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The Stretched-FrOnt-Leg (SFOL) pulse is a high-accuracy distance measuring equipment (DME) pulse developed to support alternative positioning and navigation for aircraft during global navigation satellite system outages. To facilitate the use of the SFOL pulse, it is best to use legacy DMEs that are already deployed to transmit the SFOL pulse, rather than the current Gaussian pulse, through software changes only. When attempting to transmit the SFOL pulse in legacy DMEs, the greatest challenge is the pulse shape distortion caused by the pulse-shaping circuits and power amplifiers in the transmission unit such that the original SFOL pulse shape is no longer preserved. This letter proposes an inverse-learning-based DME digital predistortion method and presents successfully transmitted SFOL pulses from a testbed based on a commercial legacy DME that was designed to transmit Gaussian pulses., Submitted to IEEE Transactions on Aerospace and Electronic Systems

Safety of air transportation strongly depends on the performance of on-board positioning sensors. Positioning by data from navigational aids is considered by international aviation community as one of the main stand-by positioning approaches onboard of civil airplanes. However, only positioning by pair of distance measuring equipment (DME) meets requirements of Performance-Based Navigation. A DME service volume model based on path loss between a pair of transmitting and receiving antennas has been proposed in the paper. The model takes into account the influence of relief on radio waves propagation and diffraction from high-altitude elements of relief. The proposed model has been used in the analysis of DME global network performance. In particular, performance of a global network is analyzed based on availability area of DME service, area of positioning by pairs of DME/DME support, availability of particular positioning accuracy, and areas of meeting various RNAV requirements. Obtained results indicate that only in 27.76% of global airspace a DME service can be provided. However, only within 15.9% of airspace, a DME/DME positioning can be used. Results of the analysis indicate about the necessity of actions for further development of global navigational aids network in order to guarantee safe airlines connections around the globe.

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.

In the context of GNSS L5/E5a interference environment dominated by DME/TACAN and JTIDS/MIDS pulses, RTCA DO-292 [1] proposes to implement a temporal blanker mechanism to mitigate the detrimental impact of the pulsed interference signals on the nominal functioning of a generic GNSS receiver. Moreover, RTCA DO-292 [1] also proposes a model to compute the received useful signal C/N_0 degradation due to the interference signals by increasing the noise power spectrum density (PSD) N_0, called the effective N_0, N_0_eff, where the N_0 increase is expressed as a function of the blanker duty cycle, bdc, and the equivalent noise level contribution of the nonblanked interference, E_I . However, the proposed computation of these two terms in RTCA DO-292 [1] makes some assumptions or neglect some effects which may decrease the final accuracy of the computation. On one hand, the collisions between pulses are not completely modelled. On the other hand, the effect of the time-domain blanker mechanism over the pulsed interference signal PSD is over bounded in RTCA DO-292 [1] by assuming a completely spread PSD over the Radio-Frequency Front-end (RFFE) filter bandwidth. In this paper, the pulse collisions effects are commented, and the true post-blanker pulsed interference signal PSD is introduced through the application of the spectral separation coefficient (SSC) with the local replica PRN code signal PSD to propose a new more accurate formula for the equivalent noise level contribution of the non-blanked interference. Moreover, the C/N_0 degradation formula is derived, and its limitations are pointed out. Finally, the new proposed formula is validated through simulations for a simplified DME/TACAN signal and for DME/TACAN signals in the US hot spot.

As an indispensable part of global satellite navigation system, the frequency band of DME will overlap with that of the navigation signal, which will cause the signal from the DME platform to be accepted by the Global Navigation Satellite System receiver and form interference. Therefore, it is of great significance to study an effective algorithm to suppress DME pulse interference. This paper has the following research on this problem. In this paper, wavelet packet transform is used to solve for the suppression of DME pulse interference method, wavelet packet analysis belongs to the linear time-frequency analysis method, it has good time-frequency localization characteristics and the signal adaptive ability, due to the function of wavelet packet and parameter selection of DME will affect the ability of interference suppression, combining with the theory of wavelet threshold, function type and decomposition series are discussed to prove the validity of the selected parameters on the pulse interference suppression.

Distance measuring equipment (DME) has been a cornerstone of aviation navigation for the last 70 years. While GNSS is taking an increasingly important role in civil aviation, DME can still play an important role in a robust aviation infrastructure in the foreseeable future. Advanced concepts have been developed to improve DME performance and capabilities. One concept is a DME-based pseudolite that position modulates existing DME pulse pairs. It is interoperable with DME operations and can be generated using the currently fielded DME transponders with an applique. This concept is suitable as a robust alternative to GNSS for aviation navigation or timing. The paper examines the performance of DME pseudolite implemented via an applique on a DME transponder. The paper examines the synchronization and data performance of the DME pseudolite signal in the air and on the ground. The paper compares the actual performance to theoretical results.

