Title:
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Design and Analysis of Pilot-Assisted Distributed 
Co-Phasing Algorithms for Dense Wireless Sensor Networks

Author(s):
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Ramesh Annavajjala
ArrayComm LLC
San Jose, CA

Abstract:
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In this paper, we are concerned with the design and analysis 
of practical distributed beamforming techniques for the 
uplink communication over a dense wireless sensor network. 
Since the conventional frequency-division duplexing (FDD) 
techniques require a prohibitively large feedback overhead, 
we focus on a time-division duplexing (TDD) approach, and 
exploit the channel reciprocity to completely 
eliminate 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 uplink co-phasing. 
For simplicity, we study binary signaling over 
a frequency-flat Rayleigh fading channel, and quantify 
the expected gains in the received signal-to-noise ratio (SNR), 
as a function of the number of sensor nodes, 
the pilot overhead and the average received pilot SNR. 
Our results show that a modest amount of accumulated pilot 
SNR is sufficient to realize a large fraction of 
the maximum beamforming gain.