Optics Communications 424 (2018) 98–102 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom Improved multiple access resource allocation in visible light communication systems Cobi Biton a , Shlomi Arnon b, * a Electro-optical Engineering Unit, Ben-Gurion University of the Negev, Beer-Sheva, Israel b Electrical and Computer Engineering Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel ARTICLE INFO Keywords: Resource allocation Discrete multi-tone (DMT) Visible light communication (VLC) Energy efficiency ABSTRACT Discrete multi-tone (DMT) and optical orthogonal frequency division multiplexing (OFDM) modulations are well- known methods used to transmit high data rate information in visible light communication (VLC) applications over the illumination infrastructure. However, the use of these techniques in a multi-user environment requires effective subcarrier and power allocation design in order to achieve the maximum data rate offered by the spatial distribution of the transmitters and receiver as well as to minimize the efficiency reduction of the illumination system due to the communication. This could be achieved by minimizing the communication signal power in an appropriate way. In this paper, we propose a heuristic allocation algorithm that minimizes the system subcarrier transmitter power while keeping the required data rate and error bit rate. The numerical calculation was done for given parameters. The results indicate that transmitter power reduction of more than 10% in a most scenario is achieved in comparison to previous algorithms. 1. Introduction The growing demand for high data rate wireless communication applications, such as mobile high definition video streaming and on- line backup storage, are devouring the wireless radio frequency (RF) spectrum, so that wireless capacity has become scarce. One of the technologies proposed to enhance the wireless system capacity is vis- ible light communication (VLC). VLC offers unlicensed and available bandwidth in the visible light region [1,2] that can be exploited on top of illumination LEDs. In addition, the necessity for cheap, simple and green wireless communication technology to support the emerging concept such as the internet of things (IOT) [2], renders VLC the natural candidate to augment RF wireless technology. For maximum utilization of the existing bandwidth of the intensity modulation di- rect detection (IM/DD) regime, a combination of DC-biased optical orthogonal frequency division multiplexing (OFDM)), is proposed [3]. In a multiple access environment (e.g. in office, aircraft or shopping mall networks) VLC is expected to provide simultaneous access and maintain high data rates for all users. Many researchers have proposed a variety of techniques to improve multi access (MA) communication performance, mainly based on transmitter diversity and evaluated in terms of noise, signal to interference ratio and signal to interference plus noise ratio [4,5]. In [6], a heuristic-based resource allocation * Corresponding author. E-mail addresses: cobi@post.bgu.ac.il (C. Biton), shlomi@bgu.ac.il (S. Arnon). algorithm that uses VLC transmitter diversity to increase the average per-user bit-rate by reuse of subcarriers and distributes power between allocated subcarriers per transmitter is proposed. The algorithm har- nesses the natural flexibility in resource allocation of DMT, in addition to its inherent spectral efficiency. In [7,8] the authors indicate that the loading of the communication functionality always comes with extra power consumption or reduction of illumination system energy efficiency in comparison to illumination-only systems in particular, with OFDM as well as binary modulation such as PAM. In this paper we extend [6] by proposing an improvement in our allocation algorithm by adding an optimization phase that performs minimization of the subcarrier transmitter power while the bit-rate is kept constant. The reduction of communication signal power is very important due to the fact that a) reducing the communication signal could increase the energy efficiency of the illumination system due to the fact that VLC and illumination systems requires always extra power consumption compared to illumination-only systems [7,8]) lower communication power could reduce optical OFDM clipping noise [9]. In our work, the allocation process is split into two phases. First, subcarrier assign to each user as proposed by [6]. Second, power alloca- tion optimization by minimizing the allocated power for maximum bit- rate for each sub-carrier. By minimizing the allocate power we reduce the cross interference and robust each lighting device against nonlinear https://doi.org/10.1016/j.optcom.2018.04.046 Received 11 December 2017; Received in revised form 17 April 2018; Accepted 19 April 2018 0030-4018/© 2018 Elsevier B.V. All rights reserved.