A prototype portable vehicle navigation system utilizing map aided GPS

The author has developed a prototype portable vehicle navigation system (PortaNav) based on a notebook computer, a PCMCIA-type GPS receiver, and a digital road map. In order to meet the requirement of portability, the system can not be permanently installed in a vehicle, eliminating the possibility of using dead reckoning sensors. It was necessary to improve the accuracy of GPS positioning in single point mode under the effects of selective availability (SA). Traditionally, this has been done by integrating dead reckoning sensors with the GPS measurements. For this system, a digital road map was used as an auxiliary source of positioning information. A Kalman filter was used to combine the raw GPS measurements with mapderived constraints to improve the positioning coverage, accuracy, and reliability of the navigation system. Software was developed to log three sets of data for comparison. First, a stand-alone GPS fix is logged to show what unaided GPS provides. Second, the map aided GPS solution is recorded to show the improvement achieved. Finally, a RINEX file is recorded for post-mission precise orbit processing, yielding the most accurate solution. Data was recorded in various urban environments to show the improvements gained. The paper describes the mathematical basis for the map aiding process. Test results showing GPS alone and map aided GPS in urban canyon, tree canopy, and open road environments are presented. Conclusions are drawn on the viability of using GPS for vehicle navigation without the use of dead reckoning sensors.