An Introduction to CDMA Air Interface:
TIA/EIA/IS-95A
Advanced Technology Center
Computer & Communications Research Laboratories
Industrial Technology Research Institute
Ray-Guang Cheng
[email protected]
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
– 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
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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
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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
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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.
• 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).
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Forward Link Channel Parameters
Channel
Sync
Data rate
1200
4800
9600
1200
2400
2
2
1
8
4
Code repetition
Modulation
symbol rate
4800
PN chips/
modulation symbol
PN chips/bit
Paging
Traffic
4800 9600 bps
2
1
19,200 19,200 19,200 19,200 19,200 19,200 sps
256
64
64
64
64
64
64
1024
256
128
1024
512
256
128
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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 vectormodulated on the RF carrier. The spreading modulation is thus
QPSK, superimposed on a BPSK code symbol stream.
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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
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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
• 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
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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
– 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
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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
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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
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Reverse CDMA Channel Parameters, Rate Set 1
Channel
Access
Data rate
4,800
Code Rate
1/3
Symbol Rate before Repetition
14,400
Symbol Repetition
2
Symbol Rate after Repetition
28,800
Transmit Duty Cycle
1
Code Symbols/Modulation Symbol
6
PN Chips/Modulation Symbol
256
PN chips transmitted/bit
256
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Traffic
1,200 2,400
4,800 9,600 bps
1/3
1/3
1/3
1/3
3,600 7,200 14,400 28,800 sps
8
4
2
1
28,800 28,800 28,800 28,800 sps
1/8
1/4
1/2
1
6
6
6
6
256
256
256
256
128
128
128
128
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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.
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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
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
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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
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CDMA Protocol
Upper Layers
(Primary Traffic)
Upper Layers
(Secondary Traffic)
Layer 2
(Primary Traffic)
Layer 2
(Secondary Traffic)
Layer 3 (Mobile Station Control Processes)
Layer 2
(Signaling)
Multiplex Sublayer (Traffic Channel)
Layer 2
(Link Layer)
Paging & Access
Channels
Layer 2
Sync
Channels
Layer 1 (Physical Layer)
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Multiplex Option Information
Format Bits
Transmit
Rate
(bps)
9600
4800
2400
1200
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Mixed
Mode (
MM )
Traffic
Type (
TT )
0
1
1
1
1
1
1
1
1
-
0
0
0
0
1
1
1
1
-
Traffic
Mode
( TM )
00
01
10
11
00
01
10
11
-
Primary
Traffic
Signaling
Traffic
Secondary
Traffic
Bits/frame
Bits/frame
Bits/frame
171
80
40
16
0
80
40
16
0
80
40
6
0
88
128
152
168
0
0
0
0
0
0
0
0
0
0
0
0
88
128
152
168
0
0
0
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Primary and Signaling Traffic
172 bits
9600 bps Primary
Traffic only
MM
=0
Primary Traffic = 171 bits
Dim & Burst with rate 1/2 MM
primary & signaling traffic =1
TT
=0
TM
=00
Dim & Burst with rate 1/4
primary & signaling traffic
MM
=1
TT
=0
TM
=01
Dim & Burst with rate 1/8
primary & signaling traffic
MM
=1
TT TM Primary Traffic
=0 =10
= 16 bits
Blank & Burst with
signaling traffic only
MM
=1
TT
=0
TM
=11
Signaling Traffic
= 88 bits
Primary Traffic
= 80 bits
Primary Traffic
= 40 bits
Signaling Traffic
= 128 bits
Signaling Traffic
= 152 bits
Signaling Traffic = 168 bits
80 bits
4800 bps primary
traffic only
Primary Traffic = 80 bits
40 bits
2400 bps primary
traffic only
Primary Traffic = 40 bits
16 bits
1200 bps Primary
traffic only
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Primary Traffic = 16 bits
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Secondary Traffic
172 bits
Dim & Burst with rate
MM
1/2 primary &
=1
Secondary traffic
TT
=1
TM
=00
Dim & Burst with rate
MM
1/4 primary &
=1
Secondary traffic
TT
=1
TM
=01
Dim & Burst with rate MM
1/8 primary &
=1
Secondary traffic
TT TM Primary Traffic
=1 =10
= 16 bits
MM
Blank & Burst with
Secondary traffic only =1
TT
=1
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TM
=11
Primary Traffic
= 80 bits
Primary Traffic
= 40 bits
Signaling Traffic
= 88 bits
Signaling Traffic
= 128 bits
Signaling Traffic
= 152 bits
Signaling Traffic = 168 bits
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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)
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
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Logical Forward CDMA Channel
Forward CDMA Channel
Pilot
Chan
W0
Sync Paging
Chan Ch 1
W32
W1
...
