Multi-User Communication - Aalborg Universitetkom.aau.dk/project/sipcom/SIPCom06/sites/SIPCOM9/courses/... · 2006-11-14 · received powers at Node B is critical to avoid near-far

1

Aalborg University, RATE/TBS, 2006slide 1

SIPCOM9-2, lecture 10MultiUserComm

Multi-User Communication

Lecture 10WCDMA Overview



Objective

• Introduce WCDMA– from a systems perspective, but with a focus

on lower layers (FDD mode)– WCDMA Release 99

• giving you, hopefully – a technology context to which you can apply

e.g. the theory on multi-user communication– a system context from which you can explore

recent advances on WCDMA (HSxPA) and its evolution (LTE)

2



Outline

• WCDMA introduction• UMTS and 3GPP specifications• UTRAN architecture• Basic radio resource management• Physical layer channels and procedures

– Short on TDD mode

• MUD in WCDMA uplink (gain potential)

• References• Acronyms



WCDMA

UE 1Time

(Code) Power

UE 2UE 3UE 4

Node BUE

Available resources: Spreading Codes (OVSF)

andTransmission Power

Soft/SofterHandover

non-orthogonal codes

orthogonal codes

DATA

Bit rate Chip rate

Channelisationcode

Scramplingcode

Chip rate

3



3

5

4

6

7

8

10

9

Cel

l ra

nge

(km

)

Ma

xim

um p

ath

loss

(dB

)

100 200 300 400 500 600 700 800 900 1000

145

150

155

160

165

Cell load (kbps)

Downlink 10WDownlink 20W

Uplink(144 kbps / 125 mW terminal)

Typisk maks. tab

3 dB forbedring af dækningsområde

Downlink 20W

Dækning er begrænsetaf uplink

Kapacitet er begrænset

af downlink

WCDMA Coverage and Capacity



3GPP Specifications

4



UMTS releases

v3.0.0 v3.1.0 v3.2.0 v3.3.0 v3.4.0

v4.0.0 v4.1.0 v4.2.0

v5.0.0 v5.1.0

etc.

Corrections New Functions

Release 99

Release 4 03/01

Release 5

12/99

06/02

Release 6

06/05 v6.0.0 etc.

etc.

etc.

Standardized by 3rd Generation Partnership Project (3GPP), see http://www.3gpp.org [North America: 3GPP2]

UMTS Long Term Evolution

UMTS used for designating 3rd generation systems (ITU: IMT-2000)



3GPP specs• Main rule for 3GPP specifications (http://www.3gpp.org):

– XX.INN• XX: series specification• I:

– (0) applies to both 3G and GSM (GPRS/EDGE)– (1,2) applies to 3G only

• GSM means GERAN 3GPP RAN while 3G means a 3GPP UTRAN RAN

• Examples• TS25.211 (v. 6.1.0), ”Physical channels and mapping of transport channels onto physical

channels (FDD), release 6”, Technical Specification Group Radio Access Network, July 2004

• TS25.213 (v. 6.0.0), ”Spreading and Modulation (FDD)”, Technical Specification Group Radio Access Network, December 2003

• TS25.104 (v. 6.8.0), ”Base Station (BS) radio transmission and reception (FDD)”, Technical Specification Group Radio Access Network, December 2004

• TS25.212 (v. 6.3.0), ”Multiplexing and channel coding (FDD)”, Technical Specification Group Radio Access Network, December 2004

• TR25.887 (v. 6.0.0), ”Beamforming enhancements (release 6)”, Technical Specification Group Radio Access Network, March 2004

• TR25.876 (v. 1.7.0), ”Multiple input multiple output in UTRA”, Technical Specification Group Radio Access Network, August 2004

• TR25.869 (v. 1.2.1), ”Tx diversity solutions for multiple antennas”, Technical Specification Group Radio Access Network, February 2004

5



3GPP Series



UTRAN Architecture

UMTS Terrestrial Radio Access Network

6



Radio-specific part

Public Land Mobile Network

UTRAN/GERAN

Uu/Um

CNUE/MS

Iu

From Release 5 GSM and UMTS have the same interface to the radiospecific part of the network

PLMN Architecture



Uu/Um

Node B/BTS RNC/

BSC

Node B/BTS

Node B/BTS

Node B/BTS

RNC/BSC

USIM

ME

Iub/Abis

Iur

MSC/VLR

GMSC

SGSN GGSN

HLR/AuC

UTRAN/GERANUE/MS CN External Network

Iu

PLMN, PSTN,ISDN, etc.

Internet,X25, etc.

PLMN

CS

PS

Radio-specific part

Public Land Mobile Network

PLMN ArchitectureThe geographical area covered by a PLMN is partitioned into MSC serving areas; a location area is a subset of a single MSC serving area.Typically, there is one (logically speaking) HLR in an operators PLMN.

