An Introduction to CDMA Air Interface: TIA/EIA/IS-95A Advanced Technology Center Computer &...

An Introduction to CDMA Air Interface: TIA/EIA/IS-95A

Advanced Technology Center

Computer & Communications Research Laboratories

Industrial Technology Research InstituteRay-Guang Cheng

[email protected]

Chung-Wei KuATC/CCL/ITRI

Advanced Technology CenterComputer & Communications Research LaboratoriesIndustrial Technology Research Institute

Contents

• Introduction

• Forward CDMA Channel

• Reverse CDMA Channel



CDMA Around the World



Multiple Access

• FDMA– Advanced Mobile Phone Service (AMPS) and Total Access Communicat

ions System (TACS)

– AMPS systems use 30 kHz "slices" of spectrum for each channel

– Narrowband AMPS (NAMPS) requires only 10 kHz per channel

– TACS channels are 25 kHz wide

• TDMA– IS-54 systems, designed to coexist with AMPS systems, divide 30 kHz o

f spectrum into three channels

– PDC divides 25 kHz slices of spectrum into three channels

– GSM systems create 8 time-division channels in 200 kHz wide carriers



Multiple Access

• CDMA – unique digital codes are used to differentiate subscribers

– codes are shared by both MS and BS

– all users share the same range of radio spectrum

• Benefits of CDMA:– Capacity increases: 8 to 10 times (AMPS); 4 to 5 times (GSM)

– Improved call quality

– Simplified system planning

– Enhanced privacy

– Improved coverage characteristics

– Increased talk time for portables

– Bandwidth on demand



CDMA

• There are two CDMA common air interface standards:– Cellular (824-894 MHz) - TIA/EIA/IS-95A– PCS (1850-1990 MHz) - ANSI J-STD-008

They are very similar in their features, with exceptions of the frequency plan, mobile identities, and related message fields.

• IS-95A– 45 MHz spacing for forward & reverse channel– Permissible frequency assignments are on 30 kHz increments– W/R = 10 log (1.2288 MHz/9600Hz) = 21 dB for the 9600 bps rate set

• ANSI J-STD-008– 80 MHz spacing for forward & reverse channel– Permissible frequency assignments are on 50 kHz increments



Frequency Plan of IS-95A



Frequency Plan of ANSI J-STD-008



Forward CDMA Channel of IS-95A

• From BSS to MS

• It carries traffic, a pilot signal, and overhead information.

• Pilot is a spread but unmodulated DSSS signal.

• Pilot and overhead channels establish the system timing and station identity.

• Pilot channel is also used in the mobile-assisted handoff (MAHO) process as a signal strength reference.

• FEC code rate is 1/2 and the PN rate is 1.2288 MHz (1.2288 MHz = 128*9600 bps).



Forward Link Channel Parameters

Channel Sync Paging Traffic

Data rate 1200 4800 9600 1200 2400 4800 9600 bps

Code repetition 2 2 1 8 4 2 1

Modulation symbol rate 4800 19,200 19,200 19,200 19,200 19,200 19,200 sps

PN chips/modulation symbol 256 64 64 64 64 64 64

PN chips/bit 1024 256 128 1024 512 256 128



Signal Structure

• The forward link consists of up to 64 logical channels (code channels).

• Code channels is one of a set of 64 so-called Walsh functions.

• Only whole periods of the Walsh functions occur in each code symbol, the Walsh makes the channels completely separable in the receiver.

• Each forward code channel is spread by the Short Code, which has I- and Q-components.

• The two coded, covered, and spread streams are vector-modulated on the RF carrier. The spreading modulation is thus QPSK, superimposed on a BPSK code symbol stream.



