PIM Downlink Subspace Acquisition via Covariance Averaging
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Solution Overview
Problem
In wireless communication systems, passive intermodulation (PIM) interference causes non-linear behavior, leading to signal degradation due to interference coupling into receivers, especially in frequency division duplex (FDD) systems with wide duplex gaps, where antenna response variations and subarray impairments complicate downlink subspace acquisition.
Innovation Solution
A method and system that utilize a natural 'PIM feedback loop' to estimate the downlink interference covariance matrix, independent of FDD uplink-to-downlink frequency separation, by determining a downlink projection matrix based on beamforming weights and scaling factors related to PIM power, averaging covariance matrix estimates over multiple OFDM symbols to capture precoding weights with equal probability, and excluding estimates below a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional PIM interference estimation methods are used in FDD systems with wide duplex gaps, then the estimation may be simplified, but the accuracy deteriorates due to antenna response variations and subarray impairments
Solution Approach 1:
The patent performs preliminary calibration of antenna response variations and subarray impairments before PIM interference estimation. By pre-characterizing the antenna system responses at different frequencies and storing correction factors, the system compensates for frequency-dependent variations when estimating PIM interference, thereby maintaining accuracy without excessive computational complexity during operation.
Solution Approach 2:
The patent changes the estimation approach by introducing frequency-dependent correction parameters that account for antenna response variations. Instead of using a fixed estimation model, the system adapts the estimation parameters based on the specific frequency offset between uplink and downlink, thereby maintaining precision across wide duplex gaps while managing complexity through parameter adaptation rather than structural complexity.
2Reliability
If null steering is applied to mitigate PIM interference, then receiver performance improves, but the system becomes more sensitive to estimation errors
Solution Approach 1:
The patent applies beforehand cushioning by implementing robust estimation techniques that pre-compensate for potential estimation errors. The system uses covariance matrix averaging and eigenvalue thresholding to create a more stable interference subspace estimate before null steering is applied, thereby cushioning against the sensitivity of null steering to estimation inaccuracies and maintaining receiver performance.
3Ease of operation
If PIM subspace is estimated during normal product operations, then no special operational mode is needed, but the estimation quality may be insufficient due to limited data samples
Solution Approach 1:
The patent implements continuity of useful action by continuously accumulating covariance matrix samples during normal product operations. Instead of requiring a special calibration mode, the system continuously estimates the interference covariance matrix using available data samples, gradually improving estimation accuracy over time while maintaining normal operational functionality throughout the process.
Data Source
AI summary
A method and radio in a network node for passive intermodulation (PIM) downlink subspace acquisition. According to one aspect, a method includes determining a downlink projection matrix that is formed using the downlink beamforming weights and determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexed, OFDM, symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that is dependent on the passive intermodulation, PIM, power generated in one or more uplink channels.