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electronics_kumar
Joined: 29 Nov 2004
Posts: 645
Helped: 24
Location: Tamilnadu
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 21 Mar 2006 14:16 source and channel coding |
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| I WAN TO understand the difference and purpose of source and channel coding
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ceaser
Joined: 26 Dec 2005
Posts: 133
Helped: 10
Location: Egypt
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| 21 Mar 2006 15:10 Re: source and channel coding |
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what iknow about encoders types is
source encoders: it is techinques to encode the signal to be sent to the write distination like 3gp, mpeg, amr, evrc, smv.
it has some types like vedio encoders, vocoders,speach encoders
these pdf will explain to you some types of source and channel encoders
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mimomod
Joined: 25 Jan 2006
Posts: 110
Helped: 15
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| 21 Mar 2006 17:21 source and channel coding |
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Hi electronics_kumar,
purpose of the source coding is to eliminate redundant data from a signal. For example, if your digital data contains many '0' as in the sequence "000010100010000011", then it is much more efficient to code that long data into "52461". "5" means that there are 4 '0' and one '1', "2" means there is one '0' and one '1', etc. In reality, indeed many physical signal such speech and image contain many redundancies, so source coding is very important. By using source coding, people could design many data compression algorithms to save data efficiently, or reduce the bandwidth for transmitting communication signal via a channel.
The purpose of channel coding is to introduce redundancies into information data. This seeems like a contradiction with that of source coding. But you must be aware that channel coding introduces redundancies in a controlled manner, whereas redundancies inherent in physical signals are random (uncontrolled). This redundancies introduced by channel coding are very important to reduce (or in some cases eliminated) the errors which may occur when you transmit or save/record information data.
best
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cwjcwjcwj
Joined: 08 Nov 2004
Posts: 188
Helped: 2
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| 22 Mar 2006 0:03 Re: source and channel coding |
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| Source coding normally involved compression, whereas channel coding will generate parity bit to correct or detect errors....
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mimomod
Joined: 25 Jan 2006
Posts: 110
Helped: 15
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| 22 Mar 2006 11:40 source and channel coding |
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coding by introducing parity bit(s) is the simplest way to do channel coding. Parity bits only can be used to detect error, but not to correct error. This is enough for example in computer systems, but not in communication systems.
Other channel coding such as convolutional coding and reed-solomon coding could also correct errors. So, generally there are two kind of channel coding: error detection and error correction.
best
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dangbien
Joined: 14 Dec 2005
Posts: 8
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| 24 Mar 2006 5:55 source and channel coding |
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hi thanks
Added after 1 minutes:
ther channel coding such as convolutional coding and reed-solomon coding could also correct errors. So, generally there are two kind of channel coding: error detection and error correction.
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ans2006
Joined: 24 Jan 2006
Posts: 15
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| 24 Mar 2006 11:08 Re: source and channel coding |
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Hello,
I guess all the above replies have given you an idea of source and channel coding.
Very simply put, source coding is about compression...'00000' may be represented as 5 '0', as mentioned in one of the replies above.
Channel coding is about adding redundancies...These redundant bits are added to detect and correct errors.
There seems to be contradiction. Why do we need both souce and channel coding??
One adds redundancies and one removes them.
For video transmission, there need to be a trade-off between source and channel coding.
Please refer to the attached paper on trade off.
Cheers,
ans2006.
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mimomod
Joined: 25 Jan 2006
Posts: 110
Helped: 15
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| 24 Mar 2006 23:44 source and channel coding |
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Hi ans2006,
as i said in my previous post, the different between redundacies at the source and redundancies introduced by channel coding is that, the first one is uncontrolled, and the second is controlled. So if one gives more attention to both, it is no contradiction at all.
best
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silawi
Joined: 24 Nov 2005
Posts: 135
Helped: 3
Location: Jordan
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| 28 Mar 2006 14:37 Re: source and channel coding |
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i have uploaded an important file concerning the source-channel coding for wireless networks,u can download it and extract the useful info for u.....
just search for it in the "digital communications" forum.....
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