Patent ID: 6757323
Filing Date: 2004-06-29
Classification: H04B

Abstract:
A method for signal acquisition between a first spread spectrum transceiver and a second spread spectrum transceiver, comprising the steps of:transmission by said first spread spectrum transceiver of a beacon signal which includes beacon packets each having a beacon packet length, said beacon packets being transmitted at regularly spaced beacon transmission times, each of said beacon transmission times being separated by a beacon cycle interval, said beacon packet length being shorter than said beacon cycle interval so that there is a period of nontransmission between each of said beacon packets, each of said beacon packets having an acyclic auto-correlation function with sidelobes having sidelobe values that are not small relative to a peak value of said acyclic auto-correlation function, said sidelobes having a structure which allows a sampling of a number of said sidelobe values to be used to provide an estimate of a location of said peak value of said acyclic auto-correlation function; initial-stage reception by said second spread spectrum transceiver over an initial-stage reception window which begins at an initial-stage reception time which is a first integer multiple of said beacon cycle interval augmented in a first direction by a first fraction of twice said beacon packet length later than a previous initial-stage reception time of said second spread spectrum transceiver if initial-stage test values from a previous execution of said initial-stage reception are less than a cut-off value, said initial-stage reception being performed by calculation of correlations between time delayed versions of said beacon packet and a received signal to produce said initial-stage test values; first intermediate-stage reception by said second spread spectrum transceiver over a first intermediate-stage reception window which begins at a first intermediate-stage reception time which is a second integer multiple of said beacon cycle interval augmented in a second direction by a second fraction of twice said beacon packet length later than said previous initial-stage reception time of said second spread spectrum transceiver if any of said initial-stage test values from said previous execution of said initial-stage reception are greater than said cut-off value, said first intermediate-stage reception being performed by calculation of correlations between said time delayed versions of said beacon packet and said received signal to produce first intermediate-stage reception values; second intermediate-stage reception by said second spread spectrum transceiver if all said first intermediate-stage reception values from said first intermediate-stage reception are less than said cut-off value, second intermediate-stage reception being performed over a second intermediate-stage reception window which begins at a second intermediate-stage reception time which is a third integer multiple of said beacon cycle interval augmented in a third direction, opposite said second direction, by said second fraction of twice said beacon packet length later than said first intermediate-stage reception time of said second spread spectrum transceiver, said second intermediate-stage reception being performed by said calculation of said correlations between said time delayed versions of said beacon packet and said received signal to produce second intermediate-stage reception values, some of said second intermediate-stage reception values being greater than said cut-off value; and determination of a location of a maximum value of a beacon packet isolated-sequence autocorrelation using said initial-stage test values which are greater than said cut-off value, using said first intermediate-stage reception values if some of said first intermediate-stage reception values are greater than said cut-off value, and using said second intermediate-stage reception values if some of said second intermediate-stage reception values are greater than said cut-off value.