WCDMA Channels

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WCDMA Channels 10th Aug 2007 Deepak

WCDMA Channels Logical Channels are not actually channels but rather they can be defined as different tasks performed by the network and the UE at different times. • They describe the type of information to be transferred. •Logical channels are categorized into control channels and traffic channels. •Control channels carry the control plane information •Traffic Channels carry the user plane information Transport channels describes how the logical channels will be transferred, or it can be defined as how and with what characteristics data is transferred over the interface. It comes into two groups: Dedicated Channels Common Channels

Radio Frame Structure In WCDMA the information is spread over 5MHz band (Wide Bandwidth). There are separate radio channels for both uplink and downlink of 5MHz. One radio frame consist of 38400 chips and 15 slots. The duration of the radio frame is 10ms which have ship rate of 3.84 Mcps. Each slots in the radio frame comprises of 2650 chips. Radio Frame (10ms) frame #i

frame #i+1

Time Slot (2560*Tc) timeslot #0

timeslot #1

timeslot #2

timeslot #13

timeslot #14

Physical Channel In uplink and downlink direction, each slot in a radio frame is defined with a code or a set of codes that carries a set of common and dedicated channels called Physical Channel. The information rate of the channel varies from 15 kbps to 1920 kbps for downlink and 30 kbps to 1920 kbps corresponding to available Spreading Factor. In Downlink spreading factor from 256 to 4 and in downlink from 512 to 4. • Physical channels are the transmission media providing platform (radio) through which information is going to be transferred • Physical Channels means different kinds of bandwidths allocated for different purposes, its actually is the physical existence of the Uu interface between UE domain and Access domain. • Physical channel are defined by specific carrier freq, scrambling and channelization code

Logical Channel Broadcast Control Channel (BCCH): It broadcast system control information for all mobiles in a cell like Code values in the cell, neighbors information, allowed power levels in downlink direction. Paging Control Channel (PCCH): It transfer paging information in downlink direction. Network page the mobile to discover the UE location or UE in a cell connected state. Common Control Channel (CCCH): Network may have certain tasks which are or may be common to UE in the cell. Its being used in both direction downlink & uplink. The CCCH is also used when UE is accessing a new cell after cell reselection. Dedicated Control Channel (DCCH) When there is dedicated/active connection means RRC connection between the network and the mobile, the control information transferred using DCCH. Its a bi-directional channel.

Logical Channel Dedicated Traffic Channel (DTCH): It is used transfer the user data between the network and the UE in both uplink and downlink directions. Common Traffic Channel (CTCH): It is used to transfer the data from one point to all mobiles or a specified group of mobiles.

Transport Channels  

Transport channels describes how the logical channels to be transferred Transport channel is defined by how and with what characteristics data is transferred over the interface.



It comes into two groups:

 

Dedicated Channels Common Channels

Transport Channels  Dedicated Traffic Channels: Dedicated Channel (DCH): It is the channel used to send dedicated control and user data between UE and the network in both uplink & downlink directions Enhanced Dedicated Channel (E-DCH): It is a enhanced uplink transport channel.

 Common Transport Channel : Random Access Channel (RACH): It is used to send a control information from UE in the uplink direction. Also may carry short user packets. Common Packet Channel (CPCH): Its an uplink shared channel used for packet data. Several UE can use the same channel for data transfer.

Transport Channels Forward Access Channel (FACH): It is a downlink common channel used to send small amounts of control and user data. Downlink Shared Channel (DSCH): It is common channel used to send dedicated control and user data. Broadcast Channel (BCH): It broadcast system information in the downlink direction for all mobile stations in a cell. Paging Channel (PCH): It’s a downlink common channel used to send paging notification messages. Dedicated Channel (DCH) It is a channel that is used to send dedicated control and user data between the UE and the network in both directions.

Physical Channels 

In Uplink there are both dedicated and common physical channels.

