Achievable DoF Bounds for Cache-Aided Asymmetric MIMO Communications

2026-03-18

AI Summary

This work addresses the degrees-of-freedom (DoF) limitation in cache-aided asymmetric MIMO communication systems arising from heterogeneous numbers of receive antennas across users. It establishes, for the first time, a cache-aided MIMO framework tailored to asymmetric antenna configurations. Four content-aware MIMO coded caching (MIMO-CC) transmission strategies—min-G, Grouping, Super-grouping, and Phantom—are proposed and integrated with three symmetric cache placement schemes. These designs enable flexible trade-offs between DoF gains and subpacketization complexity while ensuring linear decodability. Theoretical analysis and simulations demonstrate that the proposed strategy combinations significantly enhance DoF across diverse system settings, achieving both superior performance and practical implementation flexibility.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Multiagent Systems: Mechanism Design
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Cloud, edge and content delivery systems for the Web
• Web Mining and Content Analysis: Content-based information diffusion
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems

Abstract

This is an extended journal version of the conference paper published in ISIT 2025; submitted to IEEE Transactions on Communications (TCOM). Integrating coded caching (CC) into multiple-input multiple-output (MIMO) communications significantly enhances the achievable degrees of freedom (DoF). This paper investigates a practical cache-aided asymmetric MIMO configuration with cache ratio $γ$, where a server with $L$ transmit antennas communicates with $K$ users. The users are partitioned into $J$ groups, and each user in group $j$ has $G_j$ receive antennas. We propose four content-aware MIMO-CC strategies: \emph{min-$G$} enforces symmetry using the smallest antenna count among users; \emph{Grouping} maximizes intra-subset spatial multiplexing gain at the expense of some global caching gain; \emph{Super-grouping} aggregates users into optimized \emph{min-$G$}-based super-sets with identical effective receive multiplexing gains before applying \emph{Grouping} across them; and \emph{Phantom} redistributes spatial resources assuming ``phantom'' antennas at the users to bridge the performance gains of \emph{min-$G$} and \emph{Grouping}. We develop these asymmetric strategies under three reference symmetric CC placement-delivery policies with guaranteed linear decodability: a DoF-optimal policy achieving the optimal single-shot DoF, and two closed-form policies, namely combinatorial and linear cyclic low-complexity constructions, with the cyclic policy attaining DoF performance close to the others in many operating regimes. Analytical and numerical results demonstrate significant DoF improvements across various system configurations, and that policy-strategy combinations offer flexible trade-offs between DoF and subpacketization complexity.

Problem

• cache-aided
• asymmetric MIMO
• degrees of freedom
• coded caching
• DoF bounds

Innovation

• coded caching
• asymmetric MIMO
• degrees of freedom
• content-aware strategies
• spatial multiplexing