Integration and Testing of a Wide-Band Airport Pseudolite
The paper provides initial results of a series of flight tests conducted using the LAAS Test Prototype/Airport Pseudolite system.
Availability Enhancements for CAT IIIb LAAS
: Enhancements are under consideration for the Federal Aviation Administration's (FAA) Category I (CAT I) Local Area Augmentation System (LAAS) to meet the more stringent performance requirements of CAT IIIb operations. This paper analyzes the relative improvement predicted for various alternatives designed to enhance LAAS CAT IIIb availability. These enhancements include increasing the number of ranging sources, using less-conservative error models, taking credit for redundant GPS navigation sensors in the aircraft, using a second frequency to overcome the effects of ionospheric delay, or using differential carrier-phase measurements in the position solution. Availability under each scenario is computed for a vertical alert limit (VAL) ranging from 5.3 m (current requirement) to 10.0 m. Results show that unless VAL is increased beyond about 5.3 m, adequate (0.999) availability cannot be achieved merely by extending the CAT I architecture or by using any one of the above methods alone, with the exception of using dual frequency in both the ground facility and the aircraft. On the other hand, if VAL can be increased to approximately 7.5 m, some other alternatives alone and most pairwise combinations of these alternatives will provide adequate availability.
Optimal Locations of Pseudolites for Differential GPS
Because of the announced DOD policy to degrade GPS accuracy, Differential GPS has assumed increasing importance. Furthermore, the delay in operational deployment of the NAVSTAR satellites has focused increased attention on the use of pseudo-satellites (pseudolites or PLs) to enhance accuracy and provide earlier operational capability. Pseudolites perform a double function: they both calibrate the local ranging errors and significantly improve the user's geometry as measured by GDOP (Geometric Dilution of Precision). 
 
 
 
This paper examines the following problem: What is the best location for a PL when one considers the worst possible satellite outage in twenty-four hours? What is the resulting worst case GDOP? Both single and dual PL systems are considered, and the results are extrapolated to expected user receiver performance (horizontal and vertical errors). 
 
 
 
The results indicate that a dual PL system will outperform the satellite-only GPS system, even with a worst case satellite outage. In addition, there should be negligible degradation during periods when the military intentionally reduces ephemeris or clock accuracy. Furthermore, the accuracy of such a system would provide aircraft positioning very close to Category I FAA landing requirements.