Overhead Channels

• There are three types of overhead channel in the forward link:– pilot, is required in every station

– sync

– paging

• Pilot channel– pure short code with no additional cover or information content

– always code channel zero

– a demodulation reference for the mobile receivers and for handoff level measurements

– carries no information

– all stations use the same short code, distinguished by the phase

– period of the short code, 215= 26.667 ms at the 1.2288 MHz chip rate



Overhead Channels

• Pilot channel (Conti.)– pilot phases always be assigned to stations in multiples of 64 chips, givin

g a total of 215-6 = 512 possible assignments

– 9-bit number that identifies the pilot phase assignment is called the Pilot Offset

• Sync Channel– sync channel carries timing and system configuration information

– data rate is always 1200 bps

– interleaver period is also 80/3 = 26.667 ms, simplifies finding frame boundaries, once the mobile has located the pilot

– code period ambiguity is then resolved by the long code state and system time fields



Overhead Channels

• Paging channel– used to communicate with MSs when they are not assigned to a traffic ch

annel

– successful accesses are normally followed by an assignment to a dedicated traffic channel

– paging channel may run at either 4800 or 9600 bps

– each BS must have at least one paging channel per sector, on at least one of the frequencies in use



Traffic Channel

• Traffic channels – assigned dynamically, in response to MS accesses, to specific MS

– always carries data in 20 ms frames– carry variable rate traffic frames, either 1, 1/2, 1/4, or 1/8 of 9600 bps

– rate variation is accomplished by 1, 2, 4, or 8-way repetition of code symbols, but the energy per bit approximately constant

– rate is independently variable in each 20 ms frame

– the 800 bps reverse link power control subchannel is carried on the traffic channel by puncturing 2 from every 24 symbols transmitted.

• Timing– all base stations must be synchronized within a few microseconds



Reverse CDMA Channel of IS-95

• From MS to BSS

• It carries traffic and signaling information.

• FEC code rate is 1/3, the code symbol rate = 28,800 symbols/sec, 6 code symbols/modulation symbol, and the PN rate is 1.2288 MHz

• modulation is 64-ary orthogonal Walsh functions, each period of the Walsh function is repeated for four chips of the PN code

• Walsh symbol rate is 1.2288 MHz/(4 chips per Walsh chip)/(64 Walsh chips per Walsh symbol) = 4,800 modulation symbols/ second



Reverse CDMA Channel Parameters, Rate Set 1

Channel Access Traffic

Data rate 4,800 1,200 2,400 4,800 9,600 bps

Code Rate 1/3 1/3 1/3 1/3 1/3

Symbol Rate before Repetition 14,400 3,600 7,200 14,400 28,800 sps

Symbol Repetition 2 8 4 2 1

Symbol Rate after Repetition 28,800 28,800 28,800 28,800 28,800 sps

Transmit Duty Cycle 1 1/8 1/4 1/2 1

Code Symbols/Modulation Symbol 6 6 6 6 6

PN Chips/Modulation Symbol 256 256 256 256 256

PN chips transmitted/bit 256 128 128 128 128



Signal Structure

• Reverse CDMA Channel consists of 2 42-1 logical channels

• One of the logical channel is permanently and uniquely associated with each MS. The channel does not change upon handoff.

• Reverse link addressing is accomplished through manipulation of period 2 42-1 Long Code, which is part of the spreading process.

• The reverse CDMA Channel does not use strict orthogonality in any sense to separate logical channels. Rather, it uses a very long period spreading code, in distinct phases. The correlations between stations are not zero, but they are acceptably small.



Handoff

• CDMA is specifically designed not only to reduce handoff failures but also to provide seamless service.



Handoff

• Steps in a handoff– Starting in a state where only one cell is supporting the call in question.

– Informing the candidate cell of the imminent handoff

– Signaling the mobile to begin executing the handoff.

– New cell beginning to service the mobile

– Mobile beginning to use the new cell

– Entering the mid-handoff state (prolonged only in CDMA)

– Mobile discontinuing use of the old cell

– Old cell stopping service to the mobile

– Ending in a state where the new cell is supporting the call in question



AMPS v.s. CDMA

• Difference between AMPS & CDMA– CDMA handoffs do not normally require frequency tuning.

– CDMA requires change of the code channel in the forward CDMA channel.