Antennas installed on aircraft are used for communications as well as for various radio navigation systems such as direction finders, distance measuring systems, and altimeters. Generally, these systems use blade antennas operating in the L frequency band. Recently, inverted-hat empty section monopole antennas have been found to be good candidates for such uses. In this study, we propose a new design of inverted-hat antenna based on optimized elliptical shapes and a filled cavity. The dielectric material added in the cavity helps to improve the monopole stability and to adjust the resonant frequency of the antenna. The proposed antenna meets the distance measuring equipment requirements, namely an omnidirectional radiation pattern in the H-plane, a vertical polarization, a frequency band from 960 MHz to 1.22 GHz, and a gain better than 1 dB. This antenna is entirely made of aluminum in order to obtain a homogeneity with the aluminum fuselage. In addition, the solution proposed brings a better protection against weather conditions. The antenna performance is analyzed on the basis of simulation and measurement results.

Introduction & Motivation: In this paper we propose a set of range-domain checks for DME fault monitoring. The proposed methods take advantage from previous measurements in order to build suitable statistical self-consistency tests. The tests are applied in batch to measurements coming from each visible DME station. The detection of ranging faults in radio-navigation system is one of the crucial features in order to enable reliable Safety-of-Life (SoL) services, which are mostly required in aviation operations. For NavAids-based operations providing integrity is still an open challenge as witnessed by the activities carried out in SESAR WP10 APNT and EUROCAE WG-107. Unlike GNSS, where integrity is hard to monitor at satellite level, for NavAids (like DME) it is more practical to implement integrity checks on the ground. Executive monitoring is implemented directly at the transponder, on the ground, and allows to directly shut-down a ground station if a fault is detected in the transmission stage. This level of monitoring is useful in preventing signal-in-space (SiS) faults, but it does not prevent ranging errors that stem from propagation phenomena. Among the possible error sources affecting the signal propagation, that of multipath is surely one of the biggest challenges for aviation SoL applications (Schneckenburger, 2018). Previous work suggests several approaches in order to provide integrity services with DME. Some of them requires IRS to be available on-board (Crespillo, 2017) while others are enabled by system modifications for ground and/or aircraft (i.e. eDME)(Li, 2013). Despite, the promising performance achieved by these works they require significant hardware modification or the presence of specific sensors on-board which might not be te case for all aircrafts. The development of range-domain monitor is a crucial step in the development of navigation services with integrity, based on NavAids. In particular the detection of multipath-related faults is of interest. Moreover, the implementation details must be accommodated in the overall integrity budget. In light of these facts we propose two range self-consistency checks, both of which are simple enough to be implemented in any FMS. Methodology: The proposed methods are aimed to the identification of step and ramp types of fault characteristics of multipath propagation. It is assumed that faults will bias the measurements while the variance will remain unchanged. Under nominal behavior DME range errors are normal distributed with zero mean and standard deviation 0.05 NM (one sigma) (ICAO, 2008). The large variability of the range measurements, compared to the relatively smooth airplane motion, impose some constrains in the definition of suitable test statistics. Consequently, performing a test directly using previous samples versus the new measure might not be a consistent check due to large variability of the data. Range Domain Tests: We propose using a smoothed range prediction as a refence to be tested against the new measurement. The idea behind is to remove the noise component from the sequence of previous measurements in order to reduce the variability on the reference term. One is a snapshot method, while the other is based on a batch of measurements. Snapshot Test: Generate a prediction exploiting the previous ranges (smoothing). Then the test is defined as the normalize difference between prediction minus measurements. The test follows a normal distribution with unitary variance. Under null hypothesis (H0, no fault) the test has zero mean, while in case of faulty measurement (H1 hypothesis) the test is biased. An appropriate threshold will then define the two decision regions. Sequential Test: For a sequential test, we use the sum of individual normalized squared difference between prediction minus measurements over a time window. Since the residuals are Gaussian distributed the test will follow a Chi-square distribution with degree of freedom equal to the size of the time window N. Under null hypothesis (H0, no fault) the test follows a central Chi-square, while in case of faulty measurement (H1 hypothesis) the test follows a non-central Chi-square. An appropriate threshold will then define the two decision regions. Analysis: In this paper we are going to consider two kind of faults, steps and rumps. Different values for the amplitude and the duration of the faults are will be presented. In the analysis we will consider the nominal DME accuracy as well as the measured accuracy reported by (Lo, 2013; Harris, 2012). We will also present an analysis using different smoothing techniques with different smoothing parameters (e.g. weights, smoothing time, etc..). Preliminary Results and Conclusions: The preliminary results using range domain tests and simulated data show the ability of the snapshot method to detect anomalous steps in the measurements (in this simulation we injected a step fault with bias equal to 1000 [m]). Considering a probability of false alarm (Pfa) of 10^-5 and a probability of miss detection (Pmd) of 10^-5 the simulation suggests a minimum detectable bias of 810 [m]. The sequential test is currently under evaluation. We expect the results to confirm the ability of test in detecting ramp-type faults. The proposed monitors represent fundamental building blocks in the development of integrity operations based on NavAids. The ability of detect steps and ramps is particularly useful for the detection of multipath. In addition, the implementation details will be presented and can be easily integrated in an integrity budget. References: Berz, G. (2013). Can Current DME Support PBN Operations with Integrity? In Proceedings of the 26th International Technical Meeting of the ION Satellite Division, ION GNSS+. Crespillo, O. G. (2017). Detection of DME ranging faults with INS coupling. Integrated Communications, Navigation and Surveillance Conference (ICNS). Harris, M. (2012). Performance of Current Distance Measuring Equipment and Implications on Alternative Position Navigation and Timing for Aviation,. Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN. ICAO. (2008). Performance-Based Navigation (PBN) Manual ICAO DOC 9613. Li, K. (2013). Robust DME Carrier Phase Tracking under Flight Dynamics. Proceedings of the 2013 International Technical Meeting of The Institute of Navigation. Lo, S. (2013). Distance Measuring Equipment Accuracy Performance Today and for Future Alternative Position Navigation and Timing (APNT). Nashville, TN: Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013). Schneckenburger, N. (2018). Characterization and Mitigation of Multipath for Terrestrial based Aviation Radionavigation. J Inst Navig.

