Interference management techniques are critical to the performance of heterogeneous cellular networks, which will have dense and overlapping coverage areas, and experience high levels of interference. Fractional frequency reuse (FFR) is an attractive interference management technique due to its low complexity and overhead, and significant coverage improvement for low-percentile (cell-edge) users. Instead of relying on system simulations based on deterministic access point locations, this paper instead proposes an analytical model for evaluating Strict FFR and Soft Frequency Reuse (SFR) deployments based on the spatial Poisson point process. Our results both capture the non-uniformity of heterogeneous deployments and produce tractable expressions which can be used for system design with Strict FFR and SFR. We observe that the use of Strict FFR bands reserved for the users of each tier with the lowest average SINR provides the highest gains in terms of coverage and rate, while the use of SFR allows for more efficient use of shared spectrum between the tiers, while still mitigating much of the interference. Additionally, in the context of multi-tier networks with closed access in some tiers, the proposed framework shows the impact of cross-tier interference on closed access FFR, and informs the selection of key FFR parameters in open access.
The authors in @cite_9 consider an adaptive FFR strategy for mitigating inter-femtocell interference while keeping spectral efficiency as high as possible. They vary the size of FFR partitions and transmit power based on the amount of estimated interference. However they use a deterministic model for the femtocells inside of a single building and neglect macrocell or femtocell interference outside of the building. Very recent work in @cite_30 considers a deterministic model analysis of the spectral efficiency of femtocells as a function of the femtocell's location in a two-tier network with base stations modeled as a hexagonal grid and femtocells uniformly deployed in each cell. They fix the macrocell FFR sub-band allocations and then consider the spectral efficiency of a femtocell as a function of its distance from the cell center.
@cite_30 @cite_9
2121469866 2076855206
In OFDMA systems adopting fractional frequency reuse, we can allocate orthogonal bandwidth to femtocells, which mitigates throughput degradation of macrocell users. In this paper, we discuss the optimal power allocation for femtocells with different orthogonal subbands, based on analysis of macrocell interferences. In this paper, we consider the use of fractional frequency reuse (FFR) to mitigate inter-femtocell interference in multi-femtocell environments. The use of universal frequency reuse can be said optimum in terms of the ergodic system spectral efficiency. However, it may cause inter-femtocell interference near the cell edge, making it difficult to serve the whole cell coverage. To alleviate this problem, we adjust the frequency reuse factor with the aid of femtocell location information. The proposed scheme can provide reasonably high ergodic system spectral efficiency, while assuring a desired performance near the cell boundary. Simulation results show that the proposed scheme is quite effective in indoor environments such as residential or office buildings.