WCDMA Channels

WCDMA Channels10th Aug 2007

Deepak

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 ChannelsCommon Channels

WCDMA Channels

Radio Frame StructureIn 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.

frame #i frame #i+1

timeslot #0 timeslot #1 timeslot #2 timeslot #13 timeslot #14

Radio Frame (10ms)

Time Slot (2560*Tc)

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

Physical 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

Logical ChannelDedicated 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 directionsEnhanced 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 ChannelsForward 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 ChannelPhysical Common Packet Channel

Physical ChannelsDedicated Physical Control ChannelFor 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

Pilot N pilot bits

TPC N TPC bits

Data N data bits

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

T slot = 2560 chips, 10 bits

1 radio frame: T f = 10 ms

DPDCH

DPCCH FBI

N FBI bits TFCI

N TFCI bits

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

Slot #2 Slot #3

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

1 subframe = 2 ms

Physical ChannelsDedicated 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.Message partPreamble

4096 chips10 ms (one radio frame)

Preamble Preamble

Message partPreamble

4096 chips 20 ms (two radio frames)

Preamble Preamble

Physical ChannelsRACH Preamble PartEach preamble is of length 4096 chips and consist of 256 repetitions of a

signature of length 16 chips.RACH Message PartThe 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.

Pilot Npilot bits

DataNdata bits


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

Message part radio frame TRACH = 10 ms

Data

ControlTFCI

NTFCI bits

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 ChannelsDownlink 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.

One radio frame, Tf = 10 ms

TPC NTPC bits



Data2Ndata2 bits

DPDCH

TFCI NTFCI bits

Pilot Npilot bits

Data1Ndata1 bits

DPDCH DPCCH DPCCH

DPCCH + DPDCH

Physical ChannelsCommon Pilot ChannelIt 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

1 radio frame: Tf = 10 ms

Physical ChannelsPrimary 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 ChannelsPrimary 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.

Data Ndata1=18 bits


Tslot = 2560 chips , 20 bits


(Tx OFF)

256 chips

P-CCPCH + SCH

Physical ChannelsSecondary 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.



Pilot Npilot bits

Data Ndata1 bits


TFCI NTFCI bits

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

Physical ChannelsSynchronization ChannelThis channel used in the cell search procedure. It is divided into the Primary

Synchronization and Secondary Synchronization Channel Primary Synchronization ChannelIt carries primary synchronization codes transmitted in each slot of a radio frame. It is

same for cells in the network. Secondary Synchronization ChannelIt 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.

PrimarySCH

SecondarySCH

256 chips

2560 chips

One 10 ms SCH radio frame

acsi,0

acp

acsi,1

acp

acsi,14

acp

Slot #0 Slot #1 Slot #14

Physical ChannelsPhysical Downlink Shared Channel (PDSCH)It is used for data transmission by one or-several simultaneous users in the

downlink direction.CD/CA-ICHThe collision Detection Assignment Indicator Channel is used in the CPCH

Access ProcedureCSICHThe 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 ChannelsAcquisition 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. 1024 chips

Transmission Off

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

a 1 a 2 a 0 a 31 a 30

AI part = 4096 chips, 32 real-valued signals

20 ms

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.

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 (E-DPCCH) 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 (P-CCPCH) Secondary Common Control Physical Channel (S-CCPCH) Synchronisation Channel (SCH) Acquisition Indicator Channel (AICH) Paging Indicator Channel (PICH) MBMS Notification Indicator Channel (MICH) High Speed Physical Downlink Shared Channel (HS-PDSCH) HS-DSCH-related Shared Control Channel (HS-SCCH) Dedicated Physical Control Channel (uplink) for HS-

Transport Channels

DCH

RACH

BCH

FACH

PCH

Physical Channels

HS-DSCH

E-DCH

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 field0-975 976 Cf table 1 Data symbols

976-1487 512 - Midamble

1488-2463 976 Cf table 1 Data symbols

2464-2559 96 - Guard period

Data symbols976 chips

Midamble512 chips


GP96CP

2560*Tc

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


Midamble256 chips

GP96CP

2560*Tc


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.


Midamble512 chips

GP192CP

2560*Tc


Chip number (CN) Length of field in chips Length of field in symbols Contents of field


976-1487 512 - Midamble


2368-2559 192 - Guard period

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.


Midamble 320 chips


GP 128 CP

2560*Tc

Chip number (CN) Length of field in chips Length of field in symbols Contents of field0-1055 1056 Cf table 1 Data symbols

1056-1375 320 - Midamble


2432-2559 128 - Guard period

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

Data symbols Midamble Data symbols GP

TPC field

512/256 chips

2560*T c

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

Data symbols Midamble Data symbols GP

512/320/256 chips

2560*Tc

1st part of TFCI code word 2nd part of TFCI code word

Questions and discussion

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