Downlink capacity improvement and interference reduction through Reverse Frequency Allocation

Multi-tier networks comprising of macro-cellular network overlaid with less power, short range, home base stations like femtocells provide an economically feasible method for increasing the cellular capacity. Also the benefit of femtocells is found more in downlink since the traffic in downlink is several times more than in uplink. However, the femtocells share the same licensed frequency spectrum as that of the macrocell resulting in cross tier interference which degrades the downlink traffic considerably. This paper investigates a novel method for seamlessly embedding femtocells within a macrocell resource distribution framework to create a two-tier system, which incorporates a cross-tier complementary spectrum sharing known as Reverse Frequency Allocation (RFA) along with Soft Frequency Reuse (SFR) strategy. The proposed scheme guarantees inter-cell orthogonality with reduced interference. It also assures a reasonably high system spectral efficiency, while providing better performance for the users especially in the downlink. Simulation results prove that this scheme can bring about higher system throughput and lower co-channel interference irrespective of the distance of the femtocell from the macrocell base station.