L-band (960 to 1164 MHz) Digital Aeronautical Communication Systems (LDACS) is a promising technology deployed to face the challenge of saturating Very High Frequency (VHF) (118 to 137 MHz) spectrum and spectrum congestion. Interference mitigation in LDACS from the interference caused by existing users is extremely important considering the safety of the aircraft. This paper proposes LDACS receiver prototype which employs a linear clipping method, known as deep clipping to reduce the interference from the legacy user Distance Measuring Equipment (DME). The performance of deep clipping is compared with the conventional pulse blanking, clipping and joint clipping blanking methods. The reduction in bit error rates (BER) of received signal with the employment of deep clipping and the comparison of same with conventional methods are done in Matlab. The simulation results disclose that deep clipping and joint clipping blanking outperformed the conventional clipping and blanking method. Also deep clipping has the best performance for optimum depth factor than other non linear preprocessors.

BeiDou Navigation Satellite System (BDS) B2 signal works in the aeronautical radio navigation services (ARNS) band. It suffers high-power pulse interference, particularly from distance measuring equipment (DME), which will affect signal acquisition, signal tracking, as well as positioning of airborne BDS receiver. Regarding the problem, a DME pulse interference mitigation algorithm based on FLOC-TDE (Fractional Lower Order Covariance-Time Delay Estimation) is proposed in this paper, which can effectively mitigate DME pulse and retain useful BDS satellite signals. We firstly analyzed the live data collected from COMAC (Commercial Aircraft Corporation of China Ltd) Airborne BDS First Flight Project. And then, experiments on COMAC airborne BDS experiment platform were performed. The proposed algorithm, time domain pulse blanking algorithm and non-mitigation algorithm were compared in the experiments. The values of correlation peak to secondary peak ratio (CPSP) and the correlation peak to mean peak ratio (CPMP), and carrier-to-noise ratio ( C / N 0 ) using the proposed algorithm were the biggest. The results verify that the proposed algorithm can mitigate DME pulse interference, improve acquisition and tracking performance of airborne BDS receiver, which can ensure the system integrity.

As the Federal Aviation Administration (FAA) moves to a Global Navigation Satellite System (GNSS)-centric navigation strategy, the agency has not refreshed their legacy Ground-Based Navigation Aids (NAVAIDS). These NAVAIDS include Instrument Landing Systems (ILS) and Distance Measuring Equipment (DME) providing precision all-weather landing services, Very High Frequency Omni-directional Range (VOR) and DMEs providing traditional en route airways and Standard Instrument Departure/Arrival Route (SIDs/STARs) procedures, as well as DMEs operating in DME-DME networks supporting NextGen Performance Based Navigation (PBN). The legacy NAVAID fleet provides a vital role in providing GNSS resilient navigation services to Civil and Military users within the National Airspace System (NAS). The FAA faces continued supportability issues and declining availability due to the age of the legacy NAVAID fleet, directly impacting the ability of the FAA to provide navigation services in the event of a major disruption to GNSS services. A major obstacle in refreshing the NAVAID fleet is the cost of qualification and implementation of new equipment for operation within the NAS. The FAA can greatly accelerate the time to implement while simultaneously reducing the acquisition costs by using Commercial Off-The-Shelf (COTS) or Non-Developmental Item (NDI) acquisition strategies. With a COTS based acquisition strategy, the Government would seek to minimize or eliminate custom engineering, eliminate creation of Government specific documentation including manuals and training materials, and maximize use of Original Equipment Manufacturer (OEM) design documentation, safety analysis, and logistics processes and procedures. These strategies have been successfully employed by the majority of Air Navigation Service Providers (ANSPs) to reduce costs without compromising safety or quality.

