6 - Enhancements of correlation-delay-shift-keying scheme

Abstract

This chapter discusses the operation and the performance analysis of the enhancement methods, based on the correlation-delay-shift-keying (CDSK) scheme. It reviews the multiple-access capabilities of the enhancement methods, based on a permutation transformation. The analytical bit error rate (BER) of the permutation-based multiple-access CDSK system is also derived. In both the enhancement methods for CDSK, the spreading factor is set to be the same as the delay i.e. the receiver detects the symbol by correlating the received signal in the current bit duration with that in the previous bit duration. In the first method, when the symbol "+1" is to be sent, a delayed signal from the chaos generator is transmitted. The same chaotic signal is re-sent in the following bit duration as long as the next symbol is also "+1". If two consecutive "−1"s are to be sent, then the transmitted signal in the second symbol duration is the summation of a chaotic signal and the delayed and modulated version of it. Compared to the CDSK scheme, the first enhancement method combines two chaotic signals for transmission only for the symbol "−1".