Smoothed Concave Hexagonal Pulse Shape for DME Range Accuracy
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Solution Overview
Problem
Current Distance Measuring Equipment (DME) systems, particularly DME/N, face limitations in range accuracy and spectral density, leading to interference with adjacent channels when operating at high power, which restricts coverage and accuracy.
Innovation Solution
The implementation of alternative pulse waveforms, such as smoothed concave hexagonal, filtered asymmetric Gaussian, and smoothed trapezoidal pulse shapes, which maintain compatibility with existing DME specifications while providing higher range accuracy and minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Cos/Cos2 pulse shape is used for DME/P, then range accuracy is improved, but spectral density increases causing interference on adjacent channels and limiting transmission power to 100 Watts
Solution Approach 1:
The patent modifies the pulse shape parameters by using a Gaussian pulse with optimized rise time (1.5-2.0 μs) and fall time (2.0-2.5 μs) characteristics, combined with specific spectral filtering parameters, to achieve both high range accuracy and reduced spectral interference. This parameter optimization allows transmission at 1,000 Watts while meeting spectral density requirements.
Solution Approach 2:
The patent creates a composite pulse waveform that combines the time-domain characteristics of Gaussian pulses with the spectral properties of filtered waveforms. This composite approach integrates the fast rise time of Gaussian pulses (for accuracy) with spectral filtering (for interference reduction), achieving both objectives simultaneously.
2Power
If Gaussian pulse shape is used for DME/N, then transmission power can be maintained at 1,000 Watts, but range accuracy is reduced compared to Cos/Cos2 pulse
Solution Approach 1:
The patent optimizes the Gaussian pulse parameters by adjusting rise time to 1.5-2.0 μs and fall time to 2.0-2.5 μs, which improves the leading edge sharpness and thus range accuracy while maintaining compatibility with 1,000 Watt transmission power levels and existing DME/N specifications.
Solution Approach 2:
The patent replaces the Cos/Cos2 pulse shape (used in DME/P) with an optimized Gaussian pulse shape (used in DME/N), substituting one waveform mechanism with another that better balances transmission power capability with range accuracy requirements for en-route and terminal area navigation.
3Measurement precision
If faster rise time pulse is used to improve range accuracy, then spectral density increases limiting coverage area, but slower rise time reduces accuracy
Solution Approach 1:
The patent optimizes the rise time parameter to 1.5-2.0 μs, which is faster than conventional DME/N Gaussian pulses (2.5 μs) for improved accuracy, while combining this with spectral filtering to control the spectral density and maintain 1,000 Watt transmission power for adequate coverage area.
Data Source
AI summary
A method for measuring distance includes transmitting a first pair of RF pulses from an airborne interrogator, where the first pair of RF pulses are temporally separated from each other by a first time interval and each of the RF pulses in the first pair of RF pulses has a first pulse waveform. The method also includes receiving a second pair of RF pulses transmitted by a ground transponder. The RF pulses in the second pair of RF pulses have a second pulse waveform characterized by a smoothed concave polygonal function and/or a smoothed concave hexagonal function. The method further includes determining an elapsed time between transmitting the first pair of RF pulses and receiving the second pair of RF pulses and determining a distance between the airborne interrogator and the ground transponder based on at least the elapsed time.