Navigational aids network is an important component of a modern air navigation system which supports airplane navigation in airport areas by standard schemes and provides stand-by positioning capability for scenarios of primary on-board positioning system lock or malfunction. In the paper we consider a navigational aids network of each Air Navigation Service Provider (ANSP) within European airspace to provide overall configuration analysis. A network of Distance Measuring Equipment (DME) is analyzed based on the impact of particular ground transponder on positioning performance. An amount of DME pairs and impact of each transponder into the effective area of RNAV1 are used as criterions for configuration analysis of the network. The service area of navigational aids network is estimated based on the Standard service volume model of ground transponder. Also, we provide navigational aids network analysis based on graph theory. Navigational aids network is represented in the form of weighted graph to estimate centrality and betweenness for ranging network nodes. A graph of navigational aids includes edges between DMEs, which form pairs based on ICAO Doc. 1396 requirements. Obtained results of graph analysis help to identify service quality in the boundary area of the network. Graph analysis identifies network performance across European coastline, where DME service is limited. At the final stage, we provide an estimation of Horizontal dilution of precision coefficient to evaluate influence of the geometry of ground network configuration on positioning performance. Structure of each national network is composed in a different manner, due to variety of ANSP roadmaps and different periods of development that affect overall positioning performance. Obtained results of the analysis helps to highlight point for improvement in the development of European navigational aids network.

Ukrainian navigational aids network has a long history of deployment and development. Currently, navigational aids network includes ground equipment of Distance Measuring Equipment (DME), Very high-frequency Omni-directional Ranging (VOR), and Non-Directional Beacons (NDB). In our research, we would like to provide an overall study of navigational aids network configuration to specify the impact of particular ground station on the service provided. Common models of navigational aids are considered to estimate navigational aids availability and efficient pair forming in case of positioning by DME/DME and VOR/VOR. An area of correspondence to RNAV requirements is used as a criterion to estimate the impact of each navigational aid on overall network performance. Also, the navigational aids network is represented in the form of a weighted graph to estimate characteristics of centrality and betweenness for ranging network nodes. Configuration of Ukrainian navigational aids network is studied as an example. Obtained results are useful for a better understanding of navigational aids network configuration.

The LDACS 1 is an alternative to the current Very High Frequency (VHF) technology which meets needs of upcoming demands. LDACS 1, an Orthogonal Frequency Division Multiplexing (OFDM) operates in the L-Band between 960-1167MHz frequencies installed in the middle of two DME channels with 500 kHz spectral gap. In this paper, a LDACS 1 OFDM and LDACS 1 2x2 MIMO are designed and simulated without any interference. The Distance Measuring Equipment (DME) interference is introduced only to the LDACS1 OFDM, and significant degradation in the performance is observed. The pulse blanking technique helps in lowering the interference in the LDACS1 OFDM system, resulting in a performance close to the performance in the interference-free case. The BER performances for the conditions without interference, with interference and pulse blanking are compared. An improvement in the BER performance is seen with respect to design of LDACS 1 2x2 MIMO system.

The Federal Aviation Administration (FAA) Alternative Position Navigation and Timing (APNT) program developed several possibilities for improving distance measuring equipment (DME) such as DME pseudolite (PL) systems to provide data and passive ranging in addition to traditional DME operations. These enhanced DME (eDME) were designed to serve as an operational back up to GPS/GNSS, particularly to support future airspace and Next Generation Air Transportation System (NextGen) operations. While eDME concepts are not part of the current upgrades to the US DME system, there is continued interested in the ideas as they can support other airspace needs and help meet federal directives to increase the resiliency of Positioning, Navigation, and Timing (PNT) services [1].

