Chapter
4
The cdmaOne System
4.1 Introduction
In contrast to the GSM system, which was designed and developed by a number of different
organisations working together, the cdmaOne technology was designed by a single com-
pany, Qualcomm Incorporated. The first commercial cdmaOne network was launched by
Hutchison in Hong Kong on 28 September 1995 and since that time commercial networks
based on the cdmaOne technology have been launched in many countries around the world
including Korea and the United States.
Qualcomm’s CDMA technology was ‘re-branded’ as cdmaOne in 1997. Prior to this
the technology was commonly referred to as ‘IS-95’, which is the name of the standard
which describes the cdmaOne technology in the United States (i.e. Interim Standard num-
ber 95 [1]). The cdmaOne technology was originally designed to provide a high capacity
overlay for the first generation analogue Advanced Mobile Phone System (AMPS) operat-
ing in the 800 MHz cellular band in the United States. This gave an AMPS operator the
option of increasing its network capacity in specific areas by replacing a number of 30 kHz
AMPS carriers with one or more 1.25 MHz cdmaOne carrier. Dual mode cdmaOne/AMPS
mobile stations (MSs) are able to use the cdmaOne system, where available, and they will
revert to the AMPS system in areas where there is no CDMA coverage.
With the introduction of personal communications systems (PCS) in the United States,
the cdmaOne technology was modified to operate in the 1900 MHz PCS frequency band
in a single mode configuration citecdma-pcs. This version of the cdmaOne technology was
commonly referred to as ‘CDMA-PCS’ prior to the re-branding. In addition to the versions
of cdmaOne described above, other variations exist which have been modified to operate in
particular frequency bands in different countries throughout the world.
At this point it is important to clarify the terminology we shall be using in the remainder
205
GSM, cdmaOne and 3G Systems. Raymond Steele, Chin-Chun Lee and Peter Gould
Copyright © 2001 John Wiley & Sons Ltd
Print ISBN 0-471-49185-3 Electronic ISBN 0-470-84167-2

A
00
824.040–825.000 869.040–870.000
A 825.030–834.990 870.030–879.990
B 835.020–844.980 880.020–889.980
A
0
845.010–846.480 890.010–891.480
B
0
846.510–848.970 891.510–893.970
4.2. THE CDMAONE RADIO INTERFACE
207
band occupied by an analogue system, spectral guard bands must be provided between the
CDMA service and the existing analogue service. Consequently, a single CDMA carrier
operating within an analogue AMPS band will require around 1.8 MHz of spectrum.
The CDMA carrier numbering scheme for IS-95 is the same as that used for AMPS and
isshowninTable4.2,whereN is the channel number, f
u
is the reverse link frequency and
f
d
is the forward link frequency.
The table shows that the channel numbering is based on the AMPS carrier spacing of
30 kHz which allows the network operator to position a CDMA carrier at any point within
the AMPS band with an accuracy of 30 kHz. It is important to note that a single 1.25 MHz
CDMA carrier will occupy the same spectrum as around 40 AMPS carriers and, therefore,
the channel numbers of adjacent CDMA carriers will differ by around 40. The CDMA car-
riers must be positioned in such a way as to allow sufficient guard bands between other ser-
vices operating above and below the cellular band and between the A and B services. Con-

0
:
030N
+
825
:
000 1

N

777
f
u
=
0
:
030
(
N

1023
)+
825
:
000 1013

N

1023
Forward link f

1023
208
CHAPTER 4. THE CDMAONE SYSTEM
Table 4.3 : Available channel numbers for IS-95 carriers.
System A 1 - 311
689 - 694
1013 - 1023
System B 356 - 644
739 - 777
Table 4.4: PCS spectrum allocations.
Frequency (MHz)
Block Reverse link Forward link
A 1850–1865 1930–1945
D 1865–1870 1945–1950
B 1870–1885 1950–1965
E 1885–1890 1965–1970
F 1890–1895 1970–1975
C 1895–1910 1975–1990
Table 4.5 : PCS channel numbers.
Band Frequency (MHz) Channel numbers
Reverse link 1850
:
000
+
0
:
050 N 0

