Two-Hopped Carrier Signaling for Low-Complexity LEO-PNT Acquisition
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Solution Overview
Problem
Existing LEO-PNT and GNSS signal acquisition systems face challenges with increased Doppler and ionospheric delays, leading to complex acquisition processes and vulnerability to spoofing and jamming attacks, especially for FH-CDMA and OFDM-CDMA waveforms.
Innovation Solution
A method involving two hopped carrier frequencies modulated with narrow-band waveforms, symmetrical around a middle baseband frequency, and employing cyphered spreading sequences to enhance robustness against jamming and spoofing while maintaining a simple receiver architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wide bandwidth CDMA waveforms are used for LEO-PNT, then positioning accuracy and robustness against interference are improved, but acquisition complexity increases significantly
Solution Approach 1:
The patent segments the wide bandwidth signal into multiple narrowband sub-signals transmitted on different carrier frequencies. Each sub-signal can be acquired independently with lower complexity, and their results are combined to achieve the positioning accuracy of the full wide bandwidth signal. This divides the complex acquisition problem into simpler sub-problems.
Solution Approach 2:
The patent introduces a frequency dimension by transmitting the same navigation signal across multiple carrier frequencies. Instead of acquiring one wide bandwidth signal, the receiver acquires multiple narrowband signals across different frequency dimensions, transforming a single complex acquisition task into multiple simpler tasks that can be parallelized.
2Measurement precision
If carrier frequency is increased to S-, C- or higher bands, then available bandwidth and positioning accuracy are improved, but Doppler excursion increases making acquisition more difficult
Solution Approach 1:
The patent segments the high-frequency signal into multiple narrowband components across different carriers. Each component experiences reduced effective Doppler within its narrow bandwidth, making correlation-based acquisition feasible even at high frequencies where total Doppler excursion would be prohibitive.
Solution Approach 2:
The patent changes the signal parameter from a single wideband carrier to multiple narrowband carriers. This parameter change allows the system to operate at high frequencies (S-, C-, Ka-bands) while maintaining acquisition feasibility by limiting the Doppler spread within each narrowband component.
3Reliability
If cyphered spreading sequences are used to protect against spoofing, then security against spoofing and jamming is improved, but acquisition complexity increases
Solution Approach 1:
The patent segments the cyphered signal into multiple narrowband sub-signals. Each sub-signal can be independently correlated with locally generated replicas, reducing the computational burden of acquiring cyphered signals while maintaining the spoofing resistance provided by the cyphered spreading sequences.
Solution Approach 2:
The patent adds a frequency dimension to the cyphered signal transmission. By distributing the cyphered signal across multiple carrier frequencies, the system enables parallel acquisition processes that reduce overall complexity while maintaining security.
4Measurement precision
If LEO satellite altitude is used instead of MEO, then signal strength and positioning accuracy are improved, but Doppler shift increases requiring more Doppler hypotheses to be tested
Solution Approach 1:
The patent segments the signal acquisition process across multiple frequency carriers. Each narrowband carrier requires fewer Doppler hypotheses to be tested compared to a single wideband signal, reducing the overall computational complexity despite the increased total Doppler from LEO altitudes.
Solution Approach 2:
The patent introduces frequency diversity as an additional dimension for signal transmission. This allows the receiver to perform acquisition in parallel across frequency dimensions, reducing the number of Doppler hypotheses needed per frequency component while maintaining accurate positioning from LEO satellites.
Data Source
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AI summary
A method for creating and processing a signal waveform, the method comprising: generating, by a first processor, two hopped carrier frequencies, wherein the two hopped carrier frequencies are symmetrical with respect to a third carrier frequency, fm, and wherein a distance between the first and second hopped carrier frequencies, |second hopped carrier frequency - first hopped carrier frequency|, is pre-defined; modulating, by the first processor, the first hopped carrier frequency and the second hopped carrier frequency with a narrow-band waveform, wherein a first signal is a first outcome of the modulation on the first hopped carrier frequency and a second signal is a second outcome of the modulation on the second hopped carrier frequency, converting the modulated first and second hopped carrier frequencies to the central carrier frequency f0; transmitting, by a first transceiver coupled to the first processor, the modulated first signal and the modulated second signal; receiving, by a second transceiver, the transmitted first and second signals, wherein the second transceiver is couplable to a second processor configured to process the received first and second signals; and converting, by the second processor, a first baseband of the modulated first carrier frequency to a central baseband carrier frequency, and a second baseband of the modulated second carrier frequency to the central baseband carrier frequency, wherein the conversion to the central baseband carrier frequency is configured to be applied for each hop applied to the modulated first and second carrier frequencies.