Introduction Concepts of CDMA. Page 2 Cellular Access Methods Power Frequency Time FDMA Frequency PowerTime TDMA Frequency CDMA Power Time.

Introduction

Concepts of CDMA

Page 2

Cellular Access Methods

Power

Frequency

Time

FDMA

Frequency

Power

Time

TDMA

Frequency

CDMA

Power

Time

Page 3

CDMA Analogy

Page 4

CDMA is Also Full Duplex

US Cellular Channel 384Amplitude

FrequencyAMPS

CDMAFrequency

Amplitude

Reverse Link

Reverse Link

Forward Link

Forward Link

45 MHz

45 MHz

836.52 MHz

836.52 MHz 881.52 MHz

881.52 MHz

Page 5

Cellular Frequency Reuse Patterns

11

1

1

11

11

1

3

66

22

1

45

7

FDMA Reuse

CDMA Reuse

Page 6

The CDMA Concept

Interference Sources

Walsh CodeSpreading

Encoding &Interleaving

Walsh CodeCorrelator

Decode &Deinterleaving

BasebandData

BasebandData

Background Noise

External Interference

Other Cell Interference

Other User Noise

9.6 kbps

19.2 ksps

1228.8 kbps

1228.8 kbps

19.2 ksps

9.6 kbpsCDMA

TransmitterCDMA Receiver

1.25 MHz BW

fc

1.25 MHz BW

fc

10 kHz BW

0

10 kHz BW

0

1.25 MHz BW

fc

1.25 MHz BW

fcfc

-100 dB/Hz

fc

Spurious Signals

Page 7

CDMA Paradigm Shift

•Multiple users on one frequency

•Channel is defined by code

•Capacity limit is soft

Page 8

Processing Gain

AMPS = 1.5 MHz / 30 kHz = 50 Channels

Capacity = 50 Channels / 7 ( 1/7 Frequency Reuse )

AMPS = 7 Calls ( Using 1.5 MHz BW )

CDMA = 42 Calls ( Using 1.5 MHz BW )

CDMA = ____________ X _____ X _____ X (0.67) (1,230,000 ) (1) (1)(9,600) (5.01) (.40)

Capacity = _____________ X _____ X ____ X (Fr) (Data Rate) (S/N) (Vaf)

(Chan BW) (1) (1)

CDMA Capacity Gains

Page 9

CDMA Makes use of Diversity

•Spatial diversity

•Frequency diversity

•Time diversity

Page 10

CDMA Spatial Diversity

•Multiple antennas at base station

•Multiple base stations for soft handoff

Page 11

Spatial Diversity During Soft Handoff

MTSO

Vocoder / Selector

Base Station 2Base Station 1

Land Link

Page 12

CDMA Frequency Diversity

•Combats fading, caused by multipath

•Fading acts like notch filter to a wide spectrum signal

•May notch only part of signal

Amplitude

Frequency

1.25 MHz BW

Page 13

CDMA Time Diversity

•Uses rake receiver

•Data is interleaved

•Convolutional encoding

•Viterbi decoding

Page 14

The Rake Receiver

Time

Frequency

Amplitude

Page 15

CDMA Reverse Link Power Control

•All mobiles are received at base station at equal power

•Two types of control:• Open Loop Power Control

• Closed Loop Power Control

Page 16

Open Loop Power Control

•Assumes loss is similar on forward and reverse paths

•Receive Power + Transmit Power = -73• All powers in dBm

•Example:• For a Received Power of -85 dBm (at the

mobile)• Transmit Power = (-73) - (-85)

