FTN Signal Pre-Distortion for Nonlinear Satellite Uplink Amplifiers
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Solution Overview
Problem
In satellite communication systems, high power amplifiers (HPAs) operating near saturation cause nonlinear distortion and inter-symbol interference (ISI), which degrade signal quality and require complex receivers to handle increased interference levels, limiting transmission throughput and spectral efficiency.
Innovation Solution
The system employs faster-than-Nyquist (FTN) transmission symbol rates combined with tight frequency roll-off and dynamic pre-distortion at the transmitter, along with novel interference compensation techniques in the receiver to mitigate nonlinear and linear interference, maintaining manageable complexity despite increased interference memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If HPA operates near saturation to maximize efficiency, then power efficiency is improved, but nonlinear distortion and ISI increase
Solution Approach 1:
The system applies pre-distortion to the transmitted signal before it enters the HPA. This preliminary action compensates for the expected nonlinear distortion that will occur during saturation amplification, allowing the HPA to operate at saturation for maximum efficiency while the pre-distorted signal counteracts the resulting distortion effects.
Solution Approach 2:
The system converts the harmful nonlinear distortion generated by saturation operation into a beneficial effect through iterative compensation. The receiver uses multiple iterations to estimate and subtract the distortion components, transforming the harmful distortion into a correctable artifact that can be removed through mathematical processing.
2Productivity
If transmission rate is increased above Nyquist rate to improve throughput, then productivity is improved, but ISI and interference increase
Solution Approach 1:
The system applies pre-distortion filtering before transmission to pre-compensate for the inter-symbol interference that will occur due to faster-than-Nyquist signaling. This preliminary action shapes the signal spectrum and time-domain characteristics to reduce the severity of ISI before it occurs during high-rate transmission.
Solution Approach 2:
The system employs iterative feedback compensation at the receiver, where the estimated distortion from one iteration is used to improve the estimation in the next iteration. This feedback mechanism progressively reduces the ISI effects by repeatedly estimating and removing interference components from the received signal.
3Productivity
If multiple carriers are shared by single transponder to increase throughput, then productivity is improved, but nonlinear interference increases
Solution Approach 1:
The system applies pre-distortion to the composite multicarrier signal before it enters the shared HPA. This preliminary action accounts for the nonlinear interactions between multiple carriers during saturation amplification, pre-compensating for the intermodulation distortion that will be generated by the nonlinear HPA operation.
Solution Approach 2:
The system uses iterative feedback compensation to estimate and remove the nonlinear interference generated by multicarrier amplification. Each iteration refines the estimate of the nonlinear distortion components, allowing the receiver to progressively cancel the intermodulation interference caused by sharing the HPA among multiple carriers.
Data Source
AI summary
A signal transmission approach comprises encoding a source signal (comprising source symbols) to generate a corresponding encoded signal. The encoded signal is modulated by mapping each source symbol to a respective signal constellation point of an applied signal constellation to generate a modulated signal. The modulated signal is pre-distorted based on a distortion estimate to generate a pre-distorted signal. The pre-distorted signal is filtered to generate a filtered signal. The filtered signal is frequency translated and amplified to generate a transmission signal for transmission via an uplink channel of a satellite communications system. To increase throughput, the source signal is processed through the apparatus and the resulting transmission signal is generated at a Faster-than-Nyquist (FTN) symbol rate and with a tight frequency roll-off. The modulated signal is pre-distorted based on a distortion estimate relating to the nonlinearity and the filters applied before and/or after the pre-distorter.