能量检测法是一种比较简单的信号检测方法[1]， 属于信号的非相干的检测， 直接对时域信号采样值求模，然后平方即可得到；或利用FFT转换到频域，然后对频域信号求模平方也可得到。它无需知道检测信号的任何先验知识，对信号类型也不作限制。　
实际上，能量检测是在一定频带范围内作能量积累，如果积累的能量高于一 定的门限，则说明信号的存在；如果低于一定的门限，则说明仅有噪声。能量检 测的出发点是信号加噪声的能量大于噪声的能量。能量检测方法对信号没有作任何假设，是一种盲检算法。
此代码“利用FFT转换到频域，然后对频域信号求模平方”方法来实现对用户的检测。(In fact, energy detection is used for energy accumulation in a certain frequency range. If the accumulated energy is higher than a certain threshold, the existence of the signal is indicated. If the threshold is lower than the threshold, then only noise is indicated. The starting point of energy detection is that the energy of signal plus noise is greater than that of noise. The energy detection method does not make any assumptions about the signal, and it is a blind detection algorithm.

This code "converts the frequency domain into the frequency domain by FFT, then calculates the square of the square of the frequency domain signal" to realize the detection of the user.)