A Transformed Conflict Graph-Based Resource-Allocation Scheme Combining Interference Alignment in OFDMA Femtocell Networks

To deal with ever-growing wireless services and to increase network throughput, it has been proposed to deploy femtocells with frequency reuse based on orthogonal frequency-division multiple access (OFDMA). However, the interference poses big challenges, particularly for dense deployment scenarios. The resource allocation with joint consideration of subchannel assignment and interference alignment (IA) is different from the traditional problems. First, we need to select the users to perform IA since the number of participant users is limited by the feasibility constraint, and the interference power levels are different due to the path loss. Second, IA increases the degrees of freedom (DoFs) while occupying the additional signal dimension of the participant user; hence, the entirety of the participants in IA require more subchannels compared with the nonparticipants when each of the users transmits the same number of streams. In this paper, we propose a transformed conflict graph-based resource-allocation scheme, where the users are selected according to the effect of IA on the requirement under the feasibility constraint. Then, the subchannel assignment can be modeled as a classical color problem. Extensive simulations show that our scheme can approximate the optimal scheme in a small network and effectively improve the satisfactory ratio of users compared with the scheme without IA in dense femtocell networks.