MIMO IMD Cancellation for Nonlinear Interference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In cellular and wireless devices using uplink multiple-input, multiple-output (UL-MIMO) mode, nonlinear interference from antenna coupling degrades performance metrics like adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM due to cross-modulation products and intermodulation distortion.
Innovation Solution
A multiple-input, multiple-output intermodulation (MIMO IMD) cancellation block is implemented to estimate and cancel cross-modulation products by predicting them based on expected signals and transmission signals, using a Volterra model and weight factors, and injecting the inverse of these products into the signals to offset nonlinear interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple antennas transmit concurrently in the same frequency band (UL-MIMO mode), then data communication productivity is improved, but nonlinear interference from antenna coupling degrades signal quality
Solution Approach 1:
The system performs preliminary estimation of cross-modulation products using a Volterra model before signal transmission. The MIMO IMD cancellation block calculates expected nonlinear interference based on transmitted signal characteristics, enabling pre-compensation to be applied to the signal path, thereby reducing the actual nonlinear interference impact on communication quality
Solution Approach 2:
The system implements a feedback mechanism where the MIMO IMD cancellation block continuously monitors transmitted signals and adjusts weight factors based on the relationship between expected signals and actual transmission signals. This feedback loop enables dynamic optimization of interference cancellation parameters, maintaining high communication productivity while suppressing nonlinear interference
2Volume of moving object
If antennas are placed in close proximity for MIMO operation, then device compactness is improved, but antenna coupling increases causing cross-modulation distortion
Solution Approach 1:
The MIMO IMD cancellation block acts as an intermediary between the antenna array and the signal processing chain. It introduces a mathematical model (Volterra model) that mediates the coupling effects between closely spaced antennas by estimating and compensating for cross-modulation products, thereby enabling compact antenna placement without sacrificing signal quality
Solution Approach 2:
The system dynamically adjusts weight factors in the Volterra model based on operating conditions. By changing these parameters according to the actual coupling characteristics of the compact antenna arrangement, the system optimizes cancellation of cross-modulation products while maintaining the benefits of close antenna proximity for device compactness
3Use of energy by moving object
If power amplifiers operate at high efficiency, then energy consumption is improved, but nonlinear distortion increases degrading ACLR and EVM
Solution Approach 1:
The system applies preliminary anti-action by injecting the inverse of estimated cross-modulation products into the signal path before power amplification. The MIMO IMD cancellation block generates compensating signals that counteract the nonlinear distortion that will be introduced by high-power amplifiers operating at high efficiency, thereby maintaining both energy efficiency and signal fidelity
Solution Approach 2:
The system converts the harmful nonlinear distortion generated by efficient power amplifiers into a beneficial cancellation signal. By modeling the distortion characteristics using the Volterra model and generating inverse distortion signals through the MIMO IMD cancellation block, the previously harmful effect is transformed into a mechanism for improving overall signal quality while maintaining amplifier efficiency
Data Source
AI summary
The representative embodiments discussed in the present disclosure relate to techniques in which a transmitter may operate in an uplink multiple-input, multiple-output (MIMO) mode of operation. More specifically, in some embodiments, the transmitter may concurrently transmit a first and a second signal within the same frequency band via a first and second antenna, respectively. Further, in some embodiments, the transmitter may include circuitry and/or logic to offset nonlinear interference present in the transmitted signals as a result of antenna coupling between the first and second antenna and a nonlinear element (e.g., a power amplifier) within the transmitter.