Network performance of asynchronous UTRA-like FDD/CDMA systems using loosely synchronised spreading codes

Abstract

In this paper we characterize the capacity of an UTRA-like frequency division duplex (FDD) code division multiple access (CDMA,) system employing loosely synchronized (LS) spreading codes. Current CDMA systems are interference limited, suffering from inter-symbol-interference (ISI), since the orthogonality of the spreading sequences is destroyed by the channel. They also suffer from multiple-access-interference (MAI) owing to the non-zero cross-correlations of the spreading codes. LS codes exhibit 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 by simulation and compares it to that of an UTRA-like FDD/CDMA system using orthogonal variable rate spreading factor (OVSF) codes.