Squitter

Abstract: An automatic dependent surveillance (ADS) system for tracking aircraft includes a GPS navigation receiver for determining the position of an aircraft, a Mode S transponder for transmitting the position of the aircraft, and a Mode S receiving station for receiving the aircraft's position and for determining the position of the transmitting aircraft relative to other aircraft and the ground. The Mode S position information is broadcast as a squitter on a random time basis having a present average transmission rate, or in response to an interrogation signal from a Mode S receiving station. The Mode S receiver can be another aircraft, an en route ground station, and/or a terminal ground station. The en route ground station can include a multi-sector receiving antenna with each sector connected to a separate Mode S receiver. The terminal ground station can include an omni-directional antenna connected to a Mode S receiver. The Mode S transponder transmits a formatted message having airborne or surface position information including the type of GPS signal used to determine the aircraft's position, the latitude and longitude of the aircraft, the barometric altitude of the aircraft, the magnetic heading of the aircraft, and movement characteristics of the aircraft. The Mode S data link can convey differential GPS correction information to the aircraft.

Abstract: A transponder-based beacon transmitter system in an unmanned aerial vehicle is provided. The transponder-based beacon transmitter system comprises a global positioning system interface communicatively coupled to receive position information indicative of a current location of the unmanned aerial vehicle, a message formatter communicatively coupled to the global positioning system interface, and a transponder-based beacon transmitter. The message formatter formats vehicle identification of the unmanned aerial vehicle and the position information indicative of the current location of the unmanned aerial vehicle into an automatic dependent surveillance broadcast mode-select squitter message. The message formatter operates in one of a military mode, a National Airspace System mode, and a combined military/National Airspace System mode. The transponder-based beacon transmitter transmits the automatic dependent surveillance broadcast mode-select squitter messages from the unmanned aerial vehicle. Receivers in the vicinity of the unmanned aerial vehicle receive unsolicited vehicle identification and location of the unmanned aerial vehicle.

Abstract: We present a general scheme for analyzing the performance of a generic localization algorithm for multilateration (MLAT) systems (or for other distributed sensor, passive localization technology). MLAT systems are used for airport surface surveillance and are based on time difference of arrival measurements of Mode S signals (replies and 1,090 MHz extended squitter, or 1090ES). In the paper, we propose to consider a localization algorithm as composed of two components: a data model and a numerical method, both being properly defined and described. In this way, the performance of the localization algorithm can be related to the proper combination of statistical and numerical performances. We present and review a set of data models and numerical methods that can describe most localization algorithms. We also select a set of existing localization algorithms that can be considered as the most relevant, and we describe them under the proposed classification. We show that the performance of any localization algorithm has two components, i.e., a statistical one and a numerical one. The statistical performance is related to providing unbiased and minimum variance solutions, while the numerical one is related to ensuring the convergence of the solution. Furthermore, we show that a robust localization (i.e., statistically and numerically efficient) strategy, for airport surface surveillance, has to be composed of two specific kind of algorithms. Finally, an accuracy analysis, by using real data, is performed for the analyzed algorithms; some general guidelines are drawn and conclusions are provided.

Abstract: A preemptive processor for a tactical collision avoidance system (TCAS) selects mode S squitter messages from closer airplanes on a priority basis. The receiver has a higher sensitivity level to receive squitter messages at greater ranges. The high-level squitter messages preempt the lower-level squitter messages. The preemptive processor can be implemented as part of a application-specific integrated circuit (ASIC).