7072747 Umts Physical Layer

WCDMA Physical Layer Design A. Chockalingam Assistant Professor Indian Institute of Science, Bangalore-12

[email protected] http://ece.iisc.ernet.in/~achockal

Outline ◆

WCDMA Network Architecture

◆

WCDMA Physical Layer – Physical / Transport / Logical Channels – Uplink » » »

Spreading - Channelisation / Scrambling Transport Formats and Configuration Multiplexing and Channel Coding

– Downlink » Spreading / Scrambling / Channelisation » Multiplexing and Channel Coding Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

2

2G to 3G Evolution EDGE GSM

D A T A

GPRS WCDMA

IS-95A

I S 9 9

IS-95B

IMT2000

cdma2000

IMT2000: ITU’s Standardization Effort towards 3G (IMT-2000 previously termed as FPLMTS) UMTS: European Effort (Specified by 3G Partnership Project 3GPP) Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

3

UMTS NW Model Non-access Stratum (Protocols between UE and Core NW)

Access Stratum

Home Network

(Protocols between UE and Access NW)

Zu

USIM

Cu

Mobile Equipment

User Equipment

Serving Network

Access Network Uu

Iu

Access Network

PS/CS

Transit Network Yu

Core Network

Infrastructure Stratum: Refers to a way of grouping protocols handling activities Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

4

UMTS NW Architecture Uu

Iu UTRAN

Iub

Node B UE

RNS RNC

CN CN (CS Domain) 3G MSC / VLR

3G GMSC

Node B

Registers

Iur

UE

HLR/AuC/EIR RNS

Node B

(Home Network)

CN (PS Domain) RNC

Node B

SGSN

GGSN

UE

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

5

WCDMA System Features ◆

UTRA FDD mode and TDD mode

◆

UTRA FDD features – Multiple Access:

CDMA

– Channel Spacing:

5 MHz

– Chip Rate:

3.84 Mcps

– Frame Length:

10 msec

– Time Slots:

15 slots per 10 msec frame

– Spreading Factor:

4 to 512

– Multi-rate:

Through Multi-code or Orthogonal Variable Spreading

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

6

UTRA FDD Features – FEC Codes:

– – – – – – – –

Rate 1/2, 1/3 convolutional code with constraint length K = 9 Rate 1/3, 8-state Turbo coding Interleaving: Intra- or Inter-frame interleaving (10, 20 40, 80 msec) Modulation: QPSK Detection: Coherent based on pilot symbols Micro diversity: RAKE in BS and UE Power Control: Fast closed-loop at 1500 Hz rate Intra-frequency HO: Soft / Softer Handover Inter-frequency HO: Hard Handover Interference Cancellation: Support for multiuser detection

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

7

Radio Interface Protocol Model CONTROL PLANE

USER PLANE L3

RRC Control

U-Plane Radio Bearers (Radio Network Layer)

User Plane Radio Bearers

Signalling Radio Bearers

PDCP RLC

BMC

L2 (Radio Link Layer)

Logical Channels

MAC Transport Channels

PHY Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

L1 (Radio Physical Layer) 8

WCDMA Radio Channels ◆

Physical Channels – – – –

◆

Transmission media. Two types of physical channels defined in L1; FDD and TDD. FDD is characterized by frequency, code, I/Q phase Follow a layered structure of “radio frames” and “time slots”

Transport Channels

– describes the way information is transferred over the radio interface

◆

Logical Channels

– the type of information transferred characterizes a logical channel UE

BS

RNC

Logical Channels Transport Channels Physical Channels Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

9

Physical Channels ◆

◆ ◆ ◆ ◆ ◆

Corresponds to a specific carrier frequency, code, relative phase in I and Q branches Dedicated and Common Physical Channels Layered structure of radio frames and time slots A radio frame = 10 msec = 15 slots/frame 1 frame = 38400 chips, 1 slot = 2560 chips Slot configuration varies depending on the channel bit rate of the physical channel – # bits/slot different for different physical channels – may vary with time (on a frame by frame basis)