Up
to
Paging Traffic
Ch 7 Ch 1
W7
...
W8
Traffic Data
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Traffic
Ch N
...
Up
to
Traffic Traffic
Ch 24 Ch 25
W31
W33
...
Up
to
Traffic
Ch 55
W63
Mobile Power
Control Sub-Channel
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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
Walsh
Function
W0
Pilot
Channel
(All 0’s)
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PN Chips
1.2288 Mcps
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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
Walsh
Function
W32
Sync
Convolutional
Channel
Encoder
1.2
kbps
Bits
R=1/2, K=9
Code
Symbol
2.4 ksps
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Symbol
Repetition
Modulation
Symbol
4.8 ksps
Block
Interleaver
Modulation
Symbol
PN Chips
1.2288 Mcps
4.8 ksps
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Sync Channel Frame Structure
• Sync channel message has length of 93 x N bits
Message
Length
(in bytes)
Data
8 bits
N MSG = 2 ~ 1146 bits
• Sent in N superframes:
CRC
Padding
= …000...
30 bits
– 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.
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– paging
channel data rate
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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
Paging
Convolutional
Channel
Encoder
Bits 4.8 kbps R=1/2, K=9
or
9.6 kbps
Code
Symbol
9.6 ksps
or
19.2 ksps
Long Code
Mask for
Paging
Channel p
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Symbol
Repetition
Modulation
Symbol
19.2 ksps
Block
Interleaver
Walsh
Function
Wp
1p7
PN Chips
1.2288 Mcps
Modulation
Symbol
19.2 ksps
19.2 ksps
19.2 ksps
Long Code
Generator
Decimator
1.2288 Mcps
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Paging Channel Frame Structure
• Synchronized paging channel message has length of 47 x N or 95 x N bits
Message
Length
(in bytes)
Data
8 bits
N MSG = 2 ~ 1146 bits
CRC
Padding
= …000...
30 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
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Forward Traffic Channels
• 9.6, 4.8, 2.4, or 1.2 k bps; 20 ms frames
• Rate can be changed every frame
Add Frame
Forward Traffic
Quality Indicator
Channel
for 9600 &
Information 8.6 kbps
Bits for User m 4.0 kbps 4800 bps Rates
(172, 80, 40 or 2.0 kbps
16 bits/frame) 0.8 kbps
Modulation
Symbol
19.2 ksps
Long Code
Mask for
Paging
Channel p
Block
Interleaver
9.2 kbps
4.4 kbps
2.0 kbps
0.8 kbps
Modulation
Symbol
Add 8-bit
Encoder
Tail
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
Convolutional
Encoder
R=1/2, K=9
Power
Control 800 bps
Bits
PN Chips
1.2288 Mcps
MUX
19.2 ksps
19.2 ksps
Long Code
Generator
Decimator
1.2288 Mcps
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19.2 kbps
9.6 kbps
4.8 kbps
2.4 kbps
Symbol
Repetition
Decimator
800 Hz
Walsh
Function
Wm
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Forward Traffic Channel Frame Structure
9600 bps
Frame
4800 bps
Frame
2400 bps
Frame
1200 bps
Frame
F: Frame Quality Indicator (CRC)
Encoder
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Center Tail Bits
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192 bits (20 ms)
172
12
8
information bits
F
T
80
8
8
information bits
F
T
40
8
8
information bits
F
T
16
8
8
information bits
F
T
96 bits (20 ms)
48 bits (20 ms)
24 bits (20 ms)
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Forward Traffic Channel Frame Structure
• For signaling
Message
Length
(in bytes)
Data
8 bits
N MSG = 16 ~ 1160 bits
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CRC
Padding
= …000...
