Novel Precoded Index Modulation Designs for MIMO-OFDM Systems

Precoded index modulation (PIM) has emerged as an innovative approach to assist multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in carrying additional bits of information by exploiting the space-frequency resources. Conventional PIM schemes typically modulate the information on each subcarrier independently, neglecting the diversity gain and fading resistance that could be achieved by jointly modulating multiple subcarriers. In this paper, we propose two joint precoded index modulation (JPIM) schemes by grouping multiple subcarriers into blocks and using them as the units for index modulation (IM), resulting in superior bit-error-rate (BER) performance. First, the non-overlap JPIM (NO-JPIM) scheme processes the subcarriers within different blocks independently, without any interaction between different blocks. Second, the overlap JPIM (O-JPIM) scheme integrates information from adjacent blocks, providing improved BER performance at the expense of increased complexity. For the proposed schemes, we perform a theoretical analysis of their BER performance and diversity gains. Simulation results show that both proposed schemes achieve more than 5 dB improvement in terms of signal-to-noise ratio (SNR) at a BER of 10^-3 compared to the conventional PIM scheme.