EE450-U6-PhysicalLayer_Lecture-Nazarian-Summer10_1

EE450-U6-PhysicalLayer_Lecture-Nazarian-Summer10_1 -...

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University of Southern California Viterbi School of Engineering EE450 omputer Networks Computer Networks hysical Layer Physical Layer Shahin Nazarian Summer 2010
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Data and Signal Data can be ____ or ______. Analog data are continuous and take continuous values. Digital data have discrete states and take discrete values Signals can be ____ or _____. Analog signals can have an _____ number of values in a range, for example sound or video ike real numbers ) Digital signals can have only a limited (like real numbers.) Digital signals can have only a limited number of discrete values like integer numbers, however they typically have two levels, e.g., 0 and 1 or -1 and +1 ignals are a way of representing the data The representation Signals are a way of representing the data . The representation could be electrical, electromagnetic (i.e., transmission via radio), or optical (i.e., transmission via optical fiber) Shahin Nazarian/EE450/Summer 2010 2
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Periodic Signals A signal that repeats itself is periodic, e.g., periodic sine or cosine signal waveforms periodic signal can be recognized by three A periodic signal can be recognized by three parameters, its _______ , its _______ amplitude and its _______ T (Period) Shahin Nazarian/EE450/Summer 2010 3
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Signal Key Parameters (frequency, Amplitude and Phase Frequency (or inverse of period, i.e., 1/T,) denoted by f , is the signal’s rate of change and is measured in Hertz or ______ per second Peak amplitude , A , is the maximum strength of a ignal and is measured in volts or amps signal and is measured in volts or amps Phase , φ , describes the position of the waveform relative to time 0 Example: Sine wave representation: A Sin(2 π f t + ) Voltage olts) A (Volts) Shahin Nazarian/EE450/Summer 2010 4 T Time (sec)
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Periodic Signals A periodic signal with period T can be represented s sum of sinusoids using Series: as sum of sinusoids using _______ Series: x(t) = a 0 + a 1 Sin(2 π f 0 t + φ 1 ) + a 2 Sin(2 π 2 f 0 t + 2 ) + … + a k Sin(2 kf 0 t + k ) + … “DC” long-term average fundamental frequency f 0 =1/ T first harmonic k th harmonic Amplitude Spectrum | a 0 |, | 1 |, | 2 |, … Shahin Nazarian/EE450/Summer 2010 | k | determines amount of power in k th harmonic
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Periodic Signals (Cont.) Change in a short span of time means ____ frequency Change over a long span of time means ___ frequency If a signal does not change at all, its frequency is _____ If a signal changes instantaneously, its frequency is _____ he interesting fact about periodic signals is that if The interesting fact about periodic signals is that if you know the waveform for one cycle (for T seconds) you will be able to predict the signal behavior at any ime; another words if you know its frequency its time; another words if you know its frequency, its peak amplitude, and its phase you can predict it nformation is all about not how Shahin Nazarian/EE450/Summer 2010 6 Information is all about ___________ not how frequently or rarely it happens
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Units of Period and Frequency Example 1: Express a period of 100ms in microseconds Example 2: The voltage of a battery is a constant; this constant
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EE450-U6-PhysicalLayer_Lecture-Nazarian-Summer10_1 -...

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