EP0222593A2
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EP
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Digital filters and demodulators
Assignee: Signal Processors Ltd
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Filing: 1986-11-05
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Granted: —
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Expires: 2006-11-05
Abstract
Abstract Digital representations of a signal are stored in a store (8) e.g. in the order of their occurrence. Multipliers (9) multiply the samples by coefficients (C1 to C36) representing a function with which the samples are to be convolved. The signal is subject to variable time delays. To compensate for the variable time delays sets of coefficients are stored, the sets representing the function with different time delays. The set to be convolved with the signal is chosen in dependence upon the time delay of the signal. A signal indicative of the time delay is derived from an input to the shift register and fed-forward. The filter is preferably used in a digital demodulator of phase and/or amplitude modulated signals. The function is then a impulse function defining (at least in part) a desired frequency response of the filter, and the filter corrects the timing of symbols represented by the signal. In the digital demodulator, the symbol timing recovery and correction (4) takes place before carrier phase recovery (5) and demodulation.
Inventors
- 👤 Stephen Kingsley Barton
- 👤 Peter Martin Terrell
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 04:55
CPC Classifications
H; H04; H04L; H04L7/00; H04L7/0054; H04L7/007; H04L7/0016; H04L7/002; H04L7/0029
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
114 words
A demodulator for demodulating a phase and/or amplitude modulated signal in which symbols are represented by predetermined phases and/or amplitudes of the signal, the demodulator comprising: means, including an analogue-to-digital converter, for sampling the modulated signal with arbitrary phase, and digitising the samples to produce a digital representation of the modulated signal, a digital symbol timing recovery circuit for producing a signal indicative of symbol timing, a digital symbol timing correction circuit responsive to the symbol timing recovery circuit for correcting the symbol timing of the digital representation; and digital demodulation means, responsive to the symbol time corrected digital representation of the signal to recover the phase of the carrier and demodulate the signal.
Claim 2
Dependent Claim
114 words
A demodulator for demodulating a phase and/or amplitude modulated signal in which symbols are represented by predetermined phases and/or amplitudes of the signal, the demodulator comprising: means, including an analogue-to-digital converter, for sampling the modulated signal with arbitrary phase, and digitising the samples to produce a digital representation of the modulated signal, a digital symbol timing recovery circuit for producing a signal indicative of symbol timing, a digital symbol timing correction circuit responsive to the symbol timing recovery circuit for correcting the symbol timing of the digital representation; and digital demodulation means, responsive to the symbol time corrected digital representation of the signal to recover the phase of the carrier and demodulate the signal.
Claim 3
Dependent Claim
43 words
A demodulator according to claim 1 wherein the symbol timing recovery circuit is responsive to the signal at the input of the symbol timing correction circuit to derive, and feed forward to the symbol timing correction circuit, the signal indicative of symbol timing.
Claim 4
Dependent Claim
42 words
A demodulator according to claim 1, wherein the symbol timing recovery circuit is responsive to the signal at the output of the symbol timing correction circuit to derive, and feedback to the symbol timing correction circuit, the signal indicative of symbol timing.
Claim 5
Dependent Claim
40 words
A demodulator according to claim 1, wherein the symbol timing recovery circuit is responsive to the signal at the output of the demodulation means to derive, and feedback to the symbol timing correction circuit, the signal indicative of symbol timing.
Claim 6
Dependent Claim
36 words
A demodulator according to claim 1, 2 or 3, wherein the symbol timing correction circuit comprises a digital transversal filter, the phase slope of which is variable in dependence upon the signal indicative of symbol timing.
Claim 7
Dependent Claim
75 words
A demodulator according to claim 5, wherein the digital transversal filter comprises means in which the digital samples forming the digital representation of the original are stored; the samples are multiplied by respective coefficients representing a predetermined function; and sets of coefficients are stored, the sets representing the same function but with different relative time delays, and the set for multiplication with the samples is chosen in dependence upon the signal indicative of symbol timing.
Claim 8
Dependent Claim
90 words
A digital transversal filter according to claim 5 wherein the symbol timing correction circuit includes means for storing a sequence of digital samples representing the phase modulated signal, means for multiplying the stored samples with a set of coefficients representing a predetermined sampling function, means storing sets of the said coefficients, the sets representing the said function with different relative timing delays, and means responsive to the signal indicative of the timing of the symbols to choose the set appropriate to the indicated timing, for multiplication with the stored samples.