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

10

U/L Physical Channels ◆

Dedicated U/L Channels – DPDCH – DPCCH

◆

Common U/L Channels – PRACH » Preamble part » Message part

– PCPCH » Preamble part » Message part Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

11

Dedicated U/L Physical Channels ◆

Two types – Dedicated Physical Data CHannel (DPDCH) – Dedicated Physical Control CHannel (DPCCH) – Both are I/Q code multiplexed within each radio frame

◆ ◆

U/L DPDCH carries the DCH transport channel U/L DPCCH carries L1 control bits such as – – –

Pilot bits (to enable channel estimation for coherent detection at BS) Transmit power control (TPC) commands Feedback Information (FBI) » used for CL transmit diversity and Site Selection Diversity Transmission (SDTC)

– Transport Format Combination Indicator (TFCI)

» for several simultaneous services. Informs the rx of the transport format combination of the transport channels mapped to DPDCH

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

12

U/L Frame Structure ◆

There is only one U/L DPCCH on each radio link There can be 0, 1, or several DPDCHs on each radio link

◆

10 msec frames divided into 15 slots

◆

1 Frame = 15 slots = 10 msec S0

S1

DPDCH (on I-Chl) DPCCH (on Q-Chl) Dr. A. Chockalingam

S2

S3

S13

S14

1 time slot = 2/3 msec DATA (Ndata bits) Pilot

TFCI FBI TPC

10 bits = 2560 chips => SF = 256 Dept of ECE, IISc, Bangalore

13

I, Q Spreading for DPDCH, DPCCH Cc, Cd,n: Channelization codes Sdpch,n: Scrambling code Bd, Bc: Gain factors

DPDCH-1 Cd,1

Bd

Cd,3

Bd

DPDCH-3

∑

I I+jQ

DPDCH-2

Sdpch,n Cd,2

Bd

∑Q j

DPCCH-2 Cc Dr. A. Chockalingam

Bc Dept of ECE, IISc, Bangalore

Up to 6 DPDCHs in parallel 14

WCDMA Transmission Rates (U/L) ◆

System Chip Rate : 3.84 Mcps

◆

Symbol Rates on Uplink – Chl Symb Rate

Chl Bit Rate

SF

15 Ks/s

15 Kb/s

256

150

10

30 Ks/s

30 Kb/s

128

300

20

60 Ks/s

60 Kb/s

64

600

40

120 Ks/s

120 Kb/s

32

1200

80

240 Ks/s

240 Kb/s

16

2400

160

480 Ks/s

480 Kb/s

8

4800

320

960 Ks/s

960 Kb/s

4

9600

640

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

Bits/frame

Ndata

15

WCDMA Channelisation Codes ◆

Orthogonal codes

◆

Used for channel separation both in U/L and D/L directions

◆

Can have different spreading factor values (thus support different symbol rates)

◆

Cch,SF,k : SF - Spreading Factor, k is the code number 0<=k<= SF-1

◆

Spreading factor value indicates how many bits of those codes are used in a connection

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

16

U/L Channelization Codes ◆

◆ ◆

Orthogonal Variable Spreading Factor (OVSF) channelization codes Separates data / control channels from same UE Preserves orthogonality between these channels SF=1

SF=2

SF=4 (1,1,1,1)

(1,1) C(SF,k)

(1,1,-1,-1)

(1) (1,-1)

SF: Spreading Factor k: code number 0
(1,-1,1,-1) (1,-1,-1,1)

Dept of ECE, IISc, Bangalore

17

U/L Scrambling Codes ◆

Use complex valued scrambling code

◆

Long scrambling sequences (2^24) – Gold sequences (linear combination of two m-sequences)

◆

Short scrambling sequences (2^24) – from a family sequence of periodically extended S(2) codes

◆

Long or short sequences for DPCCH / DPDCH

◆

Only long sequences for message parts of PRACH and PCPCH Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

