Microwave Transmitter Predistortion for Power Amplifier Linearization
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Solution Overview
Problem
Microwave transmitters face power limitations due to non-linearity, leading to underutilization of power, especially with high peak power/average power ratios and multiple modulation levels, and existing adaptive methods are hindered by high costs and complex measurement requirements.
Innovation Solution
A system and method for determining predistortion coefficients using pseudoadaptivity, which involves a non-linear transversal equalizer in the digital baseband process to automatically linearize the input signal without traditional costly measurements, reducing the number of coefficients needed and enabling efficient power utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If adaptive feedback linearizing systems are used to counteract non-linearity effects, then linearization accuracy is improved, but device complexity and cost increase due to additional feedback circuits
Solution Approach 1:
The patent applies predistortion by pre-modifying the input signal to compensate for anticipated non-linear effects before the signal reaches the power amplifier. This preliminary action eliminates the need for complex feedback circuits by preparing the signal in advance, thereby achieving linearization without adding feedback path complexity
Solution Approach 2:
The invention extracts and removes the non-linear distortion components from the signal path by applying inverse distortion through predistortion coefficients. By taking out the harmful non-linear effects through digital signal processing rather than physical feedback circuits, the system achieves linearization with reduced device complexity
2Manufacturing precision
If individual characterization measurements are performed for each non-linear block, then linearization precision is improved, but measurement time and cost increase
Solution Approach 1:
The patent uses pseudoadaptive techniques that create a digital model or copy of the non-linear block's behavior through software algorithms rather than physical measurements. This virtual modeling approach replicates the characterization process in the digital domain, eliminating time-consuming physical measurements while maintaining linearization precision
Solution Approach 2:
The invention replaces physical measurement systems with digital signal processing methods. By substituting mechanical/electrical measurement apparatus with software-based pseudoadaptive algorithms, the system achieves accurate linearization without the time and cost constraints of traditional measurement approaches
3Manufacturing precision
If digital predistortion calculations are added to existing signal processing, then linearization capability is improved, but computational complexity increases
Solution Approach 1:
The patent implements predistortion using a limited set of pre-calculated coefficients that address the most significant non-linear effects. By applying partial correction rather than attempting to compensate for all possible distortions, the system achieves effective linearization with reduced computational complexity
Solution Approach 2:
The invention changes the operational parameters by using fixed predistortion coefficients derived from pseudoadaptive techniques. This parameter transformation converts a potentially complex real-time calculation problem into a simpler signal multiplication operation, reducing computational requirements while maintaining linearization capability
Data Source
Figure 1~2
AI summary
A system for determining predistortion coefficients for microwave transmitters comprising: a digital signal source; a predistorter for distorting said digital signal; and a transmitter for transmitting said distorted digital signal; characterised by comprising a receiver for receiving said transmitted signal and providing a demodulated signal; a delay device for delaying said digital signal; a comparison device for comparing said delayed digital signal with said demodulated signal to produce a signal indicative of the error between said two signals; and a calculation device for determining said predistortion coefficients on the basis of said error indicative signal.