網路多媒體研究所 1 WCDMA Technology Past, Present and Future Part IV: Physical Layer on WCDMA

1 網路多媒體研究所網路多媒體研究所

WCDMA TechnologyWCDMA TechnologyPast, Present and FuturePast, Present and Future

Part IV:Physical Layer on WCDMA

網路多媒體研究所網路多媒體研究所2


• Overview on WCDMA Physical Layer– WCDMA Physical Channel– Functions of WCDMA Physical Channel– Spreading in WCDMA Physical Channel

• Operations in making a phone call– Baseband Packet Formats– Important Physical Layer Procedures and Is

sues


What is Physical Layer?• Physical layer (PHY) defines how the data

(controlling data and the user data = user traffic) has been structured for the transmission over the air interface

• In mobile cellular systems the effect of the physical layer is high because of the characteristics of the radio channel (=air interface)

• Defines the maximum capacity limits of the system (maximum allowed bit-rate, maximum number of simultaneous users)

• In practice the physical layer does not necessary limit the capacity but the implementation of the equipments and the radio channel.

• Big impact on equipment complexity,– processing power, algorithms


Main Requirements on WCDMA Physical Layer

• High bit-rates• Flexible variable bit rate both in uplink and

in downlink• Multi-service• Different services have been multiplexed

on a single physical connection• Efficient packet data• Support for All IP-RAN• High spectral efficiency


WCDMA Radio Interface Protocol Architecture

PHY(W-CDMA)PHY(W-CDMA)

RLCRLC

RRCRRC

PDCPPDCP

L1

L2

L3

Control

Control Plane User Plane

Transport Channels

Logical Channels

Physical Channels

Radio Bearers

MACMAC

BMCBMC

U-plane Radio

Bearers

Signalling Radio Bearers


Physical Channels (1/3)• Common Physical Channels:

– Synchronization Channels (SCH, DL)• Primary Synchronization Channel (P-SCH)• Secondary Synchronization Channel (S-SCH)

– Common Pilot Channel (CPICH, DL)– Common Control Physical Channels (CCPCH,

DL)• Primary common physical channel (P-CCPCH)• Secondary common physical channel (S-

CCPCH)– Indication Channel

• Acquisition Indication Channel (AICH, DL)• Page Indication Channel (PICH, DL)• CPCH Access Preamble Acquisition Indicator

Channel (AP-AICH, DL)• CPCH Collision Detection Channel Assignment

Indicator Channel (CD/CA-ICH, DL)• CPCH Status Indicator Channel (CSICH, DL)

– Physical Random Access Channel (PRACH, UL)

– Physical Common Packet Channel (PCPCH, UL)

• Dedicated Physical Channels:– Dedicated Physical Data Channel (DPDCH,

DL&UL)– Dedicated Physical Control Channel (DPCCH,

DL&UL)

DPCCH

Physical Channel

Dedicated Physical Channel

Common Physical Channel

DPDCH

PCCPCH

SCCPCH

PRACH

PCPCH

PDSCH

PICH

AICH

CPICH

SCH

AP-AICH

CD/CA-ICH

CSICH


Physical Channels (2/3)


Physical Channels (3/3)

• Chip rate = 3.84 Mcps• Physical channel is characterize with frequency, code,

duration and in uplink with phase shift• 1 radio frame (10 ms) includes 15 time slots (one slot e

quals to power control period, 1/(10ms/15)=1500 Hz)• one time slot = 2560 chips• Slot structure is just for controlling the physical chann

el and its radio performance


Timing Relationship Between Physical Channels

k:th S-CCPCH

AICH access slots

Secondary SCH

Primary SCH

S-CCPCH,k

10 ms

PICH

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

Radio frame with (SFN modulo 2) = 0 Radio frame with (SFN modulo 2) = 1

DPCH,n

P-CCPCH

Any CPICH

PICH for k:th S-CCPCH

Any PDSCH

n:th DPCH

10 ms


Physical Layer Baseband Processing Block Diagram

Coding and Multiplexing of Transport Channels

CRC Attachment,Channel Coding,1st Interleaving,Rate Matching






Transport Channel MUXTransport Channel MUX

TransportChannel #1

TransportChannel #2

TransportChannel #N

CCTrCH

Physical Channel Segmentation,2nd Interleaving,

Physical Channel Mapping

Physical Channel Segmentation,2nd Interleaving,

Physical Channel Mapping Spreading&

Gain Weighting

Spreading&

Gain Weighting

PhCH #1

PhCH #2

PhCH #3

PhCH #4

DPCCH

Σ

Σ⊕⊕

j

ScramblingScrambling

Pulse ShapingPulse Shaping

ModulationModulation

To RF

I + jQ

I

Q

(DPDCH)


