Questions and Answers of Principles Communications Systems

The input to a low pass filter with impulse responseh(t) = exp (-10t) u(t) is white, Gaussian noise with single-sided power spectral density of 2 W/Hz. Obtain the following:(a) The mean of
A second-order Butter worth filter has 3-dB bandwidth of 500 Hz. Determine the unit impulse response of the filter and use it to compute the noise-equivalent bandwidth of the filter. Check your
Determine the noise-equivalent bandwidths for the four filters having transfer functions given below:(a) Ha (f) = II(f/4) + II(f/2)(b) Hb (f) = 2Λ(f/50)(c) Hc (f) = 10 / 10 + j2πf(d) Hd (f) =
A filter has frequency response functionH(f) = H0 (f - 500) + H0(f + 500) where H0(f) = 2Λ(f / 100)Find the noise-equivalent bandwidth of the filter.
Determine the noise-equivalent bandwidths of the systems having the following transfer functions. Use the time-domain approach.(a) (b) 10 H.(f) = (j2nf +2)(j2nf +25) 100 H,(f) = (j2nf +
Noise n (t) has the power spectral density shown in Figure 7.16. We writen(t) = nc (t) cos (2Ï€f0t + Î¸) - ns (t) sin(2Ï€f0t + Î¸)Make plots of the power
The double-sided power spectral density of noise n (t) is shown in Figure 7.17. If n (t) = nc(t) cos(2Ï€f0t + Î¸) - ns(t) sin(2Ï€f0t + Î¸), find and plot
A circle is divided into 21 equal parts. A pointer is spun until it stops on one of the parts, which are numbered from 1 through 21. Describe the sample space and, assuming equally likely outcomes,
Referring to (5.69) and using the fact that d (t) = ± 1 in T -second intervals, find the value of kf such that the peak frequency deviation of XFSK (t) is 10,000 Hz if the bit rate is 1000 bits
Referring to (5.68), it is sometimes desirable to leave a residual carrier component in a PSK-modulated waveform for carrier synchronization purposes at the receiver. Thus, instead of (5.68), we
Assume that the bit period of Example 5.8 is T = 1 second. That means that the sampling rate is fs= 10 sps because nsamp = 10 in the program. Assuming that a NFFT= 5000 point FFT was used to produce
A random process is composed of sample functions that are square waves, each with constant amplitude T0, and random delay Ï„ as sketched in Figure 7.15. The pdf of Ï„
Referring to Problem 7.1, what are the following probabilities for each case?(a)FX(X ‰¤ 2A,t = 4)(b)FX(X ‰¤ 0,t = 4)(c)FX(X ‰¤ 2A,t = 2)Data From Problem 7.1A fair
A fair die is thrown. Depending on the number of spots on the up face, the following random processes are generated. Sketch several examples of sample functions for each case.(a) (b) (c) 1
Find the probabilities of the following random variables, with pdfs as given in Table 6.4, exceeding their means. That is, in each case, find the probability that X ≥ mX, where X is the respective
Two Gaussian random variables, X and Y, are in dependent. Their respective means are 4 and 2, and their respective variances are 3 and 5.(a) Write down expressions for their marginal pdfs.(b) Write
Two Gaussian random variables, X and Y, are in dependent. Their respective means are 5 and 3, and their respective variances are 1 and 2.(a) Write down expressions for their marginal pdfs.(b) Write
Two jointly Gaussian random variables, X and Y, have means of 1 and 2, and variances of 3 and 2, respectively. Their correlation coefficient is Pxy = 0.2. A new random variable is defined as Z = 3X +
Two jointly Gaussian zero-mean random variables, X and Y, have respective variances of 3 and 4 and correlation coefficient Pxy = -0.4. A new random variable is defined as Z = X + 2Y. Write down an
Determine the cdf for a Gaussian random variable of mean m and variance σ2. Express in terms of the Q-function m = 0, σ = 0.5, 1, and 2.
Prove that the Q-function may also be represented as S exp еxp (-т х2 dф. О() 3 2 sin? ф ф
A random variable X has the probability-density functionExpress the following probabilities in terms of the Q-function and calculate numerical answers for each:(a) P(IXI ‰¤ 15);(b) P(10
(a) Prove Chebyshev ̓s inequality. Let Y = (X - mx) /σx and find a bound for P(IYI < k) in terms of k.(b) Let X be uniformly distributed over |x| ≤ 1. Plot P(IXI ≤ kσx) versus k and
If the random variable X is Gaussian, with zero mean and variance σ2, obtain numerical values for the following probabilities:(a) P(IXI > σ);(b) P(IXI > 2σ);(c) P(IXI > 3σ).
