Enhancing OFDM with index modulation using heuristic geometric constellation shaping and generalized interleaving for underwater VLC.

In this paper, we propose and demonstrate enhanced orthogonal frequency division multiplexing with index modulation (OFDM-IM) schemes for bandlimited underwater visible light communication (UVLC) systems via geometric constellation shaping (GCS) and subblock interleaving. Specifically, two heuristic GCS approaches based on particle swarm optimization (PSO) and hybrid genetic algorithm-PSO (GA-PSO) algorithms are proposed to generate IM-preferable constellations. Moreover, a generalized interleaving technique is further proposed to overcome the low-pass effect of bandlimited UVLC systems, where an optimal step size can be obtained to perform subblock interleaving. Simulation and experiments are conducted to evaluate the performance of the proposed enhanced OFDM-IM schemes in bandlimited UVLC systems, where both OFDM with single-mode index modulation (OFDM-SM) and OFDM with dual-mode index modulation (OFDM-DM) schemes are considered. The experimental results demonstrate remarkable signal-to-noise ratio (SNR) gains of 1.3 and 1.9 dB for OFDM-SM and OFDM-DM in comparison to the benchmark schemes, respectively.