Radio Channels

WCDMA Radio Channels

The bandwidth allocated over radio access for WCDMA users.

This resource and the functions are classified as different Channels

What is Channel ?

UE UTRAN CN

Uu Iu

Basic UMTS Architecture

USIM

ME

Cu

UE

The 3G Network terminal is called UE and it contains two separate parts, Mobile Equipment (ME) and UMTS Service Identity Module (USIM).

The Interface between USIM and ME is called Cu interface.

User Equipment (UE)

Node B

Node B

RNC

Node B

Node B

RNC

The subsystem controlling the wideband radio access is Universal Terrestrial Radio Access Network (UTRA or UTRAN ).

UMTS Radio Access Network (UTRAN)

Iur

RNS

RNS

Iub

Iub

UMTS Base Station • It is known as Node B. It logically corresponds to GSM BTS.

• It is located between the Uu and Iub interface.

•Convert the data flow between the Iub and Uu interface.

• Participate in radio resources management.

Radio Network Controller (RNC)

•It is located between the Iub and Iu interface.

•It interfaces the core network.

•It also has the interface called Iur for inter-RNS connection.

•It supports Radio Access Bearer (RAB) services with CS and PS data

•It terminates the Radio Resource Control (RRC).

•It controls the mobility and handover within the RAN.

Channel Organization

The Channel organization of the WCDMA is in three layers

• Logical Channel

• Transport Channel

• Physical Channel

• Logical channels (2 types) define what type of data is transferred. 1. Control channels for the transfer of control information 2. Traffic channels for the transfer of user information• Transport channels define how and with which type of characteristics the data is transferred by the physical layer.i.e. Transport channels are defined on the type of the information they transfer, and how it is transferred on the radio interface• Physical channel define the exact physical characteristics of the radio channel.

Channel Organization

Channel Types and their location in UTRAN

UE

Node-B RNC

Logical Channels

Transport Channels

Physical Channels

Different tasks on logical channels NW may perform certain tasks which are common

for all UEs residing in the cell NW must inform UE about the radio environment UE must be paged for knowing its location for

Mobile Terminating calls When there is dedicated, active connection, the

network sends control information concerning the connection

NW sends dedicated user traffic

UMTS RADIO NW ARCHITECTURE

GSM LOGICAL CHANNELS

•1. User Information (Traffic)

2. Signalling Inform.(Control)

THREE TYPES OF CONTROL

CHANNELS

Broadcast Control Channel (BCCH)

Common Control Channel (CCCH)

Dedicated Control Channel (DCCH)

RF Channels Overview• Broadcast Control Channels - BCCH

P-MP FCCH

SCH• Common Control Channels PCH

P-P RACH AGCH

• Dedicated Control Channels - SDCCH

P-P FACCH

SACCH

CMCC SMS SS

Possible Channel Combinations in One Cell

TRX 0

Timeslots

TRX 1

TRX 2

TRX 3

BCCH CCCH CCCH

TCH

SDCCH

SDCCH TCH

0 1 2 3 4 5 6 7

TCH TCHCCCH

TCH TCH TCH TCH TCH TCH TCH

TCH TCH TCH TCH TCH TCH TCH TCH

TCH TCH TCH TCH TCH TCH TCH

CDMA ONE LOGICAL CHANNELS

FORWARD LINK CHANNELS

REVERSE LINK CHANNELS

SUMMARY

WCDMA channels: Common and Dedicated Common channels are used where

information is transmitted to all mobile terminals without distinction. Common Transport channels do not support soft hand off

Dedicated channels are used by a single terminal by associating it with a physical channel, i.e. a code and a frequency. Dedicated Transport channels support soft hand off

Channel Organization

In

Downlink direction

WCDMA Downlink

BCCHBroadcast Control Ch.

PCCHPaging Control Ch.

CCCHCommon Control Ch.

DCCHDedicated Control Ch.

DTCHDedicated Traffic Ch. N

BCHBroadcast Ch.

PCHPaging Ch.

FACHForward Access Ch.

DCHDedicated Ch.

P-CCPCH(*)Primary Common Control Physical Ch.

S-CCPCHSecondary Common Control

Physical Ch.

DPDCH (one or more per UE) Dedicated Physical Data Ch.

DPCCH (one per UE)Dedicated Physical Control Ch.

Pilot, TPC, TFCI bits

SSCi

Logical Channels(Layers 2+)

Transport Channels(Layer 2)

Physical Channels(Layer 1)

DownlinkRF Out

DPCH (Dedicated Physical Channel)One per UE

HS-DSCHHigh Speed DL Shared Ch.

