Development of Multipath Error Budgets for JPALS Ground Station Receivers

The Local Area Augmentation System (LAAS) is the Federal Aviation Administration's ground-based augmentation system (GBAS) for local-area differential Global Positioning System (DGPS). It will support all categories of precision approach. LAAS is currently under advanced development and specification. The purpose of this paper is to provide an update on the LAAS program strategy and a technical description of the LAAS. The LAAS program involves a government-industry partnership, specification of the Ground Segment, and FAA in-house development of a test prototype containing all of the LAAS features. The technical section contains both top-level and intermediate-level descriptions of LAAS, with emphasis on the Ground Segment. Three distinguishing advances are described in more detail: multipath limiting antenna, airport pseudolite, and a method for transforming integrity parameters from the pseudorange domain to the position domain.

The Federal Aviation Administration (FAA) is investigating the feasibility of using the Global Positioning System (GPS), together with local augmentation as the primary navigation system for the Category II and III precision approach of aircraft. This augmented system would be known as a local area augmentation system (LAAS) because it would place subsystems on the ground at or near an airport to greatly enhance the performance of airborne GPS receivers approaching that airport. The LAAS would complement space-based augmentations of GPS, such as the wide area augmentation system. When complete, the integrated system will meet stringent requirements on accuracy, integrity, continuity, and availability. Indeed, the LAAS will improve the airborne accuracy from approximately 100 m for stand-alone GPS to better than 1 m. This high accuracy is required so that LAAS can guarantee the integrity and continuity of the aircraft guidance during the approach phase of flight. Integrity requires the LAAS to detect any situations which threaten the safety of the landing, and notify the aircraft within 2 s of such a threat. Continuity is a competing consideration-it requires that the total number of alarms, true plus false, sent to the aircraft is very small. High continuity guarantees that the total number of aborted approaches is manageably small. Finally, availability is the fraction of the time during which LAAS is operational-providing position fixes with the specified accuracy, integrity and continuity. This paper describes the LAAS which has been proposed by the FAA. It discusses the fundamental operation of the LAAS.

Some deficiencies of the system of exciting satellite navigation augmentation are analyzed in the application of civil aviation. Since there is no local monitoring in Wide Area Augmentation System (WAAS), the protect level is increased, and the availability is reduced, so it could not satisfy the requirement of the precise approach. Moreover, because the Local Area Augmentation System (LAAS) could not solve the problem brought by ionosphere storms, the LAAS certification becomes complex and expensive. The basic principle of the new satellite navigation augmentation system named Local Airport Monitor (LAM) proposed by Federal Aviation Administration (FAA) is introduced. And the error distribution characteristic of LAM is discussed by sorting three conditions. Moreover, the expressions of LAM protection level and availability are studied. Some conclusions are obtained by simulations. In normal condition, the position accuracy of LAM is better than the one of WAAS and similar to LAAS and the availability of LAM is better than the one of WAAS and worse than LAAS. When there are ionosphere storms, the position precision and availability of LAM and WAAS reduce a little, but the position precision and availability of LAAS reduce 20.5% and 19.3% respectively. Furthermore, the availability of LAM is analyzed and simulated. And some conclusions are obtained: airborne user should first choose satellites whose elevation is lower than 10 degree and bigger than 70 degree. Reference station and airborne should use GAD-A and AAD-B receiver respectively, thus, the availability of LAM could bigger than 99.99%

The Runway Incursion Prevention System (RIPS) program is an ongoing National Aeronautics and Space Administration (NASA) research effort intended to reduce the number of runway incursions at airports throughout the National Airspace System (NAS). The RIPS program flight tests and demonstration of technologies activities at the Dallas/Fort Worth (DFW) International Airport were completed in October 2000. The demonstration involved the application of both airborne and ground based technologies, as well as the integration of these technologies to form a complete runway incursion prevention system. This paper presents information on the research activities conducted at DFW related to the Ohio University Avionics Engineering Center (AEC) installed Global Positioning System (GPS) Local Area Augmentation System (LAAS) ground facility (LGF), it's use, the preliminary results obtained, and observations or conclusions when appropriate. A description of the RTCA DO-247 Surveillance and Guidance Sensor requirements is provided. Details of the DFW LAAS upgrade for NASA RIPS testing, AEC GPS LAAS test van equipage, and the Rockwell Collins Multimode LAAS receiver integration activities are presented. Data analysis activities have just been initiated.

: Shipboard-relative GPS (SRGPS) is a variant of the Joint Precision Approach and Landing System (JPALS) that is being developed to support automatic shipboard landings in zero-visibility conditions. At present, the navigation system requirements specify a vertical protection level of 1.1 m, an integrity risk of approximately 10−7, and a system availability of at least 99.7 percent. Because of the stringent nature of these specifications, differential carrier-phase solutions are being pursued. In this context, this paper gives a detailed analysis of the fault-free integrity and availability of SRGPS. The performance of single- and dual-frequency architectures is evaluated for both floating-ambiguity and fixed-integer carrier-phase differential GPS (DGPS) navigation. The sensitivity of SRGPS availability is quantified with respect to raw code and carrier measurement quality, spatial decorrelation of ionospheric and tropospheric errors, and broadcast service radius. Necessary conditions to achieve the desired navigation performance are defined.