18

WCDMA Code Types ◆

Scrambling Codes, Channelisation Codes Uplink

Scrambling codes User separation Channelisation codes

Downlink Cell separation

Data and Control Users within a channels from the cell same terminal

Spreading code = Scrambling code x Channelisation code

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

19

Common U/L Physical Channels ◆

Two Types – Physical Random Access CHannel (PRACH) – Physical Common Packet CHannel (PCPCH)

◆

Physical Random Access CHannel (PRACH) – – – –

carries RACH Uses S-ALOHA technique with fast Acquisition Indication Access slots (15 access slots per 2 frames) RA transmission consists of » several 4096 chip preambles (uses 256 repetitions of 16 chips signature sequence) and 1or 2 frame message

Preamble

Preamble

Message Part (1 or 2 frames)

4096 Chips Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

20

Random Access UE

BS

PRACH: Preamble sent (initial access) No detection on AICH PRACH: Preamble sent (initial access) AICH: Preamble sent detected PRACH: Random Access Info sent

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

21

Common U/L Physical Channels ◆

Physical Common Packet CHannel (PCPCH) – Carries CPCH – CPCH is based on DSMA-CD technique with fast Acquisition Indication – Access slot timing and structure are identical to those defined for RACH – Transmission consists of » » » »

Access preamble(s) - one or several each 4096 chips Collision Detection preamble DPCCH Power Control Preamble (0 or 8 slots) Message of variable length (Nx10 msec)

– PCPCH good for carrying small sized bursty data Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

22

Transport Formats / Configurations ◆

Transport Block (TB) » Basic unit of data exchanged between L1 & MAC for L1 processing

◆

Transport Block Size: Number of bits in a TB.

◆

Transport Block Set (TBS) » A set of TBs exchanged between L1 and MAC at the same time instant using the same transport channel

◆

Transport Block Set Size: Number of bits in a TBS

◆

Transmission Time Interval (TTI) » Periodicity at which a TBS is transferred by the physical layer on to the radio interface - {10, 20, 40, 80 ms} » MAC delivers one TBS to the physical layer every TTI Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

23

Transport Formats / Configurations ◆

Transport Format (TF) – Format offered by L1 to MAC (and vice versa) for the delivery of a TBS during a TTI on a given transport channel (TrCH) – Dynamic part (TB size, TBS size) – Semi-static part (TTI, type/rate of coding,size of CRC) – TB size, TBS size, TTI define the TrCH bit rate before L1 processing » e.g., TB size = 336 bits (320 bit payload + 16 bits RLC header) » TBS size = 2 TBs per TTI, TTI = 10 ms » DCH Bit rate (with RLC header) = 336*2/10 = 67.2 Kbps » User Bit rate (without RLC header) = 320*2/10 = 64 Kbps

– Variable bit rate can be achieved by changing (between TTIs) either the TBS size only, or both the TB size and TBS Size ◆

Transport Format Set (TFS)

– a set of TFs associated with a TrCH – semi-static part of all TFs in a TFS is the same Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

24

Transport Formats / Configurations ◆

Transport Format Combination (TFC) » Multiple TrCHs each having a TF » Authorized combination of the currently valid TFs that can be submitted to L1 on a CCTrCH, containing one TF from each TrCH

◆

Transport Format Combination Set (TFCS) » » » »

A set of TFCs on a CCTrCH. Produced by RNC TFCS is given to MAC by L3 for control MAC chooses between the different TFCs specified in the TFCS MAC has control over only the dynamic part of the TFs. Semi-static part relates to QoS (e.g., quality) and is controlled by RNC admission control » Bit rate can be changed quickly by MAC with no need to L3 signaling ◆

Transport Format Indicator (TFI)

» A label for a specific TF within a TFS. Used between MAC and L1

◆

Transport Format Combination Indicator (TFCI)

» Used to inform the receiving side of the currently valid TFC

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

25

Transport Formats / Configurations Transport Format Combination (TFC) DCH1

TB TTI

TB

TB TTI

TTI

Transport Block Set (TBS)

