Evaluation of DME squitter coherency

Air traffic regulations do not specify the parameter of coherency for DME system ground beacons. However, this attribute of signal has a significant impact on possibilities of digital signal processing of the DME signal. Coherent signals are often used for Doppler frequency measurement or measurement of their immediate phase which are used for high resolution TOA measurement. In this paper, we focus on description of a DSP algorithm for DME squitter coherency measurement and its implementation in an FPGA device. The function of the testing receiver was simulated in MATLAB environment and subsequently implemented in the Xilinx Spartan 3A FPGA device. For initial evaluation we used a laboratory environment consisting of a signal generator as a DME squitter beacon.