This paper quantifies the experimental measurements of aircraft carrier flexure (deformation) at sea in support of the United States Department of Defense sea-based Joint Precision Approach and Landing System (JPALS) that aims to deliver automatic landing capabilities to inbound aircraft aboard aircraft carriers. The methodology for measuring ship flexure using the Global Positioning System (GPS) and inertial sensors is described. Results indicate that flexure on the aircraft carrier used for testing has a standard deviation of approximately 1-2 cm. For the ship tested, the most significant flexure effects are in the port/starboard direction and correlate best with roll or lateral acceleration.

This paper addresses topics concerning the development of future Unmanned Aerial Vehicles (UAV) so that they can operate safely within the community of the Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO). Studies by the Defense Science Board; the Office of Science and Technology; Government Accountability Office; and the Congressional Research Service: Library of Congress; have all emphasized that soon there will be a significant number of UAVs operating sideby- side with manned civil aircraft in the FAA’s National Airspace System (NAS). It is anticipated that future UAVs will start to perform many of the dull, dirty, and dangerous civilian missions. In 2006, about 600 UAVs are expected to be manufactured in the US alone. Therefore, there is an urgent need for developers of UAVs to understand safety certification for operations in the NAS, and that safety certification starts with the safety requirements; safety design; safe development process; safety verification; and safe operating procedures in the planned operational environment. This paper presents and discusses the experiences and lessons gained by the authors on the development of end-toend aviation safety; from the safety requirements to their final safety certification in the planned operational environment. The authors’ previous and ongoing works include the Global Navigation Satellite Systems (GNSS) systems such as the GPS; WAAS; LAAS; MSAS; GPS III; and different operational environments at different airports such as Incheon International Airport. The FAA started with the two traditional safety certifications processes: airborne system certification and ground system certification; governed mostly by Federal Aviation Regulations (FAR) and FAA’s Acquisition Management System (AMS), respectively. However, when FAA started to implement GNSS, the lines between airborne and ground systems became blurred, and as a result many current Communications, Navigation, Surveillance, and Air Traffic Management (CNS/ATM) systems have to follow both processes. We will also discuss the current Safety Management Systems being developed by both FAA and ICAO as an integrated, systematic, and harmonized approach and process to sort out the differing safety requirements from FAA, SAE-ARP, MIL-STD, RTCA, ASTM, ICAO, etc. to provide the eventual safe operations within the NAS. The discussion will then focus on the real world of institutional, operational, and technical issues for safety certification worldwide. Despite the numerous standards and guidance documents, many past safety analyses and studies were guided by best practices that had been used successfully in the past to streamline the process of providing all the required documentations and verifications. One such area is in the use of the “Integrity Panel of Experts” that had been used successful in the implementation of safety for the FAA’s Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS) programs. In many areas of the world, safety certification from a technical point of view is only the first step to achieving safety certification to fly in their national and sovereign airspace. Finally, we will show the first steps that UAV manufactures need to consider if they want their UAVs to be approved to fly safely in different national civilian airspace.

Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area augmentation system are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite system user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite system satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station.

The relationship between range-domain and position-domain errors remains an open issue for GPS augmentation programs, such as the Federal Aviation Administration's Local Area Augmentation System (LAAS). This paper introduces a theorem that guarantees a conservative error bound (overbound) in the position domain given similarly conservative overbounds for broadcast pseudorange statistics. This paired overbound theorem requires that a cumulative distribution function (CDF) be constructed to bound both sides of the range-domain error distribution. The paired overbound theorem holds for arbitrary error distributions, even those that are non-zero mean, asymmetric or multimodal. Two applications of the paired overbound theorem to GPS augmentation are also discussed. First, the theorem is employed to construct an inflation factor for a non-zero mean Gaussian distribution; in the context of a simulation of worst-case satellite geometries for 10 locations in the United States and Europe, the required inflation factor for broadcast sigma is only 1.18, even for biases as large as 10 cm for each satellite. Second, the theorem is applied to bound a bimodal multipath model tightly; the result shaves more than 40% off the previously established inflation factor derived through a more overly conservative analysis.

Synthetic vision has the potential to improve safety in aviation through better pilot situational awareness and enhanced navigational guidance. The technological advances enabling synthetic vision are GPS based navigation (position and attitude) systems and efficient graphical systems for rendering 3D displays in the cockpit. A benefit for military, commercial, and general aviation platforms alike is the relentless drive to miniaturize computer subsystems. Processors, data storage, graphical and digital signal processing chips, RF circuitry, and bus architectures are at or out-pacing Moore's Law with the transition to mobile computing and embedded systems. The tandem of fundamental GPS navigation services such as the US FAA's Wide Area and Local Area Augmentation Systems (WAAS) and commercially viable mobile rendering systems puts synthetic vision well with the the technological reach of general aviation. Given the appropriate navigational inputs, low cost and power efficient graphics solutions are capable of rendering a pilot's out-the-window view into visual databases with photo-specific imagery and geo-specific elevation and feature content. Looking beyond the single airframe, proposed aviation technologies such as ADS-B would provide a communication channel for bringing traffic information on-board and into the cockpit visually via the 3D display for additional pilot awareness. This paper gives a view of current 3D graphics system capability suitable for general aviation and presents a potential road map following the current trends.

