Outage Performance of Pairwise NOMA Allowing a Dynamic Decoding Order and Optimal Pairs of Power Levels

Van-Lan Dao,Elisabeth Uhlemann,Svetlana Girs,Le-Nam Hoang

doi:10.1109/ojcoms.2020.3039536

Van-Lan Dao, Elisabeth Uhlemann + Show 2 more

Open Access

https://doi.org/10.1109/ojcoms.2020.3039536

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Abstract

In this article, we evaluate the overall outage probability (OOP) of pairwise Non-orthogonal Multiple Access (NOMA) for both uplink and downlink. We also propose a dynamic decoding order (DDO) together with a fixed pairwise power allocation (FPPA) scheme, in which the optimal decoding order is decided based on the instantaneous channel gains, and thereafter, a pair of power levels is assigned in accordance with the selected decoding order. Exact closed-form expressions of the OOPs for both uplink and downlink pairwise NOMA considering all proposed decoding orders over Nakagami-m fading are derived. Further, we find the optimal fixed power levels for different power allocation strategies so that the OOPs are minimized. Moreover, we investigate the influence of the distances between the source nodes and the access point (AP), the target transfer rates and the path-loss exponents on the OOPs for all cases of decoding orders. In addition, we benchmark our proposed DDO against other decoding orders in terms of the OOP. The results show that assigning optimal fixed power levels which takes the instantaneous decoding order into account not only improves the communication reliability, but also reduces the complexity and computational load at the AP.

Highlights

R ECENTLY, beyond 5G/6G techniques have attracted much attention, in which some technologies, e.g. NonOrthogonal Multiple Access (NOMA), massive multiple-inputmultiple-output and reconfigurable intelligent surface have become potential key technologies [1]–[3], and the combination of one or more of these techniques can bring additional benefits [4], [5]
We propose a DDO strategy with two simple steps before each transmission: first the optimal decoding order is decided at the access point (AP) based on the instantaneous channel gains, and second, the power allocation scheme is selected from a fixed predetermined set in accordance with the chosen decoding order
We propose algorithms which can find the optimal power allocation for each user in both uplink and downlink pairwise NOMA, given a certain decoding order to be used for the fixed set

Summary

Introduction

R ECENTLY, beyond 5G/6G techniques have attracted much attention, in which some technologies, e.g. NonOrthogonal Multiple Access (NOMA), massive multiple-inputmultiple-output and reconfigurable intelligent surface have become potential key technologies [1]–[3], and the combination of one or more of these techniques can bring additional benefits [4], [5]. Emerging industrial applications have a need for ultra-low latency, high reliability and often energy efficiency. There is a drive to design more spectrally and energy efficient multiple access schemes, which enable channel access with high reliability and low delay for use in future wireless networks. The superior spectral efficiency of NOMA which helps reduce the latency of communication is shown in [6]. With NOMA, an access point (AP) can communicate in both downlink and uplink transmission phases with many users at the same time using the same frequency, and instead separating the users in a different domain. We consider NOMA in the power-domain, implying that the users are separated using different transmit power levels

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