DS-CDMA techniques for mobile and personal satellite communications: An overview

The recent application of code division multiple access (CDMA) to commercial terrestrial radio networks suggested the possibility of extending the same access technique to high-efficiency low-cost satellite systems. A great research and development effort has therefore started, and is still in progress, to fulfill the requirements of modern commercial satellite networks, namely: low-cost user equipments on one side and power and spectral efficiency on the other. The aim of this contribution is to address the main topics in the development of such systems for satellite-based mobile and personal communications. More specifically, we investigate first the inherent trade-off between coding and spreading, then we touch upon the techniques for the minimisation of the self-noise effect, and the related issues of power control, multi-user detection and satellite diversity. As a key factor in the successful deployment of CDMA networks, we shortly review some technological aspects related to an efficient modem design via digital signal processing techniques, and the possible consequent low-cost, small-size application-specific integrated circuit (ASIC) implementation. The final part of the paper deals with some system-related issues, like the effect of the nonlinear satellite transponder and the mobile multipath channel on the multiplexed user signal, and highlights the applicability of CDMA to the emerging new-generation services, such as digital audio broadcasting (DAB), wideband mobile networks, and the like.