In view of the problem of the long-term variation of code multipath error (called code multipath bias) in the IGSO and MEO satellite observable, code multipath bias of BDS is analyzed using iGMAS data of multiple earth stations. In addition, the GPS and BDS multipath error variation is analyzed comparatively. The results show that the variation of BDS multipath error is related to the elevation angle, satellite orbit type and carrier frequency, but independent with the location of the receivers. And for the carrier frequency B1, B2, and B3, the code multipath bias for MEO satellite is 1.66, 1.05 and 0.53 m, respectively. For IGSO satellite the code multipath bias is 0.65, 0.44, and 0.31 m accordingly, which are smaller than that reported by earlier papers. Especially, for IGSO at frequency B2 and B3, the code multipath bias is smaller than half of that reported earlier. At the same time, in order to reduce the multipath bias, a two-order polynomial fitting algorithm is proposed in this paper. The results show that: compared with the results of piecewise linear model with 10 correction parameters, the two-order polynomial correction algorithm with three correction parameters can correct the multipath error and reduce the RMS of the multipath error more effectively. The two-order polynomial model in this paper is more convenient considering broadcasting the correction information to the users.

Regarding the problem of systematic multipath bias on BeiDou navigation system code observations, ten days BeiDou triple-frequency observations of multi-stations were collected, the relationships between the characteristic of multipath bias and the type of the satellite, the signal frequency and the satellite elevation angle were analyse d. In order to solve this problem, a modified sidereal filtering based on zero-phase filter was proposed to mitigate the multipath bias on GEO and IGSO satellites code observations, and elevation-angle correction method was introduced to decrease the multipath bias of IGSO and MEO satellite code observations. The experimental results show that the modified sidereal filtering can decrease the multipath bias of B1, B2 and B3 frequencies code observations for GEO and IGSO satellites over 17.0, 18.6 and 10.5%, respectively, and the elevation-angle correction method can reduce the multipath bias of IGSO and MEO satellite B1, B2 and B3 frequencies code measurements by 5.0, 6.8, and 4.1%, respectively. After mitigating the multipath bias of BeiDou code observations, the precision of single point position for east, north and up directions can be improved about 34, 45 and 51%, respectively.

Ground station receivers or networks’ location uses different geodetic datums. The geodetic datum defines size and shape of the Earth model and origin of orientation of coordinate systems used to map the Earth. They are modified to converge to the International Terrestrial Reference Frame (ITRF). The Thailand geodetic reference frame has been maintained by the Royal Thai Survey Department (RTSD); currently, it is based on GNSS permanent networks. Precise orbit and clock solutions, earth orientation parameters and tropospheric gradients are applied as fixing parameters to estimate station positions using a network approach where all station coordinates are simultaneously adjusted; defined as a zero-order network. They are determined with respected to ITRF with centimetre precisions and accuracies. The shape of the Earth varies over time due to oceanic tides and plate movements. Changing are more gradually when earthquakes and volcanic eruptions happen. ITRF and other geodetic datums are changing continually; therefore, frame transformations are required. The latest adjusted coordinates are based on ITRF2005, 2008 and 2014 frame and velocities are set at the epoch 2008.83, 2013.81 and 2021.93 respectively. Constraints are cast in form of transformation parameters. The grid shift is then generated to transform from global coordinate systems to local geocentric reference frames. GNSS measurements obtained from another set of ground stations are used as check coordinates. Transformed coordinates are at 1 centimetre-level of accuracy both horizontally and vertically at 95 percent confidence level. Coordinate transformations can be applied to map Thailand based on one map on one datum policy.

This paper describes the development, implementation and prototype test results of a broadband circularly polarized planar array antenna, operating at X-band. The antenna is intended for downlink implementation in the EROS series of LEO satellites. The antenna position is controlled by a two-axis antenna pointing mechanism (APM). It directs the antenna main beam towards the ground station. Antenna concept considerations and performance optimization-minded design processes are elaborated. The prototype measurement results are commented upon as well. The antenna main design goals were to achieve simultaneous broadband gain and low axial ratio operation within the structural constraints and facing the extreme LEO satellite open space environmental conditions. At the time of paper preparation, the first EROS satellite has been successfully launched. Satellite transmission signals, evaluated by the ground station receiver, confirmed successful antenna operation in open space. The measured performance matched that predicted by the design.

This simple channel simulation program is written using MATLAB to determine the influence of phase nonlinearity distortions on the bit error rate performance of BPSK signals transmitted through a satellite transponder and its ground station receiver. For simplicity, the channel is modelled as a cascade of two filters found in the IF section of the satellite transponder and ground station receiver. Coherent (synchronous) detection of the BPSK signal in the ground station receiver is assumed and the binary data is recovered using a sampling and threshold decision device. This simulation method has been applied to the UoSAT-12's Merlion bent-pipe transponder designed for 1 Mb/s BPSK data transmissions.