16 bits
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Logical Reverse CDMA Channel
Reverse CDMA Channel
Access
Ch 1
...
Access
Ch n
Traffic
Ch 1
…
Traffic
Ch m
Address by Long Code PNs
n  32
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m  62
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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 code
Access
Channel
Information
Bits
4.4
(88 bits/frame) kbps
Add 8-bit
Encoder
Tail
Code
Convolutional Symbol
Encoder
4.8
R=1/3, K=9
14.4
kbps
ksps
64-ary
Orthogonal
Modulator
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Symbol
Repetition
Code
Symbol
28.8
ksps
Block
Interleaver
Code
Symbol
28.8
ksps
4.8 ksps
Modulator
Symbol
(Walsh chip)
PN Chips 1.2288 Mcps
Long Code
Generator
Long Code Mask
Chung-Wei Ku
ATC/CCL/ITRI
Long code mask contents
41
33 32
25 24
Access Channel Paging Channel Base Station
Number
Number
Identification
110001111
32 31
41
28 27
1100011000
9
8
0
Pilot Offset for the
Forward Channel
Access Channel Long Code Mask
0
Permuted ESN
Reverse Traffic Channel Public Long Code Mask
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)
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Chung-Wei Ku
ATC/CCL/ITRI
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
• Orders response
• Data bursts
• Acknowledgements to Paging Channel message
• Registration
Access
Channel
• Basic frame structure
96 bits (20 ms)
Information Bits = 88 bits
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Encoder Tail
8 bits
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel Frame Structure
• Access channel message has length of 88 x N bits
Message
Length
(in bytes)
Data
8 bits
N MSG = 2 ~ 842 bits
CRC
Padding
= …000...
16 bits
• Access channel slot is as
96 x (4+PAM_SZ+MAX_CAP_SZ) bits
Access Channel Preamble = 000…000
Access Channel Frame
96 x (1+PAM_SZ) bits
96 bits
...
Access Channel Frame
96 bits
– 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
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Chung-Wei Ku
ATC/CCL/ITRI
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
Access Slot n
Access Channel
Slot Structure
Access Transmission
Max Length
Preamble
Access Slot
Boundary
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Access Slot n+1
Access Slot n+2
Access channel slot of five
20 ms Access Channel frames
Max Capsule Size
20 ms
Access channel frame
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel Structure
0.02  (4+PAM_SZ+MAX_CAP_SZ) sec = 96  (4+PAM_SZ+MAX_CAP_SZ) bits
Access Channel Slot
20 ms = 96 bits
AC
Frame
AC
Frame
AC
Frame
1+ PAM_SZ frame=96  (1+ PAM_SZ)bits
Access Channel Preamble
AC
Frame
AC
Frame
Nf frames=96  Nf bits
AC T
Body
AC T AC
T
Body
Body
88  Nf bits
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
AC frame = Access Channel frame
Nf :: Number of Access Channel frames
needed for message transmission
T :: Encoder Tail bits
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8 bits
MSG
Length
2~842 bits
Message Body
As Required
Padding
30 bits
CRC
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field (MSG_Length & CRC)
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
As Required
Padding
30 bits
Access Channel field
(MSG_Length & CRC)
CRC
• 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
• 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
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Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field (Message Body)
Access Channel Message Capsule
8 MSG_Length bits
As Required
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
Padding
30 bits
Access Channel field
(Message Body)
CRC
Common Layer 2 & Common Authentication
Identification field
field
Message Type
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”
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ATC/CCL/ITRI
Access Channel field (Message Body)
