University of Utah

Welcome to the Sensing and Processing Across Networks (SPAN) lab! The SPAN lab is part of the Department of Electrical and Computer Engineering at the University of Utah.

The SPAN lab develops inventions for wireless networks which improve their security, reliability, self-awareness, and sensing capabilities. Research applies statistical signal processing, networking, and radio propagation techniques. The innovations have application in localization and tracking, secret key generation for wireless networks, network design and deployment, modeling and analysis. The lab, directed by Neal Patwari, is a combination of the efforts of several graduate and undergraduate researchers.

SPAN Announcements and News

Technical Report Posted: Through-Wall Tracking Using Variance-Based Radio Tomography Networks

variance-based radio tomographic imagingJoey Wilson and Neal Patwari have posted a new technical report. The abstract reads:

This paper presents a new method for imaging, localizing, and tracking motion behind walls in real-time. The method takes advantage of the motion-induced variance of received signal strength measurements made in a wireless peer-to-peer network. Using a multipath channel model, we show that the signal strength on a wireless link is largely dependent on the power contained in multipath components that travel through space containing moving objects. A statistical model relating variance to spatial locations of movement is presented and used as a framework for the estimation of a motion image. From the motion image, the Kalman filter is applied to recursively track the coordinates of a moving target. Experimental results for a 34-node through-wall imaging and tracking system over a 780 square foot area are presented.

J. Wilson and N. Patwari, "Through-Wall Motion Tracking Using Variance-Based Radio Tomography Networks",, Oct, 2009.

Journal Paper Accepted: Parameter Derivation of Type-2 Discrete-Time Phase-Locked Loops Containing Feedback Delays

A paper by SPAN graduate student Joey Wilson, Andrew Nelson, and Behrouz Farhang has been accepted for publication in the IEEE Transactions on Circuits and Systems II. Joey performed most of the research for this paper while employed by L-3 Communications CSW in Salt Lake City, UT.

Modern implementations of discrete-time phase-locked loops (DT-PLLs) often contain delayed feedback. The delays are usually a side effect to pipelining, filtering, or other inner-loop mechanisms. Each delay increases the order of the system by introducing an additional pole to the closed-loop transfer function, and in many cases, makes the traditional type-2 loop equations obsolete. This paper describes how the second-order notions of damping and natural frequency can be applied to type-2 DT-PLLs in the presence of any number of delays. It provides equations for loop parameters that will provide a desired transient behavior based on damping and natural frequency, along with a test to ensure the accuracy of the results. The novelty of this work is that loop parameters can be found in closed-form and ensured to be accurate, without the need for human interaction, simulations, or numerical root-finding algorithms.

J Wilson, A. Nelson, B. Farhang, Parameter Derivation of Type-2 Discrete-Time Phase-Locked Loops Containing Feedback Delays, IEEE Transactions on Circuits and Systems II, Dec. 2009

University of Utah's Lassonde Center Selects SPAN Technology

The University of Utah's Lassonde center has selected the SPAN lab's radio tomographic imaging (RTI) technology for the 2009-2010 business development program. Each year, the Lassonde center chooses a few university-owned technologies that show promise of successful commercialization. Lassonde students studying business, law, and engineering form teams that research the commercial viability of the technologies, then prepare business plans.

Troy D'Ambrosio (director of the Lassonde program), Matt Dee, Deven Dustin, Vatsala Kaul, and Joey Wilson (from the SPAN lab) will make up the team. For more information about the Lassonde entrepreneur center, see their website at


SPAN Researchers Featured in ECE Newsletter

ECE Logo
The research of SPAN researchers Jessica Croft and Joey Wilson is featured in the Summer 2009 ECE Communicator newsletter. The ECE Communicator is the newsletter of the University of Utah Department of Electrical and Computer Engineering and is read by department students, alumni, friends, employers, and others. Jessica Croft's research in using the radio channel to generate shared secrets between two radios for purposes of improved privacy is featured on page 4 of the newsletter. Joey Wilson's research in radio tomographic imaging (RTI), and his award at the ACM MobiCom 2008 conference as the Student Research Competition winner, is featured on page 5. Congratulations to these students for having their research selected as two highlights of the research being conducted in the ECE Department as a whole!

A Shameless Plug for IPSN 2010

Prof. Neal Patwari will be the publicity chairperson for the 9th ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN) 2010. Naturally, he wants you to be there! The IPSN conference will take place from April 12 - 16, 2010 in Stockholm, Sweden. As in the previous two years, the conference will be part of Cyber-Physical Systems Week (CPS Week), which brings together five leading conferences - RTAS, IPSN, HSCC, CPSC and LCTES - as well as several workshops and tutorials on various aspects on the research and development of cyber-physical systems. The paper submission deadlines for IPSN 2010 are as follows:

  • Abstract deadline: Friday, October 23rd, 2009
  • Full papers due: Friday, October 30th, 2009


Paper on bit extraction accepted to IEEE Transactions on Mobile Computing

A new journal paper on bit extraction for secret key establishment has received final approval for publication in the IEEE Transactions on Mobile Computing. The paper is titled "High Rate Uncorrelated Bit Extraction for Shared Secret Key Generation from Channel Measurements" and is authored by Neal Patwari, Jessica Croft, Suman Jana, and Sneha K. Kasera. Neal Patwari and Jessica Croft are in the SPAN Lab, and Suman Jana and Sneha Kasera are in the School of Computing, at the University of Utah.

Secret key establishment from radio channel measurements is a promising alternative to public key cryptography. This paper shows methods to reliably generate secret key bits at a high rate without incurring temporal correlations between bits. Methods include interpolation filtering, de-correlation, and adaptive quantization. As high as 22 bits per second can be extracted from a radio fading signal, at a 2.2% probability of bit disagreement at opposite ends of the link.

Through-Wall Tracking Video Posted

In the following video, Joey Wilson and Neal Patwari of the University of Utah describe and demonstrate their through-wall wireless network tracking system. Joey enters a home surrounded by simple radio devices. He does not carry any kind of electronic device on his body, nor are any devices deployed inside the tested part of the home. The system estimates his position using radio tomographic imaging.

Virginia Tech Symposium Papers Posted

Two papers from the SPAN lab that were accepted to the 2009 Virginia Tech Wireless Symposium have been posted to the publications page in PDF format. They are:

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