Xiaodi You

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.

We propose an optical camera communication (OCC) system with dimming control, employing wavelength division multiplexing (WDM) with RGB and infrared (IR) light sources. The system uses pulse width modulation (PWM) for brightness adjustment, with IR transmission integrated into both PWM “ON” and “OFF” slots to compensate for data rate losses caused by dimming. To eliminate interference at the receiver, we implement a scheme that utilizes color correction and principal component analysis to separate the hybrid signal, with an optimization approach to fine-tune the IR intensity. This design achieves a data rate of 10.8 Kb/s at 30 fps under full dimming, offering a 33.3% improvement over RGB-only transmission. At a duty cycle of 0.5, the data rate further improves by 75.6%.

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.

In this work, we proposed and experimentally demonstrated a multiple-input multiple-output (MIMO) Volterra polynomial equalizer (MVPE), in a probabilistic shaping (PS) polarization-division multiplexed (PDM) 4096-quadrature amplitude modulation (QAM) coherent optical transmission system. In comparison with the conventional single-input single-output (SISO) Volterra nonlinear equalizers (VNLEs), the proposed MVPE can equalize the in-phase (I) and quadrature (Q) components in both the X and Y polarizations simultaneously and effectively alleviate nonlinear distortions. In the PS-PDM-4096-QAM experiment, the normalized generalized mutual information (NGMI) reached the threshold of DVB-S2 low-density parity-check (LDPC) codes with a 20% overhead. Compared to the SISO VNLE scheme, the MVPE scheme improves receiver sensitivity by approximately 2.8 dB while maintaining nearly similar computational complexity.

This paper presents an asynchronous visible light communication and positioning (VLCP) system leveraging the multi-carrier orthogonal coding mechanism (MC-OCM) based on complete complementary (CC) codes. Utilizing the superior correlation properties of CC codes, our system first achieves interference-free transmission from multiple access interference and inter-symbol interference, thus simultaneously enhancing the accuracy of data transmission and receiver location in asynchronous code division multiplexing-based VLCP systems. Numerical results confirm the proposed VLCP system’s superiority, featuring an average BER below the FEC standard and an average PE less than 3 cm in challenging system settings with asynchronous transmission and multipath propagation.

In the evolving landscape of sixth-generation wireless communication, the integration of visible light communication (VLC) and visible light positioning (VLP), known as visible light positioning and communication (VLPC), emerges as a pivotal technology. This study addresses the challenges of asynchronous code division multiplexing (ACDM) in VLPC networks, focusing on the enhancement of data transmission quality and positioning accuracy. Firstly, we propose an orthogonal pseudo-random code (OPRC) for ACDM-based VLP systems. Leveraging its excellent correlation properties, VLP signals preserve orthogonality even amidst asynchronous transmissions, achieving sub-centimeter average positioning errors. Next, by combining OPRC with successive interference cancellation decoding (SICD), we propose an enhanced ACDM-based VLPC system that utilizes OPRC for improved signal orthogonality and SICD for progressive elimination of multiple access interference (MAI) among VLPC signals. The results show substantial improvements in bit-error rate (BER) and positioning error (PE), approaching the performance levels observed in synchronized VLPC systems. Specifically, the SICD-OPRC scheme reduces average BER to 4.3 × 10⁻⁴ and average PE to 2.7 cm, demonstrating its robustness and superiority in complex asynchronous scenarios.

Visible light communication (VLC) and visible light positioning (VLP) systems are usually designed separately to prevent mutual interference, while terminal mobility often introduces challenges that can degrade their performance. In this paper, we propose an integrated visible light communication and positioning (VLCP) scheme designed for mobile scenarios, encompassing both multiple-input–single-output (MISO) and multiple-input–multiple-output (MIMO) configurations. This scheme integrates both functionalities into a unified system. Utilizing decision feedback channel estimation (DFCE), we effectively estimate the dynamic channel state information (CSI) for both VLC and VLP, thereby potentially enhancing both communication and positioning performance. Simulation results across various routes verify the effectiveness of the proposed scheme. It is observed that when the terminal moves at 1 m/s, the VLCP scheme with DFCE can maintain reliable transmission quality, ensuring bit error rates (BERs) consistently below 1.3 × 10⁻². Additionally, the mean positioning errors remain within the centimeter range in different routes, not exceeding 4.3 cm and 15.5 cm in the MISO and MIMO scenarios, respectively.