Cluster-based Collaborative Caching for Amorphous User Cell Association

Increasing cell capacity with non-ideal backhaul link is the most challenging issue in small cell technology. In this paper, we propose amorphous user cell association strategy which is a combination of caching and multiple access schemes to achieve a substantial capacity enhancement in dense hotspot zone without requirement of ideal backhaul link. The objective of user cell association strategy is to maximize average utility function by joint design of caching and multiple access schemes in two different time scales. At off-peak hours, cluster-based collaborative caching (CCC) scheme is optimized according to long-term popularity distribution of files. Based on availability of files on collaborative caches, cache-enabled multiple access (CEMA) scheme is introduced to opportunistically broadcast coded parity bits to multiple users with same user request and to choose optimal biasing factor to scale cell size dynamically at peak-traffic hours. Our simulation results show that by taking into account of channel state information (CSI) and user request profile (URP) for user cell association, significant capacity gain can be achievable in ultra-dense networks.