We consider cache-aided wireless communication scenarios where each user requests both a file from an a-priori generated cacheable library (referred to as ‘content’), and an uncacheable ‘non-content’ message generated at the start of the communication session. This scenario is easily found in real-world wireless networks, where the two types of traffic coexist and share limited radio resources. We focus our investigation on singletransmitter wireless networks with cache-aided receivers, where the wireless channel is modelled by a degraded Gaussian broadcast channel (GBC). For this setting, we study the (normalized) delay-rate trade-off, which characterizes the content delivery time and non-content communication rates that can be achieved simultaneously. We propose a scheme based on the separation principle, which isolates the coded caching problem from the physical layer transmission problem, and prove its informationtheoretic order optimality up to a multiplicative factor of 2:01. A key insight emerging from our scheme is that substantial amounts of non-content traffic can be communicated while maintaining the minimum content delivery time, achieved in the absence of non-content messages; compliments of ‘topological holes’ arising from asymmetries in wireless channel gains.
Fundamental limits of wireless caching under mixed cacheable and uncacheable traffic
ISIT 2020, IEEE International Symposium on Information Theory, 21-26 June 2020, Los Angeles, CA, USA (Virtual Conference)
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