Hybrid division duplex for cognitive small cell networks

With the exponential increase in high rate traffic driven by a new generation of wireless devices, the volume of data traffic is expected to overwhelm cellular network capacity in the near future. To tackle this issue, small cell networks have been recently proposed as an efficient and cost-effective approach to provide unprecedented spectral efficiency and coverage. However, the dense and random deployment of small cells together with their decentralized operation bring several issues regarding interference pollution and network sustainability. Motivated by the flexible subchannel allocation capabilities of cognitive radio, we propose a cognitive hybrid division duplex (CHDD), in which a pair of frequency bands is used to perform frequency division duplex (FDD) on the macrocell while underlaid cognitive small cells simultaneously operate in time division duplex (TDD) on the same bands. We propose a spatial randomness-aware methodology on how to design optimal switching mechanism for cognitive TDD operation of small cells. Specifically, by using tools from stochastic geometry, we derive key performance measures in terms of success probability, network area spectral efficiency, and spatial average capacity for the proposed CHDD scheme for the case when the macro tier is in uplink mode.