  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 called the backhaul-limited cached dense
wireless network (C-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 MIMO cooperation gain and cache-assisted
Multihopping gain. Two fundamental questions are addressed. Can we exploit the
PHY caching to achieve linear capacity scaling with limited payload backhauls?
If so, how much cache is needed? We show that the capacity of the
backhaul-limited C-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 quantify the throughput gain due to cache-induced MIMO cooperation over
conventional caching schemes (which exploit purely the cached-assisted
multihopping). Interestingly, the minimum BS cache size needed to achieve a
significant cache-induced MIMO cooperation gain is the same as that needed to
achieve the linear capacity scaling.