– No tuning, either frequency or code channel is required in the reverse CDMA channel at any time.

• AMPS– Hard handoff (communication is interrupted briefly)

– not simultaneous communication with more than one BS

– BS do the signal quality measurement



CDMA Protocol

Upper Layers(Primary Traffic)

Upper Layers(Secondary Traffic)

Layer 2(Primary Traffic)

Layer 2(Secondary Traffic)

Layer 2(Signaling)

Multiplex Sublayer (Traffic Channel)

Layer 2(Link Layer)

Paging & AccessChannels

Layer 2Sync

Channels

Layer 3 (Mobile Station Control Processes)

Layer 1 (Physical Layer)



Multiplex Option Information

Format Bits PrimaryTraffic

SignalingTraffic

SecondaryTraffic

TransmitRate(bps)

MixedMode (MM )

TrafficType (TT )

TrafficMode( TM )

Bits/frame Bits/frame Bits/frame

0 - - 171 0 01 0 00 80 88 01 0 01 40 128 01 0 10 16 152 01 0 11 0 168 01 1 00 80 0 881 1 01 40 0 1281 1 10 16 0 152

9600

1 1 11 0 0 1684800 - - - 80 0 02400 - - - 40 0 01200 - - - 6 0 0

Format Bits PrimaryTraffic

SignalingTraffic

SecondaryTraffic

TransmitRate(bps)

MixedMode (MM )

TrafficType (TT )

TrafficMode( TM )

Bits/frame Bits/frame Bits/frame

0 - - 171 0 01 0 00 80 88 01 0 01 40 128 01 0 10 16 152 01 0 11 0 168 01 1 00 80 0 881 1 01 40 0 1281 1 10 16 0 152

9600

1 1 11 0 0 1684800 - - - 80 0 02400 - - - 40 0 01200 - - - 6 0 0



Primary and Signaling Traffic

MM=0

MM=1

MM=1

MM=1

MM=1

TT=0

TT=0

TT=0

TT=0

TM=00

TM=01

TM=10

TM=11

Primary Traffic = 171 bits


Signaling Traffic = 88 bits









9600 bps Primary Traffic only

Dim & Burst with rate 1/2primary & signaling traffic



Blank & Burst withsignaling traffic only

4800 bps primarytraffic only

2400 bps primarytraffic only

1200 bps Primarytraffic only

172 bits

80 bits

40 bits

16 bits



Secondary Traffic

MM=1

TT=1

TM=00



MM=1

TT=1

TM=01



MM=1

TT=1

TM=10



MM=1

TT=1

TM=11


Dim & Burst with rate1/2 primary &

Secondary traffic


Secondary traffic


Secondary traffic

Blank & Burst withSecondary traffic only

172 bits



Sync Channel

• Signaling on all channels use a synchronized bit-oriented protocol.

• Sync channel is used during the system acquisition stage.

• Sync channel frame length is the length of pilot PN sequence.

• Only the Sync Channel Message is sent on the sync channel.

• MS – obtains information from Sync Channel Message

– adjusts its timing to normal system timing

– begins monitoring its Paging Channel



Paging Channel

• Data rate: 2400, 4800, 9600 bps

• One 9600 bps Paging Channel can support 180 pages/sec.

• Paging Channel conveys four major types of messages:– overhead– paging– order– channel assignment

• Configuration of the system is conveyed in four overhead messages:– System Parameter Message– Access Parameter Message– Neighbor List Message– CDMA Channel List Message



Overhead Messages

• System Parameter Message:– configuration of the Paging Channel– registration parameters– parameters to aid pilot acquisition

• Access Parameter Message– configuration of the Access Channel– control parameters used to stabilize the Access Channel

• Neighbor List Message– time offset of the pilot– basic neighbor configuration

• CDMA Channel List Message– CDMA frequency assignment that contain Paging Channels



Paging Channel Messages

• Page Message: – contains pages to one or more mobile stations.

• Order Message: – a broad class of messages used to control a particular MS.

