7B-4-2 
coordinates (latitude, longitude, height) of a 
vehicle, digital maps to define the location of 
the vehicle relative to its surroundings, 
communication devices sending information 
to the vehicle and back to the control center, 
and computers to control the operation as 
well as perform the numerical calculations. 
In this paper, emphasis has been placed on 
the positioning component. 
Positioning and navigation systems using 
DGPS have been investigated since the early 
1980’s, see Hunter et al. (1990). Various 
methods have been developed to improve 
positioning accuracy caused by the Selective 
Availability (SA) error. In this paper, a real 
time smoothing algorithm for differential 
code pseudorange using carrier phase 
measurements is applied to improve the 
positioning accuracy of a moving vehicle. 
Since carrier phase measurements are 
sensitive to cycle slips, a method dealing 
with cycle slips is proposed. The advantage 
of this approach is that cycle slips must be 
detected but they do not necessarily have to 
be corrected. 
Since the GPS signal from the satellites is 
frequently blocked in the urban 
environment, a DR system composed of 
distance and direction sensors, is 
used to provide autonomous 
positioning information for the 
vehicle. As the positioning errors of 
the DR system build up rapidly with 
time, an integrated DGPS/DR 
vehicle navigation system is 
proposed. The extended Kalman 
filter (EKF) is applied with a 
smoothed code pseudorange 
measurements. Since the EKF is 
computationally intensive for our 
application this might be a problem 
for real-time vehicle tracking 
applications. Therefore, a 
computation-ally effective 
representation of the EKF exploiting 
the structure of the system and 
covariance matrices is proposed. 
2. Positioning Algorithms 
2.1 DGPS Algorithmes 
Two DGPS techniques are quite 
common: the differential 
pseudorange and differential phase 
techniques in which the differential 
pseudorange technique has been 
widely used (Parkinson and Spilker, 
1995). The basic concept of the 
differential pseudorange technique is