IS 95 STANDARD 569
code sequence shall be input to a 14-bits shift register, which is shifted at 1.2288 MHz.
The contents of this shift register shall be loaded into a 14-bit latch exactly one power
control group (1.25 ms) before each reverse traffic channel frame boundary.
b
0
b
1
b
2
b
3
b
4
b
5
b
6
b
7
b
8
b
9
b
10
b
11
b
12
b
13
The binary (0 and 1) contents of this latch shall be denoted as where b
0
shall represent
the first bit to enter the shift register and b
13
shall represent the last (or most recent) bit to
enter the sift register. Each 20-ms reverse traffic channel frame shall be divided into 16
equal length (i.e. 1.25 ms) power control groups numbered from 0 to 15. The data burst
randomizer algorithm shall be as follows:
Data rate selected: 9600 bps
Frame transmission shall occur on power control groups numbered
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
Data rate selected: 4800 bps
Frame transmission shall occur on power control groups numbered
b
0
, 2 + b
1
, 4 + b
2
, 6 + b
3
, 8 + b
4
, 10 + b
5
, 12 + b
6
Data rate selected: 2400 bps
Frame transmission shall occur on power control groups numbered
b
0
if b
8
= 0, 2 + b
1
if b
8
= 1
4 + b
2
if b
9
= 0, 6 + b
3
if b
9
= 1
8 + b
4
if b
10
= 0, 10 + b
5
if b
10
= 1
12 + b
6
if b
11
= 0, 14 + b
7
if b
11
= 1
Data rate selected: 1200 bps
Frame transmission shall occur on power control groups numbered
b
0
if (b
8
= 0andb
12
= 0), 2 + b
1
if (b
8
= 1andb
12
= 0)
4 + b
2
if (b
9
= 0andb
12
= 1), 6 + b
3
if (b
9
= 1andb
12
= 1)
8 + b
4
if (b
10
= 0andb
13
= 0), 10 + b
5
if (b
10
= 1andb
13
= 0)
12 + b
6
if (b
11
= 0andb
13
= 1), 14 + b
7
if (b
11
= 1andb
13
= 1)
An example is shown in Figure 16.5.
570 STANDARDS
b
0
b
1
b
3
b
5
b
6
b
7
b
8
b
1
0
b
1
2
b
2
b
4
b
9
b
1
3
b
1
1
20 ms = 193 bits = 576 code symbols
= 96 walsh symbols = 16 power control groups
1.25 ms = 12 bits = 36 code symbols
= 6 Walsh symbols = 1 power control group
Code symbols transmitted:
Code symbols transmitted:
Code symbols transmitted:
Code symbols transmitted:
Previous frame
Previous frame
Previous frame
PN bits used
for scrambling
Sample masking streams shown
are for the 14-bit PN sequence:
(
b
0
,
b
1
, …,
b
13
) = 0 0 1 0 1 1 0 1 1 0 0 1 0 0
PCG 15
PCG 14
Power control group number
1 33 65 97 … 481 513 545 2 34 66 98 … 452 514 546
1 17 33 49 … 241 257 273 2 18 34 50 … 242 258 274
1 9 17 25 … 121 129 137 2 10 18 26 … 122 130 138
1 5 9 13 … 61 65 69 2 6 10 14 … 62 66 70
Full rate
1/2 rate
1/4 rate
1/8 rate
121314150123456789101112 1413 15
121314150123456789101112 1413 15
121314150123456789101112 1413 15
121314150123456789101112 1413 15
Figure 16.5 Reverse CDMA channel variable data rate transmission example.
16.1.5 Reverse traffic channel frame quality indicator
Each frame of the traffic channel shall include a frame quality indicator. For the default
multiplex option’s 9600-bps and 4800-bps transmission rates, the frame quality indicator
shall be a cyclic redundancy check (CRC). For the 9600-bps and 4800-bps rates, the
frame quality indicator (CRC) shall be calculated on all bits within the frame, except the
frame quality indicator (CRC) itself and the encoder tail bits. The 9600-bps transmission
rate shall use a 12-bit frame quality indicator (CRC), which shall be transmitted within
the 192-bit long frame. The generator polynomial for the 9600-bps rate
g(x ) = x
12
+ x
11
+ x
10
+ x
9
+ x
8
+ x
4
+ x + 1
The 4800-bps transmission rate shall use a 8-bit CRC, which shall be transmitted within
the 96-bit long frame. The generator polynomial for the 4800-bps rate
g(x ) = x
8
+ x
7
+ x
4
+ x
3
+ x + 1
16.1.6 The CRCs procedure
The circuit block diagrams for 9600 and 4800 bps are shown in Figures 16.6 and 16.7,
respectively. Initially, all shift register elements shall be set to logical one and the switches
shall be set in the up position. The register shall be clocked 172 times (for 192-bit frame)
or 80 times (for 96-bit frame) with the traffic or the signaling bits and mode/format
indicators as input. The switches shall be set in the down position, and the register shall
be clocked an additional 12 times (for 192-bit frame) or 8 times (for 96-bit frame).
