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Visible light communication (VLC) systems have typically operated at data rates below 10 Gbps and operation at this data rate was shown to be feasible by using laser diodes (LDs), imaging receivers and delay adaptation techniques (DAT imaging LDs-VLC). However, higher data rates, beyond 10 Gbps, are challenging due to the low signal to noise ratio (SNR) and inter symbol interference (ISI). In this paper, for the first time, to the best of our knowledge, we propose, design and evaluate a VLC system that employs beam steering (of part of the VLC beam) using adaptive finite vocabulary of holograms in conjunction with an imaging receiver and a delay adaptation technique to enhance SNR and to mitigate the impact of ISI at high data rates (20 Gbps). An algorithm was used to estimate the receiver location, so that part of the white light can be directed towards a desired target (receiver) using beam steering to improve SNR. Simulation results of our location estimation algorithm (LEA) indicated that the required time to estimate the position of the VLC receiver is typically within 224 ms in our system and environment. A finite vocabulary of stored holograms is introduced to reduce the computation time required by LEA to identify the best location to steer the beam to the receiver location. The beam steering approach improved the SNR of the fully adaptive VLC system by 15 dB at high data rates (20 Gbps) over the DAT imaging LDs-VLC system in the worst case scenario. In addition, we examined our new proposed system in a very harsh environment with mobility. The results showed that our proposed VLC system has strong robustness against shadowing, signal blockage and mobility.

-In this paper, we introduce a new adaptive optical wireless system that employs a finite vocabulary of stored holograms. We propose a fast delay, angle and power adaptive holograms (FDAPA-Holograms) approach based on a divide and conquer methodology and evaluate it with angle diversity receivers in a mobile optical wireless (OW) system. The ultimate goal is to increase the signal to noise ratio (SNR), reduce the effect of inter-symbol-interference (ISI), and eliminate the need to calculate the hologram at each transmitter and receiver location. A significant improvement is achieved in the presence of very directive background illumination noise, receiver noise, multipath propagation, mobility, and shadowing typical in a realistic indoor environment. The combination of beam delay, angle and power adaptation offers a degree of freedom to the link design, resulting in a system that is able to achieve higher data rates (5 Gb/s). At a higher data rate of 5 Gb/s, and under eye safety regulations, the proposed FDAPAHolograms system offers around 13 dB SNR with full mobility in a realistic environment where shadowing exists. The fast search algorithm introduced based on divide and conquer (D&C) reduces the computation time required to identify the optimum hologram. Simulation results show that the proposed system, FDAPA-Holograms, can reduce the time required to identify the optimum hologram position from taken by a classic adaptive hologram to about .---

The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on visible light communication (VLC) systems. Although VLC systems provide lighting and communications simultaneously from light emitting diodes, LEDs, the uplink channel design in such a system is a challenging task. In this paper, we propose a solution in which the uplink challenge in indoor VLC is resolved by the use of an Infrared (IR) link. We introduce a novel fast adaptive beam steering IR system (FABS-IR) to improve the uplink performance at high data rates while providing security for applications. The goal of our proposed system is to enhance the received optical power signal, speed up the adaptation process and mitigate the channel delay spread when the system operates at a high transmission rate. The channel delay spread is minimised from 0.22 ns given by hybrid diffuse IR link to almost 0.07 ns. At 2.5 Gb/s, our results show that the imaging FABS-IR system accomplished about 11.7 dB signal to noise ratio (SNR) in the presence of multipath dispersion, receiver noise and transmitter mobility.Index Terms-uplink channel, beam steering IR, delay spread, SNR.

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