Vehicle-to-vehicle relative navigation of a network of vehicles travelling in an urban canyon is assessed using least-squares and Kalman filtering covariance simulation techniques. Between-vehicle differential GPS is compared with differential GPS augmented with between-vehicle ultrawideband range and bearing measurements. The three measurement types are combined using both least-squares and Kalman filtering to estimate the horizontal positions of a network of vehicles travelling in the same direction on a road in a simulated urban canyon. The number of vehicles participating in the network is varied between two and nine while the severity of the urban canyon was varied from 15-to 65-degree elevation mask angles. The effect of each vehicle’s azimuth being known a priori, or unknown is assessed. The resulting relative positions in the network of vehicles are then analysed in terms of horizontal accuracy and statistical reliability of the solution. The addition of both range and bearing measurements provides protection levels on the order of 2？m at almost all times where DGPS alone only rarely has observation redundancy and often exhibits estimated accuracies worse than 200？m. Reliability is further improved when the vehicle azimuth is assumed to be known a priori. 1. Introduction While single point GPS positioning may be sufficient for user navigation and guidance on most highways, other applications require a more precise intervehicle relative position. This paper assesses the utility of integrating between-vehicle differential GPS with direct measurements of intervehicle range using ultrawideband ranging (UWB) radios and direct observation of intervehicle bearing. Relative positioning between vehicles, or vehicle-to-vehicle (V2V) navigation, using GPS has been a topic of interest for at least a decade [1]. With more and more vehicles equipped with GPS receivers, the establishment of ad hoc networks of vehicles exchanging position information becomes possible and enables many vehicle navigation applications that depend on relative positioning. Some examples include slow or stopped vehicle ahead, vehicle in blind-spot warnings, or smart cruise control coordination for vehicles travelling in platoons on highways [2]. While relative GPS can provide V2V navigation in many environments, in urban canyons and under dense foliage GPS alone may not be able to provide a reliable solution estimate [3], and information from other vehicle sensors will be required [4]. In this light, UWB is a relatively new technology, having only been FCC approved in 2002. UWB
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