IS 95 STANDARD 571
Denotes modulo-2 addition
Up for first 172 bits
Down for last 12 bits
Output
0
0
Denotes one-bit storage element
Input
X
0
X
1
X
3
X
4
X
7
X
8
X
9
X
10
X
11
Figure 16.6 Reverse traffic channel frame quality indicator calculation at 9600-bps rate for the
default multiplex option(1).
Denotes modulo-2 addition
Output
0
0
Denotes one-bit storage element
Up for first 80 bits
Down for last 8 bits
Input
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
Figure 16.7 Reverse traffic channel frame quality indicator calculation at 4800-bps rate for the
default multiplex option(1).
The 12 or 8 additional output bits shall be the check bits. The bits shall be transmitted in
the order calculated.
16.1.7 Base station
Transmitter
Each BS within a given system shall use the same CDMA frequency assignments for
each of the CDMA channels. The channel structure is shown in Figures 16.8 and 16.9.
Variable data rate transmission
The forward traffic channel shall support variable data rate operation. Four data rates
are supported: 9600, 4800, 2400 and 1200 bps. The data rate shall be selectable on a
frame-by-frame (i.e. 20-ms) basis without consideration for the rate in the previous or
subsequent frames. Although the data rate may vary on a 20-ms basis, the modulation
572 STANDARDS
W1
W33
Up
to
Forward CDMA channel
(1.23-MHz channel
transmitted by base station)
Pilot
chan
Sync
chan
Paging
Ch 1
Paging
Ch 7
Traffic
Ch 1
Traffic
Ch
N
Traffic
Ch 24
Traffic
Ch 25
Traffic
Ch 55
W0 W32 W7 W8
Up
to
Up
to
W31
W63
W = Walsh symbol number
Traffic
data
Mobile power
control
subchannel
Figure 16.8 Example of a forward CDMA channel transmitted by a base station.
symbol rate is kept constant by code repetition at 19.2 kilo-symbols per second (ksps).
The modulation symbols that are transmitted at the lower data rates shall be transmitted
using lower energy, as shown in Table 16.2.
Note that all the symbols in the interleaver block are from the same frame. Thus they
are all transmitted a t the same energy. Power control bits are always transmitted with
energy E
b
.
Pilot channel
The pilot channel is transmitted at all times by the BS on each active forward CDMA
channel. It is an unmodulated spread spectrum signal that is used by a mobile station
operating within the geographic coverage area of the base station. It is used by the
mobile station to acquire synchronization with the pilot PN sequence, to provide a phase
reference and to provide sync channel frame timing.
The acquisition of the pilot channel pilot PN sequence is the first step in the process
of the mobile station acquiring the system timing or reacquiring the system timing. Code
for the pilot channel shall be a quadrature sequence of length 2
15
(i.e. 32768 PN chips
in length).
Code polynomial
P
I
(x) = x
15
+ x
13
+ x
9
+ x
8
+ x
7
+ x
5
+ 1
P
Q
(x) = x
15
+ x
12
+ x
11
+ x
10
+ x
6
+ x
5
+ x
4
+ x
3
+ 1
for the in-phase (I) sequence and for the quadrature (Q) phase sequence is used. The length
of these sequences is 2
15
–1. I n order to generate a pilot PN sequence of length 2
15
,a
binary 1 is inserted in the sequence generator output after the contiguous succession of 14
binary 0 outputs (that occurs only once per period of the sequence). The chip rate for the
pilot PN sequence shall be 1.2288 Mcps. The pilot PN sequence period is 26.666 ms.
Exactly 75 pilot PN sequence repetitions occur every 2 s.