7



BSC

B TS

B TS

B S S (R AN /G E R AN )

RN C

Node B

N ode B

U TR AN

M E

S IM

U S IM

M S

SG SN

P S D om ain

G G SN

C S M G W

C S D om ain HSS/AuC

RN C

M SC -Serv./VLR A bis

S IM -M E

Iu b is C u

U m

U u

Iu C s G b

A

Iu PS

C

D

Iu r

G n

G r G c

G s

C S M G W M SC -Serv./V LR

C S M G W

G M SC -Serv.

IM S D om ain

(R e lease 5)

M b/G i

C x

M c

N b

N b

G /E /N c

N c

M c

U ser Equ ipm ent D om ain

A ccess N etwork D om ain C ore N etwork D om ain

In frastruc tu re D om ain

Circuit-switched core network

MSC

Packet-switched core network

SGSN



NRT Packet Switched Data

Protocol stack of a NRT packet switched session in UMTS Release 99

Retransmission, sequence numbering, flow control, multiplexing, etc.

8



Basic RRM

Radio Resource Management



I

u

b

I

u

b

Uu Iub

UE Node B RNC

PC

AC

LC

PS

RM

HC PC

PC LC

RRM Overview

AC – Admission Control; PS – Packet Scheduler; LC – Load Control; RM Resource Manager; HC – Handover control; PC – Power Control

RRM in UMTS Release 99

9



Power Control

Fast Closed Loop Power Control (CLPC)at rate 1500 Hz

RNC adjusts the SIR target in the Node B for the fast CLPC

in response to link quality

UE

Node B RNC

Node B adjusts the power to keep the SIR at the SIR target

Slow Outer Loop Power Control (OLPC)at rate 2-100 Hz

In uplink to keep the received signal level the same for all

users (near-far effect)

In downlink to increase the reception quality of stationary

users and users at the cell edge

To increase spectral efficiency

?



Uplink Fast PC

• UE1 and UE2 are transmitting at the same frequency => equalizing received powers at Node B is critical to avoid near-far problems

• Closed loop power control: Node B commands UE to increase or to decrease its transmission power at a rate of 1.5 kHz (±1 dB steps)

• Closed loop power control follows also the fast fading pattern at low and medium speeds (< 50 km/h)

Fast PC algorithm in Node B:If Eb/N0 < Eb/N0,target,

send "power-up" command.Else If Eb/N0 > Eb/N0,target,

send "power-down" command.

PC commands

UE1

UE2

Node B

L1

L2

10



500 1000 1500 2000 2500 30004

4.5

5

5.5

6

6.5

7

1 minute period

Estimated quality better than

required?NoYes Increase

Eb/N0 targetDecrease

Eb/N0 target

Outer Loop PC• General outer loop algorithm

• Example adjustments of Eb/N0target for AMR speech service, BLER target 1%

• If error in frame, increaseEb/N0 target by 0.5 dB

• If no errors, decrease Eb/N0target with such a rate that BLER = 1% on average.



Softer Handover

• Softer handover– UE is connected to

two sectors of one base station

• Softer handover probability 5 - 15 %

• UL/DL– Basically same

Rake combining as for multipath and antenna diversity (Node B and UE)

RNC

Sector 1

Sector 2

Uplink combing from two sectorsin Node B Rake receiver (maximal ratio combining)

11



Soft Handover• Soft handover

– UE is connected to two base stations

• Soft handover probability is 20 -50 %

• Required to avoid near-far effects

• Extra transmission over Iub• More baseband processing

needed (both base stations)• DL

– Maximal ratio combining in UE in the same way as with softer handover or multipath diversity

• UL– Frame selection combining in

RNC

RNC

Uplink combing from two base stations in RNC(selection combining)



Soft Handover Execution (1/2)

• Active Set (AS) cells have the knowledge of service used by UE• RNC informs the new cell (to be added to AS) about the needed

connection, forwarding the following:– Coding schemes, number of parallel code channels, the different

transport channel configuration parameters in use by UL and DL

– UE ID and uplink scrambling code

– The relative timing information of the new cell with respect to the existing connection (as measured by the UE at its location). Based on this, the new Node B can determine what should be the timing of the transmission initiated with respect to the timing of the common channels (CPICH) of the new cell

• MS is informed about the channelisation codes to be used in transmission and relative timing information through existing connection

12



Soft Handover Execution (2/2)

PCCCHframe

PDCH/PCCHframe

Measure Toffset

Handovercommandand Toffset

UTRANNetwork

Transmision channeland Toffset

BS Bchannelinformation

BS ABS B

Toffset

• The relative timing information, which needs to be made available at the new cell is indicated in the above figure

• It makes transmissions capable to be combined in the Rake receiver from timing point of view



Fast Power Control in Soft Handover

BS 1

BS 2

Both Node BsDetect downlink PC command from mobile

Adjust downlink transmission power

RNC:Power drifting

control

UE:Check reliability of uplink PC command

Adjust uplink transmission power

Powerdrifting

Reliabilitycheck

Independent power control commandsare sent from Node Bs to UE to controluplink transmission power

Base stations detect independently the power control command from mobile to control downlink transmission power

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DATA

Bit rate Chip rate

Channelisationcode

Scramplingcode

Chip rate

Uplink DownlinkSpreading Separate bearer

servicesSeparate users/ bearer services

Scrambling Separate users Separate cells

• Code Allocation and Code Tree Management

• All physical channels are spread with individual spreading codes, Cm(n) and subsequently by the scrambling code, CFSCR

• Resource Manager generates DL spreading codes.• The code layer, m and the code number, n designates each and

every code in the layered orthogonal code sequences.

