Alternative Positioning, Navigation, And Timing Research Articles

Enhancement of MF R-Mode ranging accuracy by exploiting measurement-based error mitigation techniques

Nowadays, the maritime sector strongly relies on global navigation satellite systems (GNSS) for the provision of position, navigation, and timing (PNT) information. The standard functionality of several ships’ bridge instruments depends on such information, which becomes critical to have a safe and reliable navigation. Nevertheless, the possibility of GNSS outages combined with unintentional and intentional interference to GNSS signals, which have been increasing over the last years, can severely threaten the nominal activity of the crew onboard of vessels. For these reasons, alternative position, navigation, and timing (APNT) systems become fundamental in order to provide operational continuity. R(anging)-Mode is a terrestrial alternative system to GNSS for the maritime domain. In one of its possible implementation, it exploits synchronized medium frequency (MF) signals transmitted by maritime radio beacons. In the MF band, the radio waves are attenuated and distorted by the change of electrical properties of the ground along the propagation path. Moreover, these signals are affected by terrain elevation changes and large metallic infrastructures which induce an overall loss in the accuracy of the system. In this paper, we propose a mitigation technique based on the estimation of these additional error sources by using in-field range measurements. The theoretical details are explained in depth and the technique is validated with real data gathered on a measurement campaign. A clear and significant performance improvement is achieved on the range accuracy when the proposed approach is applied.

Heuristic search for multi‐distance measuring equipment station selection

To support alternative positioning, navigation and timing (A-PNT), multi-DME with better geometry than distance measuring equipment (DME)/DME can be used to improve the performance. Different from the existing station selection methods that have been proposed for DME/DME, a station selection method for multi-DME should be considered in order to prevent unnecessary emission of navigation signals because DME receivers have limited number of channels and constrained real-time processing power, and also to limit DME to GNSS L5/E5a interference. A heuristic algorithm is constructed to determine the quasi-optimal selection of DME stations based on geometrical and computational cost restrictions, which is different from a brute-force method checking all possible subsets and selecting the best one. A station selection method for multi-DME is proposed based on the heuristic search. Meanwhile, the degradation of GNSS L5/E5a signal processing that is caused by DME signals is discussed. An advanced station selection method where the DME to GNSS signal interference is taken into account is also proposed. The experimental results show that the methods based on heuristic search can effectively select the quasi-optimal subset of DME stations with less computational expense.

Multi-DMEs for alternative position, navigation and timing (A-PNT)

AbstractDistance measuring equipment (DME/DME) as the main reversionary method provides alternative positioning, navigation and timing (A-PNT) services for use during a Global Navigation Satellite System (GNSS) outage. Considering the geometry limitation of DME/DME, multi-DMEs with better geometry can be used to increase the accuracy and integrity performance of positioning. This paper discusses the opportunities and challenges related to use of multi-DMEs as an alternate source of positioning, navigation and timing. To support the performance for A-PNT, the basic idea is considering the existing installed equipment. In this paper, barometer altimeter and TACAN are used to help improve the performance of A-PNT provided by multi-DMEs both in accuracy and integrity. Based on the database of EUROCONTROL, the test results demonstrate that 79⋅7% of a reference area roughly matching with the continental European locations achieve RNP 1 using multi-DMEs when the DME measurement accuracy is 0⋅2 NM (95%). When the DME measurement accuracy is 0⋅1 NM (95%), 87⋅9% of the reference area can achieve RNP 1 using multi-DMEs. The usage of barometer/TACAN measurements aided multi-DMEs improves the performance of the accuracy and integrity monitoring.

Automatic Dependent Surveillance‐Broadcast (ADS‐B) Universal Access Transceiver (UAT) transmissions for Alternative Positioning, Navigation, and Timing (APNT): Concept & practice

<h3>Abstract</h3> The vulnerability of Positioning, Navigation, and Timing (PNT) services derived from Global Navigation Satellite Systems (GNSS) makes having a resilient and accurate Alternative PNT (APNT) based on high-power terrestrial radio sources necessary. The L-band is very crowded spectral real estate with GNSS, Distance Measuring Equipment (DME) and Air Traffic Control Beacon System (ATCRBS) signals occupying the band from 900–1600 MHz. Thus, as getting new signal and spectrum for APNT would be difficult, we must leverage existing transmissions and infrastructure. The ∼660 Automatic Dependent Surveillance-Broadcast (ADS-B) ground stations in the United States represent significant infrastructure that can be leveraged for APNT. However, as ADS-B was designed for surveillance, it does not inherently possess features necessary to support APNT goals. This paper describes and demonstrates techniques for using ADSB Universal Access Transceiver (UAT) signals for PNT. We develop methods to use all ground UAT signals to provide robust, multi-frequency pseudoranges. We examine the ranging and positioning performance of the UAT signal on the ground and in flight, to demonstrate its ranging accuracy, and hence the timing and synchronization of the station. We demonstrate and analyze navigation using UAT signals, as well as the intra-system interference challenges of using multiple UAT stations.

