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Signals and Systems Problems

Module by: Don Johnson

Summary: (Blank Abstract)

Problem Set
Problem 1:

Complex-valued Signals

Complex numbers and phasors play a very important role in electrical engineering. Solving systems for complex exponentials is much easier than for sinusoids, and linear systems analysis is particularly easy.
  1. Find the phasor representation for each, and re-express each as the real and imaginary parts of a complex exponential. What is the frequency (in Hz) of each? In general, are your answers unique? If so, prove it; if not, find an alternative answer for the complex exponential representation.
    1. 3sin24t 3 24 t
    2. 2cos2π60t+π4 2 2 60 t 4
    3. 2cost+π6+4sint-π3 2 t 6 4 t 3
  2. Show that for linear systems having real-valued outputs for real inputs, that when the input is the real part of a complex exponential, the output is the real part of the system's output to the complex exponential (see Figure 1). SℜAⅇⅈ2πft=ℜSAⅇⅈ2πft S A 2 f t S A 2 f t
sys28.png
Figure 1
Problem 2:

For each of the indicated voltages, write it as the real part of a complex exponential ( vt=ℜVⅇst v t V s t ). Explicitly indicate the value of the complex amplitude VV and the complex frequency ss. Represent each complex amplitude as a vector in the VV-plane, and indicate the location of the frequencies in the complex ss-plane.
  1. vt=cos5t v t 5 t
  2. vt=sin8t+π4 v t 8 t 4
  3. vt=ⅇ-t v t t
  4. vt=ⅇ-3tsin4t+3π4 v t 3t 4 t 3 4
  5. vt=5ⅇ2tsin8t+2π v t 5 2 t 8 t 2
  6. vt=-2 v t -2
  7. vt=4sin2t+3cos2t v t 4 2 t 3 2 t
  8. vt=2cos100πt+π6-3sin100πt+π2 v t 2 100 t 6 3 100 t 2
Problem 3:

Express each of the following signals as a linear combination of delayed and weighted step functions and ramps (the integral of a step).
sig1.png
Subfigure 2.1
sig2.png
Subfigure 2.2
sig3.png
Subfigure 2.3
sig4.png
Subfigure 2.4
sig5.png
Subfigure 2.5
Figure 2
Problem 4:

Linear, Time-Invariant Systems

When the input to a linear, time-invariant system is the signal xt xt , the output is the signal yt y t (Figure 3).
sig34a.png
Figure 3
  1. Find and sketch this system's output when the input is the depicted signal.
  2. Find and sketch this system's output when the input is a unit step.
sig34b.png
Figure 4
Problem 5:

Linear Systems

The depicted input xt x t to a linear, time-invariant system yields the output yt y t .
sig39.png
Figure 5
  1. What is the system's output to a unit step input ut u t ?
  2. What will the output be when the input is the depicted square wave?
sig40.png
Figure 6
Problem 6:

Communication Channel

A particularly interesting communication channel can be modeled as a linear, time-invariant system. When the transmitted signal xt xt is a pulse, the received signal rt rt is as shown.
sig45a.png
Figure 7
  1. What will be the received signal when the transmitter sends the pulse sequence x 1 t x 1 t ?
  2. What will be the received signal when the transmitter sends the pulse signal x 2 t x 2 t that has half the duration as the original?
sig45b.png
Figure 8

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