Resource Management



Code Types• Downlink

– OVSF channelisation (or spreading) codes (SF 4 - 512)– Scrambling codes

• long scrambling code (Gold code with 18 degree polynomial), but using only one frame (38400 chips)

– complex valued code is formed by time delayed version of the same code

• limited to 512 possible codes divided into 64 code groups

• Uplink– OVSF channelisation (or spreading) codes (VSF 4 – 256)– Scrambling codes

• short and long codes – long scrambling code (Gold code with 25 degree polynomial), but

using only 38400 chips» complex valued code is formed by time delayed version of the same code

– short 256 chips extended S(2) code family» complex valued code is formed by combining two codes

• millions of scrambling codes

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Resource ManagerCode Allocation

• Code Allocation Algorithm chooses the proper spreading code depending on the transport format combination type.

• The codes are layered from 0 to 11 according to the code type (~SF)• Only layers 2 to 8 are available for DL and 2 to 7 for UL

C0(0)=(1)

C1(0)=(1,1)

C1(1)=(1,-1)

C2(0)=(1,1,1,1)

C2(1)=(1,1,-1,-1)

C2(2)=(1,-1,1,-1)

C2(3)=(1,-1,-1,1)

C3(0)=(…)

C3(1)=(…)

C3(2)=(…)

C3(3)=(…)

C3(4)=(…)

C3(5)=(…)

C3(6)=(…)

C3(7)=(…)

Layer 0

Layer 1 Layer

2 Layer 3



RM Examples

• Examples:– Ordinary DL speech 30 kbps channel (AMR 12.2-4.75

kbps & control part with 1/3 channel coding - code type 7 (128 chips/symbol)

• C2(1) ⇒ code layer = 2; code number = 1 ⇒ code = 11002

– 120 kbps channel - code type 5 (32 chips/symbol)• C4(5) ⇒ code layer = 4; code number = 5 ⇒ code = 11001100

001100112

• The Resource Manager maintains code tree orthogonality

– If a code Cm(n) is in use, all the codes that are below it in the same branch and the codes that are above it in the same branch to the root are made unavailable

15



Physical Layer

Channels and Procedures



Transportchannels

Medium Access Control (MAC), Layer 2

Physical Layer, Layer 1

MAC selects appropriate bit rate according to the instantaneous

source bit rate.

Physical layer supports variable bit rates up to 2 Mbps

Logical channels

Physical channels

Channel Types

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WCDMA ChannelsBCH

Broadcast

PCCPCHPrimary Common

Control

SCCPCHSecondary

Common Control

PRACH

DPDCH

DPCCHPDSCH

PCPCH

SCHSynchronisation CPICH

Common Pilot

AICHAcquisition Indication

PICHPaging

Indication

CSICHCPCH Status

Indication

CD/CA-ICHCollision

Detect/Avoidance

FACHForward Access

CPCHCommon Packet

PCHPaging

RACHRandom Access

DCHDedicated

DSCHDownlink SharedTransport Channels

Physical Channels

how and with what

characteristics



Transport Channels (1/2)

Random access channel RACH: Data + signaling from one user

Dedicated channel DCH: data + signaling to one user

Broadcast channel BCH: Cell and system info

Forward access channel FACH: Data + signaling for one or more users within one cell

Paging channel PCH: For mobile terminated calls

Downlink shared channel DSCH: Packet data channel. Time multiplexed by several users.

Common packet channel CPCH:Extension of RACH for longer data packets

Mobile

Node B

DSCH optional for network

CPCH optional for network

17



Transport Channels (2/2)

• Due to direct support of variable bit rate and service multiplexing in UTRA/FDD there is only one dedicated transport channel (DCH). DCH contains user data and control information from higher layers.

• There exist a total of six common transport channels in UTRA/FDD:– Broadcast channel (BCH): General information of UTRA network or the current

cell (e.g. random access codes, access slots). BCH is sent at low data rate (single TF) and high power to reach all users in intended coverage area.

– Forward access channel (FACH): Downlink transmission of control information to UE's in current cell. Slow power control and low data rates.

– Paging channel (PCH): Downlink paging information (e.g. call initiation).– Random access channel (RACH): Uplink control information (e.g. UE requests to

set up connection/initiate call). Single frame only.– Optional uplink common packet channel (CPCH): Extended RACH for sending

data over multiple frames.– Optional downlink shared channel (DSCH): Somewhat similar to RACH but can

be shared by multiple users to increase data throughput.