Ranging Method for Navigation Based on High-Speed Frequency-Hopping Signal

The lack of sufficient spectral resources in many alternative positioning, navigation, and timing (APNT) systems for aviation has led to the problem of mutual interferences. Building APNT system with the cognitive radio and frequency-hopping (FH) techniques can resolve above problem, however, the main challenge is to achieve a long and high-precision range with high-speed FH signals. In this paper, we propose a novel ranging method called time–frequency matrix ranging (TFMR), which is based on the FH signals. Using the TFMR method, we built a jam-resistant APNT system to meet the accuracy and coverage requirements of aviation. We employed a dual-tone signal for the TFMR to estimate the pseudoranges between the ground stations and the aircrafts. One major challenge we faced was that what was good for ranging accuracy was bad for coverage. For example, increasing the dual-tone interval can improve the ranging accuracy; however, this led to a decrease in the unambiguous measurement range (UMR). To overcome this challenge, we employed different dual-tone intervals in different hops of the frequency-hopping signal. Finally, we formed a time–frequency matrix, so that a high UMR could be guaranteed without any harmful consequences on the ranging accuracy in the middle to high levels of the signal-to-noise ratio. The Cramer–Rao lower bound of TFMR is derived as the benchmark of the method. Using extensive simulations, we investigated the ranging performance of the TFMR method. The simulation results showed that the proposed TFMR could satisfy the APNT requirements of the Federal Aviation Administration.

국내 PBN 이행을 위한 대안 항법 적용 방안

한국은 성능기반항행 (PBN; performance-based navigation)으로 전환하기 위한 단계적 PBN 이행계획을 2010년에 수립하고 로드맵에 따른 새로운 비행절차를 개발 중에 있다. PBN 비행절차에는 GNSS (global navigation satellite systems), DME (distance measuring equipment), VOR (VHF omnidirectional range), INS (inertial navigation system) 등의 항행시설 (NAVAID; navigation aid)이 활용되는 것으로 되어있다. 그 중에서 GNSS를 이용한 PBN 업무제공이 중심을 이루고 있는 실정이다. 그러나 위성항법신호의 인위적, 자연적 간섭에 의한 취약성이 발견됨에 따라 세계 각국은 다양한 대안항법(APNT; alternative positioning, navigation and timing) 기술을 연구하고 있다. 본 논문에서는 GNSS 신호가 가용하지 않을 경우 기존의 항행시스템으로 지속적인 PBN 운항이 가능한지를 분석하였으며, 결과적으로 국내 일부 공항은 접근 단계 구역에서 대안항법의 구축이 필요한 것으로 나타났다. Republic of Korea has established its performance-based navigation (PBN) implementation plan in 2010 for ensuring a smooth transition to PBN operations and relevant new flight procedures are being developed in accordance with the roadmap. Various Navigation aids (NAVAIDs) like global navigation satellite systems (GNSS), distance measuring equipment (DME), VHF omnidirectional range (VOR), inertial navigation system (INS) are used to support PBN procedures. Among them, GNSS would play a central role in PBN implementation. However, vulnerability of satellite navigation signals to artificial and natural interferences has been discovered and various alternative positioning, navigation and timing (APNT) technologies are under development in many countries. In this paper, we study whether continuous PBN operations can be achievable without GNSS signals. As a result, it shows that some of the domestic airports require the construction of APNT in the approach area.

A Single Distance Measuring Equipment (DME) Station-Based Positioning System for Alternative Position Navigation and Timing (APNT)

A single station-based positioning system, known as Mosaic/DME, is introduced. This new system has been designed for the Alternative PNT (APNT) solution to air services as it acts as a backup navigation system in case of GNSS outage. The Mosaic/DME is a single station consisting of conventional DME and multiple pseudolites. The DME is operated using two-way round signals for range measurements, with pseudolites broadcasting one-way continuous signals for carrier phase measurements. The receiver in the aircraft receives both signals and calculates its own position after the ambiguity resolution process. In this paper, the feasibility of this system is studied via two topics: the performance of the navigation accuracy and ambiguity resolution using the weighted dilution of precision and Monte Carlo simulations. The results conclude that this system satisfies the required navigation accuracy of the APNT and yields a very fast and easy ambiguity resolution.