Spreading Codes in WCDMA• Channelisation Codes (Spreading code, orthogonal code)

– Length is dependent on spreading factor– Used for channel separation from the single source– Good orthogonality properties => decreased interference– Usage have to be managed: If one code with low spreading factor is used, the code in t

he same code tree branch can not be used– Same codes in every cell / mobiles and therefore the additional scrambling code is ne

eded• Scrambling Codes

– Very long (38400 chips), many codes available– Uplink: to separate different mobiles– Downlink: to separate different cells/sectors– Good correlation properties:– The correlation between two codes (two mobiles) is low– The autocorrelation is low when the phase shift ≠ 0. Then the multipath propagation

does not have big impact on the interference levels


Channelisation and Scrambling codes


Two code layer scheme, downlink


Utilization of Channelisation and Scrambling Codes

Uplink Downlink

ChannelisationCodes

Identify the physical channels for the same user if multi-code is used

Identify the physical channels of each user

ScramblingCodes

Identify the users

Identify the cells


Channelization Codes – OVSF Codes

• The OVSF (Orthogonal Variable Spreading Factor) code is described as Cch,SF,k, where SF is the spreading factor of the code and k is the code number, 0 ≦ k ≦ SF-1.


Downlink scrambling code (1/2)

• Long scrambling code (2^18-1=262143 codes)• Only 38400 chips from the beginning of the code is used• The DL scrambling code is time aligned with the scrambling code of PCC

PCH channel which is the timing reference• From these only 8192 codes, devidid into 512 sets, are used in WCDMA in

order to speed up the cell search• Each code set includes 1 primary and 15 secondary scrambling (other Ph

CH) codes.• 512 primary scr. codes has been divided into 64 subgroups• Each cell is allocated one primary scrambling code (carrying P-CCPCH,

P-CPICH, PICH, AICH and S-CCPCH)• Other channels can use the primary scrambling code or secondary code

from the same set. If the secondary code is used the orthogonality is lost reduction of system performance


Downlink Scrambling Code (2/2)

• Configuration of DL scrambling code generator.

I

Q

1

1 0

02

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

17

17

16

16

15

15

14

14

13

13

12

12

11

11

10

10


Uplink Scrambling Code• The definition of the nth scrambling code word for the in phase and

quadrature components follows as: C1,n=<xn(0)+y(0), xn(1)+y(1),…, xn(N-1)+y(N-1)> C2,n=<xn(M)+y(M), xn(M+1)+y(M+1),…, xn(M+N-1)+y(M+N-1)> where N is the period in chips and M = 16,777,232.

cn1,

cn2,

MSB LSB


Block Diagram of WCDMA PHY

MultipathFading Channel

ChannelEncoder

Rate Matching

BlockInterleaver

DataModulator

SpreaderPulse

ShapingFilter

I/Q Modulator &Up-converter

Channeldecoder

De-rate Matching

BlockDe-Interleaver

DataDemodulator

PulseShaping

Filter

Down-converter &I/Q Demodulator

RAKEReceiver

Synchronizer

Searcher

• AFC• N. B. AGC• SIR-Measurement W. B. AGC

Despreading

Spreading



• Overview on WCDMA Physical Layer– WCDMA Physical Channel– Functions of WCDMA Physical Channel– Spreading in WCDMA Physical Channel

• Operations in making a phone call– Baseband Packet Formats– Important Physical Layer Procedures and Is

sues


Physical Layer Operations in making a phone call

MSMS BSBS

Listen Broadcast Information

Wait for Paging

Power on

Cell Search

Establish a dedicate connection for a callEstablish a dedicate connection for a call

Release connection for a callRelease connection for a call

Data Transmission and ReceptionData Transmission and Reception



MSMS BSBS


Wait for Paging

Power on

Cell Search




1.1.