Dedicated Channels: Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH) Common Channels: Physical Random Access Channel Physical Common Packet Channel

Physical Channels Dedicated Physical Control Channel For each radio link, there is one DPCCH, it carries control information like  Pilot bits (used to support channel estimation at rake receiver)  Transmit Power Control (TPC) commands (Used power control)  Feedback information (FBI) needed with transmit diversity  Transport Format Combination Indicator (TFCI) Spreading factor is always 256.

Physical Channels Data Ndata bits

DPDCH

T slot = 2560 chips, N data = 10*2 k bits (k=0..6) Pilot N pilot bits

DPCCH

TFCI NTFCI bits

FBI NFBI bits

TPC N TPC bits

Tslot = 2560 chips, 10 bits

Slot #0

Slot #1

Subframe #0

Slot #2

Subframe #1

Slot #3

Subframe #2

1 subframe = 2 ms 1 radio frame: T f = 10 ms

Slot #i

Subframe #3

Slot #14

Subframe #4

Physical Channels Dedicated Physical Data Channel Each radio link may have no DPDCHs or several DPDCHs.  Spreading factor for the DPDCH can be between 256 and 4.  DPCCH & DPDCH are time – multiplexed in downlink but uplink these are I/Q modulation.

Physical Channels  Physical Random Access Channel (PRACH) It carries the Random Access Channel (RACH transport Channel). UE uses when physical random access procedure is initiated. Preamble

Preamble

Preamble

4096 chips

Preamble 4096 chips

Message part 10 ms (one radio frame)

Preamble

Preamble

Message part 20 ms (two radio frames)

Physical Channels RACH Preamble Part Each preamble is of length 4096 chips and consist of 256 repetitions of a signature of length 16 chips. RACH Message Part The 10 ms message part spilt into 15 slots each length of 2560 ships. Each slot consist of data part onto which RACH transport part is mapped and control part that carries layer 1 control information. The 20ms message consists of two consecutive 10ms message part radio frames. Data Ndata bits

Data Pilot Npilot bits

Control

TFCI NTFCI bits

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

Slot #0

Slot #1

Slot #i Message part radio frame T RACH = 10 ms

Slot #14

Physical Channels  Physical Common Packet Channel (PCPCH) It carries Common Packet Channel (CPCH Transport Channel). The access transmission consists of Access Preambles (AP), one collision Detection Preamble (CDP), a DPCCH Power Control Preamble (PCP) and message. Check out the Structure from ECE book.

Physical Channels Downlink Dedicated Channel  In downlink there is only one dedicated channel DPCH. The control data and user data are time multiplexed with one DPCH.  The length of frame is 10 ms divided into 15 slots  The no. of bits in the data part depends on the spreading factor between 512 and 4 correspondence of 15kbps to 1,920kbps.

DPCCH

DPDCH Data1 Ndata1 bits

TPC NTPC bits

TFCI NTFCI bits

DPDCH

DPCCH

Data2 Ndata2 bits

Pilot Npilot bits

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

Slot #0

Slot #1

Slot #i One radio frame, Tf = 10 ms

Slot #14

DPCCH + DPDCH

Physical Channels Common Pilot Channel It has pre-defined bit sequence transmitted with a bit rate of 30 Kbps (Fixed Scrambling code 256) CPICH is divided into pilot channels: Primary Common Pilot Channel (P-CPICH) Secondary Common Pilot Channel (S-CPICH) Reason for low bit rate as it is transmitted with high power to reduce the interference. It is phase reference, must be transmitted in whole cell. Pre-defined bit sequence Tslot = 2560 chips , 20 bits

Slot #0

Slot #1

Slot #i 1 radio frame: Tf = 10 ms

Slot #14

Physical Channels Primary Common Pilot channel (P-CPICH) It has following characteristics:

•The same channelization code is always used •The P-CPICH is scrambled by primary scrambling code •There is only one P-CPICH per cell •The P-CPICH broadcast over the entire cell

Secondary Common Pilot Channel (S-CPICH) It has following characteristics: •An arbitrary channelization code is used SF256

