This paper first addresses the problem of known signal detection over both Rayleigh and Nakagami fading channels. More specifically, it studies the effect of different diversity schemes as a remedy to improve the probability of detection. Maximum ratio combining, selection combining, and switch and stay diversity schemes over Rayleigh fading channels are investigated. Closed form expressions for the average probability of detection for no diversity and diversity cases are obtained. The second part of this paper deals with both generalized likelihood ratio and uniformly most powerful tests for unknown-signal detection over Rayleigh fading channels. For this purpose, a simple decision criterion assuming only the knowledge of the noise power spectral density and the signal bandwidth is provided.