A gradient projection based self-optimizing algorithm for inter-cell interference coordination in downlink OFDMA networks

Fractional frequency reuse (FFR) is an inter-cell interference coordination (ICIC) scheme wherein the whole bandwidth is divided into regions using different frequency reuse factors in orthogonal frequency division multiple access (OFDMA) networks. However, it is hard to achieve the balance of cell-edge and cell-center user throughput in practice as all base stations (BS) are configured with static transmission power for each sub-band in traditional FFR. To solve this problem, a gradient projection based self-optimizing (GPB-SO) algorithm for ICIC is proposed to adjust transmission power of each sub-bands set by exchanging the gradient direction information, aiming to maximize the overall network utility. Furthermore, a closed-form of gradient direction is attained to update the transmission power of each BS in a distributed manner. With the simulation results, it is demonstrated that the proposed algorithm not only provides a better tradeoff between spectrum efficiency and cell-edge user throughput, but also increases the system energy efficiency due to interference reduction.