•A S-CPICH may scrambled with primary or secondary scrambling code •There may be zero, one or several S-CPICH per cell •A S-CPICH transmitted over the entire cell or part of the cell

Physical Channels Primary Common Control Physical Channel (P-CCPCH) It has fixed bit rate of 30 Kbps (Fixed Scrambling code 256) There are no TPC, Pilot bits and first 256 chips of the slot are used for the primary and secondary synchronization Channel. This used to carry the FACH and the PCH. 256 chips Data Ndata1=18 bits

(Tx OFF)

Tslot = 2560 chips , 20 bits

Slot #0

Slot #1

Slot #i 1 radio frame: Tf = 10 ms

Slot #14

P-CCPCH + SCH

Physical Channels Secondary Common Control Physical Channel (S-CCPCH) It has variable bit rate from 30kbps to 1,920 kbps. There are data bits, pilot bits and optional TFCI bits. It is transmitted only to smaller are of the cell. TFCI NTFCI bits

Data Ndata1 bits

Pilot Npilot bits

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

Slot #0

Slot #1

Slot #i 1 radio frame: Tf = 10 ms

Slot #14

Physical Channels The only difference between the P-CCPCH and S-CCPCH the transport channel mapped on this can only have fixed predefined transport format combination and in case S-CCPCH support multiple transport format combination using TFCI

Physical Channels Synchronization Channel This channel used in the cell search procedure. It is divided into the Primary Synchronization and Secondary Synchronization Channel  Primary Synchronization Channel It carries primary synchronization codes transmitted in each slot of a radio frame. It is same for cells in the network.  Secondary Synchronization Channel It consist of the secondary Synchronization codes (SSC). System selects the SSC to be transmitted in a slot, based on the scrambling code group and the slot number. Slot #0 Primary SCH Secondary SCH

acp i,0

acs

Slot #1 acp

Slot #14 acp

i,1

i,14

acs

acs

256 chips 2560 chips One 10 ms SCH radio frame

Physical Channels Physical Downlink Shared Channel (PDSCH) It is used for data transmission by one or-several simultaneous users in the downlink direction. CD/CA-ICH The collision Detection Assignment Indicator Channel is used in the CPCH Access Procedure CSICH The CPCH Status Indicator Channel (CSICH) is associated with a CPCH. This is uses the free spaces that occurs in the AICH. It is used to inform the UE about CPCH existence and configuration. The duration of CSICH is 20ms. Each frame consist of 15 slots. The length of slot is 40 bits. Each slot has a part that is no transmitted and a status indicator part that includes 8 status indicator bits.

Physical Channels Acquisition Indicator Channel (AICH) It is used in a random access procedure by the network to indicate that the RACH preamble was detected.  It has 15 consecutive access slots.  Length of access slot is 5120 chips  Each access slot is further divided into 32 Acquisition indicators and one part has no transmission. AI part =

4096 chips, 32 real-valued signals

a0 a1 a2

AS #14

AS #0

AS #1

a30 a31

AS #i 20 ms

1024 chips Transmission Off

AS #14

AS #0

Channel Mapping •The data can be sent through logical layer via different channels in the transport layer. •And also one transport channel can be sent via different physical channels.

•These selection of channels in the transport and physical layer depends on the data itself and radio resource management and its parameters.

Transport Channels DCH

E-DCH

RACH

BCH FACH PCH

HS-DSCH

Physical Channels

Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH) Fractional Dedicated Physical Channel (F-DPCH) E-DCH Dedicated Physical Data Channel (E-DPDCH) E-DCH Dedicated Physical Control Channel (EDPCCH) E-DCH Absolute Grant Channel (E-AGCH) E-DCH Relative Grant Channel (E-RGCH) E-DCH Hybrid ARQ Indicator Channel (E-HICH) Physical Random Access Channel (PRACH) Common Pilot Channel (CPICH) Primary Common Control Physical Channel (PCCPCH) Secondary Common Control Physical Channel (SCCPCH) Synchronisation Channel (SCH) Acquisition Indicator Channel (AICH) Paging Indicator Channel (PICH) MBMS Notification Indicator Channel (MICH) High Speed Physical Downlink Shared Channel (HSPDSCH) HS-DSCH-related Shared Control Channel (HSSCCH) Dedicated Physical Control Channel (uplink) for HS-

