Intermodulation Distortion Cancellation in RF Front-End Modules
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Solution Overview
Problem
In wireless communication systems like EN-DC, simultaneous transmission from multiple antennas leads to intermodulation distortion, causing desense and sensitivity degradation in receive signals, which is difficult to rectify.
Innovation Solution
A mobile device with a front-end module that calculates and removes intermodulation signals by analyzing digital signals received during simultaneous and separate transmission time slots, using frequency division duplexing and a duty cycle to isolate and subtract IMD from the receive signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If simultaneous transmission from multiple antennas is supported, then communication capabilities and features are enhanced, but intermodulation distortion occurs causing receive signal sensitivity degradation
Solution Approach 1:
The system performs preliminary characterization of the intermodulation distortion by having the transmitter send known training sequences through the power amplifiers. The receiver measures the actual IMD generated by the specific hardware combination and stores this characterization data before normal communication begins, allowing the distortion to be compensated for during subsequent operations
Solution Approach 2:
The receiver creates a digital model or copy of the intermodulation distortion characteristics by measuring the response to known training sequences. This digital representation of the IMD is then stored and subsequently subtracted from received signals to cancel out the distortion effect
2Measurement precision
If intermodulation distortion is cancelled through signal processing, then receive signal sensitivity is improved, but device complexity increases
Solution Approach 1:
The system performs the complex characterization and model creation during idle periods using known training sequences, so that during normal communication the cancellation process is simplified to just subtracting the pre-computed IMD model from received signals, reducing real-time processing complexity
Solution Approach 2:
The system uses its own transmitted training sequences to automatically characterize its own intermodulation distortion without requiring external calibration equipment or additional hardware, making the complex measurement process self-contained
Data Source
AI summary
A mobile device includes an antenna and a radio frequency front-end module coupled to the antenna. The module includes a first radio frequency circuit configured to transmit and receive over a first frequency division duplex communication band, and a second radio frequency circuit configured to transmit and receive over a second frequency division duplex communication band. A baseband processor can be configured to cause the first radio frequency circuit to transmit according to a duty cycle and analyze a signal received during the duty cycling by the first radio frequency circuit or by the second radio frequency circuit. Based on the analysis, the baseband processor can calculate intermodulation distortion between the first radio frequency circuit and the second radio frequency circuit.