LEO Satellite AIS Decoding for Overlapping Signal Separation
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Solution Overview
Problem
Low Earth Orbit (LEO) satellites face challenges in decoding Automatic Identification System (AIS) signals due to the large field of view, which results in overlapping signals from numerous ships, making it difficult to accurately decode and synchronize AIS transmissions in high-traffic areas.
Innovation Solution
The method involves receiving AIS signals with a LEO satellite, preprocessing them to generate digital input data, and using correlation techniques with predefined signals to identify candidate AIS message signals by computing correlation signals with different Doppler offsets, refining these signals to remove overlaps, and decoding them using a Viterbi decoder for proper formatting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If LEO satellite receives AIS signals from large field of view, then coverage area is improved, but signal overlap and interference increase
Solution Approach 1:
The patent segments the received signal into multiple candidate signals by identifying correlation peaks at different time offsets. Each peak represents a separate AIS message candidate that can be processed independently, effectively dividing the overlapping signal mixture into separable components for decoding.
Solution Approach 2:
The patent performs preliminary correlation processing to identify candidate AIS messages before full decoding. By pre-identifying correlation peaks and extracting candidate messages with their estimated parameters (Doppler shift, timing, frequency offset), the system prepares the signal in advance for selective decoding, reducing the impact of overlap.
2Difficulty of detecting and measuring
If correlation processing is performed on overlapping signals, then candidate AIS messages can be identified, but false detections and decoding errors increase
Solution Approach 1:
The patent implements feedback through iterative decoding and validation. Candidate messages are decoded using Viterbi decoder with feedback from syndrome checking and CRC validation. If decoding fails or validation doesn't pass, the system adjusts parameters and re-attempts decoding, using the feedback from failed attempts to improve subsequent decoding accuracy.
Solution Approach 2:
The patent changes multiple parameters during processing including Doppler shift estimates, frequency offsets, and timing synchronization parameters. By adjusting these parameters based on correlation results and decoding feedback, the system optimizes the detection of candidate messages while reducing false detections from overlapping signals.
3Measurement precision
If multiple candidate signals are processed for decoding, then signal separation is improved, but computational complexity increases
Solution Approach 1:
The patent applies partial action by selectively processing only the most promising candidate messages for full decoding. Instead of exhaustively decoding all possible candidates, the system prioritizes candidates with highest correlation strength and valid formatting, performing full decoding only on a subset that passes initial validation checks, thus reducing computational complexity while maintaining separation accuracy.
Solution Approach 2:
The patent performs preliminary filtering and validation of candidate messages before full decoding. By checking message formatting, validating CRC codes, and verifying Doppler shift consistency in advance, the system eliminates invalid candidates early, reducing the number of computationally intensive full decoding operations required.
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 effectively decodes AIS signals even in the presence of overlapping signals, enhancing the ability to monitor maritime traffic over a large region by improving signal detection and decoding accuracy.
Implementation Method 1
processing the digital input data by correlating the digital input data with a plurality of predefined signals having different Doppler offsets to compute a plurality of corresponding correlation signals
Implementation Method 2
employing multiple antennas for phase-shifting to maximize signal amplitude
Data Source
AI summary
Various embodiments are described herein for a system and method of detecting Automatic Identification System (AIS) signals in space and decoding these signals. In one aspect, a system for performing this function is described which includes a receiver configured to receive the plurality of AIS signals and pre-process the plurality of AIS signals to produce digital input data, and a processing unit configured to process the digital input data to identify one or more candidate AIS message signals based on Doppler offsets associated with the digital input data, determine corresponding Doppler offset estimates and time estimates of the one or more candidate AIS message signals, decode the one or more candidate AIS message signals to obtain corresponding message segments and validate the decoded message segments for proper AIS formatting.