System capacity analysis of hybrid cellular networks with cognitive radio relay

Hybrid cognitive radio (CR) networks can jointly utilize both licensed and unlicensed radio resources to gain better performance over pure licensed/unlicensed networks. This paper studies the system-level capacity of a hybrid cellular network that consists of licensed base stations (BSs) and unlicensed CR relays. Two limiting cases are considered, in which the CR relays are assumed to have infinite cache and no cache, respectively. We systematically derive the system capacity under different simplifying assumptions on interference and path loss. Our results reveal how the system capacity is related to various system parameters such as BS/relay density, bandwidth, power, and CR reliability. Such an insight can be useful for the planning of future heterogeneous cellular networks.