Passive Intermodulation Aware Beamforming for 5G MIMO
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Solution Overview
Problem
Passive intermodulation (PIM) products caused by metallic objects in the vicinity of antenna arrays can lead to interference and sensitivity degradation in wireless communication systems, particularly in multi-user massive multiple input multiple output (MIMO) 4G/5G beamforming frequency division duplex (FDD) systems, affecting signal power and signal-to-noise ratio (SNR).
Innovation Solution
An apparatus and method that determine the level of PIM signals for each beam direction of an antenna array, identify beam directions with PIM levels above a threshold, and adapt beamforming settings to mitigate PIM interference by redirecting or nulling beams to avoid PIM sources, thereby improving received signal power and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beamforming is used to improve signal directionality and gain, then signal power and SNR are improved, but PIM interference is generated when beams point toward metallic objects
Solution Approach 1:
The beamforming configuration is made dynamic by continuously monitoring PIM levels and adapting beam directions in real-time. The system transitions from static beamforming to dynamic beam steering that responds to detected PIM conditions, allowing the beam directions to change based on current interference levels
Solution Approach 2:
A feedback mechanism is implemented where PIM levels are measured at the receiver and fed back to the transmitter. This feedback loop enables the system to identify which beam directions cause PIM interference and adjust subsequent beamforming configurations to avoid those directions, creating a closed-loop control system
2Object-affected harmful factors
If beam directions are adjusted to avoid PIM sources, then PIM interference is reduced, but system adaptability and coverage flexibility are limited
Solution Approach 1:
The 360-degree coverage space is segmented into multiple discrete beam directions, allowing the system to selectively activate only those directions that do not cause PIM interference. This segmentation enables granular control over beam placement, maintaining coverage flexibility while avoiding harmful directions
Solution Approach 2:
The system changes beamforming parameters (beam directions, weights) based on detected PIM conditions. By dynamically adjusting these parameters, the system maintains adaptability to different coverage requirements while avoiding fixed beam directions that would cause PIM interference
3Object-affected harmful factors
If PIM measurement and beamforming adaptation are implemented for each beam direction, then PIM interference is mitigated, but computational complexity and processing overhead increase
Solution Approach 1:
PIM measurements are performed in advance for each beam direction during system initialization or calibration phases. This preliminary action creates a lookup table or database of PIM-prone directions, eliminating the need for continuous real-time measurements and reducing ongoing processing complexity
Solution Approach 2:
The receiver performs PIM measurements and generates feedback information that the transmitter uses for beamforming adaptation. This self-service approach distributes the measurement burden and enables the system to autonomously identify and avoid PIM-causing directions without external intervention
Data Source
AI summary
The present subject matter relates to an apparatus for a communication system. The apparatus is configured for: for each beam direction of a set of beam directions of an antenna array of the communication system, determining a level of a passive intermodulation, PIM, signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction, identifying beam directions of the set of beam directions whose PIM level is higher than a predefined threshold, adapting a beamforming of signals in at least part of the identified beam directions to mitigate the PIM level at the receiver.