A distortion compensation apparatus executes a process including: Performing distortion compensation that compensates in advance for a nonlinear distortion occurring when a transmission signal is amplified by a power amplifier; determining whether power of the transmission signal is smaller than a predetermined threshold; holding a gain relating to the distortion compensation or a result of the distortion compensation when the power of the transmission signal is determined to be smaller than the predetermined threshold; and outputting to the power amplifier, when the power of the transmission signal is determined to be smaller than the predetermined threshold, the result of the distortion compensation, and outputting to the power amplifier, when the power of the transmission signal is determined to be equal to or greater than the predetermined threshold, a result of distortion compensation performed using the held, gain, or the held result of the distortion compensation.

A circuit for signal classification in a digital pre-distortion (DPD) system is provided. The circuit includes a first frequency path with a positive frequency translation to generate a first power level corresponding to a signal output of the first frequency path, a second frequency path with a negative frequency translation to generate a second power level corresponding to a signal output of the second frequency path, and a third frequency path configured to filter the input signal via a high pass filter (HPF) and to generate a third power level corresponding to a signal output of the third frequency path. The circuit further includes a processing unit configured to compute frequency content metrics corresponding to the input signal based on the first power level, the second power level and the third power level for selecting a set of DPD coefficients for the DPD circuit.

It is provided a method designed, for OFDM-based communication systems, to slightly modify the signal to be emitted before the power amplifier input of the transmitter. The guiding idea is that the minimal IBO value for which the slightly modified signal still fulfills the standard requirements is inferior to the smallest IBO value for which the transmitted signal still meets the standard requirements in terms of EVM and spectral mask without implementing the proposed method.

The present disclosure provides a method for compensating an imbalance between an I path and a Q path of a receiver. The method includes: sending a cosine signal and a sine signal through a signal generator, transmitting the cosine signal and the sine signal in the I path and Q path respectively; calculating autocorrelation values of the I path and the Q path in the signal receiving direction; determining a comparison result of amplitudes of the cosine signal received by the I path and the sine signal received by the Q path according to the autocorrelation values; calculating an adjustment compensation value of an analog domain gain amplifier, and an amplitude value and a phase value in a digital domain according to the comparison result of amplitudes; and compensating and adjusting the signal according to the adjustment compensation value, the amplitude value and the phase value.

The present disclosure provides a method for compensating an imbalance between an I path and a Q path of a receiver. The method includes: sending a cosine signal and a sine signal through a signal generator, transmitting the cosine signal and the sine signal in the I path and Q path respectively; calculating autocorrelation values of the I path and the Q path in the signal receiving direction; determining a comparison result of amplitudes of the cosine signal received by the I path and the sine signal received by the Q path according to the autocorrelation values; calculating an adjustment compensation value of an analog domain gain amplifier, and an amplitude value and a phase value in a digital domain according to the comparison result of amplitudes; and compensating and adjusting the signal according to the adjustment compensation value, the amplitude value and the phase value.

A distortion compensation apparatus executes a process including: Performing distortion compensation that compensates in advance for a nonlinear distortion occurring when a transmission signal is amplified by a power amplifier; determining whether power of the transmission signal is smaller than a predetermined threshold; holding a gain relating to the distortion compensation or a result of the distortion compensation when the power of the transmission signal is determined to be smaller than the predetermined threshold; and outputting to the power amplifier, when the power of the transmission signal is determined to be smaller than the predetermined threshold, the result of the distortion compensation, and outputting to the power amplifier, when the power of the transmission signal is determined to be equal to or greater than the predetermined threshold, a result of distortion compensation performed using the held, gain, or the held result of the distortion compensation.

Disclosed are methods, systems, devices, apparatus, media, and other implementations, including a method for digital predistortion for a power amplifier system. The method includes determining one or more system characteristics for the power amplifier system comprising at least a power amplifier that produces output with non-linear distortions, with the one or more system characteristics corresponding to an estimate for a complex load metric for the power amplifier system coupled to a load. The method further includes determining, based on the one or more system characteristics corresponding to the estimate for the complex load metric, digital predistortion (DPD) coefficients to compensate for the nonlinear behavior of the power amplifier system.

Certain aspects of the present disclosure are directed to a digital predistortion (DPD) device for use within a wireless transmitter that permits the use of a downstream digital-to-analog converter that operates at a clock rate close to the bandwidth of a digital baseband input signal. In some examples, a sampling rate of a digital baseband input signal is increased using an upsampler to obtain an increased rate digital input signal. Predistortion is applied to the increased rate digital input signal using a DPD device to obtain a predistorted digital signal. The sampling rate of the predistorted digital signal is then decreased using a downsampler to obtain a lower-rate predistorted digital signal with a sampling rate below the increased rate of the upsampler (e.g. close to the bandwidth of a digital baseband input signal). A low pass filter may be provided to filter out-of-band signal components from the predistorted digital signal.

Various examples are directed to systems and methods for digital predistortion (DPD). A linear digital predistortion (DPD) circuit may be programmed to generate a pre-distorted signal linear component based at least in part on a complex baseband signal. A nonlinear DPD circuit may be programmed to generate a pre-distorted signal nonlinear component based at least in part on the complex baseband signal. A mixer circuit programmed to generate a pre-distorted signal based at least in part on the pre-distorted signal linear component and the pre-distorted signal nonlinear component.

A radio frequency (RF) transmitter includes an analog RF power amplifier and a digital Dynamic Error Vector Magnitude (DEVM) correction module. The DEVM correction module compensates for time-dependent variations in an instantaneous gain of the RF power amplifier. The time-dependent variations may be variations that occur during a period the RF power amplifier is turned on. The RF transmitter may further include one or more analog baseband circuits, and one or more respective baseband digital pre-distortion (DPD) modules that compensate for amplitude modulation to amplitude modulation (AM2AM) nonlinearities in the analog baseband circuits. The digital DEVM correction module and baseband DPD modules may each include respective look-up tables having values determined by respective calibration operations.