GPS Receiver Signal Acquisition Using Doppler Compensation and Stack-Accumulation
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Solution Overview
Problem
Conventional GPS/GNSS receivers struggle to accurately acquire and track signals at sub-microsecond levels when the signals are weak, such as those received indoors or in urban areas, due to severe attenuation, which limits their ability to maintain time transfer accuracy.
Innovation Solution
A method for high-sensitivity GPS/GNSS signal acquisition and tracking in a stationary receiver, involving a front-end section for signal processing, which includes Doppler compensation, synchronous summation, cross-correlation, and stack-accumulation to enhance signal detection and synchronization, allowing for sub-microsecond time transfer even with weak signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional GPS/GNSS receivers use standard signal processing methods, then they can achieve acceptable bit error rates with strong signals, but they fail to maintain sub-microsecond time transfer accuracy with weak signals suffering severe attenuation
Solution Approach 1:
The patent segments the received signal into multiple individual satellite signals and processes each separately through independent acquisition and tracking channels. This allows the receiver to optimize processing for each weak signal independently, accumulating energy over time through integration techniques to achieve sub-microsecond time transfer accuracy even when individual signals are severely attenuated
Solution Approach 2:
The patent performs preliminary Doppler compensation and code phase alignment before final correlation and time transfer calculation. By pre-compensating for expected frequency shifts and timing offsets based on satellite ephemeris data, the receiver prepares the weak signals in advance, enabling accurate time transfer measurement even with signal levels as low as -160 to -170 dBm
2Reliability
If GPS/GNSS receivers require signal power above -148 dBm to maintain acceptable bit error rates, then demodulation accuracy is preserved, but time transfer capability is lost in indoor or urban canyon environments where signals are weaker
Solution Approach 1:
The patent implements continuous signal tracking and time transfer measurement without interruption, even when signal strength fluctuates below conventional thresholds. By maintaining continuous integration and accumulation of timing information from weak signals over extended periods, the receiver achieves reliable time transfer in previously unusable environments such as indoor locations and urban canyons
Solution Approach 2:
The patent changes the operating parameters of the receiver to accommodate weak signals by adjusting integration time, correlation threshold, and tracking loop bandwidth. These parameter modifications enable the receiver to operate reliably with signal powers as low as -160 to -170 dBm, expanding the operational environment range to include indoor and urban canyon scenarios while maintaining acceptable bit error rates
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
Enables accurate sub-microsecond time transfer and position determination with signals as weak as -160 to -170 dBm, maintaining time accuracy using a single satellite and facilitating seamless handovers between satellites.
Implementation Method 1
Doppler-compensating the captured baseband signal segment using a phase rotator. A phase rotation in the phase rotator may be calculated as a function of time based on the center frequency of the frequency bin and the rate of change in the frequency
Implementation Method 2
cross-correlating each compressed sample block with one period of reference C/A code for a selected satellite to produce an N-value correlation function per compressed sample block
Implementation Method 3
stack-accumulating a number of the N-value correlation magnitude functions into an array with precession compensation so as to determine a correlation peak having a largest value in the array
Data Source
AI summary
A method and apparatus provide high-sensitivity GPS/GNSS signal acquisition in a stationary GPS/GNSS receiver. The uncertainty in frequency due to apparent Doppler shift is partitioned into a plurality of contiguous frequency bins, and the uncertainty in location of navigation data bit boundaries is partitioned into equally spaced trial bit boundary locations. For each combination of the trial bit boundary location and the frequency bin, a signal block of captured complex baseband signal is Doppler-compensated using a phase rotator, and then synchronously summed with a periodicity of one period of C/A code so as to produce a compressed sample block having N samples. Each compressed sample block is cross-correlated with one period of reference C/A code to produce an N-value correlation function. A predetermined number of magnitudes of the N-value correlation functions are stack-accumulated into an array with precession compensation so as to find a correlation peak having the largest value.