CDMA Reference Blockset

IS-95A Short Code Generator

Generate the I and Q short PN code sequences

Library

IS-95A Common

Description

This block generates the I and Q short PN code sequences to be used in the quadrature spreading and despreading of CDMA signals. At the IS-95A chip rate of 1.2288 Mcps, these binary sequences are periodic with period of 2¹⁵ chips (32768 chips) and are based on the specified characteristic polynomials in the IS-95A specification. The sequences repeat exactly 75 times every 2 seconds.

The specified polynomials generate sequences of length 2¹⁵-1 with 14 consecutive 0's in each period of the I and Q codes. A zero is inserted after the 14 zeros to produce a sequence of 15 consecutive zeros, making the period 2¹⁵. The sequence generators are implemented as linear feedback shift registers with polynomials specified in the IS-95A specification.

The state of the shift register is masked (bit-wise AND) with a 15-bit number and a bit generated as the modulo-2 addition result. The sequence of bits thus generated is the PN code sequence. The selection of different masks shifts the time to different points in the sequence being generated without changing the actual periodic sequences. The masks involve an AND operation between the LSB of the mask and the bit of the shift register used for feedback.

Inputs

Integer vector of size 2 representing short PN code mask for the in-phase and quadrature components. This determines the phase of the PN sequences' output. It is given as a complex number whose real and imaginary parts are integers between 0 and 2¹⁵-1. If a real mask is given, then real and imaginary parts use the same mask. If the given mask is 0, then the default value of 1 is used for both masks of I and Q sequences resulting in a zero shifted sequence. The value of 1 implies that the feedback bit of the PN state registers will be output.

Outputs

PN I

Integer vector representing the in-phase PN sequence in bipolar format. The output is a frame-based signal with frame size specified by the Output frame size parameter.

PN Q

Integer vector representing the quadrature PN sequence in the bipolar format. 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 length of the PN I and PN Q output vectors. The default size, 64, corresponds to the number of chips in a forward channel symbol.

Sample time

Real scalar that specifies the block sample time.

See Also

IS-95A Rev Ch Short Code Despreader
IS-95A Rev Ch Rake Finger
IS-95A Fwd Ch Rake Finger
IS-95A Fwd Ch Detector
IS-95A Reverse Traffic Channel Transmitter Demo
IS-95A Forward Traffic Channel Detection Demo
IS-95A Reverse Traffic Channel Detection Demo

Specification References

IS-95A 6.1.3.1.9
J-STD-008 2.1.3.1.9

IS-95A Rev Ch Walsh Modulator

IS-95A Syndrome Detector