第四章 模拟调制系统·1.引言一调制的定义一调制的分类一线性调制原理一非线性调制----角度调制一调制系统的比较（抗噪声性能分析和比较）－ FDM原理一总结一重点：调制系统的抗噪声性能
• 1. 引言 – 调制的定义 – 调制的分类 – 线性调制原理 – 非线性调制-角度调制 – 调制系统的比较（抗噪声性能分析和比较） – FDM原理 – 总结 – 重点：调制系统的抗噪声性能 第四章 模拟调制系统
1.调制的定义: Definition:A baseband waveform has a spectral magnitudethat is nonzero for frequencies in the vicinity of the originand negligible elsewhere.Definition:A bandpass waveform has a spectral magnitudethat is nonzero for frequencies in some band concentratedabout a frequency f- ±f,where f>>0.The spectralmagnitude is negligible elsewhere. f. is called the carrierfrequency.f may be arbitrarily assigned.Definition:Modulation is the process of imparting thesource information onto a bandpass signal with a carrierfrequency fc by the introduction of amplitude and/or phaseperturbation.This bandpass signal is called the modulatedsignal s(t),and the baseband source signal is called themodulating signal m(t)
• Definition:A baseband waveform has a spectral magnitude that is nonzero for frequencies in the vicinity of the origin and negligible elsewhere. • Definition:A bandpass waveform has a spectral magnitude that is nonzero for frequencies in some band concentrated about a frequency f= ±fc ,where fc>>0.The spectral magnitude is negligible elsewhere. fc is called the carrier frequency.fc may be arbitrarily assigned. • Definition:Modulation is the process of imparting the source information onto a bandpass signal with a carrier frequency fc by the introduction of amplitude and/or phase perturbation.This bandpass signal is called the modulated signal s(t),and the baseband source signal is called the modulating signal m(t). 1.调制的定义
Diagram of a typical modulation system.modulationm(t)s(t)ModulatorBaseband signalBandpass signalCarriercosoctLocalModulatingoscillatorsignalModulated signal
• modulation Diagram of a typical modulation system m(t) Baseband signal Modulating signal Modulator s(t) Bandpass signal Modulated signal Local oscillator cosωc t Carrier
: Bandpass communication systems(t)m(t)ModulatorchannelBandpassBaseband signalsignal noisecosoctCarrierLocalModulated signalModulatingoscillatorsignalm'(t)DemodulatorCorruptedCorruptedbaseband signalbandpass signal
• Bandpass communication system m(t) Baseband signal Modulating signal Modulator s(t) Bandpass signal Local oscillator cosωc Carrier t Modulated signal channel Demodulator m’(t) Corrupted baseband signal Corrupted bandpass signal noise
2.线性调制系统·调制系统的分类：幅度调制（线性调制），非线性调制（角度调制）和数字调制(PCM)线性调制：AM,DSB-SC,SSB,VSB
• 调制系统的分类：幅度调制（线性调制），非线性调 制（角度调制）和数字调制（PCM） • 线性调制：AM,DSB-SC,SSB,VSB 2.线性调制系统