CTCHCommon Traffic Ch.

CPICHCommon Pilot ChannelNull Data

Data Encoding

Data Encoding

Data Encoding

Data Encoding

Data Encoding

HS- PDSCH (one or more per UE) High Speed Physical Downlink shared Channel

S/P

S/P

S/P

I+jQ I/QModulator

Q

I

Cch

Cch 256,1

Cch 256,0

GS

PSC

GP

Sync Codes(*)

* Note regarding P-CCPCH and SCH

Sync Codes are transmitted only in bits 0-255 of each timeslot;P-CCPCH transmits only during the remaining bits of each timeslot

Filter

Filter

Gain

Gain

Gain

SCH (Sync Channel)

DTCHDedicated Traffic Ch. 1

DCHDedicated Ch.

Data Encoding M

UX

MUX

CCTrCHDCHDedicated Ch.

Data Encoding

Sdl,n

Sdl,n

Sdl,n

S/P

Cch GainSdl,n

S/P

C16 GainSdl,n

AICH (Acquisition Indicator Channel)

PICH (Paging Indicator Channel )

Access Indication data

Paging Indication bits S/P

S/P

Cch

CchGain

Gain

Sdl,n

Sdl,n

HS-SCCH (<=4 per UE)High Speed Shared Control Channel .

S/P

C128 GainSdl,n

TFRI, UE Identity, HARQ Data Encoding

HSDPA

Common Downlink Logical Channels

BCCH (Broadcast Control Channel) - Broadcasts cell and system information to all UEPCCH (Paging Control Channel) - Transmits paging information to a UE when the UE’s location is unknownCCCH (Common Control Channel) - Transmits control information to a UE when there is no RRC ConnectionCTCH (Common Traffic Channel) - Traffic channel for sending traffic to a group of UE’s.

DCCH (Dedicated Control Channel) - Transmits control information to a UE when there is a RRC Connection

DTCH (Dedicated Traffic Channel) - Traffic channel dedicated to one UE

Dedicated Downlink Logical Channels

Common Downlink Transport Channels

BCH (Broadcast Channel) - Continuous transmission of system and cell information. As the terminal cannot register to the cell without the possibility of decoding the broadcast channel, this channel is needed for transmission with relatively high power in order to reach all the users within the intended coverage area PCH (Paging Channel) - Carries control information to UE when location is unknown. Transmits the paging message to the terminal on the paging channel of those cells belonging to the location area

Common Downlink Transport ChannelsFACH (Forward Access Channel) - Used for transmission of idle-mode control information to a UE. More than one FACH in a cell for multiple users and the messages transmitted need to include in band identification information to ensure their correct receipt. DSCH (Downlink Shared Channel) - Addition of FACH. Used for dedicated control or traffic data (bursty traffic). Shared by several users .use a variable spreading factor on a frame-by-frame basis. In this case the channelisation codes taking care of the spreading are allocated from the same branch of the code tree to ease the terminal implementation

DSCH code tree

Mapping of Channels (Downlink Direction)

BCCH PCCH CTCH CCCH DCCH DTCH

BCH PCH FACH DCH DSCH

Logical Channels

Transport Channels

Channel Organization

In

Uplink direction

Logical Channels(Layers 2+)

Transport Channels(Layer 2)

Physical Channels(Layer 1)

UplinkRF Out

UEScrambling

Code

I+jQI/Q

Mod.Q

I Filter

Filter

I

DPDCH #1Dedicated Physical Data Ch.

DPDCH #3 (optional)Dedicated Physical Data Ch.

DPDCH #5 (optional) Dedicated Physical Data Ch.

DPDCH #2 (optional) Dedicated Physical Data Ch.

DPDCH #4 (optional) Dedicated Physical Data Ch.

DPDCH #6 (optional) Dedicated Physical Data Ch.

Q

DPCCHDedicated Physical Control Ch.Pilot, TPC, TFCI bits

Chd,3 Gd

Chd,5 Gd

Chd,2 Gd

Chd,4 Gd

Chd,6 Gd

Ch256,0 Gd

j

DCCHDedicated Control Ch.

DTCHDedicated Traffic Ch. N

DCHDedicated Ch.

Data Encoding

DTCHDedicated Traffic Ch. 1

DCHDedicated Ch.

Data Encoding M

UX

CCTrCH

DCHDedicated Ch.

