Antenna Geometry Estimation Using a Robust Multilateralization Technique

This paper describes further efforts towards antenna geometry estimation in the WPI Precision Personnel Locator system, which is under development as a portable, zero-fixedinfrastructure, and spectrally compliant RF-based system for location and tracking of personnel situated in indoor environments. The system consists of transmitters worn by individuals to be tracked, and receiver hardware which collectively estimates position mounted upon response vehicles. Pursuit of any location solution requires the availability of an estimate of the receivers’ antenna positions of sufficient accuracy so as not to contribute superfluous error to personnel location estimates. By utilizing each receiving antenna temporarily as a transmitter, sufficient information is collected to derive a solution for the antenna positions, however, while these antennas are outdoors, they experience the same multipath effects as the indoor-to-outdoor radio channel and require application of a robust multilateralization technique not considered in the previous paper. This paper presents methods for antenna geometry estimation based on such a technique and will present results, from a number of experimental tests, illustrating antenna location error as well as total system error when driven by such antenna geometry solutions. INTRODUCTION: WPI PRECISION PERSONNEL LOCATOR SYSTEM The Worcester Polytechnic Institute (WPI) Precision Personnel Locator (PPL) system is the result of an ongoing multiyear research and engineering effort to develop a robust realtime positioning and tracking solution for first responders and other personnel in indoor environments. To date, published papers on these efforts have detailed the system concept [1], signal structure and performance bounds [2], [3], hardware design [4], and experimental test results [5] paralleling the development and refinement of the system’s hardware realization and signal processing methods. Figure 1 is an artist’s rendition of the PPL concept. To be tracked, personnel carry a transmitter emitting a multicarrier wideband (MC-WB) signal [2], which is sensed by receiving stations fixed upon emergency response vehicles. Upon arrival, the receiving stations form an ad-hoc network and establish a local coordinate system using methods that are the subject of this paper. A previous paper [6] (to which the current paper is a sequel) described initial signal processing efforts towards estimation of the stations’ coordinates. Given the receiving stations’ positions and the signals collected at each station, location solutions for each transmitter may be computed and then conveyed to command-and-control software in the hands of the incident commander. Accumulated track data can provide valuable insight into building layout to assist with self-rescue (exit guidance) or search-and-rescue operations. Beyond being lost or trapped, cardiac distress is also a leading cause of firefighter death [7], and the system incorporates physiological status monitoring into the incident commander’s display. ION ITM 2009 Session D3: Urban and Indoor Navigation Technology, January 26-28, 2009, Anaheim CA 1 Fig. 1. PPL concept illustration In the following sections we describe the MC-WB signal, the SART method for robust multilateralization, the problem of geometric antenna configuration (GAC), and methods for the solution of GAC. The performance of these methods is presented in terms of antenna location error as well as impact upon the final transmitter location estimates desired. Throughout the paper the terms receiver, station, and antenna are used interchangeably to refer to the fixed points of signal reception used for positioning, despite their transmit capability during GAC; transmitter refers to the individual being located.