N


neighbouring cells to assess the suitability of the cell for handover. In this respect the pilot
channel in the cdmaOne system may be likened to the BCCH carrier in the GSM system.
The pilot carrier of the serving cells is also used by the MS as a coherent reference in the
demodulation process and in the reverse link power control algorithm.
Another forward channel is the synchronisation channel which, as its name suggests,
allows the MS to achieve time synchronisation with the BS and the network. The synchro-
nisation channel also carries information relating to system time, and the contents of the
BS’s internal registers which are used in the coding, spreading and encryption processes.
There are also a number of paging and traffic channels. The paging channels are used to
page MSs to alert them to an incoming call. The paging channel is also used to carry general
network information and channel assignment messages. The traffic channels are assigned
to the users as required and they may carry speech or user data at bit rates of up to 9.6 kb/s
for IS-95 and 14.4 kb/s for CDMA-PCS.
Each forward channel on a CDMA carrier is assigned a different 64-bit Walsh code, and
these codes are shown in Figure 4.1. Each row of the table represents a different 64-bit
Walsh code with the bit positions shown at the top of the table, and the index of the Walsh
code shown in the left-hand column. We note that these codes are orthogonal, i.e. the value
of any two codes, multiplied together and summed over a period of 64 chips, is zero, pro-
vided the ‘0’ bits are replaced by a ‘

1’ and the ‘1’ bits are replaced by a ‘+1’. Multiplying
a Walsh code by itself produces a constant level of +1 when the two codes are in time syn-
chronisation. We note that although the codes shown in Figure 4.1 are true Walsh codes
they are not indexed (or numbered) in the conventional manner. A Walsh code’s index is
normally given by the number of transitions that occur between the different levels during a
code period (i.e. 64 chips). In the cdmaOne specifications, however, the Walsh codes have
been numbered as shown in Figure 4.1. In this discussion we will always use the code index
numbers shown in Figure 4.1 to avoid confusion and we will refer to the codes as Walsh
Hadamard (WH) codes.
The full block diagram of the cdmaOne BS transmitter is shown in Figure 4.2. Each

23 0110100101101001100101101001011001101001011010011001011010010110
24 0000000011111111111111110000000000000000111111111111111100000000
25 0101010110101010101010100101010101010101101010101010101001010101
26 0011001111001100110011000011001100110011110011001100110000110011
27 0110011010011001100110010110011001100110100110011001100101100110
28 0000111111110000111100000000111100001111111100001111000000001111
29 0101101010100101101001010101101001011010101001011010010101011010
30 0011110011000011110000110011110000111100110000111100001100111100
31 0110100110010110100101100110100101101001100101101001011001101001
32 0000000000000000000000000000000011111111111111111111111111111111
33 0101010101010101010101010101010110101010101010101010101010101010
34 0011001100110011001100110011001111001100110011001100110011001100
35 0110011001100110011001100110011010011001100110011001100110011001
36 0000111100001111000011110000111111110000111100001111000011110000
37 0101101001011010010110100101101010100101101001011010010110100101
38 0011110000111100001111000011110011000011110000111100001111000011
39 0110100101101001011010010110100110010110100101101001011010010110
40 0000000011111111000000001111111111111111000000001111111100000000
41 0101010110101010010101011010101010101010010101011010101001010101
42 0011001111001100001100111100110011001100001100111100110000110011
43 0110011010011001011001101001100110011001011001101001100101100110
44 0000111111110000000011111111000011110000000011111111000000001111
45 0101101010100101010110101010010110100101010110101010010101011010
46 0011110011000011001111001100001111000011001111001100001100111100
47 0110100110010110011010011001011010010110011010011001011001101001
48 0000000000000000111111111111111111111111111111110000000000000000
49 0101010101010101101010101010101010101010101010100101010101010101
50 0011001100110011110011001100110011001100110011000011001100110011
51 0110011001100110100110011001100110011001100110010110011001100110
52 0000111100001111111100001111000011110000111100000000111100001111

