<< Chapter < Page Chapter >> Page >

This practical guide leads the reader through solving the problem from start to finish. You will learn to: define a problem clearly,organize your problem solving project, analyze the problem to identify the root causes, solve the problem by taking corrective action, andprove the problem is really solved by measuring the results.

—Jeanne Sawyer, When Stuff Happens: A Practical Guide to Solving Problems Permanently , Sawyer Publishing Group, 2001

There is nothing new in this chapter. Really. By peeling away the outer, most accessible layers of thecommunication system, the previous chapters have provided all of the piecesneeded to build an idealized digital communication system, and this chapter just shows how to combine the piecesinto a functioning system. Then we get to play with the system a bit, asking a series of “what if” questions.

In outline, the idealized system consists of two parts, rather than three, since the channel is assumed to be noiseless anddisturbance free.

The Transmitter

  • codes a message (in the form of a character string) into a sequence of symbols,
  • transforms the symbol sequence into an analog signal using a pulse shape, and
  • modulates the scaled pulses up to the passband.

The Digital Receiver

  • samples the received signal,
  • demodulates to baseband,
  • filters the signal to remove unwanted portions of the spectrum,
  • correlates with the pulse shape to help emphasize the “peaks” of the pulse train,
  • downsamples to the symbol rate, and
  • decodes the symbols back into the character string.

Each of these procedures is familiar from earlier chapters, and you may have already written M atlab code to perform them. It is time to combine the elements into a full simulation ofa transmitter and receiver pair that can function successfully in an ideal setting.

An ideal digital communication system

The system is illustrated in the block diagram of [link] . This system is described in great detail in "Simulating the Ideal System" , which also provides a M atlab version of the transmitter and receiver. Once everything is pieced together, it is easy toverify that messages can be sent reliably from transmitter to receiver.

Unfortunately, some of the assumptions made in the ideal setting are unlikely to hold in practice;for example, the presumption that there is no interference from other transmitters, that there is no noise,that the gain of the channel is always unity, that the signal leaving the transmitteris exactly the same as the signal at the input to the digital receiver. All of these assumptions will almost certainly be violated in practice.Stuff happens!

Block diagram of an ideal communication system.
Block diagram of an ideal communication system.

"Flat Fading: A Simple Impairment and a Simple Fix" begins to accommodate some of the nonidealities encountered in real systems byaddressing the possibility that the channel gain might vary with time.For example, a large metal truck might abruptly move between a cell phone and the antenna at the base station,causing the channel gain to drop precipitously. If the receiver cannot react to such achange, it may suffer debilitating errors when reconstructing the message. "Flat Fading: A Simple Impairment and a Simple Fix" examines the effectiveness of incorporating an automatic gain control (AGC) adaptive element(as described in [link] ) at the front-end of the receiver.With care, the AGC can accommodate the varying gain. The success of the AGC is encouraging.Perhaps there are simple ways to compensate for other common impairments.

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, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Software receiver design' conversation and receive update notifications?

Ask