Cooperative Analog and Digital (CANDI) Time Synchronization for large two-dimension multihop networks

For large multihop networks, the time synchronization (TS) error accumulates as the hop number increases using conventional methods, such as Timing-sync Protocol for Sensor Networks (TPSN), Reference Broadcast Synchronization (RBS), and Flooding Time Synchronization Protocol (FTSP). In this paper, to reduce the number of hops to cover the large network and exploit the spatial averaging of TS error between clusters, a novel method is proposed combining Concurrent Cooperative Transmission (CCT) and Semi-Cooperative Spectrum Fusion (SCSF). This method, named Cooperative Analog and Digital (CANDI) Time Synchronization protocol, consists of two phases: The digital stage and the analog stage. The digital stage uses CCT to broadcast a TS packet containing time information. Cooperating nodes transmit the digitally encoded message simultaneously in orthogonal channels, so that the receiver combines the multiple packet to achieve significant SNR advantage. In the analog stage, the cooperating nodes simultaneously transmit their slightly different individual estimates of the propagation time by using frequency shift modulation. Nodes receiving this signal prevent fading and reduce estimation error in one step through the averaging inherent in diversity combining. Simulation results for two-dimension (2-D) networks are given in order to evaluate the performance of CANDI, and CANDI is compared with TPSN.