Burst Types – Dedicated Physical Channel    

There are four different types of bursts All contains two data fields, midamble and GP. Length of each is different in each bursts. The no. of data symbol depends on SF or burst type. Spreading factor (SF)

Burst Type 1

Burst Type 2

Burst Type 3

Burst Type 4

1

1952

2208

1856

2112

2

976

1104

928

N/A

4

488

552

464

N/A

8

244

276

232

N/A

16

122

138

116

132

Burst Type - I    

This burst type used for both Uplink and Downlink It has larger training sequence due to longer midamble field Data field has 976 chips long, no. of symbol depends on the SF Midamble is 512 chips long and GP is 96 chips period. Chip number (CN)

Length of field in chips

Length of field in symbols

Contents of field

0-975

976

Cf table 1

Data symbols

976-1487

512

-

Midamble

1488-2463

976

Cf table 1

Data symbols

2464-2559

96

-

Guard period

Data symbols 976 chips

Midamble 512 chips 2560*Tc

Data symbols 976 chips

GP 96 CP

Burst Type - II    

This burst type used for both Uplink and Downlink It has shorter training sequence due to longer midamble field Data field has 1104 chips long, no. of symbol depends on the SF Midamble is 256 chips long and GP is 96 chips period. Chip number (CN)

Length of field in chips

Length of field in symbols

Contents of field

0-1103

1104

cf table 1

Data symbols

1104-1359

256

-

Midamble

1360-2463

1104

cf table 1

Data symbols

2464-2559

96

-

Guard period

Data symbols 1104 chips

Midamble 256 chips 2560*Tc

Data symbols 1104 chips

GP 96 CP

Burst Type - III    

This burst type used for Uplink only It has longer guard period suitable for initial access or accss to new cell after handover Data field has 976 and 880 chips long, no. of symbol depends on the SF Midamble is 512 chips long and GP is 192 chips period. Chip number (CN)

Length of field in chips

Length of field in symbols

Contents of field

0-975

976

Cf table 1

Data symbols

976-1487

512

-

Midamble

1488-2367

880

Cf table 1

Data symbols

2368-2559

192

-

Guard period

Data symbols 976 chips

Midamble 512 chips 2560*Tc

Data symbols 880 chips

GP 192 CP

Burst Type - IV    

This burst type used for downlink MBSFN It has longer guard period suitable for initial access or accss to new cell after handover It has two data fiels each of 1056 chips long, no. of symbol depends on the SF Midamble is 320 chips long and GP is 128 chips period.

Chip number (CN)

Length of field in chips

Length of field in symbols

Contents of field

0-1055

1056

Cf table 1

Data symbols

1056-1375

320

-

Midamble

1376-2431

1056

Cf table 1

Data symbols

2432-2559

128

-

Guard period

Data symbols 1056 chips

Midamble 320 chips

2560*Tc

Data symbols 1056 chips

GP 128 CP

TPC    

Transmission of TPC burst is done in the data parts of traffic burst. Data in TPC is always transmit at SF 32 irrespective SF of user data TPC information is to be transmitted immediately after the midamble Shall be transmitted with same channelization code and timeslot of TFCI

TPC field Data symbols

Midamble 512/256 chips 2560*Tc

Data symbols

GP

TFCI    

Transmission of TFCI is done in the data parts of the respective physical channel. In Downlink the TFCI code word bit and data bit subjected to the same spreading procedure In Uplink, independent to the SF of data bits TFCI code is applied with SF 32 TFCI is code to be transmitted directly adjacent to the midamble 1st part of TFCI code word

Data symbols

2nd part of TFCI code word

Midamble

512/320/256 chips

2560*Tc

Data symbols

GP

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