Data Encoding

HS-DPCCHHigh Speed Dedicated Physical Control Ch.

Chd,1 Gd

CCCHCommon Control Ch.

RACHRandom Access Ch.

PRACHPhysical Random Access Ch.

Data Coding

j

RACH Control Part

Chd Gd

Chc Gc

Ch256 Gd

ACK, CQIHSDPA

j

WCDMA Uplink

Uplink Logical Channels

In the Uplink direction the logical channel requirement is smaller. There are only three logical channels

CCCH , DTCH and DCCH

These abbreviation have the same meaning as in the downlink direction

Common Uplink Transport Channels

Uplink Transport Channels

RACH Random Access Channel - Carries access requests, control information - Subject to random access collisions

Dedicated Uplink Transport Channels

DCH Dedicated Channel - Carries dedicated traffic and control data from one UE

Mapping of Channels (Uplink Direction)

CCCH DTCH DCCH

RACH DCH

Logical Channels

Transport Channels

Transport Channels Each transport channel is accompanied by the

Transport Format Indicator (TFI) at each time event at which data is expected to arrive for the specific transport channel from the higher layers.

The physical layer combines the TFI information from different transport channels to the Transport Format Combination Indicator (TFCI).

The TFCI is transmitted in the physical control channel to inform the receiver which transport channels are active for the current frame;

Transport Channels

Mapping with Physical Channels

(Downlink Direction)BCCH PCCH CTCH CCCH DCCH DTCH

BCH PCH FACH DCH DSCH

Logical

Channels

Transport

Channels

P-CCPCH S-CCPCH DPDCH DPCCH PDSCH Physical

Channels

Mapping with Physical Channels

(Uplink Direction)CCCH DTCH DCCH

RACH DCH

Logical Channels

Transport Channels

PRACH DPDCH DPCCH Physical Channels

Features of Physical Channel Data generated at higher layers is carried

over the air on physical channels. Physical channels are not directly visible to

higher layers and are mandatory from the system function point of view, to be transmitted from every base station

Support variable bit rate transport channels to offer bandwidth-on-demand services and able to multiplex several services to one connection.

Physical Channel Physical channels exist in Uu interface and

RNC is not aware of their structure at all. (in GSM, BSC recognises the physical chl and their structure)

Instead of physical channels, RNC sees the transport channels where the different information flows over Uu interface (on physical channel) is mapped to the transport chl by Node B

Physical Channels

The physical channel actually form the physical existence of the Uu interface between the UE domain and access domain.

UE

Node-B

Physical Channels

Uu

WCDMA Physical Channel’s structure

• Each WCDMA user is allocated with one

radio frame

•One Frame length period is 10ms.

• One frame is divided into 15 slots.

• 1 slots = 10/15 ms = 0.666ms.

• One frame is able to handle 38400 chips.

• One slot in a frame carry 2560 chips.•The frame structure also employs a longer period, called the system frame period. The paging procedure or random access procedure, are examples of procedures that need a longer period than 10 ms

Physical Channel’s structure Each slot consists of a no. of symbols which varies

according to the bit rate of the service to be transmitted. It is the minimum element of the physical channel for which the transmission power is maintained constant. By means of power control, the power is increased or decreased at each slot

Symbol: this is the User information (bit rate) and each symbol is multiplied by a no. of chips equal to the spreading factor of the service to be transmitted in order to obtain a constant 2560 chips per slot and also 3.84Mchips per second chip rate

User Bitrate and Spreading FactorSF Chiprate

Mchips/sUser BitrateUplink

3,84

3,84

3,84

3,84

3,84

3,84

3,84

256

128

64

32

16

8

4

15

30

60

120

240

480

960

3,84

3,84

3,84

3,84

3,84

3,84

3,84

3,84

512

256

128

64

32

16

8

4

15

30

60

120

240

480

960

1920

SF ChiprateMchips/s

User BitrateDownlink

SF ChiprateMchips/s

User BitrateUplink

3,84

3,84

3,84

3,84

3,84

3,84

3,84

256

128

64

32

16

8

4

15

30

60

120

240

480

960

Uplink Dedicated Physical Channels

In U/L dual BPSK modulation is used DPDCH & DPCCH channels are transmitted

independently on modulator components I &Q

The 2 data streams are multiplied by two different spreading sequences

Spreading factor for DPCCH channel is always 256 and for DPDCH, SF varies in accordance with data rate.

