Physical layer caching in 5G wireless networks

Abstract

The spectral efficiency of small-cell wireless networks is limited by the severe interference from the neighboring base stations (BSs) as well as the backhaul capacity of the BSs. In this thesis, we propose a physical layer (PHY) caching scheme to address these two issues. To address the interference issue, by properly caching some popular contents at the BSs, the proposed PHY-caching can opportunistically transform the topology of the radio access network (RAN) from an unfavorable topology (e.g., relay or interference topology) into a more favorable multiple-input and multiple-output (MIMO) broadcast topology and enjoy spectrum efficiency gain without large backhaul consumption. To address the backhaul issue, we consider a joint design of frequency reuse and caching in small-cell wireless networks. Spatial caching diversity (i.e., caching different subsets of popular content files at neighboring BSs) can greatly improve the cache hit probability, thereby leading to a better overall system performance. A key issue in exploiting spatial caching diversity is that the cached content may not be located at the nearest BS, which means that to access such content, a user needs to overcome strong interference from the nearby BSs. Using our proposed scheme, the benefit of an improved cache hit probability induced by spatial caching diversity and the benefit of interference coordination induced by frequency reuse can be achieved simultaneously. Moreover, we further propose an interference-aware dual-mode caching and user-centric open-loop cooperative transmission scheme that embraces spatial caching diversity and user-centric open-loop cooperative transmission, and alleviate the interference issue in the system. For each of the above proposed schemes, we propose corresponding cache storage capacity allocation algorithms that maximize the spectral efficiency benefits induced by PHY caching, and quantify the benefits with respect to some important system parameters such as cache capacity and content popularity distribution. The proposed solution for each problem is compared with some state-of-the-art baselines, and it is shown through simulations that significant performance gain can be achieved.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology