A cooperative system for visible light positioning (VLP) and visible light communication (VLC) is proposed based on the spread-spectrum plugin of optical identification (OPID). By keeping the existing VLC frame structure untouched, two different implementation schemes were designed by adding the location information field into the communication information field for VLP applications. It is deemed to be a good solution to overcome the mutual exclusion between VLP and 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 ( $m$ CAP-MM) scheme for bandlimited visible light communication (VLC) systems. More specifically, the information bits of the proposed $m$ CAP-MM scheme are conveyed through both multiple distinguishable modes and their full permutation indices. For $m$ 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 $m$ 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 $m$ CAP-MM scheme. The feasibility and superiority of the proposed $m$ 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 $m$ 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 $m$ 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.

We proposed and experimentally demonstrated a general pilot structure for probabilistic shaped (PS)-polarization division multiplexing (PDM) M-ary quadrature amplitude modulation (MQAM) coherent optical transmission, where a portion of PS-MQAM symbols is exploited as the pilot symbols with the same information entropy as the transmitted signal. The pilot symbols are simultaneously used in the entire digital signal processing (DSP) modules for polarization de-multiplexing, frequency offset estimation, carrier phase recovery, nonlinear equalization, and linear equalization. Compared to the conventional quadrature phase shift keying (QPSK) pilot structure, the proposed MQAM pilot structure can yield the nonlinear properties of the overall signal so that nonlinear equalization can effectively improve the performance of the normalized generalized mutual information. The remarkable performance has been achieved at the shaping parameters of 3.25 and 4.35 for 1024QAM and 4096QAM signals based on the proposed pilot scheme, which corresponds to the raw spectral efficiency of 16.190 and 20.381 bit/s/Hz, respectively. The pilot ratio is optimized to 5% for higher achievable information rates (AIRs).