• A cell range expansion framework for closed access Femtocell networks

      Tariq, Faisal; Dooley, Laurence S.; Allen, Ben; Poulton, Adrian S.; Liu, Enjie; University of Bedfordshire; Open University (Springer New York LLC, 2014-12-17)
      While femtocell networks represent a promising solution for extending high data-rate wireless services in indoor environments, despite their many benefits the short coverage distances involved can lead to frequent handovers being triggered resulting in overloading the macrocells. This handover problem is further exacerbated for users operating at the cell boundary. One solution is to keep the mobile station (MS) connected to the femtocell access points (FAP) by applying a handover bias to expand the femtocells coverage, though arbitrarily increasing the cell range can have a detrimental effect on system performance as the received interference will increase and may exceed tolerable levels. Many disparate factors including: FAP deployment density; resource constraints; and cell range expansion (CRE) influence the crucial interference-system performance nexus, and this was the motivation to analyse this relationship in order to facilitate successful FAP deployment. This paper critically analyses the impact of femtocell range expansion with a system-level simulation being undertaken for cooperative and non-cooperative resource allocation strategies. A new CRE framework for femtocell networks is then proposed, which takes cognisance of the interplay between key system parameters, with results confirming the cooperative model consistently outperforms the non-cooperative approach so affording enhanced system flexibility in terms of FAP range expansion.
    • Threshold power based UE admittance and contention free resource allocation for interference mitigation in cognitive femtocells

      Safdar, Ghazanfar Ali; Tariq, Faisal; Kpojime, Harold Orduen; University of Bedfordshire; Queen Mary University of London (Springer, 2017-11-17)
      Femtocells are aimed at providing strong coverage in the indoor area where typical macrocell coverage is very poor. It has hugely attracted network operators and stakeholders mainly due to its simple plug and play operation and low cost. Femtocells operate on a much lower power compared to macrocell and thus provide a number of benefits including energy efficiency and frequent spatial reuse of the spectrum. Femtocells are overlaid on macrocells and designed to co-exist with them sharing the same spectrum pool. However, since they are deployed by the end user, no pre-deployment resource planning is possible. So, interference among the femtocells as well as between femtocells and macrocells remain a major bottleneck for successful operation of femtocell networks. This paper proposes a novel threshold power based admittance and contention free resource allocation for interference mitigation in cognitive femtocell networks. In our proposed scheme, a Femtocell Access Point with Cognitive radio capability known as Cognitive Femtocells (CF), sets a threshold value on the mutual interference between itself and a close by macrocell user equipment (MUE). To mitigate cross-tier interference, a CF classifies MUEs with higher than threshold interference value as Undesirable MUEs (UMUEs) and subsequently admits it as one of its user equipment. MUEs with lower than threshold interference values are classified as Desirable MUEs (DMUEs). To mitigate co-tier interference, proposed scheme introduces a scheduling engine which employs matching policy attributes and assigns resource blocks (RBs) of unique DMUEs to CFs to avoid any possible contention problems, thus providing improved co-tier interference. System level simulations have been performed to demonstrate effectiveness of scheme and significant performance improvement in terms of SINR, throughput and spectrum efficiency.