How the L-DACS2 Radio-Frequency signals modulation affects the DME performance

In this paper, we consider the Radio-Frequency Compatibility (RFC) of a candidate system within future aeronautical communication infrastructure, being developed since 2004 to accommodate the evolution of the aeronautical environment. The system presented in this paper is one of the two preselected proposals for the L-band Digital Aeronautical Communication System (L-DACS), in charge of the continental communications. It is named L-DACS2 and will use the 960 to 1164 MHz band, allocated to the Aeronautical Mobile Service reserved for communications relating to safety and regularity of flight. This band is characterized by a very dense spectral occupation by a large number of aeronautical systems. The RFC (branch of electrical science that studies the coexistence of radio systems in the same electromagnetic environment) is very important for L-DACS deployment and if it is not satisfied, the flight safety could be endangered. We propose to study in this paper the impact of the LDACS2 on the Distance Measuring Equipment (DME), which has been using the L-band for decades. According to recent studies performed in the frequency domain (continuous transmissions and no time domain variations), the achieved RFC level seems insufficient. The objective of this work is to analyze the RFC between LDACS2 and DME considering the time domain aspects of both systems. The idea is to quantify the impact of the radio-frequency signals generated by L-DACS2 interferer (transmitter) on the performance of a DME victim (receiver). The study is performed for the co-site case (equipments onboard of the same aircraft). To study the RFC between the two systems, we investigate various modulations for the future communication system. The results are obtained through computer simulations and laboratory measurements with an aeronautical test-bed using a commercial DME unit. The DME performance degradation is evaluated for some values of the Signal to Interference Ratio.