Interference Alignment in a Frequency Selective X Channel with Blind Transmitters, Relay and Limited Channel Extensions

Interference alignment (IA) is a powerful interference controlling technique that can eliminate limited interferences in restricted bandwidth systems. In this paper, IA is applied in a frequency selective X channel, and A relay is deployed to obtain more realistic results. The problems of infinite symbol extensions and CSIT requirement are overcome by using a relay with ability to precode the messages. In the assumed relay assisted X channel, all transmitters are considered to be blind, and the optimal DoF at low SNR regime is achievable. The number of relay antennas, which makes IA implementation possible are derived. The simulation results show sum-mean-square-error (SMSE) converges and the small number of subcarriers is required. For example, 5000 users can exchange their data over 10000 subcarriers over an X channel.