One of the bigger challenges in providing ground-based navigation with integrity, to aviation users, is the ranging error due to multipath propagation. A particular flavor of the problem is sometimes referred to as “line-of-sight multipath”, which is a ranging error that appears when there is direct visual contact between the location and the ground station. To some this effect may seem counter-intuitive and the standard error model does not account for its existence. The conventional approach to modeling multipath in terrestrial ranging for aviation is the two-ray model. The current standard for Distance Measuring Equipment (DME) [DME_MOPS] accounts for a maximum of 100 m in ranging error due to multipath. The two-ray model does not explain line-of-sight multipath greater than 100 m, nor does it explain the numerous occurrences have been documented, where ranging errors far exceed this value. We understand this as evidence for the deficiency of the two-ray model. In our paper we will describe a modified approach to modeling terrestrial ranging errors due to multipath. The new approach differs from the standard method in that the underlying fault hypothesis is different. To understand the fault hypothesis it is useful to understand the four-component model proposed in [Schneckenburger]. This four-component model includes the following effects: a) Lateral multipath b) Ground multipath c) Occlusions d) Antenna misalignment In this approach lateral multipath refers to rays that are reflected without coherence, typically by virtue of having phase delays greater than the wavelength of the carrier. Ground multipath, on the other hand, refers to coherently reflected signals that cause electromagnetic interference and, therefore, erasure of the line-of-sight signal. In simplified terms the components b, c and d have the effect of reducing the power of the line of sight signal, thus making the receiver vulnerable to locking on to the strongest reflections from lateral multipath, which lead to faulted range measurements. Shortcomings in the Two-Ray Model Empirical evidence suggests that lateral multipath is impossible to prevent and is, in essence, always present in a ground-air channel [Schneckenburger,Osechas]. Thus the threat of ranging errors due to multipath stems from reductions in the power of the line of sight signal. A direct consequence of this observation is that the two-ray model is under-conservative, making it ineffective for integrity purposes. Our claim is substantiated by the existence of multipath-induced ranging errors greater than 100 m. Instances of such errors are known in France, Japan and Spain, but could well be more wide-spread than currently acknowledged. In our paper we will introduce a new approach to modeling multipath errors that accounts for lateral multipath in a new way. The conventional approach is to model the maximum ranging error for a given delay, assuming that the two-ray model is accurate. This does not account for situations where the line of sight power is reduced through destructive interference. A power drop in the line-of-sight signal, which can be caused caused by a single reflector, can open the floodgates for strong components of lateral multipath. For a given coherent reflector (i.e. ground multipath), the maximum possible power drop is usually large enough to attenuate the LoS signal below the reflections received from lateral multipath (non-coherent reflectors). Given that lateral multipath can occur anywhere, there is no reason why it would be bounded. In consequence, the ranging error due to multipath propagation is, for all practical purposes, unbounded. Again, this observation is consistent with the findings of our colleagues in France, Japan and Spain. A second consequence of the four-component model is that the worst-case ranging error due to multipath is not guaranteed to be detected by inspection of the received spectrum, at least not in a single snapshot. In the final paper we will substantiate this claim with a model-driven analysis of the worst-case ranging error. Monitoring the distortion over time, however, makes multipath errors observable. In the paper we will also present evidence to support this claim, based on equations, as well as measurement data from previous flight campaigns. It is important to note that some of the effects of Multipath on ranging errors are not specific to on technology. They may appear in DME signals as much as in other terrestrial ranging signals, such as the L-Band Digital Aeronautical Communications System (LDACS). In our approach we will focus on the changing transfer function of the multipath channel; as such we expect our results to work on a variety of terrestrial ranging systems. Outline of the Proposed Solution Distortion-based monitoring is effective against the aforementioned line-of-sight multipath, when observed over a batch of epochs. The fact that there errors exibit a particular phase relationships between the line-of-sight signal and the ground multipath form the basis of the proposed monitor.The basis of the monitor is that these errors occur under very particular phase relationships between the line-of-sight signal and the ground multipath. In this sense, the absence of distortion over a number of epochs gives a measure of certainty that multipath did not occur during those epochs. Similar to the approach in bounding multipath with a two-ray scenario we seek a bound on the worst-case situation. For that purpose we look at channel impulse responses and their respective transfer functions, to model the resulting ranging error. Using the changing of the channel over time we analyze the affected signals over time, assessing the likelihood that a particular batch of measurements is faulted by multipath propagation or not. This part of the work includes a theoretical model for the channel, both instantaneously and over time. Once we have established the worst-case error situation, we expect to transition from theory and simulation to real data. For that purpose we resort to several sets of channel-sounding data, collected in a variety of measurement flights, both in Germany [Schneckenburger] and in the USA [Osechas]. This data-driven analysis may not be critical in developing the fault model or understanding its implications. It will, however, give a feeling for the frequency with which pathological channel responses can be expected to occur in the environments that were tested. The sensitivity of the monitor depends on the nominal level of distortion, naturally encountered in situations that are free of multipath-induced errors. Currently ongoing work focuses on quantifying this sensitivity, both in terms of false positive detections and false negatives. References [DME-MOPS] EUROCAE: ED-57. Minimum Performance Specification for Distance Measuring Equipment (DME/N and DME/P) (Ground Equipment). October 1992. [Schneckenburger] Schneckenburger, Jost, Shutin, Walter, Thiasiriphet, Schnell, Fiebig: Measurement of the L-Band Ground-to-Air Channel for Positioning Applications. Transactions in Aerospace and Electronic Systems. [Osechas] Osechas, Schneckenburger, Pelgrum, Nossek, Meurer: Characterization of the Ground-to-Air Ranging Performance of the 960-1215 MHz ARNS Band Using OFDM Measurements in the 902-928 MHz ISM Band. Proceedings of ION ITM 2016, Monterey, CA.

Distance Measuring Equipment is included into the main list of on-board navigation equipment of civil airplanes. Current performance-based navigation considers DME as a primary sensor for stand-by on-board positioning equipment. During the cycle of range measuring, on-board DME interrogator interacts with a ground-based navigational aids network. Accuracy of range measuring depends on performance and workload of navigational aids network. Navigation signals of Distance Measuring Equipment use Gaussian pulse-pairs form, which does not support signal identification in the ground-based transponder. We propose an algorithm for identification of Distance Measuring Equipment interrogations with a particular air space user. Proposed algorithm is based on navigation signal amplitude detection, clusterization by mean value, and interrogation identification with airspace users located in the operational range of navigational aid based on range criteria. A method of maximal posterior probability is used for interrogation identification with a particular airspace user, which supports recognition with the highest level of probability. Proposed algorithm was integrated into a passive system based on two Software Defined Radios for navigation signal monitoring. Integration of proposed algorithm at the software level of secondary data processing system in the national navigational aids network makes possible to provide user-based service analysis in order to improve overall network performance.

