Delivery Time Minimization in Edge Caching: Synergistic Benefits of Subspace Alignment and Zero Forcing

TL;DR

This paper investigates the fundamental limits of cache-aided wireless networks, demonstrating how combining multicasting, zero-forcing, and interference alignment can minimize delivery latency at high SNR.

Contribution

It introduces a novel converse and an achievable scheme that optimally trade off cache storage and latency for small network configurations.

Findings

Established optimal cache-latency tradeoffs for specific network sizes.

Developed a new achievability scheme combining multiple transmission techniques.

Provided a converse bound applicable to arbitrary network parameters.

Abstract

An emerging trend of next generation communication systems is to provide network edges with additional capabilities such as additional storage resources in the form of caches to reduce file delivery latency. To investigate this aspect, we study the fundamental limits of a cache-aided wireless network consisting of one central base station, $M$ transceivers and $K$ receivers from a latency-centric perspective. We use the normalized delivery time (NDT) to capture the per-bit latency for the worst-case file request pattern at high signal-to-noise ratios (SNR), normalized with respect to a reference interference-free system with unlimited transceiver cache capabilities. For various special cases with $M=\{1,2\}$ and $K=\{1,2,3\}$ that satisfy $M+K\leq 4$, we establish the optimal tradeoff between cache storage and latency. This is facilitated through establishing a novel converse (for arbitrary $M$ and $K$) and an achievability scheme on the NDT. Our achievability scheme is a synergistic combination of multicasting, zero-forcing beamforming and interference alignment.