P-CCPCH

WCDMA Cell Search

One timeslot=625 sec

Base 1

Base 2

Base 3

Mobile Searcher

Base 1

Base 3

Base 2

P-CCPCHP-SCH

S-SCH P-CCPCHP-SCH

S-SCH P-CCPCHP-SCH

S-SCH

P-CCPCHP-SCH

S-SCH P-CCPCHP-SCH

S-SCH

P-SCH

S-SCH

P-CCPCH P-CCPCHP-SCH

S-SCH P-CCPCHP-SCH

S-SCH

P-SCH

S-SCH


Cell Search Procedure (1/2)

How to do cell search? --> Three steps fast cell search algorithm

–Step 1: Slot synchronization–Step 2: Frame synchronization and code-

group identification–Step 3: Scrambling code identification


Cell Search Procedure (2/2)


Synchronisation Channel (SCH)

• For initial cell search for the MS• The Synchronisation Channel (SCH):

– A downlink signal used for cell search– Consists of two sub channels:

• Primary SCH• Secondary SCH


Downlink Common Pilot Channel (CPICH)

• Primary and secondary CPICH

• Primary CPICH– Unmodulated, fixed rate, fix

ed power channel scrambled with the cell specific primary scrambling code

– Used as a phase reference– 15 kbps, SF=256 (Cch,256,0)SF=256 (Cch,256,0)– Used in handover measure

ments: • CPICH Ec/I0

– Used for channel estimation• Secondary CPICH

– Used with multiple antenna beams


Modulation Pattern for CPICH in case of Transmit Diversity

• In case of Transmit Diversity (open or closed loop), the CPICH shall be transmitted from both antennas using the same channelization and scrambling code. In this case, the pre-defined symbol sequence of the CPICH is different for Antenna 1 and Antenna 2.

slot #1

Frame#i+1 Frame#i

slot #14

Antenna 2

Antenna 1

slot #0

Frame Boundary

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1


Downlink spreading and modulation

P-CPICHS-CPICH



MSMS BSBS


Wait for Paging

Power on

Cell Search




2.2.


Primary Common Control Physical Channel (P-CCPCH)

• Carrying the Broadcast Channel (BCH)

• Contains random access codes, code channels of other common channels

• Pure DATA channel: channel estimation from Common pilot channel

• Needs to be demodulated by all the terminals in the system: High Tx power needed

• Fixed data rate (30 kbps=15ksps), channellization code length 256 Cch,256,0

• No power control• P-CCPCH and SCH are time multi

plexed (SCH used in TxOFF period of above shown figure)



MSMS BSBS


Wait for Paging

Power on

Cell Search




3.3.


Secondary CCPCH• The S-CCPCH is used to carry the FACH and PCH.

– Forward Access Channel (FACH) and Paging Channel (PCH) which can be mapped to same or different S-CCPCH

• There are two types of S-CCPCH: those that include TFCI and those that do not include TFCI. It is the UTRAN that determines if a TFCI should be transmitted, hence making it mandatory for all UEs to support the use of TFCI.

• The parameter k determines the spreading factor SF of the S-CCPCH as SF = 256/2k. The spreading factor range is from 256 down to 4.

• No TPC• Active only when data available


Secondary CCPCH

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

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

Pilot Npilot bits

DataNdata bits

1 radio frame: Tf = 10 ms

TFCI NTFCI bits


S-CCPCH FieldsSlot Format

#i

Channel Bit

Rate (kbps)

Channel

Symbol Rate

(ksps)

SF Bits/ Frame Bits/

Slot

Ndata Npilot NTFCI

0 30 15 256 300 20 20 0 0

1 30 15 256 300 20 12 8 0

2 30 15 256 300 20 18 0 2

3 30 15 256 300 20 10 8 2

4 60 30 128 600 40 40 0 0

5 60 30 128 600 40 32 8 0

6 60 30 128 600 40 38 0 2

7 60 30 128 600 40 30 8 2

8 120 60 64 1200 80 72 0 8*

9 120 60 64 1200 80 64 8 8*

10 240 120 32 2400 160 152 0 8*

11 240 120 32 2400 160 144 8 8*

12 480 240 16 4800 320 312 0 8*

13 480 240 16 4800 320 296 16 8*

14 960 480 8 9600 640 632 0 8*

15 960 480 8 9600 640 616 16 8*

16 1920 960 4 19200 1280 1272 0 8*

17 1920 960 4 19200 1280 1256 16 8*


Page Indicator Channel (PICH)

• A terminal registered to the network is allocated a paging group• When there are paging messages coming for any UEs of that group the Paging Ind

icator will be send on PICH.• After that UE decodes the next PCH message on S-CCPCH to find out whether ther

e was paging messages intended for it• This procedure decreases the power consumption of the UE

b1b0

288 bits for paging indication 12 bits (undefined)

One radio frame (10 ms)

b287 b288 b299

PICH=7680 chips

Associated S-CCPCH frame

PICH frame containing paging indicator



MSMS BSBS


Wait for Paging

Power on

Cell Search




4.4.


