Abstract: Mode S signals are exposed to heavy A/C fruits when used in multilateration and ADS-B systems. Current decoding methods will lead to many decoding errors and low confidence declaration. Mode S decoding techniques are introduced in this paper. There are center amplitude method, baseline multi-sample technique, multi-sample technique with table lookup technique and reduced table lookup technique. The overlapping probability on 40,000 fruit per second is analyzed, then a method is proposed to simulate true jamming environment. Finally, effects of algorithms are evaluated by a great of decoding experiments. High decoding accuracy in experiments shows that these methods are very effective.