WCDMA for UMTS Training

WCDMA for UMTSby Dr. Hatem MOKHTARI Cirta Consulting LLC

Contents History of the WCDMA Standard Spectrum Allocation Bearer Services CDMA Principles WCDMA Radio Access Network Architecture Physical Layer Radio Interface Protocols Packet Transmission TDD Mode Network Planning

CDMA Principles CDMA System Overview Direct Sequence CDMA

CDMA Principles In FDMA and TDMA systems, traffic channelscannot share the same radio channel at the same time

In Code Division Multiple Access (CDMA)systems, traffic channels share the same radio channel and are distinguished by a Code:

CDMA Principles Frequency hopping (FH) CDMA where traffic channelshop across the same group of narrow-band channels with a different hop sequenceThe Code determines the hop sequence:FH sequenceF1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6

time

Direct Sequence (DS) CDMA where traffic channelsare spread across the same wide-band radio channel using a pseudo-random bit sequence (PRBS). The Code determines the PRBS

CDMA PrinciplesDS CDMA System OverviewA rBaseband signal f PRBS/PN Modulation

A WTransmitted signal f

Transmission

PRBS/PN

ADemodulation

A

Signal recovery

f

Received signal f

WCDMA Main Parameters in WCDMA Spreading and Despreading Rake Reception Power Control Handovers

WCDMAMain Parameters in WCDMA WCDMA is a wideband Direct-Sequence CodeDivision Multiple Access system (DS-CDMA). The chip rate of 3.84 Mchips/s gives a carrier bandwidth of approximately 5MHz WCDMA supports highly variable user data rates. The concept of bandwidth on demand. WCDMA supports 2 basic modes of operation: FDD where separate 5 MHz carrier frequencies are used for uplink and downlink TDD where only one 5 MHz carrier is time shared between uplink and downlink

WCDMAMain Parameters in WCDMA WCDMA supports the operation of asynchronous basestations. WCDMA employs coherent detection on the uplink and downlink based on the use of pilot symbols or common pilot. The WCDMA air interface has been designed to allow advanced CDMA receiver concepts, e.g. multiuser detection and smart adaptive antennas. WCDMA is designed to work in conjunction with GSM.

WCDMASpreading and DespreadingSymbol1

DataChip

-1

Spreading1 -1 1 -1

Spreading Code Spread Signal = Data x Code Despreading

1

Spreading Code Data = Spread Signal x Code Spreading and Despreading in DS-CDMA

-1 1 -1

Spreading and DespreadingWanted Signal1 Desired Spread Signal -1 1 Spreading Code -1 1 -1 8 -8

WCDMA

Data after Despreading Data after Integration

Interfering Signal1 Interfering Spread Signal Interfering Sig. After Despreading Interfering Sig. After Integration -1 1 -1 8 -8

The CDMA Correlation Receiver

WCDMASpreading and Despreading Example of Processing Gain If the data rate of a speech service is 12.2 Kb/s Processing Gain = 10 x log (3.84x106/12.2x103) = 25 dB After despreading Eb/No should be >= 5 dB for speech Desired C/I of the spread signal = 5 - processing Gain = 20 dB In this case the wanted signal power can be 20 dB below the level of the interference or system noise.

Physical Layer Channels Interface Between Higher Layers and Physical Layer Transport Channels Uplink Physical Channels Downlink Physical Channels Transport Channel to Physical Channel Mapping Dedicated Physical Channels

Physical LayerChannels RF Channel Physical Channel Transport Channel (New in UMTS) Logical Channel

Physical LayerInterface Between Higher Layers and Physical LayersTransport Ch 1 Transport Block TFI Transport Block TFI Transport Ch 2 Transport Block Transport Block TFI Transport Block & Error Indication Transport Block & Error Indication TFI Transport Block & Error Indication Transport Block & Error Indication

Higher Layers Physical Layer TFCI Physical Control Ch Coding & Multiplexing Physical Data Ch TFCI Decoding Physical Control Ch Decoding & Demultiplexing Physical Data Ch RECEIVER

TRANSMITTER

Physical LayerTransport Channels

Common Channels (CCHs)

Dedicated Channel (DCH) (Uplink/Downlink)

Broadcast Channel (BCH) (Downlink) Forward Access Channel (FACH) (Downlink)

Paging Channel (PCH) (Downlink)

Common Packet Channel (CPCH) (Uplink) Downlink Shared Channel (DSCH) (Downlink)

Random Access Channel (RACH) (Uplink)

Physical LayerUplink Physical ChannelsDedicated Physical Channels Common Physical Channels

Dedicated Physical Control Channel (Uplink DPCCH)

Physical Random Access Channels (PRACH) Dedicated Physical Data Channels (Uplink DPDCH) Physical Common Packet Channel (PCPCH)

Physical LayerDownlink Physical ChannelsDedicated Physical Channel (Downlink DPCH) (Time multiplex of downlink DPDCH and downlink DPCCH Common Physical Channels

Synchronisation Common Pilot Page Primary Common Channel (SCH) Channel (CPICH) Control Physical Indication Physical Downlink Channel Channel (P-CCPCH) Shared Channel (PICH) Secondary Common (PDSCH) Secondary CPICH Control Physical Channel Acquisition Indication Primary CPICH (S-CCPCH) Channel (AICH)

Physical LayerTransport Channel to Physical Channel MappingTransport Channels BCH FACH PCH RACH CPCH DCH DSCH

Physical Channels

CPICH

S-CCPCH

PCPCH DPDCH

DPCCH SCH

PDSCH

AICH

P-CCPCH

PRACH

PICH

Physical LayerDedicated Physical Channel (DPCH)DPCH DPDCH DPDCH - Dedicated Physical Data Channel Carries dedicated transport channels DPCCH

DPCCH - Dedicated Physical Control Channel Carries control information at layer 1 (known pilot, transport format combination indicator (TFCI), feedback information and transmit power control (TPC) command.

Physical LayerUplink DPCH Frame Structure10ms

0DPDCH

1

2

3

... Data

12 13 14

DPCCH

Pilot

TFCI2560 chips

FBI

TPC

Physical LayerUplink DPDCH data RatesDPDCH Spreading Factor 256 128 64 32 16 8 4 4 with 6 parallel codes DPDCH Channel bit rate (Kb/s) 15 30 60 120 240 480 960 5740 Maximum user data rate with rate coding (approx.) 7.5 kb/s 15 kb/s 30 kb/s 60 kb/s 120 kb/s 240 kb/s 480 kb/s 2.3 Mb/s