Digital compensator for a non-linear system
First Claim
1. A method of signal predistortion for linearizing a non-linear circuit, the method comprising:
- processing an input signal (u) to produce a plurality of transformed signals (w);
determining a plurality of phase-invariant derived signals (r), each derived signal (rj) of the plurality of derived signals being equal to a respective non-linear function of one or more of the transformed signals, at least some of the derived signals being equal to respective functions of different one or more of the transformed signals;
transforming each derived signal (rj) of the plurality of phase-invariant derived signals according to a parametric non-linear transformation to produce a time-varying gain component (gi) of a plurality of gain components (g);
forming a distortion term by accumulating a plurality of terms, each term being a product of a respective transformed signal of the plurality of transformed signals and a respective time-varying gain, the time-varying gain being a function (Φ
) of a one or more of the phase-invariant derived signals, the function of the one or more of the phase-invariant derived signals being decomposable into a combination of one or more parametric functions (ϕ
) of a corresponding single one of the phase invariant derived signals (rj) yielding a corresponding one of the time-varying gain components (gi); and
providing an output signal (v) determined from the distortion term for application to the non-linear circuit.
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Abstract
A pre-distorter that both accurately compensates for the non-linearities of a radio frequency transmit chain, and that imposes as few computation requirements in terms of arithmetic operations, uses a diverse set of real-valued signals that are derived from the input signal. The derived real signals are passed through configurable non-linear transformations, which may be adapted during operation, and which may be efficiently, implemented using lookup tables. The outputs of the non-linear transformations serve as gain terms for a set of complex signals, which are functions of the input, and which are summed to compute the pre-distorted signal. A small set of the complex signals and derived real signals may be selected for a particular system to match the classes of non-linearities exhibited by the system, thereby providing further computational savings, and reducing complexity of adapting the pre-distortion through adapting of the non-linear transformations.
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Citations
36 Claims
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1. A method of signal predistortion for linearizing a non-linear circuit, the method comprising:
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processing an input signal (u) to produce a plurality of transformed signals (w); determining a plurality of phase-invariant derived signals (r), each derived signal (rj) of the plurality of derived signals being equal to a respective non-linear function of one or more of the transformed signals, at least some of the derived signals being equal to respective functions of different one or more of the transformed signals; transforming each derived signal (rj) of the plurality of phase-invariant derived signals according to a parametric non-linear transformation to produce a time-varying gain component (gi) of a plurality of gain components (g); forming a distortion term by accumulating a plurality of terms, each term being a product of a respective transformed signal of the plurality of transformed signals and a respective time-varying gain, the time-varying gain being a function (Φ
) of a one or more of the phase-invariant derived signals, the function of the one or more of the phase-invariant derived signals being decomposable into a combination of one or more parametric functions (ϕ
) of a corresponding single one of the phase invariant derived signals (rj) yielding a corresponding one of the time-varying gain components (gi); andproviding an output signal (v) determined from the distortion term for application to the non-linear circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A method of signal predistortion for linearizing a non-linear circuit comprising a radio-frequency section including a radio-frequency modulator configured to modulate an output signal to a carrier frequency to form a modulated signal and an amplifier for amplifying the modulated signal, the method comprising:
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processing an input signal (u) to produce a plurality of transformed signals (w), the input signal (u) comprising quadrature components of a baseband signal for transmission via the radio-frequency section, and the plurality of transformed signals (w) comprising complex-valued signals; determining a plurality of phase-invariant real-valued derived signals (r), each derived signal (rj) of the plurality of derived signals being equal to a respective non-linear function of one or more of the transformed signals, at least some of the derived signals being equal to respective functions of different one or more of the transformed signals; transforming each derived signal (rj) of the plurality of phase-invariant derived signals according to a parametric non-linear transformation to produce a time-varying gain component (gi) of a plurality of gain components (g), including transforming a first derived signal (rj) of the plurality of phase-invariant derived signals according to one or more different parametric non-linear transformation to produce corresponding time-varying gain components, wherein transforming the first derived signal of the plurality of derived signals according to a parametric non-linear transformation comprises performing a table lookup in a data table corresponding to said transformation according to the first derived signal to determine a result of the transforming, and wherein the parametric non-linear transformation comprises a piecewise linear transformation, and the data from the data table corresponding to said segment characterizes endpoints of said segment and transforming the first derived signal comprises interpolating a value on a linear segment of said transformation; forming a distortion term by accumulating a plurality of terms, each term being a product of a transformed signal of the plurality of transformed signals and a time-varying gain, the time-varying gain being a function (Φ
) of a one or more of the phase-invariant derived signals, the function of the one or more of the phase-invariant derived signals being decomposable into a combination of one or more parametric functions (ϕ
) of a corresponding single one of the phase invariant derived signals (rj) yielding a corresponding one of the time-varying gain components (gi);providing an output signal (v) determined from the distortion term for application to the non-linear circuit; and adapting configuration parameters of the parametric non-linear transformation according to sensed output of the non-linear circuit, including updating values in the data table.
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35. A digital predistorter circuit comprising:
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an input port for receiving an input signal (u); an output port for providing an output signal (v); storage for values of a plurality of configuration parameters (x); wherein the circuit is configured to perform operations comprising; receiving the input signal (u) via the input port; processing the input signal (u) to produce a plurality of transformed signals (w); determining a plurality of phase-invariant derived signals (r), each derived signal (rj) of the plurality of derived signals being equal to a respective non-linear function of one or more of the transformed signals, at least some of the derived signals being equal to respective functions of different one or more of the transformed signals; transforming each derived signal (rj) of the plurality of phase-invariant derived signals according to a parametric non-linear transformation to produce a time-varying gain component (gi) of a plurality of gain components (g); forming a distortion term by accumulating a plurality of terms, each term being a product of a transformed signal of the plurality of transformed signals and a time-varying gain, the time-varying gain being a function (Φ
) of a one or more of the phase-invariant derived signals, the function of the one or more of the phase-invariant derived signals being decomposable into a combination of one or more parametric functions (ϕ
) of a corresponding single one of the phase invariant derived signals (rj) yielding a corresponding one of the time-varying gain components (gi); andproviding the output signal (v) determined from the distortion term via the output port. - View Dependent Claims (36)
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Specification