Coherent DAS Polarization Merging for Reduced Memory
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Solution Overview
Problem
Coherent distributed acoustic sensing (DAS) systems face high processing complexity and memory requirements due to the need to combine four polarization diversity terms from the beating process, which doubles the memory and bandwidth needed.
Innovation Solution
The solution involves merging X and Y polarizations before beating, aligning them to the same direction, and using rotations to maintain phase continuity, resulting in a single input and output for the beating module, thereby reducing processing complexity and memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If four polarization diversity terms (X-X, X-Y, Y-X, Y-Y) are used from the beating process, then full power utilization is achieved, but processing complexity and memory requirements double
Solution Approach 1:
The patent performs polarization alignment before the beating process by rotating one polarization to match the other using the slow-varying polarization state information. This preliminary alignment ensures that only one polarization term needs to be processed during beating, eliminating the need to handle all four diversity terms while still capturing full power through proper phase continuity maintenance
Solution Approach 2:
The patent separates the polarization handling into two distinct stages: (1) a preliminary polarization alignment stage using slow-varying state information, and (2) a beating stage using the aligned single polarization. This segmentation allows full power utilization in the alignment stage without carrying the complexity of four diversity terms into the beating stage
2Loss of information
If four polarization diversity terms are processed after beating, then complete signal information is captured, but memory and bandwidth requirements double
Solution Approach 1:
The patent performs polarization alignment before beating using the slow-varying polarization state, ensuring that the alignment is established in advance. This preliminary action prevents the need to store and process four separate diversity terms, reducing memory and bandwidth requirements while maintaining complete signal information through proper phase continuity
Solution Approach 2:
Instead of the conventional approach of beating first and then combining four polarization diversity terms, the patent inverts the sequence by aligning polarizations before beating. This inversion eliminates the need for subsequent combination processing, directly reducing memory and bandwidth requirements while preserving signal information
3Reliability
If frame-by-frame processing is performed for each location, then polarization diversity combining is achieved, but processing complexity increases
Solution Approach 1:
The patent performs polarization alignment as a preliminary step before the frame-by-frame beating process. By using the slow-varying polarization state to pre-align the polarizations, the subsequent frame-by-frame processing only needs to handle a single aligned polarization term, maintaining reliability through proper diversity combining while reducing processing complexity
Solution Approach 2:
The patent dynamically adjusts the polarization alignment based on the slowly varying polarization state, updating the alignment parameters before each frame or sequence of frames. This dynamic adaptation ensures optimal polarization alignment is maintained without requiring complex real-time adjustments during the beating process itself
Data Source
AI summary
Aspects of the present disclosure are directed to improved systems, methods, and structures providing coherent detection of DAS. In sharp contrast to the prior art, systems, methods, and structures according to aspects of the present disclosure advantageously reduce the beating diversity terms such that required memory and bandwidth are reduced over the art.