Nonlinear Distortion Interference Cancellation in Satellite Receivers
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Solution Overview
Problem
Existing digital communication systems face challenges in effectively canceling nonlinear-distorted interference in satellite communication systems, particularly due to dispersive nonlinear distortions caused by power amplifiers, which limit frequency reuse and increase bit-error rates.
Innovation Solution
A receiver system that processes received signals to estimate and cancel distorted interference using a series expansion of nonlinearity, involving a receiver filter/sampler, synchronizer, block generator, estimator signal generator, and combiner to produce residual-interference signals for demodulation, improving convergence and performance over conventional Volterra series expansion techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Volterra series expansion techniques are used to cancel nonlinear distortion, then interference cancellation is achieved, but convergence is slow and performance is limited
Solution Approach 1:
The patent transforms the complex-valued Volterra series into a real-valued series by separating in-phase and quadrature components. This parameter transformation enables faster convergence and improved computational efficiency while maintaining the same interference cancellation capability, directly resolving the contradiction between cancellation performance and convergence speed.
2Productivity
If frequency reuse is implemented in satellite communication, then bandwidth efficiency is improved, but relayed interference increases bit-error rates
Solution Approach 1:
The patent converts the harmful relayed interference into a beneficial signal by using it to train the equalizer. The interference, which would normally degrade bit-error rates, is instead utilized to characterize the nonlinear channel and compute compensation coefficients, thereby enabling frequency reuse while maintaining communication reliability.
Solution Approach 2:
The patent implements a feedback mechanism where the received signal (containing interference) is fed back through the equalizer to generate compensation coefficients. These coefficients are then used to cancel the interference in subsequent transmissions, creating a closed-loop system that enables frequency reuse without sacrificing bit-error rate performance.
3Power
If power amplifier nonlinearity is increased to improve transmit power, then signal strength is improved, but dispersive nonlinear distortions increase
Solution Approach 1:
The patent applies preliminary anti-action by pre-computing equalization coefficients that compensate for the power amplifier's nonlinearities before the signal is transmitted. The equalizer is trained on the distorted signal characteristics and generates compensation coefficients that counteract the dispersive nonlinear distortions, allowing high transmit power to be used without excessive distortion.
Data Source
AI summary
The present disclosure provides methods and apparatuses for demodulating discrete-time desired signals in a period-Td bandpass desired signal in the presence of interference that results from a period-T bandpass interference signal that has been nonlinear distorted. Estimation of the nonlinear-distorted interference and subsequent cancellation from a received signal, that includes the interference and desired signal, produces residual-interference signals. The demodulation of the residual-interference signals uses an equalization technique when Td is not equal to T. The estimation, cancellation, and demodulation are adapted for changing nonlinear distortion effects.