Interception Probability versus Capacity in Wideband Systems: The Benefits of Peaky Signaling

Spread-spectrum techniques have found extensive use in broadband communications, both in military and commercial applications, for their low interception probability. However, it has been shown that these techniques prove ineffective on non-coherent fading channels with very large bandwidths since its capacity decreases with the increase of the bandwidth, eventually going to zero as the bandwidth goes to infinity. Peaky frequency-shift keying is a promising alternative modulation technique expected to achieve high data rates while maintaining a low interception probability. The current study explores such modulation techniques and outlines the conditions for which the reliability and capacity of the system increase while reducing the probability of interception compared to typical spread spectrum schemes. We show that peaky frequency-shift keying achieves a considerably higher transmission rate than non-peaky signaling for any given target level of interception probability, especially for outdoor fading scenarios in the low signal-to-noise ratio regime.