Sensor-Augmented EGNOS/Galileo Receiver for Handheld Applications in urban and indoor environments
Background & Objectives
In the personal mobility sector in dense urban, indoor and outdoor environments, nearly all of the current applications rely on satellite navigation, sometimes also exploiting regional or local augmentations to improve positioning accuracy. As applications move into safety-critical and other domains, where service reliability is a major concern, users and service providers are becoming aware of the importance of positioning accuracy, availability and service quality. In pedestrian user environments, like dense urban canyons or indoors, the GNSS (Global Navigation Satellite System) positioning performance reaches well-known technological limits.
These limitations can be overcome by adding additional sources of information to the system. Imagine a fire fighter in a building full of heavy smoke, unable to find his way back outdoors. A positioning and communication unit providing reliable position information and instructions from outside can help to save his life. This scenario or similar ones can be seen as the main motivation for the SARHA project.
The purpose SARHA is to combine a modern satellite navigation receiver with augmentation sensors and to develop an optimised hybrid navigation software for the system. While satellite navigation reaches technological limits in urban canyons or indoors, the SARHA system bridges GPS outages with autonomous sensor technology.
The SARHA system architecture follows the concept of integrated pedestrian navigation systems combining GNSS with a dead-reckoning approach, by measuring the walking velocity and the heading. Thus, in case of GPS/EGNOS outages in, for example, urban canyons or indoors, the dead-reckoning component will deliver position information. To increase positioning accuracy and availability, especially in difficult environments, the SARHA system incorporates, besides a u-blox GNSS receiver, a magnetic compass and gyroscopes for obtaining heading information, and accelerometers for velocity determination based on the principle of step detection and speed modelling. Also the system is enhanced by a transponder system for absolute indoor positioning updates. For 3D positioning, the system contains a barometric altimeter which provides pressure and temperature information.
In addition to the different sensor types, the SARHA system contains a single-board computer for the overall data and interface management. For user interaction and visualisation purposes, the mobile unit provides a man-machine interface (MMI), which can be useful for navigating in cities and buildings or for route guidance. Furthermore, a communication link provides access from the mobile unit to a service centre, which also supports visualisation and communication capabilities. This is especially important for safety-of-life operations (e.g. fire fighters) or search and rescue applications. While the pedestrian navigation unit and the MMI communicate via Bluetooth, the MMI and the service centre are connected via cellular communication networks, such as GPRS or UMTS.
In the near future, small and portable devices will assemble seamless communication, navigation and geo-information capabilities in a highly integrated hardware. This will be offered at reasonable costs and with high positioning performance. The SARHA positioning device, focusing on safety-of-life operations aims to increase accuracy, availability, reliability and integrity compared to stand-alone GNSS receivers.
Therefore a hybrid navigation system architecture has been chosen which will allow indoor and outdoor navigation. The SARHA system integrates state-of-the-art sensors to provide higher availability and accuracy of positioning solutions, greater robustness, and a miniaturisation and simplification of system complexity at reasonable cost. Furthermore, the interaction between a mobile device and a service centre via communication enhances security and affords additional services. An accompanying study analyses the benefits of the Galileo system and signals in target handheld applications.
Work performed & results
The SARHA system is designed to meet the stringent requirements of fire fighters, rescue services, police, special task forces, solitary and lone workers for handheld applications in environments with unfavourable satellite signals, whilst providing maximum reliability and robustness with a hybrid navigation system architecture. The hybridisation of complementary sensors allows seamless indoor/outdoor navigation and maximises security, availability and accurate performance even under severe environments. Furthermore, the interaction with communication enhances security and affords additional services. Besides the system development, the SARHA project incorporated a technical study analysing the impact of Galileo on the SARHA design for future developments. Influences of Galileo and assisted Galileo on the SARHA system performance and the system design have been further analysed.