ADS-B Receiver Antenna Array Multipath Mitigation
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Solution Overview
Problem
ADS-B message reception is often unreliable on the airport surface due to multipath reflections from nearby structures, leading to missed receptions, especially when aircraft are stationary or moving slowly, as these reflections can cause deep fades and interfere with the direct signal.
Innovation Solution
A system combining RF signal processing and digital signal processing techniques using an array of horizontally spaced antennas to form beams with different azimuth patterns, along with a digital signal processing algorithm to estimate and remove multipath interference, effectively mitigating both short and long delay multipath effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If aircraft are stationary or moving slowly on the airport surface, then more ADS-B squitters can be received, but multipath reflections cause deep fades and hide true squitters
Solution Approach 1:
The patent divides the signal reception task into multiple independent antenna elements (at least two antennas) that separately receive signals. Each antenna captures a version of the ADS-B squitter signal with different multipath characteristics, allowing the system to process and combine these segmented signals to eliminate deep fades caused by multipath reflections.
Solution Approach 2:
The patent changes the temporal parameter of signal processing by introducing time diversity through multiple antennas with different propagation paths. By processing signals at different time instances and combining them, the system transforms the static deep fade problem into a dynamic signal combination process that eliminates multipath interference.
2Area of stationary object
If multipath reflections are present from nearby structures, then signal coverage is extended to stationary aircraft, but destructive interference causes missed receptions
Solution Approach 1:
The patent converts the harmful multipath reflections into a beneficial resource by using multiple antennas to capture different versions of the reflected signals. Instead of treating multipath as purely destructive interference, the system exploits the temporal and spatial diversity of multiple reflection paths to reconstruct the original signal and eliminate deep fades.
Solution Approach 2:
The patent introduces signal processing algorithms as an intermediary between the received signals and the final decoded message. This intermediary process includes operations such as signal combination, interference cancellation, and error correction that mediate the harmful effects of multipath reflections and recover the lost information.
3Device complexity
If traditional single-antenna receivers are used, then device complexity is low, but reception reliability deteriorates in multipath environments
Solution Approach 1:
The patent segments the reception function across multiple antennas, where each antenna handles a portion of the signal acquisition task. This segmentation increases reliability by providing redundant signal paths while keeping each individual antenna element simple in structure.
Solution Approach 2:
The patent merges the output signals from multiple antennas through combination processing to achieve improved reception reliability. By combining signals in the digital domain with appropriate weighting and phase alignment, the system achieves diversity gain that compensates for the increased hardware complexity.
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
This approach significantly improves the reliability of ADS-B message reception by reducing destructive multipath interference, allowing for accurate decoding of ADS-B messages even in environments with severe multipath propagation.
Implementation Method 1
The RF signals from these antennas are combined by the receiver so as to form a set of beams with different azimuth antenna patterns
Implementation Method 2
An exemplary system combines RF signal processing and digital signal processing techniques using an array of horizontally spaced antennas
Data Source
AI summary
Systems and methods for receiving ADS-B messages in environments where multipath propagation corrupts the messages or blocks the reception of the messages. An exemplary system combines RF signal processing and digital signal processing techniques to make it possible to receive ADS-B messages in the presence of multipath reflections from nearby structures and/or farther out structures. The system uses an array of horizontally spaced antennas. The RF signals from the antennas are combined by the receiver so as to form a set of beams with different azimuth antenna patterns to increase the probability that the multipath does not combine destructively with the line-of-sight path in at least one of the beams. This effectively removes multipath reflections where the delay of the multipath relative to the line-of-sight path is less than 100-200 nanoseconds. The system is also configured to remove multipath reflections with greater delays relative to the line-of-sight path.