Time-Domain Beamforming Distortion Correction for Spectral Regrowth
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Solution Overview
Problem
The sudden coefficient change in time-domain beamforming causes spectral regrowth, leading to unsatisfactory radio performance that fails to meet regulatory emission masks, particularly in 5G wireless communication systems.
Innovation Solution
Implementing a method and system for forward distortion correction (FDC) using band stop filters and group delay filters in parallel with time-domain beamformers, combined with zero insertion, to mitigate spectral regrowth and meet emission masks with sufficient margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If beamforming weights are updated on a symbol or slot basis in time-domain beamforming, then beamforming flexibility and adaptability are improved, but spectral regrowth occurs causing harmful emissions that fail to meet regulatory masks
Solution Approach 1:
The patent applies preliminary action by inserting zeros into the cyclic prefix before the channel filter in advance of the beamforming weight updates. This pre-conditioning of the signal with zero insertion creates a smooth transition region that prevents spectral regrowth when beamforming weights are updated on symbol or slot basis, allowing beamforming flexibility while meeting regulatory emission masks
2Object-generated harmful factors
If baseband zero insertion is applied to meet FCC emission masks, then unwanted emissions are reduced, but link-level performance deteriorates due to lengthy zero insertion requirements
Solution Approach 1:
The patent applies parameter changes by modifying the characteristics of the zero insertion process. Instead of using lengthy zero insertion sequences, the patent changes the approach by inserting zeros at specific positions in the cyclic prefix and combining this with time-domain beamforming. This parameter optimization reduces the length of zero insertion needed while maintaining compliance with emission masks and preserving link-level performance
3Device complexity
If the channel filter is positioned upstream of the time-domain beamformer, then signal processing flow is simplified, but distortion close to the carrier cannot be removed
Solution Approach 1:
The patent introduces an intermediary element - the zero insertion in the cyclic prefix - positioned between the channel filter and the time-domain beamformer. This intermediary zero insertion region acts as a buffer that allows the channel filter to remain upstream of the beamformer for simplified processing, while the zeros provide a transition zone that enables removal of distortion close to the carrier by attenuating spectral regrowth before it reaches the beamforming stage
Data Source
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AI summary
A method and network node for forward distortion correction for time domain beam forming are provided. According to one aspect, a method in a network node includes filtering each signal output by the time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer. The method also includes filtering each signal output by the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer. The method also includes subtracting an output of each band stop filter from an output of a corresponding group delay filter.