Design of a Passive Ranging System Using Existing Distance Measuring Equipment (DME) Signals &amp; Transmitters

The US Federal Aviation Administration (FAA) is developing alternative navigation concepts to maintain operational capacity and efficiency even with the loss of Global Positioning System (GPS). One concept being studied for alternative position navigation and timing (APNT) is a ground based passive ranging system. This system has few capacity constraints and can provide other benefits. The APNT passive ranging system would use existing FAA terrestrial infrastructure, particularly distance measuring equipment (DME) ground beacons. APNT project team has developed a DME Pseudolite (PL) concept that enables a passive ranging signal on DME that is compatible with existing DME operations. It can provide additional benefits for APNT and non-APNT users with its data transmission. This paper introduces the DME PL concept and assesses the potential performance of the system. The paper focuses on signal structure design for best data capacity. It formulates a methodology and modeling for the developing the design. Copyright © 2015 Institute of Navigation.

Performance analysis of the use of ADS-B for the alternative positioning navigation and timing

The global positioning system (GPS) is the core element of the next-generation communication, navigation, surveillance, and air traffic management (CNS/ATM) system. However, GPS signals are vulnerable to radio-frequency interference (RFI), which can significantly impact the normal operation of the CNS/ATM system. In order to maintain CNS/ATM system operation during GPS outages and to meet safety requirements, an alternative positioning, navigation and timing (APNT) based on a radio link of the automatic dependent surveillance-broadcast (ADS-B) can be used. This study first evaluates two navigation algorithms for an ADS-B radio link, and the real aircraft ADS-B data collected at the civil aviation authorized ground stations are used to evaluate the positioning performance of the proposed backup aviation navigation and surveillance system. In addition, the main factor affecting the positioning performance of the radio navigation system is the geometric distribution of ground stations. Therefore, the geometric distribution of the actual ADS-B ground stations in the CNS/ATM system is evaluated using horizontal dilution of precision for a specific flight information region. Overall, the results of the actual flight data show that it is highly feasible to apply the ADS-B radio link as an APNT solution.

Capacity Study of Multilateration (MLAT) based Navigation for Alternative Position Navigation and Timing (APNT) Services for Aviation

United States air traffic is anticipated to increase twofold over the next 15 years. To support those levels, the Federal Aviation Administration is implementing the NextGen. NextGen relies heavily on GPS. However, alternative position navigation and timing (APNT) systems will be necessary to allow users to navigate when GPS is unavailable. One alternative is to use multilateration (MLAT) using automatic dependent surveillance broadcast (ADS-B) signals (currently being implemented for surveillance). The APNT must be capable of supporting the full capacity of future airspace. ADS-B frequencies are shared amongst all aircraft and so MLAT has a finite capacity. Additionally, using MLAT for navigation involves changes from the surveillance MLAT that further stresses capacity. This paper models MLAT capacity for the two ADS-B protocols and uses the model to examine means of improving capacity. Results indicate methods of implementing MLAT that can increase capacity and make it a more viable APNT. Copyright © 2012 Institute of Navigation.

Assessing the Capability of Distance Measuring Equipment (DME) to Support Future Air Traffic Capacity

Alternative position, navigation, and timing (APNT) systems are needed by aviation to maintain operations for prolonged periods during an absence of Global Positioning System (GPS) service. This is especially important in the future as the Federal Aviation Administration (FAA) Next Generation Air Transportation System (NextGen) utilizes GPS to efficiently handle the anticipated twofold increase in air traffic over the next 15 years. Thus, an APNT system must be able to support the full capacity of future airspace. One candidate APNT system is distance measuring equipment (DME). Since DME has capacity limits, it is important to understand these limits and how they may be increased. This paper models DME capacity and uses the model to examine potential means of improving capacity. Results indicate that increasing DME station reply rate reduces availability for avionics at the current minimum operational performance standards (MOPS). However, with reasonable MOPS changes, DME could support anticipated air traffic levels. Copyright © 2012 Institute of Navigation.

GNSS 대안항법시스템 요구사항 및 기술 분석

The recent transition to Performance Based Navigation in aviation enhances the accuracy of aircraft position, safety and efficiency in air traffic operations by using satellite-based navigation system such as GNSS. However, intentional interferences with GNSS signal as well as ones coming from natural phenomena such as solar storm increase. GNSS have very low power and therefore their signals are more susceptible to interferences than ground-based navigation signals. This paper introduces requirements of alternative positioning, navigation and timing(APNT) system and relevant technologies when the GNSS signals are not valid.