1 978-1-5386-1782-3/17/$31.00 ©2017 IEEE A NOMA Scheme for Visible Light Communications using a Single Carrier Transmission 1 Bangjiang Lin, 1 Xuan Tang, 2 Zabih Ghassemlooy, 1 Chun Lin, 1 Min Zhang, 1 Zhenlei Zhou 3 Yi Wu and 3 Hui Li 1 Quanzhou Institute of Equipment Manufacturing, Haixi Institutes, Chinese Academy of Sciences, Fujian, China; 2 Optical Communications Research Group, NCRLab, Faculty of Engineering and Environment, Northumbria University, NE1 8ST, Newcastle, U.K.; 3 Key Laboratory of OptoElectronic Science and Technology for Medicine of Ministry of Education, Fujian Normal University, China. linbangjiang@163.com Abstract—We propose a non-orthogonal multiple access (NOMA) scheme for visible light communications (VLC) based on single carrier (SC) transmission and frequency-domain successive interference cancellation. The scheme can achieve a low peak-to-average power ratio (PAPR), a good balance between the throughput and fairness, and a higher system capacity for a larger number of users. We show that the proosed scheme offers improved bit error rate performance compared to the orthogonal frequency domain multiplexing based VLC system. Keywords—non-orthogonal multiple access; single carrier; visible light communications I. INTRODUCTION The visible light communication (VLC) system is gaining a growing interest in both wireless and optical communities. This is due to a number of advantages including license-free spectrum, inherent security (since light stays within a confined space), higher transmission speed compared to the radio frequency (RF) based wireless technologies, lower energy consumption (i.e., a green technology based on the energy efficient light emitting diodes (LEDs) lighting fixtures), and relatively low cost [1-4]. The key features of the LED lighting sources are that they can be used for illumination, data communications, indoor localization and sensing. The radio access technologies for RF based mobile communications are typically characterized by multiple access schemes such as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA) in order to increase the transmission throughput. These multiple access technologies are also adopted in VLC systems to support multiple services to multiple users concurrently as well as increase the transmission data rate. Orthogonal multiple access (OMA) techniques such as the time domain multiple access (TDMA), orthogonal frequency domain multiple access (OFDMA) and interleaved frequency division multiple access (IFDMA) have been introduced in VLC systems [5-9]. However, these schemes suffer from the tradeoff between the throughput and fairness. Recently, the non-orthogonal multiple access (NOMA) scheme, which is a novel multiple access strategy, has drawn great attention [9-12]. The basic signal waveform for NOMA could be based on OFDM or Fourier transform spread OFDM as well as LTE radio access, although alternative waveforms including a filter bank multicarrier could be used. However, unlike the conventional multiple access technologies, NOMA superposes user data in the power domain and uses successive interference cancellation (SIC) as well as capacity-achieving channel codes such as the Turbo and low-density parity check (LDPC) codes at the receiver (Rx) to separate the user data, so that all of the users can use the whole time-frequency resources. As a result, NOMA can balance the throughput and fairness. It has been regarded as a promising solution to enhance the spectral efficiency for the 5th generation (5G) wireless networks [9-12].With good feasibility and performance, it has also been adopted in VLC systems [13-15]. In [16], a phase pre-distortion method was proposed to improve the symbol error rate performance of the NOMA uplink with SIC decoding in VLC. In [17], we propose a NOMA scheme combined with OFDMA for VLC, which offered flexible bandwidth allocation and a higher system capacity. In this paper, we propose a NOMA scheme for the VLC system, which uses a single carrier (SC) format and a novel frequency domain SIC (FD-SIC). SC transmission can outperform OFDM in terms of the peak to average power ratio (PAPR), which is critical in VLC system due to the high nonlinearity characteristics (i.e., power vs current) of LEDs [18]. In this work, we experimentally verify the feasibility of the proposed NOMA-VLC with SC transmission. The effect of power allocation ratio (PAR) on the bit error rate (BER) performance is also investigated. The experiment results show that, compared with OFDM, the SC transmission for NOMA- VLC offers improved BER performance. The rest of the paper is organized as follows. In section 2, we introduce the SC and FD-SIC based NOMA scheme for VLC systems. Section 3 presents the experiment setup and results for the NOMA-VLC followed by the concluding remarks in Section 4. II. TECHNIQUE PRINCIPLE Figure 1 shows the schematic system diagram of the proposed NOMA-VLC with N-user and FD-SIC. At the transmitter (Tx), the source data d s (t) for each user is mapped to the amplitude quadrature modulation (QAM) format and grouped into blocks prior to power allocation, respectively. The cyclic prefix (CP) is added at the start of each block to combat the multi-path induced inter-symbol interference (ISI)