Speech is sometimes idealized as having a Laplacian-amplitude pdf. That is, the amplitude is distributed according to fX(x) = (a/2) exp (-a|x|)(a) Express the variance of X, Ïƒ2, in
Compare the Q-function and the approximation to it for large arguments given by (6.202) by plotting both expressions on a log-log graph. (Note: MATLAB is handy for this problem.)
(Chi-squared pdf) Consider the random variable Y = ˆ‘N i = 1 where the Xi€™s are independent Gaussian random variables with pdfs n(0,Ïƒ).(a) Show that the
Consider the Cauchy density functionfX(x) = K / 1 + x2 , -∞ ≤ x ≤ ∞(a) Find K.(b) Show that var {X} is not finite.(c) Show that the characteristic function of a Cauchy random variable is
Compare the binomial, Laplace, and Poisson distributions for(a) n = 3 and p = 1/5(b) n = 3 and p = 1/10(c) n = 10 and p = 1/5(d) n = 10 and p = 1/10
The random variable X has a probability-density function uniform in the range 0 ≤ x ≤ 2 and zero elsewhere. The independent variable Y has a density uniform in the range 1 ≤ y ≤ 5 and zero
An honest coin is flipped 10 times.(a) Determine the probability of the occurrence of either 5 or 6 heads.(b) Determine the probability of the first head occurring at toss number 5.(c) Repeat
Passwords in a computer installation take the form X1, X2, X3, X4, where each character Xi is one of the 26 letters of the alphabet. Determine the maximum possible number of different passwords
Assume that 20 honest coins are tossed.(a) By applying the binomial distribution, find the probability that there will be fewer than 3 heads.(b) Do the same computation using the Laplace
A digital data transmission system has an error probability of 10-5 per digit.(a) Find the probability of exactly 1 error in 105 digits. (b) Find the probability of exactly 2 errors in 105
Assume that two random variables X and Y are jointly Gaussian with mx = my = 1, σ2x = σ2y = 4.(a) Making use of (6.194), write down an expression for the marginal pdfs of X and of Y.(b) Write down
A random variable X is defined by fX(x) = 4e-8|x|The random variable Y is related to X by Y = 4 + 5X.(a) Determine E[X], E[X2], and σ2x.(b) Determine fY(y).(c) Determine E[Y], E[Y2], and
Using the definition of a conditional pdf given by Equation (6.62) and the expressions for the marginal and joint Gaussian pdfs, show that for two jointly Gaussian random variables X and Y, the
Two Gaussian random variables X and Y, with zero means and variances Ïƒ2, between which there is a correlation coefficient p, have a joint probability-density function given byThe marginal
Two random variables X and Y have means and variances given below:mx = 1 σ2x = 4 my = 3 σ2y = 7A new random variable Z is defined as Z = 3X - 4YDetermine the mean and variance
The random variable has pdfwhere u(x) is the unit step. Determine the mean and the variance of the random variable thus defined. fx(x) = ;5(x – 5) + lu(x – 4) – u(x – 8)]
Ifshow that (a) E[X2n] = 1 · 3 · 5 ··· (2n - 1) Ïƒ2n, for n = 1,2,...(b) E[X2n-1] = 0 for n = 1,2,... fx(x) -(2π σ') exp 2σ2
A random variable X has the pdf fX(x) = Ae -bx [u(x) - u(x - B)]where u(x) is the unit step function and A, B, and b are positive constants.(a) Find the proper relationship between the constants
Verify the entries in Table 6.5 for the mean and variance of the following probability distributions:(a) Rayleigh;(b) One-sided exponential;(c) Hyperbolic;(d) Poisson;(e)
(a) Consider a random variable uniformly distributed between 0 and 2. Show that E(X2) > E2(X).(b) Consider a random variable uniformly distributed between 0 and 4. Show that E(X2) > E2(X).(c)
Let fX(x) = A exp (-bx) u(x - 2) for all x where A and b are positive constants.(a) Find the relationship between A and b such that this function is a pdf.(b) Calculate E(X) for this random
A nonlinear system has input X and output Y. The pdf for the input is Gaussian as given in Problem 6.16.Determine the pdf of the output, assuming that the nonlinear system has the following
Given the Gaussian random variable with the pdfwhere Ïƒ > 0 is the standard deviation. If Y = X2, find the pdf of Y. Note that Y = X2 is symmetrical about X = 0 and that it is impossible
(a) For what value of α > 0 is the function f(x) = αx-2u(x - α)a probability-density function? Use a sketch to illustrate your reasoning and recall that a pdf has to integrate to one.
