Tradeoffs between storage and latency for cache-aided relay interference channels with No CSIT

Abstract

In this paper, we investigate the tradeoffs between storage and latency for a K-user cache-aided relay interference channel with K antennas at the relay when channel state information (CSI) is not available at the transmitters. We propose a cache placement and content delivery scheme, and mainly focus on the case when each transmitter has a cache size capable of storing 1 out of K files in the library. The main contribution of our work is that by applying the relay decode-and-forward (DF) protocol, we can achieve a normalized delivery time (NDT) delta(mu)= (2K - 1)/K, which is the upper bound for the K-user interference channel with instantaneous CSI at the Transmitter (CSIT) when the normalized cache size at the transmitter is 1/K. We then consider caching at the relay, and based on the sum-Degree of Freedom (DoF) result, we found the achievable NDT to be (K alpha + K - 1 - beta)/(K alpha - beta), where alpha is the file splitting parameter and beta is related to the relay cache size. We also analyze the case when the transmitter has a normalized cache size of 1. To our knowledge, no one had studied a relay interference channel with no CSIT but with caching. Our results show that caching at the relay side shortens the latency effectively, especially for a network with a large number of users. Furthermore, the presence of a relay in the network renders instantaneous CSIT unnecessary, which is a more practical situation in such systems.