Development of DSP algorithm for DME coherency measurement

Air traffic regulations do not specify the parameter of coherency for DME system ground beacons, however this attribute of signal has a large impact on possibilities of digital signal processing of the signal. For example, coherent signal might be used for Doppler frequency measurement or measurement of their immediate phase can be used for high resolution time measurement. Concerning DME this can lead to higher precision measurements of both radial length and radial speed of the airplane making the measurement. In this paper there is described one possibility of DSP algorithm, that can be used to evaluate coherency of DME ground beacon signal, or any impulse signal with analogical attributes to DME. For the development we use vector signal generator to generate as similar signal to DME as possible and the algorithm itself is implemented on FPGA device, which perfectly suits this application. Before this we evaluated the credibility of the algorithm with MATLAB simulations, results of which are also shown in this paper.