[show abstract][hide abstract] ABSTRACT: The positioning methods based on received signal strength (RSS) measurements, link the RSS values to the position of the mobile station(MS) to be located. Their accuracy depends on the suitability of the propagation models used for the actual propagation conditions. In indoor wireless networks, these propagation conditions are very difficult to predict due to the unwieldy and dynamic nature of the RSS. In this paper, we present a novel method which dynamically estimates the propagation models that best fit the propagation environments, by using only RSS measurements obtained in real time. This method is based on maximizing compatibility of the MS to access points (AP) distance estimates. Once the propagation models are estimated in real time, it is possible to accurately determine the distance between the MS and each AP. By means of these distance estimates, the location of the MS can be obtained by trilateration. The method proposed coupled with simulations and measurements in a real indoor environment, demonstrates its feasibility and suitability, since it outperforms conventional RSS-based indoor location methods without using any radio map information nor a calibration stage.
IEEE Journal of Selected Topics in Signal Processing 11/2009; · 3.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: A mobile station (MS) location can be estimated from the measurement of the time of arrival of the signals that travel between each base station and the MS. In this scenario, the existence of non-line-of-sight (NLOS) propagation paths has been considered to be the main drawback to achieve high precision in positioning, since NLOS propagation introduces large and unpredictable errors in the time estimates that are obtained from the measurements. In this paper, we propose a new technique, called prior NLOS measurement correction (PNMC), to effectively correct the measurements from NLOS propagation in a previous stage to the positioning process. PNMC is based on a statistical processing of a record of measurements taken over a time window. This processing relies on the statistical estimate of the NLOS measurement ratio present in our record. This estimate is used to range the NLOS recorded measurements into segments. Finally, the correction is carried out by subtracting the expected NLOS errors for each segment. Several simulations have been conducted to show the increase in accuracy obtained by the usage of PNMC and the great improvement that this prior measurement correction means to subsequent wireless location and positioning techniques.
IEEE Transactions on Vehicular Technology 07/2009; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: The final precision achieved by a wireless location system depends basically on the accuracy of the range estimates and on the geometric distribution between anchors and target, being the second issue easier to manage in the design of a wireless location system. The results related to the impact of the geometric distribution, addressed for GNSS location systems, cannot be used directly to other wireless location systems, since the trilateration algorithms used and the characteristics of range estimates can be rather different. In this paper we develop an exhaustive study on the impact of the geometric distribution of anchors for the two most usual algorithms used in non-GNSS wireless location systems, taking into account the non ideal characteristics of the range noises in those location systems. From this study we present two parameters, particular to these two algorithms, which quantify the suitability of the geometric distribution taking values between 0 and 1, depending only on the geometric distributions. We show that armed with these new parameters, it is possible to design the wireless location system in an optimum way. Moreover, we present more optimum geometric distributions than the ones known in the literature.
[show abstract][hide abstract] ABSTRACT: The development of location techniques in urban and indoor environments by using measurements of received signal strength (RSS) has as a main drawback the fact that in such environments the value of RSS depends on many unpredictable and changeable factors, not only on the actual distance between mobile station (MS) and the different base stations (BSs). With the aim of solving these limitations of RSS-based location systems, in this paper we present a novel technique to find out which model best describes the different propagations of signals traveling between the MS and the different BSs. This method estimates accurately and dynamically, all the path loss exponents that model the signal attenuation in propagation paths to each BS, only by using the received signal strength measurements that are obtained in each moment. Therefore, our method does not need any previous knowledge about user position or kind of propagation environment. From the estimation of the different path loss exponents, we obtain much more accurate distance estimations than those obtained by using a generic and unique propagation model previously fixed. We present the results obtained by using the methods described in this paper, from real measurements taken in a GSM network as well as from computer simulations. By using the techniques presented in this paper we can see the great improvement in the precision on estimating distances from the MS and the different BSs. The results obtained from the real measurements support the simulations results and show how that improvement in the distance estimation makes the location much more accurate.
Position, Location and Navigation Symposium, 2008 IEEE/ION; 06/2008
[show abstract][hide abstract] ABSTRACT: Personal exposure meters for assessing exposure to RF electric or magnetic fields are subject to errors associated with perturbations of the fields by the presence of the human body. Although these alterations are complex they are not completely unpredictable. This article concludes that this error in a common worst-case scenario could reach up to 30 dB and therefore is of concern for exposure assessment. We present several guidelines to address this issue and a useful insight into the overall problem based on finite-difference time-domain simulations and experimental verification.
[show abstract][hide abstract] ABSTRACT: The main drawback to improve the precision in cellular location systems based on time delays is the presence of non-line-of-sight (NLOS) propagation, introducing significant and hardly predictable errors in the measurements used in location. In this paper we propose a technique to previously detect and estimate the NLOS ratio present in the measurements. A comprehensive research on the Time of Arrival (TOA) dependence on the NLOS ratio existing in the measurements leads to estimate that ratio from the deviation calculated directly from the available measurements. NLOS detection and ratio estimate is very useful to classify and weight the measurements available in order to perform the following location estimate with the most accurate ones. Several simulations have been conducted to show the precision of ratio estimate and the measurements rating based on it.
Proceedings of the 66th IEEE Vehicular Technology Conference, VTC Fall 2007, 30 September - 3 October 2007, Baltimore, MD, USA; 01/2007
[show abstract][hide abstract] ABSTRACT: We propose a novel multipurpose genetic algorithm based in Pareto optimality to design logical topologies for wavelength-routed optical networks with the aim of minimizing both the global average end-to-end delay and the average end-to-end delay of the most delayed traffic flow. The algorithm determines which nodes should be connected by means of lightpaths, solves the routing and wavelength assignment problem, and routes the traffic in the logical topology. When compared with another multipurpose genetic algorithm based in random selections of two fitness functions (one for each parameter to be optimized), the novel algorithm leads to reductions of up to 5% in both parameters
Transparent Optical Networks, 2006 International Conference on; 07/2006
[show abstract][hide abstract] ABSTRACT: The presence of non-line-of-sight (NLOS) propagation is a key issue that limits the accuracy of wireless location systems.
The lack of direct sight causes the measurements obtained by location systems to be so unpredictable that they can produce
high inaccuracies in the estimation of the mobile station location. In this paper we propose a novel technique to improve
location reliability and accuracy in cases where NLOS propagation is present. For that, in registers of time of arrival (TOA)
measurements taken from each base station (BS) in view, we detect the presence of NLOS propagation and estimate the ratio
of the measurements coming from NLOS propagation. With this estimate we can assess how much is NLOS propagation affecting
the measurements taken from each BS and then we can identify the best measurements and BSs to achieve the highest accuracies
Wireless Personal Communications 53(1):35-52. · 0.43 Impact Factor