Multilateration of Demodulated Radio Signals

In commercial Air Traffic Control (ATC), voice communications between pilots and air traffic operators rely primarily on AM-modulated radio signals, mostly within the VHF frequency band. When multiple radio receivers operate at the same frequency but are located in separate places, this setup is known as Radio Coverage. During a pilot's radio transmission, the signal is received by multiple receiver sites at slightly different points in times, depending on the distance of the receiver site to the transmitter. Radio voice communications do not include any information about the location of the transmitter. To determine the location of the transmitter from the radio signals additional UHF/VHF Direction Finders can be used. (Wide Area) Multilateration is a well-known technique to estimate the location of a transmitter using multiple sensors at separate locations which receive the same transmitted signal, but at different points of time. The estimations of these time differences between the received and demodulated audio signals of separate receiver sites can be used to estimate the location of the transmitting aircraft in real-time. Compared to other surveillance applications, such as radar or ADS-B, which allow the precise determination of an aircraft's location, Multilateration of Demodulated Radio Signals shows a reduced accuracy in estimating the location of the transmitter. However, it can serve effectively as a backup mechanism or as a replacement for UHF/VHF Direction Finders. This paper discusses implementations of Multilateration of Radio Signals. The key for suitable implementations is the association of received and demodulated radio signals of different radio sites to a reference time frame. An implementation with digital radio receivers together with its realization is presented and discussed in detail. But for this implementation, which supports an estimation of a transmitter in real-time further investigations of the presented mechanisms will be necessary.