CDMA and Spread Spectrum Techniques Versus FDMA and TDMA in Cellular Mobile Radio Applications

In cellular mobile radio a changeable number K of users has to be accommodated. Each of the K different users may access an M-ary symbol alphabet. Therefore, some sort of multiple access principle must be implemented. To date, in the second generation mobile telecommunication system (GSM) FDMA and TDMA are used. CDMA and spread spectrum techniques are ideal means to combat time-variant multipath channels. There are further advantages over FDMA and TDMA like graceful degradation and reduced timing organization as well as the possibility of position location. With respect to a novel coherent multiple transmission (CMT) and reception (CMR) scheme a considerable gain can be achieved when using CDMA and spread spectrum and at the same time the carrier-to-interference ratio will be noticeably reduced. In this paper we shall emphasize the potential of CDMA and spread spectrum techniques in an illustrative way without going into technical details.