IS-95A Syndrome Detector (CDMA Reference Blockset)

Check the CRC bits to determine the frame quality, and output the decoded data and frame quality decision

Library

IS-95A Common

Description

This block detects a frame error in the Traffic frame by checking the received CRC bits. It regenerates the CRC bits using the received data and compares them with the received CRC. After checking for a frame error, the block removes the CRC and tail bits according to the IS-95A specification. The Frame In input size equals the maximum possible size of 288 (Rate Set II, Traffic Full Rate). Similarly, the Frame Out output size equals the maximum possible size of 268 (Rate Set II, Traffic Full Rate).

For the Sync and Paging channel, the block passes the data to the output without any processing. In the case of the Access channel, the block removes the tail bits before passing the data to the output.

The following table shows the number of relevant input and output bits. Any unused output bits are set to zero.

Channel Type
Number of Relevant Inputs Bits
Number of CRC Bits
Number of Tail Bits
Number of Relevant Output Bits

Sync, Eighth Rate
32
0
0
32

Paging, Full Rate
192
0
0
192

Paging, Half Rate
96
0
0
96

Access
96
0
8
88

Traffic, Rate Set I, Full Rate
192
12
8
172

Traffic, Rate Set I, Half Rate
96
8
8
80

Traffic, Rate Set I, Quarter Rate
48
0
8
40

Traffic, Rate Set I, Eighth Rate
24
0
8
16

Traffic, Rate Set II, Full Rate
288
12
8
268

Traffic, Rate Set II, Half Rate
144
10
8
126

Traffic, Rate Set II, Quarter Rate
72
8
8
56

Traffic, Rate Set II, Eighth Rate
36
6
8
22

Channel Type	Number of Relevant Inputs Bits	Number of CRC Bits	Number of Tail Bits	Number of Relevant Output Bits
Sync, Eighth Rate	32	0	0	32
Paging, Full Rate	192	0	0	192
Paging, Half Rate	96	0	0	96
Access	96	0	8	88
Traffic, Rate Set I, Full Rate	192	12	8	172
Traffic, Rate Set I, Half Rate	96	8	8	80
Traffic, Rate Set I, Quarter Rate	48	0	8	40
Traffic, Rate Set I, Eighth Rate	24	0	8	16
Traffic, Rate Set II, Full Rate	288	12	8	268
Traffic, Rate Set II, Half Rate	144	10	8	126
Traffic, Rate Set II, Quarter Rate	72	8	8	56
Traffic, Rate Set II, Eighth Rate	36	6	8	22

Inputs

Rate

Integer scalar that specifies the data rate for the input signal. To indicate a rate fraction of Full, Half, Quarter, or Eighth, use an input value of 0, 1, 2, or 3, respectively. The table below shows all valid channel types and rate fractions, along with their associated data rates and Rate input values.


Channel Type	Data Rate (bps)	Input Value
Sync (always Eighth rate)	1200	3
Paging, Full	9600	0
Paging, Half	4800	1
Access (always Half rate)	4800	1
Traffic, Rate Set I, Full	9600	0
Traffic, Rate Set I, Half	4800	1
Traffic, Rate Set I, Quarter	2400	2
Traffic, Rate Set I, Eighth	1200	3
Traffic, Rate Set II, Full	14400	0
Traffic, Rate Set II, Half	7200	1
Traffic, Rate Set II, Quarter	3600	2
Traffic, Rate Set II, Eighth	1800	3

Frame In

Binary vector of size 288 representing the decoded data followed by the CRC and tail bits.

Outputs

Frame Out: Binary vector of size 268 representing the data without CRC and tail bits.
Frame Error: Real scalar of binary data representing the output of the CRC syndrome. A value of zero indicates that the detected frame was decoded correctly. A value of one indicates that the detected frame was decoded erroneously.

Dialog Box

Parameters

Rate set: The rate set, either Rate Set I or Rate Set II.
Channel type: The channel type, either Sync, Paging, Access, or Traffic.

IS-95A Short Code Generator IS-95A Walsh Code Generator