Marc Ciurana

Performance evaluation of a TOA-based trilateration method to locate terminals in WLAN

Nowadays, several systems are available for outdoor localization, such as GPS, assisted GPS and other systems working on cellular networks. However, there is no proper location system for indoor scenarios. Research into designing location systems for 802.11 networks is being carried out, so locating mobile devices on global networks (GSM/cellular + GPS + WLAN) finally seems feasible. The technique presented in this paper uses existing wireless LAN infrastructure with minor changes to provide an accurate estimation of the location of mobile devices in indoor environments. This technique is based on round-trip time (RTT) measurements, which are used to estimate distances between the device to be located and WLAN access points. Each RTT measurement estimates the time elapsed between the RTS (Request-to-Send) and the CTS (Clear-to-Send) frame of the 802.11 standard. By applying trilateration algorithms, an accurate estimation of the mobile position is calculated.

On the scalability of a novel WLAN positioning system based on time of arrival measurements

TOA-based methods represent an interesting alternative to overcome important constraints of the existing fingerprinting solutions to locate WiFi devices indoors, especially in terms of accuracy, stability and quick deployment. However, in some situations the scalability of TOA-based methods to large number of users is expected to be degraded because of the traffic generated by the positioning process. This paper describes the architecture of a novel TOA-based WiFi location system and as main contribution presents an assessment of the systems scalability considering different location-based services and scenarios. Achieved results show that system is viable even in scenarios with a high density of terminals and allows reconsidering some system design issues in order to improve the quality of the positioning service.

A Ranging Method with IEEE 802.11 Data Frames for Indoor Localization

IEEE 802.11 networks constitute a suitable infrastructure for accurate indoor positioning. However, existing approaches based on fingerprinting present drawbacks that make them not suitable for most of applications. This paper presents an innovative TOA-based ranging technique over IEEE 802.11 networks intended to be the essential step of an indoor location system. This approach is based on round trip time measurements using standard IEEE 802.11 link layer frames and a statistical post-processing to mitigate the noise of the measurements. A prototype has been implemented in order to assess the validity and evaluate the performance of the proposed technique. First results show ranging accuracies of less than one meter of error in LOS situations.

Indoor tracking in WLAN location with TOA measurements

Authors presented recently an indoor location technique based on Time Of Arrival (TOA) obtained from Round-Trip-Time (RTT) measurements at data link level and trilateration. This new approach uses the existing IEEE 802.11 WLAN infrastructure with minor changes to provide an accurate estimation of the position of static wireless terminals. This paper presents advances on how to incorporate tracking capabilities to this approach in order to achieve a noticeable enhancement in the positioning accuracy while maintaining the computational cost low, both essential requirements in some critical applications of indoor pedestrian navigation in which people carrying light mobile devices has to be tracked with precision. Taking as a basis the Discrete Kalman Filter, customizations and optimizations have been designed and presented. Results obtained after conducting extensive simulations fed with actual ranging observables demonstrate the validity and suitability of the researched algorithms and its ability to provide very high performance level in terms of accuracy and robustness.

WLAN indoor positioning based on TOA with two reference points

This paper presents a new approach to providing accurate pedestrian indoor positioning using a Time of Arrival (TOA) based technique, when only two access points in an IEEE 802.11 network are in range of a mobile terminal to be located. This allows to enhance the availability and reliability of the positioning system, because existing trilateration-and tracking-based systems require at least three reference points to provide 2D positions. This contribution demonstrates the feasibility of the technique proposed and presents encouraging performance figures obtained through simulations with real observable data.

SofTOA: Software Ranging for TOA-Based Positioning of WLAN Terminals

TOA-based trilateration constitutes an interesting choice to locate terminals employing WLAN networks. A major limitation of this technique is the requirement for hardware modifications in the WLAN device in order to achieve accurate ranging. This paper presents an approach that overcomes this limitation. It is based on RTT measurements performed through time-stamping the transmission and reception of IEEE 802.11 MAC frames from the WLAN drivers code, employing the CPU clock as time-base. Some statistical processing is needed in order to mitigate the noise of the measurements. This paper presents experimental results obtained with a prototype showing ranging errors of a few meters when applied to estimate distances up to 25 meters in both indoor and outdoor environments.

Performance stability of software ToA-based ranging in WLAN

This article proposes a set of strategies to improve the performance stability and reliability of purely software ToA-based ranging with off-the-shelf WLAN equipment. Taking as starting point the core design lines proposed in [1], where timing measurements were taken at OS level using the CPU clock of the client device, we optimize the OS configuration and the capture of the time-stamps. Results obtained with a prototype demonstrate that the proposed enhancements improve the performance stability by a factor four. The interest in this kind of ranging methods is because they enable cost-effective and accurate positioning in GNSS-less environments.

Tracking mobile targets indoors using WLAN and time of arrival

This article presents a novel technique to track WLAN terminals based on Time of Arrival (TOA). The objective of this research is enhancing the accuracy and availability of Newton-based WLAN positioning. Two tracking algorithms have been designed for this purpose. Results obtained from simulations run using true ranging observables demonstrate the suitability of the proposed algorithms. This technique allows the tracking of mobile terminals in real-time indoors with around 1.5m of error with three access points at sight. Additionally, tracking with only two access points is possible with an accuracy drop of around 1m. Other advantages of the proposed solution include its flexibility of deployment and cost-effectiveness.

Comparative performance evaluation of IEEE 802.11v for positioning with time of arrival

Time of Arrival (TOA) based techniques are expected to overcome performance limitations of existing WLAN positioning approaches. The upcoming IEEE 802.11v standard is expected to play a key role because it will include new specific mechanisms for TOA-based positioning with WLAN. This article analyzes some of these new capabilities and evaluates the performance enhancement that they can provide in practice. To this end, a comparative assessment between an existing WLAN TOA-based approach that uses IEEE 802.11 b/g and an analogous solution employing IEEE 802.11v is performed.

Multipath profile discrimination in TOA-based WLAN ranging with link layer frames

Indoor ranging and location in WLAN is possible through obtaining Round-Trip-Time (RTT) measurements at data link level. This procedure allows using the existing IEEE 802.11 WLAN infrastructure with minor changes in order to provide an accurate estimation of the position of the mobile terminal. In this paper, an approach to overcome the undesired impact of the indoor radio-channel multipath on the accuracy of the TOA estimation between the terminal and an Access Point is presented. Ranging errors caused by multipath are quantified for different channel profiles: Dominant Direct Path (DDP), Non Dominant Direct Path (NDDP) and Undetectable Direct Path (UDP). However, the main challenge corresponds to be able to identify this profile (i.e. the multipath condition) from the obtained RTT measurements at IEEE 802.11 link level. This allows applying a TOA estimation algorithm sensitive to the detected profile in order to minimize the TOA estimation error.