Scrambler & interleaver

Discussion in 'General Electronics Chat' started by vinodquilon, Oct 19, 2010.

  1. vinodquilon

    Thread Starter Member

    Dec 24, 2009
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    What is the use of SCRAMBLER & INTERLEAVER in a digital communication system ?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The scrambler will be for data SECURITY and the interleaver is for error detection/correction at the receiver end. It helps with the parity check on the scrambled data decoding and also will be used at times to aid in the synchronization of the trans/rcvr pair.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    Scramblers have nothing to do with data security and everything to do with avoiding longs strings of ones or zeros. The following from Wikipedia may be enlightening:

    In telecommunications and recording, a scrambler (also referred to as a randomizer) is a device that manipulates a data stream before transmitting. The manipulations are reversed by a descrambler at the receiving side. Scrambling is widely used in satellite, radio relay communications and PSTN modems. A scrambler can be placed just before a FEC coder, or it can be placed after the FEC, just before the modulation or line code. A scrambler in this context, has nothing to do with encrypting, as the intent is not to render the message unintelligeable, but to give the transmitted data useful engineering properties.
    A scrambler replaces sequences into other sequences without removing undesirable sequences, and as a result it changes the probability of occurrence of vexatious sequences. Clearly it is not foolproof as there are input sequences that yield all-zeros, all-ones, or other undesirable periodic output sequences. A scrambler is therefore not a good substitute for a line code, which, through a coding step, removes unwanted sequences.
     
    Last edited: Oct 19, 2010
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    "Scrambled" is what we always called our transmissions when they were encoded to be un-intelligible by third parties who might intercept them. That there is another use of the term is news to me.

    Thanks :)
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    I agree that the term is ambiguous. I come from a background of designing modems and networks and there it has the very specific meaning of altering the properties of the signal in the analog domain. The more common understanding is covered by encryption. That is converting "plaintext" into "cyphertext". I apologize if my previous response seemed overly abrupt.
     
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