Subtracting linear impairments for non-linear impairment digital pre-distortion error signal
Example embodiment of the systems and methods of linear impairment modeling to improve digital pre-distortion adaptation performance includes a DPD module that is modified during each sample by a DPD adaptation engine. A linear impairment modeling module separates the linear and non-linear errors introduced in the power amplifier. The linear impairment model is adjusted during each sample using inputs from the input signal and from a FB post processing module. The linear impairment modeling module removes the linear errors such that the DPD adaptation engine only adapts the DPD module based on the non-linear errors. This increases system stability and allows for the correction of IQ imbalance inside the linear impairment modeling, simplifying the feedback post-processing.
1. A process comprising:
receiving a digital input signal;
producing a digital pre-distortion signal from the digital input signal in response to a non-linear impairment digital pre-distortion error signal;
amplifying the digital pre-distortion signal with a power amplifier to produce a radio frequency output signal;
producing from the radio frequency output signal a digital feedback signal that includes linear impairments and non-linear impairments;
separating the linear impairments from the non-linear impairments;
subtracting the linear impairments from the digital feedback signal to result in a non-linear impairment digital pre-distortion error signal; and
updating the producing a digital pre-distortion signal from the digital input signal in response to the non-linear impairment digital pre-distortion error signal from the subtracting.
2. The process of claim 1 including converting the digital pre-distortion signal into an analog signal, mixing the analog signal with a signal from a local oscillator, power amplifying the mixed analog signal to form the radio frequency output signal, and applying radio frequency output signal to an antennae.
3. The process of claim 1 in which the producing from the radio frequency output signal includes receiving an analog signal from an amplified signal applied to an antennae, de-mixing the analog feedback signal with a signal from a local oscillator, and converting the de-mixed signal to the digital feedback signal.
4. A system comprising:
a digital pre-distortion module having a digital signal input, an update input, and a filtered signal output;
a power amplifier having a filtered signal input coupled to the filtered signal output, and having a radio frequency signal output;
a feedback post-processing module having an input coupled to the radio frequency signal output, and having a processed signal output;
a linear impairment modeling module having an input coupled to the digital signal input and having a linear error signal output;
an error module having an input coupled to the processed signal output, an input coupled to the linear error signal output, and a non-linear error signal output; and
a digital pre-distortion adaptation engine having an input coupled to the non-linear error signal output and an output coupled to the update input.
5. The system of claim 4 in which at least one of the digital pre-distortion module, the feedback post-processing module, the linear impairment modeling module, and the digital pre-distortion adaptation engine are embodied in a digital signal processor.
6. The system of claim 4 in which the linear impairment modeling module includes an input coupled to the feedback post-processing module.