Jouni Rantakokko

Zero-Velocity Detection—An Algorithm Evaluation

In this paper, we investigate the problem of detecting-time epochs when zero-velocity updates can be applied in a foot-mounted inertial navigation (motion-tracking) system. We examine three commonly used detectors: the acceleration-moving variance detector, the acceleration-magnitude detector, and the angular rate energy detector. We demonstrate that all detectors can be derived within the same general likelihood ratio test (LRT) framework, given the different prior knowledge about the sensor signals. Further, by combining all prior knowledge, we derive a new LRT detector. Subsequently, we develop a methodology to evaluate the performance of the detectors. Employing the developed methodology, we evaluate the performance of the detectors using leveled ground, slow (approximately 3 km/h) and normal (approximately 5 km/h) gait data. The test results are presented in terms of detection versus false-alarm probability. Our preliminary results show that the new detector performs marginally better than the angular rate energy detector that outperforms both the acceleration-moving variance detector and the acceleration-magnitude detector.

Accurate and reliable soldier and first responder indoor positioning: multisensor systems and cooperative localization

A robust, accurate positioning system with seamless outdoor and indoor coverage is a highly needed tool for increasing safety in emergency response and military urban operations. It must be lightweight, small, inexpensive, and power efficient, and still provide meter-level accuracy during extended operations. GPS receivers, inertial sensors, and local radio-based ranging are natural choices for a multisensor positioning system. Inertial navigation with foot-mounted sensors is suitable as the core system in GPS denied environments, since it can yield meter-level accuracies for a few minutes. However, there is still a need for additional supporting sensors to keep the accuracy at acceptable levels during the duration of typical soldier and first responder operations. Suitable aiding sensors are three-axis magnetometers, barometers, imaging sensors, Doppler radars, and ultrasonic sensors. Further more, cooperative positioning, where first responders exchange position and error estimates in conjunction with performing radio based ranging, is deemed a key technology. This article provides a survey on technologies and concepts for high accuracy soldier and first responder positioning systems, with an emphasis on indoor positioning.

On the performance of antenna arrays in spatial reuse TDMA ad hoc networks

We have investigated how, the capacity and average delay can be improved by using antenna arrays in an ad hoc network with Spatial Time Division Multiple Access (STDMA). The study is based on different antenna combinations consisting of a single isotropic antenna element, beam steering and adaptive beamforming. We have also studied how the number of antenna elements and the terrain affects the performance. The study shows that the maximum capacity is improved dramatically for the examined networks, with up to 980%. In addition, the average delays are decreased substantially when using antenna arrays. Depending on the beamforming combination used, the capacity gain and the average delay reduction will differ. The highest capacity gain is achieved when combining beam steering (transmitting node) and adaptive beamforming (receiving node). For broadcast traffic omni-directional transmission is most feasible (no transmit beamforming); however,,ever, beamforming is still possible in the receiving nodes. For this beamforming combination the capacity gain is significant, about 560%. The study also indicates that the benefit from antenna arrays is higher in aflat terrain than in a rough terrain.

User requirements for localization and tracking technology: A survey of mission-specific needs and constraints

Current advances in localization and tracking technology have the potential to develop into much-needed tools for the saving of lives in emergency response and rescue missions, and for the safe-keeping of lives in military operations. However, civilian and military users face different environments and consequently have different user requirements. Even within the two broad fields of civilian and military applications, different types of personnel and indeed different types of missions face different needs and constraints. For instance, firefighters engaged in the suppression of a forest fire have other requirements than firefighters suppressing a fire in a high-rise building, or a conflagration in a large industrial complex full of hazardous materials. Military personnel engaged in counter-insurgency operations face requirements different from those tasked to rescue hostages held in a closed environment. This paper aims to survey the different requirements for localization and tracking technology by mission type, so that users can more easily determine their own specific technology needs. Although primarily aimed to describe requirements for military personnel, law enforcement officers, and firefighters, needs and constraints for several types of civilian applications are covered as well. Despite differences in requirements, it makes sense to develop technologies that will target several of these end-user groups. A new joint facility for development of requirements together with representatives from the various branches, and the evaluation of existing and emerging localization and tracking systems, would assist in the enabling of reliable and user-friendly capability to respond to, and recover from, all-hazards emergencies and combat operations.

Accurate indoor positioning of firefighters using dual foot-mounted inertial sensors and inter-agent ranging

A real-time cooperative localization system, utilizing dual foot-mounted low-cost inertial sensors and RF-based inter-agent ranging, has been developed. Scenario-based tests have been performed, using fully-equipped firefighters mimicking a search operation in a partly smoke-filled environment, to evaluate the performance of the TOR (Tactical lOcatoR) system. The performed tests included realistic firefighter movements and inter-agent distances, factors that are crucial in order to provide realistic evaluations of the expected performance in real-world operations. The tests indicate that the TOR system may be able to provide a position accuracy of approximately two to three meters during realistic firefighter operations, with only two smoke diving firefighters and one supervising firefighter within range.

