Francisco Barcelo-Arroyo

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.

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.

Impact of mobility models on the cell residence time in WLAN networks

Several mobility models are available for simulating WLAN, with different impacts on network performance. This work deals with the impact of the assumed mobility model on two key teletraffic variables involved in the planning of the network: the cell residence time (i.e., time connected to an access point) and the handoff rate. These two variables are studied in different scenarios for WLANs designed for pedestrians. For this purpose, discrete event simulations are run with different mobility patterns and number of access points. The time between changes of access point (i.e., handoffs) is studied as a random variable. This research proves the importance of correctly selecting the assumed mobility pattern, as it has a strong impact on the number of handoffs. The probability density function of the cell residence time is also studied as a combination of a distribution that models fast disassociation events (i.e., short ping-pongs between two access points) and a gamma or lognormal distribution, depending on the mobility pattern, which model longer dwells.

A Survey of Routing Protocols for Energy Constrained Ad Hoc Wireless Networks

In this survey we review energy-aware routing protocols for wireless multihop ad hoc networks and critically discuss the main results in this area. The classification presented is in no case unique but summarizes the chief characteristics of the many published proposals for energy conservation. A common pitfall detected in most of the studies is the lack of unambiguous notion of networks lifetime and hence of clear objective of the designed algorithm. We, therefore, define first what operational lifetime for ad hoc networks means and then analyze the achievements from that angle. After getting insight into the different energy-aware routing protocols we point out another approach for extending networks operational lifespan, which has been overlooked in the relevant literature.

A new time-based algorithm for positioning mobile terminals in wireless networks

This paper presents a positioning algorithm, named time of arrival to time difference of arrival (TOAD), which computes time-difference-of-arrival (TDOA) measurements from the messages that time-of-arrival (TOA) stations in sight exchange while their positioning processes are running. This study addresses the accuracy of the TOAD algorithm in two different environments: line-of-sight (LOS) and non-line-of-sight (NLOS). Simulation is used to set up a wireless network. The Gauss-Newton nonlinear least squares algorithm is used to compute the positions in both TOA and TOAD stations. Results indicate that the TOAD algorithm increases the root mean square error (RMSE) of the positioning error in LOS scenarios by 10 to 20% compared with the RMSE achieved by TOA. This drop in accuracy contrasts with the results for the NLOS scenarios. The RMSE of TOAD in such scenarios is at least 10% lower than that achieved by TOA. This result is specially important since this latter scenario is the most common. Consequently, this novel technique therefore improves the scalability and integrity of TOA techniques based on RTT, making it possible for the stations to position themselves without injecting traffic and with QoS figures close and most times better than that achieved by TOA.

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.