Alfonso Bahillo

Robust Indoor Positioning Provided by Real-Time RSSI Values in Unmodified WLAN Networks

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.

Prior NLOS Measurement Correction for Positioning in Cellular Wireless Networks

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 802.11 Distance Estimation Based on RTS/CTS Two-Frame Exchange Mechanism

The addition of positioning capabilities to wide- spread communications such as IEEE 802.11 compliant networks could open up interesting markets, in particular if a low-cost hardware has to be added to the existing one and standard RTS/CTS control frames exchange could be used for this purpose. In this paper various statistical estimators of the delay profile observed, derived from Round-Trip Time measurements, are analyzed and a linear regression of the statistical estimators is applied in order to improve the accuracy of distance estimation between a Mobile User and an Access Point. A precision in distance estimation with errors in the range of a meter is achieved.

Hybrid RSS-RTT localization scheme for indoor wireless networks

Nowadays, a variety of information related to the distance between two wireless devices can be easily obtained. This paper presents a hybrid localization scheme that combines received signal strength (RSS) and round-trip time (RTT) information with the aim of improving the previous localization schemes. The hybrid localization scheme is based on an RSS ranging technique that uses RTT ranging estimates as constraints among other heuristic constraints. Once distances have been well estimated, the position of the mobile station (MS) to be located is estimated using a new robust least-squared multilateration (RLSM) technique that combines the RSS and RTT ranging estimates mitigating the negative effect of outliers. The hybrid localization scheme coupled with simulations and measurements demonstrates that it outperforms the conventional RSS-based and RTT-based localization schemes, without using either a tracking technique or a previous calibration stage of the environment.

Topology Assessment Provided by Weighted Barycentric Parameters in Harsh Environment Wireless Location Systems

In wireless location systems deployed in open areas, the statistical distributions of the range estimates are very tractable. However, due to the nature of the wireless propagation in urban and indoor environments, the behavior of the range estimates in such environments is very different. Therefore, the performance assessment results obtained for the systems operating in open areas cannot be transferred to the ones deployed in realistic urban and indoor environments. In this paper, the systematic and random errors (accuracy and precision) and the dilution-of-precision (DOP) in harsh environments are derived for the two most common multilateration algorithms, as well as the performance theoretical benchmark. We show that these quantities are determined by geometric parameters that we call topology-assessment-weighted-barycentric-parameters (TAWBAP), which are the norm of weighted barycenters obtained from the positions of anchors and target. These parameters manage the performance of the multilateration process showing the influence of the geometric configuration in connection with the specific characteristics of each range estimate. The improvement in performance obtained by using the TAWBAP parameters as a network design rule is demonstrated by means of simulations as well as by measurements taken in a real indoor environment. This improvement outperforms at least 25% the one achieved by topology deployments that have been considered as optimal in the literature.

Accurate and integrated localization system for indoor environments based on IEEE 802.11 round-trip time measurements

The presence of (Non line of Sight) NLOS propagation paths has been considered the main drawback for localization schemes to estimate the position of a (Mobile User) MU in an indoor environment. This paper presents a comprehensive wireless localization system based on (Round-Trip Time) RTT measurements in an unmodified IEEE 802.11 wireless network. It overcomes the NLOS impairment by implementing the (Prior NLOS Measurements Correction) PNMC technique. At first, the RTT measurements are performed with a novel electronic circuit avoiding the need for time synchronization between wireless nodes. At second, the distance between the MU and each reference device is estimated by using a simple linear regression function that best relates the RTT to the distance in (Line of Sight) LOS. Assuming that LOS in an indoor environment is a simplification of reality hence, the PNMC technique is applied to correct the NLOS effect. At third, assuming known the position of the reference devices, a multilateration technique is implemented to obtain the MU position. Finally, the localization system coupled with measurements demonstrates that the system outperforms the conventional time-based indoor localization schemes without using any tracking technique such as Kalman filters or Bayesian methods.

Design and Implementation of Context Aware Applications With Wireless Sensor Network Support in Urban Train Transportation Environments

Transportation system is experiencing steady growth, with the aim of providing more efficient, reliable, and comfortable services, in the framework of intelligent transportation systems. Moreover, context aware environments are one of the main drivers in the achievement of smart cities and smart regions. In this paper, wireless sensor networks (WSNs) embedded in urban transportation systems will be analyzed in terms of impact on wireless channel behavior and system performance. An in-house developed 3-D ray launching tool, with the inclusion of in-house human body model as well as with the study of interference levels is employed. Wireless channel estimations indicate an initial infrastructure node density in the order of 1node/150m2 to 1node/500m2 as a function of the employed transceivers. A practical solution has been implemented, combining an Android-based application and a system level architecture over the WSN for urban train transportation environmental monitoring, providing interaction between users and the environment, with the aid of a combined WSN/WLAN platform as well as an implemented software architecture, scalable in terms of user density and future needs.

Ubiquitous Connected Train Based on Train-to-Ground and Intra-Wagon Communications Capable of Providing on Trip Customized Digital Services for Passengers

During the last years, the application of different wireless technologies has been explored in order to enable Internet connectivity from vehicles. In addition, the widespread adoption of smartphones by citizens represents a great opportunity to integrate such nomadic devices inside vehicles in order to provide new and personalized on trip services for passengers. In this paper, a proposal of communication architecture to provide the ubiquitous connectivity needed to enhance the smart train concept is presented and preliminarily tested. It combines an intra-wagon communication system based on nomadic devices connected through a Bluetooth Piconet Network with a highly innovative train-to-ground communication system. In order to validate this communication solution, several tests and simulations have been performed and their results are described in this paper.

Ranking of TOA Measurements Based on the Estimate of the NLOS Propagation Contribution in a Wireless Location System

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 in location.

Adding indoor location capabilities to an IEEE 802.11 WLAN using real-time RTT measurements

An accurate real-time application which locates mobile users in an indoor environment is highly demanded in hospitals, warehouses, etc., provided that minor changes in their infrastructure are required. Most present-day location techniques require a great calibration effort, or special devices which are not cost-effective. Avoiding these needs, this paper implements an autonomous positioning technique based on IEEE 802.11 RTS/CTS two-frame exchange in a real scenario. Two estimators of the delay profile measured are analyzed and a linear regression of them at each distance is performed from which the distance between a mobile user and an access point is estimated. Experimental results, without any tracking information nor nonline-of-sight mitigation, reveal the effectiveness of the proposed method.