Algorithms of positioning by navigational aids are widely used as an alternative to Global Navigation Satellite System on-board of large airplanes. Distance measuring equipment is a commonly used navigational aid for alternative positioning by a pair of measured ranges. Errors of range measuring are directly connected with airplane localization in airspace and have primary influence in airplane trajectory maintaining as well as ensuring the required level of air traffic safety. The impact of errors of on-board positioning system into aviation safety is represented in the paper. A mid-air collision category of aviation safety is assessed based on risk of airplane unintentional deviation from planned location due to influence of on-board positioning system errors. Represented approach is grounded on location of a bivariate probability density function at each airspace user location and estimation of a probability of getting two airspace users within the same safety region. Airplanes separation minimums are used as size of the safety region. Numerical demonstration is provided by live air traffic data shared by Automatic Dependent Surveillance-Broadcast message and received by Software Defined Radio within a part of Ukrainian airspace volume. Risks of mid-air collisions for each pair of airspace users are estimated.

Performance-based navigation is grounded on wide usage of a pair of Distance Measuring Equipment (DME) as one of the alternative positioning methods on-board of an airplane in case of primary system malfunction. The flight measurement system automatically detects the most optimal pair of ground equipment to support positioning with high performance. A variety of available algorithms of DME selection logic may increase workload of some elements of the navigational aids network, due to the limited capacity of each transponder. In the paper, we propose a passive system for interrogation rate measurements and statistical analysis of navigational aids ground network performance. The system includes two software defined radios. One of them is used for receiving and processing of interrogation signals with DME capacity estimation. Another one detects air traffic data by receiving and decoding messages under automatic dependent surveillance broadcast. The interrogation rate in channels of Ukrainian navigational aids network has been measured and reply efficiency was estimated.

The paper presents one of the possible approaches to assessing the effects of the construction of a logistics center in a selected location on the operational parameters of Distance Measuring Equipment (DME). When examining the impact of the logistics center on the operation of DME, at least two major negative factors were found. These factors include loss of signal due to shadowing and signal degradation due to multipath propagation.

Distance measuring equipment is one of the most frequently used Navigational aids in aviation. The rate of data transferring in communication channel of distance measuring equipment limits the capacity of navigational aid service. In the paper, we consider a queuing model of distance measuring equipment in order to estimate service capacity limits. A continuous-time Markov chain is used in a model for stationary equations. A reply efficiency of distance measuring equipment transponder and probability of losses in interrogations are studied for a different number of airspace users. Obtained results approve transponder usage to support distance measuring with capacity up to 100 airspace users with various operational modes of interrogators.

The L -band digital aeronautical communications system (LDACS) is a cellular air-ground data link for air traffic control. It is a cornerstone of the future aeronautical communications infrastructure. LDACS shall operate in the frequency band 960–1164 MHz under the constraint of secondary spectrum usage. This implies strict spectral, power, and spatial separation toward current legacy systems operating in this frequency band. It has been proposed to fulfil these restrictions using cell planning for LDACS without changing frequency allocations of the legacy systems. However, the feasibility of such a cell planning is yet to be demonstrated. In this paper, we demonstrate the feasibility of LDACS cell planning under these constraints. For this purpose, we introduce the theoretical limits for such a separation enabling the coexistence of LDACS and distance measuring equipment (DME: the primary user) system in the same frequency band. Closed-form expressions are obtained such that the proper operation of DME is not harmfully affected by LDACS. These expressions are utilized in the first step to find DME-compliant locations for LDACS ground stations. In the second step, interference constraints within LDACS itself are defined and applied. This approach yields DME-compliant locations of LDACS ground stations with channel assignments fulfilling the interference constraints. The application of our method shows that LDACS cell planning in Europe is possible without disturbing the proper operation of the DME system.

The L-band digital aeronautical communications system (L-DACS1) is subject to strong interference caused by distance measuring equipment (DME). For efficient statistical processing of interference, we adopt a Gaussian mixture (GM) distribution to model the impulsive nature of DME signals. Hence, we drive the parameters of the GM model in terms of properties of DME signals. This allows us to redesign the optimum receiver for mitigating DME interference. We also provide a simple pulse detector to estimate the presence of DME signals utilizing the null subcarriers of the L-DACS1.

This paper investigates the feasibility of the distance measuring equipment (DME)-based alternative position, navigation, and timing architecture using the recent advances on DME/N (normal) signal processing techniques; an improved DME/N pulse waveform and learning-based multipath mitigation algorithm. This paper evaluates the achievable DME range accuracy by using the advanced signal processing techniques, and provides the analysis on the required augmentation of ground DME stations in a selected test region in contiguous United States.

In this paper, we analyze the impact of interference on DME operations. DME is used in air traffic. We use Kalman filtering for this analysis. The Kalman filtering is a useful method for estimating the current and future state of the dynamic system. Kalman’s filter is optimal for linear dynamic systems. However, most systems are nonlinear. We present the possibilities of modeling the distance measurement by a navigational distance meter operating under disturbance conditions. Such operating conditions of the radio navigation distance measuring equipment are typical for their use in air transport.

