System and method for identifying an arrival time of a communicated signal
First Claim
1. An apparatus for identifying an arrival time of a communicated signal which conveys a message having a plurality of bits of data, said apparatus comprising:
- a correlator for correlating said communicated signal with a PN sequence and to generate a correlation signal;
means, coupled to said correlator, for detecting the occurrence of a first bit of said message; and
means, coupled to said detecting means and to said correlator, for determining when, after said first bit, said correlation signal corresponds to a threshold, wherein said determining means comprises a comparison circuit which is disabled during said first bit.
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Accused Products
Abstract
A transmitter (12) broadcasts a PN encoded message (16). A receiver (14) includes a SAW correlator (38) configured to autocorrelate with the PN sequence used in the broadcast signal. A preamble of the message (16) conveys two successive bits (18) that are each encoded with the PN sequence. After the correlator (38) has been preloaded with the PN sequence from the first bit (18), its non-correlation output exhibits reduced amplitude time sidelobes. A timing comparison circuit (60) compares a correlation signal (46) with a timing threshold (72). The timing threshold (72) is established at a very low level to minimize the influence of multipath. False triggering on noise is prevented by disabling the timing comparison circuit (60) until after the first bit (18). At this point in time the correlator (38) has been preloaded with its PN sequence, is again being loaded with its PN sequence, and outputs reduced amplitude time sidelobes.
31 Citations
19 Claims
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1. An apparatus for identifying an arrival time of a communicated signal which conveys a message having a plurality of bits of data, said apparatus comprising:
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a correlator for correlating said communicated signal with a PN sequence and to generate a correlation signal; means, coupled to said correlator, for detecting the occurrence of a first bit of said message; and means, coupled to said detecting means and to said correlator, for determining when, after said first bit, said correlation signal corresponds to a threshold, wherein said determining means comprises a comparison circuit which is disabled during said first bit. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of identifying an arrival time of a communicated signal which conveys a message having a plurality of bits of data, said method comprising the steps of:
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initiating a clock to mark the passage of time; establishing a threshold; receiving first and second bits of said signal; correlating said first and second bits of said signal with a PN sequence, said correlating step producing a correlation signal; and
stopping said clock following said first bit at a point in time when said correlation signal corresponds to said threshold, wherein said stopping step occurs during said second bit. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A system for identifying an arrival time of a communicated signal, said system comprising:
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a spread spectrum transmitter configured to transmit said communicated signal, said communicated signal conveying a message having a plurality of bits, said bits exhibiting first or second states wherein said first state is conveyed by encoding said communicated signal with a PN sequence and said second state is conveyed by an absence of PN sequence encoding in said communicated signal; means for receiving said communicated signal; a correlator coupled to said receiving means, said correlator being configured to correlate said communicated signal with said PN sequence and to generate a correlation signal; means, coupled to said correlator, for detecting the occurrence of a first one of said bits of said message; and means, coupled to said detecting means and to said correlator, for determining when, after said first bit, said correlation signal corresponds to a threshold, wherein said determining means comprises; a comparison circuit configured to compare said correlation signal with said threshold; and means, coupled to said comparison circuit, for disabling said comparison circuit during said first one of said bits and for enabling said comparison circuit during a second one of said bits, said second one of said bits occurring immediately after said first one of said bits. - View Dependent Claims (17, 18, 19)
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Specification