Identical code‐data cyclic shift transmission for time‐dispersive channel

Abstract

Multiple access techniques working on time‐dispersive channels must employ spreading codes with good correlation properties to minimize multipath interference and multiple access interference. Popular spreading codes, such as the Walsh‐Hadamard code (orthogonal) and maximal length sequence (m‐sequence) (semi‐orthogonal), suffer from intersymbol interference (ISI). ISI increases owing to the poor autocorrelation properties of the spreading codes, resulting in a deteriorated bit‐error‐rate (BER) performance. Recently, a cyclic interleaving transmission has been proposed to enhance multipath diversity in the presence of ISI. In this study, an identical code‐data cyclic shift (ICDCS) transmission scheme is introduced to achieve improved multipath diversity in time‐dispersive channels. The proposed ICDCS transmission is designed based on cyclically shifting identical codes and data. The code and data involved in the first set of spreading are cyclically shifted for the next set of spreading, and the two sets are blended to perform cyclic interleaving. The data are despread from each multipath component at the receiver using different codes derived from a single m‐sequence through identical code cyclic shifting (ICCS). Consequently, multipath diversity increases, resulting in a significant reduction in the BER. ICDCS transmission effectively utilizes all multipath components and the codes derived from the ICCS to mitigate ISI. The simulation results confirm that the proposed ICDCS transmission significantly enhances the multipath diversity compared to the conventional cyclic interleaving transmission scheme.