On the Energy Detection of Unknown Signals Over Fading ChannelsAbstract—This letter addresses the problem of energy detection of an unknown signal over a multipath channel. It starts with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature. Detection capability is boosted by implementing both square-law combining and square-law selection diversity schemes. Index Terms—Diversity schemes, energy detection, fading channels, low-power applications, square-law detector, unknown signal detection.