basic wcdma studies1

1 © NOKIA Layer 1.ppt/ 07.12.00 / Stefano Savioli Company Confidential

WCDMA Introduction Codes & Modulation,

Channels & Physical layer

Stefano SavioliSystem Planning, Global Radio Network Planning


Agenda

• Introduction

• WCDMA Technical aspects, Overview

• WCDMA Codes

• WCDMA Modulation

• WCDMA Channels, Overview

• Physical layer procedures & Channels

• Conclusion


IMT-2000 is a single standard with three optional modes

IMT-2000

"One single standard with three optional modes"

IMT-2000

EuropeAsia / PacificNorth America

cdma2000 UMTS ARIB-CDMA

www.3gpp.org


System architecture - GSM, GPRS and UMTS

BTS

RNC

BSCBTS

SGSN

GGSN@GPRS

infrastructure

UMTS infrastructure

MSC


Agenda

• Introduction


• WCDMA Codes




• Conclusion


Available channels:•FDD: 12•TDD: 7

UMTS AIR INTERFACE (1/2)

Wideband - Code Division Multiple Access (W-CDMA)

Multiple Access Scheme

Duplex scheme

Channel spacing

(User) Data rate

•Frequency Division Duplex •Time Division Duplex

•FDD: Uplink 1920-1980 MHzDownlink 2110-2170 MHz

•TDD: 1900 - 1920 MHz 2010 - 2025 MHz

5 MHz

Up to 2 Mbit/s

Frequency band

•Users are separated by spreading codes•All users utilise the same frequency band

2 duplex schemes

25 times the channel spacing of GSM

12 times GPRS (up to 170 kbps (8 timeslots!))

Technical Aspects


Technical Aspects

UMTS AIR INTERFACE - CONTINUED (2/2)

10 msFrame length

Inter-BS synchronisation

Modulation format

•FDD: Asynchronous •TDD: Synchronous

•Data modulation: QPSK (downlink); BPSK (uplink)•Spreading modulation: QPSK

•Used for e.g.•Discontinuous transmission decisions•Rate adaptation•Assignment of uplink/downlink channels for TDD

•Trade-off between delay and reasonable interleaving depth

Chip rate 3,84 Mcps

TDD needs•GPS receiver at the base station or•common clock (signal)


Some CDMA specific properties• Continuous transmission (normally)

• Code channels, not time slots

• All users on the same frequency• Code channels, not separate carriers

• Soft handover• MS is connected to two or more BSs at the same time

• Power Vs. capacity• Capacity is limited by interference (cell load) rather

than number of physical channels

• Fast power control• For high capacity very fast and accurate (closed loop)

transmitter power control is required (near-far effect reduction)


CDMA Basic Principle

• Spread Spectrum technique• transmitting information at a bandwidth much wider

than the information rate

• Why to spread?• Information theory:

• When transmitting information at a given rate (bit/s) it is possible to have a trade-off between bandwidth and signal to noise ratio

OR• The wider the bandwidth used for transmitting at a

given information rate the lower the required signal to noise ratio

• improved tolerance to interference

• decreased spectral density of transmitted signal


FrequencyPo

we

r d

en

sit

y (

Wa

tts

/Hz) Unspread narrowband signal

Spread wideband signal

W

R

Processing gain =

W/R,

typically at least 100

Processing gain =

W/R,

typically at least 100

• A narrowband signal is spread to a wideband signal

CDMA radio access technology: spreading/despreading

WCDMAWCDMA5 MHz, 1 carrier5 MHz, 1 carrier

TDMA (GSM)TDMA (GSM)5 MHz, 25 carriers5 MHz, 25 carriers


The processing gain depends on the user data rate

PROCESSING GAIN

Voice user (12,2 kbit/s)

Packet data user (384 kbit/s)

Pow

er d

ensi

ty (

W/H

z)

W

R

Frequency (Hz)

Frequency (Hz)

Unspread narrowband signal


Processing Gain G=W/R=25 dB

Pow

er d

ensi

ty (

W/H

z)

W

R

Unspread "narrowband" signal


Processing Gain G=W/R=10 dB

•Spreading sequences of different length•Processing gain dependent on user data rate

(User data rate) x (spreading ratio)= const.=W=3,84 Mcps


WCDMA trades-off range against number of users and data rate

WCDMA ACCESS SCHEME

Limited transmission power means trade-off between

•Range •Number of users and/or user data rate

Frequency

10 ms

5 MHz

High data rate

Code, Power

Low data rate

Time

CDMA


• In DS spreading the user signal spreading (modulation) is done with spreading sequences (codes) having much higher bandwidth than the user signal (processing gain = W/R, where R = data rate, W = spread bandwidth)

• Codes are unique for each channel• Transmitting and receiving sides have the same code with the same phase.

The code to be used is determined by the transmitting side and the receiving side acquires the code from the transmitted signal (code acquisition)

SpreadingTransmitter

RX spreadingcodegenerator

ReceiverDespreading

TX spreadingcodegenerator

synchronism required

Spread signal

input narrowbandsignal(unspread)

outputsignal(detected)radio path

In WCDMA users are separated by codes


CDMA Radio Access Technology

Freq. 1

Freq. 1

Code A

Code B

Code C

BS1

BS2

Code D

Code E

• Users are separated by codes (code channels), not by frequency or time (in some capacity/hierarchical cell structure cases, also different carrier frequencies may be used).

• Signals of other users are seen as noise-like interference

• CDMA system is an interference limited system which averages the interference (ref. to GSM which is a frequency limited system)


Agenda

• Introduction


• WCDMA Codes




• Conclusion


WCDMA Codes• The spreading operation in WCDMA is done in two phases, both in uplink and

downlink. • The first phase is done by using short codes.

• The length of the short code is one symbol in chip units and the length is thus varying according to the symbol rate.

• The short codes are called spreading codes.

• in downlink they orthogonalize the transmitted physical channels of one cell.

• The second phase is done by using long codes.

• The length of the long code is 38 400 chips for uplink and downlink i.e. one radio frame.

• The long codes are called scrambling codes.

• The scrambling code of the downlink identifies the cell (sector), while in the uplink it identifies the call.

• Both codes have the same rate, i.e. chip rate.

• The spreading codes and in uplink also the scrambling codes are allocated by the system and require no actions in radio network planning. Allocating the downlink scrambling codes of the cells, or actually the scrambling code groups of the cells, can be part of the planning process.


Long and Short Codes


Scrambling Code Planning• There are totally 512 DL scrambling codes used, i.e. 8 in

each of the 64 code groups.

• All the cells that MS is able to measure in one location should have different scrambling codes.

• The first idea is to use different scrambling code groups in the neighbouring base stations. This would ensure the previous requirement in most cases.

• Probably the code group allocation will be done in network planning and there should be the corresponding functionality in the network planning tool, which reminds frequency planning in GSM planning tools.

• The reuse could be 64 as there are 64 code groups. The scrambling code group planning for different carriers can be done independently. It is for further studies whether or not more optimisation would be needed.


