Convergence Property of Transmit Time Pre-Synchronization for Concurrent Cooperative Communication

This paper proposes a preamble detection-based cooperative transmit time pre-synchronization technique specially for Concurrent Cooperative Transmission (CCT). CCT enables a collection of power-constrained radios to transmit as a group and achieve a transmit range that is much greater than the range of a single device. In the absence of a GPS system or a globally synchronized clock, each cooperating node can derive its transmit time autonomously by detecting the preamble from a received signal. The paper first compares two methods for estimating the start of packet (SOP) received in the presence of a carrier frequency offset (CFO): the peak method, which is optimal in a single diversity channel without CFO, and a mean method, which outperforms peak with large CFO. Next, the SOP is estimated by combining all diversity channels using an approximated Best Linear Unbiased Estimator (BLUE). Using theory and measurement, we show that the time error statistics are convergent as the number of hop increases.