NOMA-SM for cooperatively enhancing vehicle-to-vehicle transmissions

Inspired by the robustness of spatial modulation (SM) against channel correlation and the benefits of non-orthogonal multiple access (NOMA), in this paper, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless vehicle-to-vehicle (V2V) environments as well as to support improved bandwidth efficiency. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We derive the capacity of NOMA-SM and a pair of analytical capacity upper bounds in closed form. A power allocation optimization scheme is formulated accordingly and the optimal solution is demonstrated to be achievable with the aid of our proposed algorithm. By investigating the bit error ratio (BER) performance of NOMA with different multiple-antenna techniques and the bandwidth efficiency of SM combined with distinct multiple access methods, NOMA and SM are shown to cooperatively improve V2V transmissions.