Nonorthogonal Multiple Access for Visible Light Communications: Complementary Technology Enabling High Data Rate Services for 5G Networks
Authors: Nauryzbayev Galymzhan , Abdallah Mohamed 
Published: June 2019

Introduction: The last decades have been remarkably noticed by an explosive growth of myriad applications in wireless communications, which become an inevitable part of everyday life. Apparently, such services can be characterized by high data content and consequently require high data rates. With respect to the fundamentals of information theory, the data rate at which information can be delivered to the receiver over a wireless channel is strongly linked to the signal-to-noise-ratio (SNR) of the information signal and the corresponding channel bandwidth. These achievements in providing high data rates were mainly obtained at the price of substantially increased bandwidth (Hz) and energy (joules) resources. As a result, a significant spectrum scarcity became a noticeable burden. Moreover, it was shown that exploiting additional RF bandwidth is not anymore a viable solution to meet this high demand for wireless applications, e.g. 5G systems are assumed to provide a 1 Gbps cell-edge data rate and to support data rates of between 10 Gbps and 50 Gbps. To satisfy this demand for more data rates, optical wireless communication (OWC) has been considered as a promising research area. One of these complementary technologies is visible light communication (VLC) technology that has several advantages such as huge non-occupied spectrum, immunity to electromagnetic interference, low infrastructural expenditures, etc. VLC has gained considerable attention as an effective means of transferring data at high rates over short distances, e.g. indoor communications. A typical VLC system consists of a source (light emitting diodes, LEDs) that converts the electrical signal to an optical signal, and a receiver that converts the optical power into electrical current using detectors (photodiodes, PDs). Light beams propagating through the medium deliver the information from the transmitter to the receiver. To satisfy current and future demands for increasing high data rates, the research society has focused on non-orthogonal multiple access (NOMA) regarded as one of the emerging wireless technologies is expected to play an important role in the 5G systems due to its ability to serve many more users utilizing non-orthogonal resource allocation compared to the traditional orthogonal multiple access (OMA) schemes. Therefore, NOMA has been shown to be a promising instrument to improve the spectral efficiency of modern communication systems in combination with other existing technologies. Purpose: This work aims to investigate the performance of the spectrally and energy efficient orthogonal frequency-division multiplexing (SEE-OFDM) based VLC system combined with NOMA approach. We model the system consisting of one transmitter and two receivers located in the indoor environment. Methods: First, we specify the users’ location and estimate the channel state information to determine so-called “near” and “far” users to implement the NOMA approach. Moreover, we assume that the “near” user exploits successive interference cancellation algorithm for interference decoding while the other user treats the interfering signal as noise. Next, we consider two coefficients defining the power portions allocated for the receivers. Then we apply an algorithm to successively demodulate the transmitted signals since each user observes a superposition of the signals designated for both receivers with a predefined target bit-error rate (BER) threshold (10-4). Once the target BER is achieved, we need to estimate the data rate obtainable for a certain set of the power-allocating coefficients. Results: The results show that the indoor SEE-OFDM-based VLC network can be efficiently combined with NOMA, and the target BER can be achieved by both receivers. Moreover, the BER of the “far” user is better since more power is allocated for this user. Next, we evaluate the achievable data rate and compare the results with the ones attainable for the OMA. It can be noticed that the NOMA approach outperforms the results related to the OMA. Conclusions: We analyzed the performance for the two-user indoor VLC network scenario deployed with SEE-OFDM and NOMA techniques. It was shown that recently appeared SEE-OFDM technique can be effectively exploited along with non-orthogonal approach to achieve more spectral efficiency promised by the use of NOMA. Both receivers were shown to be able to achieve the target BER within a narrow range of the power-allocating coefficients. Finally, for the defined system parameters, it was demonstrated that the NOMA approach achieves higher data rates compared to the OMA scenario.