Satellite Positioning via Multilateration TDOA
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Solution Overview
Problem
Current satellite positioning systems for geostationary satellites are costly and unreliable due to the need for large, expensive mobile antennas and synchronization requirements among ground stations, leading to potential unavailability of orbit control and measurement functions.
Innovation Solution
Implementing a multilateration system using Time Differences Of Arrival (TDOA) measurements, where all measurements are taken on board the satellite, eliminating the need for synchronized ground stations and allowing the reuse of existing low-cost ground structures, with uplink signals of the same frequency shifted in time to determine the satellite's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated distance-measuring station with large mobile antennas is used, then measurement precision is improved, but device complexity and cost increase, and reliability decreases due to mobile parts
Solution Approach 1:
Instead of having ground stations measure the satellite position directly, the patent inverts the approach by having the satellite measure the position of ground stations relative to itself. The satellite receives signals from multiple ground stations, measures the time differences of arrival (TDOA) of these signals, and calculates its own position based on these measurements. This inversion eliminates the need for complex mobile antennas on ground stations while maintaining measurement precision.
Solution Approach 2:
The satellite performs self-positioning by utilizing signals from ground stations and its own onboard measurement capabilities. The satellite's transponder and positioning system work together to automatically determine its position without requiring external active measurement systems or complex ground infrastructure. This self-service approach improves reliability by eliminating dependency on mobile ground station equipment.
2Measurement precision
If synchronized ground stations with local clocks are used, then measurement precision is improved, but device complexity and synchronization requirements increase
Solution Approach 1:
The patent extracts the synchronization requirement from the ground station system by measuring time differences of arrival (TDOA) of signals from multiple ground stations. Instead of requiring each ground station to have synchronized clocks, the system measures the relative time differences between arrivals at the satellite, which eliminates the need for ground station clock synchronization while maintaining measurement precision.
Solution Approach 2:
The satellite acts as an intermediary that receives signals from multiple ground stations with unsynchronized clocks and performs the time difference measurements onboard. The satellite's onboard timing system serves as the reference, and it calculates position based on the TDOA of signals from different ground stations, thereby mediating between the unsynchronized ground clocks and the positioning requirement.
3Productivity
If mobile antennas with motorized parts are used, then measurement capability is improved, but reliability decreases due to mechanical failures
Solution Approach 1:
The patent replaces the mechanical mobile antenna systems on ground stations with a signal-based approach. Instead of physically moving antennas to track the satellite, the system uses fixed ground stations that transmit signals to the satellite, which then measures the time differences of arrival. This substitution of mechanical tracking with signal processing eliminates moving parts and improves reliability while maintaining measurement capability.
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 provides a reliable, cost-effective satellite positioning system that can operate with low-cost ground stations, enabling autonomous orbit determination and station-keeping maneuvers without the need for data collection systems or synchronization, and is resilient to station unavailability.
Implementation Method 1
by exploiting the principle of multilateration, also known as TDOA for 'Time Differences Of Arrival', using the signal transmission or repetition capabilities specific to this category of satellites, i.e. a receiving antenna, a repeater (electronic device making the information of the received signal available on another carrier signal, capable of being retransmitted), and a retransmission antenna which physically can be the receiving antenna, and by measuring the differences in the time of arrival of the signals due to the differences in the path of the signals
Implementation Method 2
the downlink signal sent by the satellite is transmitted by a ground transmitting station and repeated by the satellite, the satellite including means for repeating the signal received from the ground transmitting station
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
The system has transmitter stations (2) that are arranged at predetermined position for sending uplink signal (3) to the satellite (1). The measuring unit measures differences in the arrival times of the uplink signals at the satellite.