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WCDMA for UMTS by Dr. Hatem MOKHTARI Cirta Consulting LLC
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Page 1: WCDMA for UMTS Training

WCDMA for UMTS

by Dr. Hatem MOKHTARICirta Consulting LLC

Page 2: WCDMA for UMTS Training

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

Page 3: WCDMA for UMTS Training

CDMA Principles

• CDMA System Overview

• Direct Sequence CDMA

Page 4: WCDMA for UMTS Training

CDMA Principles

• In FDMA and TDMA systems, traffic channels cannot 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:

Page 5: WCDMA for UMTS Training

CDMA Principles

• Frequency hopping (FH) CDMA where traffic channels hop across the same group of narrow-band channels with a different hop sequence

The Code determines the hop sequence:

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

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:F7:F8:F1:F2:F3:F4:F5:F6

FH sequence

time

Page 6: WCDMA for UMTS Training

CDMA PrinciplesDS CDMA System Overview

Demodulation

PRBS/PN

A

f Received signal

A

f Signal recovery

A

f Baseband signal

A

f

W

Transmitted signal

Transmission

Modulation

PRBS/PN

r

Page 7: WCDMA for UMTS Training

WCDMA

• Main Parameters in WCDMA

• Spreading and Despreading

• Rake Reception

• Power Control

• Handovers

Page 8: WCDMA for UMTS Training

WCDMAMain Parameters in WCDMA

• WCDMA is a wideband Direct-Sequence Code Division 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

Page 9: WCDMA for UMTS Training

WCDMAMain Parameters in WCDMA

• WCDMA supports the operation of asynchronous base stations.

• 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. multiuserdetection and smart adaptive antennas.

• WCDMA is designed to work in conjunction with GSM.

Page 10: WCDMA for UMTS Training

WCDMASpreading and Despreading

1

-1

1

-1

1

-1

1

-1

1

-1

Chip

Despreading

Data

Spreading Code

Spread Signal = Data x Code

Spreading Code

Data = Spread Signal x Code

Symbol

Spreading

Spreading and Despreading in DS-CDMA

Page 11: WCDMA for UMTS Training

WCDMA

Interfering Signal

Wanted Signal

The CDMA Correlation Receiver

Desired Spread Signal

Spreading Code

Data after Despreading

Data after Integration

Interfering Spread Signal

Interfering Sig. After Despreading

Interfering Sig. After Integration

1

-1

1

-1

1

-18

-8

1

-11

-18

-8

Spreading and Despreading

Page 12: WCDMA for UMTS Training

WCDMA

Example of Processing Gain

If the data rate of a speech service is 12.2 Kb/sProcessing Gain = 10 x log (3.84x106/12.2x103) = 25 dB

After despreading Eb/No should be >= 5 dB for speechDesired C/I of the spread signal = 5 - processing Gain = -

20 dBIn this case the wanted signal power can be 20 dB below

thelevel of the interference or system noise.

Spreading and Despreading

Page 13: WCDMA for UMTS Training

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

Page 14: WCDMA for UMTS Training

Physical Layer

Channels

•RF Channel

•Physical Channel

•Transport Channel (New in UMTS)

•Logical Channel

Page 15: WCDMA for UMTS Training

Physical LayerInterface Between Higher Layers and Physical Layers

TRANSMITTER RECEIVER

Transport Block

Transport BlockTFI TFI

Transport Block & Error Indication

Transport Block & Error Indication

TFITransport Block & Error Indication

Transport Block & Error Indication

Transport Block

Transport BlockTFI

Higher Layers

Physical Layer

Coding & MultiplexingTFCI TFCI Decoding

Decoding & Demultiplexing

Physical Control Ch

Physical Data Ch

Physical Control Ch

Physical Data Ch

Transport Ch 1 Transport Ch 2

Page 16: WCDMA for UMTS Training

Physical LayerTransport Channels

Common Channels (CCHs) Dedicated Channel (DCH)

(Uplink/Downlink)

Broadcast Channel (BCH) (Downlink)

Forward Access Channel (FACH) (Downlink)

Paging Channel (PCH) (Downlink)

Random Access Channel (RACH) (Uplink)

Common Packet Channel (CPCH) (Uplink)

Downlink Shared Channel (DSCH) (Downlink)

Page 17: WCDMA for UMTS Training

Physical LayerUplink Physical Channels

Dedicated Physical Channels Common Physical Channels

Dedicated Physical Control Channel (Uplink DPCCH)

Dedicated Physical Data Channels (Uplink DPDCH)

Physical Random Access Channels (PRACH)

Physical Common Packet Channel (PCPCH)

Page 18: WCDMA for UMTS Training

Physical LayerDownlink Physical Channels

Dedicated Physical Channel (Downlink DPCH) (Time multiplex of downlink DPDCH and downlink DPCCH

Common Physical Channels

Common Pilot Channel (CPICH)

Primary CPICH

Secondary CPICH

Primary Common Control Physical Channel (P-CCPCH)

Secondary Common Control Physical Channel (S-CCPCH)

Synchronisation Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Page 19: WCDMA for UMTS Training

Physical LayerTransport Channel to Physical Channel Mapping

Transport Channels

Physical Channels

BCH FACH DCHRACHPCH

SCHP-CCPCH

DSCHCPCH

S-CCPCHCPICH DPCCH

DPDCHPRACH

PCPCH PDSCH

PICH

AICH

Page 20: WCDMA for UMTS Training

Physical Layer

Dedicated Physical Channel (DPCH)

DPCH

DPDCH DPCCH

DPDCH - Dedicated Physical Data Channel

•Carries dedicated transport channels

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.

Page 21: WCDMA for UMTS Training

Physical LayerUplink DPCH Frame Structure

0 1 2 3 12 13 14…...

10ms

Pilot TFCI FBI TPC

Data

2560 chips

DPCCH

DPDCH

Page 22: WCDMA for UMTS Training

Physical Layer

DPDCH Spreading Factor

DPDCH Channel bit rate (Kb/s)

Maximum user data rate with ½ rate coding

(approx.) 256 15 7.5 kb/s

128 30 15 kb/s

64 60 30 kb/s

32 120 60 kb/s

16 240 120 kb/s

8 480 240 kb/s

4 960 480 kb/s

4 with 6 parallel codes 5740 2.3 Mb/s

Uplink DPDCH data Rates