rwep final5 12 rwep final5 12 summary lecture
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8/6/2019 RWEP Final5 12 RWEP Final5 12 Summary Lecture
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Error Correction Codes for Wireless
Communication Systems
Summary and Conclusions
Sami Khorbotly, Ph.D., IEEE memberAssistant Professor
Dept. of Elec. & Comp. Eng. & Comp. Sc.Ohio Northern University
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Wireless Communications Applications
TV & radio
broadcasting
Cell phones Wireless internet
911services
Transportations
Geolocation/GPS
Military/BattlefieldLaw enforcement
http://images.google.com/imgres?imgurl=http://www.boisepubliclibrary.org/About_BPL/images/wireless.gif&imgrefurl=http://www.boisepubliclibrary.org/About_BPL/Computers/wireless.asp&h=174&w=205&sz=10&hl=en&start=8&um=1&tbnid=4a3l3RwS54X-5M:&tbnh=89&tbnw=105&prev=/images?q=wireless+laptops&um=1&hl=en&rlz=1T4ADBF_enUS247US248&sa=N -
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Error in Communication systems
Signals propagating through wires areusually immune to noise
Wired communication is relatively safe
Signals propagating in wireless
channels are significantlyaffected by noise
Wireless communication is error
prone
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Problem Definition
Error prone communication systems are unreliable
Unreliable services are often discarded
A wide range of possible applications are no moreavailable
Society is hurting
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Engineers to the Rescue Engineers are educated/trained problem solvers
Our problem to solve is:
Find a way to improve the reliability of the service considering the followingrestrictions:
1.Cost: only few people will buy a $500 cell phone
2.Size/weight: who will buy a 50lbs GPS systems
3. Trade-off balance: do we want to reduce the error if it introduces a 1 minute
delay? How about 5?
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Coder/Decoder
Manipulates the transmitted data to reduce theprobability of error in the received signal
Re-manipulates the received bits to recover theoriginal data bits
Two types were considered: Redundancy codingConvolutional coding
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Redundancy Coding
10110
3-redundancyencoder
111000111111000
Transmitter
Receiver00110
3-redundancydecoder
100000101111001
Correctable errors
Uncorrectable error
Still 1 error bit
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Convolutional Coding
Also reduces the error in communication systems
Can achieve higher error correction at a relatively lowercost, if the generator polynomials are carefully chosen
Encodes blocks of data bits instead of encoding each bitseparately (like in redundancy coding)
Unlimited coding schemes with a wide range ofperformances can be achieved by changing the codingrates and/or generator polynomials
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Redundancy Coding Results
n=1
BER=35%
Original
BER=0.0%
Fire at 100 Main St.
H@@3qz@ @XdN
n=3
BER=9,37%
F At q0 MAij tj
n=5
BER=0.62%
Fie at 100 Main St.
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Redundancy Coding Results (2)
n=1
BER=26.9%
n=3
BER=3.76%
Original
BER=0.0%
n=5
BER=0.72%
Higher encoding rates result in improved BER
Nothing is free
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What can we do?
Higher rate of encoding/decoding What is the encoding decoding cost?
In a 56Kbps wireless data link, sending 1Kbits takes:
1/5617 ms without channel coding
3/5653 ms in a 3-redundancy coding
15/56267 ms in a 15-redundancy coding
What are our options?
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Simulation Results(obtained from redundancy coding)
How much delay can we afford?
How much error can we tolerate?
1 2 3 4 5 6 70
5
10
15
20
25
30
35
ErrorP
erce
ntage
Coding factor (n)
1 2 3 4 5 6 70
50
100
150
200
Coding factor (n)
Processing
Time(sec
onds)
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Delay Sensitivity
In the cell phone industry, any delay of more than 1-secondbetween talking parties is unacceptable
Can you hear
me NOW?
Delay becomes even more critical ifthe situation involves a 911 service
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Delay Sensitivity
A 30 seconds delay is affordable when sendingan email, downloading a file, or completing anonline transaction
Watching a live game on your tv, you will noteven notice 30 seconds of delay
http://images.google.com/imgres?imgurl=http://www.boisepubliclibrary.org/About_BPL/images/wireless.gif&imgrefurl=http://www.boisepubliclibrary.org/About_BPL/Computers/wireless.asp&h=174&w=205&sz=10&hl=en&start=8&um=1&tbnid=4a3l3RwS54X-5M:&tbnh=89&tbnw=105&prev=/images?q=wireless+laptops&um=1&hl=en&rlz=1T4ADBF_enUS247US248&sa=N -
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Error Tolerance
Original Image Received Image (10% BER)
Image received with around 10% of error Noise is clearly noticeable, but image is still visible
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Error Tolerance
Fire at 100 S. Main St. Dr$t 10 s Ial d.
Original text Received text at 10% BER
Text received also with around 10% of error
Received text is totally useless
Different applications have different error tolerances
ECC systems must be designed accordingly
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Who Makes Those Decisions?
You will Make those decisions
By the time you graduate, youll be
able to smartly make those decisions
Weigh-in design standards, customerinput, and your engineering skills to
make these decisions
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Last But Not Least
Medical doctors save lives
Soldiers protect ourfreedom
Artists and athletes
entertain people
Electrical & computer engineers just solve Math &Physics equations
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Math and physics are just tools that you need to know
Buckle up and get ready for a fantastic ECE career
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