Interference Mitigation for Faster-Than-Nyquist $m$CAP in Bandlimited VLC: A Low-Complexity Gapped Index Modulation Approach

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Abstract
In this paper, a novel gapped index modulation (GIM) scheme is proposed and investigated to mitigate the inter-band interference (IBI) with low complexity in faster-than-Nyquist multi-band carrierless amplitude and phase modulation (FTN-$m$CAP) based bandlimited visible light communication (VLC) systems. More specifically, the introduction of FTN sampling reduces the required bandwidth to achieve the same data rate via spectrum compression in the frequency domain at the transmitter, which results in increased IBI. To efficiently mitigate the IBI, by innovatively combining low-complexity GIM with FTN-$m$CAP, the proposed GIM aided FTN-$m$CAP (FTN-$m$CAP-GIM) scheme achieves a target data rate with a narrower bandwidth. Compared with FTN-$m$CAP, a larger compression factor can be supported at a target bit error rate (BER) when applying the proposed FTN-$m$CAP-GIM scheme in bandlimited VLC systems. Numerical simulations and hardware experiments have been conducted to verify the superior BER performance of the proposed FTN-$m$CAP-GIM in comparison to the conventional FTN-$m$CAP scheme. The experimental results show that the feasible compression factor is increased from 0.22 to 0.38 when FTN-4CAP is replaced with the proposed FTN-4CAP-GIM at a target BER of $3.8 \times 10^{-3}$ with a roll-off factor of 0.5, while FTN-6CAP-GIM with a roll-off factor of 0.5 achieves a maximum compression factor of 0.44 at BER = $3.8 \times 10^{-3}$. Moreover, FTN-6CAP-GIM with a roll-off factor of 0.5 also achieves a substantial spectral efficiency (SE) improvement of 78.2% in comparison to conventional 6CAP.
Funding Information
  • National Natural Science Foundation of China (62271091)
  • National Natural Science Foundation of China (62001319)
  • Suzhou Science and Technology Bureau-Technical Innovation Project in Key Industries (SYG202112)
  • Open Fund of IPOC (IPOC2020A009)

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