Patent ID: 7471235

Claim:
A Mode S transponder transmission signal decoder for decoding a Mode S transponder transmission signal transmitted by a transponder mounted on an aircraft, comprising: a differential processing unit which performs differential processing for the Mode S transponder transmission signal; an auto correlation arithmetic operation unit which performs an arithmetic operation of a degree of auto correlation between an increasing change rate and decreasing change rate of a power level in the signal which has been subjected to the differential processing; a pulse regeneration unit which specifies a position of a pulse in the signal which has been subjected to the auto correlation arithmetic operation processing and regenerates the pulse based on the degree of auto correlation and a standard of a Mode S signal, the degree having been obtained by the auto correlation arithmetic operation processing; a pattern selection unit which selects a pattern of the pulse, the pattern most closely resembling a pattern of the regenerated pulse, from patterns of pulses defined by the standard of the Mode S signal; a position synchronization unit which performs pulse position synchronization processing based on the selected pattern of the pulse; and a decoding unit which decodes the Mode S transponder transmission signal based on the pulse which has been subjected to the pulse position synchronization processing, wherein the position synchronization unit includes a correction value calculation unit which calculates a correction value of an error when the error occurs in a reference position in a case of selecting the resembling pattern of the pulse, and the pattern selection unit sequentially corrects the reference position based on the correction value.