Femtocell and fractional frequency reuse (FFR) for LTE network performance enhancement

Abstract

The introduction of low-power and small-service-area Femtocell into Long Term Evolution-Advance (LTE-A) Macrocell network, the service coverage is extended but causes more severe inter-cell interference (ICI). ICI occurs due to sharing of resource between adjacent cells. Among the methods to mitigate interference, power and frequency allocation schemes are deployed in this thesis. Fractional Frequency Reuse (FFR) is one of the ICI technique for signal quality enhancement. The challenges of FFR is to design an efficient resource allocation scheme. With FFR, spectrum sharing between Macrocell and Femtocell network causes unavailability of dedicated resource and thus more severe ICI occurs. Furthermore, when solely power control scheme is used, universal frequency reuse (FRF=1) causes more severe ICI problem in crowded network. The modeling of downlink LTE-A Heterogeneous network (HetNet) is done using MATLAB in this research. The FFR method is revisited and Orthogonal Resource Allocation (ORA) scheme is proposed to allocate resource by region. Besides, the suggested Dynamic Femtocell Resource Allocation (DFRA) scheme is deployed to ensure the resources assigned to Femtocells are mutually exclusive with adjacent Macrousers or Femtocells. In the scenario of high density Femtocells (orthogonal resource exhausted), the power control schemes such as Power based Femtocell Base Station Power Control (PPC) and SINR based Femtocell Base Station Power Control (SPC) are combined into the system. The power of Femtocell Base station is further optimized with the proposed SINR based Neighbouring Femtocell Power Control (SNPC) scheme to take care of interference between Femtocells. In comparison with the deployment of contemporary FFR approach in HetNet, the deployment of Dynamic Frequency Allocation-Power based Femtocell Base Station Power Control (DFRA-PPC) and Dynamic Frequency Allocation-Signal to Interference & Noise Ratio (SINR) based Femtocell Base Station Power Control (DFRA-SPC) approach increases the resource utilization and number of active user by 8.7% and 8.72% respectively in sparsely populated Femtocells. Apart from this, data rate is augmented by 15.73% and 15.51% with the improvement done in DFRA-PPC and DFRA-SPC mechanisms. From the perspective of spectral efficiency, these two techniques enhanced the performance by 15.68% and 15.48% correspondingly. On the other hand, in congested network (with 150 randomly located Femtocells), the resource utilization and number of active user grows by 11.43% for Dynamic Frequency Allocation-SINR based Femtocell Base Station Power Control-SINR based Neighbouring Femtocell Power Control (DFRASPC- SNPC) scheme. Besides, by deploying this scheme, the data rate and spectral efficiency in this congested network are improved by 13.52% and 13.53% respectively. The proposed mechanisms ORA, DFRA, SPC, PPC and SNPC improved the system performance in terms of resource utilization, subcarrier efficiency, data rate and spectral efficiency.