Services in UMTS are classified according to their QoS requirements into one of 4 service classes

The service classes are characterised by certain bearer attributes provided by the UMTS Radio Access Bearer

Each Radio Access Bearer (RAB) is transmitted on a specific Transport Channel (TrCh)

In a multi-service environment (with different QoS requirements) transmission is done on a combination of TrChs which are transmitted on

the same physical channel(s)

RABs and TrChs

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• Transport Format (TF)group of parameters describing the transmission "mode" on a specific TrCh during a TTI (TTI size is part of the TF)

• TF Set (TFS)corresponds to a group of TFs applying to one specific TrCh

• TF Combination Set (TFCS)the product of TF Sets of all the TrChs forming the combination

• TF Indicator (TFCI)Each TF Combination (TFC) of the TFCS is indexed with the TFC Index (TFCI) at the physical layer

TrCh Details (1/2)



8

16

32

64

128

256

320

384

8

16

32

64

Examplebit rates for

NRT

64

Peak bit ratein bearer

parametersis requested

from PS

256

Scheduledbit rate

TFS for NRTRB includes

allintermediate

rates

64

32

TFS subsetfor TFCS

construction

0 0 0

32

64

0

16

0

TFCS (SL & NRTRB)

TFCI 0TFCI 3

TFCI 1TFCI 4

TFCI 2TFCI 5

TrCh1

TrCh2

TFI0

TFI1

TFI2

TFI3

TFI4

TFI0

TFI4

TFI3

TFI0

TFI1

TFI0

TFI3

TFI4

TFCI TFITrC

H1

TFITrC

H20 0 0

1 0 3

2 0 4

3 1 0

4 1 3

5 1 4TFCS Construction by cartesian product

Example with radio bearer for user

data and signalling

TrCh Details (2/2)

19



Dedicated Channel (DCH/DPCH)

Speech and data services



Target

Characteristics for UL and DL

Dedicated physicalcontrol channel (DPCCH)

Dedicated physicaldata channel (DPDCH)

Keep physical layer connection running

Carry user data and higher layer control data

Content

(1) Reference symbol: Channel and SIR estimation(2) Power control signaling(3) TFCI: bit rate information

(1) User data(2) Higher layer signaling

(RRC)

Bit rate Constant bit rate for reliable detection

Variable bit rate. Bit rate indicated with TFCI on DPCCH.

• Dedicated channel (DPCH) consists of two physical channels:– DPCCH keeps physical layer connection running reliably– DPDCH carriers user bits with variable bit rate– Possible to have a power offset between the two channels

20



Solution

Target

Multiplexing of DPCCH and DPDCH

• The code consumption is not an issue in uplink since the number of codes is very large

• The discontinuous transmission is not an issue in downlink sincecommon channels (10-20% of BTS max power) are transmitted all the time

• Blind rate detection (no TFCI bits) is easier for the mobile when the channel bit rate remains constant in time multiplexed solution

• Variable rate transmission for data can be implemented by discontinuous transmission (DTX) on a slot interval (DL) and frame (UL) basis, symbol repetition where frame is always full, or variable spreading factor (UL).

Uplink Downlink

I/Q code multiplexing Time multiplexing

Continuous transmission⇒ reduce audible interference

(1) Only one code needed⇒ saves orthogonal codes(2) Support for blind rate detection



Variable Rate in Uplink

DPCCH

DPDCH

Service in DTX(e.g. silence in speech)Higher bit rate Low bit rate

• Continuous mobile transmission regardless of the bit rate (also during service DTX)– Reduced audible interference to other equipment (nothing to do

with normal interference, does not affect the spectral efficiency)– Services can still have DTX, like silence period in speech. During

that time no DPDCH transmitted but still continuous DPCCH

• Fast power control keeps received power of DPCCH constant

10 ms frame 10 ms frame 10 ms frame

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DPCH (DPCCH/DPDCH)

SF = (4 - 256)

DPCCH

DPDCH

DPDCH

TTI

TCFI, (DL) TPC, PILOT

Paired with

UL

DL

10 ms

SF = 256

Code (Power)

TCFI, (UL) TPC, (PILOT)

SF = 4 - 256

DPCCH

DPDCH

DPDCH

Transmission Time Interval (TTI)

TFCI (DL), TPC, PILOT

TFCI (UL), TPC, (PILOT)

Paired with

Cod

e (P

ower

)Channel Structure

(DPCH)

Carries the Dedicated (DCH) transport channel

DPCH (DPCCH/DPDCH)

DPDCH Dedicated Physical Data ChannelDPCCH Dedicated Physical Control Channel

TFCI Transport Format Combination IndicatorTPC Transmitter Power Control



Uplink DPDCH/DPCCH

Pilot Npilot bits

TPC NTPC bits

DataNdata bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10 bits

1 radio frame: Tf = 10 ms

DPDCH

DPCCHFBI

NFBI bitsTFCI

NTFCI bits

Tslot = 2560 chips, Ndata = 10*2k bits (k=0..6)

Fixed SF256

Let’s the receiver know what is

coming – which TrCh’s are active

in frame!

