Radio Beacon Bearing Using Coherent Antenna Despreading
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Solution Overview
Problem
Conventional amplitude-based direction finding systems are ineffective for second-generation COSPAS SARSAT beacon signals due to their spread spectrum characteristic, and satellite-determined locations may not always be reliable.
Innovation Solution
An apparatus and method using a combination of non-directional and directional antenna systems to perform coherent despreading operations, extracting bearings by correlating direct-sequence spread-spectrum signals, enabling accurate direction finding even with spread-spectrum signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional amplitude-based direction finding systems are used, then the system is simple and compatible with existing hardware, but it cannot effectively process spread spectrum signals from second-generation COSPAS SARSAT beacons
Solution Approach 1:
The patent changes the signal processing parameters from conventional amplitude-based detection to coherent despreading operations. By correlating the received spread spectrum signal with a local replica of the spreading code, the system extracts bearing information from second-generation COSPAS SARSAT signals while maintaining compatibility with existing hardware through software-based processing.
Solution Approach 2:
The patent replaces the mechanical/amplitude-based direction finding approach with a signal processing-based coherent despreading system. Instead of relying on physical antenna orientation and amplitude variations, the system uses digital correlation techniques to determine bearing, enabling processing of spread spectrum signals without hardware modification.
2Reliability
If satellite-determined locations are used, then hardware changes are not required, but the location estimates may not always be reliable
Solution Approach 1:
The patent introduces coherent despreading operations as an intermediary processing step between signal reception and bearing determination. By correlating the received spread spectrum signal with a local code replica, the system reliably extracts bearing information even when satellite location data is unavailable or unreliable, maintaining system functionality without requiring additional hardware.
3Measurement precision
If coherent despreading operations are performed to extract bearings from spread spectrum signals, then bearing determination becomes reliable for second-generation beacons, but the processing complexity increases
Solution Approach 1:
The patent replaces complex hardware-based signal processing with software-based coherent despreading operations. By performing correlation processing in the digital domain using a local replica of the spreading code, the system achieves accurate bearing measurements from second-generation COSPAS SARSAT signals while avoiding the need for complex hardware modifications.
Solution Approach 2:
The patent creates a universal signal processing approach that can handle both conventional and spread spectrum signals through coherent despreading. The same hardware infrastructure supports multiple signal types by applying appropriate processing algorithms, achieving multi-functionality without dedicated hardware for each signal type.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable bearing determination to radio beacons using second-generation COSPAS SARSAT signals, compatible with existing hardware through software upgrades, without requiring hardware changes.
Implementation Method 1
receive, at the arrangement of radio antennas, a direct-sequence spread-spectrum (DSSS) radio signal, transmitted by a radio beacon
Implementation Method 2
perform a coherent despreading operation by coherently intercorrelating the digital signal from the directional antenna system with at least a portion of the digital signal from the non-directional antenna system to determine a correlation value
Data Source
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AI summary
An apparatus (1) for determining a bearing to a radio beacon (2) comprises an arrangement of radio antennas (3) comprising a non-directional antenna system (Σ) and one or more directional antenna systems. The non-directional antenna system (Σ) has a receiving pattern that is omni-directional in a first plane. Each directional antenna system has a respective receiving pattern that is directional in a respective direction in the first plane. The apparatus (1) receives, at the arrangement of radio antennas (3), a direct-sequence spread-spectrum radio signal, transmitted by a radio beacon (2). It generates, for each antenna system, a respective digital signal from an electrical signal output by the antenna system in response to the received radio signal. For each of the one or more directional antenna systems, it performs a coherent despreading operation by intercorrelating the digital signal from the directional antenna system with at least a portion of the digital signal from the non-directional antenna system to determine a correlation value for the directional antenna system. It processes the one or more determined correlation values to determine a bearing to the radio beacon (2) relative to the arrangement of radio antennas (3).