An Experimental Evaluation on Network-Listening Based Synchronization with Loop-Back Interference Avoidance

In deploying co-channel heterogeneous networks, which use the same frequency band for both macro and small cells, it is essential to avoid mutual interference. This can be achieved by enhanced Inter-Cell Interference Coordination (eICIC), in which some of the downlink transmitted signals are muted in order to reduce the interference from a macro-cell base station to small cells or vice versa. Because 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 even for indoor small-cell base stations, which cannot utilize GPS- based synchronization. It uses only the macro-cell downlink signal to establish synchronization with the overlaying macro cell. However, the loop-back signal from the small-cell base station itself interferes with the reception of the macro-cell downlink signal. To solve this issue, we proposed a synchronization method that avoids loop-back interference and clarified its synchronization accuracy by computer simulations. In this paper, we propose an advanced synchronization- timing detection algorithm that improves the tolerance of loop-back self-interference. Furthermore, we prototype the proposed synchronization method and clarify its feasibility and performance by computer simulations and laboratory experiments on actual equipment. Moreover, we propose a control architecture for network-listening based synchronization that enables accurate synchronization even in dense small cell deployments where neighboring small-cell interference degrades the accuracy of macro-cell signal detection.