(
x
) =
x
15
+
x
13
+
x
9
+
x
8
+
x
7
+
x
5
+
1

(4.1)
PNQ
(
x
) =
x
15

are extended to 2
15
length sequences by inserting a ‘0’ after 14 consecutive 0’s, which will
occur once for each repetition of the code.
The two PN sequences are generated at a chip rate of 1.2288 Mchips/s and the period will
be
2
15
=
122880
=
32768
=
1228800
=
26
:
666 ms (4.3)
which results in exactly 75 PN sequence repetitions every 2 s.
EXORing the PN sequences with an all zeros data sequence will leave the PN sequences
unchanged. The two sequences are then pulse shaped using low pass filters. The character-
istics of the low pass filters are shown in Figure 4.3 in the form of a response mask taken
from the specifications [1, 2]. In the diagram, S
(
f
)
is the frequency response of the filter.
The filter pass band extends from 0 to f
p
and the stop band extends from f

CHAPTER 4. THE CDMAONE SYSTEM
W
i
19.2kb/s
W
19.2kb/s
j
W
32
4.8ksym/s
19.2ksym/s
W
0
CDMA
Transmitted
Signal
Combining
Weighting and
Quadrature
Modulation
Pilot
Channel
(all 0’s)
Sync
Channel
Data
1.2kb/s
Convolutional
Encoder and
Repetition

Symbol Scrambler
and Power Control
Multiplexer
Symbol
Scrambler
Power
Control Bits
Symbol
Cover
Symbol
Cover
Symbol
Cover
PNI
1.2288Mchips/s
1.2288Mchips/s
PNQ
Figure 4.2: Block diagram of a cdmaOne BS transmitter (rate set 1).
1
1
2
0
20 log |S(f)|
ff
ps
frequency
Figure 4.3: Pulse shaping filter requirements.
4.2. THE CDMAONE RADIO INTERFACE
213
Q-Channel


1) occurs just prior to quadrature modulation; however, this
translation may occur at an earlier stage. For example, the PNI and PNQ sequences could
be produced as logical levels directly.
Having described the construction of the pilot channel we now examine its functions.
One of the main functions of the pilot channel is to allow the MS to detect and identify the
BSs. Since all BSs use the same PN sequences and the same carrier frequency, the only
way in which the different pilot channels may be distinguished is by the phase of their PN
sequences. In IS-95, each BS within a geographical area will use a different time offset for
the PN sequence and this offset will be defined in integer multiples of 64 chips.
For the PN offset to have any meaning across the system it must be referenced to a com-
mon timing source. This requirement means that all BSs within a network must be time
synchronised. This is currently achieved using global positioning system (GPS) satellite
links as a source of universal coordinated time (UTC). The network system time is synchro-
nised to UTC; however, it differs from UTC because the system time does not include the
leap seconds that are added to UTC. The even seconds of system time are also important
when we consider frame synchronisation. These represent points in system time when the
number of accumulated seconds is divisible by two, i.e. every other second.
The 2
15
=
32768
=
512

64 length PN sequences allow 512 different offsets of 64 chips
from 0 (i.e. zero offset PN sequence) to 511. At switch-on, an MS will sweep a searcher
correlator over all possible pilot PN offsets to identify the different BSs within its local area.
The amplitude of the correlator output will indicate the strength of the BS using a given pilot
PN offset. An example of a searcher correlator output is shown in Figure 4.5, where both

D
+
D
2
+
D
3
+
D
5
+
D
7
+
D
8

g
1
=
1
+
D
2
+
D
3
+
D
4

TIME).
As we have already seen, the sync channel data is generated at a rate of 1.2 kb/s or, to be
more specific, one frame of 32 bits every 26.66 ms. Each sync channel frame is aligned with
the start of the PN sequences, and consequently the MS may acquire the sync channel frame
timing information from the pilot channel. The interleaving on the sync channel is also
performed over each 26.66 ms frame. Only one message is transmitted on the sync channel;
the structure of the sync channel message is shown in Figure 4.6. The first eight bits of the
message give the length of the message (MSG
LENGTH) in octets. This length will include
the 8-bit MSG
LENGTH parameter itself, the message body and a 30-bit checksum. The
message body contains the sync channel information (e.g. LC
STATE and SYS TIME). The
sync channel message is protected by a 30-bit cyclic redundancy checksum (CRC) which is
appended at the end of the message and is defined by the following generator polynomial:
g
(
x
) =
x
30
+
x
29
+
x
21
+
x
20

