During high-speed flight, the signal reception stability of an Airborne AIS receiver is affected by a complex interplay of factors, including the device's own technical characteristics, as well as external environmental factors and operational procedures. From a design perspective, receiver sensitivity is a core indicator determining signal acquisition capability. At high speeds, the relative speed between the Airborne AIS receiver and the ship significantly increases, exacerbating the Doppler frequency shift effect. If the Airborne AIS receiver does not optimize its frequency shift compensation algorithm for high-speed scenarios, it may lose signal due to frequency shift exceeding the demodulation range. For example, when an aircraft flies at high speed over a target sea area, the frequency of the AIS signal will shift significantly due to relative motion. If the Airborne AIS receiver cannot dynamically adjust its demodulation parameters, even with sufficient signal strength, it may fail to correctly resolve data due to frequency mismatch.
Antenna performance is equally crucial to signal reception stability. Airflow impacts from high-speed flight can cause antenna vibration or deformation, altering its radiation pattern. If antenna gain attenuates in a specific direction, it may cause previously receivable weak signals to fall below the sensitivity threshold. Furthermore, antenna polarization and signal matching also affect reception performance. AIS signals typically employ vertical polarization. If the airborne antenna experiences polarization mismatch due to installation angle deviations or changes in flight attitude, additional polarization loss will be introduced, weakening the signal strength. For example, during steep climbs or dives, the angle between the antenna and the signal polarization direction may increase significantly, leading to decreased reception efficiency.
Electromagnetic interference in the flight environment is another critical factor. During high-speed flight, the airborne AIS receiver may enter electromagnetically complex areas, such as the coverage areas of high-voltage power lines, radar stations, or communication base stations. The electromagnetic noise generated by these interference sources can overwhelm the AIS signal, especially when the interference frequency overlaps with the AIS band, directly blocking the signal channel. Furthermore, the aircraft's own electronic equipment, such as navigation systems, communication radios, or radar, may also generate harmonic interference, further deteriorating the reception environment. For example, if sidelobe signals emitted by the airborne radar fall into the AIS band, it may cause front-end saturation of the airborne AIS receiver, resulting in a brief signal interruption.
Dynamic changes in the signal propagation path also affect reception stability. During high-speed flight, the relative position between the Airborne AIIS receiver and the ship changes rapidly, and the signal may attenuate due to the Earth's curvature, obstacle obstruction, or atmospheric refraction. For example, when the aircraft flies at low altitudes, the signal may experience multipath interference due to ground reflection, leading to phase fluctuations in the received signal and increasing demodulation difficulty. At high altitudes, the signal propagation distance is extended, and the signal strength may decrease due to atmospheric absorption or rain attenuation. Furthermore, when the aircraft traverses different weather regions, changes in humidity and temperature may alter the signal propagation characteristics, further affecting reception.
The installation and integration method of the equipment is equally important. The Airborne AIIS receiver needs to be deeply integrated with the aircraft platform. An inappropriate installation location, such as near the engine, power system, or high-frequency equipment, may affect equipment performance due to vibration, temperature, or electromagnetic interference. For example, prolonged exposure to high temperatures may accelerate the aging of internal components in the Airborne AIIS receiver, reducing sensitivity; vibration may cause poor contact or mechanical failure, leading to signal interruption. In addition, power supply stability is also a critical factor. Voltage fluctuations or ripple interference in the power supply system may affect the linearity of the Airborne AIIS receiver's front-end amplifier, weakening signal processing capabilities.
Finally, operational procedures and maintenance levels have a long-term impact on reception stability. Failure to periodically calibrate the equipment can lead to frequency drift, decreased sensitivity, or demodulation parameter mismatch; improper maintenance, such as loose antenna connectors, interface oxidation, or outdated software versions, can also cause intermittent failures. For example, poor antenna connector contact can cause intermittent signal interruptions, while software defects can lead to data packet loss due to processing logic errors. Therefore, strict equipment maintenance procedures and operational standards are a crucial foundation for ensuring reception stability.
