Download - An Introduction to CDMA Air Interface
An Introduction to CDMA Air Interface:
TIA/EIA/IS-95A
Advanced Technology Center
Computer & Communications Research Laboratories
Industrial Technology Research Institute
Ray-Guang Cheng
Contents
• Introduction
• Forward CDMA Channel
• Reverse CDMA Channel
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CDMA Around the World
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Multiple Access
• FDMA
– Advanced Mobile Phone Service (AMPS) and Total Access
Communications System (TACS)
– AMPS systems use 30 kHz "slices" of spectrum for each channel
– Narrowband AMPS (NAMPS) requires only 10 kHz per channel
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– 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 of
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:
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• 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.
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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
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Frequency Plan of ANSI J-STD-008
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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.
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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
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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
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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
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• 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,
giving a total of 215-6 = 512 possible assignments
– 9-bit number that identifies the pilot phase assignment is called the Pilot
Offset
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• 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
channel
– successful accesses are normally followed by an assignment to a
dedicated traffic channel
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– 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
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– 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
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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
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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.
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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.
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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
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– 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.
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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 3 (Mobile Station Control Processes)
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Layer 2
(Primary Traffic)
Layer 2
(Secondary Traffic)
Layer 2
(Signaling)
Multiplex Sublayer (Traffic Channel)
Layer 2
(Link Layer)
Paging & Access
Channels
Layer 2
Sync
Channels
Layer 1 (Physical Layer)
Multiplex Option Information
Format Bits Primary
Traffic
Signaling
Traffic
Secondary
Traffic
Transmit
Rate
(bps)
Mixed
Mode (
MM )
Traffic
Type (
TT )
Traffic
Mode
( TM )
Bits/frame Bits/frame Bits/frame
0 - - 171 0 0
1 0 00 80 88 0
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1 0 01 40 128 0
1 0 10 16 152 0
1 0 11 0 168 0
1 1 00 80 0 88
1 1 01 40 0 128
1 1 10 16 0 152
9600
1 1 11 0 0 168
4800 - - - 80 0 0
2400 - - - 40 0 0
1200 - - - 6 0 0
Primary and Signaling Traffic
MM
=0
MM
=1
MM
=1
MM
TT
=0
TT
=0
TT
TM
=00
TM
=01
TM
Primary Traffic = 171 bits
Primary Traffic
= 80 bits
Signaling Traffic
= 88 bits
Primary Traffic
= 40 bits
Signaling Traffic
= 128 bits
Primary Traffic Signaling Traffic
9600 bps Primary
Traffic only
Dim & Burst with rate 1/2
primary & signaling traffic
Dim & Burst with rate 1/4
primary & signaling traffic
Dim & Burst with rate 1/8
172 bits
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MM
=1
MM
=1
TT
=0
TT
=0
TM
=10
TM
=11
Primary Traffic
= 16 bits
Signaling Traffic
= 152 bits
Signaling Traffic = 168 bits
Primary Traffic = 80 bits
Primary Traffic = 40 bits
Primary Traffic = 16 bits
Dim & Burst with rate 1/8
primary & signaling traffic
Blank & Burst with
signaling traffic only
4800 bps primary
traffic only
2400 bps primary
traffic only
1200 bps Primary
traffic only
80 bits
40 bits
16 bits
Secondary Traffic
MM
=1TT
=1
TM
=00
Primary Traffic
= 80 bits
Signaling Traffic
= 88 bits
MM
=1TT
=1
TM
=01
Primary Traffic
= 40 bits
Signaling Traffic
= 128 bits
Dim & Burst with rate
1/2 primary &
Secondary traffic
Dim & Burst with rate
1/4 primary &
172 bits
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=1 =1 =01 = 40 bits = 128 bits
MM
=1TT
=1
TM
=10
Primary Traffic
= 16 bits
Signaling Traffic
= 152 bits
MM
=1TT
=1
TM
=11Signaling Traffic = 168 bits
1/4 primary &
Secondary traffic
Dim & Burst with rate
1/8 primary &
Secondary traffic
Blank & Burst with
Secondary traffic only
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.
