Method and system for multiple-shift code acquisition of optical orthogonal codes in optical CDMA systems
First Claim
1. A method for determining an arbitrary delay in a source code word propagated over a channel that introduces the arbitrary delay in the source code word to produce a received code word, the source code word and the received code word encompassing a given time interval, the method comprisingpartitioning the time interval into cells and grouping a plurality of cells into groups of cells,examining each of the groups to locate a particular one of the groups containing the arbitrary delay with reference to the source code word and the received code word,estimating the arbitrary delay within the particular one of the groups with reference to the source code word and the received code word, wherein the examining includes:
- generating a composite code pattern with reference to the source code word to examine each of the groups,randomly selecting one of the groups, andcomputing an overlap value between the received code word and the composite code pattern for the randomly selected one of the groups.
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Abstract
A technique for determining an arbitrary delay in a source code word propagated over a channel that introduces the arbitrary delay in the source code word to produce a received code word. The technique is based upon a multiple-shift algorithm to determine the delay by a coarse synchronization process to locate synchronization as contained within a composite code pattern, and a fine synchronization process to pinpoint the delay by examining shifts in the source code word used to form the composite code pattern.
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Citations
19 Claims
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1. A method for determining an arbitrary delay in a source code word propagated over a channel that introduces the arbitrary delay in the source code word to produce a received code word, the source code word and the received code word encompassing a given time interval, the method comprising
partitioning the time interval into cells and grouping a plurality of cells into groups of cells, examining each of the groups to locate a particular one of the groups containing the arbitrary delay with reference to the source code word and the received code word, estimating the arbitrary delay within the particular one of the groups with reference to the source code word and the received code word, wherein the examining includes: -
generating a composite code pattern with reference to the source code word to examine each of the groups, randomly selecting one of the groups, and computing an overlap value between the received code word and the composite code pattern for the randomly selected one of the groups. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for determining an arbitrary delay in a source code word propagated over a channel that introduces the arbitrary delay in the source code word to produce a received code word, the source code word and the received code word encompassing a given time interval, the method comprising
(a) partitioning the bit interval into a number of cells, (b) grouping the cells into a plurality of groups, (c) generating a composite code pattern by combining shifts in the source code word with reference to a shift parameter and a previously unused one of the groups, (d) computing an overlap value by evaluating the overlap of the received code word with the composite code pattern, (e) if the overlap value exceeds a given threshold, continuing with (f); - otherwise returning to (c),
(f) sequentially comparing the received code word for a selected one of the shifted versions of the source code word used to form the composite code pattern to produce a second overlap value, and (g) whenever the second overlap value exceeds a predetermined threshold, equating the shift in the compared shifted version of the source code word to the arbitrary delay;
otherwise, either returning to (f) until all shifted versions are processed or to (c) until all groups are processed. - View Dependent Claims (13)
- otherwise returning to (c),
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14. A method for detecting an arbitrary delay in a received code word corresponding to a source code word propagated from a transmitter to a receiver over a channel that introduces the arbitrary delay in the source code word, both the source code word and the received code word covering a bit interval subdivided into a plurality of chip intervals, the method comprising
(a) partitioning the bit interval into F cells, each of the cells having a duration substantially equal to the chip interval, (b) determining a group number Q from the relation -
F L ⌉ , where L is a shift parameter, 1<
L<
F,(c) generating a composite code pattern by combining L shifts in the source code word with reference to a randomly selected number from the set {1, 2, . . . , Q}, excluding previously-selected members of the set, (d) computing an overlap value by evaluating the overlap of the received code word with the composite code pattern, (e) if the overlap value exceeds a given threshold, continuing with (f);
otherwise returning to (c),(f) comparing the received code word with a previously unprocessed one of the L shifted versions of the source code word used to form the composite code pattern to produce a second overlap value, and (g) whenever the second overlap value exceeds a predetermined threshold, equating the shift in the compared shifted version of the source code word to the arbitrary delay;
otherwise, if shifts remain to be processed, returning to (f) if not, returning to (c).- View Dependent Claims (15, 16, 17, 18)
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19. A receiver for determining an arbitrary delay in a source code word propagated over a channel that introduces the arbitrary delay in the source code word to produce a received code word, the source code word and the received code word encompassing a given time interval, the method comprising
means for partitioning the time interval into cells and for grouping a plurality of cells into groups of cells, means for examining each of the groups to locate a particular one of the groups containing the arbitrary delay with reference to the source code word and the received code word, means for estimating the arbitrary delay within the particular one of the groups with reference to the source code word and the received code word, wherein the means for examining includes: -
means for generating a composite code pattern with reference to the source code word to examine each of the groups, means for randomly selecting one of the groups, and means for computing an overlap value between the received code word and the composite code pattern for the randomly selected one of the groups.
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Specification