Uplink interference alignment for OFDM systems

This paper focuses on the uplink transmission in a cellular system in which the channels in two neighboring cells are modeled as two mutually interfering multiple access channels (2-IMAC). The base stations (BSs) are equipped with multiple antennas while each user has only one antenna and K users are active in each cell. By increasing the number of users, it is shown in that for single-antenna BSs, using interference alignment, each cell can approach the interference-free degrees of freedom (DOF) provided that the bandwidth is sufficiently large. But as the number of users grows, the correlation between adjacent subcarriers increases and this degrades the performance of interference alignment. The proposed scheme incorporates the concept of cyclic delay diversity (CDD) to reduce the correlation among subcarriers with the help of multiple antennas at the BSs. Simulation results show the performance improvement of the proposed scheme.