On the Design of Superimposed Pilots in MIMO-OFDM with Index Modulation

Multiple-input multiple-output and orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) deliver information bits by both the indices of activated subcarriers and conventional constellations, enabling a trade-off between spectral efficiency (SE) and system performance. To obtain the channel state information (CSI) without reducing the SE of the system, a superimposed pilot transmission scheme for MIMO-OFDM-IM, along with multiple superimposed pilot patterns, is proposed in this paper. Meanwhile, a modified channel estimation process is explored to cancel the mutual interference between pilots and information signals, improving the channel estimation and the bit error rate (BER). The simulation results demonstrate that within a tolerable complexity, the proposed MIMO-OFDM-IM assisted with superimposed pilot scheme exhibits higher SE than the conventional comb-type pilot scheme without loss of BER performance.