Cdma system

CDMA System

Course NameCourse Name

cdma2000 Systemscdma2000 Systems

ContentsContents

The characteristics of mobile communications

CDMA migration from 2G to 3G

CDMA spectrum usage

CDMA Codes

CDMA Channels

The advantage of CDMA

cdma2000 -1x

Characteristics of Mobile Characteristics of Mobile CommunicationCommunication

• Mobility：– flexible and convenient ， global personal

communication

• Poor environment and conditions ：– Co-channel interference, multi-path(space and

time)shadow effect and delay, power change and other noise

• Multiple MS and channels：– Interference, near and far effect

• Limit of frequency resources

• Reliability is important

– registration, handoff, switching

Communications SystemCommunications System

AMPS: Advanced Mobile Phone SystemTACS: Total Access Communication System

GPRS: General Packet Radio Services

11GG 22GG 33GG

Analog cellular

DDiiggiittaall cceelllluullaarr DDiiggiittaall cceelllluullaarr

VVooiiccee VVooiiccee //ddaattaa VViiooccee // hhiigghh ssppeeeedd ddaattaa

AAMMPPSS CCDDMMAA 11XXRRtttt CCDDMMAA22000000

TTAACCSS GGSSMM GGPPRRSS WW__CCDDMMAA

8800’’ 11999922 11999999 22000011 22000033

CDMA Evolution PathsCDMA Evolution Paths

2Mbps

153.6kbps

CDMA1xRTT

CDMA 1xEV-DV

CDMAIS-95

CDMA1xEV-DO

CDMA3x 5x

2G 2.5G 3G

9.6kbps

CDMA-Its History & StatusCDMA-Its History & Status

CDMA-Its History & StatusCDMA-Its History & Status 1993, the first CDMA standard IS-95 was issued; In 1995, CDMA technology was put into commercialization in

Hong Kong and America on large scale; In April, 2001, China Unicom began to construct CDMA networks

—the largest in the world (about 70Million line now); At present, CDMA commercial networks are established in about

40 countries or area, almost 20% of all users in the world.

CDMA Subscriber Growth History:CDMA Subscriber Growth History:Sept.1997 through Sept.2003Sept.1997 through Sept.2003

CDMA 800 MHz Cellular CDMA 800 MHz Cellular Spectrum UsageSpectrum Usage

Possible CDMA Center Freq. Assignments

Channel Numbers

Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)824MHz

849MHz

869MHz

894MHz

otherusesA” A”A B A’ B’

1 10 10 1.5 2.5

A B A’ B’

1 10 10 1.5 2.5

991

10231 333

334

666667

716717

799

991

10231 333

334

666667

716717

799

~300 kHz. “guard bands” possibly required if adjacent-frequency signals are non-CDMA (AMPS, TDMA, ESMR, etc.)

• All CDMA RF carriers are 1.25 MHz. wide– Can serve ~20 users /8 kb vocoder

CDMA PCS 1900 MHz CDMA PCS 1900 MHz Spectrum UsageSpectrum Usage

Guard Bands

Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)1850 MHz

BTA

BTA

BTA

BTA

BTA

BTA

Paired Bands

MTA BTAMTABTA MTAMTA

1910 MHz

1930MHz

1990MHz

Data Voice

A D B E F C A D B E F C

15 51010 1515151515 555 55

Licensed Licensed

Unlicensed

0

Channel Numbers 299

300

400

699700

800

900

1199 0

299300

400

699700

800

900

1199

CDMA Frequency ChannelCDMA Frequency ChannelAssignment at 800 MHz CellularAssignment at 800 MHz Cellular

1

334

667

991

1023

333

666

715

799

716

ChannelNumbers

A Band B Band A’A” B’

1019 37 78 119 160 201 242 283 384 425 466 507 548 589 630 691 777

CDMA A-Band Carriers CDMA B-Band Carriers

8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 9 9 8

* **** Requires frequency

coordination with non-cellular interferers

** Requires frequency coordination with A-band carrier

A Band Primary Channel 283A Band Secondary Channel 691

B Band Primary Channel 384B Band Secondary Channel 777

736

Multiple AccessMultiple Access

Each pair of users enjoys a dedicated,

private circuit through the transmission

medium, unaware that the other users exist.

Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit. Transmission

Medium• Types of Media -- Examples:– Twisted pair - copper– Coaxial cable– Fiber optic cable– Air interface (radio signals)

Advantages of Multiple Access–Increased capacity: serve more users–Reduced capital requirements since fewer media can carry the traffic–Decreased per-user expense–Easier to manage and administer

Multiple Access SchemesMultiple Access Schemes

FrequencyTime

Power

FrequencyTime

Power

FrequencyTime

Power

FDMA

TDMA

CDMA

• FDMA Frequency Division Multiple Access– Each user on a different frequency– A channel is a frequency

• TDMA Time Division Multiple Access– Each user on a different window

period in time (“time slot”)– A channel is a specific time slot on

a specific frequency• CDMA Code Division Multiple Access

– A channel is a unique code pattern– Each user uses the same frequency

all the time, but mixed with different distinguishing code patterns

Frequency ReuseFrequency Reuse

CDMA (IS-95)frequency reuse = 1

TDMA (IS-136)frequency reuse = 7

Terms & DefinitionsTerms & Definitions• CDMA Channel or CDMA Carrier or CDMA Frequency

– Duplex channel made of two 1.25 MHz-wide bands of electromagnetic spectrum, one for Base Station to Mobile Station communication (called the FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base Station communication (called the REVERSE LINK or the UPLINK)

– In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart– In 1900 MHz PCS they are 80 MHz apart

• CDMA Forward & Reverse Channel– 1.25 MHz Forward / Reverse Link

• CDMA Code Channel– Each individual stream of 0’s and 1’s contained in either the CDMA Forward Channel

or in the CDMA Reverse Channel– Code Channels are characterized (made unique) by mathematical codes– Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic channels– Code channels in the reverse link: Access and Reverse Traffic channels

45 or 80 MHz

CDMA CHANNELCDMA

ReverseChannel 1.25 MHz

CDMAForwardChannel 1.25 MHz

Walsh CodesWalsh Codes

• 64 Sequences, each 64 chips long– A chip is a binary digit (0 or 1)

• Each Walsh Code is Orthogonal to all other Walsh Codes– This means that it is possible to recognize and

therefore extract a particular Walsh code from a mixture of other Walsh codes which are “filtered out” in the process

– Two same-length binary strings are orthogonal if the result of XORing them has the same number of 0s as 1s

Short PN SequencesShort PN Sequences

• The two Short PN Sequences, I and Q, are 32,768 chips long

• Together, they can be considered a two-dimensional binary “vector” with distinct I and Q component sequences, each 32,768 chips long

• Each Short PN Sequence (and, as a matter of fact, any sequence) correlates with itself perfectly if compared at a timing offset of 0 chips

• Each Short PN Sequence is special: Orthogonal to a copy of itself that has been offset by any number of chips (other than 0)

The Long PN SequenceThe Long PN Sequence

• Each mobile station uses a unique User Long Code Sequence generated by applying a mask, based on its 32-bit ESN, to the 42-bit Long Code Generator which was synchronized with the CDMA system during the mobile station initialization.

• Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete.

Long Code Register (@ 1.2288 MCPS)

Public Long Code Mask (STATIC)

User Long CodeSequence

(@1.2288 MCPS)

1 1 0 0 0 1 1 0 0 0 P E R M U T E D E S N

AND

=S U M

Modulo-2 Addition

Coding Process on CDMA Coding Process on CDMA Forward ChannelsForward Channels

WALSH19

BTSPilot Walsh 0

Walsh 19

Paging Walsh 1

Walsh 6

Walsh 11

Walsh 20

Sync Walsh 32

Walsh 42

Walsh 37

Walsh 41

Walsh 56

Walsh 60

Walsh 55

PN OFFSET 116BTS

PN OFFSET 226BTS

PN OFFSET 510BTS

S PN

372

x

x

xPN OFFSET

ANALOG

SUM/MUXPN OFFSET 372

CDMA Code SummaryCDMA Code Summary

Walsh Codes

Short PN Sequences

Long PNSequences

Type of Sequence

Mutually Orthogonal

Orthogonal with itself at any time shift value except 0

near-orthogonal if shifted

Special Properties

64

2

1

How Many

64 chips1/19,200 sec.

32,768 chips26-2/3 ms

75x in 2 sec.

