Code synchronization in CDMA satellite wireless communications system using uplink channel detection

A method of synchronizing a satellite wireless communications system with a terminal, the method comprising:

• receiving a radio signal at the satellite wireless communications system;
• detecting a preamble of a transmitted R-ACH message in the received radio signal, wherein detecting a preamble of a transmitted R-ACH message comprises:
• determining a correlation of the received radio signal with a PN sequence;
• and
• detecting the preamble of a transmitted R-ACH message from the determined correlation;
• and
• synchronizing the satellite wireless communications system with a terminal that transmitted the R-ACH message responsive to detection of the preamble of the R-ACH message;
• wherein determining a correlation of the received radio signal with a PN sequence comprises determining a correlation of the received radio signal with the PN sequence over a range of time shifts;
• wherein determining a correlation of the received radio signal with the PN sequence over a range of time shifts comprises:
• generating respective sets of correlation measures for respective ones of a plurality of time segments, the sets of correlation measures including respective correlation measures for respective time shifts of the range of time shifts;
• and
• averaging the correlation measures for the respective time shifts over the plurality of sets of correlation measures to generate a set of average correlation measures;
• and
• wherein detecting a preamble of a R-ACH message comprises detecting a peak value in the set of average correlation measures.

An apparatus for synchronizing a satellite wireless communications system with a terminal that transmits an uplink signal including a known information element spread according to a spreading code specific to a component of a satellite wireless communications system, the apparatus comprising:

• a receiver configured to receive the uplink signal transmitted by the terminal, to determine a correlation of the received uplink signal with the spreading code over a range of time shifts, to detect the known information element from the determined correlation and to synchronize with the terminal responsive to detection of the known information element, wherein the receiver comprises:
• means for generating respective sets of correlation measures for respective ones of a plurality of time segments, the sets of correlation measures including respective correlation measures for respective time shifts of the range of time shifts;
• means for averaging the correlation measures for the respective time shifts over the plurality of sets of correlation measures to generate a set of average correlation measures;
• and
• means for detecting a peak value in the set of average correlation measures.

An apparatus for synchronizing a satellite wireless communications system with a terminal, the apparatus comprising:

• a receiver configured to receive a radio signal at the satellite wireless communications system, to detect a preamble of a R-ACH message transmitted by a terminal and to synchronize with the terminal responsive to detection of the preamble of the R-ACH message, wherein the receiver is configured to determine a correlation of the received radio signal with a PN sequence, and to detect the preamble of the transmitted R-ACH message from the determined correlation, wherein the receiver is configured to determine a correlation of the received radio signal with the PN sequence over a range of time shifts, wherein the receiver comprises:
• means for generating respective sets of correlation measures for respective ones of a plurality of time segments, the sets of correlation measures including respective correlation measures for respective time shifts of the range of time shifts;
• means for averaging the correlation measures for the respective time shifts over the plurality of sets of correlation measures to generate a set of average correlation measures;
• and
• means for detecting a peak value in the set of average correlation measures,
• wherein the means for generating respective sets of correlation measures for respective ones of a plurality of time segments comprises:
• means for correlating respective sets of samples of the received radio signal for the respective time segments with multiple time shifts of the PN sequence to generate respective sets of correlation values;
• and
• means for generating respective sets of magnitude measures for the respective time segments from the respective sets of correlation values;
• and
• wherein the means for averaging the correlation measures for the respective time shifts over the plurality of sets of correlation measures comprises means for averaging the magnitude measures for the respective time shifts over the sets of magnitude measures to generate the set of average correlation measures.