Improved spectral efficiency of SM-OFDM using a set of rotated constellations

Spatial Modulation (SM) is a technique that targets to achieve a compromise between the two conflicting objectives in multiple-input multiple-output (MIMO) networks, namely the simultaneous enhancements of data reliability and data rate, by adjusting the index of the operational transmit antenna in the transmitted information bits. Orthogonal frequency division multiplexing (OFDM) has become a widely accepted technique to combat inter-symbol interference (ISI) present in frequency selective channels, such as the ones conveying very high data rates. In this paper, a new SM-OFDM-based scheme is proposed, which adds another element of information in the transmitted SM-data block consisting of a chosen constellation among the available rotated set. To attain this, an additional index is used to select the specific constellation. At the receiver, a set of detectors is proposed to jointly estimate the transmitted symbol, as well as the used constellation and the active transmit antenna indices. The comparison of the performance of this new scheme against the conventional SM-OFDM shows an increased spectral efficiency at the price of a slight degradation in bit error rate. The proposed scheme permits a trade-off between the quality of the communication and the achieved spectral efficiency.