Spaceborne AIS Receiver Overlapping Sub-bands
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Solution Overview
Problem
Satellite-based Automatic Identification System (AIS) receivers face challenges such as message collisions, Doppler shift, and low signal-to-noise ratios due to the spaceborne nature of the system, leading to unsatisfactory bit error rates and packet error rates, especially when dealing with uncoordinated AIS emitters and higher propagation delays.
Innovation Solution
A space-borne AIS receiver with multiple processing sections that synchronize, demodulate, and detect AIS messages across overlapping frequency sub-bands, utilizing filtered replicas for timing and carrier frequency estimations, and employing interference cancellation and Doppler diversity to improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional 2-bits differential demodulator is used for space-borne AIS receiver, then device complexity is reduced, but bit error rate and packet error rate performance deteriorates
Solution Approach 1:
The receiver processes the AIS channel by dividing it into multiple overlapping frequency sub-bands, with each sub-band processed by a dedicated processing section. This segmentation allows each section to focus on a specific frequency range, improving synchronization and demodulation accuracy for each sub-band while maintaining overall system manageability.
Solution Approach 2:
The invention introduces an auxiliary signal path dimension alongside the main signal path. The auxiliary path is used specifically for timing error and carrier frequency estimations, while the main path handles the actual AIS message detection. This dimensional separation allows independent optimization of synchronization accuracy without compromising detection performance.
2Device complexity
If processing sections use non-overlapping frequency sub-bands, then device complexity is reduced, but interference rejection capability deteriorates
Solution Approach 1:
The invention extracts and processes interference signals by creating overlapping frequency sub-bands. Each processing section handles a specific sub-band, and the overlapping design ensures that interference components are captured and can be separately processed and cancelled, removing harmful interference from the detection process.
Solution Approach 2:
The invention changes the frequency domain parameters by introducing overlapping sub-bands with different center frequencies and bandwidths. This parameter variation allows the system to capture signals and interference from different spectral perspectives, enabling better interference rejection through comparative processing.
3Device complexity
If timing synchronization is not optimized for each sub-band, then device complexity is reduced, but measurement precision of AIS messages deteriorates
Solution Approach 1:
The synchronization function is segmented and distributed to each processing section, with each section performing timing error and carrier frequency estimations independently for its assigned sub-band. This segmentation allows each processing section to optimize synchronization parameters specifically for its frequency range, improving overall timing precision.
4Area of stationary object
If satellite-based AIS receives signals from uncoordinated emitters, then coverage area is expanded, but packet error rate increases due to message collisions
Solution Approach 1:
The received signal is divided into multiple overlapping frequency sub-bands, with each processing section handling a specific sub-band. This segmentation allows the system to process signals from multiple uncoordinated emitters simultaneously in different frequency ranges, reducing packet collisions by distributing the processing load across multiple independent channels.
Solution Approach 2:
The invention converts the harmful effect of message collisions into a beneficial processing approach by using interference cancellation techniques. Colliding messages are processed as interference signals that can be estimated and subtracted from the received signal, allowing the system to recover useful information even from collided packets.
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
The solution significantly enhances the bit error rate and packet error rate performance as a function of signal-to-noise ratio, effectively rejecting interference and maintaining accurate detection of AIS messages even under conditions of maximum Doppler shift, thereby providing reliable maritime traffic monitoring over large areas.
Implementation Method 1
Satellite motion with respect to the emitters induces a significant Doppler shift of the carrier frequency
Data Source
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AI summary
An Automatic Identification System - AIS - receiver comprising at least one processing section (PS1, PS2) for synchronizing, demodulating and detecting AIS messages contained in a received signal, said processing steps being carried out separately for a plurality of frequency sub-bands (SB1, SB2, SB3) spanning an AIS channel (CH1, CH2); the receiver being characterized in that: - said sub-bands overlap with each others; and - said or each processing section is adapted for synchronizing, demodulating and detecting said AIS messages within each subband on the basis of timing error and carrier frequency estimations obtained from filtered replicas of said received signal, propagating along respective auxiliary signal paths.