Ameliorated Resource Allocation in Two-Tier Femtocell–Macrocell Networks with Six Directional Antennas for Macrocells

Abstract

Femtocells are deployed in the coverage area of traditional macrocell networks and can provide high data rates and good quality of service with low transmission power. In order to achieve the high spectral efficiency, allocated resources to the femtocells should be from the same licensed spectrum band of the macrocell network. Therefore, interference management is an important challenge in two-tier femtocell---macrocell networks. Previously, it was shown that cross-tier interference from macrocell to femtocell can be reduced by using directional antennas in macrocell tier. In this paper, we propose a new spectrum partitioning approach by dividing the spectrum to four sub-bands and then allocating them to different sectors of the macrocell with six directional antennas in a proper manner to reduce interferences. Therefore, first, we calculate the interference from the adjacent macrocells in different sectors. Then, based on the results of interference analysis, we propose a sub-band exchanging allocation strategy for improving the macrocells' and femtocells' performance. Moreover, we analyze the downlink outage probability of the two-tier femtocell---macrocell network based on the orthogonal-frequency-division-multiple-access. Finally, simulation and theoretical results demonstrate that the proposed cellular network achieves lower downlink outage probability of femtocell and macrocell in comparison with the previous cellular model and consequently, system throughput increases substantially.