An Experimental Study on Network-Listening Based Synchronization with Loop-Back Self-Interference Canceller

The overlaid cell structure, in which a large number of small cells are deployed in a macro-cell coverage area, is considered to be a promising approach in order to accommodate rapidly increasing mobile data traffic. In the overlaid cell structure, eICIC (enhanced Inter-Cell Interference Coordination) is an essential technique to avoid the interference between the macro cells and the small cells when co- channel deployment is used. Because eICIC conducts interference coordination in the time domain, accurate timing synchronization is required between the macro cells and the small cells. We have proposed a network-listening based synchronization method, which enables accurate synchronization even indoors without receiving GPS signal. In the proposed method, a small-cell eNB receives a macro- cell downlink synchronization signal and establishes synchronization with the macro-cell eNB. However, we need to update synchronization periodically and receive a macro-cell signal even while there is a loop-back interference signal from the small-cell eNB itself. In order to solve the problem, we have proposed a method to mute the transmission and avoid loop-back self-interference. Although this works well, it is an issue that the spectral efficiency is deteriorated by the signal stopping. In this paper, we propose a synchronization method that cancels loop-back self-interference without stopping the transmission of small-cell eNB and clarify the effect of the proposed method by computer simulations and laboratory experiments using the first-ever prototype system.