Abstract
Device-free passive sensing of the human targets using wireless signals have acquired much attention in the recent past because of its importance in many applications including security, heating, ventilation and air conditioning, activity recognition, and elderly care. In this paper, we use receiver-side beamforming to isolate the array response of a human target when the line of sight array response is several magnitudes stronger than the human response. The solution is implemented in a 5G testbed using a software-defined radio (SDR) platform. As beamforming with SDRs faces the challenge to train the beamformer to different azimuth angles, we present an algorithm to generate the steering vectors for all azimuth angles from a few training directions amidst imprecise prior information on the training steering vectors. We extract the direction of arrival (DoA) from the array response of the human target, and conducting experiments in a semi-anechoic chamber, we detect the DoAs of up to four stationary human targets and track the DoA of up to two walking persons simultaneously.
Highlights
Device free human sensing has gained interest because of its importance in many applications that includes human safety in industry settings [1], security and surveillance [2], heating, ventilation and air conditioning [3], and assisted living [4]
Device-free passive human sensing is a challenging task because the signals scattered off the humans are several magnitudes weaker than that of the line of sight (LoS) signal
Previous attempts have looked at signal strength [10], direction of arrival (DoA) [11], time of flight [12] and Doppler shift [13], [14] or a combination of those [15] to extract the parameters of the channel for activity recognition, presence detection or localization and tracking
Summary
Device free human sensing has gained interest because of its importance in many applications that includes human safety in industry settings [1], security and surveillance [2], heating, ventilation and air conditioning [3], and assisted living [4]. We use beamforming at the receiver end and steer the beam to different directions to construct the array response to detect the human presence and to estimate the direction of that person. Current super-resolution algorithms that detect the DoA, e.g. multiple signal classification (MUSIC) [16], require the number of sources as prior information for an accurate estimation of the DoAs [17] Using beamforming, such problems can be mitigated as the DoAs of the interested targets can be simultaneously estimated from the amplitude of the array response using our approach. Use reference directions to train the beamformer by transmitting from a limited number of azimuth angles and measure the steering vectors at the receiver for those directions using the relative phases of the antenna array.
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