Research Article Source Geolocation in Urban Environments Using Multipath Fingerprinting Ram M. Narayanan, 1 Brian R. Phelan, 1 and Erik H. Lenzing 2 1 Department of Electrical Engineering, he Pennsylvania State University, University Park, PA 16802, USA 2 he Applied Research Laboratory, State College, PA 16803, USA Correspondence should be addressed to Ram M. Narayanan; ram@ee.psu.edu Received 16 December 2014; Revised 18 March 2015; Accepted 18 March 2015 Academic Editor: Ana Alejos Copyright © 2015 Ram M. Narayanan et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A method for determining the location of Global Systems for Mobile Communications (GSM) mobile transmitters is proposed. Our approach estimates the location of a source without the use of multilateration or Line-of-Sight (LOS) techniques. A Multipath Characteristic Database (MCD) containing the multipath feature vectors, for each possible transmitter location within an area of interest, is populated via ray-tracing sotware simulations. he multipath characteristics of interest are angle-of-arrival (AOA) (azimuth) and time-of-arrival (TOA). By minimizing the “distance” between estimated and simulated multipath feature vectors, an estimate for the actual source location can be obtained. he development of the estimation method is presented, followed by a detailed analysis of its estimation accuracy. Since the proposed method utilizes a simulated multipath signature database based upon the knowledge of the environment and the terrain, the need for a priori soundings from the area of interest is eliminated, thus making this location estimation system suitable for application in denied territories. Location accuracies compare favorably with the requirements for the location of wireless 9-1-1 callers as recommended by the Federal Communications Commission (FCC). 1. Introduction Spatial localization of cellular emitters in dense urban envi- ronments can provide a valuable tool for a variety of users such as emergency services, law enforcement, and military personnel. Navigation, social media, and location-dependent searching would also beneit from advances in localization techniques. he ability to use Non-Line-of-Sight (NLOS) and nonmultilateration techniques would allow the end user to perform the localization from an arbitrary position anywhere within a given range of the target. he concept of using the multipath ingerprint composed of time- and angle-of-arrival data for wireless location inding in urban environments was developed using electromagnetic ray-tracing techniques and validated using computer-aided design (CAD) models of a real city [1]. he fundamental premise of this approach is to extract the features of the multipath signals to create a unique ingerprint, such as angle-of-arrival, time delay, and signal strength, which is then compared to a database of known ingerprints, each corresponding to a known location. A matching ingerprint found in the database provides an estimate for the correct location of the transmitter. A ingerprinting technique using the channel’s impulse response information combined with an artiicial neural network was developed for geolocation in mines or other conined environments with rough sidewall surfaces with a location accuracy of 2 m [2]. A ingerprinting technique exploiting the spatial-temporal characteristics of the multipath signals received by the base station antenna array was proposed in [3]. he spatial-temporal ingerprint was based on a lower dimensional subspace of the spatial- temporal covariance matrix capturing the AOAs and the diferential delays of the dominant multipath relections. Localization accuracies of about 1 m were achieved in typical indoor environments. Similar ingerprinting techniques were also proposed and developed for emergency location services [4], Global Navigation Satellite System (GNSS) indoor posi- tioning [5], indoor geolocation for ultrawideband (UWB) systems [6], and channel estimation in multipath-rich mobile communication scenarios [7]. Hindawi Publishing Corporation International Journal of Antennas and Propagation Volume 2015, Article ID 453157, 11 pages http://dx.doi.org/10.1155/2015/453157