TMBOC Matched Filter Nulling for Narrowband GNSS Receivers
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Solution Overview
Problem
Consumer GNSS receivers are unable to effectively receive the wider bandwidth of TMBOC(6,1) signals due to their narrower bandwidth, resulting in a significant loss of approximately 0.6 dB in carrier to noise density ratio (CN0), which is crucial for signal reception in challenging environments.
Innovation Solution
A modified matched filter architecture that includes a nulling register to prevent high frequency samples from affecting the correlation result, specifically aligned with the timing of the BOC(6,1) signal, allowing for improved CN0 by effectively nulling the impact of BOC(6,1) during correlation, thereby enhancing signal reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a narrowband receiver is used for L1-C signal reception, then the receiver bandwidth is reduced for cost and complexity reasons, but the CN0 deteriorates due to inability to pass the wider bandwidth of BOC(6,1) signal
Solution Approach 1:
The patent segments the correlation process into two distinct parts: a first correlation operation that processes only BOC(1,1) components, and a second correlation operation that processes BOC(6,1) components. This segmentation allows the narrowband receiver to handle wideband signals by separating the processing of different signal components, thereby maintaining CN0 performance without requiring increased receiver bandwidth.
Solution Approach 2:
The patent extracts and removes the harmful interference caused by BOC(6,1) signal components during the first correlation operation. By explicitly identifying and eliminating the interference terms that arise from correlating BOC(6,1) signals with BOC(1,1) local codes, the system prevents CN0 degradation while using a narrowband receiver architecture.
2Device complexity
If matched filter correlation is performed on TMBOC(6,1) signals with narrowband receivers, then signal processing is simplified, but high frequency samples affect the correlation result and reduce CN0
Solution Approach 1:
The patent applies preliminary anti-action by pre-calculating and pre-subtracting the expected interference terms from BOC(6,1) signal components before they can degrade the correlation result. The method computes correction terms based on the known structure of BOC(6,1) signals and removes their harmful effects in advance, ensuring accurate correlation results without requiring complex filtering operations.
Solution Approach 2:
The patent performs preliminary processing by separately correlating BOC(1,1) components first, then using the results to guide the subsequent processing of BOC(6,1) components. This staged approach prepares the correlation data in advance, allowing the system to maintain high correlation accuracy while using simplified narrowband receiver architecture.
Data Source
AI summary
A method and an apparatus are provided for improving a carrier to noise density ratio (CNO) of a matched filter. A signal is received at a signal register of the matched filter. A local code is received at a local code register and a nulling register of the matched filter. An adder tree of the matched filter correlates the signal register and the local code register with respect to the nulling register to obtain a correlation result. The nulling register prevents high frequency samples of the signal register from affecting the correlation result.