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Properties of Angle Modulation Properties of Angle Modulation Properties of Angle Modulation Reference: Sections 4.2 and 4.3 of Professor Deepa Kundur S. Haykin and M. Moher, Introduction to Analog & Digital University of Toronto Communications, 2nd ed., John Wiley & Sons, Inc., 2007. ISBN-13 978-0-471-43222-7. Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 1 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 2 / 25 Angle Modulation carrier I Phase Modulation (PM): θi (t) = 2πfc t + kpm(t) 1 dθ (t) k dm(t) f (t) = i = f + p message i 2π dt c 2π dt sPM (t) = Ac cos[2πfc t + kpm(t)] amplitude modulation I Frequency Modulation (FM): Z t θi (t) = 2πfc t + 2πkf m(τ)dτ 0 phase 1 dθ (t) modulation f (t) = i = f + k m(t) i 2π dt c f Z t sFM (t) = Ac cos 2πfc t + 2πkf m(τ)dτ 0 frequency modulation Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 3 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 4 / 25 carrier carrier message message amplitude amplitude modulation modulation phase phase modulation modulation frequency frequency modulation modulation Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 5 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 6 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Constancy of Transmitted Power Constancy of Transmitted Power: AM 1 I Consider a sinusoid g(t) = Ac cos(2πf0t + φ) where T0 = or T0f0 =1. f0 I The power of g(t) (over a 1 ohm resister) is defined as: Z T0=2 Z T0=2 1 2 1 2 2 P = g (t)dt = Ac cos (2πf0t + φ)dt T0 −T0=2 T0 −T0=2 2 Z T0=2 Ac 1 = [1 + cos(4πf0t + 2φ)] dt T0 −T0=2 2 2 T0=2 Ac sin(4πf0t + 2φ) = t + 2T 4f 0 0 −T0=2 A2 T −T sin(4πf T =2 + 2φ) − sin(−4πf T =2 + 2φ) = c 0 − 0 + 0 0 0 0 2T0 2 2 4πf0 2 2 Ac sin(2π + 2φ) − sin(−2π + 2φ) Ac = T0 + = 2T0 4πf0 2 I Therefore, the power of a sinusoid is NOT dependent on f0, just its envelop Ac . Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 7 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 8 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Constancy of Transmitted Power: PM Constancy of Transmitted Power: FM Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 9 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 10 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Constancy of Transmitted Power Nonlinearity of Angle Modulation Consider PM (proof also holds for FM). I Suppose s1(t)= Ac cos [2πfc t + kpm1(t)] s2(t)= Ac cos [2πfc t + kpm2(t)] Therefore, angle modulated signals exhibit constancy of transmitted power. I Let m3(t)= m1(t)+ m2(t). s3(t)= Ac cos [2πfc t + kp(m1(t)+ m2(t))] 6= s1(t)+ s2(t) * cos(2πfc t + A + B) 6= cos(2πfc t + A) + cos(2πfc t + B) Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 11 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 12 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Nonlinearity of Angle Modulation Irregularity of Zero-Crossings Therefore, angle modulation is nonlinear. I Zero-crossing: instants of time at which waveform changes amplitude from positive to negative or vice versa. Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 13 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 14 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Zero-Crossings: AM Zero-Crossings: PM Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 15 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 16 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Zero-Crossings: FM Irregularity of Zero-Crossings Therefore angle modulated signals exhibit irregular zero-crossings because they contain information about the message (which is irregular in general). Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 17 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 18 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Visualization Difficulty of Message Visualization: AM I Visualization of a message refers to the ability to glean insights about the shape of m(t) from the modulated signal s(t). Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 19 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 20 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Visualization: PM Visualization: FM Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 21 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 22 / 25 4.2 Properties of Angle Modulation 4.2 Properties of Angle Modulation Visualization Difficulty of Message Bandwidth vs. Noise Trade-Off I Noise affects the message signal piggy-backed as amplitude modulation more than it does when piggy-backed as angle Therefore it is difficult to visualize the message in angle modulated modulation. signals due to the nonlinear nature of the modulation process. I The more bandwidth that the angle modulated signal takes, typically the more robust it is to noise. Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 23 / 25 Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 24 / 25 4.2 Properties of Angle Modulation carrier message amplitude modulation phase modulation frequency modulation Professor Deepa Kundur (University of Toronto) Properties of Angle Modulation 25 / 25 .
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