Differential Encoding

Discussion in 'Homework Help' started by abdulsamad4321, Jun 20, 2014.

  1. abdulsamad4321

    Thread Starter Member

    Nov 24, 2013
    30
    0
    In Digital Logic Design there is topic regarding differential encoding which prevent phase inversion of transmitted signal please tell me its practical use.
    Thanks.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Care to post a link to said topic?
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    " its practical use " Well mainly to preserve data integrity. If the data being transmitted is not an accurate representation of the original - what good is it other than to mislead? If some bits get inverted it is telling you something that is NOT true, right? What value is there in bad data other than to the mainstream media and the politically motivated masters of deceit?
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    I was tryign to get the OP to clarify, as the question is very vague. Are we talking about differential signals, aka differential trasmission lines?
    Or are we talking about differential encoding, which for example would be DPCM?
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Vague questions require either vague answers (my prev. answer) or guessing the question in OP and providing answers to what was not asked (what a lot of responders do).
    Way too many times the 'answerer' has to question the 'questioner' extensively to find out what the real question is (kubeek's response above).

    His vagueness may be due to a few inverted bits causing the received data not being an accurate indication of the transmitted (vague) information.
     
  6. abdulsamad4321

    Thread Starter Member

    Nov 24, 2013
    30
    0
    I simply want to know practical use of differential encoding . Do you know any device using this method to remove error then please tell me.
    Thank you.
     
  7. abdulsamad4321

    Thread Starter Member

    Nov 24, 2013
    30
    0
    Nobody knows about it?
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Ok, so let me try and explain once again. Differential encoding has nothing to do with error correction.

    Differential signalling on the other hand is used to minimize susceptibility to noise. You have two wires, and one has for example +1V and the other -1V. The receiver calculates the difference between those two wires, so you get either +2V or -2V, depending on which of the wires is positive and which is negative.

    Any voltage that gets induced into these two wires is likely to be the same amount in both, so if some interference adds 20V to both the wires, then one will have 21V and the other 19V, but the difference is still 2V so correct signal goes through the line.
    See http://en.wikipedia.org/wiki/Differential_signaling for more

    P.S.: when you are asking for help, and someone asks you a question, try to either answer it or ask what he meant. If you dont react at all most people will just ignore any further posts beacuse you dont seem to care enough to qualify for them helping you. Time is precious and most of us will rather spend it replying to posts where the OP cooperates, rather then replying to OP who doesnt give back any reasonable feedback.
     
    Last edited: Jun 24, 2014
  9. dougc314

    Member

    Dec 20, 2013
    38
    11
    As an old time analog modem man I can say...

    The differential encoding technique used in communications in order to prevent phase reversal of transmitted signal is used in communications systems when there is phase ambiguity between the sender and receiver. The classic example is BPSK modulation over a radio signal. The TX sends one carrier phase, or another, with 180 degrees between them. One represents a one, the other a zero.

    While the RX demodulator can recover the the frequency, the phase of the carrier is ambiguous, and the RX modem cannot decide whether the recovered bit is a one or a zero. It can tell the difference between them however, so if the TX data is deferentially encoded, than a change of TX phase represents a 1, and no change represents a zero. (or vice-versa)



    One undesired effect of differential encoding is that one demod bit error generates two bit errors at the decoder output. This technique is used often in many different data communication schemes besides over the air. It has another nice property of turning idle marking into a 1-0 pattern so that bit timing recovery can always occur. This feature is a bit old fashioned, for modern systems.

    As for a link, how about wikipedia
    http://en.wikipedia.org/wiki/Differential_encoding
     
Loading...