The joint pdf of two random variables isotherwise Find the following:(a) The constant C(b) fXY (1, 1.5)(c) fXY (x, 3) C(1+xy), 0
The joint pdf of two random variables isotherwise Find the following:(a) The constant C(b) fXY (1, 1.5)(c) fXY (x, 3)(d) fX|Y(x | 3) C(1+xy), 0
Test X and Y for independence if (a) fXY (x,y) = Ae-|x| -2|y| (b) fXY (x,y) = C(1 - x - y), 0 ≤ x ≤ 1- y and 0 ≤ y ≤ 1Prove your answer.
The following functions can be pdfs if the constants are chosen properly. Find the proper conditions on the constants so that they are. [A, B, C, D, α, β, γ, and τ are positive constant and u (x)
A certain continuous random variable has the cumulative-distribution function(a) Find the proper values for A and B.(b) Obtain and plot the pdf fX(x).(c) Compute P(X > 5).(d) Compute P(4
Three fair coins are tossed simultaneously such that they don’t interact. Define a random variable X = 1 if an even number of heads is up and X = 0 otherwise. Plot the cumulative-distribution
Two dice are tossed.(a) Let X1 be a random variable that is numerically equal to the total number of spots on the up faces of the dice. Construct a table that defines this random variable.(b) Let
Given the table of joint probabilities of Table 6.5,(a) Find the probabilities omitted from Table 6.5,(b) Find the probabilities P(A3 | B3), P(B2 | A1), and P(B3 | A2). Table 6.5 Table of
Given a binary communication channel where A = input and B = output, let P(A) = 0.45, P(B | A) = 0.95, and P(B̅ | A̅) = 0.65. Find P(A | B) and P(A | B̅).
Figure 6.20 is a graph that represents a communication network, where the nodes are receiver/repeater boxes and the edges (or links) represent communication channels, which, if connected, convey the
Check the validity of the central-limit theorem by repeatedly generating n independent uniformly distributed random variables in the interval (-0.5,0.5), forming the sum given by (6.187), and
Using the results of Problem 6.26 and the Gaussian random number generator designed in Computer Exercise 6.2, design a Gaussian random number generator that will provide a specified correlation
Two events, A and B, have respective marginal probabilities P (A) = 0.2 and P(B) = 0.5, respectively. Their joint probability is P (A ∩ B) = 0.4.(a) Are they statistically independent? Why or why
What equations must be satisfied in order for three events A, B, and C to be independent? (They must be independent by pairs, but this is not sufficient.)
If five cards are drawn without replacement from an ordinary deck of cards, what is the probability that(a) Three kings and two aces result;(b) Four of a kind result;(c) All are of the same suit;(d)
Referring to Computer Example 4.4, draw the block diagram of the system represented by the simulation loop, and label the inputs and outputs of the various loop components with the names used in the
Using xr(t) = m(t) cos(2Ï€fct) and e0(t) = 2 cos (2Ï€fct + Î¸) for the assumed Costas PLL input and VCO output, respectively, verify that all signals shown at the
It is desired to transmit data at 9 kbps over a channel of bandwidth 7 kHz using raised-cosine pulses. What is the maximum value of the roll-off factor, β, that can be used?
If |Hc (f)| = [1 + (f /5000)2] -1/2 , provide a plot for |HT (f)| = |HR (f)| assuming the pulse spectrum PRC(f) with 1/T = 5000 Hz for (a) β = 1; (b) β = 1/2
Sketch the following spectra and tell which ones satisfy Nyquist€™s pulse-shape criterion. For those that do, find the appropriate sample interval, T, in terms of W. Find the corresponding
Show that (5.31) and (5.32) are Fourier-transform pairs.
Show that (5.32) is an ideal rectangular spectrum for β = 0. What is the corresponding pulse-shape function?
Using the superposition and time-in-variance properties of an RC filter, show that (5.27) is the response of a low pass RC filter to (5.26) given that the filter’s response to a unit step is [1 -
Given the step response for a second-order Butter worth filter as in Problem 2.65c, use the superposition and time-in-variance properties of a linear time-invariant system to write down the filter??s
A channel of bandwidth 4 kHz is available. Determine the data rate that can be accommodated for the following line codes (assume a bandwidth to the first spectral null):(a) NRZ
A symbol synchronizer uses a fourth-power device instead of a squarer. Modify the MATLAB program of Computer Example 5.3 accordingly and show that a useful spectral component is generated at the
Write a MATLAB program that will compute the weights of a transversal-filter zero forcing equalizer for a given input pulse sample sequence.
