Synchronous time multiplexing for non-line-of-sight multiple-input multiple-output optical camera communications.

In typical multiple-input multiple-output (MIMO) optical camera communication (OCC) systems, the spatial correlation of MIMO channels is large. Optical signals between light sources can easily interfere with each other, negatively impacting the overall transmission performance. In this work, we propose a time-multiplexing integral modulation scheme for a non-line-of-sight MIMO OCC system, where each LED transmits different signals to improve both the data rate and security of the system. A genetic algorithm (GA)-based adaptive multi-threshold scheme is designed to demodulate the blurred fringes in multi-level pulse amplitude modulation. The experimental results show that at a distance of 2.5 m, a data rate of 16.4 kb/s can reach with the BER performance of 3.01 × 10-3, which validates the superiority and reliability of our proposed schemes.

Confidential multiple-input multiple-output optical camera communication aided by a two-dimensional pilot.

Optical camera communication (OCC) has attracted increased attention for its inherent security advantage. However, there still exists the risk of eavesdropping on the broadcasting channel of OCC. To achieve confidential communication, we propose the confidentiality-interference dual light-emitting diode (LED) communication (CIDLC) scheme at the transmitter (TX) and elimination of interference (EI) scheme at the receiver (RX). Meanwhile, interference signals refer to the bit shift of confidential signals. Further, we propose the two-dimensional pilot-aided channel estimation (2D-PACE) scheme to enhance the reliability of multiple-input multiple-output (MIMO) OCC. Experiment results validate the effectiveness of our schemes, which guarantee confidentiality while performing well at a 2 m non-line-of-sight (NLOS) distance. Finally, the communication-illumination integration OCC is constructed via the energy equalization coding (EEC) scheme.

Non-line-of-sight optical camera communication aided by a pilot.

Currently, optical camera communication (OCC), as an emerging network access mode for the fifth-generation (5G), is valued for its advantages over radio frequency (RF). In the long-distance communication scenario, the data rate of line-of-sight (LOS) OCC is restricted. To address this, we propose a pilot-aided demodulation scheme to realize extending the communication distance, while also ensuring the data rate and reliability of the non-line-of-sight (NLOS) OCC. The experiment result validates the effectiveness of the proposed pilot-aided signal layer estimation (PSLE) and extreme value clustering (EVC) scheme, which can perform well against a heterogeneous background with ghost shadows at 2.5 m distance.

Research on an uplink carrier sense multiple access algorithm of large indoor visible light communication networks based on an optical hard core point process.

The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.