A Novel Low-Complexity Adaptive Bit Mapping Scheme for Spatial Modulation

We propose a novel low-complexity adaptive bit mapping scheme for spatial modulation (SM) called the nearest point method (NPM). In this scheme, the SM symbols are first sorted according to a certain sorting order, then bit sequences that are different only in 1 bit are assigned to subsequent SM symbols according to that sorting order. To determine the sorting order, NPM starts with the pair of SM symbols that has the minimum distance. From one of the SM symbols in that pair, it identifies the nearest SM symbol and continues to do so until it visits all the SM symbols without visiting the same SM symbol more than once. Simulation results show that NPM achieves performance close to the lower bound of the BER for SM and space shift keying (SSK) using full channel state information at the transmitter. It also achieves BER improvement for SSK using the channel distribution and correlation information. The complexity of the proposed NPM is on the order O(K
²
), where K is the number of symbols, which is remarkably low.