Short code detection method

DETAILED DESCRIPTION A method is disclosed for receiving a transmitted signal in a communication system employing CDMA techniques wherein the transmitted signal includes a plurality of short codes, each of which is transmitted repetitively over a fixed period of time.
The method is particularly useful in rejecting CW interference which may be received with the transmitted signal.
The method includes using a SPRT for detecting the presence of the short code in a plurality of phases of the received signal by calculating a likelihood ratio for each phase.
For each signal phase examined, the likelihood ratio is updated until its value either reaches a threshold that is consistent with the presence of a detected short code or reaches a threshold that is consistent with the absence of a short code.
A likelihood ratio is a comparison of the signal's Probability Distribution Function (PDF) with a background noise PDF.
The PDFs are calculated by passing the signal through a RAKE despreader.
The background noise PDF is calculated by combining in the RAKE the current short pilot code with the input signal.
A new background noise PDF is calculated when the pilot code changes.