GPS World, September 2010

GOVERNMENT Emergency Response Technique sensor Navigation information Typical accuracy Selected characteristics Radio frequency RF GPS GNSS Position coordinates Velocity X Y Z Vx Vy Vz 10 meters 1 3 meters DGPS 005 meters second 02 meters second Å TABLE 1 Typical sensors for multi sensor integration observables and their characteristics where X Y Z are the 3D coordinates v x v y v z are the 3D velocities is the direction of motion heading in XY horizontal plane a tan is the tangential acceleration and a rad is the radial acceleration in XY horizontal plane a z is the vertical acceleration In a larger network the selection of a sub network of nodes is an important issue as in case of a large number of users in the entire network computational and communication loads may not allow for the entire network to be treated as one entity Still information exchange among the sub networks must be assured Conceptually the sub networks can consist of nodes of equal hierarchy or may contain master anchor nodes that normally have a better set of sensors and collect measurements from all client nodes to perform a collaborative navigation solution TABLE 1 lists example sensors and techniques that can be used in collaborative navigation The concept of a master node is also crucial from the stand point of distributed Å FIGURE 1 Collaborative navigation concept Line of sight system Results in a global reference system Pseudolites X Y Z v x v y v z Comparable to GPS Line of sight system Operate at GPS and non GPS frequencies WLAN Signal strength based method Fingerprinting method X Y Z X Y Z 2 6 meters 1 3 meters Indoor positioning in a local system Signal attenuation due to distance penetration through walls and multipath Interference from other users of 24GHz frequency band UWB X Y Z decimeter level accuracy theoretically achievable at 10 20 meter range Resistant to multipath fading Strong signal penetration Possible interference with GPS Positioning approach similar to WLAN IMU Accelerometer a tan a rad a z 003 meter second2 Subject to drifts Should be calibrated when GPS is available Gyroscope Heading 05 3 Short term accuracy stability Not subject to external disturbances Subject to drifts Should be calibrated when GPS is available Optical systems Image based X Y Z few meters Line of sight system Network approach is geometry dependent Optical sensor network X Y Z optional few meters Image overlap required for 3D Laser X Y Z centimer to decimeter Local or global reference system Others Digital compass magnetometer Heading 05 3 Long term accuracy stability Subject to magnetic disturbances Sensitive to tilt Digital barometer Z 1 3 m Requires calibration by a given initial height GPS World September 2010 www gpsworld com 36