DPDCH

DPCCH

CCH,di

CCH,di

Q

I

IQMux

I+jQ

Cscramb

BPSK (dual)modulation

CCH,di:Channelization codes (OVSF codes, 4 - 256 chips)Cscramb:Scrambling code (long Gold code, 38400 chips, or short VL Kasami code, 256 chips)

Uplink Spreading and Modulation

Downlink Dedicated Physical Channels

In D/L QPSK modulation is used. Multiplexed DPDCH & DPCCH channels

data stream is divided between the two components ( I & Q )of the modulator.

The resulting two streams are multiplied by the spreading sequence and transmitted.

DPDCH/

DPCCH

S Pbits to

symbols

Cch

OVSF codes ensure DL orthogonality even with different rates and spreading factors for different users

Cch: Channelization codes (OVSF codes, 4-512 chips)

Cscramb: Downlink scrambling code (Gold code, 38400 chips)

Cscramb

Downlink Spreading and Modulation

QPSKmodulation

I

Q

Common Downlink Physical Channels Primary Common Control Physical Channel (Primary CCPCH)

The physical channel carrying the Broadcast Channel (BCH).

Needs to be demodulated by all the terminals in the system.

The parameters with respect to, the channel coding and spreading code etc. are conveyed.

Common Downlink Physical Channels Secondary Common Control P.Channel (Secondary CCPCH)

Carries two different common transport channels: the Forward Access Channel (FACH) and the Paging Channel (PCH).

In the minimum configuration each cell has at least one Secondary CCPCH.

The Secondary CCPCH does not contain power control information

Dedicated Downlink

Physical ChannelsDedicated Downlink Physical Data Channel (DPDCH) - Used for sending dedicated user data .Dedicated Downlink Physical Control Channel (DPCCH) - Used for transmitting the control information during the dedicated connection e.g power control information.The bit rate of the DPCCH is constant, while the bit rate of DPDCH can change from frame to frame.

Shared Downlink

Physical ChannelsHigh-Speed Physical Downlink Shared Channel (HS-PDSCH) - Used for sending users data (Shared mode).HS-SCCH - High-Speed Shared Control Channel(s) - physical downlink channel that carries control information how to decode the information on HS-PDSCH and which UE that shall decode it.

Signalling channels

Physical channels which are not associated with a transport channel

They are used to transport physical layer information that does not need to be sent to the higher layers

1. Common Pilot Channel (CPICH)

An un modulated code channel, which is scrambled with the cell-specific primary scrambling code.

Aid the channel estimation at the terminal for the dedicated channel and provide the channel estimation reference for the common channels when they are not associated with the dedicated channels

1. Common Pilot Channel (CPICH)

Primary CPICH is always under the primary scrambling code with a fixed channelisation code allocation and there is only one such channel for a cell or sector. Used in the measurements for the handover and cell selection/reselection.

Secondary CPICH may have any channelisation code of length 256 and intended for service provision at specific ‘hot spots’or places with high traffic density.

2. Synchronisation Channel (SCH)

Is needed for the cell search. The Primary SCH uses a 256-chip spreading sequence

identical in every cell. The Secondary SCH uses sequences with different code word

combination possibilities representing different code groups. Once the terminal has identified the secondary synchronisation channel, it has obtained frame and slot synchronisation as well as information on the group the cell belongs to. There are 64 different code groups in use, pointed out by the 256 chip sequences sent on the secondary SCHs.

3. Random Access Channel (RACH)

To register the terminal after power-on to the network or to perform location update or to initiate a call.

The RACH that can be used for initial access has a relatively low payload size, since it needs to be usable by all terminals.

The ability to support 16 kbps data rate on RACH is a mandatory requirement for all terminals regardless of what kind of services they provide.

4. Acquisition Indicator Channel (AICH)

AICH is used to indicate from the base station to inform the mobile terminal that there is a message on the FACH channel in response to an access attempt.

For the detection of AICH the terminal needs to obtain the phase reference from the common pilot channel.

5. Paging Indicator Channel (PICH)

Operated together with the Paging Channel (PCH) to provide terminals with efficient sleep mode operation.

PICH is in downlink and use a channelisation code of length 256. The paging indicators occur once per slot on the corresponding physical channel, the Paging Indicator Channel (PICH) to provide the information about the message in PCH

For detection of the PICH the terminal needs to obtain the phase reference from the CPICH and as PICH needs to be heard by all terminals in the cell, it needs to be sent at high power level without power control.