Downlink:

Uplink:•Millions of Scrambling Codes available

Prim ary Scram bling Code

Secondary Scram bling C ode #1



C hann elisatio n C od e S et (25 6 C od es)




Prim ary Scram bling Code








- 5 1 2 C o d e S ets x 1 6 S c ra m b lin g C o d es = 81 9 2 C o d es n u m b e re d fro m 0 ... 81 9 1 a va ilab le

Scrambling Code PlanningIn case intelligent antennas are used it is possible to use a second set of scrambling codes called Secondary Scrambling Codes


Tree of Orthogonal Short Codes in Downlink

• Hierarchical selection of short codes from a "code tree" to maintain orthogonality

• Several long scrambling codes can be used within one sector to avoid shortage of short codes

C1(0) = [ 1 ]

C2(0) = [ 1 1 ]

C2(1) = [ 1 0 ]

C4(0) = [ 1 1 1 1 ]

C4(1) = [ 1 1 0 0 ]

C4(2) = [ 1 0 1 0 ]

C4(3) = [ 1 0 0 1 ]

C8(0) = [ 1 1 1 1 1 1 1 1 ]

C8(1) = [ 1 1 1 1 0 0 0 0 ]

. . .

. . .

Spreading factor:

SF = 1 SF = 2 SF = 4 SF = 8

C8(2) = [ 1 1 0 0 1 1 0 0 ]

C8(3) = [ 1 1 0 0 0 0 1 1]

. . .

. . .

C8(4) = [ 1 0 1 0 1 0 1 0 ]

C8(5) = [ 1 0 1 0 0 1 0 1 ]

. . .

. . .

C8(6) = [ 1 0 0 1 1 0 0 1 ]

C8(7) = [ 1 0 0 1 0 1 1 0 ]

. . .

. . .

Example ofcode allocation


Cross Correlation and OrthogonalityAn easy way to find the Cross Correlation is to count the number of agreements/disagreements. +1 for each agreement, -1 for the disagreement. If the result is 0 then the codes are not correlated thus Orthogonal

Code C4,3 = 1001Code C4,2 = 1010 ==> +1+1-1-1=0 ORTHOGONALWhen comparing the mother with the son we should bare in mind that the chip rate is constant, so for each bit transmitted with SF 4 correspond to 2 bits transmitted with SF 2Ex: If the C2,1 (10) has to transmit the bits 10 then the multiplication with the code gives 1001 which is equal to C4,3, while if it transmits 11 it is equal to C4,2 so it is not unique and it cannot be used


Half rate speechFull rate speech

64 kbps

Physical Layer Bit Rates (Downlink)

• The number of orthogonal channelization codes = Spreading factor• The maximum throughput with 1 scrambling code ~2.5 Mbps or ~100 full rate speech users

128 kbps384 kbps

2 Mbps


Number of Orthogonal Codes in Downlink

• Part of the orthogonal codes must be reserved for• common channels• soft handover overhead

• The maximum capacity with one set of orthogonal codes = code limited capacity per sector per 5 MHz

• Full rate speech (SF=128) : 98 channels• Half rate speech 7.95 kbps (SF=256) : 196 channels• Data : 2.5 Mbps; 10 Common Channels SF 128; 20% SHO

overhead

• Typically, air interface interference limits the capacity before the code limitation (see the capacity discussion later)

• Code limitation can be avoided with 2nd set of codes (which are not orthogonal) by using 2 scrambling codes per sector

• 2nd set of codes is probably needed with smart antennas which improve the air interface capacity.


CDMA Spread Spectrum Multiple Access

M1(t)

M2(t)

C2(t)

C1(t)

M1(t)C1(t)

M2(t)C2(t)

TX

M1(f)

f

M2(f)

f

S(f)

f

E.g. two users

S(t)RX

bTt

t

M1

bTt

t

M2

C1(t)

C2(t)

Spreading Despreading and detection


Spreading

Data xCode

Data

Code

Code(pseudonoise)

Data

+1

+1

+1

+1

+1

Symbol

-1

-1

-1

-1

-1

ChipChip

DespreadiDespreadingng

Spectrum

Symbol


Detecting own signal. Correlator

Code

Data aftermultiplication

+1

+1

+1

-1

-1

-1

Ownsignal

+8

-8

Data afterIntegration

Code

Data aftermultiplication

+1

+1

+1

-1

-1

-1

Othersignal

+8

-8

Data afterIntegration


Agenda

• Introduction


• WCDMA Codes




• Conclusion


Downlink modulation

• QPSK (Quadrature Phase Shift Key) modulation is used, one symbol transmitted equals two bits of information

• The two bits of information are mapped on a 2 dimensions space, one bit refers to the real axis while the other to the imaginary one.

• Control streams are time multiplexed in the frame

Time

Control

Data

1 Time Slot


Downlink modulation

The BTS need linear power amplifier because of the zero crossing during the transmission of the bit stream 00 11, etc..

SpreadedInformation

Oscillator

90° Phase Shift

RF Out

I Branch

Q Branch

Degrees and Bits:'1' '0'180° 0°

Degrees and Bits:'1' '0'90° - 90°

Bit combinations in Radio Path:

'10'135°

'00'45°

'11'225°

'01'315°

ComplexScrambling


Uplink modulation

• OQPSK (Offset Quadrature Phase Shift Key) modulation, to avoid the zero crossing and in particular the use of linear amplifier (big & heavy) in the UE

• Control and Data stream are treated separately, mainly for two reasons.• Power amplifier efficiency, low peak-to-average ratio, minimal amplifier back-off requirements• to avoid the audible noise during the DTX transmission. One Channel will be mapped into the imaginary axis and the other to the real axis

Control

Data


Uplink modulationIntroducing delay in one branch will avoid the zero crossing, nolinear power amplifier neededThe Throughput is half compared to downlink as one bit per symbol is dedicated to the control channel

ComplexScrambling

Oscillator

90° Phase Shift

RF Out

I Branch

Q Branch

Degrees and Bits:'1' '0'180° 0°

Degrees and Bits:'1' '0'90° - 90°

Bit combinations in Radio Path:

'10'135°

'00'45°

'11'225°

'01'315°

Delay*

*) Delay length is 0.5 bits in time

SpreadedInformation


DPDCH1

Channelization codes(OVSF) gain factors

*j

I+jQ

I

Q

Cch,

1

d

DPCCHCch,

0

c

Cscramb

Up to 6 DPDCH can be multiplexed in uplink.In case of multiservicethe SF must be 4

DPDCH3

DPDCH5

DPDCH2

DPDCH4

DPDCH6

Cch,

4

Cch,

3

Cch,

6

Cch,

2

Cch,

5

d

d

d

d

d

Signalling values for

c and d

Quantized amplitude ratios

c and d

15 1.014 0.933313 0.866612 0.800011 0.733310 0.66679 0.60008 0.53337 0.46676 0.40005 0.33334 0.26673 0.20002 0.13331 0.06670 Switch off

Uplink modulation


Uplink Modulation• Dual channel QPSK

• Designed to maximise terminal PA efficiency and minimise the audible interference (due to discontinuous transmission)

