Sequential detection system and method with adaptive bias

In a wideband code division multiple access (W-CDMA) communications system having a base station transmitting at least one channel of information spread with a unique first long code and organized into frames, with each frame including a predetermined number of slots, and each slot including a predetermined number of chips, a method for a mobile station receiver to acquire the base station through variable window size sequential detection of the first long code from a plurality of long code candidates, the method comprising the steps of:

• a) selecting the short code matched filter output peak whose corresponding long code is to be identified, whereby the received signal frame, slot, and symbol timing is determined;
• b) detecting the peak short code matched filter output, when the long code masked symbol occurs, whereby a bias parameter is determined for every slot;
• c) generating a new candidate long code, setting candidate and update flags to 0, and candidate counter to 0;
• d) integrating the results of the chip correlation of the candidate long code generated in Step c) and the received first long code;
• e) in response to the bias determined in Step b), adjusting the integrated correlation results of Step d);
• f) comparing the results of the biased chip correlation of Step e) to acceptance and rejection thresholds as follows:
• 1) when results are greater than, or equal to, an acceptance threshold, then setting the candidate flag equal to 1, and incrementing the candidate counter, whereby the candidate long code is potentially selected;
• 2) when results are less than, or equal to, the rejection threshold, setting the update flag equal to 1, whereby the candidate long code is rejected;
• and
• 3) when results are less than the pass threshold, but greater than the fail threshold, go to Step d), whereby a decision on the candidate long code is postponed;
• g) if candidate flag is equal to 1, then compare the candidate counter to a third predetermined number as follows:
• 1) when candidate counter is equal to the third number, incrementing an acceptance counter for the candidate long code, setting the update flag to 1, and the candidate flag to 0;
• and
• 2) when candidate counter is less than the third number, setting the candidate flag to 0;
• h) comparing the number of frames correlated to a fifth number as follows:
• 1) if the number of frames equals the fifth number, then selecting the long code with the largest acceptance counter as the transmitted long code and reset all acceptance counters;
• and
• 2) if the number of frames is less than the fifth number, continuing;
• and
• i) checking the update flag as follows:
• 1) if update flag is set to 1, then reinitializing correlator integration, resetting update flag to 0, and going to Step c);
• and
• 2) if update flag is set to 0, reinitialize the correlation integrator, and going to Step d).

In a wideband code division multiple access (W-CDMA) communication system including a base station transmitting a channel of information spread with a unique first long code, a sequential searching receiver with adaptive threshold biasing comprising:

• a short code matched filter having an input to receive the transmitted channel of information spread with the first long code, and an output to provide an output peak signal corresponding to the first long code masked symbol;
• a timing and code management circuit having an input operatively connected to said short code matched filter output, said timing and code management circuit computing a bias based on the amplitude of the first long code masked symbol peak output, and computing timing relationships from the interval between long code masked symbol peak outputs, said timing and code management circuit having an output to provide the bias;
• and
• a searcher unit having a first input to accept the transmitted spread first long code and a second input operatively connected to said timing and code management circuit output, said searcher unit correlating the first long code against candidate long codes, integrating the correlation results, using the bias to adjust the integrated correlation results, and comparing the biased integrated correlation results to pass/fail criteria, said searcher generating a selected candidate code to despread the first long code, whereby the bias adjusts for the effects of fading in the transmitted signal.