Precision Landing Tests with Improved Integrity Beacon Pseudolites

Stanford’s Integrity Beacon Landing System uses ground-based pseudo-satellite transmitters known as Integrity Beacons to resolve carrier phase ambiguities on final approach, giving IBLS both high integrity and centimeter-level accuracy. This paper discusses two improved Integrity Beacon designs and the results of flight tests with these new beacons. The original Integrity Beacons were not synchronized to GPS time. The IBLS reference station was required to measure the beacon carrier phase reference information using a direct cable connection to each Integrity Beacon, which proved inconvenient in practice. We therefore constructed a pair of Autonomaus Integrity Beacons, pseudolites whose transmitted signals are synchronized to GPS satellite signals using the Omni-Marker principle invented at Stanford. Flight tests using these beacons showed that IBLS performance was maintained with the reference station in a convenient location some six kilometers from the beacons. The original Integrity Beacons produced a short-range “bubble” of usable signals. While this was sufficient to demonstrate the IBLS concept, a longer-range beacon would have additional applications. To this end, we constructed an Autonomous Integrity Beacon with a range of greater than four kilometers, using a pulsing scheme similar to that recommended by RTCM-104 to alleviate the near/far problem. Flight tests showed that this long-range beacon provided useful information to IBLS everywhere within its expanded bubble, without blocking satellite reception by IBLS or conventional GPS receivers.