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• 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
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– 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
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• 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:
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• 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
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– 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
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• 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
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– 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
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– 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
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• 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
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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
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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)
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• 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
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Pilot
Chan
Sync
Chan
W0 W32
Paging
Ch 1
W1
...Up
to W7
Paging
Ch 7
W8
...Up
to
Traffic
Ch N
Traffic
Ch 1
Traffic DataMobile Power
Control Sub-Channel
...
W31
Traffic
Ch 24Up
to
...
W63
Traffic
Ch 55
W33
Traffic
Ch 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
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• Used in initial system acquisition and handoff for MS
Pilot
Channel
(All 0’s)
Walsh
Function
W0
PN 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
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Sync
Channel
Bits 1.2 kbps
Convolutional
Encoder
R=1/2, K=9
Code
Symbol
2.4 ksps
Symbol
Repetition
Block
Interleaver
Modulation
Symbol
4.8 ksps
Modulation
Symbol
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:
Message
Length
(in bytes)
8 bits
Data
N MSG = 2 ~ 1146 bits
CRC
30 bits
Padding
= …000...
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– 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
Paging Channels
• 4.8 k or 9.6 k bps
• Same time alignment as the traffic channels
• To page MS and to process other ordersWalsh
Function
W p
1 ≤ p ≤ 7
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Paging
Channel
Bits 4.8 kbps
or
9.6 kbps
Convolutional
Encoder
R=1/2, K=9
Code
Symbol
9.6 ksps
or
19.2 ksps
Symbol
Repetition
Block
Interleaver
Modulation
Symbol
19.2 ksps
Modulation
Symbol
19.2 ksps
PN Chips
1.2288 Mcps
Long Code
Mask for
Paging
Channel p
Long Code
Generator1.2288 Mcps
Decimator
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:
Message
Length
(in bytes)
8 bits
Data
N MSG = 2 ~ 1146 bits
CRC
30 bits
Padding
= …000...
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• 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
Forward Traffic Channels
• 9.6, 4.8, 2.4, or 1.2 k bps; 20 ms frames
• Rate can be changed every frame
Forward Traffic
Channel
Information
Bits for User m8.6 kbps
Convolutional
Encoder
R=1/2, K=9
Symbol
Repetition
Add Frame
Quality Indicator
for 9600 &
4800 bps Rates
Add 8-bit
Encoder
Tail9.2 kbps 9.6 kbps 19.2 kbps
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Bits for User m
(172, 80, 40 or
16 bits/frame)
4.0 kbps
2.0 kbps
0.8 kbps
R=1/2, K=9
Block
Interleaver
Modulation
Symbol
19.2 ksps
Modulation
Symbol
19.2 ksps
4800 bps RatesTail
4.4 kbps
2.0 kbps
0.8 kbps
4.8 kbps
2.4 kbps
1.2 kbps
9.6 kbps
4.8 kbps
2.4 kbps
Long Code
Mask for
Paging
Channel p
Long Code
Generator
1.2288 Mcps
Decimator
19.2 ksps Walsh
Function
W m
PN Chips
1.2288 Mcps
Decimator
MUX
Power
Control
Bits800 bps
800 Hz
Forward Traffic Channel Frame Structure
8
T
12
F
172
information bits
192 bits (20 ms)9600 bps
Frame
8880
96 bits (20 ms)4800 bps
Frame
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8
T
8
F
80
information bits
Frame
8
T
8
F
40
information bits
48 bits (20 ms)2400 bps
Frame
8
T
8
F
16
information bits
24 bits (20 ms)1200 bps
Frame
F: Frame Quality Indicator (CRC)
T: Encoder Tail Bits
Forward Traffic Channel Frame Structure
• For signaling
Message
Length
(in bytes)
8 bits
Data
N MSG = 16 ~ 1160 bits
CRC
16 bits
Padding
= …000...
