A Joint Bit-to-Symbol Mapping Scheme in Cooperative Spatial Modulation System

In this paper, a joint bit-to-symbol mapping scheme in a cooperative spatial modulation (SM) system with amplify-and-forward (AF) and decode-and-forward (DF) protocols is proposed to improve the system performance, such as the transmission bit rate and the average bit error rate (BER). The system model and the corresponding signal processing with maximum likelihood (ML) detection for the cooperative SM system without a direct link are presented first. With the consideration of both the cosine similarity among the relay nodes and the channel state information (CSI) of each transmit antenna, the bit-to-symbol mapping scheme that jointly selects the cooperative relay node, the transmit antenna, and the signal constellation is proposed. Then, its average BER performance is derived based on the moment generation function (MGF). For the proposed mapping scheme, a detailed realization process has been given as an example. Furthermore, the simulation results verify that the proposed mapping scheme effectively increases the system transmission bit rate and also improves the system average BER performance compared with the traditional natural mapping scheme.