• Channel Assignment Message:– let BS to assign a MS to the traffic channel

– change Paging Channel Assignment

– direct the MS to use the analog FM system



Access Channel

• Access Channel provides communications from MS to BS when MS is not using a Traffic Channel.

• All Access Channel use 4800 bps mode

• Access Channel Message:– call origination

– response to pages

– orders

– registrations

• One or more Access Channel are paired with every Paging Channel

• Control of Access Channel transmission is accomplished through the Access Parameter Message sent on the Paging Channel



Framing and Signaling on the Traffic Channel

• Both forward & reverse Traffic Channels use 20 ms frames.

• Frames can be sent at 9600, 4800, 2400, or 1200 bps

• Signaling– blank-and-burst signaling:

• sent at 9600 bps

• replace one or more frames of primary traffic data

– dim-and-burst signaling:

• sent at 9600 bps

• sends both signaling and primary traffic data in a frame

• degradation in voice quality is essentially undetectable



Traffic Channel Messages & Service Option

• Four types of control messages on the Traffic Channel– messages controlling the call itself

– messages controlling handoff

– messages controlling forward link power

– messages for security and authentication

• IS-95 supports different user applications, called service options

• Two different service options can be simultaneous supported:– primary traffic

– secondary traffic

• MS can specify the desired service option at call origination.



IS-95 Standard

• Forward Link– Pilot Channel

– Sync Channel

– Paging Channels (max. 7)

– Traffic Channels• Power Control Sub-Channel

• Reverse Link– Access Channels

– Traffic Channels



Forward CDMA Channel

• Forward link consists of up to 64 logical channels (code channels)• The code channels are distinguished by a set of 64 Walsh

functions• Walsh function code number zero is always reserved as the pilot• Short Code (with period 215, 27.667 ms at 1.2288 MHz)

– spreading the CDMA Forward Channel– used in conjunction with the Long Code for spreading the CDMA Reverse

Channel

• Long Code (with period 242 - 1)– spreading the CDMA Reverse Channel– Long Code Mask serves as a reverse link address



Generation of Forward Code Channel



Forward Channel Modulator (Spreading)

• Identical I, Q signals; but different I, Q PN sequences (short code)

• Transmitted power is reduced by 3, 6, or 9 dB for variable data rates at 9.6 k, 4.8 k, 2.4 k, and 1.2 kbps

• QPSK modulation



Forward Link Modulation Parameters

• 64 othoronal Walsh codes per sector to identify channels– (S/N is not infinite due to AWGN, multipath, and the neighboring cell)

• Long code (period 2 42 -1) to scramble data

• DS at 1.2288 Mcps

• Every cell uses the same PN sequence (period 2 15 or 26.67ms) and is identified by a pre-defined offset (64 x n chips)

• Coherent QPSK demodulation

• Diversity– time diversity: coding + interleaving

– path diversity: soft handoff and RAKE receiver



Logical Forward CDMA Channel

Forward CDMA Channel

PilotChan

SyncChan

W0 W32

PagingCh 1

W1

...Upto W7

PagingCh 7

W8

...Upto

TrafficCh N

TrafficCh 1

Traffic Data Mobile PowerControl Sub-Channel

...W31

TrafficCh 24

Upto

...W63

TrafficCh 55

W33

TrafficCh 25



Pilot Channel

• Unmodulated signal

• Unique per sector/cell

• Signal level is 4~6 dB higher than traffic channel

• Perfect phase/time/signal strength reference for MS

• Used in initial system acquisition and handoff for MS

PilotChannel(All 0’s)

Walsh Function

W0PN Chips

1.2288 Mcps



Sync Channel

• 1200 bps

• To convey pilot PN sequence offset, time of day, and long code state to allow immediate sync of MS to the network