• Variable SF from 4 to 256 on a frame-by-frame basis are supported in the uplink

22



Uplink Processing

Frame 1 Frame 2 Frame 72

Super frame 720 ms

10 ms


Slot 1 Slot 2Slot 1 Slot 2 Slot 15

(2) Detect PC commandand adjust DL tx power

Slot 0.667 ms = 2/3 ms

Pilot TFCI

Data

DPCCH

DPDCH

TPC

(1) Channel estimate+ SIR estimate for PC for

adjusting UL tx power

(3) Detect TFCI(10 ms frame)

(4) Interleaving (TTI) :Detect data



Uplink TX (I)

• CRC encoding: Cyclic redundancy check (CRC) attachment is done to enable error detection at the receiver. The CRC indicator length can be set to 0/8/12/16/24 bits depending on the desired error detection accuracy.

• Encoder block size adjustment: Transport block concatenation is used for smaller amounts of data in order to reduce the overhead of tail bits and to increase the block size to improve the channel encoding performance. On the other hand, code blocks segmentation is done to avoid excessively large block sizes.

CRC encoding

Encoder block sizeadjustment

Raw bits

23



Uplink TX (II)

• Channel encoding is done in order to improve the bit or frame error rate (BER/FER) performance of the link. Variable coding is supported (from no coding to high coding). For the relatively low data rates (similar to second generation systems), convolutional encoding (½ and 1/3 rate) is used for simplified detection and good performance. The highest data rates uses 1/3-rate Turbo encoding for best coding gain.

• Radio frame equalization is done by either concatenating transport blocks together or by segmenting blocks such that data is divided into equal-sized blocks when they do not fit a single 10 ms frame.

Radio frameequalization

Channelencoding



Uplink TX (III)

• Inter-frame interleaving is done whenever the delay-budget (for the current QoS) allows for more than 10 ms (1 frame) of delay. The interleaving length may be 20/40/80 ms. Interleaving reduces correlation between adjacent chips and thus improves detection (basic assumption for efficient channel decoding).

• Radio frame segmentation is padding the input bit sequence in order to ensure that the output can be segmented in an integer number of data segments of same size (subclause 4.2.6 in TR25.212). The frame segmentation is only performed in the uplink since in the downlink, the rate matching output block length is always an integer multiple of the desired number of data segments.

Inter-frameinterleaving

Radio framesegmentation

24



Rate matching

Transport channelmultiplexing

+intra-frameinterleaving

+physical layer

mapping

DPCCH/DPDCH#

Uplink TX (IV)

• Rate matching ensures that the frames are filled up with data. To do this, either by puncturing or by repetition. Repetition is usually preferred for the uplink. The rate matching is dynamically updated on a frame-to-frame basis. The rate matching algorithm is detailed in TR25.212.

• Multiplexing: Finally, all the active transport channels are multiplexed and a 10 ms intra-frame interleaving is conducted. After the interleaving, the data is mapped onto the physical channels.



Uplink TX (V) –block diagram

• Depending on which data rate is desired, each user can simultaneously have 6 DPDCH channels (data) and one DPCCH channel (control information).

SpreadingDPDCH1

DPDCH3

DPDCH2

DPCCH

Spreading

Spreading

Spreading

Scaling

Scaling

Rotation

Scaling

Scaling

βd

βd

j

Σ

Σ

ComplexScrambling

Re{}

Im{}

cos(ωt)

sin(ωt)

RRC

RRC

S(t)

Dual-channel QPSK modulation(BPSK modulation + I/Q code multiplexing)

βd

βc

Example 3 x DPDCH configuration

25



Slot Format #i Channel Bit Rate (kbps)

Channel Symbol Rate (ksps)

SF Bits/ Frame

Bits/ Slot

Ndata

0 15 15 256 150 10 10 1 30 30 128 300 20 20 2 60 60 64 600 40 40 3 120 120 32 1200 80 80 4 240 240 16 2400 160 160 5 480 480 8 4800 320 320 6 960 960 4 9600 640 640

Physical Layer Rates (Uplink)

• A single code at SF 4 allows 960 kbps which turns into a user data rate of 480 kbps with ½ rate coding; 6 parallel DPDCHs at ½ rate coding leads to a maximum user data rate in excess of 2 Mbps.

• Beneficial to stick to a single DPDCH for as long as possible to reduce Peak to Average Ratio (PAR).



Downlink DPDCH/DPCCH

One radio frame, Tf = 10 ms

TPC NTPC bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10*2k bits (k=0..7)

Data2Ndata2 bits

DPDCH

TFCI NTFCI bits

Pilot Npilot bits

Data1Ndata1 bits

DPDCH DPCCH DPCCH

Let’s the receiver know what is

coming – which TrCh’s are active

in frame!

