How Much Cache is Needed to Achieve Linear Capacity Scaling in Backhaul-Limited Limited Dense Wireless Networks
Abstract: Dense wireless networks are a promising solution to meet the huge capacity demand in 5G wireless systems. However, there are two implementation issues, namely, the interference and backhaul issues. To resolve these issues, we propose a novel network architecture ecture called the backhaul backhaul-limited limited cached dense wireless network (C-DWN), DWN), where a physical layer (PHY) caching scheme is employed at the base stations (BSs), but only a fraction of the BSs have wired payload backhauls. The PHY caching can replace the role of wired backhauls to achieve both the cache-induced induced multiple multiple-input-multiple-output output (MIMO) cooperation gain and cache-assisted assisted multihopping gain. Two fundamental questions are addressed. Can we exploit the PHY caching to achieve linear capacity scaling with wit limited payload backhauls? If so, how much cache is needed? We show that the capacity of the backhaul-limited C-DWN DWN indeed scales linearly with the number of BSs if the BS cache size is larger than a threshold that depends on the content popularity. We also lso quantify the throughput gain due to cache cache-induced induced MIMO cooperation over conventional caching schemes (which exploit purely the cachedcached assisted multihopping). Interestingly, the minimum BS cache size needed to achieve a significant cache--induced MIMO cooperation operation gain is the same as that needed to achieve the linear capacity scaling.