Comparison of System Configurations Achieving 3 Bits per Symbol in Spatial Modulation (SM) Systems

In Spatial Modulation (SM) systems where each symbol carries 3 bits of information (equivalent to 3 bit/s/Hz spectral efficiency), we conduct the following comparative analysis:

1. Configuration with 4 transmit antennas using BPSK modulation: This setup utilizes antenna indexing to convey additional information bits, where log2(4) = 2 bits are transmitted through antenna selection, and the remaining 1 bit is carried by the BPSK symbol.

2. Configuration with 2 transmit antennas using 4-QAM modulation: Here, log2(2) = 1 bit is transmitted via antenna selection, while the 4-QAM constellation carries 2 bits per symbol, achieving the total 3-bit requirement.

Through this comparison, we can better understand the performance differences between these configurations in terms of implementation complexity, error probability, and system capacity. Key implementation aspects include antenna selection algorithms, constellation demapping techniques, and spectral efficiency verification through mathematical modeling.