The CRC is generated for both the 8 MSG
LENGTH bits and the message body. It is
used by the MS to check for any errors in the sync channel message that remain uncorrected
following the one-half rate convolutional forward error correction (FEC) decoding.
The sync channel message is mapped onto the sync channel frames as shown in Figure 4.6.
Each frame consists of a single-bit start-of-message (SOM) flag followed by 31 information
bits. The 31 information bits are used to carry the contents of the sync channel message,
while the SOM flag is used to indicate the point at which a new message begins. Setting
the SOM flag to a ‘1’ indicates that the information contained in the remainder of the frame
is the start of a new message. When the SOM flag is set to a ‘0’ this indicates that the
information contained in the frame is part of a message that began in an earlier frame.
The sync channel frames are formed into superframes, which consist of three consecu-
tive frames. The superframe is 80 ms in length, as shown in Figure 4.6. A sync channel
message will always be mapped onto an integer number of sync channel superframes, and
consequently a certain amount of padding is added at the end of the message to fill-up the
final superframe. This also means that a new sync channel message will only begin at the
superframe boundaries. The sync channel superframes are aligned such that, for a zero off-
4.2. THE CDMAONE RADIO INTERFACE
217
MSG_LENGTH
Message Body CRC Padding
31 Information Bits
The Sync Channel Message
1 Superframe = 3 Frames = 80ms
S
=0 =0
S
=0
S
=0

to which the information refers. In the case of a pilot with a zero PN offset, the information
contained in the sync channel message will become valid 320 ms, which is equal to four
superframe periods, after the end of the last superframe containing a part of the sync chan-
nel message. Alternatively, we can say that the LC
STATE and the SYS TIME parameters
contained in the sync channel message refer to a time 320 ms after the last message super-
frame. Where the pilot PN offset is not zero, the content of the message becomes valid at
a time equal to 320 ms minus the PN offset after the last superframe carrying the message.
This is shown in Figure 4.8.
4.2.2.3 The paging channel
The paging channel performs a number of different functions in addition to carrying pag-
ing messages between the network and an MS. It conveys general system information (e.g.
the handover thresholds), access information (e.g. the maximum allowed number of unsuc-
218
CHAPTER 4. THE CDMAONE SYSTEM
2 Seconds
75 Pilot PN Cycles
80ms
Pilot PN Offset
Pilot PN Offset
Even Second
Marks
Zero pilot
offset
Sync Channel
superframes for
zero PN offset
Non-zero
pilot offset
Sync Channel

Sync Channel
superframes for a
zero pilot PN offset
320ms-pilot PN offset later
becomes valid at this point,
The data contained
in a Sync Channel
Message which ends
in this superframe
Sync Channel
superframes for a
non-zero pilot PN offset
Figure 4.8: The content of the sync channel message.
bits to reset the coder between frames.
Referring to Figure 4.2, we note that the interleaved code symbols are scrambled by EX-
ORing them with a data stream generated at a rate of 19.2 ksymbols/s. This scrambling
sequence is derived from a higher rate sequence produced by a long code generated at
1.2288 Mchips/s. This long code is 2
42

1 bits in length and is formed by a 42-bit feedback
register and associated logic, as shown in Figure 4.9. The characteristic polynomial for the
feedback register is
p
(
x
) =
x
42
+

x
17
+
x
16
+
x
10
+
x
7
+
x
6
+
x
5
+
x
3
+
x
2
+
x
+
1
:
(4.6)
The long PN code is produced by logically ANDing the content of the 42-bit shift register,

