CDMA Reference Blockset

IS-95A Rev Ch Rake Finger

Despread the received signal with the short PN and long codes, and then correlate the despread signal with all of the Walsh code sequences

Library

IS-95A Base Station Receiver

Description

This is a hierarchical block that downsamples the input signal using the PN phase offset and despreads the received signal with the short PN code and the long code sequences. The despreading interval equals to one quarter of the Walsh code interval for the short PN code. The long code correlator subsection of this block buffers the despread signal to reconstruct a symbol, then despreads the signal over a symbol interval with the long code and integrates it over four chip intervals to construct a Walsh symbol. Finally, this block correlates the despread signal with all of the 64 Walsh code sequences, and outputs the correlation result. The first output sample corresponds to the correlation result between the despread signal and the zeroth-order Walsh code. Subsequent output samples correspond to the correlation result between the despread signal and the subsequent Walsh codes.

Inputs

Rx I

Real vector representing the in-phase component of the received data sequence. The vector size is the Oversampling rate parameter times the Walsh code length. The Walsh code length is 2^W, where W is the Walsh order parameter. The default size, 512, corresponds to Oversampling rate = 8 and Walsh order = 6.

Rx Q

Real vector representing the quadrature component of the received data sequence. The vector size is the same as that of the Rx I input vector.

PN I

Real vector of bipolar data representing the in-phase component of the PN code sequence. The vector size equals the Walsh code length. The default size, 64, corresponds to a symbol interval.

PN Q

Real vector of bipolar data representing the quadrature component of the PN code sequence. The vector size equals the Walsh code length. The default size, 64, corresponds to a symbol interval.

Long Code

Real vector of bipolar data of size four times the Walsh code length representing the long code values. The default size, four times 64, corresponds to a Walsh symbol interval.

Path Delay

Integer scalar representing the PN phase offset in number of samples applied to a finger.

Outputs

Real vector representing the output of all Walsh correlators. The output vector size equals the Walsh code length. The default size is 64.

Dialog Box

Parameters

Walsh order

Real scalar that specifies the order of the Walsh code.

Output size (in number of Walsh functions)

Integer scalar that specifies the number of output values per Walsh correlator.

Tracking buffer size (in number of symbols)

Integer scalar that specifies the buffer length in the short code despreader. This buffer length limits the maximum PN phase offset between received multipaths. The default value, 3, corresponds to 192 chips.

Oversampling rate

Integer scalar that specifies the number of samples per chip.

See Also

IS-95A Rev Ch Short Code Despreader
IS-95A Rev Ch Walsh Demodulator

IS-95A Rev Ch Interleaver/Deinterleaver

IS-95A Rev Ch Repeater/Derepeater