Multi-Level Aiding Signals for Rapid Satellite Long-Code Acquisition
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Solution Overview
Problem
Conventional satellite-based navigation systems face challenges in quickly acquiring ranging codes, especially in cold start scenarios or when using encrypted codes, due to the long acquisition times required for synchronization, particularly with low Earth orbit satellites that have short visibility periods.
Innovation Solution
The use of an aiding signal comprising a sequence of short codes with a predetermined time relationship to a long code, allowing for rapid synchronization and decryption of encrypted long codes by determining the sequence of short codes and utilizing a predetermined time alignment to reduce the search space for acquiring the long code.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional GPS receivers observe the long code to achieve synchronization, then location fix can be obtained, but acquisition time is several minutes which is too long for LEO satellite visibility
Solution Approach 1:
The patent segments the long code acquisition process into two parts: first acquiring a short code sequence from the aiding signal, then using that to rapidly acquire the corresponding long code. This segmentation reduces the total acquisition time from several minutes to under one minute, enabling effective utilization of LEO satellite visibility periods.
Solution Approach 2:
The patent implements preliminary action by transmitting the short code sequence in advance within the aiding signal. This allows the receiver to have a head start in the acquisition process, eliminating the need to search through the entire long code sequence from scratch and enabling rapid location fixes during the brief LEO satellite pass.
2Reliability
If encrypted ranging codes are used for security, then code protection is improved, but warm start reacquisition becomes difficult and time-consuming
Solution Approach 1:
The patent introduces an intermediary element - the short code sequence in the aiding signal - that bridges the gap between encrypted long codes and rapid acquisition. The short code acts as a key or pointer that enables the receiver to quickly locate and acquire the encrypted long code without having to search through all possible codes, thus maintaining security while enabling fast warm start reacquisition.
3Area of stationary object
If LEO satellites are used for navigation, then system coverage is improved, but signal visibility duration is reduced to less than 10 minutes
Solution Approach 1:
The patent changes the temporal parameters of signal transmission by incorporating the short code sequence in the aiding signal that repeats at a known rate. This allows the receiver to acquire the long code within the brief visibility window of LEO satellites, effectively adapting the acquisition process to the constrained time available during satellite passes.
Data Source
AI summary
Disclosed herein are methods and systems that involve an aiding signal that can be used to acquire a long code in a. wireless signal, such as a ranging code in a wireless navigation signal transmitted by a satellite. A receiver may receive a first wireless signal and a first aiding signal transmitted by a first transmitter of a plurality of transmitters. The first wireless signal comprises a first, long code. The first aiding signal comprises repeating instances of a sequence of short codes, wherein the sequence has a predetermined time relationship with the first long code and is specific to the first transmitter. The receiver may use the first aiding signal to acquire the first long code by determining the sequence of short codes in the first aiding signal and using the predetermined time relationship to synchronize with the first long code.