IS 95 STANDARD 573
bit
+
Wp
cover
+
+
+
+
+
+
+
19.2
Power
19.2
MHz
MHz
Symbol
W32
1.2288
scrambling
MHz
+
W0
MHz
Symbol
ksps
ksps
1.2288
1.2288
1.2288
control
WI
WJ
+
+
+
+
+
+
+
+
+
+
I-channel pilot PN
sequence
Pilot channel: all O´s
Sync channel
data
1200 bps
Convolutional
encoder and
repetition
Convolutional
encoder and
repetition
Convolutional
encoder and
repetition
Convolutional
encoder and
repetition
Block
interleaver
Block
interleaver
Block
interleaver
Block
interleaver
4800
sps
Repeat
four
times
19.2
ksps
19.2
ksps
Long
generator
Long
generator
Long code
generator
Symbol
scrambling
Symbol
cover
Q-channel pilot PN
sequence
M
u
x
M
u
x
Symbol
cover
Power
control
bit
Symbol
cover
Paging channel
p
Long code mask
User
i
long
code mask
User
j
long
code mask
Modulo-2 addition
Paging channel
data
9.6 kbps
4.8 kbps
2.4 kbps
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
Forward traffic
channel data
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
Forward traffic
channel data
Figure 16.9 Forward CDMA channel structure.
Pilot channel index
Each BS shall use a time offset of the pilot P N sequence to identify its forward CDMA
channel. Time offsets may be reused within a CDMA cellular system, so long as the
coverage area of the BS emitting a given pilot P N sequence time offset does not overlap
the coverage area of another BS using the same pilot PN sequence time offset. Distinct
pilot channels shall be designated by an index identifying an offset value from a zero
offset pilot PN sequence (in increments of 64 PN chips). The zero offset pilot PN sequence
574 STANDARDS
Table 16.2 Transmitted
symbol energy versus
data rate
Data rate
(bps)
Energy per
modulation
symbol
9600 E
S
= E
b
/2
4800 E
S
= E
b
/4
2400 E
S
= E
b
/8
1200 E
S
= E
b
/16
shall be such that the start of the sequence shall be output at the beginning of every even
second in time, referenced to system time. The start of the zero offset pilot PN sequence
for either the I or the Q sequence shall be defined as the state of the sequence generator
for which the previous 15 outputs were ‘0’. Five hundred and eleven unique values shall
be possible for the pilot PN sequence offset (the offset index of ‘111 111 111’ binary shall
be reserved). The pilot P N sequence offset shall be denoted as a 9-bit binary pilot PN
sequence index for a given BS. The timing offset for a given pilot PN sequence shall
be equal to the offset index value multiplied by 64 multiplied by the pilot channel chip
period (= 813.802 ns). For example, if the pilot PN sequence offset index is 15 (decimal),
the pilot PN sequence offset will be 15 × 64 × 813.802 ns = 781.1 µs.
In this case the pilot PN sequence will start 781.1 µs after the start of every even
second of the system time. The same pilot PN sequence offset shall be used on all
CDMA frequency a ssignments for a given BS.
The sync channel shall be an encoded, interleaved, modulated direct-sequence spread
spectrum signal that is used by mobile stations operating within the geographic coverage
area of that BS (a cell or a sector within a cell) to acquire synchronization to the long
code sequence and to acquire system timing. Sync channel acquisition is the second step
that the mobile station takes in acquiring the system.
Forward traffic channel data scrambler
The forward traffic channel data shall be scrambled by an additional modulo-2 addition
operation prior to transmission. This data scrambling shall be performed on the data
output from the block interleaver at the 19 200-cps rate. The data scrambling shall be
accomplished by performing the modulo-2 addition of the interleaver output symbol with
the binary value of the PN chip that is valid at the start of the transmission period for
that symbol as shown in Figure 16.10. This sequence generator shall operate at 1.2288-
MHz clock rate although only one output of 64 shall be used for data scrambling (i.e.
at a 19 200-cps rate). The PN sequence used for data scrambling shall be the decimated
version of the sequence used by the mobile station for direct-sequence spreading of the
reverse traffic channel (either the public long code or the private long code).
CDMA2000 575
1
4
Long
code
generator
Convolutional
encoder and
code
repetition
Block
interleaver
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
Long
code
mask
19.2
kbps
19.2
kbps
19.2
kHz
1.2288
Mcps
DecimatorDecimator
800 Hz
52.0833 µs = one code symbol
64 PN chips per code symbol
PN chip used for scrambling (input to x or gate)
800
Hz
MUX
MUX timing control
Power control bit
Scrambled code
symbol
or Power control bit
Figure 16.10 Data scrambler timing.
