Bi-Directional Cooperative NOMA without Full CSIT

TL;DR

This paper introduces bi-directional cooperative NOMA, a novel multiple access scheme that maintains high efficiency without full channel state information and improves data rates over existing NOMA and OMA methods.

Contribution

The paper proposes a new bi-directional cooperative NOMA system that performs well with similar channel gains and without accurate CSI, providing analytical capacity and outage probability results.

Findings

Achieves higher ergodic capacity than other NOMA techniques.

Provides better data rates than existing NOMA and OMA schemes.

Offers power and diversity gains over traditional methods.

Abstract

In this paper, we propose bi-directional cooperative non-orthogonal multiple access (NOMA). Compared to conventional NOMA, the main contributions of bi-directional cooperative NOMA can be explained in two directions: 1) The proposed NOMA system is still efficient when the channel gains of scheduled users are almost the same. 2) The proposed NOMA system operates well without accurate channel state information (CSI) at the base station (BS). In a two-user scenario, the closed-form ergodic capacity of bi-directional cooperative NOMA is derived and it is proven to be better than those of other techniques. Based on the ergodic capacity, the algorithms to find optimal power allocations maximizing user fairness and sum-rate are presented. Outage probability is also derived, and we show that bi-directional cooperative NOMA achieves a power gain over uni-directional cooperative NOMA and a diversity gain over non-cooperative NOMA and orthogonal multiple access (OMA). We finally extend the bi-directional cooperative NOMA to a multi-user model. The analysis of ergodic capacity and outage probability in two-user scenario is numerically verified. Also, simulation results show that bi-directional cooperative NOMA provdes better data rates than the existing NOMA schemes as well as OMA in multi-user scenario.