Precoding Based Downlink OAM-MIMO Communications with Rate Splitting

TL;DR

This paper proposes a precoding optimization method for downlink OAM-MIMO communications with rate splitting, enhancing sum capacity and privacy, using fractional programming and quadratic transformation techniques.

Contribution

It introduces a novel integration of rate splitting into OAM-MIMO systems and derives an optimal precoding scheme to maximize sum capacity.

Findings

Achieves higher sum capacity than traditional schemes.

Effectively guarantees user privacy with rate splitting.

Demonstrates the effectiveness of the proposed precoding algorithm through simulations.

Abstract

Orbital angular momentum (OAM) and rate splitting (RS) are the potential key techniques for the future wireless communications. As a new orthogonal resource, OAM can achieve the multifold increase of spectrum efficiency to relieve the scarcity of the spectrum resource, but how to enhance the privacy performance imposes crucial challenge for OAM communications. RS technique divides the information into private and common parts, which can guarantee the privacies for all users. In this paper, we integrate the RS technique into downlink OAM-MIMO communications, and study the precoding optimization to maximize the sum capacity. First, the concentric uniform circular arrays (UCAs) are utilized to construct the downlink transmission framework of OAM-MIMO communications with RS. Particularly, users in the same user pair utilize RS technique to obtain the information and different user pairs use different OAM modes. Then, we derive the OAM-MIMO channel model, and formulate the sum capacity maximization problem. Finally, based on the fractional programming, the optimal precoding matrix is obtained to maximize the sum capacity by using quadratic transformation. Extensive simulation results show that by using the proposed precoding optimization algorithm, OAM-MIMO communications with RS can achieve higher sum capacity than the traditional communication schemes.