LDACS1-Based Non-Cooperative Surveillance

Kurzfassung

In civil aviation, ADS-B is expected to become the primary surveillance technology. To ensure that accurate surveillance services can be provided even during possible ADS-B outages or when the localization of a non-cooperative aircraft is of interest, a backup system is required. Inspired by the recent advancements in passive radar technology, we propose to reuse the infrastructure and signals of the future L-band digital aeronautical communications system type 1 (LDACS1) to establish a non-cooperative backup surveillance application. LDACS1 is a multi-carrier system that uses frequency-division duplexing and is designed to operate in the lower part of the L-band. Its main advantage is that LDACS1 channels are placed in the spectral gaps between the channels of the distance measuring equipment - a legacy radio navigation system currently used in civil aviation. The LDACS1 surveillance functionality is enabled through the reuse of the forward link signals which are continuously transmitted by the LDACS1 ground stations. The emitted signals are reflected by aircraft in all directions toward the ground and can be picked up by dedicated surveillance receivers. An appropriate processing of the received reflections allows for the detection of the aircraft and estimation of its position on the ground. This implementation essentially mimics a passive radar system, where commercial transmitters are used as illuminators of opportunity to detect and estimate airborne targets. The main difference to the proposed surveillance technology is that transmitted signals can be readily made available at the receivers since the same infrastructure is used for both communication and surveillance purposes; in other words, there is no need to reconstruct the original transmitted signal at the receivers. The challenges associated with the LDACS1-based surveillance application arise from the relatively low transmit power and small bandwidth characteristics of the LDACS1 signal. This makes the practical implementation of such a surveillance concept challenging. It is thus of great importance to investigate and assess the suitability and limitations of the LDACS1 communication signals for passive radar detection applications.