Unit_5__Modulation.ppt

Pulse modulation does not involve a carrier. The resulting modulated signal is still base-band but is no longer the original information signal. Both cw and pulse modulation may be classed as analog modulation which involves varying the modulated parameter continuous-ly as a linear function of the information signal [1]. There are several variations of suppressed carrier (SC) modulation which depend on how modulated signal spectral components are dispersed in relation to the carrier frequency w0, These are called double-sideband, single-sideband, and vestigial-sideband suppressed carrier (AM-DSB-SC, AM-SSB-SC, and AM-VS8-SC, respectively) modulation. vestigial-sideband 残留边带 Hardware costs and complications are minimized if the fractional bandwidth is kept within 1% ~ 10%. Fractional bandwidth considerations account for the fact that modulation units are found in receivers as well as in transmitters. It likewise follows that signals with large bandwidth should be modulated on high frequency carriers. Unit 5 Modulation Vocabulary categorize amplitude cosine argument quantize disperse vestigial prescribe impress 分类 幅度 余弦 变量 量化 分散，散开 残留的，剩余的 指定，规定 施加，外加 Vocabulary antenna fractional rupture jumble telemetry stereophonic round off DM, ADM, DPCM ASK, FSK, PSK, DPSK 天线 部分的，小数的 破裂，割裂 混杂 遥感、遥测 立体声的 舍入，四舍五入 （See textbook） Modulation is a process by which an information signal f(t) may be converted to a more useful form. It is helpful to categorize modulation broadly according to three basic methods. Each method is then subdivided into various types of modulation. Carrier Wave Modulation Method One of the most common modulation methods is to alter a carrier wave of the form Acos(w0t + q0), (5.1) where q0 is an arbitrary constant, A is the wave peak amplitude, and w0 is the carrier frequency. More or less obvious modulation approaches are to make A a function of the information signal f(t) or to add a phase term to the cosine argument which depends on f(t). Th