Network listening based synchronization techniques for femtocell systems

Network synchronization is a requirement for a time division duplex (TDD) femtocell network to prevent multi-access and inter-slot interference. Network Listening (NL) is a technique used for network synchronization where a base station (BS) is synchronized directly with another BS over-the-air, based on BS-BS measurements. Spanning tree based NL is the recommended technique for a local area indoor TDD femtocell network synchronization by The 3rd Generation Partnership Project (3GPP). We propose a novel User Equipment (UE) assisted NL to improve the local area network synchronization, in which, in addition to direct BS-BS measurements, UE helps the serving BS to synchronize with neighboring synchronized base stations (BSs). The performance of the proposed UE assisted NL is analyzed and compared with the existing NL synchronization technique. Moreover, NL suffers from the interference of other synchronous and non-synchronous BSs, when a non-synchronous BS is trying to synchronize with the specific synchronous BS. We propose three novel network synchronization algorithms namely stratified, fully orthogonal and macro diversity synchronization to reduce interference from other synchronous BSs, and thereby improve NL technique. Performance of all three network synchronization algorithms is analyzed with and without UE assistance. Out of the three proposed algorithms, macro diversity based NL with UE assistance outperforms the other two and considerably improve the local area femtocell network synchronization.