Abstract
Recently, non-orthogonal multiple access (NOMA) has attracted considerable interest as one of the 5G-enabling techniques. However, users with better channel conditions in downlink communications intrinsically benefits from NOMA thanks to successive decoding, judicious designs are required to guarantee user fairness. In this paper, a two-user downlink NOMA system over fading channels is considered. For delay-tolerant transmission, the average sum-rate is maximized subject to both average and peak power constraints as well as a minimum average user rate constraint. The optimal resource allocation is obtained using Lagrangian dual decomposition under full channel state information at the transmitter (CSIT), while an effective power allocation policy under partial CSIT is also developed based on analytical results. In parallel, for delay-limited transmission, the sum of delay-limited throughput (DLT) is maximized subject to a maximum allowable user outage constraint under full CSIT, and the analysis for the sum of DLT is also performed under partial CSIT. Furthermore, an optimal orthogonal multiple access (OMA) scheme is also studied as a benchmark to prove the superiority of NOMA over OMA under full CSIT. Finally, the theoretical analysis is verified by simulations via different trade-offs for the average sum-rate (sum-DLT) versus the minimum (maximum) average user rate (outage) requirement.
Highlights
Related WorkThe above fairness issues were considered for non-orthogonal multiple access (NOMA) in (quasi-)static or added white Gaussian noise (AWGN) channels
Non-orthogonal multiple access (NOMA) has attracted considerable interest as one of the 5G-enabling techniques
We verify the theoretical analysis for the considered two-user downlink non-orthogonal multiple access (NOMA) system via numerical results
Summary
The above fairness issues were considered for NOMA in (quasi-)static or added white Gaussian noise (AWGN) channels. Assuming perfect channel state information (CSI) at both the transmitter (Tx) and the receivers (Rxs), dynamic power and rate allocations for various transmission schemes including code division (CD) with and without successive decoding, time division, and frequency division over different fading states were studied for the ergodic capacity region (ECR) and the (zero-) outage capacity region (OCR) in [18] and [19], respectively. The (zero-) OCRs were inexplicitly characterized by deriving the outage probability regions given a rate vector in [19] The boundaries of these regions were obtained by solving equivalent sum-reward maximization problems [19]. Unlike [19] that defined the usage probability via the power set of the users, we equivalently reformulate this continuous variable by arithmetic operation over multiple discrete variables via an indicator function [20]
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