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P-code generation

  • US 5,202,694 A
  • Filed: 09/10/1991
  • Issued: 04/13/1993
  • Est. Priority Date: 09/10/1991
  • Status: Expired due to Fees
First Claim
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1. Apparatus for generation of a code sequence P(t) as a function of time t for use in determining position on a surface of a body such as the Earth from position data provided from one or more satellites, the apparatus comprising:

  • a clock pulse source that provides a sequence of clock pulses of predetermined period T;

    first clock control means having a clock pulse input terminal and a clock pulse output terminal, for receiving the sequence of clock pulses at the input terminal and passing through and issuing this sequence of clock pulses at the output terminal, the first clock control means further having a first control input terminal for halting pass-through of clock pulse sequences when a halt signal is received at this first control input terminal, and having a second control input terminal for resuming pass-through of clock pulse sequences when a reset signal is received at the second control input terminal after receipt of a halt signal at the first control input terminal;

    second clock control means having a clock pulse input terminal and a clock pulse output terminal, for receiving the sequence of clock pulses at the input terminal and passing through and issuing this sequence of clock pulses at the output terminal, the second clock control means further having a first control input terminal for halting pass-through of clock pulse sequences when a halt signal is received at this first control input terminal, having a second control input terminal for resuming pass-through and issuance of clock pulse sequences when a reset signal is received at the second control input terminal after receipt of a halt signal at the first control input terminal;

    third clock control means having a clock pulse input terminal and a clock pulse output terminal, for receiving the sequence of clock pulses at the input terminal and passing through and issuing this sequence of clock pulses at the output terminal, the third clock control means further having a first control input terminal for halting pass-through of clock pulse sequences when a halt signal is received at this first control input terminal, and having a second control input terminal for resuming pass-through of clock pulse sequences when a reset signal is received at the second control input terminal after receipt of a halt signal at the first control input terminal;

    first, second, third and fourth register means that receive a clock pulse sequence from the first clock control means, from the clock pulse source, from the second clock control means and from the third clock control means, respectively, and generate and issue a predetermined code sequence X1B(t), X1A(t), X2A(t) and X2B(t), respectively, for each clock pulse received at a sequence of times t=mT (m=1, 2, . . . );

    first decoder means, connected to the first register means, for receiving the code sequence values X1B(t) (t=m1 T;

    m1 =1, 2, . . . M1) issued by the first register means, for detecting occurrence of a predetermined code sequence value X1B0, and for producing and issuing a first halt signal that is received by the first control input terminal of, and halts the pass-through of clock pulses at, the first clock control means when the predetermined code sequence value X1B0 is received, where M1 is a predetermined positive integer;

    second decoder means, connected to the second register means, for receiving the code sequence values X1A(t) (t=m2 T;

    m2 =1, 2, . . . M2) issued by the second register means, for detecting occurrence of a predetermined code sequence value X1A0, and for producing and issuing a first reset signal that is received by the second control input terminal of, and resumes the pass-through and issuance of clock pulses at, the first clock control means when the predetermined code sequence value X1A0 is received, where M2 is a predetermined positive integer;

    third decoder means, connected to the third register means, for receiving the code sequence values X2A(t) (t=m3 T;

    m3 =1, 2, . . . M3) issued by the third register means, for detecting occurrence of a predetermined code sequence value X2A0, and for producing and issuing a first halt signal that is received by the first control input terminal of, and halts the pass-through of clock pulses at, the second clock control means when the predetermined code sequence value X2A0 is received, where M3 is a predetermined positive integer;

    fourth decoder means, connected to the fourth register means, for receiving the code sequence values X2B(t) (t=m4 T;

    m4 =1, 2, . . . M4) issued by the fourth register means, for detecting occurrence of a predetermined code sequence value X2A0, and for producing and issuing a first halt signal that is received by the first control input terminal of, and halts the pass-through of clock pulses at, the third clock control means when the predetermined code sequence value X2B0 is received, where M4 is a predetermined positive integer;

    a period counter that receives and counts the number of first reset signals issued by the second decoder means, that issues a first period counter output signal when this count has reached a fifth predetermined integer M5-1, and that issues a second period counter output signal when this count has reached the integer M5precession means for receiving a sequence of clock pulses from the clock pulse source, for receiving output signals from the third decoder means and from the fourth decoder means, and for receiving the first and second period counter output signals, for counting a predetermined number M6 of clock pulses, after receipt of a predetermined output signal from the third decoder means, and after receipt of a predetermined output signal from the first period counter, and for then issuing a second reset signal that is received by and commands the second clock control means and the third clock control means to resume pass-through and issuance of the sequence of clock pulses;

    first logic means for receiving the first and second code sequences X1B(t) and X1A(t) and for forming and issuing an Exclusive-Or combination signal X1(t)=X1B(t) ⊕

    X1A(t) as an output signal;

    second logic means for receiving the third and fourth code sequences X2A(t) and X2B(t) and for forming and issuing a time delayed Exclusive-Or combination signal X2(t)=X2A(t-KT) ⊕

    X2B(t-KT) as an output signal, where K is a predetermined non-negative integer;

    third logic means for receiving the code sequence signal X1(t) and X2(t) and for forming and issuing an Exclusive-Or combination signal P(t)=X1(t) ⊕

    X2(t);

    where the third register means and the fourth register means include a first latch with a first latch choice input terminal and a second latch with a second latch choice input terminal, respectively, that allows a choice of the contents of the first and second register means, respectively, from among M6 different initial code sequence values for the third register means and from among M7 different code sequence values for the fourth register means, where M6 and M7 are predetermined positive integers.

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