• Therefore I branch: discontinuous data & Q branch: continuous control channel(lower power than the data channel) resulting in high peak to average ratio power

• Avoided by complex scrambling

• Modulation with real scrambling may result in BPSK or near BPSK

• Modulation with complex scrambling will result in QPSK or rotated QPSK for whatever power difference of I & Q branches

Data(DPDCH) Data(DPDCH)DTX Periodx1

x2

I channel

Q channel


Uplink Modulation

• Constellation with real scrambling• Case1: X2=0.5X1 Case 2: X2=X1 Case 3: X2

nonzero,X1=0

• Constellation with complex scrambling

• Case1: X2=0.5X1 Case 2: 0.5X2=X1 Case 3: X2=X1

Case 4: X1=0

I

Q

x

xx

x

I

Q x

xx

x

I

Q

x

x

I+Q

I-Q x

x

x

x

x

x

x

x

I-Q

I+Q

I-Q

I+Q

x

x

xx

I-Q

I+Q

xx

xx


Agenda

• Introduction


• WCDMA Codes




• Conclusion


WCDMA Channels

3 Different Channels

Radio Resource Control (RRC)

Medium Access Control(MAC)

Transport channelsPhysical

layer

Con

trol

/ M

easu

rem

ents

Layer 3

Logical channelsLayer 2

Layer 1 Physical channels


WCDMA Logical ChannelBroadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Control Channel (CCH)

Dedicated Traffic Channel (DTCH)Traffic Channel (TCH)

ODMA Dedicated Control Channel (ODCCH)

ODMA Common Control Channel (OCCCH)

ODMA Dedicated Traffic Channel (ODTCH)

Common Traffic Channel (CTCH)

Shared Channel Control Channel (SHCCH)


Broadcast Control Channel (BCCH)A downlink channel for broadcasting system control information.

Control Channel (PCCH) PagingA downlink channel that transfers paging information. This channel is used when the network does not know the location cell of the mobile, or, the mobile is in the cell connected state (utilising UE sleep mode procedures).

Common Control Channel (CCCH)Bi-directional channel for transmitting control information between network and UEs. This channel is commonly used by the mobiles having no RRC connection with the network and by the UEs using common transport channels when accessing a new cell after cell reselection.

Dedicated Control Channel (DCCH)A point-to-point bi-directional channel that transmits dedicated control information between a mobile and the network. This channel is established through RRC connection setup procedure.

WCDMA Logical Channel


Dedicated Traffic Channel (DTCH)A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one mobile, for the transfer of user information. A DTCH can exist in both uplink and downlink.

Common Traffic Channel (CTCH)A point-to-multipoint unidirectional channel for transfer of dedicated user information for all or a group of specified mobiles.

Shared Channel Control Channel (SHCCH)Bi-directional channel that transmits control information for uplink and downlink shared channels between network and mobiles. This channel is for TDD only

WCDMA Logical Channel


Logical to Transport Channel Mapping (Downlink Direction)

Logical Channels

Transport Channels

CCCH

FACH

DCCH / DTCH

DCH

BCCH

BCH

PCCH

PCH

CTCH

DSCH

(Uplink Direction)

Transport Channels

Logical ChannelsCCCH

RACH

DCCH / DTCH

DCHCPCH


WCDMA Common Transport Channel

BCH – Broadcast Channel The Broadcast Channel (BCH) is a downlink transport channel that is used to broadcast system- and cell-specific information. The BCH is always transmitted over the entire cell with a low fixed bit rate.PCH – Paging Channel The Paging Channel (PCH) is a downlink transport channel. The PCH is always transmitted over the entire cell. The transmission of the PCH is associated with the transmission of a physical layer signal, the Paging Indicator Channel, to support efficient sleep-mode procedures.FACH – Forward Access Channel The Forward Access Channel (FACH) is a downlink transport channel. The FACH is transmitted over the entire cell or over only a part of the cell using beam-forming antennas.


WCDMA Common Transport Channel

RACH –Random Access Channel The Random Access Channel (RACH) is an uplink transport channel. The RACH is always received from the entire cell. The RACH is characterised by a limited size data field, a collision risk and by the use of open loop power control.CPCH – Common Packet Channel The Common Packet Channel (CPCH) is an uplink transport channel. The CPCH is a contention based random access channel used for transmission of bursty data traffic. CPCH is associated with a dedicated channel on the downlink which provides power control for the uplink CPCH.DSCH – Downlink Shared Channel The downlink shared channel (DSCH) is a downlink transport channel shared by several mobiles. The DSCH is associated with a DCH.


WCDMA Physical ChannelMapping of Transport Channels on Physical Channel

D O C U M E N T T Y P E

T y p e U n i t O r D e p a r t m e n t H e r eT y p e Y o u r N a m e H e r e T y p e D a t e H e r e

T r a n s p o r t C h a n n e l s

D C H

R A C H

C P C H

B C H

F A C H

P C H

D S C H

P h y s i c a l C h a n n e l s

D e d i c a t e d P h y s i c a l D a t a C h a n n e l ( D P D C H )

D e d i c a t e d P h y s i c a l C o n t r o l C h a n n e l ( D P C C H )

P h y s i c a l R a n d o m A c c e s s C h a n n e l ( P R A C H )

P h y s i c a l C o m m o n P a c k e t C h a n n e l ( P C P C H )

C o m m o n P i l o t C h a n n e l ( C P I C H )

P r i m a r y C o m m o n C o n t r o l P h y s i c a l C h a n n e l ( P - C C P C H )

S e c o n d a r y C o m m o n C o n t r o l P h y s i c a l C h a n n e l ( S - C C P C H )

S y n c h r o n i s a t i o n C h a n n e l ( S C H )

P h y s i c a l D o w n l i n k S h a r e d C h a n n e l ( P D S C H )

A c q u i s i t i o n I n d i c a t i o n C h a n n e l ( A I C H )

P a g e I n d i c a t i o n C h a n n e l ( P I C H )

CPCH Status Indication Channel (CSICH)

Collision Detection/Channel Assignment Indicator Channel (CD/CA-ICH)


WCDMA Physical ChannelService provided to higher layers

• Macrodiversity distribution/combining and soft handover execution• Error detection on transport channels and indication to higher layers• FEC encoding/decoding of transport channels• Multiplexing and demultiplexing of transport channels• Rate matching of coded transport channels to physical channels• Mapping of coded composite transport channels on physical channels• Modulation and spreading/demodulation and despreading of physical channel• Frequency and time (chip, bit, slot, frame) synchronisation• Radio characteristics measurements including FER, SIR, Interference Power, etc., and indication to higher layers• Inner - loop power control


WCDMA Physical Channel

BSUE

CCPCH-1

CCPCH-2

SCH 1 & 2

PDSCH

CPICH

PICH

PCPCH

AICH

PRACH

DPDCH

DPCCH


Agenda

• Introduction


• WCDMA Codes




• Conclusion


Cell Search

Synchronisation Channel


WCDMA cell search operation• When searching cells:

• the MS measures the impulse response first by using the 1st Synchronisation channel, which is unique in the whole system.

