Sub-Band DPD Filtering for Power Amplifier Memory Effects
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Solution Overview
Problem
Current Digital Pre-Distortion (DPD) techniques for compensating intermodulation distortion (IMD) in power amplifiers require significant computational resources and power consumption, especially when accounting for memory effects, which lead to increased in-band and out-of-band IMD.
Innovation Solution
A distortion compensating device employing a Sub-band FIR filter and a memoryless DPD unit that superimposes filter coefficients on subcarrier signals to reduce computational load and power consumption, while maintaining Error Vector Magnitude (EVM) and Adjacent Channel Leakage Ratio (ACLR) performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If memory polynomial-based DPD is used to compensate distortion due to memory effects, then distortion compensation performance is improved, but computational load and power consumption increase enormously
Solution Approach 1:
The patent segments the distortion compensation task by separating memory effect compensation from instantaneous distortion compensation. The filter unit processes subcarrier signals to generate filter coefficients that account for memory effects, while the DPD unit uses these coefficients along with instantaneous power information to generate distortion compensation coefficients. This segmentation allows memory polynomial-based compensation to be achieved without the enormous computational load of applying full memory polynomial DPD to all signal processing.
2Reliability
If memory polynomial-based DPD is applied to compensate for memory effects, then in-band IMD compensation is improved, but the amount of calculations increases enormously
Solution Approach 1:
The filter unit performs preliminary processing by generating filter coefficients based on subcarrier signals before the DPD unit performs distortion compensation. These pre-calculated filter coefficients capture the memory effect characteristics, allowing the DPD unit to use them directly without performing complex memory polynomial calculations during the main distortion compensation process. This preliminary action reduces the computational burden while maintaining compensation effectiveness.
3Reliability
If full memory polynomial DPD is used, then both in-band and out-of-band IMD are compensated, but power consumption during signal processing increases
Solution Approach 1:
The patent merges the filter unit that processes subcarrier signals with the DPD unit that performs distortion compensation. The filter coefficients generated by the filter unit are combined with instantaneous power information in the DPD unit to produce distortion compensation coefficients. This merging allows the system to achieve comprehensive IMD compensation (both in-band and out-of-band) through a coordinated approach that avoids the redundant calculations of full memory polynomial DPD, thereby reducing power consumption during signal processing.
Data Source
AI summary
A distortion compensating device includes: a filter that receives input of a transmitting signal including a plurality of subcarrier signals assigned to respective frequencies and that superimposes filter coefficients on the respective subcarrier signals; a first signal converting unit that converts the subcarrier signals, on which the respective filter coefficients are superimposed, from a frequency domain into a time domain to obtain an input signal; a distortion compensating unit that superimposes a distortion compensation coefficient on the input signal to obtain an output signal; a power amplifier that amplifies and outputs the output signal; and a control unit that generates the filter coefficients according to an arithmetic equation using the subcarrier signals and a feedback signal from the power amplifier, and outputs the filter coefficients to the filter.