In recent years, code division multiple-access (CDMA) techniques have received a great deal of attention for mobile terrestrial/satellite communication systems. Primarily considered for the noteworthy features of low power flux density emission and robustness to interference and multipath, CDMA is known to bear reduced bandwidth and power efficiency when compared to traditional TDMA and FDMA due to the intrinsic cochannel self-noise. Early attempts to increase the capacity of CDMA-based systems for commercial applications relied on voice activation and frequency reuse. More recently, practical solutions to implement (synchronous) orthogonal CDMA signaling are being developed independently in Europe and in the USA. This paper is focused on the comparative performance analysis of those two orthogonal CDMA schemes in the operating renditions of a mobile satellite communications system. In particular, the two CDMA systems are compared in the presence of that and frequency-selective multipath fading and a typical satellite transponder nonlinearity. Most numerical results are derived through a time-domain system simulation that confirms and integrates the theoretical findings.>

We investigate performance of decision-directed maximum-likelihood carrier phase synchronizers for M-PSK signalling (M/spl les/8) on the AWGN channel. Decision-directed feedback (DD-FB) and feedforward decision feedback (FF-DFB) structures are analyzed and compared in detail. A new, accurate model for the FF-DFB synchronizer is presented. Open loop characteristics and closed loop performance, in terms of steady-state jitter and cycle slip rate, are presented in the same framework for both the DD-FB and FF-DFB synchronizers. Performance comparison between the two phase estimator architectures is finally made for each modulation scheme investigated.