• By finding a delay, which produces a local maximum correlation with this code, the MS gets slot and symbol synchronisation with a base station/sector( Matched filter).

• The correlation peaks of different cells appear with different delays. This is achieved by offsets in the transmission time of the search symbols and partly by different propagation delays.

• After the MS gets the slot/symbol synchronisation it can use the 2nd Synchronisation channel to find the frame synchronisation and to identify the code group to which the cell's scrambling code belongs to.

• This is required at least in the initial power on.

• The 2nd Synchronisation channel's code changes from slot to slot in a sequence which has a period of 15 slots (i.e. 1 frame). There are 64 sequences chosen each defining a code group for the actual scrambling code of the cell.

• By solving this sequence the MS gets the frame synchronisation with the BS and identifies the code group from which the scrambling code of the BS has been taken.

• MS knows the scrambling codes of each scrambling code group and finally after finding the right code MS can start decoding the BCH.

• If the MS has a neighbour list available the search procedure may be different.


SYNCHRONISATION CHANNEL

Cp = Primary Synchronisation Code

Cs = Secondary Synchronisation Code

CP CP CP

2560 Chips 256 Chips

Cs1 Cs2 Cs15

Slot 0 Slot 1 Slot 14

10 ms Frame


64 D

iffere

nt

com

bin

ati

on

Sequence of length 15

5th row matches with the secondary

SCH channel

Matrix made by 16 different codes



8 D

iffere

nt

Cod

es

64 Different group

5th row, theCell Scrambling code is

within that group


Total number of Scrambling Code 64 x 8 = 512


Scrambling CodeC256,0

C256,

1

CPICH

BCH

SCH 2

SCH 1

Finding the BCH

Allchannels

CSF

,n


Common Pilot Channel

• Physical channel: carries a pre-defined bit/symbol sequence at fixed rate (15 ksps, SF= 256)

• It is used for channel estimation and for measurement of the neighbour cells

Pre-defined symbol sequence

Tslot = 2560 chips , 20 bits = 10 symbols


Parameters involved in the Cell Search

• PtxPrimaryCPICH The parameter determines the transmission power of the primary CPICH channel. Range: -20 dBm … 43 dBm, step 1 dB

• PtxPrimarySCH Transmission power of the primary synchronization channel, the value is relative to primary CPICH transmission power Range: -35 … 15 dB, step size 0.1 dB

• SecondarySCHTransmissionPower Transmission power of the secondary synchronization channel, the value is relative to primary CPICH transmission power Range: -35 … 15 dB, step size 0.1 dB


Common Control Physical ChannelPrimary and Secondary


Primary CCPCH

• IT IS THE PHYSICAL CHANNEL THAT CARRIES THE BCH

• It is a fixed rate channel without power control because it must be decoded by all the mobiles in the cell.• The channelisation code is fixed by specification and has a SF=256, the channel bit rate is 30 Kbps but in order to reduce the total interference it is sent alternates with the SCH giving a "net" bit rate of 27 Kbps• It doesn't have any pilot bits in the frame because the channel estimation is done through the Common Pilot Channel


Primary CCPCH


10 ms Frame

CP CP CP

2560 Chips 256 Chips

SCH2304 Chips

CCPCH

CCPCH

CCPCH


Secondary CCPCH• It carries 2 different common transport channel, the FACH (Forward Access Channel) and the PCH (Paging Channel)• It is on air only when it has something to transmit• On a cell there can be more then one Secondary CCPCH. FACH and PCH can be mapped in two different physical channels.• FACH Open Loop power control can be implemented only if the S-CCPCH is dedicated, uplink PC information through the RACH (RAN 2)

• The data rate should be low enough in order to be listened by all mobile's classes. • S-CCPCH SF=256 .. 4, channel symbol rate 15, … , 960 Ksps RAN1 supports 15, 30 and 60 Ksps

Tslot = 2560 chips, 20*2k bits (k=0..6)

Pilot Npilot bits

DataNdata bits

TFCI NTFCI bits


Parameters in the Common Control Ch.

• PtxPrimaryCCPCH This is the transmission power of the primary CCPCH channel, the value is relative to primary CPICH transmission power Range: -35 … 15 dB, step size 0.1 dB

• SCCPCHtransmissionPower This is the transmission power of the secondary SCCPCH channel, the value is relative to primary CPICH transmission power. Range: -35 … 15 dB, step size 0.1 dB


CALL SET UP

PCH Channel


Paging Indicator Channel• The Paging Channel operates together with the Paging Indicator Channel PICH to provide terminals with efficient sleep mode operation. It is always associated with a S-CCPCH• Paging Indicator uses a channelisation with SF=256 and it occur once per slot on the PICH, depending on the paging indicator ratio there can be 18, 36, 72 or 144 paging indicators per frame• To each terminal registered to the network is allocated a paging group which corresponds to a PI• When mobile detect the PI then it decodes the next PCH frame transmitted on the Secondary CCPCH, if the PICH is received with low reliability then the PCH is decoded• The less often the mobile must listen the PICH the longer the battery life becomes, with the drawback of a longer response time for a network originated call


Page Indication Channel (PICH)

• PICH frame of length 10 ms consists 300 bits: 288 bits are used to carry Page Indicators, remaining 12 bits are not used

288 bits {b0, …, b287} (for paging indication) 12 bits (unused)

One frame (10 ms)

PICH

Associated S-CCPCH

7680 Chips = 3 TS


Parameters in the Paging procedure

• PICHtransmissionPower This is the transmission power of the PICH channel, the value is relative to primary CPICH transmission power

•


FACH Channel


FACHForward Access Channel

• The FACH can be used for transmission of user packet data, it is usually multiplexed on the Secondary Common Control Channel

• The main differences with the dedicated channel are the fast set up time and the absence of the fast power control. Slow power control is possible for long data transfer, in that case the information regarding the quality is sent through the RACH channel. This is possible only if the S-CCPCH is dedicated to the FACH

• Messages on FACH need in-band signalling to tell for which of the user the data is.


Parameters in the FACH• FachDataAllowed Maximum allowed data amount on FACH, if the maximum amount in downlink capacity request is exceeded, DCH is allocated • SCCPCH_PilotPowerOffset Cell based parameters. The pilot fields shall be offset relative to the power of the data field. The power offsets shall vary in time according to the bit-rate

• FachLoadThresholdCCH Threshold for the total load of FACH/PCH channel . If the threshold is exceeded, DCH is allocated. FACH/PCH load is measured as a ratio of current channel bit rate and the maximum bit rate, which the spreading factor defines. The current channel bit rate is the averaged value, which is calculated as a total bits transferred on the transport channel per measuring period, which is defined as a number of transmission time intervals


CALL SET UP

RACH Channel


Uplink Common Channel: RACH

4096chips

The length of the preamble is bigger then a TS of a radio frame The TSs are grouped 2 by 2 and the preamble is sent at the beginning of every second TSTwo Radio Frames are joined to form a "15 TS RACH frame"


Uplink Common Channel: RACH• With Random Access Channel (RACH) power ramping is needed with

preambles since the initial power level setting in the mobile is calculated measuring the received power of the CPICH

