Correlation data communications system
First Claim
1. A digital communications system comprising:
- means for generating a selected one of a plurality of n-bit binary code words from a received k-bit data word to provide a generated binary code word, where k and n are integers;
means for transmitting said generated binary code word;
means coupled to said transmitting means for receiving said generated binary code word;
first modulation means for modulating the output of a variable frequency local oscillator having a predetermined center frequency with said generated binary code word;
second modulation means for modulating the output of a fixed frequency local oscillator with the output of said first modulation means;
a reference code generator for generating a plurality of digital reference code words;
correlation means coupled to the output of said second modulation means and said reference code generator for comparing each of said digital reference code words with said generated binary code word and for providing a correlation output signal representing the correlation of one of said plurality of digital reference code words with said generated binary code word;
means responsive to a changing characteristic of said correlation output signal for determining a frequency translation error which occurred during transmission and reception of said generated binary code word; and
,means responsive to said determining means for adjusting the frequency of the output of said variable frequency oscillator in a direction to minimize the effect of said frequency translation error at the output of said correlation means.
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Abstract
A digital data communications system employing correlation detection is disclosed as comprising an encoding system which encodes successive k-bit data words from a data source into predetermined start-stop phases of either a 2k -bit repeating pseudorandom binary code or a 2k -1 bit repeating pseudorandom binary code and a decoding system which receives the stream of ones and zeros in the pseudorandom binary code from the encoder and reproduces therefrom, using a correlation detector and associated circuitry, a replica of the original k-bit data word from the data source. Undesirable signal variations in the output of the correlation detector caused by a frequency translation error introduced in the transmission and reception of the pseudorandom binary code is eliminated by a feedback system which detects the effects of the frequency translation error at the output of the correlation detector and applies a frequency correction signal component to the pseudorandom binary code which offsets the frequency translation error prior to introduction of the pseudorandom binary code to the correlation detector.
28 Citations
31 Claims
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1. A digital communications system comprising:
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means for generating a selected one of a plurality of n-bit binary code words from a received k-bit data word to provide a generated binary code word, where k and n are integers; means for transmitting said generated binary code word; means coupled to said transmitting means for receiving said generated binary code word; first modulation means for modulating the output of a variable frequency local oscillator having a predetermined center frequency with said generated binary code word; second modulation means for modulating the output of a fixed frequency local oscillator with the output of said first modulation means; a reference code generator for generating a plurality of digital reference code words; correlation means coupled to the output of said second modulation means and said reference code generator for comparing each of said digital reference code words with said generated binary code word and for providing a correlation output signal representing the correlation of one of said plurality of digital reference code words with said generated binary code word; means responsive to a changing characteristic of said correlation output signal for determining a frequency translation error which occurred during transmission and reception of said generated binary code word; and
,means responsive to said determining means for adjusting the frequency of the output of said variable frequency oscillator in a direction to minimize the effect of said frequency translation error at the output of said correlation means. - View Dependent Claims (3, 4, 7, 8, 9, 10, 11, 12, 13, 14)
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2. A digital communications system comprising:
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means for generating a selected one of a plurality of n-bit binary code words from a received k-bit data word to provide a generated binary code word, where k and n are integers; means for transmitting said generated binary code word; means coupled to said transmitting means for receiving said generated code word; first modulating means for modulating the output of a fixed frequency local oscillator with said generated binary code word; second modulating means for modulating the output of a variable frequency local oscillator with the output of said first modulation means; a reference code generator for generating a plurality of digital reference code words; correlation means coupled to the output of said second modulation means and said reference code generator for comparing each of said reference digital code words with said generated binary code word and for providing a correlation output signal representing the correlation of one of said plurality of digital reference code words with said generated binary code word; means responsive to a changing characteristic of said correlation output signal for determining a frequency translation error which occurred during transmission and reception of said generated binary code word; and
,means responsive to said determining means for adjusting the frequency of the output of said variable frequency oscillator in a direction to minimize the effect of said frequency translation error at the output of said correlation means. - View Dependent Claims (5, 6)
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15. An encoding system for transmitting digital code data comprising:
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means for receiving k-bit data words; means for generating from a received k-bit data word, a selected one of a plurality of n-bit pseudorandom code sequences which is assigned to said received k-bit data word and for adding to said selected pseudorandom code sequence at least one additional binary bit to produce a pseudorandom code word which contains an even number of data bits, half of which are of ones and half of which are zeros; and means for tansmitting said pseudorandom code word at a predetermined chipping frequency to a receiver. - View Dependent Claims (16, 17, 18)
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19. An encoding system for transmitting digital code data comprising:
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means for receiving k-bit data words; means for generating from a received k-bit data word a selected one of a plurality of n-bit pseudorandom code words which is assigned to said received k-bit data word, said means for generating being responsive to at least one predetermined k-bit data word to generate one of said plurality of pseudorandom code words with an inverted polarity; and
,means for transmitting the pseudorandom code words produced by said generating means.
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20. A data decoding system comprising:
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means for receiving a plurality of n-bit binary code words respectively generated from k-bit data words, where k and n are integers; first modulating means for modulating the output of a variable frequency oscillator having a predetermined center frequency with said received n-bit binary code words; second modulation means for modulating the output of a fixed frequency local oscillator with the output of said receiving means; a reference code generator for generating a plurality of digital reference code words; correlation means coupled to the output of said second modulation means and said reference code generator for comparing each of said digital reference code words with said generated binary code word and for providing a correlation output signal representing the correlation of one of said plurality of digital reference code words with said generated binary code word; means responsive to a changing characteristic of said correlation output signal for determining a frequency translation error which occurred during transmission and reception of said generated binary code word; and
,means responsive to said determining means for adjusting the frequency of the output of said voltage controlled oscillator in a direction to minimize the effect of said frequency translation error at the output of said correlation means. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 31)
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21. A data decoding system comprising:
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means for receiving a plurality of n-bit binary code words respectively generated from k-bit data words, where k and n are integers, said n-bit binary code words being modulated by first modulation means on the output of a fixed frequency oscillator; second modulation means for modulating the output of a variable frequency local oscillator with the output of said first modulation means; a reference code generator for generating a plurality of digital reference code words; correlation means coupled to the output of said second modulation means and said reference code generator for comparing each of said digital reference code words with said generated binary code word and for providing a correlation output signal representing the correlation of one of said plurality of digital reference code words with said generated binary code word; means responsive to a changing characteristic of said correlation output signal for determining a frequency translation error which occurred during transmission and reception of said generated binary code word; and
,means responsive to said determining means for adjusting the frequency of the output of said voltage controlled oscillator in a direction to minimize the effect of said frequency translation error at the output of said correlation means. - View Dependent Claims (30)
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Specification