A DELAY INDEPENDENT DECORRELATING DETECTOR FOR QUASI-SYNCHRONOUS CDMA

The decorrelating detector is a near-far resistant linear joint detect or for a code-division multiple-access (CDMA) system. It consists of a bank of matched filters followed by a decorrelating matrix. For prope r operation, both the matched filter bank and the decorrelating matrix require knowledge of the delays of all users. The delays are due to t he different propagation times from each user to the base station. Del ay estimation is a weak link in this system since it is complex and pr one to error. The proposed decorrelating detector does not require exa ct knowledge of the user delays, but instead requires that the delays be bounded to a fraction of a symbol interval. The delays are naturall y bounded in this way in many microcell and picocell systems where the round trip propagation time is small compared to the symbol interval. The new delay independent decorrelating detector is shown to be near- far resistant and, through appropriate spreading code selection, to ex perience a modest 3 dB signal-to-noise ratio (SNR) loss relative to or thogonal access schemes. It is also shown to limit capacity to a maxim um of 50% of the spreading gain when the delays are bounded by a singl e chip interval. The complexity is similar to the conventional correla ting receiver which is far less complex than the joint detection schem es proposed to date.