242 chips~41 days

Length

Orthogonal Modulation

(information carrier)

Quadrature Spreading

(Zero offset)

Distinguish users

Reverse Link Function

User identitywithin cell’s

signal

Distinguish Cells & Sectors

Data Scrambling to avoid strings

of 1’s or 0’s

Forward Link Function

CDMA AdvantagesCDMA Advantages• Spread Spectrum• Soft & Softer Handoff• Rake Receiver• Variable Rate Vocoder• High quality voice• Power Control• Coverage• Simple Network Planning• Green Handset• Smooth migration to 3G and the operator’s benefit is protected at

the most

Spread Spectrum (1)Spread Spectrum (1)S(f)

ff0

Before spreading

Signal

S(f)

ff0

After spreading

Signal

S(f)

ff0

After despreading

signal

Interfering noise

f

S(f)

f0

Before despreading

Signal

Interfering noise

Spread Spectrum(2)Spread Spectrum(2)

Radio Channel

Channel Coding(SS)

Carrier Modulation

DS-PN

Source Coding

Transmit

Antenna

Radio Channel

ChannelCoding

(SS)

CarrierModulation

DS-PN

SourceCoding

Transmit

Channel Decoding

Carrier Demodulation

DS-PN

Source Decoding

Receive

Channel Decoding

CarrierDemodulation

DS-PN

SourceDecoding

Receive

Antenna

A B

Spreading Spectrum (3)Spreading Spectrum (3)“Principle of Using Multiple Codes”“Principle of Using Multiple Codes”

SpreadingSequence

A

SpreadingSequence

B

SpreadingSequence

C

SpreadingSequence

C

SpreadingSequence

B

SpreadingSequence

A

InputData

X

RecoveredData

X

X+A X+A+B X+A+B+C X+A+B X+A

Spread-Spectrum Chip StreamsORIGINATING SITE DESTINATION

Spread Spectrum Spread Spectrum ((44))

Advantages of Spread Advantages of Spread SpectrumSpectrum

Avoid interference arising from jamming signal or multi-path effects.

Covert operation:Difficult to detect

Achieve Privacy: Difficult to demodulate, Noise like signal.

Impossible to Eavesdrops on the signal expect using the same PN sequence

Soft & Softer HandoffSoft & Softer Handoff

Connection first and disconnection afterwards in handoff.High quality of service and effective reduction of call drops.

Connection first and disconnection afterwards in handoff.High quality of service and effective reduction of call drops.

Softer handoff: same BS & frequency, between different sectors.

Softer handoff: same BS & frequency, between different sectors.

Soft handoff: adjacent cells of the same frequency.

Soft handoff: adjacent cells of the same frequency.

BSC

BSC MSC

Rake Receiver (1)Rake Receiver (1)

d1 d2

t t t

d3

transmission

receivingRaker combination

noise


Correlator 1

Correlator 2

Correlator 3

Search Correlator

Co

mb

ine

r

To De-Interleaver, Viterbi Decoder

Multipath Delay Components

( 150 s > t > 1s)

Rake receiver can isolate multipath spaced > 1 chip length.


• Handset uses combined outputs of the three traffic correlators “rake fingers”

• Each finger can independently recover a particular PN offset and Walsh code

• Fingers can targeted on delayed multipath reflections, or even on different BTSs

• Searcher continuously checks pilots

Intelligent VocoderIntelligent Vocoder

High Quality Voice(1)High Quality Voice(1)

Voice quality

64kPCM

presentGSM

8k CDMA

13kCDMA

8k EVRCCDMA

High Quality Voice(2)High Quality Voice(2)

High quality

Voice??

Voice activity Technology

Echo Cancellation

Accurate power control,

Rake receiver

Spread spectrum

Power ControlPower Control

Autonomous power controlOn the Uplink tells the MS to vary it’s transmitted power inversely

with the power level it receive from the BS.

Direct power controlOn the Uplink measures Eb/No at the base station and sends power

Control Bits over the Downlink to the MS to instruct the MS to either increase or decrease its transmit power.

Downlink power controlAttempts to use minimum power needed to meet to a Frame Error Rate

(FER) threshold at the MS s.

CoverageCoverage

• The coverage radius is 2 times of

standard GSM.

• Coverage of 1000 km2: GSM needs

200 BTS 's, while CDMA requires

only 50.