• Transmit Power = +12 dBm

Page 17

Closed Loop Power Control

•Directed by base station

•Updated every 1.25 ms

•1 dBm step size

•Corrects Open Loop Power Estimate

Page 18

CDMA Variable Rate Speech Coder

• 20 Millisecond blocks of speech

•Full data rate of 9600 bps

•Lowest rate (1/8) of 1200 bps

•Mobile transmits in bursts of 1.25 msec

•Base repeats bits and lowers power

•System capacity increases by 1/Voice Activity Factor

Page 19

CDMA Frame Formats

15

24 bits in a ms frame

39

79

171 266

124

54

201200 bpsFrame

8

Mixed Mode Bit Information Bits1-bitReserved

8

8

88

12 12 8

10 8

6

88

8

Mixed Mode Bit

Mixed Mode Bit

Mixed Mode Bit

Information Bits

Information Bits

Information Bits

2400 bpsFrame

9600 bpsFrame

4800 bpsFrame

192 bits in a ms frame

96 bits in a ms frame

48 bits in a ms frame

1800 bpsFrame

3600 bpsFrame

7200 bpsFrame

14400 bpsFrame

288 bits in a ms frame

144 bits in a ms frame

72 bits in a ms frame

36 bits in a ms frame

1-bitReserved

1-bitReserved

1-bitReserved

MixedMode Bit

MixedMode Bit

MixedMode Bit

MixedMode Bit

Encoder Tail Bits

CRC

CRC

Encoder Tail Bits

Encoder Tail Bits

Encoder Tail Bits

Information Bits

Information Bits

Information Bits

Information BitsEncoder Tail Bits

Encoder Tail Bits

Encoder Tail Bits

Encoder Tail Bits

CRC

CRC CRC

CRC

Page 20

Mobile Power Bursting

•Each Frame is Divided into 16 Power Control Groups

•Each Power Control Group Contains 1536 Chips (represents 12 encoded voice bits)

•Average Power is Lowered 3 dB for Each Lower Data Rate

CDMA Frame = 20 msFull Rate

Half Rate

Quarter Rate

Eighth Rate

Page 21

Walsh Codes

W =2

0 00 1

4W =

0 0 0 00 1 0 10 0 1 10 1 1 0

W = 01

n

n

n

n

W WW WW =2n

Page 22

Forward Link Traffic Channel Physical Layer

WalshCover

I Short Code

Q Short Code

FIR

FIR1.2288Mbps

Walsh Code Generator

I1.2288Mbps

1.2288 Mbps

1.2288 Mbps

Long Code

19.2 kbps

19.2 kbps

Vocoded Speech data

20 ms blocks

Interleaver

Power Control

Puncturing

19.2 kbps

19.2 kbps

800 bps

800 bps

P.C.MUX

9.6 kbp

s

19.2 kbps

3/4 rate

1/2 rate

14.4 kbp

s

19.2 kbps

Convolutional

Encoder Long Code

Scrambling

Short Code Scrambler

Q

Page 23

Long Code Generation

Modulo-2 Addition

Long Code Output

34 12

User AssignedLong Code

Mask42 bits

4142 55

Long Code Generator

Page 24

Forward Link Channel Format

Walsh Code 32

Walsh Code 0

Pilot Channel

Sync Channel

Walsh Codes 1 to 7

Walsh Codes 8-31, 33-63

Traffic Channels1 up to 55

Channels

All 0's

19.2 kbps 1228.8 kbps

1228.8 kbps

1228.8 kbps

I

Convert to I/Q & PN Spreading

Convert to I/Q & PN Spreading

Convert to I/Q & PN Spreading

FIR LP Filter &D/A Conversion

FIR LP Filter &D/A Conversion

FIR LP Filter &D/A Conversion

FIR LP Filter &D/A Conversion

Q

4.8 kbps

I Data

I Data

I Data

I Data

Q Data

Q Data

Q Data

Q Data

Paging Channels1 up to 7

Channels

19.2 kbps 1228.8 kbps

Convert to I/Q & PN Spreading

Page 25

Interleaver

I Short Code

Q Short Code

1.2288Mbps

I

Q

307.2 kbps

t/2

1/2 Chip Delay28.8 kbps

20 ms blocks

Vocoded Speech Data

64-ary Modulator

1.2288 Mbps

1 of 64 Walsh Codes

Long Code

1.2288 Mbps

1.2288 Mbps

FIR

FIR

Walsh Code 1

Walsh Code 2

Walsh Code 0

Walsh Code 62

Walsh Code 63

Walsh Code 61

Convolutional

Encoder

9.6 kbps

28.8 kbps

1/3 rate

1/2 rate

14.4 kbps

28.8 kbps

Long Code Modulator

Short Code Scrambler

Reverse Link Traffic Channel Physical Layer

Page 26

CDMA Modulation Formats

I

Q

I

Q

Base Station

Transmitter

Mobile Station Transmitter

Filtered QPSK Filtered Offset QPSK

Page 27

Ten Minutes in the Life of a CDMA Mobile Phone• System access

• Continue travel• Initiate Soft Handoff

• Terminate Soft Handoff

• End call

• Turn-on• System access

• Travel• Idle State Hand-Off

• Initiate call

Page 28

CDMA Turn On Process

•Find all receivable pilot signals• Choose strongest one

•Establish Frequency and PN Time Reference (Base station I.D.)

