Due to the low sampling rate of the camera based receiver, the movement of communication devices becomes a factor that cannot be ignored in the demodulation of optical camera communications (OCC). In this paper, we propose the block matching demodulation (BMD) algorithm, which is a movement-robust and optical-interference-resistant demodulation method for OCC. The BMD algorithm can resist the movement of communication devices by locating communication light source per image and immunize optical interference by utilizing the fast time-varying characteristic of communication light source. Moreover, in order to enhance the reliability of communication systems, BMD algorithm and Manchester decoding are combined to realize error detection and correction without increasing the overhead of encoding. Finally, we build a practical mobile OCC system to test the performance of BMD algorithm. Experimental results show that the BMD algorithm can resist the movement of communication devices effectively and achieve reliable demodulation.

Due to the directionality of light, the hidden device problem and the obstruction cannot be ignored for carrier sense multiple access with collision avoidance (CSMA/CA)-based uplink visible light communication (VLC). In this paper, we introduce multipacket reception (MPR) to handle the hidden device problem in VLC system. We model the traffic of the device with on/off Markov source. With the unsaturated traffic, we formulate a two dimensional (2D) Markov chain to model the CSMA/CA-based slotted random access procedure to evaluate the effects of hidden devices and obstructions on the performance of MPR-aided VLC system, which are mapped into the transition probabilities of the Markov chain. Then, we analyze the throughput and the reception power efficiency (RE) of MPR-aided VLC system with the obstructed optical channel. Numerical results show that the effect is negative when hidden devices or obstructions appear solely. But when they appear simultaneously, they will interact with each other to mitigate the negative effects.

The medium access control (MAC) protocol for indoor visible light communication (VLC) with energy harvesting is explored in this paper. The unfairness of throughput exists among devices due to the significant difference of their energy harvesting rates which changes with distance, acceptance angle and the obstruction probability. We propose an energy harvesting model, a new obstruction probability model and an energy adaptive contention algorithm to overcome the unfairness problem. This device can adjust its contention window according to the energy harvesting rate. As a result, the device with lower energy harvesting rate can get shorter contention window to improve its transmission opportunity. Simulation results show that our MAC protocol can achieve a higher degree of fairness.

This paper exploits an optical large multiple input multiple output (MIMO) system. We first establish the non-reciprocity compensation correction factor to solve the channel non-reciprocity problem. Then we propose an antenna selection algorithm with the goal of realizing maximum energy efficiency (EE) when satisfying the outage EE. The simulation results prove that this non-reciprocity compensation correction factor can compensate beam energy attenuation gap and spatial correlation gap between uplink and downlink effectively, and this antenna selection algorithm can economize the number of transmit antennas and achieve high EE performance. Finally, we apply direct current- biased optical orthogonal frequency division multiplexing (DCO-OFDM) modulation in our system and prove that it can improve the bit error rate (BER) compared with on-off keying (OOK) modulation, so the DCO-OFDM modulation can resist atmospheric turbulence effectively.

To facilitate the efficient support of quality-of-service (QoS) for promising free-space optical (FSO) communication systems, it is essential to model and analyze FSO channels in terms of delay QoS. However, most existing works focus on the average capacity and outage capacity for FSO, which are not enough to characterize the effective transmission data rate when delay-sensitive service is applied. In this paper, the effective capacity of FSO communication systems under statistical QoS provisioning constraints is investigated to meet heterogeneous traffic demands. A novel closed-form expression for effective capacity is derived under the combined effects of atmospheric turbulence conditions, pointing errors, beam widths, detector sizes and QoS exponents. The obtained results reveal the effects of some significant parameters on effective capacity, which can be used for the design of FSO systems carrying a wide range of services with diverse QoS requirements.