Multi-Mode Index Modulation Aided Multi-Band CAP With Balanced Pairwise Coding for Bandlimited VLC Systems

In this paper, we for the first time propose and demonstrate a multi-mode index modulation aided multi-band carrierless amplitude and phase modulation (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM) scheme for bandlimited visible light communication (VLC) systems. More specifically, the information bits of the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM scheme are conveyed through both multiple distinguishable modes and their full permutation indices. For <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM, due to the importance of choosing an appropriate constellation design strategy, we consider partitioning the circular (7,1)-quadrature amplitude modulation (QAM) constellation to obtain multiple distinguishable constellation modes. Moreover, an enhanced log-likelihood ratio (LLR) detector is also developed for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM, which can solve the error propagation problem existed in the conventional LLR detector and achieve nearly optimal performance as the maximum likelihood (ML) detector but with a much lower complexity. In addition, aiming at the problem of signal-to-noise ratio (SNR) imbalance among different subbands due to the low-pass effect in practical VLC systems, a novel balanced pairwise coding (B-PWC) technique is further proposed and incorporated into the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM scheme. The feasibility and superiority of the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM scheme with enhanced LLR detection and B-PWC coding have been successfully verified by both simulations and experiments. Specifically, simulation results verify the superiority of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula>CAP-MM employing the designed multiple constellation modes and enhanced LLR detection over the additive white Gaussian noise (AWGN) channel, and then the validity of B-PWC in bandlimited <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> CAP-MM VLC systems is verified via proof-of-concept experiments. Experimental results demonstrate that a bandwidth extension of 19.9% can be achieved by the proposed 8CAP-MM with B-PWC in comparison to that with traditional PWC.