Performance Analysis for Reconfigurable Intelligent Surface-Aided Cache-Enabled Wireless Networks

Locally caching at base stations (BSs) can increase the network capacity as well as reduce the backhaul burden. However, it iremains an open problem whether it could increase energy efficiency (EE) for the future sixth-generation (6G) network when the offloading link is in a deep fading condition. In order to analyse this problem, we attempt to analyse the energy efficiency of cache-enabled wireless communication system assisted by reconfigurable intelligent surfaces (RIS), which is a new paradigm to increase EE. First, by considering the central limit theorem and Jensen's inequality, we obtain the approximated expression for EE when the number of RIS reflecting elements is very large. Secondly, due to the adoption of the RIS-User/BS random association and a new BS-RIS-User wireless link, we analyse the performance between EE and the number of RIS reflecting elements under some condition. Finally, it is shown by full simulation that it is valid of our analysis, meanwhile, we gain the optimal cache capacity and the optimal transmission power of BS to maximize EE. Moreover, we show that the help of RIS can improve EE when the system is noise-limited due to RIS can improve the signal power and has very low transmit power, but EE decreases in an interference-limited system. Furthermore, we obtain the optimal number of BSs at the minimum EE in interference-limited system, but EE decreases as the number of BS increases when the system is noise-limited.