Non-Orthogonal Multiple-Access for Coherent-State Optical Quantum Communications Under Lossy Photon Channels

TL;DR

This paper introduces a novel SIC-based receiver and power allocation method for uplink NOMA optical quantum communication systems using coherent states, optimizing sum-rate under lossy channels and turbulence.

Contribution

It proposes a new receiver design and power allocation algorithm for NOMA-OQC, including a low-complexity variant suitable for many users, with rigorous sum-rate analysis.

Findings

Sum-rate improved by over 20% with proposed algorithms.

Effective power allocation enhances multi-user quantum communication.

Algorithms perform well under atmospheric turbulence and lossy channels.

Abstract

Coherent states have been increasingly considered in optical quantum communications (OQCs). With the inherent non-orthogonality of coherent states, non-orthogonal multiple-access (NOMA) naturally lends itself to the implementation of multi-user OQC. However, this remains unexplored in the literature. This paper proposes a novel successive interference cancellation (SIC)-based Kennedy receiver for uplink NOMA-OQC systems, along with a new approach for power allocation of the coherent states emitted by users. The key idea is to rigorously derive the asymptotic sum-rate of the considered systems, taking into account the impact of atmospheric turbulence, background noise, and lossy photon channel. With the asymptotic sum-rate, we optimize the average number of photons (or powers) of the coherent states emitted by the users. Variable substitution and successive convex approximation (SCA) are employed to convexify and maximize the asymptotic sum-rate iteratively. A new coherent-state power allocation algorithm is developed for a small-to-medium number of users. We further develop its low-complexity variant using adaptive importance sampling, which is suitable for scenarios with a medium-to-large number of users. Simulations demonstrate that our algorithms significantly enhance the sum-rate of uplink NOMA-OQC systems using coherent states by over 20\%, compared to their alternatives.