Michel Fattouche

A spread spectrum radiolocation technique and its application to cellular radio

A method for locating mobile stations in a cellular telephone system is analyzed. This method uses hyperbolic multilateration of direct sequence radio signals that are transmitted by the mobile after it has been polled. The channel that would be necessary for the radiolocation signal could be created by reusing an entire 10-MHz mobile radio bandwidth. A direct-sequence locating system has been modeled and simulated using a multipath database for a dense urban environment. Location error statistics and statistics on locating mobiles in a cellular grid are presented.<<ETX>>

Effects of system and environment parameters on the performance of network-based mobile station position estimators

This paper provides an asymptotic performance evaluation of network-based or multilateral positioning systems, where the times and/or angles of arrival of the signals traveling from a mobile station (MS) to a set of fixed stations (FSs) are used to estimate the MSs position. The effects of the various system-design parameters as well as the effects of biased bearing and time measurements are analyzed, and explicit formulas are derived. Biased measurements can result, for example, from hardware calibration errors or multipath effects, including the lack of line of sight (LoS). Among other results, it is shown that only a few system and cellular parameters can be used to minimize their nuisance effects. The mathematical analysis is based on the Cramer-Rao lower bound (CRLB) and the maximum likelihood theory. It is completed with numerical simulations and a discussion of the positioning performance for two important second-generation cellular systems, GSM and IS-95.

Cramer-Rao bounds for the estimation of multipath parameters and mobiles' positions in asynchronous DS-CDMA systems

Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao lower bound (CRLB), which serves as an optimality criterion for the location estimation problem, is of interest. In this paper, we derive the deterministic CRLBs for the estimation of the specular multipath parameters and the positions of the mobiles in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over specular multipath fading channels. We assume a multilateral radio location system where the location estimates are obtained from some or all of the estimated signal parameters at different clusters of antennas of arbitrary geometry. Extension for unilateral and composite radio location techniques is also discussed. As an application example, we use numerical simulations to investigate the effects of specular multipath and multiple access interference (MAI) on the positioning accuracy for different radio location techniques.

Super-resolution modeling of the indoor radio propagation channel

Results from parametric modeling of the indoor channel frequency response are presented. Minimum-norm and autoregressive (AR) are two super-resolution modeling techniques that are used on frequency domain data to form the theoretical sum-of-sinusoids model for the indoor channel-impulse response. Using these techniques, it is possible to check the validity of assuming Turins model for the indoor channel. It is shown that the modeling techniques estimate the indoor channel-impulse response with a time-domain resolution better than that of current measurement systems. A competing model that matches the measured channel frequency response to a sampled finite-impulse response (FIR) filter (as opposed to AR and minimum-norm, which give arbitrary time delays) is presented. It is shown that FIR filter matching produces a parametric model that can be more compact and more accurate in terms of matching the frequency response of the channel than the conventional super-resolution techniques.

OFDM Transmission for Time-Based Range Estimation

OFDM is proposed for time-based range estimation (TBRE) and analyzed with respect to its accuracy, both theoretically, in terms of its Cramer-Rao lower bound (CRLB), and practically, in terms of its maximum likelihood estimator (MLE). The CRLB for OFDM transmission is compared to that for pseudo-noise (PN) transmission, demonstrating a large performance gap in favour of OFDM. Moveover, the MLE for TBRE is compared to the commonly used MLE for channel estimation (CE), demonstrating a performance gap in favour of the MLE for TBRE. Finally, the CRLB for OFDM is compared to its corresponding MLE for TBRE, demonstrating a good agreement in performance except for the so-called ¿threshold effect¿, which is analyzed analytically in this letter.

Cramer-Rao bound for location estimation of a mobile in asynchronous DS-CDMA systems

Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao bound (CRB), which serves as an optimality criterion for the location estimation problem, is of interest. We derive the CRB for the estimation of channel parameters and mobile position in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over fading channels. It is assumed that the location estimates are obtained from the bearings and/or propagation delays estimated at one or more cluster(s) of antenna arrays of arbitrary geometry. Among other applications, the CRB on the positioning accuracy may serve as a design tool to find an optimum antenna placement, or to evaluate the practicability of a legal demand for emergency location.

Field tests of a cellular telephone positioning system

This paper presents Cellocate, a cellular telephone positioning system. Due to rules recently adopted by the FCC, cellular licensees must automatically provide the position of cellular 911 callers with an accuracy within 125 m in 67% of all cases. Cellocate estimates position using root MUSIC (MUltiple Signal Identification and Classification) to improve TOA (Time Of Arrival) estimation and hyperbolic trilateration to estimate position. Field tests indicate that Cellocate presently has an accuracy between 180 m and 300 m (66%). It is expected that accuracy will improve when additional cell sites are used in the position estimation process.

Robust Positioning Systems in the Presence of Outliers Under Weak GPS Signal Conditions

In this paper, two epoch-by-epoch robust positioning techniques for global positioning system (GPS) are proposed to deal with the problem of positioning in weak signal conditions in which the probability of outlier in signal acquisition is larger than zero. We propose to accept outliers into the positioning algorithm, however, in this case either robust estimation or outlier detection must be used to overcome the devastating effect of such outliers on traditional positioning algorithms. In order to improve the sensitivity of a GPS receiver, we propose to use novel methods that are able to deal with the problem of estimating the position of a receiver based on pseudo-ranging measurements that are contaminated by outliers. Simulations are carried out to demonstrate the robustness of the proposed techniques in terms of success rate of the algorithms in finding the correct solution, when there are a different number of outliers in ranging measurements from satellites.

Statistical theory of the effects of radio location system design parameters on the positioning performance

This paper provides an asymptotic performance evaluation of network based or multilateral radio location estimators that use the time of arrival (TOA) and/or the angle of arrival (AOA) measurements of the signals travelling from a mobile station (MS) to a set of fixed stations (FSs) to estimate the MSs position. The analysis is based on the Cramer-Rao lower bound (CRLB) and the maximum likelihood theory, and takes into account the effects of the system design parameters as well as the effects of biased measurements, which can result for example from hardware calibration errors or multipath effects, including the lack of line of sight. Explicit formulas that provide a clear relationship between the various system design parameters and the positioning accuracy are derived and discussed. Finally, the theory is verified with numerical simulations.

Sensor Network Based Oilwell Health Monitoring and Intelligent Control

Most oil pumping units (OPUs) have been using manual control in the oilfield. This existing oil-pumping system, a high power-consuming process, has the incapability of OPUs structural health monitoring. In this paper, a sensor network based intelligent control is proposed for power economy and efficient oilwell health monitoring. The proposed sensor network consists of three-level sensors: (1) several types of basic sensors, such as load sensor, angular sensor, voltage sensor, current sensor and oil pressure sensor, which are the first level sensors (FLS), are used for oilwell data sensing; (2) our developed intelligent sensors (IS), which belong to the second level sensor, are designed mainly for an oilwells data elementary processing, main fault alarm/indication, typical data storage/indication, data/status transmission up to the third level sensor (TLS), data/status transmission between IS, and command transmission down to the OPU motor; and (3) our developed software-defined (SD) control centers with an embedded database, i.e., the TLS, are designed for hundreds of oilwells data storage/management, data processing, malfunction detection, malfunction alarm/indication, stroke-adjustment command transmission down to a specific IS for power economy and the malfunction report to the maintenance staff via global system for mobile communications (GSM) short message service (SMS). Experiment results at the Chinese Petroleums Changqing Oilfield demonstrate our proposed sensor network based system.