Physical Random Access Channel (PRACH)

• With Random Access Channel (RACH) power ramping is needed with preambles since the initial power level setting in the mobile is very coarse with open loop power control

• Preamble: mobile sends 256 repetitions of 16 chip (1 preamble = 4096 chips) signature sequence with increasing power

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

• Mobile RACH message follows the acknowledgement• Can be used also for Data transmission• Message part length 10 or 20 ms


Spreading and Modulation of Spreading and Modulation of PRACH Message PartPRACH Message Part

jccc

cd

d

Sr-msg,n

I+jQ

PRACH messagecontrol part

PRACH messagedata part

Q

I


Structure of the Random Access Message Part

Pilot Npilot bits

DataNdata bits

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

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

Message part radio frame TRACH = 10 ms

Data

ControlTFCI

NTFCI bits


Random-access Message Data and Control Fields

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

Slot Format#i

Channel BitRate (kbps)

ChannelSymbol Rate

(ksps)

SF Bits/Frame

Bits/Slot

Npilot NTFCI

0 15 15 256 150 10 8 2


PRACH access procedureStart when receive REQ from MAC

Random selection(available access slot and signature)

K := Kmax and set the Commanded Preamble Power to appropriate value

Transmit a access preamble

AI +1 nor -1

Random selection(next available access slot and signature)

K = K - 1 and increase the Commanded Preamble Power

K > 0 ? & Preamble Power not exceed?

AI = +1 ?

Send No ACK to MAC;exit;

Send ACK to MAC;Send RACH message

when receive DATA REQ from MAC;

exit;

Send NACK to MAC;exit;

Yes

No

Yes

Yes

No

No

PHY_ACCESS_RACH_REQ


Acquisition Indicator Channel (AICH)

• Acqusistion Indicator Channel (AICH)– User for RACH channel indication– For the detection of AICH MS used Common pilot channel– To all MS in the cell: high power, low data rate

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

a1 a2a0 a31 a32a30 a33 a38 a39

AI part Unused part

20 ms



MSMS BSBS


Wait for Paging

Power on

Cell Search



Data Transmission and ReceptionData Transmission and Reception5.5.


Dedicated Physical Channel

• DPCCH (Dedicated physical control channel) is constaconstant bit ratent bit rate and carries all the information in order to keep physical connection running– Reference symbols for channel estimation in coherent detecti

on and for SIR estimation in fast power control– Power control signalling bits (TPC)– Transport format information (TFCI) = bit rate, interleaving

• DPDCH (Dedicated physical data channel) is variable bvariable bit rateit rate and carriers User data– DPDCH bit rate is indicated with TFI bits on DPCCH


Downlink dedicated physical channel(1/3)

• Time multiplexed DPCCH and DPDCH:– DCH is carried by DPDCH– Discontinuous transmission in DPDCH fields in

order to handle variable data rates



• The DPDCH and DPCCH have the same power and the same SF• DPDCH spreading factor from 512 (7.5 ksps) to 4 (960 ksps)• For example: SF = 8

– 3.84x10^6/8/1000=480 ksps=960 kbps– I/Q modulation (QPSK): 2 bit = 1 symbol

• Procedure in the UE when receiving DL-DPCH:– Estimate the SIR (Pilot)– Detect TPC and adjust UL Tx power– Detect the used bit-rate and interleaving (TFCI)– Detect the data (Data): needs buffering of the Data field


Downlink DPCH FieldsDPDCH

Bits/Slot

DPCCH

Bits/Slot

Slot

Format

#i

Channel

Bit Rate

(kbps)

Channel

Symbol

Rate

(ksps)

SF Bits/

Slot

NData1 NData2 NTPC NTFCI NPilot

Transmitted

slots per

radio frame

NTr 0 15 7.5 512 10 0 4 2 0 4 15

1 15 7.5 512 10 0 2 2 2 4 15

2 30 15 256 20 2 14 2 0 2 15

3 30 15 256 20 2 12 2 2 2 15

4 30 15 256 20 2 12 2 0 4 15

5 30 15 256 20 2 10 2 2 4 15

6 30 15 256 20 2 8 2 0 8 15

7 30 15 256 20 2 6 2 2 8 15

8 60 30 128 40 6 28 2 0 4 15

9 60 30 128 40 6 26 2 2 4 15

10 60 30 128 40 6 24 2 0 8 15

11 60 30 128 40 6 22 2 2 8 15

12 120 60 64 80 12 48 4 8* 8 15

13 240 120 32 160 28 112 4 8* 8 15

14 480 240 16 320 56 232 8 8* 16 15

15 960 480 8 640 120 488 8 8* 16 15

16 1920 960 4 1280 248 1000 8 8* 16 15

Half Rate

Speech

144Kbps

384Kbps



• DPDCH bit rate can change frame-by-frame (10 ms)• Rate matching done to the maximum bit-rate of the

connection• Lower bit rates obtained with discontinuous transmission

(no audible interference)• The usable DL bit-rate allocated by the Radio Resource

