Abstract-In this paper, we consider a two-tier heterogeneous cellular network (HCN) where macrocells and distributed low power cells, namely daughtercells, are operated in a common spectrum. Due to the ad-hoc nature of daughtercell BS deployments such as pico and femto cells, the mutual interference varies and obviously the coverage probability behaves differently in terms of transmit powers and densities of macrocells and daughtercells. In this paper, we employ repulsive cell activation in the interfering daughtercell network and see the impact of a minimum separation distance between the daughtercell BSs in terms of coverage under open access and power efficiency. The control of the minimum separation distance plays a role in balancing cell load effectively according to changing user density and is justified for the coexistence of low power daughtercells. The optimal minimum separation distance in terms of user density and target per-tier user throughput requirements is found by a numerical search based on a simple bisection method. Numerical results show the benefit of cell repulsion in terms of increased user density support and less area power consumption.
In the presence of a large number of relays, some effective relays close to the source and destination nodes need to be regionally elected and the relays far from them shall be disregarded for relay selection process because of the likelihood of higher outage probability. In this paper, we propose an opportunistic feedback mechanism combining a geographical selection region where the relay whose effective channel gain is above a pre-determined threshold can only feed back, and thereby establish a relation between required relay-node density and the level of feedback threshold. It is shown that required relay-node density and selection region for a desired quality-ofservice (QoS) depend on the feedback threshold.
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