• Preamble: mobile sends 1 ms signature sequence with increasing power selecting the code from a set of 16 orthogonal signatures

• L1 acknowledgement: base station acknowledges the sequences received with high enough power level (AICH = Acquisition Indication CH)

• Mobile RACH message follows the acknowledgement

P2

Downlink / BS

RACHP1

L1 ACK / AICH

Uplink / MS

Preamble

Not detected

Message partPreamble


Uplink Common Channel: RACHPreamble

• The Preamble PRACH is a repetition of a specific signature which maps the Channelisation code used for the PRACH data part. There are 16 Different Signatures and the mobile pick up randomly one of those. In case no AICH is detected then is retransmitted with a different signature and with higher power• The Preamble is 4096 chips long and is a made by 256 repetitions of the signature which is 16 chips long.• The signatures are the channelisation code of the preamble, they are not OVSF codes

• The Preamble PRACH is then Scrambled with a PRACH Scrambling code related to the Scrambling code of the serving cell. For each primary scrambling code (downlink) there are 16 RACH scrambling code associated with it, in total there are 8192 codes


Table 7: The available uplink access slots for different RACH sub-channels

Sub-channel numberSFN modulo 8 ofcorresponding P-CCPCH frame

0 1 2 3 4 5 6 7 8 9 10 11

0 0 1 2 3 4 5 6 71 12 13 14 8 9 10 112 0 1 2 3 4 5 6 73 9 10 11 12 13 14 84 6 7 0 1 2 3 4 55 8 9 10 11 12 13 146 3 4 5 6 7 0 1 27 8 9 10 11 12 13 14

In the BCH is broadcasted which sub-channels are available in the cell

The message part length can be determined from the used signature and/or access slot, as configured by higher layers



Since the control part is always spread with a know SF of 256 it can be detected by the BTS. In the control field there is the information regarding the spreading factor used for the data. The scrambling code use for the message part of the RACH is the same as the one for the preamble



Uplink Common Channel: RACHAICH

• The AICH is a downlink physical channel with SF 256 in where an echo of the Preamble RACH is send from the BTS

• The BTS knows that there will be a message part coming and start to listen to the channelisation code indicated by the signature. At this point the BTS doesn't have any information regarding the user.

1024 chips

Transmission Off

AS #14 AS #0 AS #1 AS #i AS #14 AS #0

a1 a2a0 a31a30

AI part = 4096 chips, 32 real-valued symbols

20 ms

15

0js,sj bAIa

s

AIs can take the values +1, -1, and 0. It is the acquisitionindicator corresponding to signature s, b is the signature


• RACH access slot sets• The PRACH contains two sets of access slots

• Access slot set 1 contains PRACH slots 0 – 7 and starts p-a chips before the downlink P-CCPCH frame for which SFN mod 2 = 0

• Access slot set 2 contains PRACH slots 8 - 14 and starts (p-a –2560) chips before the downlink P-CCPCH frame for which SFN mod 2 = 1PRACH access slot and downlink AICH relation (p-a = 7680 chips, chip offset Preamble-AICH)

AICH accessslots

10 ms

#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4

p-a

#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4

PRACHaccess slots

SFN mod 2 = 0 SFN mod 2 = 1

10 ms

Access slot set 1 Access slot set 2



• In RAN1, BTS L1 shall be able to simultaneously scan 12 RACH sub-channels with 4 signatures per sub-channel from MSs situating up to 'Cell radius' distance from the BTS site. 'Cell radius' is the maximum radius of the cell and it is given from the RNC to the BTS. In RAN1, the maximum value for the 'Cell radius' is 20 km. • If more than one PRACH preamble signatures within one PRACH access slot is detected correctly, the BTS sends the AIs of all the detected signatures simultaneously in the 1st or 2nd AICH access slot after the PRACH access slot. If the number of correctly detected signatures is higher than the BTS's capability to simultaneously decode the PRACH message parts, a negative AIs is used for generating the AIs for those PRACH messages, which can not be decoded within the default message part transmission timing. A negative AI indicates to the MS that it shall exit the random access procedure. The BTS's capability to decode the PRACH message parts is determined in the RNC and transmitted to the BTS.

Uplink Common Channel: RACHAICH


Uplink Common Channel: RACHMessage Part

• The channelisation code is related with the signature used for the Preamble while the SF is decided by the mobile• The signature specifies one of the 16 nodes in the code tree that correspond to channelisation of length SF = 16• The control uses always spreading factor 256 while the data can vary from SF 32 to 256, however the system may restrict the set of codes (SF) for the data through a BCH message• The message part can be one or at maximum 2 frame long (10 - 20 ms) due to this shortness there is no power control


• Each slot consists of two parts, a data part to which the RACH transport channel is mapped and a control part that carries Layer 1 control information (data and control parts are transmitted in parallel)

• Data part SF: 256 (15 ksps), 128 (30 ksps), 64 (60 ksps), and 32 (120 ksps) All supported in RAN1

• Control part SF : 256 (15ksps) note: in UL symbols/s = bits/s

• The TFCI of a radio frame indicates the transport format of the RACH transport channel mapped to the simultaneously transmitted message part radio frame (in case of a 20 ms PRACH message part, the TFCI is repeated in the second radio frame)

Pilot Npilot bits

DataNdata bits

Tslot = 2560 chips, 10*2k bits (k=0..3)

Data

ControlTFCI

NTFCI bits



p-m

p-p

Pre-amble

Message part

PRACHaccessslots TX atUE


PRACH/AICH timing and power :

One access slot

p-a

Acq.Ind.

AICHaccessslots RX atUE

P0

Pp-m

Pre-amble


Parameters in the RACH procedure

• AICHtransmissionPower This is the transmission power of the AICH channel, the value is relative to primary CPICH transmission power

• PowerOffsetNoAcquisitionIndicator MS increases the preamble transmission power with the specified offset P0 when no acquisition indicator is received by MS in AICH channel

• PowerOffsetPRACHpreambleAndMessage Transmission power of the random access message part is modified from that of the last transmitted preamble with the specified offset Pp-m.

Range : 0 … 6 dB, step size 0.1 dB


Parameters in the RACH procedure

• RachLoadThresholdCCH Threshold for RACH load for downlink channel type selection. If the threshold is exceeded, DCH is allocated. RACH load is measured as average number of received RACH preambles per radio frame in proportion to the product of the number of access slots and number of preamble signatures allowed to use on the physical RACH


PCPCH Channel


PCPCHPhysical Common Packet Channel

• The PCPCH it is an extension of the PRACH channel. Like the PRACH it is constituted by a Preamble part and a Message Part• The Preamble part is equal as the PRACH preamble, it uses the same signatures but it can choose the scrambling code from a pool of 80 for each primary scrambling code (cell scrambling code), usually the first 16 are dedicated to the PRACH 64 are for the PCPCH• It use a Layer 1 Collision Detection CD. After having received an AICH the mobile choose randomly another signature and send it with different scrambling code, then it waits the echo of this signature on the CD Indication Channel, among the 64 scrambling codes, some are reserved for the Preamble and others for the CD Indication Channel

• The message part can last several frames and it has power control. The mobile can change the spreading factor on a frame level. The channelisation code allocation is the same as for the PRACH


• The CPCH is basically RACH with:• Longer message duration (up to 640 ms vs. 10 or 20

ms on RACH)• Fast Power control (power control commands

provided in the DPCCH in the downlink)• Status indication provided in the downlink to avoid

collisions

• It uses the same sub-channel as RACH, the scrambling code used depends on the access slot

Message

CollisiondetectionpreamblesP2

1 ms Preambles as with RACH

DPCCH (DL, SF 512)

CPCH (UL, SF 256-4)

P1

AP-AICH

. .

