Repeated index modulation for OFDM with space and frequency diversity

In this paper, an enhanced scheme of Index Modulation for Orthogonal Frequency Division Multiplexing (IM-OFDM), called Repeated IM-OFDM with Diversity Reception (ReIM-OFDM) is proposed. ReIM-OFDM achieves performance improvement over the convetional IM-OFDM at the same spectral efficiency by providing additional space and frequency diversity. Similar to IM-OFDM, the proposed ReIM-OFDM also activates K out of total N subcarriers to convey information bits using both the active sub-carriers and their indices. However, it differs from IM-OFDM in that all activated sub-carriers are modulated by the same M-ary data symbol. For signal combining, either Maximal Ratio Combining (MRC) or Selection Combining (SC) can be used in the spatial and sub-carriers domain to help ReIM-OFDM achieve both space and frequency diversity gain. In order to analyze performance of the system, the Moment Generating Function (MGF) is used to obtain the closed-form expressions for the pairwise index error probability (PEP) and the symbol error probability (SEP) in both cases: ReIM-OFDM-MRC and ReIM-OFDM-SC. Effects of various system parameters on the SEP are analyzed to select the best ReIM-OFDM configuration with minimum error probability. Our analysis proves the effectiveness of ReIM-OFDM over IM-OFDM at the same spectral efficiency. © 2017 IEEE.