not take a value of 0 and, therefore, there will be a maximum of seven paging channels on
each CDMA carrier. The paging channel mask also contains the nine-bit pilot PN offset
(PN
OFFSET) in use on the CDMA carrier that is able to specify which of the 511 offsets
are used.
The 19.2 ksymbols/s scrambling sequence is produced by taking only one chip out of
every 64 that is generated by the long code generator. The scrambling process consists
of EXORing the output of the interleaver with the 19.2 ksymbols/s scrambling sequence.
The purpose of the scrambling process on the paging channel is not obvious, since the
construction of the mask is a fairly simple task and provides minimal protection against
eavesdropping. The process does provide commonality with the forward traffic channels
where the scrambling process does provide security against eavesdropping.
Following scrambling, the paging channel data is EXORed with a Walsh code which is
generated at a rate of 1.2288 kchips/s, i.e. each data bit is represented by a Walsh code
or its inverse. As we have already seen, a CDMA carrier may support up to seven paging
channels which are assigned a Walsh code with an index in the range one to seven (see
Figure 4.1). The paging channel number (PCN) and the Walsh code index are the same for
a given paging channel, and this explains why the PCN parameter may not take the value
zero, i.e. because the Walsh code with an index of zero is used by the pilot.
The start of the Walsh code, i.e. bit zero in Figure 4.1 always aligns with the even second
41 29 28 24 23 21 20 9 8 0
1100011001101 00000 PCN 000000000000 PILOT PN
Figure 4.10: Paging channel long code mask.
4.2. THE CDMAONE RADIO INTERFACE
221
marks of system time, regardless of the pilot PN offset. This is achieved because the pilot
PN offset is defined in units of 64 chips, or one Walsh code cycle. Following Walsh code
spreading the data are quadrature spread, using the PNI and PNQ codes, baseband filtered
and modulated onto two quadrature carriers using the phase mapping described in Table 4.7.
The PNI and PNQ codes have the same offset as the pilot channel and the sync channel on

MSG LENGTH Message Body CRC

8bits
!
2 - 1146 bits
!
30 bits
!
Figure 4.11: The paging channel message format.
222
CHAPTER 4. THE CDMAONE SYSTEM
parameter. The slot cycle period, T ,isgivenby
T
=
2
SLOT CYCLE INDEX

(4.7)
where T is in units of 1.28 s, or 16 slots. For example, an MS with a SLOT
CYCLE INDEX
of 2 would monitor the paging channel once every 5.12 s or 64 slots. The MS chooses which
slot to monitor within its paging channel cycle based on its mobile identification number
(MIN). This is a 34-bit number which is a digital representation of the 10-digit telephone
number that is assigned to a particular MS. In this way the MSs within a cell are pseudo-
randomly distributed between the paging slots on the paging channel. The MS also uses its
MIN to select the paging channel to be monitored in cases where a cell has more than one
paging channel. Again the process is pseudo-random and it effectively distributes the MSs
evenly between the available paging resources.
Each paging channel slot is composed of four 20 ms frames which are, in turn, composed
of two 10 ms half frames, as shown in Figure 4.12. The half frame contains 96 bits, when the

beginning of a half frame
(SCI=1)
Paging Channel
Message Capsule
1
0
1
Message Capsule
Paging Channel
Unsynchronised Message
Capsule - does not start at
the beginning of a half frame
0
Padding
Bits
Paging Channel
Message Capsule
Paging Channel
Half Frame = 10ms
Synchronised
Capsule
Indicator (SCI)
2047
204620452044
30
24
1 Paging Channel
Slot = 80ms =
8 Half Frames
Maximum Paging Channel Slot Cycle = 2048 Slots = 163.84s

