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Physical Modelling and Cancellation of External Passive Intermodulation in FDD MIMO

Stanislav Krikunov, Viacheslav Zemlyakov, Andrey Ivanov

TL;DR

The paper tackles external air-induced PIM in FDD MIMO by introducing a physically grounded, scalable model that directly simulates external PIM sources using a point-source representation, a finite-length dipole antenna, and a MIMO array feeding baseband 5G NR OFDM signals. It enables testing of PIM cancellation via a channel-coefficients based approach and a GMP-based nonlinear element model, while accommodating near-field and polarization effects. The results show that single external PIM sources can be canceled to the noise floor in a $16\times 16$ MIMO setup, but multi-source configurations can encounter local minima and require richer adaptation, and near-field source position strongly influences power distribution across channels. Overall, the framework offers a practical, hardware-free avenue to develop and validate PIM cancellation algorithms for large-scale MIMO, complementing and aligning with real-world measurements.

Abstract

In this paper, the physical approach to model external (air-induced) passive intermodulation (PIM) is presented in a frequency-division duplexing (FDD) multiple-input multiple-output (MIMO) system with an arbitrary number of transceiver chains. The external PIM is a special case of intermodulation distortion (IMD), mainly generated by metallic objects possessing nonlinear properties ("rusty bolt" effect). Typically, such sources are located in the near-field or transition region of the antenna array. PIM products may fall into the receiver band of the FDD system, negatively affecting the uplink signal. In contrast to other works, this one directly simulates the physical external PIM. The system includes models of a point-source external PIM, a finite-length dipole antenna, a MIMO antenna array, and a baseband multicarrier 5G NR OFDM signal. The Channel coefficients method for multi-PIM-source compensation is replicated to verify the proposed external PIM modelling approach. Simulation results of artificially generated PIM cancellation show similar performance as real-life experiments. Therefore, the proposed approach allows testing PIM compensation algorithms on large systems with many antennas and arbitrary array structures. This eliminates the need for experiments with real hardware at the development stage of the PIM cancellation algorithm.

Physical Modelling and Cancellation of External Passive Intermodulation in FDD MIMO

TL;DR

The paper tackles external air-induced PIM in FDD MIMO by introducing a physically grounded, scalable model that directly simulates external PIM sources using a point-source representation, a finite-length dipole antenna, and a MIMO array feeding baseband 5G NR OFDM signals. It enables testing of PIM cancellation via a channel-coefficients based approach and a GMP-based nonlinear element model, while accommodating near-field and polarization effects. The results show that single external PIM sources can be canceled to the noise floor in a MIMO setup, but multi-source configurations can encounter local minima and require richer adaptation, and near-field source position strongly influences power distribution across channels. Overall, the framework offers a practical, hardware-free avenue to develop and validate PIM cancellation algorithms for large-scale MIMO, complementing and aligning with real-world measurements.

Abstract

In this paper, the physical approach to model external (air-induced) passive intermodulation (PIM) is presented in a frequency-division duplexing (FDD) multiple-input multiple-output (MIMO) system with an arbitrary number of transceiver chains. The external PIM is a special case of intermodulation distortion (IMD), mainly generated by metallic objects possessing nonlinear properties ("rusty bolt" effect). Typically, such sources are located in the near-field or transition region of the antenna array. PIM products may fall into the receiver band of the FDD system, negatively affecting the uplink signal. In contrast to other works, this one directly simulates the physical external PIM. The system includes models of a point-source external PIM, a finite-length dipole antenna, a MIMO antenna array, and a baseband multicarrier 5G NR OFDM signal. The Channel coefficients method for multi-PIM-source compensation is replicated to verify the proposed external PIM modelling approach. Simulation results of artificially generated PIM cancellation show similar performance as real-life experiments. Therefore, the proposed approach allows testing PIM compensation algorithms on large systems with many antennas and arbitrary array structures. This eliminates the need for experiments with real hardware at the development stage of the PIM cancellation algorithm.
Paper Structure (16 sections, 11 equations, 7 figures, 1 table)

This paper contains 16 sections, 11 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Existing approaches
  3. Contributions and Novelty
  4. System model
  5. Single antenna model
  6. Antenna field coordinate transformation
  7. Antenna array model
  8. Point source model of external PIM
  9. Nonlinear element model
  10. Simulation results
  11. Simulation setup
  12. External PIM compensation in 16T16R MIMO
  13. Single point source compensation
  14. Multiple point source compensation
  15. Near-field PIM power variation
  16. ...and 1 more sections

Figures (7)

  • Figure 1: IMD-3 generation within n3 operating band.
  • Figure 2: External PIM generation procedure.
  • Figure 3: 16 TX/RX-chain antenna structure.
  • Figure 4: Cancellation of the 5-MHz carrier PIM from a single-point PIM source in 16T16R MIMO.
  • Figure 5: Convergence of the average cancelled RX PIM signal power in 16T16R MIMO from a single-point PIM source.
  • ...and 2 more figures