Method and apparatus for detecting and decoding transponder reply signals

Abstract

Methods and apparatus for detecting and decoding transponder reply signals of the type having a plurality of associated time discrete pulses including two bracket pulses and a number of related data pulses that may have been transmitted at discrete data time intervals between the bracket pulses such that the signal content detected during the data time intervals corresponds to the reply signal data code, comprising receiver means for receiving the reply signals and producing in-phase (I), quadrature (Q) phase and video (V) signals for each received pulse; means for detecting received pulses and storing the I/Q/V signals in a first memory; means for storing in a second memory pointer values that correspond to the temporal location of pulse I/Q/V signals in the first memory; means for identifying, based on time of arrival (TOA) values, pairs of potential bracket pulses wherein each pair marks the beginning and end of a reply code; and processor means for 1) determining an angle of arrival (AOA) value for each detected pulse based on each pulse's I and Q signals, 2) selecting a reference pulse for each potential bracket pair based on relative amplitudes of the bracket pair, and 3) identifying data pulses, associated with the reply signal and detected between occurrence of the bracket pulses, based on the reference pulse to provide the reply code. Such apparatus also provides for a determination of confidence factors relating to each detected pulse and each data value assigned to a data time interval of the reply code. Such apparatus further provides for pulse sharing, pulse claiming, reply code modification and false reply identification and deletion.