An Addition-Decomposable Relaying Protocol and Signal Design for Optical Wireless Communications

Abstract

In this paper, we consider a kind of optical wireless communications cooperative relaying systems where the relay node not only forwards the source's signal, but also transmits its own signal simultaneously. We propose an addition-decomposable relaying (ADR) protocol for the relay node. In the protocol, the demodulated signal from the source and the signal from the relay are superposed with a signal design method called additively uniquely decomposable constellation pair (AUDCP). An extended Farey sequence is established to formulate the feasible power ratio region of the AUDCP signal. The error performance of the signal pair is dominated by two consecutive terms in the sequence. Making full use of the properties of the extended Farey sequence, we analyze the transmission performance of the protocol, and derive the closed-form dominant terms of symbol error rates (SERs) of the signal pair. In addition, under the average optical power constraint, we optimize power allocation for the cooperative system to minimize the average SER at the destination node. Simulation results demonstrate that the approximate SERs derived are close to the actual ones in high signal to noise ratio regimes, and the error performance of ADR outperforms that of conventional schemes.