Transmitter predistortion circuit and method therefor
First Claim
1. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
- obtaining a forward-data stream configured to convey a plurality of frequency-multiplexed communication channels;
processing said forward-data stream through said analog-transmitter components;
obtaining a return-data stream responsive to said forward-data stream after said forward-data stream has been influenced by said analog-transmitter components;
identifying a communication-signal strength for each of said communication channels in response to said forward-data stream;
identifying an error-signal strength for each of said communication channels in response to said return-data stream; and
counteracting distortion introduced by said analog-transmitter components in response to relative communication-signal strengths and error-signal strengths for said communication channels.
1 Assignment
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Accused Products
Abstract
A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200, 1800, 2800) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Distortion introduced by an analog-to-digital converter (304) may be compensated using a variety of adaptive techniques. Linear distortion is compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).
207 Citations
40 Claims
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1. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
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obtaining a forward-data stream configured to convey a plurality of frequency-multiplexed communication channels; processing said forward-data stream through said analog-transmitter components; obtaining a return-data stream responsive to said forward-data stream after said forward-data stream has been influenced by said analog-transmitter components; identifying a communication-signal strength for each of said communication channels in response to said forward-data stream; identifying an error-signal strength for each of said communication channels in response to said return-data stream; and counteracting distortion introduced by said analog-transmitter components in response to relative communication-signal strengths and error-signal strengths for said communication channels. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
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processing a forward-data stream to produce a processed-forward-data stream; converting said processed-forward-data stream into a forward-analog signal using a digital-to-analog converter (D/A); propagating said forward-analog signal through said analog-transmitter components to generate a return-analog signal; converting said return-analog signal into a return-raw-digitized-data stream using an analog-to-digital converter (A/D); compensating, in response to said forward-data stream, for quantization errors introduced into said return-raw-digitized-data stream by said A/D to produce a return-data stream; and altering said processed forward-data stream in response to said return-data stream; wherein said A/D includes a quantizer; and said compensating activity comprises evaluating said quantizer, programming a quantizer-simulator in response to said evaluating activity, operating said guantizer-simulator in response to said forward-data stream to generate a quantize-simulated-data stream and determining a difference between said forward-data stream and said quantize-simulated-data stream - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
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28. A method of compensating for distortion introduced by analog-transmitter components of a digital communications transmitter, said method comprising:
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processing a forward-data stream to produce a processed-forward-data stream; converting said processed-forward-data stream into a forward-analog signal using a digital-to-analog converter (D/A); propagating said forward-analog signal through said analog-transmitter components to generate a return-analog signal; converting said return-analog signal into a return-raw-digitized-data stream using an analog-to-digital converter (A/D); compensating, in response to said forward-data stream, for errors introduced into said return-raw-digitized-data stream by said A/D to produce a return-data stream; and altering said processed forward-data stream in response to said return-data stream; wherein said forward-data stream is configured to convey a plurality of frequency-multiplexed communication channels; and said altering activity is configured so that distortion introduced by said analog-transmitter components is reduced, and said distortion is reduced in a way that achieves greater reduction in error-vector magnitude (EVM) for ones of said communication channels having higher EVM'"'"'s than is achieved for communication channels having lower EVM'"'"'s.
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29. A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:
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an equalizer configured to receive a forward-data stream that conveys a plurality of frequency-multiplexed communication channels and to generate a processed-forward-data stream which propagates toward said analog-transmitter components; an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components; a first signal-strength-measuring circuit adapted to receive said forward-data stream and configured to identify a communication-signal strength for each of said communication channels; a second signal-strength-measuring circuit coupled to said A/D and configured to identify an error-signal strength for each of said communication channels; and a control circuit coupled to said first and second signal-strength-measuring circuits and to said equalizer, said control circuit being configured to adapt coefficients of said equalizer in response to relative communication-signal strengths and error-signal strengths for said communication channels to counteract distortion introduced by said analog-transmitter components. - View Dependent Claims (30, 31, 32, 33)
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34. A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:
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an equalizer configured to receive a forward-data stream and to generate a processed-forward-data stream; a digital-to-analog converter (D/A) coupled to said equalizer and configured to convert said processed-forward-data stream into a forward-analog signal which propagates through said analog-transmitter components; an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components, said return-analog signal being responsive to said forward-analog signal, and said A/D being configured to produce a return-raw-digitized-data stream; an A/D compensation section adapted to receive said forward-data stream, said A/D compensation section being configured to compensate for quantization errors introduced into said return-raw-digitized-data stream by said A/D and to produce a return-data stream; and a control circuit coupled to said equalizer, said control circuit being configured to alter said processed-forward-data stream in response to said return-data stream wherein said A/D includes a quantizer characterized by switching thresholds; and said A/D compensation section comprises a quantizer-simulator configured to simulate said guantizer when programmed with said switching thresholds which characterize said quantizer, said quantizer-simulator being adapted to receive said forward-data stream and to generate a quantize-simulated-data stream, and a differencing circuit configured to determine a difference between said forward-data stream and said quantize-simulated-data stream. - View Dependent Claims (35, 36, 37, 38, 39)
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40. A predistortion circuit for compensating distortion introduced by analog-transmitter components of a digital communications transmitter, said predistortion circuit comprising:
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an equalizer configured to receive a forward-data stream and to generate a processed-forward-data stream; a digital-to-analog converter (D/A) coupled to said equalizer and configured to convert said processed-forward-data stream into a forward-analog signal which propagates through said analog-transmitter components; an analog-to-digital converter (A/D) adapted to receive a return-analog signal from said analog-transmitter components, said return-analog signal being responsive to said forward-analog signal, and said A/D being configured to produce a return-raw- digitized-data stream; an A/D compensation section adapted to receive said forward-data stream, said A/D compensation section being configured to compensate for errors introduced into said return-raw-digitized-data stream by said A/D and to produce a return-data stream; and a control circuit coupled to said equalizer, said control circuit being configured to alter said processed-forward-data stream in response to said return-data stream; wherein said forward-data stream is configured to convey a plurality of frequency-multiplexed communication channels; and said control circuit is configured so that distortion introduced by said analog-transmitter components is reduced, and said distortion is reduced in a way that achieves greater reduction in error-vector magnitude (EVM) for ones of said communication channels having higher EVM'"'"'s than is achieved for communication channels having lower EVM'"'"'s.
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Specification