Analytical Coverage Probability Framework and Spectrum Sharing Prohibition Zone in Heterogeneous Cellular Networks with Sectored-FFR

—In this work, an analytical coverage probability framework is derived for all the User Equipment (UE) types in a Fractional Frequency Reuse (FFR)-aided heterogeneous network leveraging tools of stochastic geometry. This framework is used to determine the minimum distance for edge femtocells to safely reuse same spectrum resources utilized by center macro users (MUEs) for successful signal transmission and decoding. A spectrum sharing prohibition zone is thus created in which only orthogonal spectrum usage is allowed between the two tiers to avoid violating the system outage constraint, and is found to be sensitive to macrocell antenna azimuth and other key network parameters. Using the macrocell center radius, m R and the derived co-channel femtocells distance, min co F r  , a new spatial partitioning threshold, f R is obtained for the femtocell network, extending the spectrum sharing prohibition zone for further interference reduction. Analytical and numerical results show that the introduction of f R and use of extended co-channel prohibition zone offers improved protection to UEs against severe cross-tier interference with enhanced throughput performance, compared to most schemes employing a single spatial partitioning parameter. The proposed scheme therefore provides guidelines for efficient deployment of closed-access femtocells with hybrid spectrum usage in multi-tier networks for lower power consumption and improved throughput performance.