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In this article, we consider the performance of energy detection in composite multipath/shadowing fading environment. We also investigate the mitigation of the effect of these fading components on detection performance with the use of diversity techniques. Single channel, maximum ratio combining (MRC), square law combining (SLC), and square-law selection (SLS) diversities are analyzed using the rapidly convergent canonical series representation of Marcum Q-function with derivatives of moment generating function (MGF) of signal-to-noise ratio (SNR) of composite channel. On the other hand, the selection diversity combining (SDC) is analyzed using single integral of cumulative distribution function (CDF) of SNR. In all cases, we model the composite channel fading using the G-distribution which has been shown to be more accurate in representing the Suzuki and Nakagami-Lognormal distributions than K and KG and in closed formed compared to single integral expression for Rice-Lognormal distribution. Using this framework, we found out that the performance of energy detection does not degrade significantly at low and moderate shadowing conditions and that diversity detection greatly mitigates the effect of shadowing on detection performance with MRC giving the best performance, followed by SLC and then SDC or SLS depending on the average channel SNR, number of samples and level of shadowing. To the best of our knowledge, such a simple framework and resulting novel observations have never been reported before.