Multiband Digital Predistortion Using Reduced-Dimension LUTs
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Solution Overview
Problem
Traditional Lookup Table (LUT) based methods for linearizing wideband High-Power Amplifiers (HPAs) with Instantaneous Bandwidth (IBW) of 1 GHz or above are excessively costly due to high sample rate requirements and fail to achieve desired Adjacent Channel Leakage Ratio (ACLR) performance, while Separate Digital Predistortion (S-DPD) methods suffer from exponential memory growth and performance degradation with multiple frequency bands.
Innovation Solution
A method and architecture that reduces multidimensional LUTs to single-dimensional LUTs using a change of basis technique, allowing independent implementation of (B−q)-dimension LUTs for each frequency band, maintaining performance without increasing memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional LUT based methods are used for wideband HPA linearization, then high sample rate operations are achieved, but memory requirements and cost increase exponentially
Solution Approach 1:
The patent segments the multiband DPD problem into separate frequency band treatments. Instead of using a single comprehensive multidimensional LUT covering all bands simultaneously, the system divides the frequency spectrum into multiple bands and processes each band separately with its own reduced-dimension LUT, thereby reducing overall memory requirements while maintaining linearization performance.
Solution Approach 2:
The patent transforms the multidimensional LUT problem into a series of lower-dimensional LUTs by introducing a frequency band dimension. Rather than storing a single large B-dimensional LUT for B bands, the system creates multiple smaller LUTs organized by frequency band, effectively changing the data structure from a flat high-dimensional array to a hierarchical structure that reduces memory footprint.
2Quantity of substance
If separate DPD is used for each frequency band, then memory requirements are reduced, but ACLR performance deteriorates
Solution Approach 1:
The patent merges the advantages of separate band processing with overall system performance by combining multiple reduced-dimension LUTs into a unified multiband DPD structure. The system processes each frequency band separately through its own LUT while maintaining coordination between bands, thereby achieving both memory efficiency and desired ACLR performance through the synergistic combination of individual band treatments.
3Reliability
If multidimensional LUTs are used for multiband DPD, then ACLR performance is maintained, but device complexity and cost increase
Solution Approach 1:
The patent segments the complex multidimensional LUT into multiple simpler lower-dimensional LUTs, each handling a specific frequency band. This segmentation reduces the complexity of individual LUT structures and simplifies the overall implementation while maintaining the ability to achieve desired ACLR performance through coordinated processing of all bands.
Data Source
AI summary
There is provided mechanisms for operating a DPD for an access node. A method comprises receiving a plurality of input signals, each from a respective frequency band, wherein each signal is of memory order M. The method comprises, for each frequency band l=1, . . . , B of the frequency bands, generating a plurality of pre-distorted signals for the frequency band/based on the plurality of input signals coming from all the B frequency bands and using LUTs, according to which there is one LUT structure with LUT-based transforms per each combination of frequency band l=1, . . . , B and memory order m=0, . . . , M, wherein each of the LUT structures comprises combinations of LUTs of at most dimension B−q, where 1≤q≤B. The method comprises, for each frequency band l=1, . . . , B of the frequency bands, combining the plurality of pre-distorted signals for the frequency band to provide a combined pre-distorted signal for the frequency band.