Method and apparatus for transparent tone-in-band transmitter, receiver and system processing
First Claim
1. A method of processing a received signal derived by a process comprising dividing a spectrum of an original signal at a predetermined frequency and inserting a notch separating an upper spectrum portion and a lower spectrum portion of the received signal, a spectrum of the received signal containing frequency components corresponding to frequency components in the original signal, and first and second respective border regions of the upper and lower portion, respectively, containing an overlap frequency component derived from a single frequency component in an overlap frequency band of the original signal which includes the predetermined frequency, when the overlap band contains such a component,the method comprising the steps of:
- selecting first and second signals from said first and said second border regions at a location in a circuit processing the signal where the border regions have first and second roll off characteristics for the upper and lower portions, respectively, and using third and fourth roll off characteristics for the border regions of the upper and lower portions, respectively,the first and third roll off characteristics providing a composite roll off characteristic which is symmetrical about a frequency in the upper portions which is derived from the said predetermined frequency and the second and fourth roll off characteristics providing a composite characteristic which is symmetrical about a frequency in the lower portion which is derived from the said predetermined frequency,deriving a control signal from the first and second signals representative of difference in frequency and phase of the said overlap component, when present, of the upper and lower portions, andderiving, using the said control signal, an output signal containing frequency components corresponding to frequency components in the upper and lower portions in a continuous spectrum without the notch and in which the frequency and phase relationships between frequency components of the original signal are restored.
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Accused Products
Abstract
In deriving a control signal for recombining the parts of the spectrum separated by a frequency notch in transparent tone-in-band signals, cross-correlation products give rise to undesirable frequency and phase jitter. In a receiver which overcomes this problem an input signal E containing the notch is passed to two first mixers and then portions corresponding to the lower and upper portions of the input spectrum are selected by two mirror filters before being translated in frequency by two second mixers to a final output band in which the notch is eliminated. Two selection filters select parts of the spectra at the outputs of the first mixers which correspond to an overlap region of the said lower and upper portions when derived in a transmitter and apply them to a control-signal mixer. A control signal for the second mixers is derived from the output of the control-signal mixer by noise filtering and frequency division by two. The above mentioned problem is overcome by giving the mirror filters transfer functions H1- (f) and H1+ (f) which are the same as the transfer functions of mirror filters in the transmitter which produced the notch and by giving the selection filters transfer functions H2- (f) and H2+ (f) which satisfy the relationships H2- (f)=|H1- (f)|2 and H2+ (f)=|H1+ (f)|2.
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Citations
16 Claims
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1. A method of processing a received signal derived by a process comprising dividing a spectrum of an original signal at a predetermined frequency and inserting a notch separating an upper spectrum portion and a lower spectrum portion of the received signal, a spectrum of the received signal containing frequency components corresponding to frequency components in the original signal, and first and second respective border regions of the upper and lower portion, respectively, containing an overlap frequency component derived from a single frequency component in an overlap frequency band of the original signal which includes the predetermined frequency, when the overlap band contains such a component,
the method comprising the steps of: -
selecting first and second signals from said first and said second border regions at a location in a circuit processing the signal where the border regions have first and second roll off characteristics for the upper and lower portions, respectively, and using third and fourth roll off characteristics for the border regions of the upper and lower portions, respectively, the first and third roll off characteristics providing a composite roll off characteristic which is symmetrical about a frequency in the upper portions which is derived from the said predetermined frequency and the second and fourth roll off characteristics providing a composite characteristic which is symmetrical about a frequency in the lower portion which is derived from the said predetermined frequency, deriving a control signal from the first and second signals representative of difference in frequency and phase of the said overlap component, when present, of the upper and lower portions, and deriving, using the said control signal, an output signal containing frequency components corresponding to frequency components in the upper and lower portions in a continuous spectrum without the notch and in which the frequency and phase relationships between frequency components of the original signal are restored. - View Dependent Claims (2, 3, 4, 5, 6, 12, 13)
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7. A receiver processor for processing a received signal derived by a process that includes dividing a spectrum of an original signal at a predetermined frequency and inserting a notch separating an upper spectrum portion and lower spectrum portions of the received signal, the spectrum of the received signal including frequency components corresponding to frequency components in the original signal, and each of first and second border regions of the upper and lower portions, respectively, including an overlap frequency component derived from a single frequency component in an overlap frequency band of the original signal which includes the predetermined frequency, when the overlap band includes such a component,
the receiver processor comprising: -
selection means for selecting first and second signals from said first and said second border regions at a location in the receiver processor where said border regions have first and second roll off characteristics for the upper and lower portions, respectively, the selection means, in operation, employing third and fourth roll off characteristics, respectively, to select the first and second signals, and wherein the selection means being such that the first and third roll off characteristics provide a composite roll off characteristic which is symmetrical about a frequency in the upper portion which is, in operation, derived from the said predetermined frequency, and such that the second and fourth roll off characteristics provide a composite characteristic which is symmetrical about a frequency in the lower portion which is, in operation, derived from the said predetermined frequency, means for deriving a control signal from the first and second signals representative of a difference in frequency and phase of the said overlap component, when present, of the upper and lower portions, and means for deriving, using the said control signal, an output signal containing frequency components corresponding to frequency components in the upper and lower portions in a continuous spectrum with the notch and in which the frequency and phase relationships between frequency components of the original signal are restored. - View Dependent Claims (8, 9, 10, 11)
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14. A communication system comprising:
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a transmitter processor for generating a transmit signal from which a received signal is derived, the transmit signal being derived by dividing a spectrum of an original signal at a predetermined frequency and inserting a notch separating an upper spectrum portion and lower spectrum portions of the transmit signal, the spectrum of the transmit signal including frequency components corresponding to frequency components in the original signal, and each of first and second border regions of the upper and lower portions, respectively, including an overlap frequency component derived from a single frequency component in an overlap frequency band of the original signal which includes the predetermined frequency, when the overlap band includes such a component, and a receiver processor for processing the received signal comprising; selection means for selecting first and second signals from said first and said second border regions at a location in said communication system where said border regions have first and second roll off characteristics for the upper and lower portions, respectively, the selection means, in operation, employing third and fourth roll off characteristics, respectively, to select the first and second signals, and wherein the selection means being such that the first and third roll off characteristics provide a composite roll off characteristic which is symmetrical about a frequency in the upper portion which is, in operation, derived from the said predetermined frequency, and such that the second and fourth roll off characteristics provide a composite characteristic which is symmetrical about a frequency in the lower portion which is, in operation, derived from the said predetermined frequency, means for deriving a control signal from the first and second signals representative of difference in frequency and phase of the said overlap component, when present, of the upper and lower portions, and means for deriving, using the said control signal, an output signal containing frequency components corresponding to frequency components in the upper and lower portions in a continuous spectrum without the notch and in which the frequency and phase relationships between frequency components of the original signal are restored. - View Dependent Claims (15, 16)
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Specification