SyncChannel

Bits 1.2 kbps

ConvolutionalEncoder

R=1/2, K=9

CodeSymbol

2.4 ksps

SymbolRepetition

BlockInterleaver

ModulationSymbol

4.8 ksps

ModulationSymbol

4.8 ksps

Walsh Function

W32

PN Chips 1.2288 Mcps



Sync Channel Frame Structure

• Sync channel message has length of 93 x N bits

• Sent in N superframes:– 1 superframe (96 bits, 80 ms) = 3 sync channel frames

– 1 frame (32 bits, 26.67 ms) = 1-bit SOM + 31-bit data

– SOM = 1 : start of message

• Message contains:– system identification (SID) and network identification (NID)

– PN sequence offset and long code state

– system time, leap seconds, offset from UTC, etc.

– paging channel data rate

MessageLength

(in bytes)

8 bits

Data

N MSG = 2 ~ 1146 bits

CRC

30 bits

Padding= …000...



Paging Channels

• 4.8 k or 9.6 k bps

• Same time alignment as the traffic channels

• To page MS and to process other orders

PagingChannel

Bits 4.8 kbpsor

9.6 kbps


R=1/2, K=9

CodeSymbol

9.6 kspsor

19.2 ksps

SymbolRepetition

BlockInterleaver

ModulationSymbol

19.2 ksps

ModulationSymbol

19.2 ksps

Walsh Function

W p1 p 7


Long CodeMask forPaging

Channel p

Long CodeGenerator

1.2288 McpsDecimator

19.2 ksps

19.2 ksps



Paging Channel Frame Structure

• Synchronized paging channel message has length of 47 x N or 95 x N bits

• Sent in N paging channel slots:– 1 slot (80 ms) = 8 paging channel half-frames

– 1 half-frame (10 ms, 48 or 96 bits) = 1-bit SCI + 47 (or 95)-bit data

– SCI = 1 : start of a paging channel message

• Message contains:– system parameters

– access parameter (for access channel)

– channel assignment

– TMSI (temporary MS identification) assignment

MessageLength

(in bytes)

8 bits

Data

N MSG = 2 ~ 1146 bits

CRC

30 bits

Padding= …000...



Forward Traffic Channels

• 9.6, 4.8, 2.4, or 1.2 k bps; 20 ms frames

• Rate can be changed every frame

Forward TrafficChannel

InformationBits for User m(172, 80, 40 or16 bits/frame)

8.6 kbps4.0 kbps2.0 kbps0.8 kbps


R=1/2, K=9

SymbolRepetition

BlockInterleaver

ModulationSymbol

19.2 kspsModulation

Symbol

19.2 ksps

Add Frame Quality Indicator

for 9600 &4800 bps Rates

Add 8-bitEncoder

Tail9.2 kbps4.4 kbps2.0 kbps0.8 kbps


19.2 kbps 9.6 kbps 4.8 kbps 2.4 kbps

Long CodeMask forPaging

Channel p

Long CodeGenerator

1.2288 Mcps

Decimator

19.2 ksps Walsh Function

W m


Decimator

MUX

PowerControl

Bits800 bps

800 Hz



Forward Traffic Channel Frame Structure

8

T

12

F

172

information bits

192 bits (20 ms)9600 bpsFrame

8

T

8

F

80

information bits


8

T

8

F

40

information bits


8

T

8

F

16

information bits


F: Frame Quality Indicator (CRC)T: Encoder Tail Bits



Forward Traffic Channel Frame Structure

• For signaling

MessageLength

(in bytes)

8 bits

Data

N MSG = 16 ~ 1160 bits

CRC

16 bits

Padding= …000...



