rwep final5 12 rwep final5 12 summary lecture

8/6/2019 RWEP Final5 12 RWEP Final5 12 Summary Lecture

1/22

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


2/22

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


3/22

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


4/22

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


5/22

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?


6/22


7/22

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


8/22

Redundancy Coding

10110

3-redundancyencoder

111000111111000

Transmitter

Receiver00110

3-redundancydecoder

100000101111001

Correctable errors

Uncorrectable error

Still 1 error bit


9/22

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


10/22

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.


11/22

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


12/22

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?


13/22


14/22

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)


15/22

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


16/22

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


17/22

Error Tolerance

Original Image Received Image (10% BER)

Image received with around 10% of error Noise is clearly noticeable, but image is still visible


18/22

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


19/22

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


20/22

Last But Not Least

Medical doctors save lives

Soldiers protect ourfreedom

Artists and athletes

entertain people

Electrical & computer engineers just solve Math &Physics equations


21/22


22/22

Math and physics are just tools that you need to know

Buckle up and get ready for a fantastic ECE career

rwep final5 12 rwep final5 12 summary lecture

Documents