Access Channel Message Capsule
8 MSG_Length bits
As Required
Access Channel Message
8 bits
MSG
Length
Access Channel field
(Message Body)
30 bits
2~842 bits
Message Body
Message Type
Padding
CRC
Common Layer 2 & Common Authentication
Identification field
field
Reserved or others
as needed
8 fields
•ACK_SEQ:: Acknowledgement Sequence Number
•ACK_REQ:: Acknowledgement Required Indicator
•ACK_TYPE:: Acknowledgement Address Type
•MSID_LEN:: MS Identifier field length
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•
•
•
•
MSG_SEQ:: Message Sequence Number
VALID_ACK:: Valid Acknowledgement Indicator
MSID_TYPE:: MS Identifier field type
MSID:: MS Identifier
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field (Message Body)
Access Channel Message Capsule
8 MSG_Length bits
As Required
Access Channel Message
8 bits
MSG
Length
30 bits
2~842 bits
Message Body
Message Type
Padding
CRC
Common Layer 2 & Common Authentication
Identification field
field
AUTH_MODE: Authentication mode
AUTHR: Authentication data
RANDC: Random Challenge value
COUNT: Call history parameter
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Access Channel field
(Message Body)
Reserved or others
as needed
4 fields
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field: Registration Message
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
As Required
Padding
Access Channel field
Registration
Message
30 bits
CRC
REG_TYPE SLOT_CYCLE MOB_P_REV SCM
(4 bits) INDEX(3 bits)
(8 bits)
(8 bits)
MOB_TERM
(1 bits)
Reserved
(6 bits)
Registration Message
Message Type
Common Layer 2 & Common Authentication
Identification field
field
Reserved or others
as needed
AUTH_MODE AUTHR
RANDC
COUNT
(2 bits)
(0 or 18 bits) (0 or 8 bits) (0 or 6 bits)
00000001
ACK_SEQ
(3 bits)
MSG_SEQ
(3 bits)
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ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field: Order Message
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
8 bits
MSG
Length
Access Channel field
Order Message
As Required
Padding
30 bits
2~842 bits
CRC
Message Body
Reversed
(2 bits)
Order
(6 bits)
Order-specific
ADDR_
Reserved
field if used
RECORD_LEN
(5 bits)
(8  Add_record_len bits)
(3 bits)
Order Message
Message Type
Common Layer 2 & Common Authentication
Identification field
field
00000010
Reserved or others
as needed
Does NOT have This Field
ACK_SEQ
(3 bits)
MSG_SEQ
(3 bits)
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ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field: Data Burst Message
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
Access Channel field
Data Burst Message
As Required
Padding
30 bits
CRC
MSG_
NUMBER
(8 bits)
Burst_TYPE NUM_MSGS SNUM_FIELD
(6 bits)
(8 bits)
(8 bits)
CHARi
(8 bits)
Data Burst Message
Message Type
Common Layer 2 & Common Authentication
Identification field
field
Reserved or others
as needed
AUTH_MODE AUTHR
RANDC
COUNT
(2 bits)
(0 or 18 bits) (0 or 8 bits) (0 or 6 bits)
00000011
ACK_SEQ
(3 bits)
MSG_SEQ
(3 bits)
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ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field: Origination Message
Access Channel Message Capsule
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
As Required
Padding
30 bits
CRC
Access Channel field
Origination Message
1
(1 bits)
2
(3 bits)
3
(8 bits)
4
(8 bits)
5
(3 bits)
6
(1 bits)
7
(0 or 16 bits)
8
(1 bits)
9
(1 bits)
10
(0 o 3 bits)
11
(0 or 4 bits)
12
(1 bits)
13
(8 bits)
14
(4 or 8 bits)
15
(1 bits)
16
(0~7 bits)
8 MSG_Length bits
Origination Message
Message Type
Common Layer 2 & Common Authentication
Identification field
field
00000100
ACK_SEQ
(3 bits)
NUM_FIELDS occurrences of this field
Reserved or others
as needed
AUTH_MODE AUTHR
RANDC
COUNT
(2 bits)
(0 or 18 bits) (0 or 8 bits) (0 or 6 bits)
MSG_SEQ
(3 bits)
ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
