Impact of time and frequency offsets on cooperative multi-user MIMO-OFDM systems

We study impacts of frequency and time offsets on cooperative multi-user MIMO-OFDM systems. In such systems, frequency offsets cause multi-user interference in addition to the inter-carrier interference effects typically seen in traditional MIMO-OFDM systems. Also, the impact of time offsets is more severe since the time offsets are larger due to transmitter synchronization imperfections and different propagation delays from the transmitters to the receivers. We derive an expression for the SINR seen at the receiver, showing especially how frequency offsets rotate the equivalent channel, thereby causing precoding imperfections. We simulate the interference impacts in the context of LTE-Advanced with realistic assumptions. Simulation results clearly show that the impacts of time and frequency offsets are more severe in cooperative MIMO-OFDM systems than in traditional MIMO-OFDM systems.