Logical Reverse CDMA Channel

Reverse CDMA Channel

AccessCh 1

AccessCh n... Traffic

Ch 1TrafficCh m

Address by Long Code PNs

n 32 m 62

…



Access Channels

• To access the system, respond the page, make call origination and process other messages between the MS and the BS

• 4.8 kbps slotted random access channel

• MS is identified by orthogonal of long codeAccess

ChannelInformation

Bits(88 bits/frame)

4.4 kbps


R=1/3, K=9

CodeSymbol

14.4 ksps

SymbolRepetition

BlockInterleaver

ModulatorSymbol

(Walsh chip)


Add 8-bitEncoder

Tail 4.8 kbps

CodeSymbol

28.8 ksps

CodeSymbol

28.8 ksps

64-aryOrthogonalModulator Long Code

Generator

Long Code Mask

4.8 ksps



Long code mask contents

110001111Access Channel

NumberPaging Channel

NumberBase StationIdentification

Pilot Offset for the Forward Channel

1100011000 Permuted ESN

Access Channel Long Code Mask

Reverse Traffic Channel Public Long Code Mask

41 33 32 28 27 25 24 9 8 0

41 32 31 0

ESN=(E31, E30, E29, E28, E27, E26, E25, … , E2, E1, E0)Permuted ESN=(E0, E31, E22, E13, E4, E26, E17, E8, E30, E21, E12, E3, E25, E16, E7, E29, E20, E11, E2, E24, E15, E6, E28, E19, E10, E1, E23, E14, E5, E27, E18, E9)



Access Channel

AccessChannel

• Is used by the MS to initiate communication with the BS & to respond to Paging Channel message

Fixed data rate (4800 bps) & 20 ms frame duration

•Access Channel Message may carry•Origination of a call • Paging responses•Orders response • Data bursts•Acknowledgements to Paging Channel message•Registration

Information Bits = 88 bitsEncoder Tail

8 bits

96 bits (20 ms)

•Basic frame structure



Access Channel Frame Structure

• Access channel message has length of 88 x N bits

• Access channel slot is as

– Access channel frame = 88-bits + 8-bit tail bits (all 0s)

– The value of PAM_SZ and MAX_CAP_SZ are received on the paging channel

MessageLength

(in bytes)

8 bits

Data

N MSG = 2 ~ 842 bits

CRC

16 bits

Padding= …000...

Access Channel Preamble = 000…000

96 x (1+PAM_SZ) bits

Access Channel Frame

96 bits

... Access Channel Frame

96 bits

96 x (4+PAM_SZ+MAX_CAP_SZ) bits



Access Channel Slot Structure

Access ChannelSlot Structure

Is (3+MAX_CAP_SZ)+(1+PAM_SZ) Access Channel frames in length

•An Access Channel slot begins & ends on an Access Channel frame boundary.

•Access Channel slots begin at Access Channel frames in which t mod (4+MAX_CAP_SZ+PAM_SZ)=0 & t: system time in frames

Preamble Max Capsule Size

Access TransmissionMax Length

Access SlotBoundary

20 msAccess channel frame

Access channel slot of five20 ms Access Channel frames

Access Slot n Access Slot n+1 Access Slot n+2



Access Channel Structure

Access Channel Slot

ACFrame

ACFrame

ACFrame

ACFrame

ACFrame

Access Channel Preamble ACBody

ACBody

ACBody

T T T

Access Channel Message Capsule

Access Channel Message Padding

MSGLength

Message Body CRC

8 bits 2~842 bits 30 bits

8 MSG_Length bits As Required

88 Nf bits

Nf frames=96 Nf bits1+ PAM_SZ frame=96 (1+ PAM_SZ)bits

20 ms = 96 bits

0.02 (4+PAM_SZ+MAX_CAP_SZ) sec = 96 (4+PAM_SZ+MAX_CAP_SZ) bits

AC frame = Access Channel frameNf :: Number of Access Channel framesneeded for message transmissionT :: Encoder Tail bits



Access Channel field (MSG_Length & CRC)

Access Channel field(MSG_Length & CRC)



Message Body CRC



MSGLength

•The MS set the field of to the length of the message in octets, including the MSG_Length, the message body & the CRC.

