GPS Receiver Fast Acquisition Using FFT Correlation
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Solution Overview
Problem
Conventional GPS receivers are inadequate for high altitude applications due to their inability to effectively acquire and track weak GPS signals, which are 10-100 times weaker than those at Low Earth Orbits, leading to prolonged acquisition times that render signal acquisition impractical at altitudes above Low Earth Orbit.
Innovation Solution
A GPS receiver with a frequency domain correlation module and Field-Programmable Gate Array (FPGA) for fast signal acquisition and tracking, capable of acquiring GPS signals with an Effective Isotropic Received Power (EIRP) of at least -180 dBW within one minute and tracking signals with EIRP of at least -175 dBW, utilizing Fast Fourier Transform (FFT) correlation processes and operating without priori data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If serial search methods are used for signal acquisition, then the receiver can search through parameter space systematically, but acquisition time grows quadratically and becomes impractically long for weak signals
Solution Approach 1:
The patent replaces the conventional serial search mechanical process with a parallel computational approach using multiple correlators working simultaneously across different code phases and Doppler frequencies. This substitution transforms the sequential acquisition process into a parallel one, dramatically reducing acquisition time while maintaining reliable weak signal detection capability.
Solution Approach 2:
The patent introduces a parallel dimension to the acquisition process by employing multiple correlators that operate simultaneously across different parameter spaces (code phase and Doppler frequency). This dimensional expansion allows the system to search through parameter space in parallel rather than sequentially, converting quadratic time complexity into linear or constant time performance.
2Reliability
If the same hardware is reconfigured for serial search during acquisition, then the receiver can perform signal detection, but the complexity of reconfiguration increases and reduces efficiency
Solution Approach 1:
The patent segments the acquisition and tracking functions into separate hardware components: dedicated acquisition correlators for signal detection and separate tracking correlators for continuous parameter estimation. This segmentation allows each component to be optimized for its specific function, eliminating the need to reconfigure hardware between acquisition and tracking modes, thereby reducing complexity and improving efficiency.
Solution Approach 2:
The patent designs the acquisition correlators to perform multiple functions simultaneously: they detect signals, estimate code phase, and estimate Doppler frequency in parallel. This multi-functionality eliminates the need for sequential reconfiguration and reduces overall system complexity by consolidating multiple operations into a single hardware structure.
3Reliability
If more data record length is examined to acquire weaker signals, then sensitivity improves, but acquisition time increases quadratically making weak signal acquisition impractical
Solution Approach 1:
The patent implements continuous correlation accumulation where correlators continuously process incoming signal data without interruption. The correlation results are accumulated in real-time across multiple data records, allowing the system to maintain continuous useful action on the signal. This continuous processing enables weak signal detection by integrating information over time without the quadratic time penalty associated with sequential search methods.
Solution Approach 2:
The patent performs preliminary correlation accumulation during the acquisition phase, continuously integrating signal data before the actual detection decision is made. This preliminary action allows the system to build up sufficient signal energy from weak signals in advance, enabling sensitive detection while maintaining fast acquisition times through parallel processing of multiple data records simultaneously.
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 enables fast and reliable acquisition and tracking of GPS signals at high altitudes, providing a 15 dB improvement in sensitivity and significantly reducing acquisition times, making GPS navigation feasible in Geostationary and higher orbits.
Implementation Method 1
The GPS signal acquisition component may be adapted to perform a Fast Fourier Transform (FFT) correlation process on said GPS signals
Data Source
AI summary
A global positioning system (GPS) receiver and method of acquiring and tracking GPS signals comprises an antenna adapted to receive GPS signals; an analog radio frequency device operatively connected to the antenna and adapted to convert the GPS signals from an analog format to a digital format; a plurality of GPS signal tracking correlators operatively connected to the analog RF device; a GPS signal acquisition component operatively connected to the analog RF device and the plurality of GPS signal tracking correlators, wherein the GPS signal acquisition component is adapted to calculate a maximum vector on a databit correlation grid; and a microprocessor operatively connected to the plurality of GPS signal tracking correlators and the GPS signal acquisition component, wherein the microprocessor is adapted to compare the maximum vector with a predetermined correlation threshold to allow the GPS signal to be fully acquired and tracked.