Performance of a hybrid spread spectrum system against follower jamming

In a SATCOM system that uses frequency-hopping (FH) and frequency-shift keyed (FSK) modulation, an important jamming threat is one in which the jammer can follow the hopped frequencies. The jammer detects the current hop and transmits an interfering signal to the satellite before the satellite finishes receiving that frequency. Sufficiently fast hopping combats follower jamming and, in addition, combats frequency-selective fading. The error probability for a hybrid spread-spectrum architecture (frequency hop/direct sequence) in the presence of worst-case follower jamming is determined. During severe fading, a follower jammer turns out to be ineffective against the hybrid system because it cannot interfere destructively with a hop received by the satellite via multiple paths