•The field shall be 8 bits in length, & the MS shall limit the maximum Access Channel length to 110 octets or 880 bits

• The CRC includes the MSG_Length & the message body. The generator polynomial for the CRC is::

g(x)=X30+X29+X21+X20+X15+X13+X12+X11+X8+X7+X6+X2+1



Access Channel field (Message Body)

Access Channel field(Message Body)



Message Body CRC



MSGLength

Message TypeCommon Layer 2 &Identification field

Common Authenticationfield

Reserved or othersas needed

•Registration Message = “00000001”•Order Message = “00000010”•Data Burst Message = “00000011”•Origination Message = “00000110”•Page Response Message = “00000101”•Authentication Challenge Response Message = “00000110”







Message Body CRC



MSGLength




•ACK_SEQ:: Acknowledgement Sequence Number • MSG_SEQ:: Message Sequence Number•ACK_REQ:: Acknowledgement Required Indicator • VALID_ACK:: Valid Acknowledgement Indicator•ACK_TYPE:: Acknowledgement Address Type • MSID_TYPE:: MS Identifier field type•MSID_LEN:: MS Identifier field length • MSID:: MS Identifier

8 fields







Message Body CRC



MSGLength




AUTH_MODE: Authentication modeAUTHR: Authentication dataRANDC: Random Challenge valueCOUNT: Call history parameter

4 fields



Access Channel field: Registration Message

Access Channel field Registration

Message



Message Body CRC



MSGLength




00000001

Registration MessageRegistration Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

AUTH_MODE(2 bits)

AUTHR(0 or 18 bits)

RANDC(0 or 8 bits)

COUNT(0 or 6 bits)

REG_TYPE(4 bits)

SLOT_CYCLEINDEX(3 bits)

MOB_P_REV(8 bits)

SCM(8 bits)

MOB_TERM(1 bits)

Reserved(6 bits)



Access Channel field: Order Message

Access Channel field Order Message



Message Body CRC



MSGLength




00000010

Order MessageOrder Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

Reversed(2 bits)

Order(6 bits)

ADDR_RECORD_LEN

(3 bits)

Order-specificfield if used

(8 Add_record_len bits)

Reserved(5 bits)

Does NOT have This Field



Access Channel field: Data Burst Message

Access Channel field Data Burst Message



Message Body CRC



MSGLength




00000011

Data Burst MessageData Burst Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

AUTH_MODE(2 bits)

AUTHR(0 or 18 bits)

RANDC(0 or 8 bits)

COUNT(0 or 6 bits)

MSG_NUMBER

(8 bits)

Burst_TYPE(6 bits)

NUM_MSGS(8 bits)

SNUM_FIELD(8 bits)

CHARi(8 bits)



Access Channel field: Origination Message

Access Channel field Origination Message



Message Body CRC



MSGLength




00000100

Origination MessageOrigination Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

AUTH_MODE(2 bits)

AUTHR(0 or 18 bits)

RANDC(0 or 8 bits)

COUNT(0 or 6 bits)

1(1

bits

)2

(3 b

its)

3(8

bits

)4

(8 b

its)

5(3

bits

)6

(1 b

its)

7(0

or

16 b

its)

8(1

bits

)9

(1 b

its)

10(0

o 3

bits

)11

(0 o

r 4

bits

)12

(1 b

its)

13(8

bits

)14

(4 o

r 8

bits

)15

(1 b

its)

16(0

~7 b

its)

1:: MOB_TERM 2::SLOT_CYCLE_INDEX 3::MOB_P_REV 4::SCM 5::REQUEST_MODE 6::SPECIAL_SERVICE 7::SERVICE_OPATION 8::PM 9:DIGIT_MODE 10::NUMBER_TYPE 11::NUMBER_PLAN 12::MORE_FIELDS 13::NUM_FIELDS 14::CHARi 15::NAR_AN_CAP 16::RESERVED

NUM_FIELDS occurrences of this field



Access Channel field: Page Response Message

Access Channel field Page Response

Message



Message Body CRC



MSGLength




00000101

Page Response MessagePage Response Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

AUTH_MODE(2 bits)

AUTHR(0 or 18 bits)

RANDC(0 or 8 bits)

COUNT(0 or 6 bits)