Write a MATLAB program that will produce plots like those shown in Figure 5.10. The Butter worth channel filter poles and 3-dB frequency should be inputs as well as the roll-off factor,
Given the channel features or objectives below. For each part, tell which line code(s) is (are) the best choice(s).(a) The channel frequency response has a null at f = 0 hertz.(b) The channel has a
Write a MATLAB program that will produce plots like those shown in Figure 5.2 assuming a random binary data sequence. Include as an option a Butter worth channel filter whose number of poles and
Assume that an FM demodulator operates in the presence of sinusoidal interference. Show that the discriminator output is a nonzero constant for each of the following cases: Ai = Ac, Ai = -Ac, and Ai
Assuming the loop filter model for an imperfect second-order PLL described in the preceding problem, derive the steady-state phase errors under the three conditions of Î¸0,
A first-order PLL is operating with zero frequency and phase error when a step in frequency of magnitude Δω is applied. The loop gain Kt is 2π(100). Determine the steady-state phase error, in
Starting with (4.117) verify the steady-state errors given in Table 4.4. Table 4.4 Steady-state Errors O, + 0 fa # 0 R = 0 O, + 0 fa = 0 0, + 0 fa # 0 R + 0 PLL order R = 0 1 (a = 0, b = 0) 2 (a + 0,
Repeat the preceding problem assuming that the transmitter outputs are defined by(a) xc (t) = cos[2π(1000)t2](b) xc (t) = cos[2π(900)t + 10√t]Data From Problem 9A transmitter uses a carrier
Modify the simulation program given in Computer Example 4.4 to allow the sampling frequency to be entered interactively. Examine the effect of using different sampling frequencies by executing the
Develop a computer program and use the program to verify the simulation results shown in Figures 4.24 and 4.25.Figure 4.24Figure 4.25 80 Af = 40 Hz 60 ww Af = 45 Hz 20 ·Af = 35 Hz Af= 20 Hz -20 2л
Develop a computer program to generate the amplitude spectrum at the output of an FM modulator assuming a square-wave message signal. Plot the output for various values of the peak deviation. Compare
Reconstruct Figure 4.7 for the case in which 3 values of the modulation index (0.5, 1, and 5) are achieved by adjusting the peak frequency deviation while holding fmconstant. Figure 4.7 f2
Let the input to a phase modulator be m(t) = u(t - t0), as shown in Figure 4.1(a). Assume that the unmodulated carrier is Accos(2Ï€fct) and that fct0= n, where n is an integer. Sketch
Using only the Fourier transform of the unit impulse function and the differentiation theorem, find the Fourier transforms of the signals shown in Figure 2.36.
(a) Plot the single-sided and double-sided amplitude and phase spectra of the square wave shown in Figure 2.35(a).(b) Obtain an expression relating the complex exponential Fourier series coefficients
Rewrite the MATLAB simulation of Example 5.8 for the case of an absolute-value type of non-linearity. Is the spectral line at the bit rate stronger or weaker than for the square-law type of
(a) For ISI-free signaling using pulses with raised cosine spectra, give the relation of the roll-off factor, β, to data rate, R = 1/T, and channel bandwidth, fmax (assumed to be ideal low
(a) Show by a suitable sketch that the trapezoidal spectrum given below satisfies Nyquist’s pulse shaping criterion:P(f) = 2Λ (f / 2W) - Λ(f / W)(b) Find the pulse-shape function corresponding to
Given the following channel pulse response samples:pc (-3T) = 0.001 pc(-2T) = -0.01 pc(-T) = 0.1 pc(0) = 1.0pc (T) = 0.2
Repeat Problem 5.15 for a five-tap zero-forcing equalizer.Data From Problem 5.15Given the following channel pulse response samples:pc (-3T) = 0.001 pc(-2T) = -0.01 pc(-T) = 0.1
A simple model for a multi path communications channel is shown in Figure 5.20(a).Figure 5.20 (a)(a) Find Hc (f) = Y(f) / X (f) for this channel and plot |Hc(f)| for Î² = 1 and 0.5.(b) In
Given the following channel pulse response:pc (-4T) = -0.01; pc (-3T) = 0.02; pc (-2T) = -0.05; pc (-T) = 0.07; pc (0) = 1;pc (T) = -0.1; pc (2T) = 0.07; pc (3T)
Repeat Problem 5.18 for a five-tap zero-forcing equalizer.Data From Problem 5.18Given the following channel pulse response:pc (-4T) = -0.01; pc (-3T) = 0.02; pc (-2T) = -0.05; pc (-T) = 0.07; pc
In a certain digital data transmission system the probability of a bit error as a function of timing jitter is given by where z is the signal-to-noise ratio, |Î”T|, is the timing
(a) Using the superposition and time-in-variance properties of a linear time-invariant system find the response of a low pass RC filter to the inputx(t) = u(t) - 2u(t - T) + 2u(t - 2T) - u(t -

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