Optical Ranging via Sideband Modulation and PN Code Correlation
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Solution Overview
Problem
Current laser communication systems lack a standardized ranging technique, relying on separate high-power short-pulse lasers and expensive ultra-fast photodetectors, which are bulky and costly, and suffer from low echo return due to optical alignment issues, limiting ranging resolution.
Innovation Solution
Integrating ranging signaling with data communications using a higher frequency optical sideband, employing pseudorandom noise (PN) codes, and performing loopback operations to determine range between nodes, eliminating the need for separate ranging lasers and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate high power short-pulse laser is used for ranging, then ranging capability is achieved, but device complexity and cost increase
Solution Approach 1:
The patent combines the ranging signal and data communication signal into a single optical transmission channel. The ranging signal is modulated onto an optical carrier at a higher frequency sideband, while data communications occupy the baseband or lower frequency range. This merging eliminates the need for separate ranging lasers and photodetectors, reducing device complexity and cost while maintaining ranging resolution through correlation processing of the combined signal.
Solution Approach 2:
The optical transmission system is designed to perform multiple functions simultaneously: data communication and ranging. By modulating the ranging signal onto the optical carrier and combining it with data communications in the same channel, the system achieves universal functionality without requiring dedicated hardware for each function, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If separate ranging lasers are used, then ranging signaling is achieved, but optical alignment discrepancies reduce echo return
Solution Approach 1:
By combining the ranging signal with the data communication signal in the same optical transmission channel, the patent ensures that both signals share the same optical path and alignment characteristics. This eliminates the optical alignment discrepancies that occur when separate lasers are used, as the ranging signal rides on the same carrier as the communication signal, ensuring consistent alignment and stronger echo return for improved reliability.
3Measurement precision
If ultra-fast photodetectors are used for gated detection, then time counter triggering is achieved, but cost increases
Solution Approach 1:
The patent extracts the ranging signal from the combined optical transmission by utilizing frequency separation. The ranging signal is modulated at a higher frequency sideband, allowing it to be filtered and separated from the baseband data communications using standard photodetectors and signal processing techniques. This eliminates the need for expensive ultra-fast photodetectors while maintaining time measurement accuracy through correlation processing of the extracted ranging signal.
4Device complexity
If ranging and data communications use the same optical channel, then equipment cost is reduced, but signal interference may occur
Solution Approach 1:
The patent resolves signal interference by transitioning to another dimension - frequency. The ranging signal is modulated onto a higher frequency sideband of the optical carrier, while data communications occupy the baseband or lower frequency range. This frequency domain separation allows both signals to coexist in the same optical channel without significant interference, enabling equipment consolidation while maintaining signal integrity through spectral separation.
Data Source
AI summary
Provided herein are various improvements to laser communication ranging. In one example, a method includes combining a ranging signal with data communications into an optical transmission for receipt by a communication node, and obtaining an additional optical transmission transferred by the communication node comprising additional data communications combined with a retransmitted version of the ranging signal. The method includes determining an indication of a range to the communication node based at least on a comparison between properties of the ranging signal and properties of the retransmitted version of the ranging signal after separation from the additional data communications.