Kuangmin Li

eDME architecture development and flight-test evaluation

Distance Measuring Equipment, DME, plays a crucial role in current and future aviation navigation. DME has good performance, wide-spread international coverage, decades of proven robustness, and dissimilar failure modes from satellite-based navigation systems. These characteristics reaffirm DME’s potential in current and future aviation Positioning Navigation and Timing (PNT). However, with the transition to Performance-Based Navigation (PBN) [1] the requirements for PNT become significantly more stringent. This warrants upgrades of the DME/N system to enhanced DME, or eDME. This paper presents various potential eDME architectures, proof-of-concept implementations, and flight-test results. Substantial DME performance enhancements can be obtained by evolutionary technology improvements, including increased number of transponders, more precise transponder timing and processing, increased transponder capacity, and modern interrogator technology. These improvements significantly enhance the DME system performance level beyond the currently specified 0.2 nmi total system ranging error [2]. An essential next step is the revision of the DME/N performance standards such that full credit can be taken for this improved performance. Further DME performance improvements can be obtained by more “revolutionary” advancements. The eDME concept is often associated with the addition of a UTC-synchronized “beat” signal broadcasted by the transponders [3], which will enable passive ranging (pseudoranging) and hence unlimited capacity, as well as the provision of time to the user. Data broadcast is generally also considered part of the eDME advancements. A dramatic performance improvement both in terms of accuracy and integrity can be achieved by DME carrier phase tracking [4]. Carrier phase tracking combined with pseudoranging enables a class of algorithms such as Pulse pseudorange Minus Carrier, Carrier Smoothed Pulse pseudoranging and Pulse-Noise-Multipath, which increases accuracy and simultaneously provides assurance for this performance. Robust, accurate, assured, and cost-effective time synchronization of a large number of DME transponder sites is not trivial. This paper presents DME-Next, an eDME architecture that does not require accurate time synchronization of the transponders. DME-Next is a combination of DME Carrier Phase, DME pseudoranging, and occasional two-way ranging that allows the receiver/interrogator to resolve the timing offsets between transponders. This proposed system dramatically improves the capacity of DME without the challenge of transponder time synchronization. Flight test results demonstrate the potential of this concept.

A non-uniform DFT-based batch acquisition method for enhanced DME (eDME) Carrier Phase: Concept, simulations, and flight test results

This paper proposes a novel batch acquisition method for eDME Carrier Phase based on non-uniform DFT. The theoretical false acquisition, failed acquisition, and wrong acquisition upper bounds are derived analytically and validated by Monte Carlo simulations. Actual flight test data recordings suggest the existence of substantial RF interference. Two algorithms are proposed to mitigate this interference. The resulting acquisition performance shows zero false and wrong acquisition and a very acceptable failed acquisition rate for the entire flight test.