Satellite Link Adaptation for Spectral Efficiency Under Doppler Shift
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Solution Overview
Problem
Non-geosynchronous satellite-based communication systems, such as those using low-earth orbits, face challenges due to non-stationary communication environments, resulting in Doppler shifts, time delays, and changing channel characteristics, which complicate robust and reliable communications.
Innovation Solution
A method and system where a gateway receives channel state information from user terminals, encodes and modulates data blocks accordingly, and transmits them via a satellite, employing techniques like concatenated encoding and adaptive ARQ to ensure efficient data transmission, adjusting modulation and coding schemes based on channel conditions for improved error control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If non-geosynchronous satellites in low-earth orbits are used to provide communication coverage, then Earth coverage capability is improved, but communication reliability deteriorates due to Doppler shifts, time delays, and changing channel characteristics
Solution Approach 1:
The system dynamically adapts modulation and coding schemes based on real-time channel state information to handle the non-stationary nature of LEO satellite communications. The gateway and user terminals continuously adjust transmission parameters to maintain reliable communication despite changing Doppler shifts and channel characteristics.
Solution Approach 2:
The patent changes physical parameters of the communication signal including modulation order, coding rate, and resource allocation based on channel conditions. By adjusting these parameters dynamically, the system maintains communication reliability while operating in the challenging LEO environment with varying Doppler effects and signal propagation characteristics.
2Productivity
If adaptive modulation and coding schemes are used based on channel state information, then spectral efficiency is improved, but system complexity increases
Solution Approach 1:
The system segments the adaptation process into discrete steps with a finite set of predefined modulation and coding schemes. Instead of continuous adaptation, the gateway selects from predetermined schemes based on channel quality indicators, reducing computational complexity while maintaining spectral efficiency gains.
Solution Approach 2:
The system implements feedback mechanisms where user terminals report channel state information to the gateway, which then selects appropriate modulation and coding schemes. This feedback-based adaptation allows spectral efficiency improvement while distributing the complexity burden between the terminal and gateway rather than requiring complex real-time optimization at all points.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances spectral efficiency and reliability in satellite communications by adapting to varying channel conditions, improving error control and spectral efficiency, especially during re-transmissions.
Implementation Method 1
modulating by the gateway the plurality of encoded blocks into a plurality of modulated and encoded blocks, wherein the gateway modulates each encoded block according to the value of the channel state information
Implementation Method 2
A satellite is an orbiting receiver and repeater used to relay information
Implementation Method 3
there will be Doppler shifts, time delays, and changing communication channel characteristics
Data Source
AI summary
A communication satellite system provides for spectral efficient data transmissions by a gateway to multiple user terminals by way of a satellite. The gateway transmits multiple blocks in a single slot, each block intended for one of the user terminals, where each block is encoded and modulated according to a scheme that may be different for each intended user terminal. Upon re-transmission of a block if that block is lost or received in error, the block may be encoded and modulated according to another scheme that is less spectrally efficient than in the first transmission of the block.