OFDM Predistortion Using Receiver Feedback for Nonlinear Amplifiers
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Solution Overview
Problem
Existing communication systems, particularly OFDM systems, face significant challenges due to non-linear characteristics in components like power amplifiers and low noise amplifiers, leading to signal distortion and high bit error rates, with existing mitigation methods being complex and costly or limited to addressing only transmitter-side issues.
Innovation Solution
A method that estimates non-linear effects using a training sequence, calculates a predistortion function, and applies it to the signal before amplification, effectively compensating for non-linearities at both the transmitter and receiver sides, including downstream components, without requiring complex implementations or additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If output power is decreased to reduce distortion from non-linear amplifiers, then signal distortion is reduced, but signal-to-noise ratio at reception is degraded
Solution Approach 1:
The patent applies predistortion to the signal before amplification, pre-compensating for the non-linear effects that will occur during amplification. This allows the amplifier to operate at high output power without introducing significant distortion, as the distortion is counteracted by the predistorted signal characteristics.
Solution Approach 2:
The patent implements a feedback mechanism where the receiver estimates non-linear effects from the received signal and sends correction parameters back to the transmitter. This closed-loop feedback enables continuous optimization of the predistortion function to compensate for amplifier non-linearities while maintaining high output power.
2Object-affected harmful factors
If A-class amplifier is used to operate in linear range, then signal distortion is reduced, but energy consumption and manufacturing costs increase
Solution Approach 1:
The patent changes the operating parameters of the amplifier by applying predistortion to the input signal, allowing the amplifier to operate efficiently in non-linear regions while maintaining linear output characteristics. This enables the use of more energy-efficient amplifier classes (such as C-class or switching amplifiers) instead of requiring A-class amplifiers that operate in the linear range.
3Object-affected harmful factors
If complex adaptive predistortion is implemented, then non-linear mitigation is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent implements a self-calibrating system where the receiver performs the complex estimation of non-linear effects and sends results back to the transmitter. The transmitter then applies the predistortion function based on received parameters, shifting the computational burden from the transmitter to the receiver and simplifying the transmitter architecture.
4Reliability
If predistortion is applied to compensate for non-linear effects, then bit error rate is reduced, but implementation complexity increases
Solution Approach 1:
The patent applies predistortion preprocessing to the signal before transmission, which simplifies the reception process. By pre-compensating for non-linear effects at the transmitter, the receiver can use simpler processing to achieve lower bit error rates compared to attempting to compensate for non-linearities after reception.
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
AI summary
The present method mitigates a nonlinear effect in a communication system. A set of parameters describing the nonlinear effect is estimated at the receiving side and the estimated values are sent to the transmitter on a return channel. The transmitter uses these estimated values to predistort the signal upstream the stage where the non linear effect has occurred.