NOMA Beamforming in SDMA Networks: Riding on Existing Beams or Forming New Ones?

TL;DR

This paper compares two NOMA beamforming strategies in SDMA systems, highlighting their tradeoffs in performance and complexity, and finds that using existing beams reduces complexity with minimal performance loss, especially with structured channels.

Contribution

It provides a comparative analysis of NOMA beamforming strategies in SDMA systems, revealing their tradeoffs and conditions for optimal performance.

Findings

Using existing beams reduces computational complexity.

Performance loss is minimal when channels are structured.

Simple strategies can achieve optimal performance under certain conditions.

Abstract

In this letter, the design of non-orthogonal multiple access (NOMA) beamforming is investigated in a spatial division multiple access (SDMA) legacy system. In particular, two popular beamforming strategies in the NOMA literature, one to use existing SDMA beams and the other to form new beams, are adopted and compared. The studies carried out in the letter show that the two strategies realize different tradeoffs between system performance and complexity. For example, riding on existing beams offers a significant reduction in computational complexity, at the price of a slight performance loss. Furthermore, this simple strategy can realize the optimal performance when the users' channels are structured.