DSSS RF Signal Spectral Shaping for eLORAN Power Efficiency
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Solution Overview
Problem
The current eLORAN navigation system has technical drawbacks such as high power requirements, poor peak-to-average power ratio, susceptibility to interference, and limited data rate capabilities due to its outdated pulse waveform, which affects its efficiency and reliability in navigation and data communication.
Innovation Solution
The implementation of a direct sequence spread spectrum (DSSS) RF signal with spectral shaping using minimum-shift keying (MSK), binary phase shift keying (BPSK), or quadrature phase shift keying (QPSK) with root-raised-cosine filtering, ensuring 99% of the power is within the 90-110 kHz frequency range, reducing interference and enhancing data throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the current eLORAN pulse waveform is used, then navigation functionality is provided, but peak power requirements are high and power efficiency is poor
Solution Approach 1:
The patent changes the fundamental parameters of the signal waveform from traditional LORAN-C pulse modulation to spread spectrum modulation (BPSK, QPSK, MSK). This parameter change transforms the signal structure to achieve constant envelope properties, allowing efficient amplification and reducing peak power requirements while improving overall power efficiency.
Solution Approach 2:
The patent replaces the traditional pulse-based navigation signal mechanism with a spread spectrum modulation mechanism. By substituting the signal generation approach using phase and frequency modulation instead of amplitude pulse variation, the system achieves better power efficiency and reduced peak power demands.
2Reliability
If the current eLORAN pulse waveform is used, then navigation signaling is achieved, but susceptibility to interference is high
Solution Approach 1:
The patent converts the traditionally harmful wide spectral distribution of spread spectrum signals into a beneficial feature. By spreading the navigation signal energy across a wide frequency band using pseudorandom codes, the system achieves frequency diversity that provides inherent resistance to narrowband interference, converting what would be spectral dispersion into interference rejection capability.
Solution Approach 2:
The patent introduces dynamic phase and frequency modulation through spread spectrum techniques. The pseudorandom code modulation creates a dynamically varying signal structure that makes the navigation signal resistant to static and slowly varying interference, allowing the receiver to track and differentiate the desired signal from interfering sources.
3Productivity
If the current eLORAN data channel is used, then data communication is provided, but data rate capability is limited
Solution Approach 1:
The patent merges the navigation signal and data communication functions into a single integrated spread spectrum signal. By combining position/navigation data with additional data channels using the same spread spectrum modulation framework, the system achieves multiple data streams simultaneously, significantly increasing overall data throughput while maintaining navigation functionality.
4Area of stationary object
If spectral containment is enforced, then frequency allocation compliance is achieved, but signal power distribution becomes constrained
Solution Approach 1:
The patent applies local quality by using spectral shaping filters that concentrate signal power in specific frequency regions while maintaining overall spread spectrum characteristics. The root-raised-cosine filtering applies localized spectral control, ensuring 99% of power falls within the allocated bandwidth while preserving the interference rejection benefits of spread spectrum in the localized frequency regions.
Data Source
AI summary
A long range navigation system may include radio frequency (RF) transmitter stations at fixed geographical locations, each having an RF transmitter and an RF modulator coupled to the RF transmitter, and configured to generate a direct sequence spread spectrum (DSSS) RF signal being spectrally shaped so that 99% of power from the RF transmitter is within the frequency range of 90-110 KHz. Movable RF receiver units each include an RF receiver and a demodulator coupled to the RF receiver configured to demodulate the DSSS RF signal to determine a position of the movable RF receiver unit.