Management (RRM) algorithms (in this case Admission Control)

• Discontinuous transmission:


Downlink spreading and modulation

DPCHDPCH


Uplink dedicated physical channel(1/3)

• There can be several uplink DPDCH for one mobile but only one DPCCH– TFCI = Transport Format Combination Indicator– TPC = Transmitted Power Control– FBI = Feedback information (for Tx antenna diversity)

DPCCH

DPDCH



• DPDCH spreading factor from 256 (15 ksps) to 4 (960 ksps)• DPCCH spreading factor from 256 (15 ksps) = constant• For example: SF = 16

– 3.84x10^6/16/1000=240 kbps• I/Q modulation (QPSK): 1 bit = 1 symbol• Procedure in the base station when receiving UL-DPDCH/DPCCH:

– Estimate the SIR (Pilot)– Detect TPC and adjust DL Tx power– Detect the used bit-rate and interleaving (TFCI)– Detect the data (Data): needs buffering of the Data field


Uplink DPDCH Field

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


Uplink DPCCH FieldsSlot

Format#i

Channel BitRate (kbps)

ChannelSymbol Rate

(ksps)

SF Bits/Frame

Bits/Slot

Npilo

t

NTPC NTFCI NFBI Transmitted slots per

radioframe

0 15 15 256 150 10 6 2 2 0 150A 15 15 256 150 10 5 2 3 0 10-140B 15 15 256 150 10 4 2 4 0 8-91 15 15 256 150 10 8 2 0 0 8-152 15 15 256 150 10 5 2 2 1 15

2A 15 15 256 150 10 4 2 3 1 10-142B 15 15 256 150 10 3 2 4 1 8-93 15 15 256 150 10 7 2 0 1 8-154 15 15 256 150 10 6 2 0 2 8-155 15 15 256 150 10 5 1 2 2 15

5A 15 15 256 150 10 4 1 3 2 10-145B 15 15 256 150 10 3 1 4 2 8-9

• There are two possible compressed slot formats for each normal slot format. They are labelled A and B and the selection between them is dependent on the number of slots that are transmitted in each frame in compressed mode. The channel bit and symbol rates given in table 2 are the rates immediately before spreading.



• DPDCH bit rate can change frame-by-frame (10 ms)• Higher bit rate requires more transmission power• Also DPCCH power is higher for higher bit-rates in order to

enable accurate channel estimation• Continuous transmission regardless of the bit rate• Admission control in RNC allocates those bit rates that can be

used on physical layer


Uplink spreading on dedicated channels


Power Control in W-CDMA (1/4)

Power Control

Uplink

Downlink

Open Loop

Closed Loop

Inner Loop

Outer Loop

Closed Loop

Inner Loop

Outer Loop



UE

Node B

UL

Open loop

UE

Node B

Close loop

UL

DL



Node B RNCUE

Inner Loop



Node B RNCUE

Outer Loop


Illustration of Power Control

Selector

Inner LoopControl

SIRMeasurement

Outer LoopControl

FrameError

Detector

ViterbiDecoder

RAKEReceiver

MatchedFilter

RAKEReceiver

Accumulator

Tx Data

+

AGC

Base Station Mobile Station

FER

SIRtarget

SIR

Tx DataInner Loop

Outer Loop


Transmitter Power Control Timing

Data2Data1

*1,2 The SIR measurement periods illustrated here are examples. Other ways of measurement are allowed to achieve accurate SIR estimation.*3 If there is not enough time for UTRAN to respond to the TPC, the action can be delayed until the next slot.

Data1TPC

Data1TPC

PILOTPILOT

PILOT

ResponseTo TPC (*3)

TPC

DL SIRmeasurement (*1)

PILOT TFCI TPC

DL-UL timing offset (1024 chips)

Slot (2560 chips)

PILOTPILOT Data2Data1TPC

PILOTPILOT TFCI TPC

Slot (2560 chips)

Propagation delay

UL SIRmeasurement (*2)

Responseto TPC

DL DPCCHat UTRAN

Propagation delay

DL DPCCHat UE

UL DPCCHat UTRAN

UL DPCCHat UE

512 chips

TFCI

TFCI



MSMS BSBS


Wait for Paging

Power on

Cell Search




6.6.

Documents

網路多媒體研究所 1 WCDMA Technology Past, Present and Future Part IV: Physical Layer on WCDMA