Interference-Free LED Allocation for Visible Light Communications With Fisheye Lens

Due to the limited modulation bandwidth of commercial light emitting diodes (LEDs), imaging optical multiple-input multiple-output (MIMO) technology is applied in visible light communication (VLC) system to achieve high data rate. Since a receiver with a wide angle/field-of-view is preferred in the imaging optical MIMO VLC system, the fisheye lens can be utilized to concentrate the lights from the LEDs. To eliminate the inter-user interference and satisfy their target bit error rate (BER) requirements with the minimum number of LEDs, an interference-free LED allocation scheme is investigated in this paper, which is formulated as a combinatorial problem. The cost criterion of the combinatorial problem is defined as the number of the LEDs used to serve all users, and its discrete alternatives (i.e., feasible solutions) are the disjoint sets consisting of the LEDs that can be cooperatively utilized to satisfy the BER requirements for all users. For each LED in the disjoint set, its neighboring LEDs projected onto the same pixel are forbidden to serve different users. Moreover, due to the NP-hardness of the formulated problem, a location-based greedy algorithm is proposed, where the LEDs are allocated to the users sequentially based on their distances to the center of the LED array. Simulation results verify the effectiveness of our proposed algorithm and show that there exists no interference among all users while the target BER requirements for all users are satisfied with the proposed algorithm.