1:: MOB_TERM 2::SLOT_CYCLE_INDEX 3::MOB_P_REV 4::SCM 5::REQUEST_MODE 6::SPECIAL_SERVICE 7::SERVICE_OPATION 8::P M
9:DIGIT_MODE 10::NUMBER_TYPE 11::NUMBER_PLAN 12::MORE_FIELDS 13::NUM_FIELDS 14::CHARi 15::NAR_AN_CAP 16::RESERVED
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ATC/CCL/ITRI
Access Channel field: Page Response Message
Access Channel Message Capsule
RESERVED
(5 bits)
NAR_AN
_CAP
(1 bits)
PM
(1 bits)
SERVICE_
OPTION
(16 bits)
CRC
REQUEST_
MODE
(3 bits)
Message Body
30 bits
SCM
(8 bits)
2~842 bits
MOB_
P_REV
(8 bits)
8 bits
MSG
Length
Padding
SLOT_CYCLE
INDEX
(3 bits)
Access Channel Message
Access Channel field
Page Response
Message
As Required
MOB_
TERM
(1 bits)
8 MSG_Length bits
Page Response Message
Message Type
Common Layer 2 & Common Authentication
Identification field
field
00000101
ACK_SEQ
(3 bits)
Reserved or others
as needed
AUTH_MODE AUTHR
RANDC
COUNT
(2 bits)
(0 or 18 bits) (0 or 8 bits) (0 or 6 bits)
MSG_SEQ
(3 bits)
ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
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Chung-Wei Ku
ATC/CCL/ITRI
Access Channel field:
Authentication Challenge Response Message
Access Channel Message Capsule
8 MSG_Length bits
Access Channel Message
8 bits
MSG
Length
2~842 bits
Message Body
As Required
Padding
Access Channel field
Authentication Challenge
Response Message
30 bits
CRC
RESERVED
(4 bits)
Authentication Challenge Response Message
Message Type
00000110
ACK_SEQ
(3 bits)
Common Layer 2 & Common Authentication
Identification field
field
Reserved or others
as needed
RESERVED
AUTHR
(2 bits)
(0 or 18 bits)
MSG_SEQ
(3 bits)
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ACK_REQ VALID_ACK ACK_TYPE MSID_TYPE MSID_LEN
MSID
(1 bits)
(1 bits)
(3 bits)
(3 bits)
(4 bits) (8MSID_LEN)
Chung-Wei Ku
ATC/CCL/ITRI
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.
Code
Add
Frame
Reverse Traffic
Symbol
Convolutional
Add 8-bit
Symbol
Quality
Indicator
Channel
Encoder
Encoder
for 9600 &
Information Bits 8.6 kbps
28.8 ksps Repetition
9.2 kbps
9.6 kbps
R=1/3, K=9
Tail
(172, 80, 40 or 4.0 kbps 4800 bps Rates
14.4 ksps
4.4 kbps
4.8 kbps
16 bits/frame) 2.0 kbps
7.2 ksps
2.0 kbps
2.4 kbps
3.6 ksps
0.8 kbps
0.8 kbps
1.2 kbps
Code
Modulation Frame Data Rate
Symbol
PN Chips
Code
Symbol
64-ary
1.2288 Mcps
Symbol
(Walsh chip) Data Burst
28.8 ksps
Block
Orthogonal
Randomizer
Interleaver
28.8 ksps Modulator 4.8 ksps
Long Code
(307.2 kcps)
Mask
Long Code
Generator
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Chung-Wei Ku
ATC/CCL/ITRI
Reverse CDMA Channel Signal Generation
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Chung-Wei Ku
ATC/CCL/ITRI
Reverse Channel Modulator (Spreading)
• Identical I, Q signals; but different I, Q PN sequences (long code
+ short code)
• OQPSK modulation
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Chung-Wei Ku
ATC/CCL/ITRI
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)
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Chung-Wei Ku
ATC/CCL/ITRI
Reverse Channel Demodulation
• System with 4 fingers and 8 searchers
Antenna A
Antenna B
Nocoherent Maximal Ratio Combining
Soft Decisions to Viterbi Decoder
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Chung-Wei Ku
ATC/CCL/ITRI
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
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Chung-Wei Ku
ATC/CCL/ITRI
Signaling Flow of Registration Process
MS
BS
New
VLR
MSC
Old
VLR
HLR
Register Determination
Global Challenge
Register
Validate RAND
ISDN REGISTER
REGISTER
IS-41 REGNOT
Database Update
ISDN
REGISTER
REGISTER
Response
IS-41 REGCANC
Confirm
REGNOT Response
Register Confirm
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Chung-Wei Ku
ATC/CCL/ITRI
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
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Chung-Wei Ku
ATC/CCL/ITRI