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question regarding the acquisition and tracking of signals

Discussion in 'General Electronics' started by viswanath, Jul 29, 2004.

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  1. viswanath

    viswanath Guest

    question about acquiring and tracking a signal. Maybe its
    simple but I am missing some point there.
    Consider a CDMA DS SS signal. Assuming that we are transmitting the
    code alone and we are trying to decode the code. At the receiver end I
    have come across a lot of literature that we have 3 parameters: the
    frequency, code phase and delay have to be determined. Assume here
    that only the code phase and delay have to be determined and that the
    frequency has been taken care of first.
    In this case , is the acquiring the process of determing the code
    delay or code phase? If it is code phase, then is it trying to
    determine the position of the beginnig of the received code with
    respect to the locally generated clock? Because every time you are
    generating a local code to correlate with the incoming code you have
    the same frequecy of the clock except that its phase is different.
    Atmost the differece is one chip length. So is acquiring trying to get
    the two codes in synchronization thereby getting the clock phases to
    be the same? If so how does one know that one is acquiring the proper
    code.Remember till now there is no information about the correlation
    of the acquired and locally generated codes.
    In the other scenario of trying to get to the correlation to be
    maximum by finding the delay of the code: in acquisition do we,
    irrespective of where the receiver is being clocked to generate the
    local code, just find the delay by serial shift correlation or some
    And during tracking in the next stage try and get the receiver clock
    to be in synchrony with the incoming code generation. I think it is
    the later.It is here that I fail to understand the use of early late
    detector for tracking. Is it always that one acquires in differences
    of half chip delays and tries to track it to within a half chip? The
    receiver may start clocking at any other time apart from half the chip
    Is my understanding of this concept right? If not I would greatly
    appreciate any help in correcting my understanding since I really need
    to get this straight.
    Looking forward to your replies,

    Ps: Are any of the assumptions that I make lead to wrong conclusions
    like the above?Please also let me know.
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