They do not occur in a decided frequency, but rather through a special modulation, the radio waves identity.
他们通常不发生在确定的频率，而是通过一个特定的调治，来确定无线电波。
2
AM radio can be sent over larger distances, but the quality of the sound is not as good as a later kind of radio signal processing, called frequency modulation.
调幅广播可以发送更远的距离，但它的声音质量却不及后来一种被称为频率调制的无线电信号处理方式优越。
3
The structure of receiver in typical modulation Impulse Radio Ultra Wide Band (IR-UWB) is discussed, and the best IR-UWB receiver on AWGN cannels is given.