Multi-Channel DPD Feedback Filtering for Wider Bandwidth
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Solution Overview
Problem
Current digital predistortion (DPD) systems face challenges in increasing bandwidth without significantly increasing complexity and cost, particularly in multi-channel wideband wireless transmitters, leading to inefficiencies and higher power consumption due to the need for faster sampling rates and more complex filter designs.
Innovation Solution
The implementation of a DPD feedback signal with a narrow band-pass filter in the feedback path, allowing for a reduced digital FIR filter and the use of less stringent ceramic filters, which decreases the number of multipliers and eliminates the need for large, expensive multi-pole filters, thereby extending DPD bandwidth without costly modifications to existing digital platforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the instantaneous bandwidth for DPD is increased to meet next generation wireless system requirements, then the processing speed and sampling rate must be increased, but this results in higher system costs, increased power consumption, and greater device complexity
Solution Approach 1:
The patent divides the wideband signal processing into multiple narrowband sub-channels, each processed independently by separate DPD engines. This segmentation allows each processor to operate at lower sampling rates while collectively handling the full wideband signal, thereby reducing individual processor complexity and power consumption while maintaining overall processing capability.
Solution Approach 2:
The patent creates a multi-functional DPD system where multiple DPD engines can be configured to handle different frequency bands and modulation schemes. The system can dynamically allocate processing resources across different channels and standards, making the hardware platform adaptable to various wireless communication requirements without requiring complete redesign for each application.
2Speed
If the sampling rate is increased to support wider bandwidth DPD, then the instantaneous bandwidth capability is improved, but this leads to higher power consumption and increased system costs
Solution Approach 1:
The patent segments the wideband signal into multiple narrowband channels, allowing each DPD engine to process at lower sampling rates. This reduces the power consumption of individual processing elements while collectively maintaining the capability to handle wideband signals, as the total processing power is distributed across multiple lower-power units.
3Speed
If complex filter designs are used to handle wideband signals, then the bandwidth capability is improved, but this increases device complexity and manufacturing costs
Solution Approach 1:
The patent replaces complex wideband filters with multiple simpler narrowband filters, one for each frequency channel. Each filter has relaxed specifications and can be implemented with fewer components, reducing manufacturing complexity and cost. The segmented filtering approach achieves the same overall frequency selectivity as a complex monolithic filter would provide.
Solution Approach 2:
The patent changes the frequency parameters of the filtering operation by applying different center frequencies and bandwidths to different DPD engines and their associated filters. This allows each filter to be optimized for its specific frequency range with simpler design requirements, rather than requiring a single complex filter to cover the entire wideband spectrum.
4Productivity
If DPD is applied to multi-channel wideband systems, then spectral efficiency is improved, but nonlinearities and memory effects become more pronounced requiring more complex linearization
Solution Approach 1:
The patent applies DPD separately to each narrowband frequency channel rather than attempting to linearize the entire wideband signal simultaneously. This segmentation reduces the memory effects and nonlinearities that each individual DPD engine must compensate for, simplifying the linearization algorithm for each channel while collectively providing comprehensive linearization across the full bandwidth.
Data Source
AI summary
A method of operating a communications system includes receiving a signal at a digital predistorter (DPD), introducing predistortion to the signal using the DPD, and converting the predistorted signal to an analog signal using a digital-to-analog converter having a first bandwidth. The method also includes amplifying the analog signal, sampling the amplified signal using an analog-to-digital converter having a second bandwidth less than the first bandwidth, and extracting coefficients of the DPD from the sampled signal.