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Logical Reverse CDMA Channel
Reverse CDMA Channel
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Access
Ch 1
Access
Ch n... Traffic
Ch 1
Traffic
Ch 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
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Access
Channel
Information
Bits
(88 bits/frame)4.4
kbps
Convolutional
Encoder
R=1/3, K=9
Code
Symbol
14.4
ksps
Symbol
Repetition
Block
Interleaver
Modulator
Symbol
(Walsh chip)
PN Chips 1.2288 Mcps
Add 8-bit
Encoder
Tail 4.8
kbps
Code
Symbol
28.8
ksps
Code
Symbol
28.8
ksps
64-ary
Orthogonal
Modulator Long Code
Generator
Long Code Mask
4.8 ksps
Long code mask contents
110001111Access Channel
Number
Paging Channel
Number
Base Station
Identification
Pilot Offset for the
Forward Channel
Access Channel Long Code Mask
41 33 32 28 27 25 24 9 8 0
41 32 31 0
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1100011000 Permuted ESN
Reverse Traffic Channel Public Long Code Mask
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
• 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
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ATC/CCL/ITRI
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Access
Channel
•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
Message
Length
(in bytes)
8 bits
Data
N MSG = 2 ~ 842 bits
CRC
16 bits
Padding
= …000...
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• 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
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
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
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ATC/CCL/ITRI
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Access Channel
Slot Structure
t mod (4+MAX_CAP_SZ+PAM_SZ)=0 & t: system time in frames
Preamble Max Capsule Size
Access Transmission
Max Length
Access Slot
Boundary20 ms
Access channel frame
Access channel slot of five
20 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
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
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Access Channel PreambleAC
BodyAC
BodyAC
BodyT 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
AC frame = Access Channel frame
Nf :: Number of Access Channel frames
needed for message transmission
T :: Encoder Tail bits
Access Channel field (MSG_Length & CRC)
Access Channel field
(MSG_Length & CRC)
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
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Length
•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)
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
•Registration Message = “00000001”•Order Message = “00000010”•Data Burst Message = “00000011”•Origination Message = “00000110”•Page Response Message = “00000101”•Authentication Challenge Response Message = “00000110”
Access Channel field (Message Body)
Access Channel field
(Message Body)
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
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ATC/CCL/ITRI
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
•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
Access Channel field (Message Body)
Access Channel field
(Message Body)
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
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ATC/CCL/ITRI
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
AUTH_MODE: Authentication mode
AUTHR: Authentication data
RANDC: Random Challenge value
COUNT: Call history parameter
4 fields
Access Channel field: Registration Message
Access Channel field
Registration
Message
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
REG_TYPE
(4 bits)
SLOT_CYCLE
INDEX(3 bits)
MOB_P_REV
(8 bits)
SCM
(8 bits)
MOB_TERM
(1 bits)
Reserved
(6 bits)
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_LEN)
AUTH_MODE
(2 bits)
AUTHR
(0 or 18 bits)
RANDC
(0 or 8 bits)
COUNT
(0 or 6 bits)
Access Channel field: Order Message
Access Channel field
Order Message
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
Reversed
(2 bits)
Order
(6 bits)
ADDR_
RECORD_LEN
(3 bits)
Order-specific
field if used
(8 × Add_record_len bits)
Reserved
(5 bits)
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ATC/CCL/ITRI
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Message Body CRCLength
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_LEN)
(3 bits) (8 × Add_record_len bits)
Does NOT have This Field
Access Channel field: Data Burst Message
