Spatial modulation using analog phase shifters

In this paper, we propose an analog phase shifter aided spatial modulation scheme. The proposed scheme is able to send more spatial symbols than conventional spatial modulation (SM), while reserving the low complexity of single RF-chain MIMO structure. The main idea is to transmit N
t
different phase-shifted copies of the digitally modulated signal through N
t
antennas. In each time slot, the transmitted information bits are divided into two groups. The first group of the bits are mapped to the analog phase modulated symbol. The second group of the bits are mapped to the spatial symbol, which determines the phase shift of each antenna. We further study the optimization of transmit codebook in two steps, i.e., generate the optimal spatial codebook according to Grassmannian line packing criterion, and find the optimal tradeoff between the size of signal codebook and the size of spatial codebook. Theoretical and numerical studies show that the proposed scheme has better performance than conventional SM with the same number of transmit antennas.