16.2 IS-95B CDMA
IS-95B specifies the high-speed data operation using up to eight parallel codes, resulting in
a maximum bit rate of 115.2 kbps. The summary of IS-95A and IS-95B system parameters
is given in Table 16.3. The system block diagrams and numerology for rate set 1 and rate
set 2 are shown in Figures 16.11 and 16.12, respectively.
16.3 CDMA2000
The goal has been to provide data rates that meet the IMT-2000 performance requirements
of at least 144 kbps in a vehicular environment, 384 kbps in a pedestrian environment and
2048 kbps in an indoor office environment. The main focus of standardization has been
to provide 144 and 384 kbps with approximately 5-MHz bandwidth. The main parameters
of CDMA2000 are listed in Table 16.4.
The two main alternatives for the downlink are multicarrier and direct spread options
(see Figure 16.13). Transmission on the multicarrier downlink (nominal 5-MHz band) is
achieved by using three consecutive IS 95B carriers where each carrier has a chip rate of
1.2288 Mcps. For the direct spread option, transmission on the downlink is achieved by
using a nominal chip rate of 3.6864 Mcps.
16.3.1 Physical channels
Uplink physical channels
In the uplink, there are four different dedicated channels. The fundamental and the sup-
plemental channels carry user data.
576 STANDARDS
Table 16.3 IS-95 interface parameters
Bandwidth 1.25 MHz
Chip rate 1.2288 Mcps
Frequency band uplink 869–894 MHz
1930–1980 MHz
Frequency band downlink 824–849 MHz
1850–1910 MHz
Frame length 20 ms
Bit rates Rate set 1:9.6 kbps
Rate set 2:14.4 kbps
IS-95B: 115.2 kbps
Speech codec QCELP 8 kbps
EVRC 8 kbps
ACELP 13 kbps
Soft handover Yes
Power control Uplink: Open loop + fast closed loop
Downlink: Slow quality loop
Number of RAKE fingers 4
Spreading codes Walsh + long M-sequence
800 bps
A
A
A
A
800
bps
Pilot
channel
(all 0’s)
Sync
channel
bits
Paging
channel
bits
Downlink traffic
channel code channel
information bits for
User
m
with rate set 1
(172, 80,40, or
16 bits/frame)
8.6 kbps
4.0 kbps
2.0 kbps
0.8 kbps
Long code
mask for
User
m
*Power control bits are not multiplexed in for supplemental code channels of the downlink
traffic channels.
9.6 kbps
4.8 kbps
1.2 kbps
Walsh Function 0
Walsh Function 32
Walsh Function
p
Convolutional
encoder
r
= 1/2,
K
= 9
Convolutional
encoder
r
= 1/2,
K
= 9
Convolutional
encoder
r
= 1/2,
K
= 9
Code
symbol
Code
symbol
Add frame
quality
indicators
Long code
generator
1.2288 mMcps
Decimator
Decimator
Decimator
Walsh Function
m
Modulation
symbol
Power control bit
Block
interleaving
Symbol
repetition
Symbol
repetition
Symbol
repetition
19.2 ksps
9.6 ksps
Long code
mask for paging
Channel
p
Add 8-bit
encoder tail
per frame
Modulation
symbol
Modulation
symbol
Modulation
symbol
Modulation
symbol
Modulation
symbol
Block
interleaving
Block
interleaving
Long code
generator
1.2288 Mcps
19.2 ksps
4.8 ksps
9.6 kbps
4.8 kbps
2.4 kbps
1.2 kbps
19.2 ksps
19.2 ksps
19.2 kbps
9.6 kbps
4.8 kbps
2.4 kbps
MUX
*
19.2 ksps
19.2 ksps
2.4 ksps
4.8 ksps
Figure 16.11 System block diagram for rate set 1.