MO

B_

TE

RM

(1 b

its)

SLO

T_C

YC

LE

IND

EX

(3 b

its)

MO

B_

P_R

EV

(8 b

its)

SCM

(8 b

its)

RE

QU

EST

_M

OD

E(3

bit

s)

SER

VIC

E_

OP

TIO

N(1

6 b

its)

PM

(1 b

its)

NA

R_A

N_C

AP

(1 b

its)

RE

SER

VE

D(5

bit

s)



Access Channel field: Authentication Challenge Response Message

Access Channel field Authentication Challenge

Response Message



Message Body CRC



MSGLength




00000110

Authentication Challenge Response MessageAuthentication Challenge Response Message

ACK_SEQ(3 bits)

MSG_SEQ(3 bits)

ACK_REQ(1 bits)

VALID_ACK(1 bits)

ACK_TYPE(3 bits)

MSID_TYPE(3 bits)

MSID_LEN(4 bits)

MSID(8MSID_LEN)

RESERVED(2 bits)

AUTHR(0 or 18 bits)

RESERVED(4 bits)



Reverse Traffic Channels

• Variable data rates and format are as forward traffic channel. But transmission duty cycle is reduced accordingly. (Bits are not repeated on this channel.)

• Message format is identical to the forward traffic channel.

Reverse TrafficChannel

Information Bits(172, 80, 40 or16 bits/frame)



R=1/3, K=9

SymbolRepetition

BlockInterleaver

CodeSymbol

28.8 kspsCode

Symbol

28.8 ksps

Add Frame Quality Indicator

for 9600 &4800 bps Rates

Add 8-bitEncoder

Tail9.2 kbps4.4 kbps2.0 kbps0.8 kbps


CodeSymbol

28.8 ksps14.4 ksps 7.2 ksps 3.6 ksps

Long CodeMaskLong Code

Generator

PN Chips 1.2288 Mcps64-ary

OrthogonalModulator

ModulationSymbol(Walsh chip)

4.8 ksps(307.2 kcps)

Data BurstRandomizer

Frame Data Rate



Reverse CDMA Channel Signal Generation



Reverse Channel Modulator (Spreading)

• Identical I, Q signals; but different I, Q PN sequences (long code + short code)

• OQPSK modulation



Reverse Link Modulation Parameters

• 20 ms interleaver for time diversity

• Orthogonal 64-ary Walsh modulation symbols

• Long code of period 2 42 -1 (for channel identification) concatenated with PN codes of length 2 15.

• Noncoherent OQPSK

• Diversity– time diversity: coding + interleaving

– path diversity: RAKE receiver

– spatial diversity: 2 Rx antennas (4 Rx antennas available during handoff)



Reverse Channel Demodulation

• System with 4 fingers and 8 searchers

Antenna BAntenna A

Nocoherent Maximal Ratio Combining

Soft Decisions to Viterbi Decoder



Signaling Flow of Registration Process

• MS notifies BS of its presence (location, status, identification, etc.) in the system

• IS-95 supports the following registration types:– power-up registration

– power-down registration

– timer-based registration

– distance-based registration

– zone-based registration

– parameter-change registration

– ordered registration

– implicit registration



Signaling Flow of Registration Process

MS BS MSCNewVLR

OldVLR

HLR

Register Determination

Global Challenge

Register

Validate RAND

ISDN REGISTERREGISTER

IS-41 REGNOT

Database Update

IS-41 REGCANC

ConfirmREGNOT ResponseREGISTER ResponseISDN

REGISTERRegister Confirm



Initialization and Call Processing of MS

• Acquires the pilot channel

• Receives the sync channel with sync channel message

• Adjust to system timing

• Receives the paging channel message

• Sends origination message (also registration) on the access channel

• Receives channel assignment message on the paging channel

• Initializes the traffic channel

• Enters conversion substate

Date post:	14-Dec-2015
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An Introduction to CDMA Air Interface: TIA/EIA/IS-95A Advanced Technology Center Computer &...

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