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Achievable DoF Bounds for Cache-Aided Asymmetric MIMO Communications

Mohammad NaseriTehrani, MohammadJavad Salehi, Antti Tölli

TL;DR

The paper addresses caching in MIMO networks with asymmetric receiver antennas and derives achievable DoF bounds. It introduces three content-aware delivery schemes—min-G, Grouping, and Phantom—that jointly optimize the number of served users and per-user streams while preserving linear decodability. Each scheme provides closed-form DoF expressions and highlights distinct trade-offs between coding gain and spatial multiplexing, with numerical results showing substantial DoF improvements, particularly when device heterogeneity is pronounced. The phantom scheme, in particular, smooths the gap between min-G and grouping by dynamically reallocating spatial resources via virtual antennas, offering practical gains for heterogeneous networks. Overall, the work advances practical cache-aided MIMO designs by delivering flexible, analytically tractable DoF benchmarks for asymmetric antenna configurations.

Abstract

Integrating coded caching (CC) into multiple-input multiple-output (MIMO) communications can significantly enhance the achievable degrees of freedom (DoF) in wireless networks. This paper investigates a practical cache-aided asymmetric MIMO configuration with cache ratio $γ$, where a server equipped with $L$ transmit antennas communicates with $K$ users, each having $G_k$ receive antennas. We propose three content-aware MIMO-CC strategies: the \emph{min-G} scheme, which treats the system as symmetric by assuming all users have the same number of antennas, equal to the smallest among them; the \emph{Grouping} scheme, which maximizes spatial multiplexing gain separately within each user subset at the cost of some global caching gain; and the \emph{Phantom} scheme, which dynamically redistributes spatial resources using virtual or ``phantom'' antennas at the users, bridging the performance gains of the min-$G$ and Grouping schemes. These strategies jointly optimize the number of users, $Ω$, and the parallel streams decoded by each user, $β_k$, ensuring linear decodability for all target users. Analytical and numerical results confirm that the proposed schemes achieve significant DoF improvements across various system configurations.

Achievable DoF Bounds for Cache-Aided Asymmetric MIMO Communications

TL;DR

The paper addresses caching in MIMO networks with asymmetric receiver antennas and derives achievable DoF bounds. It introduces three content-aware delivery schemes—min-G, Grouping, and Phantom—that jointly optimize the number of served users and per-user streams while preserving linear decodability. Each scheme provides closed-form DoF expressions and highlights distinct trade-offs between coding gain and spatial multiplexing, with numerical results showing substantial DoF improvements, particularly when device heterogeneity is pronounced. The phantom scheme, in particular, smooths the gap between min-G and grouping by dynamically reallocating spatial resources via virtual antennas, offering practical gains for heterogeneous networks. Overall, the work advances practical cache-aided MIMO designs by delivering flexible, analytically tractable DoF benchmarks for asymmetric antenna configurations.

Abstract

Integrating coded caching (CC) into multiple-input multiple-output (MIMO) communications can significantly enhance the achievable degrees of freedom (DoF) in wireless networks. This paper investigates a practical cache-aided asymmetric MIMO configuration with cache ratio , where a server equipped with transmit antennas communicates with users, each having receive antennas. We propose three content-aware MIMO-CC strategies: the \emph{min-G} scheme, which treats the system as symmetric by assuming all users have the same number of antennas, equal to the smallest among them; the \emph{Grouping} scheme, which maximizes spatial multiplexing gain separately within each user subset at the cost of some global caching gain; and the \emph{Phantom} scheme, which dynamically redistributes spatial resources using virtual or ``phantom'' antennas at the users, bridging the performance gains of the min- and Grouping schemes. These strategies jointly optimize the number of users, , and the parallel streams decoded by each user, , ensuring linear decodability for all target users. Analytical and numerical results confirm that the proposed schemes achieve significant DoF improvements across various system configurations.
Paper Structure (14 sections, 3 theorems, 42 equations, 1 figure, 2 tables)

This paper contains 14 sections, 3 theorems, 42 equations, 1 figure, 2 tables.

Table of Contents

  1. Introduction
  2. System Model
  3. Asymmetric MIMO-CC Delivery Schemes
  4. min-G Scheme
  5. Grouping Scheme
  6. Phantom Scheme
  7. Numerical Examples
  8. Conclusion
  9. Appendix
  10. Proof of Theorem \ref{['Th:Linear_Dec']}
  11. Transmission vector Design: Example
  12. The min-G scheme
  13. The grouping scheme
  14. The phantom scheme

Key Result

Theorem 1

The transmission vectors ${\mathbf{x}}_{\textrm{MC}}(s)$ in sig_model_phantom are linearly decodable by each user $k \in {\mathcal{K}}_{\textrm{MC}}(s)$.

Figures (1)

  • Figure 1: Asymmetric MIMO-CC downlink serving a target UE set ${\mathcal{K}}$ of size $K$, where each UE has the same cache size $MF$ bits. Different colors represent UEs with varying capabilities.

Theorems & Definitions (8)

  • Remark 1
  • Theorem 1
  • proof
  • Lemma 1
  • proof
  • Theorem 2
  • proof
  • Example 1