Theoretical Limits of a Novel Multiplexing Method

A novel method to multiplex digital information over cable networks has recently been proposed [1]. This new method baptized ScDMA - standing for Scattering Division Multiple Access - leads to unprecedented advantages [2]. Two important differences with usual communication systems have to be highlighted. Firstly, the usual flow of physical signals carrying information is changed. Even though information is sent by the source, the source does not emit any physical signal. Indeed, the receiver reads the information of the source by sending a signal and analyzing the reflected signal. Secondly, the channel is somehow controlled in a deterministic manner, while in usual communication systems the channel is uncontrolled and considered as random. These two differences have impacts on the theoretical limit performance. In particular the usual expression of the system capacity C is modified: the maximization of the average mutual information I(X; Y) has to be done not only on the input symbol probabilities P(X) but also on the conditional probabilities P(Y|X) since the channel itself can be controlled. In addition, the case of the multi-rate multi-user capacity leads to unexpected results.