TB DCH2

TB TTI

Transport Format Set (TFS) Dr. A. Chockalingam

TB

TB

TB

TB

TTI

Transport Format (TF) Dept of ECE, IISc, Bangalore

TTI Transport Format Combination Set (TFCS) 26

TFI and TFCI (Transmitter) E.g: Two transport channels mapped to a single physical channel Transport Chl 1 Transport Block Higher Layer

Transport Block

TFI

Transport Chl 2 Transport Block TFI

Transport Block This dotted line represents the Iur interface in case of NW side

Physical Layer

Coding and Multiplexing

TFCI Physical Control Chl

Physical Data Chl

DPCCH (Q-Chl) Dr. A. Chockalingam

DPDCH (I-Chl)

Dept of ECE, IISc, Bangalore

27

TFI and TFCI (Receiver) Transport Chl 1

Transport Chl 2

Transport Block & EI Higher Layer

Transport Block & EI

TFI

Physical Layer

Transport Block & EI TFI

EI: Error Indication

Decoding and Demultiplexing

TFCI Decode Physical Control Chl

Physical Data Chl

DPCCH (Q-Chl) Dr. A. Chockalingam

Transport Block & EI

DPDCH (I-Chl)

Dept of ECE, IISc, Bangalore

28

TFI and TFCI ◆

Each transport channel is accompanied by a TFI at each time event at which data is expected to arrive from HL

◆

Physical layer combines the TFI info from different transport channels to the TFCI

◆

TFCI is sent on the DPCCH to inform the receiver about the instantaneous transport format combination of the transport channels mapped to the U/L DPDCH transmitted simultaneously

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

29

Transport Format (e.g., Speech) ◆

Conversational Speech (12 Kbps) – 12.2 Kbps max. – TTI: 20 msec – Transport Formats (TF) available: TF

RAB1

RAB2

TF0v 0 x 81 0 x 103 TF1v 1 x 81 1 x 103 two other formats too (see Stds. Doc.)

RAB3 0 x 60 (e.g., silence) 1 x 60 (e.g, active voice)

– TFC: (TF0, TF0, TF0) e.g., during silence (TF1, TF1, TF1) e.g., during active voice periods Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

30

Transport Format (e.g., Data) ◆

Interactive/Background Data (64 Kbps) – 64 Kbps max. – TTI: 20 msec – Transport Block (TB) size = 336 bits – Transport Formats (TF) available: » TF0 - 0 x 336 » TF1 - 1 x 336 » TF2 - 2 x 336 » TF3 - 3 x 336 » TF4 - 4 x 336

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

31

Transport Format (Speech + Data) ◆

Conversational speech (12 Kbps) + Interactive/Background Data (64 Kbps) Voice TrCH

Data TrCH

TFC1: TFC2:

(TF0v, TF0v, TF0v) (TF0v, TF0v, TF0v)

TF0d TF1d

TFC3:

(TF0v, TF0v, TF0v)

TF2d

TFC4:

(TF0v, TF0v, TF0v)

TF3d

TFC5:

(TF0v, TF0v, TF0v)

TF4d

TFC6: TFC7: TFC8: TFC9: TFC10:

(TF1v, TF1v, TF1v) (TF1v, TF1v, TF1v) (TF1v, TF1v, TF1v) (TF1v, TF1v, TF1v) (TF1v, TF1v, TF1v)

TF0d TF1d TF2d TF3d TF4d

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

32

Multiplexing & Channel Coding ◆ ◆ ◆

Data arrives at the coding/mux unit in transport block sets, once every transmission time interval (TTI) TTI depends on the transport channel; {10, 20, 40, 80 ms}) Main steps – – – – – – – – – – –

Add CRC to each block transport block concatenation and block segmentation channel coding first interleaving (per TTI) radio frame segmentation (when TTI > 10 ms) rate matching (repetition or puncturing) multiplexing of transport channels (CCTrCH) insertion of DTX indication bits physical channel segmentation second interleaving (per radio frame, ie., among bits in 1 radio frame) mapping to physical channel

