WCDMA Channels

WCDMA Channels

10th Aug 2007Deepak

WCDMA Channels

Logical Channels are not actually the channel rather they can defined as a different task performed by the network and the UE at different times. They describes the type of information to be transferred.Logical channels are categorized into control channels and traffic channels.Controls channels carry the control plane informationTraffic Channels carry the user plane information

Transport channels describes how the logical channels to be transferred. Or it can be defined by how and with what characteristics data is transferred over the interface.It comes into two groups:Dedicated ChannelsCommon 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.

Physical Channel

In uplink and downlink direction, each slot in a radio frame 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 US 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 an bi-directional channel.

Logical Channel

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

Transport Channels

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

It comes into two groups:

Dedicated ChannelsCommon Channels

Transport ChannelsDedicated Traffic Channels:

Dedicated Channel (DCH): It is the channel used to send dedicated control and user data between UE and the networks in both uplink & downlink directionEnhanced 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 users packet.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):Its 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 direction.

Physical ChannelsIn 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 likePilot bits (used to support channel estimation at rake receiver)Transmit Power Control (TPC) commands (Used power control)Feedback information (FBI) needed with transmit diversityTransport 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 ChannelsPhysical Random Access Channel (PRACH)

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

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.

Physical ChannelsPhysical 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 ChannelIn 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 slotsThe no. of bits in the data part depends on the spreading factor between 512 and 4 correspondence of 15kbps to 1,920kbps.

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

Slot #0

Slot #1

Slot #i

Slot #14

T

slot

= 2560 chips , 20 bits

1 radio frame: T

f

= 10 ms

Physical Channels

Primary Common Pilot channel (P-CPICH)It has following characteristics:The same channelization code is always usedThe P-CPICH is scrambled by primary scrambling codeThere is only one P-CPICH per cellThe P-CPICH broadcast over the entire cell

Secondary Common Pilot Channel (S-CPICH)It has following characteristics:An arbitrary channelization code is used SF256A S-CPICH may scrambled with primary or secondary scrambling codeThere may be zero, one or several S-CPICH per cellA 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.

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.

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 TFCIPhysical Channels

Physical ChannelsSynchronization ChannelThis 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.

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 chipsEach 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 MappingThe 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-DSCH (HS-DPCCH)

HS-DSCH

PCH

FACH

BCH

RACH

E-DCH

Physical Channels

Transport Channels

DCH

Burst Types Dedicated Physical ChannelThere are four different types of burstsAll 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 1Burst Type 2Burst Type 3Burst Type 41195222081856211229761104928N/A4488552464N/A8244276232N/A16122138116132

Burst Type - IThis burst type used fr both Uplink and DownlinkIt has larger training sequence due to longer midamble fieldData field has 976 chips long, no. of symbol depends on the SFMidamble is 512 chips long and GP is 96 chips period.

Chip number (CN)Length of field in chipsLength of field in symbolsContents of field0-975976Cf table 1Data symbols976-1487512-Midamble1488-2463976Cf table 1Data symbols2464-255996-Guard period

Burst Type - IIThis burst type used for both Uplink and DownlinkIt has shorter training sequence due to longer midamble fieldData field has 1104 chips long, no. of symbol depends on the SFMidamble is 256 chips long and GP is 96 chips period.

Chip number (CN)Length of field in chipsLength of field in symbolsContents of field0-11031104cf table 1Data symbols1104-1359256-Midamble1360-24631104cf table 1Data symbols2464-255996-Guard period

Burst Type - IIIThis burst type used for Uplink onlyIt has longer guard period suitable for initial access or accss to new cell after handoverData field has 976 and 880 chips long, no. of symbol depends on the SFMidamble is 512 chips long and GP is 192 chips period.


Burst Type - IVThis burst type used for downlink MBSFNIt has longer guard period suitable for initial access or accss to new cell after handoverIt has two data fiels each of 1056 chips long, no. of symbol depends on the SFMidamble is 320 chips long and GP is 128 chips period.


TPCTransmission 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 dataTPC information is to be transmitted immediately after the midambleShall be transmitted with same channelization code and timeslot of TFCI

Data symbols

Midamble

Data symbols

GP

TPC field

512/256 chips

2560*T

c

TFCITransmission 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 procedureIn Uplink, independent to the SF of data bits TFCI code is applied with SF 32TFCI is code to be transmitted directly adjacent to the midamble

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WCDMA Channels

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