•Demodulate sync channel

•Establish system time

•Determine paging channel Long Code Mask

Page 29

CDMA Service Options

•Service Options Are: 1- Voice Using 9600 bps IS-96-A Vocoder 2- Rate Set 1 Loopback (9600 bps) 3- Voice Using 9600 bps (EVRC) 4- Asynchronous Data Service (circuit

switched) 5- Group 3 Fax 6- Short Message Service (9600 bps) 7- Internet Standard PPP Packet Data 8- CDPD Over PPP Packet Data 9- Rate Set 2 Loopback (14400 bps) 14-Short Message Service (14400 bps) 32,768- Voice Using 14400 bps (CDG)

Page 30

CDMA Protocol Stacks

IS -95 Rev 0Original System-never actually deployed

ARIB T53Japan CDMA

System CellularProtocol

IS -95 Rev ABackwards compatible with IS-95. First Deployed Protocol

TBS- 74Cellular Protocol that adds 14400 Channel Support

J-STD-008Not Backwards Compatible, PCS only Protocol

EIA/TIA-95 Rev BCombines TSB-74 & J-STD-008 for a Universal Protocol

Page 31

Sync Channel Message

•Contains the Following Data:

Base Station Protocol Revision Min Protocol Revision Supported SID, NID of Cellular System Pilot PN Offset of Base Station Long Code State System Time Leap Seconds From Start of

System Time Local Time Offset from System

Time Daylight Savings Time Flag Paging Channel Data Rate Channel Number

SYNC

Page 32

Paging Channel Messages

–Overhead Messages System Parameters Access Parameters CDMA Channel List Extended System

Parameters Extended Neighbor

List

–Other Messages Order Channel

Assignment Data Burst

–More Messages Authentication SSD Update Feature

Notification Status Request Service

Redirection General Page Global Service

Redirection TMSI

Assignment

• J-STD-008 Paging Messages

Page 33

CDMA Idle State Handoff

•No Call in progress

•Mobile Listens to new Cell

•Move Registration Location if entering a new zone

Page 34

CDMA Call Initiation

• Dial numbers, then press send

• Mobile transmits on a special channel called the Access Channel

• The Access Probe uses Long Code Mask based on:

• Access & Paging Channel Numbers

• Base station ID

• Pilot PN offset

Page 35

CDMA Call Completion

•Base answers Access Probe using the Channel Assignment Message

•Mobile goes to a Traffic Channel based on the Channel Assignment Message information

•Base station begins to transmit and receive traffic channel

Page 36

CDMA Soft Handoff Initiation

•Mobile finds second Pilot of sufficient power (exceeds T_add Threshold)

•Mobile sends Pilot strength message to first Base station

•Base station notifies MTSO

•MTSO requests New Walsh Assignment from second Base station

• If available, New Walsh Channel Info is relayed to first Base station

Page 37

CDMA Soft Handoff Completion

•First Base station orders Soft Handoff with New Walsh Assignment

•MTSO sends Land Link to second Base Station

•Mobile receives Power from two Base Stations

•MTSO chooses better quality frame every 20 milliseconds

Page 38

Ending CDMA Soft Handoff

•First BS Pilot Power Goes low at Mobile Station (drops below T_drop)

•Mobile sends Pilot Strength Message

•First Base station stops transmitting and frees up Channel

•Traffic channel continues on Base station Two

Page 39

CDMA End of Call

•Mobile or land initiated

•Mobile and Base stop transmission

•Land connection broken

Page 40

CDMA Conclusions

•New access method• Code based

•Designed for use in interfering environment

•Uses multipath to advantage

•Has high capacity• 6 to 20 times analog

CDMA