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BCH help

Discussion in 'Mathematics and Physics' started by c36041254, Dec 16, 2014.

  1. c36041254

    c36041254 Member

    Joined:
    Apr 1, 2008
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    Location:
    Newzealand, Auckland
    Hi !
    I am trying to understand how bch works, it is just like a CRC code and I am trying to get BCH(31,21) as per this
    As per my understanding to get this BCH working ,all one needs to do is divide the 21 bits of data with the genpoly and then append the remainder to data.
    This way the data should still be intact within the codeword. So if I convert the data (i.e the word "Salam" on the given link) into binary and put it onto notepad and convert the codeword hex results into binary which are also displayed on the link site, and then, if I run a Ctrl+f on notepad and search for the original data (at least the first 20 bits)
    I should find it in the codeword binary string, but seems that the original data is completely changed in the codeword. I have tried changing endienness but no joy. Please look at the attached screenshot/file.
    The encoded message works if I transmit to a pager as pager receives the message (BCH is used for POCSAG pager transmission), but I don't understand why the message is completely twisted in binary? Can any body explain me how BCH works (Without diving into Polynomials and stuff please), A binary example would be great. I checked couple of such example online but in all of them the codeword has original data as is, just appended with remainder. If anyone can explain the example in the link that would be really helpful.
     

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  2. c36041254

    c36041254 Member

    Joined:
    Apr 1, 2008
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    154
    Likes:
    1
    Location:
    Newzealand, Auckland
    Since no reply...I did some more research and I thin here it is explained in more detail. As you can see in section 2.1 in the link, bits 1-20 are just row bits from actual message, so the same format should be in the first link
    When we covert the message "Salam" in binary and the encoded hex message in binary the first 20 bits of the message "Salam" should be visible as is as bits 1-20 in that encoded hex message. But it is not !! So I am confused that how come both are BCH encoding methods and still differ from each other ??
     

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