Reconfigurable Intelligent Surface-Assisted Multiple-Antenna Coded Caching

TL;DR

This paper explores how reconfigurable intelligent surfaces (RIS) can enhance multi-antenna coded caching systems by optimizing interference nulling and grouping strategies to maximize degrees of freedom (DoF).

Contribution

It introduces a novel RIS-assisted interference nulling algorithm, an optimal grouping strategy, and a new RMAPDA framework for improved cache placement and delivery.

Findings

Proposed a faster convergence interference nulling algorithm.

Developed an optimal grouping strategy to maximize DoF.

Designed a new RMAPDA framework for cache management.

Abstract

Reconfigurable Intelligent Surface (RIS) has emerged as a promising technology to enhance the wireless propagation environment for next-generation wireless communication systems. This paper introduces a new RIS-assisted multiple-antenna coded caching problem. Unlike the existing multi-antenna coded caching models, our considered model incorporates a passive RIS with a limited number of elements aimed at enhancing the multicast gain (i.e., Degrees of Freedom (DoF)). The system consists of a server equipped with multiple antennas and several single-antenna users. The RIS, which functions as a passive and configurable relay, improves communication by selectively erasing certain transmission paths between transmit and receive antennas, thereby reducing interference. We first propose a new RIS-assisted interference nulling algorithm to determine the phase-shift coefficients of the RIS. This algorithm achieves faster convergence compared to the existing approach. By strategically nulling certain interference paths in each time slot, the transmission process is divided into multiple interference-free groups. Each group consists of a set of transmit antennas that serve a corresponding set of users without any interference from other groups. The optimal grouping strategy to maximize the DoF is formulated as a combinatorial optimization problem. To efficiently solve this, we design a low-complexity algorithm that identifies the optimal solution and develops a corresponding coded caching scheme to achieve the maximum DoF. Building on the optimal grouping strategy, we introduce a new framework, referred to as RIS-assisted Multiple-Antenna Placement Delivery Array (RMAPDA), to construct the cache placement and delivery phases. Then we propose a general RMAPDA design to achieve the maximum DoF under the optimal grouping strategy.