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

33

Multiplexing & Channel Coding (U/L) TrCH-1

CRC Attachment

CRC Attachment

TrBk Concatenation/ Code Block Segmentation

TrBk Concatenation/ Code Block Segmentation

Channel Coding

Channel Coding

Radio Frame Equalization

Radio Frame Equalization

1st Interleaving

1st Interleaving

Radio Frame Segmentation

Radio Frame Segmentation

Rate Matching

Rate Matching

TrCH-2

TrCH Multiplexing CCTrCH

Physical Channel Segmentation

2nd interleaving Dr. A. Chockalingam

Physical Channel Mapping Dept of ECE, IISc, Bangalore

PhCH#1

PhCH#2

34

Multiplexing & Channel Coding (..cntd) ◆

Applicable to DCH, RACH, CPCH, DSCH, BCH, FACH, PCH

◆

CRC – add CRC to each transport block for error detection – CRC calculated on entire transport block – Size of CRC: 24, 16, 12, 8, 0 bits – what CRC size is used for each TrCH is signaled from higher layers

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

35

Multiplexing & Channel Coding (..cntd) ◆

TrBk Concatenation & Code Block Segmentation – all transport blocks in a TTI are concatenated – if no. of bits in a TTI after concatenation (X) is greater than the maximum size of the code block (in the channel coding block), then code block segmentation is done – max. size of the code block (Z) depends on whether » Convolutional code ( Z = 504 bits) or » Turbo code ( Z = 5114 bits) is used for the TrCH

– Code blocks after segmentation are of the same size – Filler bits (zeros) added to 1st coded block to » to make integer number of code blocks, or » if X < 40 bits when Turbo code is used

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

36

Multiplexing & Channel Coding (..cntd) ◆

Channel Coding Type of TrCH

Coding Scheme

Coding Rate

BCH

Convolutional Coding (constraint length = 9)

1/2

PCH RACH DPCH, DCH, DSCH, FACH

1/3, 1/2 Turbo Coding

1/3

If number of coded blocks is greater than 1, they are serially concatenated Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

37

Multiplexing & Channel Coding (..cntd) ◆

Radio Frame Equalization – padding the input bit sequence in order to ensure that the output can be segmented into data segments of equal size – I.e., number of bits per segment is same after radio frame equalization – performed only on the U/L

◆

1st Interleaving – block interleaver – among bits in a TTI Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

38

Multiplexing & Channel Coding (..cntd) ◆

Radio Frame Segmentation – when TTI > 10 msec, input bit sequence is segmented and mapped on to Fi consecutive radio frames

◆

Rate Matching – means that bits on a transport channel are repeated or punctured to ensure that the total bit rate after TrCH multiplexing is identical to the total channel bit rate of the allocated dedicated physical channels – higher layers assign a rate-matching (semi-static) attribute for each transport channel – this attribute is used to calculate the number of bits to repeat or puncture, spreading factor, number of PhCHs needed, rate matching pattern Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

39

Multiplexing & Channel Coding (..cntd) ◆

TrCH Multiplexing – every 10 msec, one radio frame from each TrCH is delivered to the TrCH multiplexing – these radio frames are serially concatenated into a coded composite transport channel (CCTrCH)

◆

Physical Channel Segmentation – when more than once PhCH is used, the physical channel segmentation divides the bits among different PhCHs

◆

2nd Interleaving – among bits within a radio frame Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

40

Multiplexing & Channel Coding (..cntd) ◆

Insertion of Discontinuous Transmission (DTX) Indication Bits – only on the D/L – used to fill up the radio frame with bits – insertion point depends on whether fixed positions (1st Insertion) or flexible positions (2nd Insertion) of the TrCHs in the radio frame are used – During connection setup, NW decides if fixed or flexible position is used for each CCTrCH – DTX Indication bits are not transmitted; they only tell when the Tx must be turned off Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

41

Multiplexing & Channel Coding (..cntd) ◆

Transport Format Detection – TFCI Based Detection – Explicit Blind Detection » using receive power ratio » by use of channel decoding and CRC check

– Guided Detection » Explicit blind detection used on Guiding TrCH » Guiding TrCH has the same TTI as the TrCH under consideration Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

