Loosely synchronized spreading code aided network performance of quasi-synchronous UTRA-like TDD/CDMA systems

Abstract

In this paper we investigate the achievable capacity of a UTRA-like Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes. The family of operational CDMA systems is interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the frequency selective channel. They also suffer from Multiple-Access-Interference (MAI) owing to the non-zero cross-correlations of the spreading codes. By contrast, the family of LS codes exhibits a so-called Interference Free Window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance in comparison to that of a UTRA-like TDD/CDMA system using Orthogonal Vari- MSO able Rate Spreading Factor (OVSF) codes