Constrained Partial Group Decoding With Max–Min Fairness for Multi-Color Multi-User Visible Light Communication

Abstract

A visible light communication (VLC) system can adopt multi-color light emitting diode (LED) arrays to support multiple users. In this paper, a multi-layer coding and constrained partial group decoding (CPGD) method is proposed to tackle strong color interference and increase the system throughput. After channel model formulation, user information rates are allocated and decoding order for all the received data layers is obtained by solving a max-min fairness problem using a greedy algorithm. An achievable rate is derived under the truncated Gaussian input distribution. To reduce the decoding complexity, a map on the decoding order and rate allocation is constructed for all positions of interest on the receiver plane and its size is reduced by a classification-based algorithm. Meanwhile, the symmetrical geometry of LED arrays is exploited. Finally, the transmitter-user association problem is formulated and solved by a genetic algorithm. It is observed that the system throughput increases as the receivers are slightly misaligned with corresponding LED arrays due to the reduced interference level, but decreases afterwards due to the weakened link gain. Index TermsVisible light communication, multi-layer transmission, constrained partial group decoder, interference cancellation, transmitter-user association. 2 I. INTRODUCTION With the increasing amount of data transmitted via wireless links, the spectrum shortage has become a critical problem for the next generation communication systems. Visible light communication (VLC) has emerged as a competent supplement [1], [2] to radio-frequency communication due to its unique advantages, such as large bandwidth and free of electromagnetic radiation. Combining with its other advantages, such as simple transceiver structures due to its intensity modulation-direct detection (IM-DD) method, VLC has attracted extensive research attentions in recent years [3]-[6].Light emitting diode (LED) array can be adopted to provide required illumination and simultaneously increase the system's data rate [7], [8]. In a multi-user scenario, where each LED and photodiode (PD) pair serves one user, the PD receives not only the desired signal but also the signals from adjacent LEDs as interferences. It is typical that these interferences are strong and thus treating them as noise will penalize the system throughput or even cause a decoding failure. To tackle this problem, interference can be suppressed by designing a resource allocation scheme [9] or aligned [10], [11] via transmitter-side signal processing.One the other hand, it is generally accepted that while a receiver is not interested in decoding the messages from interferers, decoding them is often beneficial for recovering the desired message [12]. Multi-layer coding and group decoder [13] provide an interference cancellation framework that exploits this benefit. At the transmitter, each data stream is split into multiple layers that are encoded individually using independent codebooks, followed by an LED sending the superposition of t...

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