CSK communication system
First Claim
1. A Code Shift Keying (CSK) communication system for transmitting and receiving digital data each of which is a bit having a value of either "1" or "0," the system comprising:
- a transmitter includingmeans for processing each of its input bits,means for continuously generating two M-series codes, a first M-series code being identical to a second M-series code except in its phase,means for selecting one of said two M-series codes depending on the value of a particular bit being processed, andmeans for outputting as a transmitted signal the selected code in a period of time spanning the duration of the particular bit; and
a receiver includingmeans for recapturing the transmitted signal as a received signal,means for obtaining two correlation signals by correlating the received signal with each copy of the two M-series codes,means for partitioning each correlation signal into a sequence of consecutive periods,means for comparing during each period the largest peak of one correlation signal with the largest peak of the other correlation signal,means for deciding during each period whether the received signal spanning the period has value of "1" or "0" depending on the result of comparing the sizes of the peaks, andmeans for generating a sequence of bits each of which has value of either "1" or "0."
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Accused Products
Abstract
The present invention provides new arrangements for various components of a CSK communication system: modulator, correlators, demodulator, carrier detection circuit, and synchronization control circuit. The various improvements provide more accurate demodulation of data from the received signal in the presence of noise and signal deterioration. A modulator configuration permits the CSK system to use two M series codes in which the second code is simply a phase shifted version of the first code. The PN correlators, via shift-registers, efficiently output two correlation signals. The demodulator accepts two correlation signals from the correlators, detects auto-correlation peaks in the correlation signals, and uses the peaks to accurately determine whether the received bit has a value of "1" or "0". The carrier detecting circuit detects the presence of data in the received signal. A carrier detecting circuit conveniently allows demodulation of data without exact synchronization of the center of demodulator'"'"'s monitoring window to auto-correlation peaks. The synchronization control circuit generates accurate timing pulses that mark the start and end of each data bit. If auto-correlation peaks appear consistently in one location for the duration of N consecutive data bits, subsequent timing pulses are delayed in accordance with weighted averages of the stored locations of auto-correlation peaks. In one embodiment, separate correlation signal monitoring windows for demodulation and synchronization tracking may be set independently of each other, enabling the demodulator to clearly distinguish between an actual auto-correlation peaks and an inter-correlation peak, and the synchronization control circuit to attain stability by "averaging" out temporal effects of noise.
86 Citations
43 Claims
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1. A Code Shift Keying (CSK) communication system for transmitting and receiving digital data each of which is a bit having a value of either "1" or "0," the system comprising:
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a transmitter including means for processing each of its input bits, means for continuously generating two M-series codes, a first M-series code being identical to a second M-series code except in its phase, means for selecting one of said two M-series codes depending on the value of a particular bit being processed, and means for outputting as a transmitted signal the selected code in a period of time spanning the duration of the particular bit; and a receiver including means for recapturing the transmitted signal as a received signal, means for obtaining two correlation signals by correlating the received signal with each copy of the two M-series codes, means for partitioning each correlation signal into a sequence of consecutive periods, means for comparing during each period the largest peak of one correlation signal with the largest peak of the other correlation signal, means for deciding during each period whether the received signal spanning the period has value of "1" or "0" depending on the result of comparing the sizes of the peaks, and means for generating a sequence of bits each of which has value of either "1" or "0." - View Dependent Claims (2)
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3. A Code Shift Keying (CSK) communication system transmitter for processing and transmitting digital data each of which is a bit having a value of either "1" or "0," the transmitter comprising:
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M-series code generating means for continuously generating a first and a second M-series codes in a period of time spanning the duration of a particular bit, the first M-series code being identical to the second M-series code in its sequence of 1'"'"'s and 0'"'"'s but different in its phase; and a switching circuit for selecting one of said two M-series codes depending on the value of said particular bit, and for outputting, as transmitted signal, the selected code in a period of time spanning the duration of the particular bit. - View Dependent Claims (4, 5)
