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IS-95A Rev Ch Short Code Despreader
Despread the input sequence with the I and Q short PN codes
Library
IS-95A Base Station Receiver
Description
This block despreads the input sequence with the I and Q short PN codes. The block downsamples the in-phase and quadrature components of the input complex signal at the sampling phase selected and despreads them with the delayed version of the I and Q short PN codes. By using the appropriate delay with the PN codes, it despreads the signal of interest without despreading those signals that are received from different mobiles or through different propagation paths. The block keeps an internal buffer for the received sequence. The delay adjustment for the despreading involves selecting the samples for despreading based on the input path delay information. The block then adjusts the received sequence with the delayed version of the PN code.
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 size parameter.
- Rx Q
- Real vector representing the quadrature component of the received data sequence. The vector size is the Oversampling rate parameter times the Walsh size parameter.
- PN I
- Real vector of bipolar data of size Walsh size representing the in-phase component of the PN code sequence.
- PN Q
- Real vector of bipolar data of size Walsh size representing the quadrature components of the PN code sequence.
- Path Delay
- Real nonnegative integer scalar that represents the delay in the desired signal path to be used for selecting the samples for despreading, in terms of number of sampling intervals or ticks. This delay should include the filtering and multipath delays that the PN sequence based despreading should take into account.
Outputs
- Data I
- Real vector representing the in-phase component of the despread signal. The default size is 64, corresponding to the default input interval.
- Data Q
- Real vector representing the quadrature component of the despread signal. The default size is 64.
Dialog Box
Parameters
- Input frame size (in number of symbols)
- Integer scalar that specifies the number of input symbols.
- Walsh size
- Integer scalar that specifies the length of the Walsh code sequence.
- Tracking buffer size (in number of symbols)
- Integer scalar that specifies the length of the buffer needed in the despreader in terms of number of symbols. This buffer is used for the delay adjustment and its length limits the maximum PN phase delay.
- Oversampling rate
- Integer scalar that specifies the number of samples per chip. The default value, 8, corresponds to a chip interval.
See Also
IS-95A Rev Ch Rake Finger
IS-95A Rev Ch Walsh Demodulator
IS-95A Rev Ch Walsh Modulation and Spreading
| | IS-95A Rev Ch Repeater/Derepeater | | IS-95A Rev Ch Viterbi Decoder | |