• Constant SFs from 4 to 512 are supported in the downlink (some restrictions for SF 512).

• The SF for the highest transmission data rate determines the channelisation code reserved from the code tree.

26



Downlink Processing


Slot 1 Slot 2 Slot 16

PilotData

Super frame 720 ms

10 ms

Slot 0.667 ms = 2/3 ms

TPC


Slot 1 Slot 2 Slot 15

DPDCH DPDCH

Data

DPCCH DPCCH

TFCI

(2) Detect PC commandand adjust UL tx power

(1) Channel estimate+ SIR estimate for PC for

adjusting DL tx powerCan use CPICH

(3) Detect TFCI(10 ms frame

(4) Interleaving (TTI) :Detect data



Re{}

Im{}

sin(ωt)

RRC

RRC

S(t)

All channels(except SCH)Odd

bit

Evenbit

Rotation

j

Downlink transmitter

• The downlink uses time multiplexing between data and control information. This is possible since there are multiple users and there are always general control channels being transmitted from the BS (e.g. SCH). On the uplink, multiplexing like this would cause audible interference during discontinuous transmission.

Spreading

Spreading

ComplexScrambling

Otherchannels(users)

.... ..

...

Σ

SCH

cos(ωt)

27



Physical Layer Rates (Downlink)

Spreading factor

Channel symbol

rate (kbps)

Channel bit rate (kbps)

DPDCH channel bit rate range

(kbps)

Maximum user data rate with ½-

rate coding (approx.)

512 7.5 15 3–6 1–3 kbps 256 15 30 12–24 6–12 kbps 128 30 60 42–51 20–24 kbps 64 60 120 90 45 kbps 32 120 240 210 105 kbps 16 240 480 432 215 kbps 8 480 960 912 456 kbps 4 960 1920 1872 936 kbps

4, with 3 parallel codes

2880 5760 5616 2.8 Mbps

Half rate speech

Full rate speech

144 kbps

384 kbps

2 Mbps

Symbol_rate=Chip_rate/SF

Bit_rate=Symbol_rate*2

User_bit_rate=Channel_bit_rate/2

DPCCHoverhead



Signaling 3.4 kbps with 40 ms interleaving

Speech 12.2 kbps Speech 12.2 kbps

40 ms

Radio frame Radio frame Radio frame Radio frame

10 ms

81 class A bits 12 CRC 8 tail 103 class B bits 8 tail 60 class C bits 8 tail+ +AMR 12.2 kbps

136 data bits RLC+MAC 12 bits 24 CRCDPCH 3.4 kbps

Downlink Speech + Signalling

Example

28



AMR Class A 1/3 rate conv

AMR Class B 1/3 rate conv

AMR Class C 1/2 rate conv

DPCH 1/3 rate conv

Channel coding

SF=256 240 bits

SF=128 510 bits

Downlink L1 bit rates

Spreading factor Bits per frame

960 bits

2040 bits

Bits per 40 ms

Bits per 20 ms Bits per 40 ms

AMR 12.2 kbps 772 bits 1544 bits

DPCH 3.4 kbps - 516 bits

2060 bits

1544 bits

AMR12.2+DPCH

AMR 12.2Rate

matching

1% puncturing

32% repetition

AMR12.2+DPCH

AMR 12.2

SF=128

SF=128

Channelcoding

Transport channelmultiplexing

Most suitable spreading factors and required rate

matching

Example



Speech, full rate 128 channels Number of codes with spreading factor of 128

(AMR 12.2 kbps *(128 – 4)/128 Common channel overhead

and 10.2 kbps) /1.2 Soft handover overhead

= 103 channels

Speech, half rate 2*103 channels Spreading factor of 256

(AMR ≤ 7.95 kbps) = 206 channels

Packet data 3.84e6 Chip rate

*(128 – 4)/128 Common channel overhead

/1.2 Soft handover overhead

*2 QPSK modulation

*0.9 DPCCH overhead

/3 1/3 rate channel coding

/(1 – 0.3) 30% puncturing

= 2.65 Mbps

4 channels withSF=128 for commonchannels assumed

20% soft handoveroverhead assumed

Result103 speech channels or

2.65 Mbps data withone scrambling code

Note: usually interference limits the capacity before the number of orthogonal codes

Downlink Capacity

29



Basic Procedures

Common channels and synchronisation



SCH, CPICH, AICH, PICHThese channels do not carry transport channels

but are needed for network operation

Synchronization channel SCH

Common pilot channel CPICH

Acquisition indicator channel AICH

Paging indicatorchannel PICH

For the mobile to synchronize to the cell.

