A Code Selection Criterion Based on Autocorrelation Properties for Quasi-Synchronous CDMA Communication System

Abstract

Code selection plays a prominent role in the performance of CDMA based communication systems. Codes are designed to have desirable autocorrelation and crosscorrelation properties. In this work, a new expression for autocorrelation is presented for delays within a chip period. Based on this expression, a new criterion is proposed for Code selection in quasi-synchronous CDMA communication. This criterion may be used to select a finite number of codes from a given codeset in quasi-synchronous environment. It is found that with the proposed criterion there is about 0.9 dB and 2 dB improvement in BER performance at synchronization errors of 0.1 Tc and 0.2 Tc respectively for WH codes of length 64, compared to random selection of codes. The analysis is limited to codes employing rectangular pulse shape.