Method and apparatus for controlling peak factor of coherent frequency-division-multiplexed systems
First Claim
1. A method for controlling the peak factor of a coherent Frequency-Division-Multiplexed (FDM) system comprising the steps of:
- (a) providing means for generating a plurality of coherent carriers each having a phase angle which can be controlled in response to a corresponding phase angle error signal;
(b) establishing the frequencies of said coherent carriers such that each is an integral multiple of a predetermined fundamental frequency;
(c) combining said coherent carriers into a composite signal;
(d) digitally sampling said composite signal at a predetermined sampling rate, made coherent with said coherent carriers, so as to derive sampled composite data;
(e) digitally processing said sampled composite data to resolve the phase angle of each of said coherent carriers;
(f) comparing each of said resolved phase angles of said coherent carriers against a respective predetermined desired phase angle with the individual differences producing an array of corresponding phase angle error signals;
(g) applying the said array of corresponding phase angle error signals to adjust said phase angles of said coherent carriers; and
(h) repeating steps (d) through (g) such that each of said corresponding phase angle error signals converges toward zero as said resolved phase angles of said coherent carriers converge toward said respective predetermined desired phase angles.
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Abstract
A system is disclosed which can measure and control the absolute phase angles of individual coherent Frequency-Division-Multiplexed (FDM) carriers which have been combined to form a composite signal. User-specified phase relationships for the carriers are predetermined to produce an optimum peak factor (peak power to average power ratio) of the composite signal for a given application. In the preferred embodiment, phase relationships chosen to minimize peak factor can dramatically reduce the presence of intermodulation distortion products which can be detrimental to present communication architectures, such as Community Antenna Television (CATV). As CATV providers move toward using fiber-optic transmission networks for support of larger customer bases and inclusion of digital channels, there is a greater risk for rising signal amplitudes to induce clipping of CATV laser transmitters, thereby creating distortion which degrades analog picture quality and causes digital transmission errors to exceed maximum thresholds. Higher peak factors may be desirable, however, when testing individual components including CATV amplifiers, or subsystems such as linear fiber-optic transmission equipment, in order to more accurately characterize field performance. The disclosed invention uses a combination of RF, baseband, and digital techniques to repeatedly acquire and maintain desired peak factor conditions within coherent FDM systems.
247 Citations
16 Claims
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1. A method for controlling the peak factor of a coherent Frequency-Division-Multiplexed (FDM) system comprising the steps of:
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(a) providing means for generating a plurality of coherent carriers each having a phase angle which can be controlled in response to a corresponding phase angle error signal; (b) establishing the frequencies of said coherent carriers such that each is an integral multiple of a predetermined fundamental frequency; (c) combining said coherent carriers into a composite signal; (d) digitally sampling said composite signal at a predetermined sampling rate, made coherent with said coherent carriers, so as to derive sampled composite data; (e) digitally processing said sampled composite data to resolve the phase angle of each of said coherent carriers; (f) comparing each of said resolved phase angles of said coherent carriers against a respective predetermined desired phase angle with the individual differences producing an array of corresponding phase angle error signals; (g) applying the said array of corresponding phase angle error signals to adjust said phase angles of said coherent carriers; and (h) repeating steps (d) through (g) such that each of said corresponding phase angle error signals converges toward zero as said resolved phase angles of said coherent carriers converge toward said respective predetermined desired phase angles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for controlling the peak factor of a coherent FDM system comprising:
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(a) means for generating a plurality of coherent carriers and for controlling each of said coherent carrier'"'"'s phase angles in response to corresponding phase angle error signals; (b) means for establishing the frequencies of said coherent carriers such that each is an integral multiple of a predetermined fundamental frequency; (c) means for combining said coherent carriers into a composite signal; (d) means for digitally sampling said composite signal at a predetermined sampling rate, made coherent with said coherent carriers, so as to derive sampled composite data; (e) means for digitally processing said sampled composite data to resolve the phase angle of each of said coherent carriers; (f) means for comparing each of said resolved phase angles of said coherent carriers against a respective predetermined desired phase angle with the individual differences producing an array of corresponding phase angle error signals; and (g) means for applying the said array of corresponding phase angle error signals to adjust said phase angles of said coherent carriers. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification