Performance Evaluation of Non-Orthogonal Multiple Access in Visible Light Communication

Abstract

In this paper, the performance of non-orthogonal multiple access (NOMA) is characterized in a downlink visible light communication (VLC) system for two separate scenarios. For the case of guaranteed quality of service (QoS) provisioning, we derive analytical expressions of the system coverage probability and show the existence of optimal power allocation coefficients on two-user paired NOMA. For the case of opportunistic besteffort service provisioning, we formulate a closed-form expression of the ergodic sum rate, which is applicable for arbitrary power allocation strategies. The probability that NOMA achieves higher individual rates than orthogonal multiple access (OMA) is derived. Also, we give an upper bound of the sum rate gain of NOMA over OMA in high signal-to-noise ratio (SNR) regimes. Both simulation and analytical results prove that the performance gain of NOMA over OMA can be further enlarged by pairing users with distinctive channel conditions. We also find out that the choice of light emitting diodes (LEDs) has a significant impact on the system performance. For the case of guaranteed QoS provisioning, LEDs with larger semi-angles have better performance; while for the case of opportunistic besteffort service provisioning, LEDs with 35 • semi-angle give nearly optimal performance.Index Terms-Non-orthogonal multiple access (NOMA), visible light communication (VLC), coverage probability, ergodic sum rate, order statistics.

Performance analysis of gain ratio power allocation strategies for non-orthogonal multiple access in indoor visible light communication networks

“…The received signal transmitted from the LED to the k-th user is assumed in (8), where s k denotes the onoff keying (OOK) signal and n k denotes the zero-mean Gaussian noise caused by many independent sources [7,10,25,30,31].…”

“…• Several studies [9,10,15] have continued to use the Shannon capacity formula, which may not be accessible without the maximizing input distribution. However, the bound can be referred to as the achievable bound.…”

“…To maximize the advantages of high-density coverage within a VLC cell, non-orthogonal multiple access (NOMA) [9][10][11][12] as a promising candidate for nextgeneration wireless networks, has been introduced into VLC networks for promoting of network system throughput. Compared with orthogonal multiple access (OMA) [5,13], NOMA can exploit the entire bandwidth for the time-frequency utilization of all degrees of freedom to increase spectral efficiency.…”

“…In NOMA, gain ratio power allocation (GRPA) [5,11,14] considers user channel conditions to ensure efficient and fair power allocation of LED transmitted signal power, while enhancing the achievable throughput in VLC networks. In RF and VLC, the power allocation of NOMA extends research goals in several major respects, such as user fairness [15,16], channel allocation [17,18], user scheduling [7,9,18], energy efficiency [9,[19][20][21], quality of service (QoS) requirement [9,10,22,23], and sum rate maximization [11,16,24,25].…”

“…In [9], a power allocation strategy considering residual interference was optimized by the QoS constraint and numerical search with both max-min and max-sum rate criteria. In [10], analytical expressions of user outage probability for guaranteed QoS and an ergodic sum rate for opportunistic best-effort service were derived. In [11,26], a GRPA strategy based on a power law criterion that considers user channel conditions was presented.…”