Demonstration system for using shipboard-relative GPS

GPS World, April, 2005 by Kathleen Boseley, Jim Waid

Figure 8 presents the test statistic information for the fault-free case. The three plots are the test statistic versus time, the distribution of the magnitude of the test statistic, and the time history of the chi-squared statistic for the double differences created as part of the normal relative Kalman filter processing. No anomalies are present.

Figure 9 shows the same information for the case where a one-half carrier cycle slip was injected into a single satellite signal on the aircraft measurement data at 30 seconds prior to the end of the simulation. The data clearly demonstrates that something unusual is taking place. The test statistic immediately exceeds the expected range of values and the chi-squared statistic shows a clear bias.

Figure 10 shows the results when the exercise is repeated only introducing a full one-cycle slip. The results are as expected. The test cases for two- and five-cycle slips are not presented here, but they are even more pronounced than the single-cycle case. Further evaluation and testing is being conducted to build confidence in the missed detection and false alert rates required for this detection technique. We are also investigating cycle slip repair with details on the approach we are using available in the article by C. Altmayer cited previously. Initial results are encouraging, and Honeywell is confident that this monitoring technique will meet the requirements for Sea Based JPALS demonstration system.

Program Status

Honeywell recently conducted a critical design review (CDR) for Sea Based JPALS. This meeting included presentations of the requirements, the proposed interfaces, the system and software architectures, the relative navigation KF design, the integrity design, the at-sea align capability and the testing strategies.

The CDR reinforced the notion that the current effort is a demonstration program and as such requirements are still not entirely stable and a revised systems requirements document (SRD) was released in June 2004. Another release of this document is imminent although the expected changes are minimal. The focus of the TD phase has become risk reduction, the refinement of the requirements, and the determination of realistic, achievable goals for the SDD phase.

Honeywell is continuing the development and integration of the 24-channel receiver with TNL and is on schedule to deliver units to support the Sea Based JPALS programs as planned.

TABLE 1 Existing landing systems and the communities they serve.

System              User

Instrument Landing  Commercial and
System (ILS)        limited military
Microwave Landing   Commercial
System (MLS)        (Europe) and very
                    limited military
Precision Approach  Military
Radar (PAR)
Mobile Microwave    Military
Landing System
(MMLS)
Marine Remote       Military
Area Approach and
Landing System
The Instrument      Military
Carrier Landing
System (SPN-46)

TABLE 2 Summary of Landing System Requirements

                      Sea Based          LAAS MASPS
                      JPALS              (DO-245)
                      Autoland (AL)      PT3 (CAT IIIb)

Accuracy
Lateral
(95% NSE)             0.3 meters         6.2 meters
Vertical
(95% NSE)             0.3 meters         2.0 meters

Integrity
P(HMI)                1X10-6 / approach  1X10-9 / 15 sec (Lateral)
                                         1X10-9 / 30 sec (Vertical)
Time To Alert (TTA)   1 sec              1 sec
Vertical Alert Limit
(VAL)                 1.1 meters         5.3 meters
Lateral Alert Limit
(LAL)                 1.1 meters         15.5 meters

Availability          0.997              0.99 to 0.99999

Continuity of                            1.8X10-6 /30 sec (Lateral)
Function              4X10-6/15 sec      1.9X10-6 /15 sec (Vertical)