42

Multiplexing & Channel Coding (..cntd) ◆

Blind Transport Format Detection – Using Received Power Ratio (for the case of 2 TFs) » Ratio of the power received on DPDCH (Pd) and DPCCH (Pc) » Full Rate TF: if ratio Pd/Pc > threshold » Zero rate TF: if ratio Pd/Pc < threshold

– Using CRC (for the case of multiple TFs) » Receiver knows only the possible TFs or end bit (thru’ L3 signaling) » Receiver performs FEC (Viterbi) decoding » path metric selection among the surviving paths in the decoding

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

43

D/L Physical Channels ◆

Dedicated D/L Channels – DPDCH – DPCCH

◆

Common D/L Channels – Common PIlot CHannel (CPICH) » Primary CPICH » Secondary CPICH

– Common Control Physical CHannel (CCPCH) » Primary CCPCH, » Secondary CCPCH

– Synchronization CHannel (SCH) » Primary SCH, » Secondary SCH

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

44

Dedicated D/L Physical Channels ◆

Dedicated Physical CHannel (D/L DPCH) – transmits dedicated data generated at L2 and above – time-multiplexes with L1 control bits (Pilot, TPC, TFCI)

◆

D/L DPCH – Time-multiplex of a D/L DPDCH and a D/L DPCCH

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

45

DL Frame Structure ◆

10 msec frames divided into 15 slots 1 Frame = 15 slots = 10 msec S0

S1

S2

S3

S13

S14

1 time slot = 2/3 msec DATA 1 DPDCH

TPC TFCI

DATA 2

DPCCH

DPDCH

Pilot DPCCH

◆

No. of bits in different DPDCH field (Npilot, Ntpc, Ntfci, Ndata1, Ndata2) are given in tables

◆

Which slot format to use is configured (and reconfigured) by higher layers

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

46

D/L Transmission ◆

Multicode Transmission on D/L – Multicode transmission can be employed on the D/L – I.e., CCTrCH is mapped on to several parallel D/L DPCHs using the same spreading factor – In this case, L1 control information is sent only on the first downlink DPCH

◆

Multiple CCTrCHs – In case there are several CCTrCHs mapped to different DPCHs transmitted to the same UE, different spreading factors can be used on DPCHs – multiple CCTrCHs feature for future release Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

47

WCDMA Transmission Rates (D/L) ◆

System Chip Rate : 3.84 Mcps

◆

Symbol Rates on Downlink – Symb Rate

Chl bit rate

SF

7.5 Ks/s

15 Kb/s

512

15 Ks/s

30 Kb/s

256

30 Ks/s

60 Kb/s

128

60 Ks/s

120 Kb/s

64

120 Ks/s

240 Kb/s

32

240 Ks/s

480 Kb/s

16

480 Ks/s

960 Kb/s

8

960 Ks/s

1920 Kb/s

4

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

48

Common D/L Physical Channels ◆

Common Pilot CHannel (CPICH)

– 30 Kbps fixed rate channel (SF = 256) – Primary CPICH » » » » »

Always uses the same channelization code Scrambled by primary scrambling code There is one and only one P-CPICH per cell Broadcast over the entire cell Provides a phase reference for several D/L channels

– Secondary CPICH » » » » »

Uses an arbitrary channelization code of SF=256 Scrambled either by the primary or a secondary scrambling code A cell may contain 0,1, or several S-CPICH Broadcast over entire OR part of a cell A S-CPICH can be a phase reference to some D/L channels (which is communicated to the UE thru’ higher layer signaling)

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

49

Common D/L Physical Channels ◆

Common Control Physical CHannel (CCPCH) – Primary CCPCH (P-CCPCH) » » » »

30 Kbps fixed rate channel with SF=256 Carries BCH transport channel No TPC, TFCI, pilot bits are sent the transport channel mapped to P-CCPCH (I.e., BCH) can only have a fixed predefined TFC

– Secondary CCPCH (S-CCPCH) » » » »

