Digital Pre-Distortion Feedback Alignment With Subsampled Loops
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Solution Overview
Problem
Existing pre-distortion systems require high-bandwidth feedback loops to accurately compensate for transmission channel and feedback channel responses, which can be complex and limited by ADC sampling rate constraints, especially in scenarios with export control restrictions.
Innovation Solution
The implementation of a sub-sampled digital pre-distortion (DPD) system that uses a lower sampling rate in the feedback loop, incorporating a feedback-model circuit to transform and align input signals with feedback signals, allowing for error calculation and adaptation of DPD coefficients while accommodating arbitrary feedback signal transformations without information loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-bandwidth feedback loop is used to accurately compensate for transmission channel and feedback channel responses, then measurement precision is improved, but device complexity increases and ADC sampling rate constraints are exceeded
Solution Approach 1:
The patent extracts and removes the feedback channel response from the measurement process by using a tap signal that bypasses the feedback channel. Instead of measuring the complete output signal that has been distorted by both transmission and feedback channels, the system extracts only the transmission channel response by comparing the input signal with a tap signal that was taken before feedback channel distortion occurred. This eliminates the need for complex deconvolution of feedback channel effects.
Solution Approach 2:
The patent introduces a tap signal as an intermediary that provides a reference copy of the input signal at a point where it has not been distorted by the feedback channel. This intermediary signal serves as a mediator between the input signal and the error calculation process, allowing the system to isolate and measure only the transmission channel response without the confounding influence of feedback channel distortion.
2Device complexity
If the feedback signal is subsampled to reduce feedback complexity and accommodate converter-data-rate limits, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent extracts the essential information needed for pre-distortion adaptation by using only the necessary portions of the feedback signal. Instead of requiring full-rate feedback signals, the system extracts transmission channel response characteristics from subsampled feedback signals combined with the tap signal, removing unnecessary high-frequency components and focusing only on the relevant distortion information.
Solution Approach 2:
The patent applies partial action by using subsampled feedback signals that contain only the necessary information for pre-distortion adaptation. The feedback signal is sampled at a lower rate than the full transmission signal rate, capturing only the essential distortion characteristics needed for adaptation while discarding redundant high-frequency information that does not contribute to pre-distortion performance.
3Productivity
If feedback signal subsampling is applied to operate within ADC sampling rate constraints, then productivity is improved by enabling operation under export control restrictions, but loss of information occurs
Solution Approach 1:
The patent extracts and preserves only the essential information from the feedback signal that is necessary for pre-distortion adaptation. By using a tap signal combined with subsampled feedback, the system extracts transmission channel response characteristics while discarding redundant information, thereby minimizing information loss while enabling operation under ADC sampling rate constraints and export control restrictions.
Solution Approach 2:
The patent creates a simplified copy of the feedback signal at a lower sampling rate that retains the essential distortion information needed for pre-distortion. Instead of requiring the complete high-rate feedback signal, the system uses a subsampled copy combined with the tap signal to achieve the necessary measurement accuracy, thereby reducing data rate requirements while maintaining operational capability.
Data Source
AI summary
Embodiments of the invention provide a DPD system where the transmit reference signal is transformed, including sub-sampling, frequency translation, and the like, to match the feedback signal, which goes thru a similar transformation process, to obtain an error signal. The same transformation is applied to a system model, which may be Jacobian, Hessian, Gradient, or the like, in an adaptation algorithm to minimize error.