For the mobile synchronization, channel estimation, andfor the neighbor cell measurements

Response to RACH preamble

For indicating to the mobile that there is paging on PCH

Additional Downlink Physical Channels

30



Common channels (I)

• Common pilot channel (CPICH):– Purpose of run-time synchronization between

the BS and UE's located in the cell. – CPICH unmodulated, scrambled by cell-

specific primary scrambling code (SF=256). – Used for initial synchronization, channel

estimation and measurements for handover and cell selection.

– With multiple BS antennas (antenna diversity),CPICH's from each BS antenna are separated by simple modulation patterns.



• CPICH is transmitted continuously and it takes typically 5-15% of the base station max power (IS-95 typically 20-25%, narrowband => relatively higher overhead)

• CPICH is used for downlink channel estimation in the mobile for coherent combining of multipath components

CPICH is unmodulatedsignal under the cell specific scrambling

code

Channel estimation

Other cell measurements

CPICH

31



Common channels (II)

• Synchronization channel (SCH): – Purpose of initial synchronization between the BS and

UE's located in the cell. – SCH is used for cell search. It consists of primary and

secondary synchronization channels.– The primary channel uses a 256-chip spreading

sequence which is identical for every cell (global). – Secondary channels use sequences individual to each

group of cells and which identify one out of 64 possible scrambling code groups. Once the UE has found the secondary SCH it has obtained both frame and slot synchronization.

• (determined by the sequence used on the secondary SCH channel)



SCH

0 1 14...PrimarySCH

0 1 14...SecondarySCH

256-chip sequencemodulated, identifies the code

group of the cell

2560-256=2304 chips256 chips

256-chip sequencethe same in every cell

32



Cell Search

• 512 scrambling codes in downlink are divided into 64 groups to speed up the cell search, each group contains 8 codes (8 x 64 = 512)

(1) Chip synchronization(2) Symbol synchronization(3) Slot synchronization

Primary SCH

(1) Code group (which of 64)(2) Frame synchronizationSecondary SCH

Exact scrambling code (which of 8)Pilot channelCPICH

Which part of synchronization is obtainedWhich channelis used

Step 1

Step 2

Step 3

• Note: SCH is not under the cell specific scrambling code because it must be received before knowing the scrambling code

• As a consequence, SCH is non-orthogonal to other channels• All other downlink channels are under the scrambling code



• ML approach: Correlate with the PN sequence at all delays within the uncertainty region, and then determine the delay τ. Thus, the mean synchronization time equals KLT, where T is the correlation time and K is the number of correlations per chip interval.

• Serial search: Correlate with the PN sequence at one delay and determine if the output is above the noise+MAI floor. If the output is below the the noise+MAI floor, then move the correlator to the next delay. Here the mean synchronization time is less than KLT.

Synchronization

33



Serial Acquisition Scheme



Probability of Detection and False Alarm

34



Dual-Dwell Serial Search



Tracking of PN-Sequences

• After coarse synchronization is obtained within +/- one chip, a more accurate synchronization is initiated (tracking).

• Tracking of the received PN-sequence is performed separately for each RAKE finger.

• Tracking is performed continuously during the transmission since there is a time-varying drift between the received and locally generated PN-sequence.

• The time-drift is mainly caused by two factors:– Movement of mobile unit. At a speed of 100km/h, the time drift is on

the order of 100nsec/sec.– Oscillator drift between Tx and Rx.

35



Early-Late Gate Tracking

• The early-late gate algorithm aims at maximising the auto-correlation between the received and the locally generated PN-sequence.

• The tracking algorithm is a simple gradient search algorithm

• The two power estimates can be obtained from the pilot signal/symbol.



Tracking UncertaintyDeterministic uncertainty due to filtering

36



TDD Mode

In brief!



General Characteristics

• Combined TDMA/CDMA (TDD) multiple access• Allows operation in unpaired band• Requires synchronization between base stations

to avoid uplink/downlink interference• Allows for assymmetric uplink/downlink capacity• Discontinuous transmission leads to power

disadvantage – cell range reduction• Has the advantage of a reciprocal channel

– used for (open loop) uplink power control

37



WCDMA TDD

UE 1

Time

(Code) Power

UE 2UE 3UE 4

Node BUE

non-orthogonal codes

orthogonal codes

Available resources: Spreading Codes (OVSF)

and SlotsUp to 16 users code multiplexed per slot

Single-user detection Multi-user

detection

UE 1

UE 2

frame n frame n+1



Generalized TDD Frame

Data symbols (976 chips)


Midamble(512 chips)

Guard(96 chips)

2560 chips



Guard(96 chips)

TS 0 TS 14

10 ms

Burst Type I

Number of allocated time slots# allocated codes (SF=16)

2.54 Mbps781 kbps195 kbps16

1.26 Mbps390 kbps97 kbps8

158 kbps48.8 kbps12.2 kbps1

1341

Midamble (training sequence) for joint channel estimation

38



MultiUser Detection

Interference Cancellation



MUD analysis

• If we define the Interference Cancellation receiver efficiency, β, as the ratio between the equivalent intra-cell interference after and before interference cancellation [Hämäläinen], then the required (matched filter) SINR (Eb/No) of user j (per antenna) can be expressed as

– where W is the chip rate, Rj the selected data rate for transmission, Pj the total receiver power (per antenna), Pown the total received own-cell power (per antenna), Pother the total received other-cell power (per antenna), and Pnoise is the background noise power (per antenna).