.

. .

.Power control preamble, 0 or 8 slots

Uplink Common Packet Channel (PCPCH)

CD/CA-ICH


• CPCH is uplink common channel (= fast access).

• CPCH is similar than RACH channel, except:• CPCH bitrates will be higher, SF between 4 and 256

=> Higher data rates.• CPCH allocation time is longer, 20 to 640 ms.

=> More data.• CPCH has fast power control.

=> More spectrum efficient.• CPCH has access control, at least collision detection,

maybe also channel assignment.

• In CSICH channel is broadcast the available data rate for the CPCH.

• Available from RAN 2

Physical Common Packet Channel


Physical Common Packet Channel• RACH preamble signature sequences are used

• Collision detection preamble part: RACH preamble signature sequences used, different scrambling code

• Power control preamble segment is a [10] ms DPCCH Power Control Preamble (PC-P)

4096 chips

P0

P1Pj Pj

Collision DetectionPreamble

Access Preamble Control Part

Data part

0 or 8 slots N*10 msec

Message Part


The L1 parameters for CPCH are: Access preamble (AP) scrambling code Access preamble signature set. The maximum number of these is 16. These can be shared with RACH or separate AP slot sub-channels group Collision detection (CD) preamble scrambling code CD preamble signature set. The number of these is 16 and can be shared or separate with RACH CD preamble slot sub-channels group CD-AICH preamble channelization code CPCH scrambling code CPCH channelization code (variable, depends on bitrate) DPCCH DL channelization code

Physical Common Packet Channel


CPCH benefits • Capacity:

• For short data bursts CPCH is better that DCH, because it can be better multiplexed in time domain . This may improve overall system capacity

• CPCH may also degrade capacity, due to lack of SHO. For longer transmission, it is the best to use DCH

• CPCH uses fast power control, which gives better capacity than non-power control RACH

• Quality:• CPCH allocation is faster than DCH => better suited for

bursty data. CPCH may be a good channel for QoS packet data

• Due to lack of SHO, CPCH quality may be poor in the edge of the cell

• Coverage:• CPCH has an inferior coverage when compared to DCH• CPCH coverage is equal to RACH


CPCH challenges and possibilities

Possibilities:

• CPCH has faster access than in DCH in uplink. DCH set-up: few hundred ms, CPCH access few tens ms.

• Higher data amounts than in RACH. Example: RACH bitrates is suitable e.g. for 160 bytes SMS, CPCH could be used for 10 Kbytes document (128 kbits times 640 ms).

Challenges:

• BS implementation

• Standardization not finished.

• Coverage of high bitrates without SHO.


Dedicated Channel


Variable Bit Rate (Dedicated Channels)

• DPCCH (Dedicated physical control channel) is constant bit rate and carries all information needed to keep physical connection running

• DPDCH (Dedicated physical data channel) is variable bit rate

• Reference symbols (pilots) for channel estimation in coherent detection and for SIR estimation in fast power control

• Power control signalling bits (TPC)• Transport format combination information (TFCI) = bit rate,

interleaving

• User data• Higher layer signalling, e.g. mobile measurements, active set

updates, packet allocations

• DPDCH bit rate is indicated with TFCI bits on DPCCH

• One DPCCH and up to 6 DPDCH can be transmitted simultaneously in uplink


Uplink Dedicated Physical Channel

Frame 1 Frame 2 Frame 72

Super frame 720 ms

10 ms


Slot 1 Slot 2Slot 1 Slot 2 Slot 15

• I-Q/code multiplexed DPCCH and DPDCH

• Frame 10 ms, slot 0.667 ms (=2/3 ms), 2560 Chips

(2) Detect PC commandand adjust DL tx power

Slot 0.667 ms = 2/3 ms

PilotPilot TFCITFCI

DataData

DPCCH

DPDCH

TPCTPC

(1) Channel estimate+ SIR estimate for PC

(3) 10 ms frame :Detect TFCI

(4) Interleaving :Detect data


Uplink Variable Rate

DPCCH

DPDCH

Lower bit rate Higher bit rate Medium bit rate

• DPDCH bit rate can change frame-by-frame (10 ms)

• Higher bit rate requires more transmission power

• Continuous transmission regardless of the bit rate• Reduced audible interference to other equipment (nothing to do

with normal interference, does not affect the spectral efficiency)• GSM interference frequency ~217 Hz (=1/4.615 ms)

• Admission control in RNC allocates those bit rates that can be used on physical layer

10 ms frame 10 ms frame 10 ms frame


Downlink Dedicated Physical Channel



PilotData

Super frame 720 ms

10 ms

Slot 0.667 ms = 2/3 ms

TPC TFCI



• Time multiplexed DPCCH and DPDCH

• Support for blind rate detection

• Discontinuous transmission

DPDCH

Data

DPCCHDPDCH DPCCH


Downlink Variable Rate

DPCCH DPDCH

Maximum bit rate of that connection

10 ms frame

Lower bit rate (discontinuous transmission)

...

• DPDCH bit rate can change frame-by-frame (10 ms)

• Rate matching done to the maximum bit rate of that connection

• Lower bit rates obtained with discontinuous transmission (audible interference not a problem in downlink)

• Admission control allocates those bit rates that can be used on physical layer


• Multicode• Several parallel downlink DPCHs are transmitted for one CCTrCH using

the same SF (L1 control information is put on only the first downlink DPCH)

• The total bit rate to be transmitted on one downlink CCTrCH exceeds the maximum bit rate for a downlink physical channel

• In case there are several CCTrCHs mapped to different DPCHs transmitted to the same UE different spreading factors can be used on DPCHs to which different CCTrCHs are mapped (L1 control information is only transmitted on the first DPCH while DTX bits are transmitted during the corresponding time period for the additional DPCHs)

Transmission

Power Physical Channel 1

Transmission

Power Physical Channel 2

Transmission

Power Physical Channel L

DPDCH

One Slot (2560 chips)

TFCI PilotTPC

DPDCH

……………….

Not implemented in RAN1

Downlink Dedicated Physical Channel


Decoding of Dedicated Physical Channel

The uplink receiver in the base station needs to perform typically the followingtasks when receiving the transmission from UE

• Despreads the DPCCH and buffers the DPDCH according to the maximum bit rate, smallest SF.

