Transmitter Front-End Distortion Compensation via Intermodulation
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Solution Overview
Problem
Telecommunication devices face challenges in compensating for transmitter distortions due to RF imperfections, as existing methods require external equipment that is inconvenient and often configured during manufacturing, and there is no known technique to separate transmitter and measurement receiver imperfections.
Innovation Solution
A method and digital front end system that generates a single complex tone signal, compensates its gain and phase, and updates offsets based on measured power to isolate and reduce inter-modulation signals indicative of transmitter distortions, allowing for in-device compensation of phase and gain distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external equipment is used to measure and compute compensation values for transmitter distortions, then measurement precision is improved, but device complexity and ease of operation deteriorate due to requiring external equipment and long data transfers
Solution Approach 1:
The measurement receiver within the telecommunication device performs self-measurement of transmitter distortions using internal resources. The system generates test signals, measures the transmitted signal through the measurement receiver, and computes compensation values entirely within the device without requiring external equipment, thereby making the device self-sufficient for distortion compensation
Solution Approach 2:
The measurement receiver is designed to serve multiple functions: it acts as both a regular communication receiver and a distortion measurement instrument. By utilizing the existing measurement receiver for both communication and measurement purposes, the system eliminates the need for separate external measurement equipment while maintaining measurement precision
2Manufacturing precision
If factory configuration is used to compensate transmitter distortions, then manufacturing precision is improved, but adaptability deteriorates as compensations are fixed during manufacturing and cannot be adjusted later
Solution Approach 1:
The system implements dynamic distortion compensation by enabling runtime measurement and adjustment of compensation values. Instead of fixed factory-configured compensations, the measurement receiver continuously or periodically measures transmitter distortions and updates compensation parameters during device operation, allowing the system to adapt to changing conditions and maintain optimal performance
Solution Approach 2:
The system performs preliminary distortion measurements and computes compensation values during factory configuration, but retains the capability to re-measure and re-compute compensations during device operation. This preliminary action establishes initial compensation while preserving future adaptability through runtime adjustment capabilities
3Measurement precision
If a measurement receiver is introduced to perform measurements on the transmitter signal, then measurement precision is improved, but device complexity increases due to additional components and the inability to separate transmitter and receiver imperfections
Solution Approach 1:
The system extracts and isolates the inter-modulation signal component that specifically indicates transmitter distortions from the total received signal. By filtering and analyzing only the inter-modulation products generated by transmitter non-linearities, the system separates transmitter imperfections from receiver imperfections, enabling precise measurement of transmitter distortions without being confounded by measurement receiver characteristics
Solution Approach 2:
The inter-modulation signal acts as an intermediary indicator of transmitter distortions. Rather than directly measuring the transmitted signal and dealing with the mixture of transmitter and receiver imperfections, the system uses the inter-modulation products generated by non-linear components as a mediator that specifically reveals transmitter distortion characteristics, simplifying the measurement process
Data Source
AI summary
There is described a method for compensating the phase and gain distortions of a transmitter analog front end affected by a leakage of a local oscillator. The method comprises generating a single complex tone signal in a digital front end, wherein the generation comprises compensating the signal gain and phase with gain and phase offsets. The method comprises feeding the compensated signal into the transmitter analog front end. The method comprises feeding a corresponding output signal of the transmitter analog front end into a nonlinear component, thereby generating an inter-modulation between the complex tone signal and at least one tone signal due to the local oscillator leakage. The method comprises feeding the output of the nonlinear component into a measurement receiver analog front end. The method comprises filtering the output of the measurement receiver analog front end with a band pass filter in order to isolate the inter-modulation, which is indicative of the distortions introduced by the transmitter analog front end. The method comprises measuring the power of the filtered signal. The method comprises updating the gain and phase offsets according to the measured power, by reducing said measured power. The disclosure also relates, in particular, to a digital front end, to an analog system, to a telecommunication device, to a computer program, and to a storage medium.