GPS World, September 2010

Emergency Response GOVERNMENT A performance assessment demonstrates the ability of a networked group of users to locate themselves and each other navigate and operate under adverse conditions in which an individual user would be impaired The technique for robust GPS positioning in a dynamic sensor network uses a distributed GPS aperture and RF ranging signals among the network nodes I n situations where GPS signals are subject to potential degradations users may operate together using partial satellite signal information combined from multiple users Thus collectively a network of GPS users hereafter referred to as network nodes may be able to receive sufficient satellite signals augmented by internodal ranging measurements and other sensors such as inertial measurement unit IMU in order to form a joint position solution This methodology applies to numerous U S Department of Defense and civilian applications including navigation of dismounted soldiers emergency crews on the fly formation of robots or unmanned aerial vehicle UAV swarms collecting intelligence disaster or environmental information and so on which heavily depend on availability of GPS signals That availability may be degraded by a variety of factors such as loss of lock for example urban canyons and other confined and indoor environments multipath and interference jamming In such environments using the traditional GPS receiver approach individual or all users in the area may be denied the ability to navigate A network of GPS receivers can in these instances represent a spatially diverse distributed aperture which may be capable of obtaining gain and interference mitigation Further mitigation is possible if selected users nodes use an antenna array rather than a single element antenna In addition to the problem of distributed GPS aperture RF ranging among network nodes and node geometry connectivity forms another topic relevant to collaborative navigation The challenge here is to select nodes which can receive GPS signals reliably further enhanced by the distributed GPS aperture to serve as pseudo satellites for the purpose of positioning the remaining nodes in the network Collaborative navigation follows from the multi sensor navigation approach developed over the past several years where GPS augmentation was provided for each user individually by such sensors as IMUs barometers magnetometers odometers digital compasses and so on for applications ranging from pedestrian navigation to georegistration of remote sensing sensors in land based and airborne platforms Collaborative Navigation The key components of a collaborative network system are inter nodal ranging sub system each user can be considered as a node of a dynamic network optimization of dynamic network configuration time synchronization optimum distributed GPS aperture size for a given number of nodes communication sub system and selection of master or anchor nodes FIGURE 1 illustrates the concept of collaborative navigation in a dynamic network environment Sub networks of users navigating jointly can be created ad hoc as indicated by the circles Some nodes users may be parts of different sub networks Challenged Positions Dynamic Sensor Network Distributed GPS Aperture and Inter nodal Ranging Signals Dorota A Grejner Brzezinska Charles Toth Inder Jeet Gupta Leilei Li and Xiankun Wang www gpsworld com September 2010 GPS World 35