Analysis of coverage range expansion in closed access cognitive femtocell networks

Femtocells are low-power nodes which aim to extend high data-rate wireless services in indoor environments. While low power operation allows more frequent spectrum reuse and significant improvement in network capacity, it also suffers from frequent handoffs between the macro and femtocell due to the short distances involved. It can potentially generate considerable redundant control data for hand over management. An alternative is to apply handover bias which artificially expands the coverage range of a femtocell to keep a user connected to a femtocell access point (FAP). This eliminates the handover problem or ping pong effect, but at the cost of reduced throughput. This paper proposes an enhanced virtual cluster formation (EVCF) algorithm that allows the coverage range of the femtocells to be expanded. The impact of FAP coverage expansion on system performance of closed access femtocell networks for various FAP deployments has been analysed and is compared to a random resource allocation system with similar range expansion capability. Results reveal that while FAP range extension inevitably decreases the signal to interference plus noise ratio (SINR) and corresponding throughput, the resultant degradation can be minimised by adopting the EVCF model with a commensurate enhancement in the system quality-of-service (QoS) provision.