In the communications system, the proportion of base-band signal is often an effective band of the spectrum with low frequency components, such as direct transmission channel, it will seriously affect the effectiveness of signal transmission and reliability. Therefore not suitable for direct transmission. In communication systems usually require the transmitter modulation process, the removal of the signal spectrum to the desired position, so that suitable channel into the modulation signal transmission. The receiving end in the demodulation process is required in order to restore the original useful signal. Modulation and demodulation process often determines the performance of a communication system. With the digital waveform measurement technology and the development of computer technology, you can use the method of digital modulation and demodulation process. At the same time, modulation can also improve performance, especially the anti-interference ability, as well as better use of bandwidth.
This design mostly multiplied a carrier signal and a signal of sidebands of suppressed by multiplication sign to carry the spectral. To resume the barbarism signal by carrying the spectral of the modulated signal.For this mode of demodulation,having a good ability of demur Noise and Molest,a good validity power and so on.
Key words: Modulation, Demodulation, Base-band signal, Modulation signal