ECE 4371, Fall, 2014 Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 17 Oct. 27 th, 2014

Outline Project 2, Due 12/3 Vote for exam 2 time Term project ARQ FEC Basics

Project 2 Due 12/3/14 Take a selfie Show time signal, eye diagram, and constellation for no noise, SNR=0, SNR=5dB and SNR=10dB. (1 point) Calculate BER for SNR=0. SNR=2.5dB and SNR=5dB, compared with theoretic result. Change symb to sufficiently large. (2 point) For QPSK and 16QAM, redo the above step (2 point) Transmit images (3 point) –Test small image first –Alignment for both sampling and data –Calculate PSNR for SNR=0dB, SNR=2.5dB, and SNR=5dB. –Print images Timing: sampling at the wrong time. 2 point –1/16, 2/16, … for BER vs. SNR, PSNR vs. SNR

ISI

Scatter Plot

Eye Diagram

BER and PSNR vs. SNR Error Floor for sampling errors SNR PSNR

Image Original, 5 dB, 2.5 dB, 0 dB, and

Technical Writing Structure, Logic (between sentences and paragraphs), and Strictness (no holes). Know who is your audiences Structure –Title and keyword: concise and hit the point, for google users –Abstract: 200 words, for directors who have 20 seconds u Why it is a good topic u What is the idea and contribution u What are the results –Introduction: 1 pages, for managers who have 5 minutes u Why it is a good topic u What are in the literature, or what are the competitors u What is the idea and contribution u What are the results u (Organization) –System model –Problem formulation, proposed scheme, and analysis –Results –Conclusions –Citations For peer

Term Project, Choice One Due at last regular class so that I can talk about it during additional class. Goal: If you have interview on company for wireless project xxx, what you should know Source –The company listed on the web or some company you know. –Select the cool project interesting you. Send me an by 11/10 Structure –Abstract: 100 words for the company, the project and why interests –Introduction: 1 pages for the company: history, competitors, project lines, future, stocks, etc. –Main body of 3 pages for a specific product: 2 pages for the thing you have studied from this class, 1 page for something new.

Term Project, Choice two What is the state of art of xxx –Bluetooth, UWB, WLAN, WMAN, 3G, Ad hoc/Sensor Networks Cognitive Radio, Fiber communication, Cable communication, Power line communication, Satellite communication, etc. Source –IEEE communication magazine to get some tutorial papers –Important citations can be found by IEEE Xplore –Citeseer to test if the paper is well cited and recognized –Select a topic by 11/10. Writing –Goal: suppose you were me and want to give a lecture on the state of art of xxx. –200 words abstract, 1 page introduction and 3 pages details, excluding the figures. –Citations are needed if you “copy” some ideas.

Automatic Repeat-reQuest (ARQ) Alice and Bob on their cell phones –Both Alice and Bob are talking What if Alice couldn’t understand Bob? –Bob asks Alice to repeat what she said What if Bob hasn’t heard Alice for a while? –Is Alice just being quiet? –Or, have Bob and Alice lost reception? –How long should Bob just keep on talking? –Maybe Alice should periodically say “uh huh” –… or Bob should ask “Can you hear me now?”

ARQ Acknowledgments from receiver –Positive: “okay” or “ACK” –Negative: “please repeat that” or “NACK” Timeout by the sender (“stop and wait”) –Don’t wait indefinitely without receiving some response –… whether a positive or a negative acknowledgment Retransmission by the sender –After receiving a “NACK” from the receiver –After receiving no feedback from the receiver

Error Correcting Codes Adding redundancy to the original message To detect and correct errors Crucial when it’s impossible to resend the message (interplanetary communications, storage..) and when the channel is very noisy (wireless communication) Message = [ ] Noise = [ ] Message = [ ]

Types of Error Correcting Codes Repetition Code Linear Block Code, e.g. Hamming Cyclic Code, e.g. CRC BCH and RS Code Convolutional Code –Tradition, Viterbi Decoding –Turbo Code –LDPC Code Coded Modulation –TCM –BICM

Repetition Code Simple Example: reduce the capacity by 3 Simple Example: reduce the capacity by 3 Recovered state

Parity Check Add one bit so that xor of all bit is zero –Send, correction, miss –Add vertically or horizontally Applications: ASCII, Serial port transmission

ISDN Number ISBN 10 –a modulus 11 with weights 10 to 2, using X instead of 10 where ten would occur as a check digitmodulus –ISBN ISBN 13 –Calculating an ISBN 13 check digit requires that each of the first twelve digits of the 13- digit ISBN be multiplied alternately by 1 or 3. Next, take the sum modulo 10 of these products. This result is subtracted from 10.check digitmodulo –ISBN

Hammings Solution A type of Linear Block Code Encoding: H(7,4) Multiple Checksums Message=[a b c d] r= (a+b+d) mod 2 s= (a+b+c) mod 2 t= (b+c+d) mod 2 Code=[r s a t b c d] Coding rate: 4/7 –Smaller, more redundancy, the better protection. –Difference between detection and correction Message=[ ] r=(1+0+0) mod 2 =1 s=(1+0+1) mod 2 =0 t=(0+1+0) mod 2 =1 Code=[ ]

Error Detection Ability 100,000 iterations Add Errors to (7,4) data No repeat randoms Measure Error Detection Error Detection One Error: 100% Two Errors: 100% Three Errors: 83.43% Four Errors: 79.76% Stochastic Simulation: Results:

How it works: 3 dots Only 3 possible words Distance Increment = 1 One Excluded State (red) It is really a checksum. Single Error Detection No error correction ABC ABC AC Two valid code words (blue) This is a graphic representation of the “Hamming Distance”

Hamming Distance Definition: –The number of elements that need to be changed (corrupted) to turn one codeword into another. The hamming distance from: –[0101] to [0110] is 2 bits –[ ] to [ ] is 2 bits –“butter” to “ladder” is 4 characters –“roses” to “toned” is 3 characters

Another Dot The code space is now 4. The hamming distance is still 1. Allows: Error DETECTION for Hamming Distance = 1. Error CORRECTION for Hamming Distance =1 For Hamming distances greater than 1 an error gives a false correction.

Even More Dots Allows: Error DETECTION for Hamming Distance = 2. Error CORRECTION for Hamming Distance =1. For Hamming distances greater than 2 an error gives a false correction. For Hamming distance of 2 there is an error detected, but it can not be corrected.

Multi-dimensional Codes Code Space: 2-dimensional 5 element states Circle packing makes more efficient use of the code-space

Cannon Balls Efficient Circle packing is the same as efficient 2-d code spacing Efficient Sphere packing is the same as efficient 3-d code spacing Efficient n-dimensional sphere packing is the same as n-code spacing

Example Visualization of eight code words in a 6-typle space