Kitz Forum
Broadband Related => ADSL Issues => Topic started by: konrado5 on April 26, 2014, 06:03:39 PM
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I have 2 mbps lower synchronization rate when I off trellis. I've read trellis lower synchhronization rate, on my line trellis raises. It is very strange.
Best regards
konrado5
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Where did you read that? Trellis helps the connection, great article here http://www.kitz.co.uk/adsl/error_correction.htm
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I know trellis corrects errors. However I've read also it exploit throughput. My synchronization is curiosly lower when trellis is off. It is should be higher.
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My connection is also slower, if you notice less bits per tone are assigned.
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I think without trellis more bits per tone should be assigned.
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Why would you think that? If it was better with trellis on, then leave it on!
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Because trellis uses additional bits.
EDIT: I've found: trellis encoding introduces coding gain: 5.5 dB. Therefore, at the same SNR more bits can be used.
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Where did you get that from? How can trellis use more bits?
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Trellis allows more bits can be used with the same SNR, thereby synchronization rate is higher with the same SNR margin.
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Sorry I misinterpreted what you were saying. ::)
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I know trellis corrects errors. However I've read also it exploit throughput. My synchronization is curiosly lower when trellis is off. It is should be higher.
Perhaps someone getting Convolutional Coding (such as TCM) mixed up with Block Coding (such as RS). Trellis is highly efficient and unlike Reed Soloman doesnt carry huge overheads. The downside is that TCM doesnt offer much protection against burst type errors whilst RS does by using redundancy.
>> Trellis allows more bits can be used with the same SNR, thereby synchronization rate is higher with the same SNR margin.
Its algorithm is more efficient when it comes to coding gain (http://en.wikipedia.org/wiki/Coding_gain).
Dont ask me to explain any more about the algorithms though, because as soon as I see equations like that, then my eyes glaze over and my brain explodes. ???
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Its algorithm is more efficient when it comes to coding gain.
Sorry, I don't understand.
Perhaps someone getting Convolutional Coding (such as TCM) mixed up with Block Coding (such as RS).
I've had 2 mbps lower synchronization rate with trelliss off and RS off than with trelliss off and RS off.
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I've had 2 mbps lower synchronization rate with trelliss off and RS off than with trelliss off and RS off.
Eh???
I think my brain just exploded...........................................................................
.... kitz has left the building.
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It should be: I've had 2 mbps lower synchronization rate with trelliss off and RS off than with trelliss on and RS off.
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Block coding - such as RS carries overheads (redundancy) which is why the sync speed will be lower.
Convolutional coding is an efficient method of transmitting data it has a coding gain and can correct very tiny errors. It works entirely different to RS.
I was suggesting that perhaps someone had got the 2 methods mixed up when they said "I read trellis lower synchhronization rate".
I dont know where you read it, but we never ever suggest turning off TCM. I think there may have been one instance where Ive read someone said their line worked better with TCM off, but iirc it was a very long line and Im still dubious.
Im not a professor in algorithms nor data encoding - these are very in-depth subjects and would take a mathematics genius to analyse the different algorithms.
What little I know actually relates to data compression algorithms which I studied at degree level, the 2 types of general algorithms (compression and error correction) may share some similarities when it comes to handling data which is why I have a basic understanding... but not the actual mathematics behind the algorithms.
Im not clever enough to be able design and analyse algorithms such as this... if I did Id be earning mega bucks, rather than sat here on a forum typing out replies for free :'(
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I thought that turn off trellis slightly raise my synchronization rate because I didn't know about coding gains. I known only about overheads. Doesn't trellis carries any overhead?
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So you found out weve always said dont turn off TCM.. and youve actually proved turning it off is a bad idea.
Does it matter now that you know the theory is correct?
>>> Doesn't trellis carries any overhead?
Yes it does.
But the answer isnt that simple... it uses parity bits.
Cue a long answer which I do actually know the answer to... but Konrado you exhaust me.. and I dont have the will power to type out an hour long post.
Clue research data transmission and you will find that all types of modulation or protocols or even data storage contains at least some form of parity or redundancy. There are different methods and protocols for data transmission, some are more efficient than others, but may carry a price in other areas. ie speed v reliability.
Every single data transmission carries some sort of redundancy or parity. The internet wouldnt work without it. Try also researching modulation.
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As kitz has said, if it works better leave it on, if nit turn it off, bitswapping makes my connection drop within minutes on a 9db noise margin, and seconds on a 6db noise margin, my connection works when bitswapping is off, therefore I leave it off. I questioned this on the forum, and it just seems to be one of those things. So leave trellis well alone as it improves your connection!