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Serial search acquisition system with adaptive threshold and optimal decision for spread spectrum systems

  • US 5,642,377 A
  • Filed: 07/25/1995
  • Issued: 06/24/1997
  • Est. Priority Date: 07/25/1995
  • Status: Expired due to Term
First Claim
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1. A method for PN code acquisition in a PN code signal transmitted in a Code Division Multiple Access (CDMA) Direct Sequence Spread Spectrum (DSSS) system, comprising the steps of:

  • receiving a transmitted PN code signal and multiplying said signal with a PN code replica signal to produce an input signal for use in determining the phase alignment of said PN code signals;

    integrating the signal energy of said input signal over a time interval to obtain a first result;

    establishing a noise estimate;

    establishing a signal detection threshold having a value greater than that of said noise estimate;

    establishing a signal classification threshold, having a value between that of said signal detection threshold and said noise estimate;

    establishing a first number CN of PN phases i to be searched and a total number q of PN phases for said PN code replica signal;

    maintaining a count cn of said PN phases i; and

    searching for said alignment by detecting the signal energy levels and the noise levels of said input signal by the steps of;

    evaluating whether said first result is equal to or exceeds the value of said signal detection threshold;

    if NO, evaluating whether said first result exceeds the value of said signal classification threshold; and

    if NO, updating the value of said noise estimate with the value of said first result and updating said count cn by 1, and determining whether said updated count is equal to or exceeds CN ;

    if YES, ending the search;

    if NO, determining whether the PN phase i of said PN code replica signal equals q;

    if YES, ending the search;

    if NO, updating the PN phase i of said PN code replica signal by 1, and continuing the search by repeating the foregoing steps using the phase updated PN code replica signal to multiply said transmitted PN code signal;

    if YES, resetting said count cn to 0, and determining whether the PN phase i of said PN code replica equals q;

    if YES, ending the search;

    if NO, updating the PN phase i of said PN code replica signal by 1, and continuing the search by repeating the foregoing steps using the phase updated PN code replica signal to multiply said transmitted PN code signal.

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