A Wireless Time-synchronized Cots Sensor Platform: Applications to Beamforming

In recent years, sensor network system has been proposed for various applications. In the past, most reported systems involve custom-made hardware. In this paper, we consider the use of Compaq iPAQ 3760s with their build-in StrongARM processors, ROM and RAM memories, and microphones and codecs for acoustic acquisition and processing, plus external wireless Ethernet cards for radio communication to form a distributed sensor network to perform acoustical beamforming. Time synchronization among the microphones is achieved by the Reference-Broadcast Synchronization method of Elson-Estrin. Two beamforming algorithms, based on the time difference of arrivals (TDOAs) among the microphones and least-squares estimation of the TDOAs method, and the maximum-likelihood (ML) parameter estimation method, are used to perform source detection, enhancement, localization, delay-steered beamforming, and direction-of-arrival estimation. Theoretical CramérRao bound analysis of the system performance and experimental beamforming results using the iPAQs and the wireless network are reported.