Reliable Symbol Synchronization in Software-Driven Acoustic Sensor Networks

Symbol synchronization in traditional hardware- driven communication systems has relied on the transmission of training sequences of symbols just before the beginning of the frame symbols. The use of training sequences is not suitable for software-driven communication systems, such as lightweight acoustic underwater sensor networks [4,5], in which the high symbol loss rate may cause the loss of training symbols, preventing accurate symbol synchronization. Software-driven communication networks require symbol synchronization that is resilient to a high loss environment, that does not represent large communication or processing overhead, and that is tunable to the noise profile of different environments. These requirements are emphasized for mote-based acoustic underwater sensor networks in which the bandwidth and processing capability are sparse. This paper proposes the use of a short signature synchronization symbol (S⁴) as both a preamble and post-amble to enable receiver synchronization in mote-based acoustic communication systems that rely on software modems. To synchronize to an incoming signal, the receiver performs cross-correlation of N reference signature symbols with the incoming signal to identify the beginning of the preamble and post-amble. The output of the cross-correlation yields 2N peak values, from which the receiver chooses the sharpest and most symmetric for synchronization to the beginning of the frame. Empirical experiments confirm a synchronization accuracy within 5 ms in air within a range of 10.5 m, and 11 ms in water within a range of 15 m.