Methods and apparatus for rejection of interference in a digital communications system
First Claim
1. A method for minimizing interference to a data carrier in a data communications system having a potentially-interfering signal system-wide signal at a known frequency (fS) and harmonics of said system-wide signal, comprising the steps of:
- (a) generating said data carrier at a frequency (fC)substantially midway between an adjacent pair of the N-th and the N+1-st harmonics of said system-wide single signal; and
(b) locking the frequency (fC) of said data carrier to an odd multiple (2N+1) of the first subharmonic (fS/2) of the known frequency (fS) of said single system-wide signal such that fC =(2N+1)(fS /2), where N is an integer greater than zero, to maintain the frequency of said data carrier with essentially equal frequency seapration from each of said adjacent pair of harmonics even if said known frequency varies.
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Accused Products
Abstract
A digital communications system of the type transmitting data on a plurality of modulated FDM carriers interspersed between harmonics of a system-wide signal and utilizing a main synchronized detector at a receiving end, is immunized to signal degradation due to reception of "noise" from both the shifting of signal harmonics and the modulation sidebands of adjacent carriers into the passband of the desired communications signal during at least synchronization acquisition by methods of interference minimization including: emplacing each data carrier at a frequency mid-way between adjacent harmonics; locking the frequency of the data carrier to the system-wide signal frequency to maintain the communications frequency exactly mid-way between two adjacent harmonics of the latter signal; transmitting the data in digital form and modulating each data carrier at a baud essentially equal to an exact even submultiple of the system-wide potentially-interfering signal, and detecting the transmitted digitally-modulated carrier at the receiving end by use of long-time-constant bandpass filters. Similar integrating filters, having means for discharging the storage elements thereof after each baud time period as determined by a baud clock synchronized to the system-wide signal, are utilized for the main synchronized data detector.
68 Citations
19 Claims
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1. A method for minimizing interference to a data carrier in a data communications system having a potentially-interfering signal system-wide signal at a known frequency (fS) and harmonics of said system-wide signal, comprising the steps of:
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(a) generating said data carrier at a frequency (fC)substantially midway between an adjacent pair of the N-th and the N+1-st harmonics of said system-wide single signal; and (b) locking the frequency (fC) of said data carrier to an odd multiple (2N+1) of the first subharmonic (fS/2) of the known frequency (fS) of said single system-wide signal such that fC =(2N+1)(fS /2), where N is an integer greater than zero, to maintain the frequency of said data carrier with essentially equal frequency seapration from each of said adjacent pair of harmonics even if said known frequency varies. - View Dependent Claims (2, 3)
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4. A method for minimizing interference in a data communications system having a data carrier, at least one other data carrier, and a potentially-interfering system-wide signal at a known frequency, each of said data carrier and said at least one other data carrier simultaneously carrying an associated data sequence, said method comprising the steps of:
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(a) generating said data carrier at a frequency substantially midway between an adjacent pair of harmonics of said system-wide signal; (b) locking the frequency of said data carrier to the known frequency of said system-wide signal to maintain the frequency of said data carrier with essentially equal frequency separation from each of said adjacent pair of harmonics, even if said known frequency varies; (c) generating each of said at least one other data carriers at a frequency substantially midway between each of at least one other pair of harmonics of said known frequency and differing from the pair of harmonics adjacent to said data carrier; (d) locking the frequency of each of said at least one other data carriers to said known frequency to maintain essentially frequency separation between each of said at least one other data carriers and each of the associated pair of harmonics of said known frequency, even if said known frequency varies; (e) digitizing each data sequence; (f) modulating each of said data carrier and said at least one other data carrier in accordance with the associated digitized data sequence; and (g) selecting the modulation characteristics to position a null of the modulation envelope of each modulated data carrier at the carrier frequencies of all of the remaining data carriers. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12)
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13. A digital communications system for the transmission of data in media having a potentially-interfering system-wide signal of known frequency, said system comprising:
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transmitting means including first means for generating a data carrier at a frequency essentially midway between a pair of adjacent harmonics of said known frequency; second means responsive to said known frequency for locking the frequency of said first means exactly midway between said pair of adjacent harmonics; third means for generating a baud essentially equal to an even integer submultiple (m) of said known frequency, where m is greater than 1; fourth means for storing a data sequence to be transmitted, said fourth means having an output at which sequential single bits of said data sequence are present responsive to sequential cycles of said baud; fifth means for varying an electrical parameter of said data carrier responsive to said sequential single bits at said output of said fourth means, said fifth means having an output coupled to the transmission media of said system; and receiving means comprising sixth means for acquiring said baud at the initiation of a data transmission of said data carrier; seventh means for coupling said sixth means to said media; and eighth means coupled to said seventh means for synchronously demodulating said data carrier responsive to the baud established by said sixth means. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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Specification