encoder to a known state after the frame has been encoded. The two higher rate frames
(9.6 kb/s and 4.8 kb/s) contain a frame quality indicator in the form of a CRC code. This
code is used to detect bit errors that have not been corrected by the convolutional decod-
ing process at the receiver. Only the higher rate frames are given this additional level of
protection because these will be carrying important speech information.
Referring to Figure 4.2, the traffic channel frames are convolutionally encoded using a
one-half rate coder. The code is exactly the same as that used on the synchronisation and
paging channels, and the generator polynomials are given in Equation (4.4). The main
difference between the convolutional coding on the traffic channels and that used on the
paging and sync channels is that the convolutional coder is initialised to the ‘all zero’ state
at the end of each frame in the case of the traffic channels.
The coder output rates will be 19.2 ksymbols/s, 9.6 ksymbols/s, 4.8 ksymbols/s and
2.4 ksymbols/s, depending on the input data rate. The symbols are then repeated to produce
a constant symbol rate of 19.2 ksymbols/s, regardless of the input data rate. For example,
an input data rate of 1.2 kb/s results in a symbol rate of 2.4 ksymbols/s after convolutional
encoding. Each symbol is repeated seven times (i.e. eight copies of the symbol in total) to
produce a symbol rate of 19.2 ksymbols/s. Table 4.8 gives the number of symbol repetitions
that are required for each input data rate.
The symbols are interleaved over each 20 ms frame, which contains 384 code symbols at
a rate of 19.2 ksymbols/s. Following interleaving, the code symbols are scrambled using a
19.2 ksymbols/s scrambling sequence derived from the long PN code using either the public
or private long code mask. The construction of the 42-bit public long code mask is shown
in Figure 4.13, where ESN signifies the electronic serial number of the MS. This is a 32-bit
4.2. THE CDMAONE RADIO INTERFACE
225
Table 4.8 : Symbol repetitions on the IS-95 traffic channel.
Input data No. of symbol
rate (kb/s) repetitions
9.6 0
4.8 1

19.2 ksymbol/s. The BS measures the reverse link received power over each power control
group, decides whether the MS should increase or decrease its power, and transmits the
corresponding power control bit two power control groups later on the forward link traffic
channel. This is shown in Figure 4.14. We note that, at the BS, the reverse link and forward
41 32 31 0
1100011000 Permuted ESN
Figure 4.13: Traffic channel public long code mask.
226
CHAPTER 4. THE CDMAONE SYSTEM
link traffic frames are displaced by the round trip propagation delay between the BS and
the MS.
Each power control bit has the same duration as two code symbols (i.e. approximately
104µs) and, consequently, it will be used to replace two symbols per power control group.
The position of the power control bits is effectively ‘randomised’ within each power control
group to prevent the generation of line spectra in the transmitted signal. Each power control
group consists of 24 code symbols and the start of the power control bit may occur at any
point within the first 16 symbols. The actual position is defined by the last four bits of the
scrambling sequence that was used in the previous power control group. In the example in
Figure 4.14, the last four bits of the scrambling sequence are 1101. Taking the last bit (i.e.
bit 24) as the most significant, this gives the four-bit number 1011
2
=
11
10
, which means
that the power control bit starts in position 11 in the power control group and it will replace
code symbols 11 and 12.
The process of replacing the code symbols with the power control bits will introduce
errors; however, these may be corrected by the powerful one-half rate code. We also note
that the MS receiver will always know the position of the power control bits. This technique

4.2. THE CDMAONE RADIO INTERFACE
227
0 1 2 3 4 5876 9 10 131211 14 15 181716 19 2220 21 23
Not used for power control bits
23222120
1011
1 Power Contol Group = 1.25ms = 24 code symbols
The last four bits of
scrambling sequence
in the previous power
control group
(1011 =11)
two power control bits
starting position of the
are used to define the
{
.....................................
2
12 453 786910 11 12 130 14 15
120 12345678 10911 1513 14
The BS measures the up-link signal strength
and
sends the corresponding power control
bit two power control groups later
Round-trip
delay
Up-link traffic
channel frames
channel frames
Down-link traffic

x
4
+
x
+
1
:
(4.8)
The 4.8 kb/s frames carries an eight-bit CRC and this is defined by the generator polyno-
mial
g
(
x
) =
x
8
+
x
7
+
x
4
+
x
3
+
x
+
1
:

96 bits (20ms)
!
4.8kb/s
Frame 80 8 8
Information bits F T

48 bits (20ms)
!
2.4kb/s
Frame 40 8
Information bits T

24 bits (20ms)
!
1.2kb/s
Frame 16 8
Information bits T
F = The Frame Quality Indicator (CRC)
T = Encoder Tail Bits
Figure 4.15: Forward link traffic channel frames.