Interference Mitigation Using Conjugate Data Repetition

In the emerging broadband wireless networks such as IEEE 802.16m and LTE-A networks which employ universal frequency reuse-1, the cell coverage is predominantly limited by the co-channel interference. Bit level data repetition, and conventional multi-antenna maximal-ratio-combining (MRC) techniques are typically used to improve the signal-to-interference-plus- noise ratio (SINR) at the receiver. Simple data repetition does not guarantee efficient interference suppression and it reduces spectrum efficiency. In this paper, we propose a symbol level data repetition technique called conjugate data repetition (CDR), which transmits the modulation alphabet of the desired signal and its complex-conjugate in distinct sub carriers. The CDR operation is performed across all base stations in a synchronous manner. We show that minimum mean-square error (MMSE) filtering of the complex-valued signal and its conjugated copy, provides a high interference cancellation (IC) gain. For repetition factor greater than 2, we propose a combination of conjugate repetition and random phase rotation of the repeated symbols. Simulation results show that CDR with a repetition factor 2 or 3 can provide a significant advantage in coverage/reliability for cell edge users.