CDMA2000 577
Code
symbol
I
Q
A
Downlink traffic channel code channel
information bits for User
m
with rate
set 2 (267, 125, 55, or 21 bits/frame)
13.35 kbps
6.25 kbps
2.75 kbps
1.05 kbps
Long code
mask for
User
m
I-channel pilot PN sequence
1.2288 Mcps
Add one
reserved/Flag
bit
Add frame
quality
indicators
Add 8-bit
encoder tail
per frame
14.4 kbps
7.2 kbps
3.6 kbps
1.8 kbps
Modulation
symbol
Puncture
(delete) 2 of
every 6 inputs
19.2 ksps
A
Walsh function
m
Mux*
800 bps
Repeated
symbol
28.8 ksps
Symbol
repetition
28.8 kbps
14.4 kbps
7.2 kbps
3.0 kbps
Convolutional
encoder
r
= 1/2,
K
= 9
Power control bit
800 bps
Modulation
symbol
Q-channel pilot PN sequence
Long code
generator
1.2288 Mcps
Block
interleaving
19.2 ksps 19.2 ksps
Decimator Decimator
I(
t
)
Baseband
filter
Baseband
filter
sin(2π
f
c
t
)
cos(2π
f
c
t
)
Q(
t
)
Σ
s
(
t
)
*Power control bits are not multiplexed in for supplemental code channels of the downlink traffic channels
Figure 16.12 System block diagram for rate set 2.
• A dedicated control channel, with a frame length 5 or 20 ms, carries control infor-
mation such as measurement data, and the pilot channel is used as a reference signal
for coherent detection. The pilot channel also carries time-multiplexed power control
symbols. Figure 16.14 illustrates the different uplink dedicated channels separated by
Walsh codes.
• The reverse access channel (R-ACH) and the reverse common control channel
(R-CCCH) are common channels used for communication of layer 3 and medium
access control (MAC) layer messages, discussed in Chapters 11 and 12. The R-ACH
is used for initial access, while the R-CCCH is used for fast packet access.
• The fundamental channel conveys voice, signaling and low rate data. It will operate at
low frame error rate (FER) (around 1%) and it supports basic rates of 9.6 and 14.4 kbps
and their corresponding subrates (i.e. rate sets 1 and 2 of IS-95). It always operates in
soft handover mode and does not operate in a scheduled manner; thus permitting the
mobile station to transmit acknowledgments or short packets without scheduling. This
reduces delay and the processing load due to scheduling. Its main difference is using
repetition coding rather than gated transmission.
• The supplemental channel provides high data rates. The uplink supports one or two
supplemental c hannels. If only one supplemental channel is transmitted, then the Walsh
code (+−) is used on the first supplemental channel. If two supplemental channels are
transmitted, then the Walsh code (+−+−) is used. A repetition scheme is used for
variable data rates on the supplemental channel.
578 STANDARDS
Table 16.4 CDMA2000 parameter summary
Channel bandwidth 1.25, 5, 10 and 20 MHz
Downlink RF channel structure Direct spread or multicarrier
Chip rate 1.2288/3.6864/7.3728/11.0593/14.7456 Mcps for
direct spread n × 1.2288 Mcps (n = 1, 3, 6, 9, 12)
for multicarrier
Roll-off factor Similar to IS-95
Frame length 20 ms for data and control/5 ms for control
information on the fundamental and dedicated
control channel
Spreading modulation Balanced QPSK (downlink)
Dual-channel QPSK (uplink)
Complex spreading circuit
Data modulation QPSK (downlink)
BPSK (uplink)
Coherent detection Pilot time-multiplexed with PC and EIB (uplink)
Common continuous pilot channel and auxiliary
pilot (downlink)
Channel multiplexing in uplink Control, pilot, fundamental and supplemental
code-multiplexed
I&Q multiplexing for data and control channels
Multirate Variable spreading and multicode
Spreading factors 4–256
Power control Open loop and fast closed loop (800 MHz, higher
rates under study)
Spreading (downlink) Variable length Walsh sequences for channel
separation, M-sequence 2
15
(same sequence with
time shift utilized in different cells, different
sequence in the I&Q channels)
Spreading (uplink) Variable length orthogonal sequences for channel
separation, M-sequence 2
15
(same for all users,
different s equences in the I&Q channels),
M-sequence 2
41
– 1 for user separation (different
time shifts for different users).
Handover Soft handover
Interfrequency handover
Downlink physical channels
Downlink has three different dedicated channels and three common control channels. The
fundamental and supplemental c hannels carry user data. The dedicated control channel
control messages. The dedicated control channel contains power control bits and rate
information. The synchronization channel is used by the mobile stations to acquire initial
time synchronization. One or more paging channels are used for paging the mobiles. The
pilot channel provides a reference for coherent detection, cell acquisition and handover.
In the downlink, CDMA2000 has a common pilot channel, which is used a s a reference
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