Claim 9
Dependent Claim
107 words
A demodulator for demodulating a modulated signal in which symbols are represented by predetermined phases and/or amplitudes of the signal, the demodulator comprising: means, including an analogue-to-digital converter, for sampling the modulated signal with arbitrary phase and digitising the samples to produce a digital representation of the modulated signal, a digital symbol timing correction circuit having an input for receiving the digital representation of the modulated signal for correcting the timing of the symbols, and a digital symbol timing recovery circuit, responsive to the signal at the input of the correcting circuit for deriving and feeding forward to the correcting circuit, a signal indicative of symbol timing.
Claim 10
Dependent Claim
107 words
A demodulator for demodulating a modulated signal in which symbols are represented by predetermined phases and/or amplitudes of the signal, the demodulator comprising: means, including an analogue-to-digital converter, for sampling the modulated signal with arbitrary phase and digitising the samples to produce a digital representation of the modulated signal, a digital symbol timing correction circuit having an input for receiving the digital representation of the modulated signal for correcting the timing of the symbols, and a digital symbol timing recovery circuit, responsive to the signal at the input of the correcting circuit for deriving and feeding forward to the correcting circuit, a signal indicative of symbol timing.
Claim 11
Dependent Claim
31 words
A demodulator according to claim 7 wherein the correcting circuit comprises a digital transversal filter the phase slope of which is variable in dependence upon the signal indicative of symbol timing.
Claim 12
Dependent Claim
70 words
A demodulator according to claim 7 or 8 wherein the correcting circuit means comprises means in which the digital samples are stored the samples are multiplied by respective coefficients representing a predetermined function, sets of coefficients are stored, the sets representing the same sampling function but with different relative time delays, and the set for multiplication with the samples is chosen in dependence upon the signal indicative of symbol timing.
Claim 13
Dependent Claim
108 words
A demodulator according to any of claims 1 to 10, wherein the symbol timing recovery circuit comprises a digital filter for producing the said indicative signal which represents the phase of the symbols relative to a digital phase reference signal having a sample rate half the symbol rate, the filter being arranged to produce the product ( a . b ) of those components falling within a predetermined frequency response around zero frequency of signals a , b where a represents the product of the symbols with the phase reference signal and b represents the product of the complex conjugate of the symbols with the phase reference signal.
Claim 14
Dependent Claim
95 words
A digital transversal filter in which a digital representation of a signal which is subject to variable time delays is convolved with a predetermined function to effect filtering, the filter comprising means in which the digital samples are stored, the symbols are multiplied by respective coefficients representing the function which which they are to be convolved, sets of the coefficients are stored, the sets representing the said function having different time delays, and the set for multiplication with the samples is chosen in dependence upon the time delay of the digital representation of the signal.
Claim 15
Dependent Claim
95 words
A digital transversal filter in which a digital representation of a signal which is subject to variable time delays is convolved with a predetermined function to effect filtering, the filter comprising means in which the digital samples are stored, the symbols are multiplied by respective coefficients representing the function which which they are to be convolved, sets of the coefficients are stored, the sets representing the said function having different time delays, and the set for multiplication with the samples is chosen in dependence upon the time delay of the digital representation of the signal.
Claim 16
Dependent Claim
100 words
A digital filter for producing a digital signal representing the phase of a complex digital symbol stream relative to a digital phase reference signal having a sample rate half the symbol rate of the symbol stream, the filter being arranged to produce the product ( a . b ) of those components falling within a predetermined frequency response around zero frequency of signals a , b , where a represents the product of the complex symbol stream with the phase reference signal, and b represents the product of the complex conjugate to the symbol stream with the phase reference signal.
Claim 17
Dependent Claim
100 words
A digital filter for producing a digital signal representing the phase of a complex digital symbol stream relative to a digital phase reference signal having a sample rate half the symbol rate of the symbol stream, the filter being arranged to produce the product ( a . b ) of those components falling within a predetermined frequency response around zero frequency of signals a , b , where a represents the product of the complex symbol stream with the phase reference signal, and b represents the product of the complex conjugate to the symbol stream with the phase reference signal.
Claim 18
Dependent Claim
69 words
A filter according to claim 13, wherein the phase reference signal is a complex signal of the form +1,+j,-1,-j and wherein the said components of signal a are derived from the sum of the imaginary and real parts of the product of the phase reference signal and the symbol stream, and the said components of signal b are derived from the difference of the said imaginary and real parts.
References Cited (Backward Citations)
EP0092400A2
Cited
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