IS-95A Long Code Generator (CDMA Reference Blockset)

Generate the long code sequence used for reverse channel spreading and scrambling and for forward channel scrambling

Library

IS-95A Common

Description

This block generates either the long code sequence or a decimated version of the long code sequence. The long code sequence is used for reverse channel spreading, while the decimated long code sequence is used for forward channel scrambling. This long code is periodic with period 2⁴¹ - 1 chips and uses the specified characteristic polynomial in the IS-95A specification.

The block generates the long code sequence based on the 42-bit Initial state parameter and a 42-bit mask. A mask value applied to the long code generator results in an instantaneous shift in the sequence output with respect to the unmasked long code generator. A mask value of 0 results in no shift between the masked and unmasked long code generator.

The block outputs a decimated version of the long code sequence when the Decimation ratio parameter is an integer greater than one. If the Decimation ratio parameter is N, then the block's output consists of the 1st, (N+1)st, (2N+1)st, etc. values from the long code sequence.

Outputs

Binary vector corresponding to the long code sequence values or the decimated long code sequence values as specified by the parameters. The output is a frame-based signal with frame size specified by the Output frame size parameter.

Dialog Box

Parameters

Output frame size: Integer scalar that specifies the number of output long code bits at each sample time.
Decimation ratio: Integer scalar that specifies the decimation factor by which the long code sequence output is decimated.
Long code mask: Integer scalar that specifies the mask to be applied when generating the long code sequence. The mask value can be between 0 and 2⁴² - 1.
Initial state: Integer scalar that specifies the initial state of the long code generator. Its value is between 0 and 2⁴² - 1. If this parameter is an empty matrix, then the block uses a default value of 2⁴¹.
Sample time: Real scalar that specifies the block output sample time.

Specification References

IS-95A 6.1.3.1.8
J-STD-008 2.1.3.1.8.1, 2.1.3.1.8

IS-95A Fwd Ch Viterbi Decoder IS-95A Rev Ch Burst Randomizer