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US4843615A
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CPFSK communication system employing nyquist-filtered modulator/demodulator
Assignee: Harris Corp
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Filing: 1987-05-08
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Granted: 1989-06-27
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Expires: 2007-05-08
Abstract
Abstract An improved narrowband continuous phase modulation system incorporates a filtering mechanism in the transmitter and receiver sites that enables the radiated spectrum characteristic to have a substantially reduced response at frequencies other than the channel of interest and thereby achieve a significant reduction in unwanted adjacent channel interference. Each of the transmitter and receiver sites contains a square root Nyquist filter upstream and downstream of the modulator and demodulator, respectively. The output of the Nyquist filter in the receiver is coupled to an accumulator which sums successive samples of the demodulated data signals (including noise). The noise is reduced as a consequence of its inherent negative correlation properties (utilized in the accumulation of successive samples of the recovered signal).
Inventors
- 👤 Robert C. Davis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 10:25
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/18; H04L27/20; H04L27/2003; H04L27/2007; H04L27/2017; H04L27/22; H04L27/233; H04L27/2334
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
81 words
For use in a communication system wherein frequency modulated signals, representative of information signals that have been transmitted from a transmitter site over a communications link, are demodulated at a receiver, a method of enhancing the characteristics of the recovered information signals comprising the steps of: (a) filtering the demodulated information signals by way of a Nyquist filtering mechanism; and (b) accumulating successive samples of the filtered demodulated signals, so as to derive information output signals having reduced noise signal content.
Claim 2
Dependent Claim
81 words
For use in a communication system wherein frequency modulated signals, representative of information signals that have been transmitted from a transmitter site over a communications link, are demodulated at a receiver, a method of enhancing the characteristics of the recovered information signals comprising the steps of: (a) filtering the demodulated information signals by way of a Nyquist filtering mechanism; and (b) accumulating successive samples of the filtered demodulated signals, so as to derive information output signals having reduced noise signal content.
Claim 3
Dependent Claim
40 words
A method according to claim 1, wherein said transmitter site contains a Nyquist filtering mechanism through which said information signals have been filtered in the course of generating said frequency modulated signals that have been transmitted over said communications link.
Claim 4
Dependent Claim
31 words
A method according to claim 2, wherein said receiver contains a frequency discriminator through which said frequency modulated signals are demodulated prior to being filtered in accordance with a step (a).
Claim 5
Dependent Claim
25 words
A method according to claim 2, wherein each of the Nyquist filtering mechanisms at the transmitter and receiver sites comprises a square root Nyquist filter.
Claim 6
Dependent Claim
19 words
A method according to claim 4, wherein said square root Nyquist filter comprises a square root raised cosine filter.
Claim 7
Dependent Claim
14 words
A method according to claim 1, wherein said information signals comprise digital data signals.
Claim 8
Dependent Claim
20 words
A method according to claim 5, wherein said frequency modulated signals comprise M-ary encoded continuous phase frequency shift keyed signals.
Claim 9
Dependent Claim
42 words
A method according to claim 1, wherein step (b) accumulates successive samples of demodulated information signals over a plurality of sampling intervals the periods of which correspond to integral multiples of the inverse of the data repetition rate of the information signals.
Claim 10
Dependent Claim
100 words
For use in a communication system wherein frequency modulated signals, representative of information signals that have been transmitted from a transmitter site over a communications link, are demodulated at a receiver, an arrangement for enhancing the characteristics of the recovered information signals comprising: first means, coupled to receive the demodulated information signals, for filtering said demodulated information signals by way of a Nyquist filtering mechanism; and second means, coupled to receive the Nyquist-filtered signals produced by said first means, for accumulating successive samples of the filtered demodulated signals, so as to derive information output signals having reduced noise signal content.
Claim 11
Dependent Claim
100 words
For use in a communication system wherein frequency modulated signals, representative of information signals that have been transmitted from a transmitter site over a communications link, are demodulated at a receiver, an arrangement for enhancing the characteristics of the recovered information signals comprising: first means, coupled to receive the demodulated information signals, for filtering said demodulated information signals by way of a Nyquist filtering mechanism; and second means, coupled to receive the Nyquist-filtered signals produced by said first means, for accumulating successive samples of the filtered demodulated signals, so as to derive information output signals having reduced noise signal content.
Claim 12
Dependent Claim
40 words
An arrangement according to claim 9, wherein said transmitter site contains a Nyquist filtering mechanism through which said information signals have been filtered in the course of generating said frequency modulated signals that have been transmitted over said communications link.
Claim 13
Dependent Claim
29 words
An arrangement according to claim 10, wherein said receiver contains a frequency discriminator through which said frequency modulated signals are demodulator prior to being filtered by said first means.
Claim 14
Dependent Claim
25 words
An arrangement according to claim 10, wherein each of the Nyquist filtering mechanisms at the transmitter and receiver sites comprises a square root Nyquist filter.
Claim 15
Dependent Claim
19 words
An arrangement according to claim 12, wherein said square root Nyquist filter comprises a square root raised cosine filter.
Claim 16
Dependent Claim
14 words
An arrangement according to claim 9, wherein said information signals comprise digital data signals.
Claim 17
Dependent Claim
20 words
An arrangement according to claim 13, wherein said frequency modulated signals comprise M-ary encoded continuous phase frequency shift keyed signals.
Claim 18
Dependent Claim
45 words
An arrangement according to claim 9, wherein said second means accumulates successive samples accumulates successive samples of demodulated signals over a plurality of sampling intervals the periods of which correspond to integral multiples of the inverse of the data repetition rate of the information signals.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-06-26 | 1992-12-26 | 1993-06-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-06-26 | 1996-12-26 | 1997-06-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-06-26 | 2000-12-26 | 2001-06-27 | $7700.00 | Window Closed / Lapsed |