Modern radio telescopes, like the proposed Square Kilometre Array (SKA), are extremely sensitive and the faint signals they receive can easily be contaminated irreversibly by stray radio frequency interference (RFI). Understanding how radio telescope performance is degraded by RFI is important. In this paper we describe an RFI simulation framework that can be used to generate test stimulus and verify a telescope’s performance. The framework can be used during design to investigate the impact of various RFI scenarios and develop mitigation strategies. As well, it can be used to exercise and test hardware firmware after a system is installed. A prototype of the framework was implemented in the Python computer language to demonstrate the key concepts. Additionally, we outline the framework requirements, describe a suitable software structure and discuss a prototype implementation. As well, we present measurements made to verify the software generates correct test stimulus, for RFI from aircraft distance measuring equipment (DME). The work described was carried out to evaluate the impact of RFI on the Square Kilometre Array, an international effort to build the largest most sensitive radio telescope.

An algorithm of positioning by navigational aids is a common stand-by approach on-board of aircraft in case of Global Navigational Satellite System fault. In paper we analyze implementation of alpha-beta-gamma filter in Kalman model representation to reduce noise in trajectory data of aircraft. We consider sensor noise filtration of Distance Measuring Equipment and VHF omnidirectional Range as an initial data processing and noise reduction at trajectory data processing. Multiple changes of navigational aids in pairs lead to pure noise filtration of distances and angles measurements. Noise filtration at top level provides better performance of trajectory data processing in comparison with sensor data filtration.

Existing VHF band based air-to-ground communication (A2GC) is suffering from severe congestion especially in Europe and the US where air-traffic has increased significantly in the last decade. To overcome this problem, a new L-band digital aeronautical communication system (LDACS) is being explored by ICAO. Recently, we proposed reconfigurable filtered OFDM based LDACS (Ref-OFDM) which has the potential to improve the spectrum efficiency of existing OFDM based LDACS. In this paper, we develop an experimental setup using universal software radio peripherals (USRPs) and analyze the performance of these two LDACS. The comparison is made in terms of interference to the legacy distance measuring equipment (DME) channels in L-band and BER for various channel conditions. Specifically, we analyze the performance by varying three parameters related to the LDACS/DME transmitter and receiver: 1) Altitude, 2) Distance, and 3) DME antenna gain. We also consider different channels such as Rayleigh fading channel (LOS path) and Rician channel (non-LOS paths). The proposed Ref-OFDM performs superior in all considered scenarios, and experimental results closely match the simulation results making Ref-OFDM based LDACS as an attractive alternative to the next generation LDACS.

To solve the shortcoming of the present method of pulse overlap calculation that the pulse stream must accord with the Poisson distribution, probability statistics method is used to construct a model to calculate pulse overlap probability based on the periodic characteristics of pulses in this paper. Using this periodic pulse overlap method (PPOM), we analyzed the interference in the time domain from Distance Measuring Equipment (DME) to Joint Tactical Information Distribution System (JTIDS) [4]. Compared with the present Poisson distribution method (PDM), PPOM is much more consistent with simulation than PDM especially when pulse stream does not correspond with Poisson distribution.

The aeronautical communication system has an influential role in future because the air traffic is increasing day by day. The Future Communication Infrastructure(FCI) for aeronautical communication is seeking for a better transmission scheme. As the demand for frequency spectrum for aeronautical communication is raising up, and the VHF spectrum utilization is almost saturated, FCI has developed two candidates for communication; L-DACS1 and L-DACS2 which are operating in L-band frequencies. These systems are inserted in L-band in an inlay approach. The majority part of L- band is occupied by DME(Distance Measuring Equipment) which induces interference to the communication candidates. So, for a better communication in L-band, we have to combat against the DME interference. Here presenting a survey on several methods to mitigate DME interference.

A method that estimates absolute aircraft position and velocity based on time-series of accumulated delta range measurements from distance measuring equipment (DME) ground transponders is analyzed. This method provides an Alternative Position and Navigation – but not quite Timing – system for use in airplanes as a back-up to a Global Navigation Satellite System such as GPS. The results show that a steady-state accuracy level better than 0.025 nm is achievable for the whole duration of a simulated flight trajectory with the tracking of four DME ground stations when aided by sporadic absolute range measurements. The system with only accumulated delta range measurements is challenged in low speed cases; however, this system exhibits convergence times of about 340 and 130 s, respectively, for an aircraft speed of 200 and 500 kn when tracking five DME ground stations.

The study presents a method of defining a mathematical model for dipole antennas with reflector. We employ functional matrix operators to provide a compact formulation of the radiation field computation problem for such antenna systems. We use an asymptotic correspondence between three-dimensional and two-dimensional problem solutions to design an antenna system for distance measuring equipment. Consequently, we propose a numerical technique for investigating the mathematical model; we use a non-linear objective function for optimising the excitation function of the antenna system.