• For every slot• obtain channel estimation from the pilot bits• estimate the SIR from the pilot bits of each slot• send the TPC command in downlink to control the uplink power• decode the TPC bit in each slot and adjust the downlink power

• For every second or fourth slot decode the FBI bits and adjust the diversity antenna phases, or phases and amplitudes, depending on the transmission diversity mode


Decoding of Dedicated Physical Channel

• For every 10 ms frame decode the TFCI from the DPCCH to obtain the bit rate and channel decoding parameters for the DPDCH

The same functions are valid also for the downlink with the following exceptions

• In downlink SF is constant• FBI bits are not used


Parameters in the DCH• UlMinimumAllowedBitRate Minimum allowed bit rate in uplink that can be allocated by PS

• DlMinimumAllowedBitRate Minimum allowed bit rate in downlink that can be allocated by PS

• DeltaPrxMaxUp Maximum received uplink power increase in cell when bit rates are allocated or increased, relative to PrxTotal

• DeltaPtxMaxUp Maximum transmitted downlink power increase in cell when bit rates are allocated or increased, relative to PtxTarget

• DeltaPrxMaxDown Maximum received uplink power decrease in cell when bit rates are decreased, relative to PrxTotal

• DeltaPtxMaxDown Maximum transmitted downlink power decrease in cell when bit rates are decreased, relative to PtxTarget


Parameters in the DCH• PowerOffsetDLdpcchPilot The parameter defines the power offset for the pilot symbols in relative to the data symbols in dedicated downlink physical channel Range : 0 … 6 dB, step size 0.25 dB

• PowerOffsetDLdpcchTpc The parameter defines the power offset for the TPC symbols relative to the data symbols in dedicated downlink physical channel Range : 0 … 6 dB, step size 0.25 dB

• PowerOffsetDLdpcchTfci The parameter defines the power offset for the TFCI symbols relative to the data symbols in dedicated downlink physical channel. Range : 0 … 6 dB, step size 0.25 dB


• InactivityTimerUplinkDCH The time how long the radio and transmission resources are reserved after silence detection on uplink DCH before release procedures. This parameter is defined for each bit rate Range : 0…20 s, step 0.5 s

• InactivityTimerDownlinkDCH The time how long the radio and transmission resources are reserved after silence detection on downlink DCH before release procedures. This parameter is defined for each bit rate Range : 0…20 s, step 0.5 s

Parameters in the DCH


Downlink Shared Channel


• The number of orthogonal codes in downlink is limited and the code is reserved according to the maximum bit rate in transport format set

variable bit rate connections consume a lot of code resources

downlink shared channel concept

• DSCH bitrate can be much higher than associated DCH bitrate.

• DSCH spreading factor can be between 4 and 256 and vary as function of time.

• DSCH is given to one user at each time. Multiple DSCHs possible.

• DSCH will add new parameters to be planned into network.

Downlink Shared Channel (DSCH)



• DSCH is time shared between a group of downlink users and it is always associated with a downlink DCH which includes TPC, TFCI and pilot bits for both channels. DSCH contains only data

• DSCH is not frame synchronized with the corresponding dedicated channel.

• TFCI indicates which user has an access to DSCH and which transport format (= bitrate, coding and code) is used there.

• DSCH power control is supported by associated DCH

Slot 0.667 ms

Physical channel 2 (SPCH)DSCH

Frame structure for the DSCH when associated to a DCH.

DPCCH DPDCH

PilotData TPC TFCI Data

DPDCH DPCCH


Downlink Shared Channel (DSCH) Timing between DCH and DSCH

The start of a DPCH frame is denoted TDPCH and the start of the associatedPDSCH frame is denoted TPDSCH. Any DPCH frame is associated to one PDSCH frame through the relation

46080 chips TPDSCH - TDPCH < 84480 chipsi.e. the associated PDSCH frame starts anywhere between three and eighteen slot after the end of the DPCH frame.

TDPCH

Associated PDSCH frame

DPCH frame

TPDSCH


SF=4

SF=8

SF=16

SF=32

Lowestspreading factor

Spreading codes in the sub-tree

• Conceptually DSCH can be seen as reserving a code resource and then sharing it in time and code domain.

• Example: frame N one user with SF 8, frame N+1 two users with SF 16.



• Used only in downlink, together with associated two directional dedicated channel.

• High bitrate in downlink, good for asymmetric packet traffic.

• DSCH supports fast power control and beamforming, but does not have soft handover.

• DSCH can be allocated fast (max. once per 10 ms) for different users I.e. shared in time domain.

• Bitrate up to 512 kbit/s?

U ser 1U ser 2

U ser 4U ser 3

1 2 3 2124

C ellresources

T im e

D S C H

D C H 's

DS

CH

DC

H

DC

H

Dow nlink Uplink



DSCH Radio Resource Management• Requires both control of DSCH and associated two-

directional DCH.• DCH is keep running longer than DSCH (good for RNC

capacity and for power control).• DSCH user and bitrate can be changed in each 10 ms or

slower.

• DSCH users can be prioritized (most important first, bigger ones first, etc…).

• Number of active DSCH users is limited.

D L D C H

U L D C H

DS

CH

D L D C H

U L D C H

D S C H a llocationsC an be used by

other bearers

D C H re lease a fte r tim eout


DSCH effects to Network Planning

• DSCH does not have soft handover => lower coverage• DSCH handover is always 'hard' cell selection, which is

decided based on either measured Ec/I0 from neighbouring cells or the transmission powers of cells in the active set of associated DCH. DCH can have soft handover or not.

• SHO on DCH will generate problems for power control. In this case we have to decide which one should have power control DCH or DSCH.

=> DCH is used only for signalling. Now DSCH should decide on the power control commands. Thus, DCH will have non-optimal power control. (In this case the DCH should not even be in SHO). => DCH is used for user data, like speech. Now, both SHO and fast power control should be provided to higher priority DCH. DSCH can not use fast power control because it does not have signalling. Instead a slow open-loop power control should be used in there.


DSCH effects to Network Planning

B S M S2

M S3

M S1

M S4

D S C H

A ssocia tedD C H 's

B itra te

P ower

D S C H

A ssocia tedD C H 's

D S C H b itra tedepends on loca tion

D C H b itra teis constan t

D S C H pow er isabout constant

• DSCH can have high and variable bitrates.=> The idea is to have high bitrates close to the BTS and low

bitrates at the cell edge. The TxPower remains "constant" and so the total interference


DSCH Challenges and Possibilities

Challenges:

• No SHO => effect to coverage and capacity?

• Fast allocation => bursty interference and resource reservation.

• Power control from DCH.

• DSCH is major change for BS and RNC.

• Iub resource usage => need for statistical multiplexing.

Possibilities:

• Fast allocation => more efficient code and other resource usage.

• User prioritization easy.

• Shorter end-user delay. (Set-up delay is the same than in DCH!)

• Better controllable in overload situations.

• Higher peak bitrates can be used.


Overview of RAN packet access

• In RAN2 we may have three very different logical channels for packet data, uplink: RACH/CPCH/DCH, downlink: FACH/DSCH/DCH.

=> Clear rules what is used and when are needed.

Downlink:

• FACH: For signaling and for low data amounts (in magnitude of SMS).