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6. A Code Shift Keying (CSK) communication system receiver for receiving a signal and processing the received signal which is capable of including series of a first and a second M-series codes which is identical to the first code except in its phase, the receiver comprising:
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a first correlator for generating a first correlation signal by correlating a local replica of the first code and the received signal; a second correlator for generating a second correlation signal by correlating a local replica of the second code and the received signal; and a demodulator for periodically monitoring the first and the second correlation signals, for comparing during each monitoring period the largest peak of the first correlation signal with the largest peak of the second correlation signal, for deciding during each monitoring period whether the received signal spanning the monitoring period has value of "1" or "0" depending on the result of comparing sizes of said largest peaks, and for generating sequence of bits each of which has value of either "1" or "0." - View Dependent Claims (7)
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8. A Code Shift Keying (CSK) communication system receiver which includes two correlators for generating two correlation signals from a received signal, a demodulator for generating sequence of data bits based on two correlation signals and periodic timing pulses, a carrier detecting circuit for providing signals to and accepting signals from a timing pulse generator and accepting signals from two correlators, and the timing pulse generator for generating the timing pulses partly based on signals within or from the carrier detecting circuit, wherein the carrier detecting circuit comprises:
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a peak position detecting circuit including operating means for outputting peaks of a signal formed by processing two correlation signals, means for detecting each position of said peaks, each peak within a single period of time spanned by one bit, and means for outputting a peak position detection signal; a peak position memory buffer for storing detected peak positions over a duration of time spanned by N data bits; partitioning means for assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups; first means for determining, for each duration of time spanning one bit of data, which of M subintervals contain a correlation peak, whose position is stored in said peak position memory buffer; means for counting the total number of correlation peaks contained within each subinterval group based on outputs from said first determining means, and for outputting each of M counts resulting from the counting; second means for determining if any of M counts is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and for outputting various signals including a carrier detection signal thereafter. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A Code Shift Keying (CSK) communication system receiver which includes two correlators for generating two correlation signals from a received signal, a demodulator for generating a sequence of data bits based on two correlation signals and periodic timing pulses, a carrier detecting circuit for providing signals to and accepting signals from a timing pulse generator and accepting signals from two correlators, and the timing pulse generator for generating the timing pulses partly based on signals from the carrier detecting circuit, wherein the carrier detecting circuit comprises:
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a peak position detecting circuit including operating means for outputting peaks of a signal formed by processing two correlation signals, means for detecting each position of said peaks, each peak within a single period of time spanned by one bit, and means for outputting a peak position detection signal;
a peak position determining circuit includingpartitioning means for assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups, and means for determining, for each duration of time spanning one bit of data, which of M subintervals contain a correlation peak based on said peak position detection signal; counting means for counting the total number of correlation peaks contained within each subinterval group based on outputs from said peak position determining circuit, and for outputting each of M counts resulting from the counting; an m/N determining circuit for determining if any of said M counts is equal to or greater than a prescribed number m, for deciding that a carrier has been detected if one of the counts is not less than m, and for outputting various signals including a carrier detection signal thereafter. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A Code Shift Keying (CSK) communication system receiver comprising:
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two correlators for generating two correlation signals from a received signal; a carrier detecting means for receiving signals from said two correlators and accepting signals from and providing signals to a synchronization control circuit; the synchronization control circuit including first monitoring means for periodically monitoring two correlation signals, means for generating timing pulses partly based on outputs from the first monitoring means, and on outputs from said carrier detecting means; and
a demodulator includingfirst monitoring means for periodically monitoring two correlation signals, means for generating a sequence of data bits based on outputs from the first monitoring means and based on the periodic timing pulses.