• A practical IC implementation (with acceptable complexity) can achieve an efficiency of 30%, whereas about optimum for multi-stage IC achieves 70% efficiency

( )( )1j

jj own j other noise

PWR P P P P

γβ

=− − + +

39



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

Cel

l thr

ough

put g

ain

[%]

i = 0.0i = 0.2i = 0.4i = 0.6i = 0.8i = 1.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10

20

30

40

50

Cel

l thr

ough

put g

ain

[%]

i = 0.0i = 0.2i = 0.4i = 0.6i = 0.8i = 1.0• The gain from IC can be

approximated as:

35

βηi

iG

UL ⋅−++

≅1

1

• The cell throughput gain from IC decreases with i since IC is only effective towards intra-cell interference.

• Also, the impact of the IC efficiency βon the cell throughput gain is scaled by the uplink fractional load ηUL.

18%54%

β = 0.7

i is the other-to-own interference ratioβ is the efficiency of the IC receiverηUL is the uplink fractional load

ηUL

ηUL

β = 0.3

27%100%

IC Gain

from [ C. Rosa, “Enhanced plink Packet Access in WCDMA, Ph.D. dissertation, AAU, December 2004]



• Wideband received power based RRM

• Throughput based RRM

rise Noise

1- rise Noise1 =−=

total

NUL I

Pη

( ) ( )( )

∑ ∑= =

⋅⋅+

⋅+=⋅+=N

j

N

j

jjjb

jUL

RNE

WiLi

1 1

0/1

111

υ

η

Measure total widebandreceived power Itotal

Calculate sum of the bit rates in a cell

Noise Rise and fractional load

40



References and Acronyms



References• H. Holma and A. Toskala, “WCDMA for UMTS – Radio Access for Third

Generation Mobile Communications”, John Wiley & Sons, 3rd edition, 2004 (HSDPA chapter!)

• T.E. Kolding et al.,”High Speed Downlink Packet Access: WCDMA Evolution”, IEEE Vehicular Technology Society (VTS) News, vol. 50, no. 1, pp. 4-10, February 2003

• S. Hämäläinen, H. Holma, and A. Toskala, “Capacity Evaluation of a Cellular CDMA Uplink with Multiuser Detection, International Symposium on Spread Spectrum Techniques and Applications, vol. 1, pp. 339-343, September 1996

• C. Rosa, T.B. Sørensen, J. Wigard, and P.E. Mogensen, “Interference Cancellation and 4-Branch Antenna Diversity for WCDMA Uplink Packet Access”, Proceedings of VTC Spring 2005, Stockholm, Sweden, May-June 2005

• B. Vejlgaard, “Data Receiver for the Universal Mobile Telecommunications System (UMTS), Ph.D dissertation, AAU, 2000

41



Acronyms• 3GPP 3rd Generation Partnership Project• AC Admission Control• AuC Authentication Centre• BSS Base Station Subsystem• BTS Base Transceiver Station• CDMA Code Division Multiple Access• CN Core Network• CS Circuit Switched• DL Downlink (broadcast)• EUTRA Evolved UMTS Terrestrial Radio Access• FDD Frequency Division Duplexing• FDMA Frequency Division Multiple Access• GERAN GSM Evolved Radio Access Network• GGSN Gateway GPRS Support Node• GPRS General Packet Radio Service• GSM Global System for Mobile communications• HC Handover Control• HLR Home Location Register• HSS Home Subscriber Services• HSxPA High Speed Downlink/Uplink Packet Access• IMS Internet Multimedia Subsystem• IMT International Mobile Telephony (ITU-2000)• ITU International Telecommunications Union• LTE Long Term Evolution• LC Load Control• ME Mobile Equipment• MS Mobile Station



Acronyms (cont.)• MSC Mobile Switching Centre• PLMN Public Land Mobile Network• PS Packet Switched• QoS Quality of Service• PC Power Control• PS Packet Scheduler• RM Resource Manager• RNC Radio Network Controller• RNS Radio Network Subsystem• RRM Radio Resource Management• RTT Round Trip Time• SF Spreading Factor• SGSN Serving GPRS Support Node• SHO Soft Handover• SIP Session Initiation Protocol• SS7 Signalling System 7• TDD Time Division Duplexing• TDMA Time Division Multiple Access• TMSI Temporary Mobile Subscriber Identity• UE User Equipment• UL Uplink (multiple access)• UMTS Universal Mobile Telecommunications System• USIM UE Subscriber Identification Module• UTRAN UMTS Terrestrial Radio Access Network• VLR Visitor Location Register• VSF Variable Spreading Factor• WCDMA Wideband Code Division Multiple Access

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