Indoor positioning using multi-frequency RSS with foot-mounted INS

This paper presents a system which combines a zero-velocity-update-(ZUPT-)aided inertial navigation system (INS), using a foot-mounted inertial measurement unit (IMU), with opportunistic use of multi-frequency received signal strength (RSS) measurements. The system does not rely on maps or pre-collected data from surveys of the radio-frequency (RF) environment. Instead it builds its own database of collected RSS measurements during the course of the operation. New RSS measurements are continuously compared with the stored values in the database, and when the user returns to a previously visited area this can thus be detected. This enables loop-closures to be detected online and used for error drift correction. The system utilises a distributed particle simultaneous localization and mapping (DP-SLAM) algorithm which provides a flexible 2D navigation platform that can be extended with more sensors. The experimental results presented in this paper indicates that the developed RSS SLAM algorithm can, in many cases, significantly improve the positioning performance of a foot-mounted INS.

Scenario-based evaluations of high-accuracy personal positioning systems

Foot-mounted inertial sensors combined with GPS-receivers, magnetometers, and barometric pressure sensors have shown great potential in providing high-accuracy positioning systems for first responder and military applications. Several factors, including the type of movement, surface, and the shape of the trajectory, can strongly influence the performance of foot-mounted inertial navigation systems. There is a need for realistic scenario-based evaluations as a complement to the controlled environment tests that have been published in the literature. In this work we evaluate the performance of a foot-mounted inertial navigation system using three-axis accelerometers, gyroscopes and magnetometers during realistic scenario-based measurements. The position accuracy is evaluated by using a camera-based reference system which positions itself towards visual markers placed at pre-surveyed positions, using a slightly modified version of the ARToolKitPlus software. Maximum position errors of 2.5 to 5.5 meters were obtained during four separate high-tempo building clearing operations that lasted approximately three and a half minutes each. Further improvements in accuracy, as well as improved robustness towards different movement patterns, can be achieved by implementing an adaptive stand-still detection algorithm.

Cooperative localization using a foot-mounted inertial navigation system and ultrawideband ranging

This paper aims to evaluate the performance gains that can be obtained by introducing cooperative localization in an indoor firefighter localization system, through the use of scenario-based simulations. Robust and accurate indoor localization for firefighters is a problem that is not yet resolved. Foot-mounted inertial navigation systems (INS) have been examined for first responder localization, but they have an accumulating position error that grows over time. By using ultrawideband (UWB) ranging between the firefighters and combining range measurements with position and uncertainty estimates from the foot-mounted INS via a cooperative localization approach it is possible to reduce the position error significantly. An error model for the position estimates received from single and dual foot-mounted INS is proposed based on experimental results, and it contains a scaling error which depends on the distance travelled and a heading error which grows linearly over time. The position error for dead-reckoning systems depends on the type of movement. Similarly, an error model for the UWB range measurements was designed where the range measurements experience a bias and variance, which is determined by the number of walls between the transmitter and receiver. By implementing these error models in a scenario-based simulation environment it is possible to evaluate the performance gain of different cooperative localization algorithms. A centralized extended Kalman Filter (EKF) algorithm has been implemented, and the position accuracy and heading improvements are evaluated over a smoke diving operation scenario. The cooperative localization scheme reduces the position errors by up to 70% in a scenario where a three-person smoke diver team performs a search and rescue operation.

On broadband adaptive beamforming for tactical radio systems

An adaptive antenna array has the ability to change its pattern automatically in response to changes in the signal environment. In this paper we have examined, through extensive simulations, the capabilities and limitations with two broadband adaptive beamforming. A broadband circular 16-element antenna array intended for the frequency range 200-500 MHz has been constructed at FOI. Tapped-delay lines are used to achieve broadband properties. The first algorithm is a constrained minimum variance beamformer while the second minimizes the mean square error between a reference signal and the output of the beamformer. We show how various parameters (e.g. signal strength, bandwidth, the number of taps and samples) influence the performance of the beamformer. Further, the constrained minimum variance beamformer has been examined for sensitivity to discrepancies between the look-direction and the direction of the desired signal. Methods to improve the robustness of the beamformers, i.e., diagonal loading, noise eigenvalue equalization, and derivative constraints, have also been examined Finally, we illustrate the sensitivity of the adaptive beamforming algorithms against unknown phase and gain errors in the receiver channels.

Integration of GNSS-receivers with dual foot-mounted INS in urban and indoor environments

In safety-critical applications, including firefighter and law enforcement operations, infrastructure-free localization systems are typically required. These systems must provide accurate localization in all scenarios. Seamless indoor and outdoor localization and navigation, including in dense urban environments, are needed. Multi-sensor fusion algorithms constitute an integral part in all state-of-the-art indoor positioning systems. GNSS-receivers typically provide poor estimates of their own position uncertainty in dense urban and indoor environments, where significant position errors can be expected, which makes the design of a robust sensor fusion algorithm a challenge. Sensor fusion strategies for integration of a GNSS-receiver with foot-mounted inertial navigation systems (INS) are described and evaluated in this work. For a loosely coupled integration strategy, we suggest to use a cut-off criteria that governs when to discard the GNSS-positions and demonstrate that it can improve the position and heading accuracy in outdoor/indoor transition regions. Similarly, for a tightly coupled integration strategy, we suggest an approach with heavy-tailed measurement noise and demonstrate its capability to suppress inconsistent data and improve performance in the same regions.