CDMA technical question

Discussion in 'Wireless & RF Design' started by maleen, Jan 31, 2011.

  1. maleen

    Thread Starter New Member

    Jan 31, 2011
    This is a question I have been having about CDMA which I have not got a proper answer anywhere.

    In CDMA, a given message is XORed with a known bit pattern and then transmitted. And as I've learned, at the receiver the received signal is again XORed with the known pattern to reproduce the original message, and all others would appear as noise.

    The question that I am having is, how does the receiver distinguish between the different messages from all the messages coming in from separate transmitters reach its antenna?
    Since messages are coming in through a common frequency there is no way to use a filter, isn't it?

    i.e how does it identify, "this bit is from this channel, next bit is from the other channel etc..
  2. nanovate

    Distinguished Member

    May 7, 2007
    They are not filtered. The received signal is the "sum" of the noise plus data -- XOR this to get the data back out.
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Each packet has a header with Tx ID and Rx ID at the hardware level. Receivers listen/decode all, and only act on those that match the receiver ID.