Cubic spline predistortion, algorithm and training, for a wireless LAN system
First Claim
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1. A method of calibrating a system including a predistorter in communication with a power amplifier, including:
- over a range of probabilities of clipping an OFDM symbol, calculating clipping noise resulting from calibrating an input range to the predistorter to a particular probability of clipping; and
determining tolerance to random noise resulting from operating at an average power output of the power amplifier corresponding to the particular probability of clipping;
selecting a parameter corresponding to a preferred probability of clipping an OFDM symbol; and
calibrating the input range to the predistorter and the average power output of the power amplifier to the parameter.
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Abstract
The present invention includes methods and devices to apply predistortion to correct nonlinearities of a power amplifier in an OFDM symbol transmission system. More particularly, predistortion is patterned to take into account clipping of symbols and to match an effective input range of the predistorter with an average power output of the power amplifier. This invention may be applied to a variety of standards utilizing OFDM technology, including IEEE 802.11a, Hiperlan/2 and MMAC.
149 Citations
22 Claims
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1. A method of calibrating a system including a predistorter in communication with a power amplifier, including:
over a range of probabilities of clipping an OFDM symbol, calculating clipping noise resulting from calibrating an input range to the predistorter to a particular probability of clipping; and
determining tolerance to random noise resulting from operating at an average power output of the power amplifier corresponding to the particular probability of clipping;
selecting a parameter corresponding to a preferred probability of clipping an OFDM symbol; and
calibrating the input range to the predistorter and the average power output of the power amplifier to the parameter.
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2. A method of calibrating an OFDM symbol transmission system including:
- a predistorter in communication with a power amplifier, including;
over a range of power amplifier power back-offs, calculating a probability of clipping an OFDM symbol corresponding to a particular power back-off and a corresponding clipping noise; and
determining tolerance of the system to random noise resulting from the particular power back-off;
selecting a preferred power back-off corresponding to the clipping noise and tolerance of random noise; and
calibrating a predistortion pattern of the predistorter and the average power output of the power amplifier to the selected power back-off. - View Dependent Claims (3, 4, 5)
- a predistorter in communication with a power amplifier, including;
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6. A method of determining a predistortion pattern and a power back-off setting for a system including a predistorter in communication with a power amplifier, the method including:
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measuring a PA response curve of the power amplifier and deriving an inverse PA response curve;
from a range of power back-off settings, selecting a particular power back-off setting corresponding to a calculated OFDM symbol clipping noise and to random noise tolerance of the system;
mapping an upper input threshold derived from the particular power back-off to an output level of the power amplifier that will be saturated or nearly saturated; and
loading the system with the inverse PA response curve scaled to the upper input threshold and with a power back-off parameter. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method of configuring a system including a predistorter in communication with a power amplifier, the method including:
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calculating a first parameter that maximizes a tolerance of the system to a combination of clipping noise and random noise for an OFDM symbol sequence;
deriving from the first parameter a power back-off value for the power amplifier and an upper input threshold for the predistorter;
determining an inverse response curve corresponding to a PA response curve and to the upper input threshold; and
loading the system with a representation of the inverse response curve and with the power back-off value. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A method of determining an upper input threshold for a predistorter in communication with a power amplifier, the method including:
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determining a power probability distribution for a sample OFDM symbol sequence;
determining a PA response curve;
selecting an ideal response curve for which a weighted sum of differences between corresponding points along the ideal response curve and the PA response curve is approximately zero, wherein weights correspond to the power probability distribution; and
deriving a power-off value from a point on the selected ideal response curve at which output of the power amplifier will saturate or nearly saturate. - View Dependent Claims (21, 22)
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Specification