Access Channel field
Data Burst Message
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
MSG_
NUMBERBurst_TYPE NUM_MSGS SNUM_FIELD CHARi
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_LEN)
AUTH_MODE
(2 bits)
AUTHR
(0 or 18 bits)
RANDC
(0 or 8 bits)
COUNT
(0 or 6 bits)
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
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
1
(1 b
its)
2
(3 b
its)
3
(8 b
its)
4
(8 b
its)
5
(3 b
its)
6
(1 b
its)
7
(0 o
r 1
6 b
its)
8
(1 b
its)
9
(1 b
its)
10
(0 o
3 b
its)
11
(0 o
r 4
bit
s)1
2
(1 b
its)
13
(8 b
its)
14
(4 o
r 8
bit
s)1
5
(1 b
its)
16
(0~
7 b
its)
Chung-Wei Ku
ATC/CCL/ITRI
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_LEN)
AUTH_MODE
(2 bits)
AUTHR
(0 or 18 bits)
RANDC
(0 or 8 bits)
COUNT
(0 or 6 bits)
(0 o
r 1
6 b
its)
(0 o
3 b
its)
(0 o
r 4
bit
s)
(4 o
r 8
bit
s)
(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
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength M
OB
_
TE
RM
(1 b
its)
SL
OT
_C
YC
LE
IND
EX
(3 b
its)
MO
B_
P_
RE
V
(8 b
its)
SC
M
(8 b
its)
RE
QU
ES
T_
MO
DE
(3 b
its)
SE
RV
ICE
_
OP
TIO
N
(16
b
its)
PM
(1 b
its)
NA
R_
AN
_C
AP
(1 b
its)
RE
SE
RV
ED
(5 b
its)
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Message Body CRCLength
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_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)
SL
OT
_C
YC
LE
IND
EX
(3 b
its)
MO
B_
P_
RE
V
(8 b
its)
SC
M
(8 b
its)
RE
QU
ES
T_
MO
DE
(3 b
its)
SE
RV
ICE
_
OP
TIO
N
(16
b
its)
(1 b
its)
NA
R_
AN
_C
AP
(1 b
its)
RE
SE
RV
ED
(5 b
its)
Access Channel field:
Authentication Challenge Response Message
Access Channel field
Authentication Challenge
Response Message
Access Channel Message Capsule
Access Channel Message Padding
Message Body CRC
8 bits 2~842 bits 30 bits
8× MSG_Length bits As Required
MSGLength
RESERVED
(4 bits)
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Length
Message TypeCommon Layer 2 &
Identification field
Common Authentication
field
Reserved or others
as needed
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
(8×MSID_LEN)
RESERVED
(2 bits)
AUTHR
(0 or 18 bits)
(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 Traffic
Channel
Information Bits
Convolutional
EncoderSymbol
Repetition
Add Frame
Quality Indicator
for 9600 &
Add 8-bit
Encoder
Code
Symbol
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Information Bits
(172, 80, 40 or
16 bits/frame)
8.6 kbps
4.0 kbps
2.0 kbps
0.8 kbps
Encoder
R=1/3, K=9Repetition
Block
Interleaver
Code
Symbol
28.8 ksps
Code
Symbol
28.8 ksps
for 9600 &
4800 bps Rates
Encoder
Tail9.2 kbps
4.4 kbps
2.0 kbps
0.8 kbps
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
28.8 ksps
14.4 ksps
7.2 ksps
3.6 ksps
Long Code
MaskLong Code
Generator
PN Chips
1.2288 Mcps64-ary
Orthogonal
Modulator
Modulation
Symbol
(Walsh chip)
4.8 ksps
(307.2 kcps)
Data Burst
Randomizer
Frame Data Rate
Reverse CDMA Channel Signal Generation
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Reverse Channel Modulator (Spreading)
• Identical I, Q signals; but different I, Q PN sequences (long code
+ short code)
• OQPSK modulation
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ATC/CCL/ITRI
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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
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ATC/CCL/ITRI
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• 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
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ATC/CCL/ITRI
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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
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ATC/CCL/ITRI
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– 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 MSCNew
VLR
Old
VLRHLR
Register Determination
Global Challenge
Register
Validate RAND
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Validate RAND
ISDN REGISTERREGISTER
IS-41 REGNOT
Database Update
IS-41 REGCANC
ConfirmREGNOT ResponseREGISTER
ResponseISDN
REGISTER
Register 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
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ATC/CCL/ITRI
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• Sends origination message (also registration) on the access
channel
• Receives channel assignment message on the paging channel
• Initializes the traffic channel
• Enters conversion substate