Patent ID: 8102302

Claim:
An air traffic control system for processing a digital data stream containing a preamble and flight information data transmitted from an aircraft, comprising: a receiver for receiving digital radar signals from an aircraft, the receiver being arranged to provide amplitude and phase signal outputs; a signal splitter arranged to divide the amplitude and phase signal outputs from the receiver between an odd channel and an even channel that are arranged to carry a set of odd-numbered pulses and a set of even-numbered pulses, respectively; an odd channel data decoder connected to the signal splitter for extracting from signals encoded in the odd channel and forming an odd data stream an even channel data decoder connected to the signal splitter for extracting data from signals encoded in the even channel and forming an even data stream; a preamble correlator connected to the odd and even channel decoders for correlating the odd and even data streams with a predefined preamble mask and detecting potential valid preambles, the preamble correlator comprising; an odd channel amplitude correlator having a first input connected to the signal splitter to receive signals that indicate the odd channel amplitude and a second input connected to the odd channel data decoder to receive decoded odd signals, the odd channel amplitude correlator being arranged to produce an odd channel amplitude correlator sum signal; an odd channel phase correlator connected to the odd channel data decoder to receive signals that indicate the phase of odd channel signals, the odd channel phase correlator being arranged to produce an odd phase correlator sum signal; an even channel amplitude correlator having a first input connected to the signal splitter to receive signals that indicate the even channel amplitude and a second input connected to the even channel data decoder to receive decoded even signals, the even channel amplitude correlator being arranged to produce an even channel amplitude correlator sum signal; and an even channel phase correlator connected to the even channel data decoder to receive signals that indicate the phase of even channel signals, the even phase correlator being arranged to produce an even phase correlator sum signal; an odd channel differential phase detector in the odd channel between the signal splitter and the odd channel data decoder; an even channel differential phase detector in the even channel between the signal splitter and the even channel data decoder; and preamble decision logic arranged to process signals output from the preamble correlator and identify which of the potential valid preambles actually are valid.