maximum transmitter power of the user ment is in the range of 21 to 33 dBm (that is, 125 mW to 2 W) Thereceiver sensitivity, which is nominally defined as the minimum

equip-receiver input power at the antenna port such that the bit error ratio

(BER) is 0.001 or less, is 117 dBm for the UE and 121 dBm for abase transceiver station.3With transmit power control (TPC) com-

mands, the UE adjusts its transmitter power output by 8 to 12 dB insteps of 1 dB, by 16 to 24 dB in steps of 2dB and by 16 to 26 dB insteps of 3 dB A base station, on the other hand, adjusts its transmitpower by 8 to 12 dB in steps of 1 dB and by 4 to 6 dB in steps of 0.5

dB These features are summarized in Table 6-1

Chapter 6192

Wide-band CDMA (W-CDMA).”

improved using multipath diversity, adaptive antenna arrays, or multiuser detection techniques.