Carries FACH and PCH S-CCPCH can be with TFCI and without TFCI NW decides if TFCI has to be sent So UE should be (mandatory) capable of receiving with or without TFCI (i.e., blind) » S-CCPCH can support multiple TFCs using TFCI – Main difference between CCPCHs and Dedicated Physical Channels : a CCPCH is NOT inner loop Power Controlled Dr. A. Chockalingam Dept of ECE, IISc, Bangalore 50

Common D/L Physical Channels ◆

Synchronization CHannel (SCH) – Downlink signal used for cell search – Consists of Primary and Secondary subchannels – Primary SCH » Uses Primary Sychronization Code (PSC), TX once every slot » PSC is the same for every cell in the system – Secondary SCH » Tx in parallel with Primary SCH » SSC indicates which of the code groups (64 groups) the cell’s DL scrambling code belongs to

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

51

D/L Spreading I DL Physical Serial to Channel data Parallel Conv.

I+jQ

Cd,SF,m

Sdl,n

Q j

Channelisation code: - Differentiate users in a cell - OVSF - UTRAN assigns channelisation codes to diff. phy. chls Scrambling Code: Differentiate cells Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

52

Scrambling Codes ◆

# possible D/L scrambling codes = 2**18 -1 = 262143

◆

Scrambling codes divided into 512 sets – 1 primary scrambling code and 15 secondary scrambling codes – So, there are 512 x 16 = 8192 codes

◆

Each cell is allocated one and only primary scrambling code – The primary CCPCH (Common Control Physical CHannel) is Tx always using this primary scrambling code – Other D/L physical channels can be Tx with either the PSC or SSC from the set associated with the PSC of the cell

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

53

Multiplexing & Channel Coding (D/L) TrCH-1

CRC Attachment

CRC Attachment

TrBk Concatenation/ Code Block Segmentation

TrBk Concatenation/ Code Block Segmentation

Channel Coding

Channel Coding

Rate Matching

Rate Matching

1st Insertion of DTX Indication

1st Insertion of DTX Indication

1st Interleaving

1st Interleaving

Radio Frame Segmentation

Radio Frame Segmentation

2nd Insertion of DTX Indication

TrCH-2

TrCH Multiplexing CCTrCH

Physical Channel Segmentation

2nd interleaving Dr. A. Chockalingam

Physical Channel Mapping

Dept of ECE, IISc, Bangalore

PhCH#1

PhCH#2

54

Multiplexing & Channel Coding (..cntd)

◆

Physical Channel Mapping – on U/L: PhCHs are either completely filled or not used at all – on D/L: No bits in locations with DTX indication » in compressed mode, no bits are mapped to certain slots in a PhCH. Reducing the SF by a factor of 2, 7.5 slots per frame is used in compressed mode

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

55

Multiplexing & Channel Coding (..cntd) ◆

Insertion of Discontinuous Transmission (DTX) Indication Bits – only on the D/L – used to fill up the radio frame with bits – insertion point depends on whether fixed positions (1st Insertion) or flexible positions (2nd Insertion) of the TrCHs in the radio frame are used – During connection setup, NW decides if fixed or flexible position is used for each CCTrCH – DTX Indication bits are not transmitted; they only tell when the Tx must be turned off Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

56

WCDMA Physical Channels

UE

P-CCPCH S-CCPCH DPDCH DPCCH PDSCH PCPCH PRACH

BS

AICH P-SCH S-SCH CSICH CPICH PICH CD/CA-ICH Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

57

Channel Mapping on the U/L Logical Channels

CCCH

DTCH

DCCH

Transport Channels

RACH

DCH

CPCH

Physical Channels

PRACH

Dr. A. Chockalingam

DPDCH

DPCCH

Dept of ECE, IISc, Bangalore

PCPCH

58

Channel Mapping on the D/L Logical Channels

BCCH

PCCH

CTCH

CCCH

DCCH

Transport Channels

BCH

PCH

FACH

DCH

DSCH

Physical Channels

P-CCPCH

S-CCPCH

DPDCH

DPCCH

PDSCH

Dr. A. Chockalingam

Dept of ECE, IISc, Bangalore

DTCH

59