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23. A Code Shift Keying (CSK) communication method for transmitting and receiving digital data each of which is a bit having a value of either "1" or "0," the method comprising the steps of:
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transmitting, comprising the steps of; processing each of its input bits, continuously generating two M-series codes, a first M-series code being identical to a second M-series code except in its phase, selecting one of said two M-series codes depending on the value of a particular bit being processed, and outputting as a transmitted signal the selected code in a period of time spanning the duration of the particular bit; and
receiving, comprising the steps of;recapturing the transmitted signal as a received signal, obtaining two correlation signals by correlating the received signal with each copy of the two M-series codes, partitioning each correlation signal into a sequence of consecutive periods, comparing during each period the largest peak of one correlation signal with the largest peak of the other correlation signal, deciding during each period whether the received signal spanning the period has value of "1" or "0" depending on the result of comparing the sizes of the peaks, and generating a sequence of bits each of which has value of either "1" or "0." - View Dependent Claims (24)
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25. A Code Shift Keying (CSK) communication transmitting method for processing and transmitting digital data each of which is a bit having a value of either "1" or "0," the transmitting method comprising the steps of:
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continuously generating a first and a second M-series codes in a period of time spanning the duration of a particular bit, the first M-series code being identical to the second M-series code in its sequence of 1'"'"'s and 0'"'"'s but different in its phase; selecting one of said two M-series codes depending on the value of said particular bit; outputting, as transmitted signal, the selected code in a period of time spanning the duration of the particular bit. - View Dependent Claims (26, 27)
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28. A Code Shift Keying (CSK) communication receiving method for capturing a signal and processing the captured signal which is capable of including series of a first and a second M-series codes which is identical to the first code except in its phase, the receiving method comprising the steps of:
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generating a first correlation signal by correlating a local of the first code and the captured signal; generating a second correlation signal by correlating a local replica of the second code and the captured signal; and demodulating, including the steps of; periodically monitoring the first and the second correlation signals, comparing during each monitoring period the largest peak of the first correlation signal with the largest peak of the second correlation signal, deciding during each monitoring period whether the captured signal spanning the monitoring period has the value of "1" or "0" depending on the result of comparing sizes of said largest peaks, and generating sequence of bits each of which has value of either "1" or "0." - View Dependent Claims (29)
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30. A Code Shift Keying (CSK) communication receiving method comprising steps of generating two correlation signals from a received signal, demodulating a sequence of data bits based on two correlation signals and periodic timing pulses, producing synchronization signals based on timing pulses and two correlation signals, and generating the timing pulses partly based on synchronization signals, wherein the step of producing synchronization signals comprises the steps of:
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(1) peak position detecting, including the steps of; processing two correlation signals, generating peaks of a signal resulting from the processing, detecting each position of said peaks, each peak within a single period of time spanned by one bit, and outputting a peak position detection signal; (2) storing detected peak positions over a duration of time spanned by N data bits; (3) assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups; (4) determining, for each duration of time spanning one period, which of M subintervals contain one of stored detected peaks; (5) counting, for each subinterval group, the total number of correlation peaks contained within each subinterval group based on the intermediate and final results of step (4); (6) generating each of M counts resulting from the counting (5); (7) determining if any of M counts is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and thereafter producing various synchronization signals. - View Dependent Claims (31, 32, 33, 34, 35)
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36. A Code Shift Keying (CSK) communication receiving method comprising steps of generating two correlation signals from a received signal, demodulating a sequence of data bits based on two correlation signals and periodic timing pulses, producing synchronization signals based on timing pulses and two correlation signals, and generating the timing pulses partly based on synchronization signals, wherein the producing synchronization signals comprises the steps of:
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(1) peak position detecting including the steps of; processing two correlation signals, generating peaks of a signal resulting from the processing, detecting each position of said peaks, each peak within a single period of time spanned by one bit, and outputting a peak position detection signal; (2) peak position determining, comprising the steps of;
assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups, anddetermining, for each duration of time spanning one period, which of M subintervals contain one of stored detected peaks; (3) counting, for each subinterval group, the total number of correlation peaks contained within each subinterval group based on the intermediate and final results of step (2); (4) generating each of M counts resulting from the counting in step (3); and (5) determining if any of M counts from step (4) is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and thereafter producing various synchronization signals. - View Dependent Claims (37, 38, 39, 40, 41, 42)
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43. A Code Shift Keying (CSK) communication receiving method comprising the steps of:
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generating two correlation signals from a received signal; processing two correlation signals and timing signals to produce synchronization signals; pulse generating, comprising the steps of; (1) periodically monitoring two correlation signals, (2) generating timing pulses partly based on the result of (1), and on synchronization signals; and demodulating, comprising the steps of; (3) periodically monitoring two correlation signals independently from (1), (4) generating a sequence of data bits based on the result of (3) and on the periodic timing pulses.
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Specification