<< Chapter < Page Chapter >> Page >

A novel communication system

A clever system designer claims that the depicted transmitter has, despite its complexity, advantages over the usual amplitude modulation system.The message signal m t is bandlimited to W Hz, and the carrier frequency f c W . The channel attenuates the transmitted signal x t and adds white noise of spectral height N 0 2 .

The transfer function H f is given by H f f 0 f 0

  1. Find an expression for the spectrum of x t . Sketch your answer.
  2. Show that the usual coherent receiver demodulates this signal.
  3. Find the signal-to-noise ratio that results when this receiver is used.
  4. Find a superior receiver (one that yields a better signal-to-noise ratio), and analyze itsperformance.

Multi-tone digital communication

In a so-called multi-tone system, several bits are gathered together and transmitted simultaneously ondifferent carrier frequencies during a T second interval. For example, B bits would be transmitted according to

t 0 t T x t A k 0 B 1 b k 2 k 1 f 0 t
Here, f 0 is the frequency offset for each bit and it is harmonically related to the bit interval T . The value of b k is either 1 or 1 .
  1. Find a receiver for this transmission scheme.
  2. An ELEC 241 almuni likes digital systems so much that he decides to produce a discrete-time version. Hesamples the received signal (sampling interval T s T N ). How should N be related to B , the number of simultaneously transmitted bits?
  3. The alumni wants to find a simple form for the receiver so that his software implementation runs as efficiently as possible. How would you recommend he implement thereceiver?

City radio channels

In addition to additive white noise, metropolitan cellular radio channels also contain multipath: theattenuated signal and a delayed, further attenuated signal are received superimposed. As shown in [link] , multipath occurs because the buildings reflect the signal and thereflected path length between transmitter and receiver is longer than the direct path.

  1. Assume that the length of the direct path is d meters and the reflected path is 1.5 times as long. What is themodel for the channel, including the multipath and the additive noise?
  2. Assume d is 1 km. Find and sketch the magnitude of the transfer functionfor the multipath component of the channel. How would you characterize this transfer function?
  3. Would the multipath affect AM radio? If not, why not; if so, how so? Would analog cellular telephone,which operates at much higher carrier frequencies (800 MHz vs. 1 MHz for radio), be affected or not? Analogcellular telephone uses amplitude modulation to transmit voice.
  4. How would the usual AM receiver be modified tominimize multipath effects? Express your modified receiver as a block diagram.

In digital cellular telephone systems, the base station (transmitter) needs to relay different voice signals toseveral telephones at the same time. Rather than send signals at different frequencies, a clever Rice engineersuggests using a different signal set for each data stream. For example, for two simultaneous data streams,she suggests BPSK signal sets that have the depicted basic signals .

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Fundamentals of electrical engineering i. OpenStax CNX. Aug 06, 2008 Download for free at http://legacy.cnx.org/content/col10040/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Fundamentals of electrical engineering i' conversation and receive update notifications?

Ask