• Under the same coverage conditions,

the number of BTS 's is greatly

decreased

Simple Network PlanningSimple Network Planning

Simple project design & convenient capacity expansion

13

2

4

3

2

4

24

4

1

2

3

1

4

2

31

41

11

1

11 1

11

1

1

1

1

1

1

1

11

1

11

1

Simple project design & convenient capacity expansion

Green HandsetGreen Handset

SystemsMean

transmissionpower

Maxtransmission

powerGSM 125 mW 2W

CDMA 2 mW 200mW

SystemsMean

transmissionpower

Maxtransmission

powerGSM 125 mW 2W

CDMA 2 mW 200mW

Low transmission power: Accurate power control, handoff control, voice activation

Low transmission power: Accurate power control, handoff control, voice activation

Functions of the CDMA Functions of the CDMA Reverse ChannelsReverse Channels

• There are two types of CDMA Reverse Channels:– TRAFFIC CHANNELS are used by individual

users during their actual calls to transmit trafficto the BTS.

– ACCESS CHANNELS are used by mobile stations not yet in a call to transmit registration requests, call setup requests, page responses, order responses, and other signaling information

Coding Process on CDMACoding Process on CDMAReverse ChannelsReverse Channels

• Each mobile is uniquely identified by the User Long Code, which it generates internally.

• All mobile stations transmit simultaneously on the same 1.25 MHz wide frequency band.

• Any nearby BTS can dedicate a channel element to the mobile station and successfully extract its signal.

• Mobile stations also use the other CDMA spreading sequences, but not for channel-identifying purposes.

• Short PN Sequences are used to achieve phase modulation.• Walsh Codes are used as Orthogonal Modulation to give

ultra-reliable communications recovery at the BTS.

Benefits of the cdma2000 1x Benefits of the cdma2000 1x StandardsStandards

• Increased mobile standby battery life (via Quick Paging Channel)

• Total backward compatibility to reuse switch and call processing features

• 2-3 dB better coverage• High speed 153.6 kbps packet data capabilities• cdma2000 1x = 1.25 MHz Radio Transmission

Technology

Backward Compatible withBackward Compatible withIS-95 Air InterfaceIS-95 Air Interface

IS-95 mobiles are supported in the IS-2000 standard for 1xRTT:

• No need to change any RF infrastructure• Capacity improvements will not be

realized until most IS-95 subscribers disappear

Channel List: 1xRTT vs. IS-95Channel List: 1xRTT vs. IS-95

• IS-95B built on the IS-95A channels, and introduced two new channels– Fundamental channel was the same as IS-9A traffic channel– Supplemental code channels assigned to support rates above 14.4Kbps

• IS-2000 1xRTT continue to build on the IS-95 channels– IS-95 channels continue to be supported in IS-2000 to support IS-95

mobiles

Pilot channel Sync channel Paging channel Access channelForward Traffic Channel Reverse Traffic Channel

Fundamental channel Fundamental channelSupplemental Code channel (F-SCCH) Supplemental Code channel (R-SCCH)

Supplemental channel (F-SCH) Supplemental channel (R-SCH)Quick Paging channel (F-QPCH) Reverse Pilot channel (R-PICH)

IS-95B

1xRTT

IS-95A

Forward Reverse

Discriminating Among ForwardDiscriminating Among ForwardCode ChannelsCode Channels

• A Mobile Station receives a Forward Channel from a sector in a Base Station.

• The Forward Channel carries a composite signal of up to 64 forward code channels.

• Some code channels are traffic channels and others are overhead channels.

• A set of 64 mathematical codes is needed to differentiate the 64 possible forward code channels.

– The codes in this set are called “Walsh Codes”

SyncPilotFW Traffic

(for user #1)Paging

FW Traffic(for user #2)

FW Traffic(for user #3)

Discriminating Among Base Discriminating Among Base StationStation

• A mobile Station is surrounded by Base Stations, all of them transmitting on the same CDMA Frequency.

• Each Sector in each Base Station is transmitting a Forward Traffic Channel containing up to 64 forward code channels.

• A Mobile Station must be able to discriminate between different Sectors of different Base Stations.

• Two binary digit sequences called the I and Q Short PN Sequences (or Short PN Codes) are defined for the purpose of identifying sectors of different base stations.

• These Short PN Sequences can be used in 512 different ways in a CDMA system. Each one of them constitutes a mathematical code which can be used to identify a particular sector.

A B

Up to 64Code Channels

Up to 64Code Channels

Example of cdma2000 1x Example of cdma2000 1x NetworkNetwork

Structure of a Typical CDMA Structure of a Typical CDMA systemsystem