Network-Listening Based Synchronization with Loop-Back Interference Avoidance for Small Cells in LTE-Advanced

The overlaid cell structure, in which a large number of small cells are deployed in a macro-cell coverage area, is attracting much attention recently as a promising approach to cope with rapidly increasing mobile data traffic. In the overlaid cell structure with co-channel deployment, in which the same frequency band is used in both macro and small cells, it is essential to avoid the mutual interference. The interference avoidance can be achieved by enhanced Inter-Cell Interference Coordination (eICIC), in which some parts of the downlink transmitted signals are muted in order to reduce the interference from a macro-cell eNB to small cells or vice versa. Because the interference control in eICIC is conducted in the time domain, accurate timing synchronization is required between macro and small cells. Network-listening based synchronization is recently attracting attention as an effective timing synchronization method regardless of the location of small-cell base stations or their backhaul network configuration. It uses just the macro-cell downlink signal to realize accurate synchronization. However, the loop-back signal from the small-cell eNB itself interferes the reception of the macro-cell downlink signal. In this paper, we propose a synchronization method that avoids the loop-back interference and clarify its synchronization accuracy by computer simulations. We also extend the method to incorporate the effect of time and antenna diversities and verify the performance.