TRANSACTIONS ON EMERGING TELECOMMUNICATIONS TECHNOLOGIES Trans. EmergingTel. Tech. (2014) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ett.2808 SPECIAL ISSUE PAPER Performance analysis of TCP over visible light communication networks with ARQ-SR protocol Vuong V. Mai, Ngoc-Anh Tran, Truong C. Thang and Anh T. Pham * The Computer Communications Lab., University of Aizu, Japan ABSTRACT This paper theoretically studies the performance of transmission control protocol (TCP) over visible light communications (VLC) networks when the automatic-repeat request, selective repeat (ARQ-SR) protocol is employed in the link layer. We analytically derive TCP throughput considering the impact of ARQ-SR parameters and different VLC physical factors, including inter-symbol interference (ISI), signal reflection and light power distribution. Numerical results show that TCP throughput is strongly dependent on the location of VLC user due to impacts of ISI and signal reflection. It is also seen that the use of ARQ-SR could significantly improve both the maximum value and the distribution of TCP throughput in the VLC network. Especially, with a proper selection of the number of re-transmissions by the ARQ-SR protocol, the dependence of TCP throughput on user location caused by ISI, light signal reflection and distribution could be effectively remedied. Copyright © 2014 John Wiley & Sons, Ltd. *Correspondence A. T. Pham, The Computer Communications Lab., University of Aizu, Ikki-machi, Aizuwakamatsu, Fukushima, Japan. E-mail: pham@u-aizu.ac.jp Received 15 October 2013; Revised 12 December 2013; Accepted 20 January 2014 1. INTRODUCTION Light-emitting diode (LED) has been recently consid- ered as the most effective lighting technology due to its many advantages such as high brightness, long life, energy efficiency, durability and affordable cost [1]. More impor- tantly, besides the illumination purpose, LEDs, at the same time, can be used as a transmission medium for high- speed data communications [2, 3]. Such technology is referred to as visible light communications (VLC) and it is being considered as an alternative solution for indoor broadband communications. Visible light communications technology offers a num- ber of important benefits, including the use of unregulated huge bandwidth, licence-free operation, and possibly low cost [4]. There are nevertheless a number of challenging issues in practical deployments due to the unique char- acteristics of the VLC physical channel. Over the past decade, there have been many studies dedicated to chan- nel modelling, performance analysis and solution for the performance improvement of VLC systems. For instance, fluctuations of the brightness of light (i.e. the flickering) when transferring data may be harmful to human eyes [5]. Also, dimming control is required to maintain commu- nications while a user arbitrarily dims light source [6]. Caused by object movements, such as people or paper, temporary blocking may happen in VLC links [7]. Addi- tionally, the presence of inter-symbol interference (ISI), reflection (by walls) and non-uniform of light power dis- tribution corresponds to an intentional increase of the link loss [8, 9]. So far, these issues have been considered in a wide variety of VLC studies. Completed in September 2011, the Institute of Electrical and Electronics Engineers 802.15.7 standard supports minimising the flickering and achieving dimming control methods [10]. In [11], Kim et al. proposed a resource allocation protocol for solving the problem of frequent blocking in VLC links. Further- more, the use of forward error correction codes has been introduced to combat link losses [12, 13]. On the other hand, transmission control protocol (TCP) is the most popular transport protocol used by the major- ity of Internet applications. Because there is a huge amount of Internet traffic access through wireless technologies, issues regarding the behaviour of TCP over wireless net- works have been well-studied [14]. Basically, TCP per- forms well in wired networks where TCP segment losses happen mainly due to congestions. On the other hand, in wireless networks, the losses are mostly caused by lossy links. TCP reacts to these losses by performing conges- tion control algorithms, which results in the degradation of end-to-end performance, particularly in TCP through- put, which is highly sensitive to losses. This problem has Copyright © 2014 John Wiley & Sons, Ltd.