Distributed CSMA/CA MAC Protocol for RIS-Assisted Networks

TL;DR

This paper introduces an optimal distributed CSMA/CA protocol leveraging RIS to enhance multi-user channel access, balancing spatial diversity gains and probing overhead for improved throughput in RIS-assisted networks.

Contribution

It proposes a novel distributed channel access strategy with opportunistic RIS assistance, derived from optimal sequential decision theory, and develops a low-complexity algorithm for practical implementation.

Findings

Achieves higher throughput than existing methods.

Demonstrates lower online complexity at O(1).

Verifies theoretical results through numerical simulations.

Abstract

This paper focuses on achieving optimal multi-user channel access in distributed networks using a reconfigurable intelligent surface (RIS). The network includes wireless channels with direct links between users and RIS links connecting users to the RIS. To maximize average system throughput, an optimal channel access strategy is proposed, considering the trade-off between exploiting spatial diversity gain with RIS assistance and the overhead of channel probing. The paper proposes an optimal distributed Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) strategy with opportunistic RIS assistance, based on statistics theory of optimal sequential observation planned decision. Each source-destination pair makes decisions regarding the use of direct links and/or probing source-RIS-destination links. Channel access occurs in a distributed manner after successful channel contention. The optimality of the strategy is rigorously derived using multiple-level pure thresholds. A distributed algorithm, which achieves significantly lower online complexity at $O(1)$, is developed to implement the proposed strategy. Numerical simulations verify the theoretical results and demonstrate the superior performance compared to existing approaches.