Distributed Clipping for Base Station Scalability and EVM Control
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Solution Overview
Problem
Current clipping methods in radio communications systems, such as crest factor reduction (CFR), limit scalability and increase error vector magnitude (EVM), leading to signal distortion and potential damage to power amplifiers due to inflexible clipping processes.
Innovation Solution
Implementing a distributed clipping method where a base station performs two levels of clipping, with the first processor at the baseband unit (BBU) and the second processor at the remote radio unit (RRU), allowing flexible deployment based on processing capabilities, and involving upsampling, noise extraction, and delay synchronization to reduce noise bandwidth and improve clipping performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transmitter performs clipping processing using one level of clipping at a single location (e.g., RRU), then the implementation is simple, but the clipping scalability and flexibility are limited
Solution Approach 1:
The patent divides the single clipping operation into two separate clipping stages: first clipping at the BBU and second clipping at the RRU. This segmentation allows each stage to operate with different clipping parameters and processing capabilities, thereby improving scalability while distributing the complexity across multiple locations rather than concentrating it in one device.
Solution Approach 2:
The patent introduces a new dimension to clipping by implementing it across two different spatial locations (BBU and RRU) rather than a single location. This dimensional expansion from one-point clipping to two-point clipping enables flexible deployment scenarios where different clipping algorithms and parameters can be applied at each location based on specific requirements.
2Reliability
If clipping is performed to suppress signal peaks and protect power amplifiers, then power amplifier protection is improved, but the error vector magnitude (EVM) increases causing signal distortion
Solution Approach 1:
The patent applies partial clipping action through two stages rather than one aggressive clipping stage. The first clipping at BBU reduces peak power to protect the power amplifier, while the second clipping at RRU performs additional peak suppression. This distributed partial action achieves better power amplifier protection while each stage can be tuned to minimize EVM degradation compared to a single heavy clipping operation.
Solution Approach 2:
The patent enables parameter changes by allowing different clipping thresholds, algorithms, and processing methods to be applied at the BBU and RRU respectively. This flexibility in parameters allows optimization of each clipping stage to balance power amplifier protection with signal quality maintenance, potentially using different clipping strategies (e.g., different EVM thresholds, different noise shaping parameters) at each location.
3Quantity of substance
If noise bandwidth is reduced through downsampling, then the interface bandwidth requirement between BBU and RRU is reduced, but the processing complexity increases
Solution Approach 1:
The patent performs preliminary downsampling of the noise signal before transmitting it from BBU to RRU. By reducing the noise bandwidth beforehand, the interface bandwidth requirements are lowered, and the RRU receives a pre-processed noise signal that requires less bandwidth for transmission, while the downsampling operation is performed at the BBU where processing resources are available.
Data Source
AI summary
Embodiments of the present disclosure provide a clipping method and an apparatus. The clipping apparatus is a base station, and the base station includes a baseband unit (BBU) and a remote radio unit (RRU). The BBU includes a first processor, and the RRU includes a second processor. The first processor is configured to: perform clipping after combining N input carriers, and output N carriers obtained after a first level of clipping; and the second processor is configured to: perform clipping after combining the N carriers obtained after the first level of clipping, and output N carriers obtained after a second level of clipping, where N is an integer greater than or equal to 2. The base station separately performs clipping at the BBU and the RRU, so that the base station can flexibly select, a baseband processing board or a baseband chip to deploy the first level of clipping.