Pedestrian navigation in difficult environments: Results of the ESA project SHADE

Abstract

Satellite navigation has become an important positioning source for a wide range of applications, many of which going much beyond the traditional transport sector. One example is personal mobility including dense urban, indoor, and outdoor applications. Practically all of the current applications rely on the GPS signals, sometimes also exploiting regional or local augmentations for better accuracy. As applications move into safety-critical and other areas where service reliability is of concern, users and service providers alike are becoming aware of the importance of service qualities and guarantees. Disaster management is one example of such applications. As a first step, an integrity signal is already provided with the SBAS services WAAS and EGNOS. From the year 2008 onwards, full-scale service guarantees will be available on certain signals of the GALILEO system. In pedestrian user environments like dense urban canyons or indoors, the performance of GNSS (including conventional terrestrial and/or satellite based means of augmentation) for position and integrity reaches well-known technological limits. These limitations can be overcome by adding additional information sources to the system. The ESA funded project SHADE addresses special handheld-based navigation applications in difficult environments. The main focus of the project lies in the navigation non-transport applications like rescue services, VIP tracking or lone worker protection. A highly mobile demonstration system for pedestrian use has been developed that targets sensor augmented navigation, enhanced through visual representation, in security related fields of operation (e.g. rescue operations). The system architecture is based on the combination of navigation, communication and geoinformation. Geoinformation in this context means the creation of a visualization component for a better 3D orientation at the service Center and for the mobile user. The modular system architecture of SHADE is built for information exchange between several mobile units and one or more service centers, which regulate and coordinate information and position exchange. The position information is sent from the Mobile Unit via the mobile communication link to the Service Center, where all position information of different users are managed and provided to the SHADE mission Center over fixed internet services. The mission Center accesses its database and the position updates to render images of the surrounding, based on 3D city and/or terrain models. This can be a bird's view, over the shoulder view, or any other view defined by a mission Center operator. The image is continuously updated and can be accessed by the Mobile Unit. The system that has been designed, built and tested for SHADE uses three different technologies alternatively. Each of the so-called Pilots provides position and integrity data over the mobile communication link. The first Pilot applies the assisted GPS principle. It provides position information even in dense urban environments where weak navigation satellite signals are still detectable. The EGNOS-TRAN service Center provides rapid acquisition assistance information, such as satellite almanacs and precise local time, to the mobile unit. Raw pseudo range measurements are sent back to the service Center, where the user position is calculated. Additionally, the server uses EGNOS information to differentially correct GPS measurements and to process integrity. The second Pilot implements innovative dead-reckoning technologies. GPS positioning is aided during periods of poor reception or bridged during complete signal outages, e.g. indoors or in tunnels. A custom furnished Multi-Sensor Box (MSB) is equipped with a GPS/EGNOS receiver and a number of digital sensors (accelerometers, gyros, barometer, magnetometer). In dead reckoning mode, a step detection algorithm uses accelerometer measurements to calculate displacement vectors. Adding direction measurements of the magnetometer and relative altitude data of the barometer in a Kalman filter, a three-dimensional relative coordinate update is computed. The third Pilot integrates Loran-C terrestrial radio navigation with GPS and EGNOS satellite navigation in the pseudo range domain. The integration of the Loran-C time-of-arrival (TOA) measurements provides position information in dense urban and even in light indoor environments. The performance depends on the coverage of the terrestrial system and the presence of interference. Besides a continuous position update, reliability information is of main interest in the context of disaster management. Satellite-Based Augmentation Systems and their integrity provisions have been primarily designed for aviation applications. The potential use of such augmentation systems for land-mobile and maritime applications is subject to a number of ongoing research and development projects. EGNOS and WAAS offer two types of information to the user: Differential range corrections to improve the accuracy of GPS pseudorange measurements, and integrity information consisting of differential signal-in-space accuracy input for protection level computation. The protection levels are finally compared to thresholds called the alert limits. Although the differential pseudo range corrections can be applied for non-aviation applications without modifications, the integrity concept needs re-assessment and a number of modifications in order to be useable for land-mobile. Different integrity requirement figures, necessitating changed probability multipliers, and a slightly different probability equation according to other operational procedures and user dynamics, can be handled rather easily. The magnitude and bounding of local error contributions to the integrity equation are more challenging. Atop of this, the applied sensor fusion, as in the SHADE MSB, poses new challenges on the protection level algorithms when additional types of measurement are introduced to the position computation. Consequently, each of the three SHADE Pilots implements specific adaptations to the integrity processing. Field demonstrations of the SHADE system encompass nine campaigns with different key application objectives. They have been performed over a scheduled duration of six months in spring and summer 2004. The environmental scenarios include the Expo'98 Park at Lisbon (Portugal), a scenic hotel and an office building at Bolzano (Italy) and a road tunnel in the Center of Rome (Italy). Especially for the sensor-based second Pilot, the tests showed promising results even in difficult environments. GPS outages occurring in tunnels, indoors or in urban areas just slightly degraded the navigation performance. The involvement of targeted user groups (public safety authorities, fire brigades, etc.) in the demonstrations showed user group acceptance and provided detailed feedback on the concept and the architecture. The paper presents in particular the system architecture of SHADE, the design of the three different integrated navigation technologies and the modified integrity processing approaches. Field test results and application domain feed back complement the presented technical information. © 2005 Springer-Verlag Berlin Heidelberg.