• DSCH: The main packet channel in downlink. For bursty traffic with possible high data amounts and bitrates. Especially for asymmetric services.

• DCH: Can be used for fairly constant bitrate services or when bitrate changes are not required often. Bitrate can be high or low.


Overview of RAN packet access

Uplink:

• RACH: Used for signaling. Can be used for low amounts (SMS) of data for non-CPCH capable UEs.

• CPCH: For bursty totally asymmetric packet traffic up to few tens of kilobytes. For short access (couple of seconds).

• DCH: For longer packet access. For low to high bitrates.

Possible channel combinations:

• FACH+RACH

• FACH+CPCH

• DCH+DCH

• DCH+DSCH+DCH

• Multibearer variations...


AICH accessslots

SecondarySCH

PrimarySCH

S-CCPCH,k

10 ms

PICH

#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4

P-CCPCH, (SFN modulo 2) = 0 P-CCPCH, (SFN modulo 2) = 1

Any CPICH

k:th S-CCPCH

PICH for k:th S-CCPCH

n:th DPCH DPCH,n

Any PDSCH

Timing Relationship

S-CCPCH,k = Tk 256 chip DPCH,n = Tk 256 chip, Tk {0, 1, …, 149}


Code Allocation during Soft Handover

Code 1 DL

BS 1 BS 2

UL

Code 2 DL

UL


Code Allocation during Soft Handover

• The UE transmit the information with the scrambling and channelisation codes assigned from the first BTS. From the UL point of view no changes are made for the code allocation

• Each BTS transmit with its own scrambling code and with a channel code that should have the same SF otherwise the UE will loose the combining gain

• Code 1 DL is different from Code 2 DL

• The UE will allocate the fingers of the Rake receiver to despreading both transmissions and then each finger will be combined through a maximal ratio combining


Correlator

Channelestimator

Phaserotator

DelayEqualizer

Codegenerators

Timing (Finger allocation)

Finger 1

Finger 2

Finger 3

I

Q

I

Q

Combiner

I

Q

Inputsignal

(from RF)

Matchedfilter

RAKE Diversity Receiver


• The delay profile extends from 1-3 s in urban and suburban area; it can be more of 20 s in hilly area

• The chip duration is 260 ns => the WCDMA receiver can separate multipath components and combine them if the difference in path length is at least 78 m

• The fast fading (signal cancellation) is due to the relative phase shift [difference in path (/2 = 7 cm) and reflection coefficients (boundary conditions)] of the different contributions arriving at the receiver

• The response of a matched filter identifies the delay positions at which significant energy arrives, and the correlation receivers (RAKE fingers) are allocated to those peaks

• Within each correlation receiver, the fast changing phase and amplitude values are tracked and removed (pilot symbols are used to sound the channel and provide an estimate of the momentary channel state for a particular finger, then the received symbol is rotated back, so as undo the phase rotation caused by the channel)



• The demodulated and phase-adjusted (data and pilots) symbols across all active fingers are combined (recovering the energy across all delay positions, Maximal Ratio Combining) and presented to the decoder for further processing• Processing at the chip rate (correlator, code generator and matched filter) is done in ASICs, whereas symbol level processing (channel estimator, phase rotator, combiner) is implemented by a DSP• Multiple receiver antennas (including the softer HO case) can be accommodated in the same way as multiple paths received from a single antenna (separated busses are used): by just adding additional Rake fingers to the antennas (actually the same n. of CHE fingers are shared to the peaks belonging to different antennas)



Maximal Ratio Combining of SymbolsTransmitted

symbolin a slot

• Depending on distance, medium and attenuation of path between UE and WCDMA BTS, channel can rotate signal to any phase and to any amplitude

• QPSK (pilot) symbols carry information in phase

• Energy splitted to many fingers => combining (Pilots for SIR estimation and Data symbols)

• Maximal ratio combining corrects channel phase rotation (for combining) and weights components with channel amplitude estimate

• Less bias in the signal power estimate after combining (noise cancel), a further benefit is achieved in averaging the combination upon pilot symbols on each slot

• Same method used also for antenna combining (BTS, UE) and softer handover (BTS) and soft/softer handover (UE)

finger #1

finger #2

finger #3

Receivedsymbol

+Noise

Combinedsymbol

+Residual noise

Modifiedwith

channelestimate

and relativedelay

compensation(for combining)


Matched Filter

Incoming

serial data

Predefined(parallel) data

Register 1

Register 2

When samples ofincoming serialdata are equal tobits of predefineddata, there is a maximum at filteroutput.

Tap 127

Tap 126

Tap 0

Sample 127

Sample 126

Sample 0

To make a successful despreading, code and data timing must be known. Can be detected e.g. by a matched filter.

+1

-1


Compressed mode

• To allow MS to monitor other carriers/systems during an idle period is provided by the compressed mode

• Instantaneous transmit power is increased in the compressed frame in order to keep the quality

One frame(10 ms) Transmission gap available for

inter-frequency measurements


Channel power planningDifferent Ec/Ior requirement for the common channel makes the power planning not a trivial task

Pilot coverageP-CCPCHcoverage

In this example the mobile "sees" the cell but cannot access it as it cannot decode the BCH

Possible value for the Ec/IorCPICH = -10 dBP-CCPCH = -15.6 to -12 dBS-CCPCH = -11.6 to -14.3 dB

depends on the SFSCH1= SCH2 = P-CCPCH - 3dB

Possible value for the Ec/IorCPICH = -10 dBP-CCPCH = -15.6 to -12 dBS-CCPCH = -11.6 to -14.3 dB

depends on the SFSCH1= SCH2 = P-CCPCH - 3dB


Agenda

• Introduction


• WCDMA Codes




• Conclusion


Conclusion• Two different codes are used, channel codes and scrambling codes. The first one for spreading the information while the second it is used for identify the user (uplink) or the cell (downlink)

• Three different kind of channels: Logical, Transport and Physical

• The Physical channels are then divided in two classes, Common Channels (CPICH, SCH, Primary CCPCH, Secondary CCPCH, RACH, AICH, PDSCH, PCPCH, PICH) and Dedicated Channels ( DPDCH and DPCCH)


SF 256

SF 256

SF 256 to 4 RAN1 up to 64

Data SF 32 to 256 Control 256

SF 256 to 4 not in RAN 1

SF 256

SF 256 to 4 not in RAN1

Conclusion

CCPCH-1

CCPCH-2

SCH 1 & 2

PDSCH

CPICH

PICH

PCPCH

AICH

PRACH

DPDCH

DPCCH

SF 256

SF 256


References

• 3GPP : 3G TS 25.211 V3.3.0

• 3GPP : 3G TS 25.212 V3.3.0

• 3GPP : 3G TS 25.213 V3.3.0

• 3GPP : 3G TS 25.214 V3.3.0

• 3GPP : 3G TS 25.331 V3.3.0

• Harri Holma : WCDMA for UMTS

basic wcdma studies1

Documents

user signal processing

wcdma users

frequency code channels

required signal

mbits user data rate

high data rate low data

mcps data modulation

power cdma frequency