RTCA, Inc.’s Special Committee 159 is updating its assessment of interference to GNSS in the 1164 – 1215 MHz band (L5/E5a) to support interference requirements for next-generation airborne GNSS equipment standards. These standards are now in development by RTCA and the European Organization for Civil Aviation Equipment (EUROCAE). The previous interference assessment was published in 2004 within RTCA document DO-292. One of the primary interference concerns for L5/E5a signal processing is from Distance Measuring Equipment (DME)/Tactical Air Navigation (TACAN) ground-based beacons. The assessment showed that at certain geographic locations an aviation user could observe multiple DMEs and experience aggregate pulsed interference with duty cycles in excess of 50%. This led to suggestions for aviation receiver implementation details such as more stringent radiofrequency (RF) filtering and pulse blanking. The purpose of this paper is to update this portion of the assessment with additional DME/TACAN modeling and actual flight and ground RF data collections. The GNSS RFI Environment Evaluation Tool (GREET) developed at MITRE is used to assess expected DME/TACAN interference at various flight altitudes across the conterminous United States. This tool has the capability to emulate deployed and postulated DME installations. It also simulates a representative aviation receiver and antenna design to assess the pulsed interference impacts. The paper evaluates the outputs of this tool against RF data collected during recent flight tests conducted on FAA flight inspection and test aircraft. These aircraft have been modified with top-mounted GNSS antennas with performance characteristics consistent with requirements expected in next generation aviation standards. The RF signals from these antennas were recorded digitally for replay in a laboratory environment and for RF spectral analysis to identify individual DMEs. Replay of these data sets was conducted with a NovAtel WAAS G-III reference receiver, which has the stringent RF filtering and pulse blanking mentioned above. The G-III receiver has a 24 MHz processing bandwidth, matching the widest receiver bandwidth currently envisioned for RTCA’s new dual frequency equipment standard. The blanking implemented in this receiver is configurable, allowing different threshold settings as well as no blanking to be evaluated. The testing with the G-III receiver also included a digitally filtered version of the recorded data to emulate signal reception with a 12 MHz processing bandwidth. This narrower bandwidth should reduce DME/TACAN interference and some receiver manufacturers have indicated an interest in the new standard supporting such a configuration. Lastly, the paper characterizes some interesting pulsed interference observed by the WAAS ground segment in the L2 and L5 bands. The WAAS network uses the G-III receiver mentioned above and many reference stations are located adjacent to DME/TACAN ground beacons and FPS-117 surveillance radars. The pulsed interference from space-based systems is also observable in the L2 band and is characterized and presented for general awareness.

Performance estimation of aircraft positioning system by navigational aids in three-dimensional space is proposed in the paper. Positioning system by pairs of Distance Measuring Equipment (DME/DME), Very high frequency Omni-directional Range (VOR/VOR) and their fusion (VOR/DME) is considered as stand-by approach on board of aircraft. Performance of positioning system depends on geometry of navigational aids location in space and technical characteristics of ground-based equipment. System performance analysis in tree-dimensional space gives possibility to estimate characteristics variation with altitude. Proposed approach divides investigated airspace into set of elementary cells for statistical simulation with iterative approach of performance characteristics estimation. Obtained performance levels are compared with area navigation specification requirements to detect gaps in service. Performance analysis of aircraft positioning systems in three-dimensional space by navigational aids was done for Ukrainian airspace.

The paper considers the task of accuracy estimation of aircraft coordinates detection using navigational aids data. Typical positioning methods and models of accuracy analysis by pair of Distance Measuring Equipment, Very high frequency Omnidirectional Range and their fusion were studied and compared with positioning by multiple navigational aids, available at the point of aircraft location. Based on positioning accuracy estimation, availability variations were investigated in the form of percentage of time to guarantee a certain accuracy level. Results of accuracy and availability estimation by different methods of positioning for a certain aircraft flight trajectory are represented.

Aircraft passive positioning by receiving radio signals of Distance Measuring Equipment (DME) together with processing data from Automatic Dependent Surveillance Broadcast (ADS-B) about surrounding air traffic is represented in paper. Interrogation messages of other aircraft are used with ground DME network reply messages to calculate Time Difference of Arrival and for further passive aircraft coordinates estimation by hyperbolic navigation method. Communication message transmission by ADS-B is considered as a source of DME interrogators location for relative navigation approach. Accuracy assessment of hyperbolic positioning takes into account uncertainty areas of DME interrogators location. Accuracy analysis is performed with computer-based simulation with live air traffic data.

In this paper, we investigate a relative positioning technique using the vehicle-to-vehicle communication signal. Specifically, we use the delay and Doppler information provided by the channel impulse response. Since the geometry of the vehicles has a direct impact on the delay and Doppler frequency, it is possible to deduce the relative positions of the vehicles. This particular relationship can be exploited by using prolate spheroidal coordinates. By doing an algebraic analysis in this coordinate system closed form solutions for delay and Doppler frequency can be derived. The delay and Doppler information is then used to determine the relative position similar to using the bearing and distance to a lighthouse in marine navigation or distance measuring equipment (DME) and VHF omnidirectional radio range (VOR) in aeronautical navigation.