Link Adaptation for Spatial Modulation With Limited Feedback

In this paper, link-adaptation schemes, where the transmit parameters are dynamically adapted to the changing channel conditions, are developed for spatial modulation (SM) transmission systems. The proposed schemes are based on the adaptive modulation (AM) and transmit-mode switching (TMS) techniques, to further exploit the spatial freedom of the multiple-input-multiple-output channel. More specifically, an optimal hybrid-SM (OH-SM) scheme that jointly uses both AM and TMS techniques is first developed to efficiently utilize the channel resources. In OH-SM, the transmit mode is jointly adapted with modulation orders according to the channel condition. Moreover, a suboptimal hybrid SM scheme, termed as a concatenated SM (C-SM) scheme, is also proposed. The C-SM scheme exploits the multistage adaptation strategy to balance the tradeoff between computational complexity and performance. The performance of the proposed schemes is evaluated by using the nearest neighbor approximations, to derive the parameter selection criterions. Simulation results show that, under the same spectral efficiency, the proposed schemes provide considerable system performance improvement compared with the conventional SM systems, particularly in correlated channel conditions.