Network time synchronization for large multi-hop sensor networks using the cooperative analog-and-digital (CANDI) protocol

For multi-hop wireless sensor networks (WSNs), time synchronization (TS) across distributed nodes is important for certain applications (i.e., surveillance, gunshot location system, etc.). In this paper, a method combining two forms of cooperative transmission (CT), digital-based Concurrent Cooperative Transmission (CCT) and analog-based Semi-Cooperative Spectrum Fusion (SCSF), is proposed and demonstrated to achieve fast and accurate time synchronization over large multihop WSNs. CCT, considered in many physical layer system studies and realistically demonstrated, enables range extension. Range extension implies that the source timestamp can be diffused to the network faster (i.e., in fewer hops) than non-CT-based TS protocols. SCSF is an analog CT method where different cooperators transmit correlated information simultaneously. The two methods combine to create a new distributed method of network TS, called the Cooperative Analog and Digital (CANDI) TS protocol, which promises significantly shorter protocol time and smaller time errors in multi-hop networks. This paper presents the algorithm description, and physical layer simulations as well as network experimental results over a line network that show the performance advantage of CANDI over TPSN.