On the Performance Gain of NOMA over OMA in Uplink Single-Cell Systems

Abstract

In this paper, we investigate the performance gain of non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in uplink single-cell systems. In both single-antenna and multi-antenna scenarios, the performance gain of NOMA over OMA in terms of asymptotic ergodic sumrate is analyzed for a sufficiently large number of users. In particular, in single-antenna systems, we identify two types of near-far gains brought by NOMA: 1) the large-scale near-far gain via exploiting the large-scale fading increases with the cell size; 2) the small-scale near-far gain via exploiting the small-scale fading is a constant given by γ = 0.57721 nat/s/Hz in Rayleigh fading channels. Furthermore, we have analyzed that the performance gain achieved by single-antenna NOMA can be amplified via increasing the number of antennas equipped at the base station due to the extra spatial degrees of freedom. The numerical results confirm the accuracy of the derived analyses and unveil the performance gains of NOMA over OMA in different scenarios.

On the Performance Gain of NOMA Over OMA in Uplink Communication Systems

“…1. The cell is modeled by a pair of two concentric ring- 1 We restrict ourselves to the uplink NOMA communications [49], as advanced signal detection/decoding algorithms of NOMA are more affordable at the base station. shaped discs.…”

“…, h K ] ∈ C M ×K . Note that the system model in (1) user k in single-antenna systems. We assume that the channel coefficients are independent and identically distributed (i.i.d.)…”

“…In this section, we use simulations to evaluate our analytical results. In the single-cell systems considered, the inner cell radius is D 0 = 50 m and the outer cell radius is given by D = [50,200,500] m, which corresponds to the cases of normalized cell sizes given by η = [1,4,10], respectively. The number of users K ranges from 2 to 256 and the number of antennas employed at the BS M ranges from 1 to 128.…”

“…ESG versus the total transmit power P ′ max in multi-cell systems. The normalized cell size is η = [1,4,10] in Fig. 7(a), Fig.…”

“…Additionally, in the virtual K-user M × M MIMO system, the subchannel gain between user k and the BS is forced to be identical as h k , where h k is the corresponding channel gain value between user k and the BS in the original K-user 1 × M MIMO system in (1). Furthermore, we consider an arbitrary but the identical power allocation strategy p = [p 1 , .…”