Method and apparatus for conditioning modulated signals for digital communications
First Claim
1. A method for conditioning a digitally modulated signal, comprising the steps of:
- mapping a digital information stream onto a symbol constellation to generate a sequence of channel symbols;
processing the sequence of channel symbols to provide a conditioned signal having a signal envelope that avoids signal envelope magnitudes below a minima threshold, including the steps of;
determining symbol interval minimum values for a signal envelope of a representative signal for the sequence of channel symbols when processed through a spectral shaping filter; and
generating the conditioned signal by adjusting the signal envelope of the representative signal by inserting an adjustment pulse between first and second channel symbols of the sequence of channel symbols to increase a particular symbol interval minimum value, when the particular symbol interval minimum value is below the minima threshold.
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Abstract
A digitally modulated signal is conditioned, such as to facilitate amplification. The digitally modulated signal is derived from an information stream which is mapped onto a symbol constellation to generate a sequence of channel symbols. The sequence of channel symbols is processed to provide a conditioned signal having a signal envelope that avoids signal envelope magnitudes below a threshold value (500). From a signal envelope representing the sequence of channel symbols, symbol interval minimum values are determined as the signal envelope transitions through successive channel symbols of the sequence (510). The conditioned signal is generated by localized adjustment of the signal envelope, such as by insertion of an adjustment pulse, to increase a particular symbol interval minimum value, when that value is below the threshold value (520, 530, 540, 545, 555).
106 Citations
19 Claims
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1. A method for conditioning a digitally modulated signal, comprising the steps of:
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mapping a digital information stream onto a symbol constellation to generate a sequence of channel symbols; processing the sequence of channel symbols to provide a conditioned signal having a signal envelope that avoids signal envelope magnitudes below a minima threshold, including the steps of; determining symbol interval minimum values for a signal envelope of a representative signal for the sequence of channel symbols when processed through a spectral shaping filter; and generating the conditioned signal by adjusting the signal envelope of the representative signal by inserting an adjustment pulse between first and second channel symbols of the sequence of channel symbols to increase a particular symbol interval minimum value, when the particular symbol interval minimum value is below the minima threshold. - View Dependent Claims (2, 3)
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4. A method for conditioning a digitally modulated signal, comprising the steps of:
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mapping a digital information stream onto a symbol constellation to generate a sequence of channel symbols; and processing the sequence of channel symbols to provide a conditioned signal having a signal envelope that avoids signal envelope magnitudes below a minima threshold; wherein the step of processing comprises the steps of; (a) determining that a minimum signal envelope value, Mins, corresponding to a representative signal envelope transitioning between first and second channel symbols occurring successively in the sequence, is below the minima threshold, Mind ; when Mins is less than Mind ; (b) generating a magnitude value, M=Mind -Mins ; (c) determining a signal phase rotation, Phr, for the signal envelope when transitioning between the first and second channel symbols; (d) determining a phase, Phs, for the first channel symbol; (e) generating a phase value, Phadj, wherein Phadj =Phs +Phr /2; and (f) inserting an adjustment pulse midway between the first and second symbols, the adjustment pulse having a magnitude M and a phase Phadj. - View Dependent Claims (5)
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6. A method for processing a digital information stream in a digital transmitter that includes a spectral shaping filter, comprising the steps of:
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mapping the digital information stream onto a symbol constellation to generate a sequence of symbols; determining, with respect to a signal envelope representing the sequence of symbols, symbol interval minimas, wherein a symbol interval minima corresponds to a minimum value of the signal envelope during a transition between two symbols occurring successively within the sequence; selectively inserting at least one adjustment pulse between successive symbols of the sequence of symbols to avoid symbol interval minimas below a minima threshold, thereby generating a conditioned digitally modulated signal; processing the conditioned digitally modulated signal with the spectral shaping filter to generate a filtered signal; and coupling the filtered signal to an amplifier. - View Dependent Claims (7, 8, 9)
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10. A digital transmitter, comprising:
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a digital information source providing a digital information signal; a channel symbol mapper coupled to digital information source, and being operable to map the digital information signal to a sequence of channel symbols according to a symbol constellation, thereby generating a modulated signal; and a signal conditioner coupled to the channel symbol mapper, and being operable to determine, with respect to a signal envelope representing the sequence of symbols, symbol interval minimas, wherein a symbol interval minima corresponds to a minimum value of the signal envelope during a transition between two symbols occurring successively within the sequence, the signal conditioner being operable to adjust the signal envelope to avoid symbol interval minimas below a minima threshold, thereby generating a conditioned signal; wherein the signal conditioner comprises a pulse injector that selectively inserts an adjustment pulse within the modulated signal during transitions of the signal envelope between selected channel symbols of the sequence. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A digital transmitter, comprising:
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a digital information source providing an digital information signal; a channel symbol mapper coupled to digital information source, and being responsive to the digital information signal to generate a modulated signal comprising a sequence of channel symbols according to a symbol constellation; a signal conditioner coupled to the channel symbol mapper, and being operable to determine, with respect to a signal envelope representing the sequence of channel symbols, symbol interval minimas, wherein a symbol interval minima corresponds to a minimum value of the signal envelope during a transition between two channel symbols occurring successively within the sequence, the signal conditioner being operable to adjust the signal envelope to avoid symbol interval minimas below a minima threshold, thereby generating a modified sequence of channel symbols; a spectral shaping filter responsive to the modified modulated signal and having an output of a filtered symbol sequence; and an amplifier coupled to the output of the spectral shaping filter, and providing an amplified signal; wherein the signal conditioner operates based at least in part on characteristics of the spectral shaping filter. - View Dependent Claims (17, 18, 19)
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Specification