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Pilot-Assisted Distributed Co-Phasing for Wireless Sensor Networks

This paper addresses the design and analysis of practical distributed beamforming techniques for the uplink communication over a wireless sensor network. Since the conventional frequency-division duplexing techniques require a large feedback overhead, we focus on a time-division duplexing approach, and exploit the channel reciprocity to reduce the channel feedback requirement. We consider periodic broadcast of known pilot symbols by the fusion center, and maximum likelihood estimation of the channel phase by the sensor nodes for the subsequent uplink co-phasing transmission. For simplicity, we study binary signaling over frequency-flat fading channels, and quantify the system performance such as the expected gains in the received signal-to-noise ratio (SNR) and the average probability of error at the fusion center, as a function of the number of sensor nodes and the pilot overhead. Our results show that a modest amount of accumulated pilot SNR is sufficient to realize a large fraction of the maximum possible beamforming gain.