Wireless communication system

Abstract

This aircraft radio communication system provides a system that, when interference is detected by the control tower equipment, can immediately be confirmed by the aircraft's equipment, promptly notify a higher-level terminal, and prevent aircraft from approaching each other. [Solution] This is an aircraft radio communication system in which, when the control tower-side device 1 detects interference in radio signals received from multiple aircraft, it generates a tone signal at a frequency outside the voice band range in the signal transmitted to the aircraft, synthesizes the tone signal with the voice signal within the voice band range, and transmits it to the aircraft-side device 2. The aircraft-side device 2 extracts the tone signal from the signal received from the control tower-side device 1, and if the level of the tone signal is above a threshold, it notifies the higher-level terminal 6 installed on the aircraft of the interference.

Description

Technical Field

[0001] The present invention relates to a wireless communication system for an aircraft, and particularly to a wireless communication system for an aircraft that can confirm interference on the aircraft side.

Background Art

[0002] [Conventional Technology] Some conventional aircraft wireless communication systems perform wireless communication between a ground control tower device provided in a control tower and an aircraft-side device mounted on an aircraft. In such a wireless communication system, when a plurality of aircraft-side devices transmit radio waves at the same frequency simultaneously, interference occurs in the received signal of the ground control tower device. When interference occurs, communication fails and aircraft approach each other, which may lead to a major accident.

[0003] In addition, some aircraft wireless communication systems use software radios. <00000,16>A software radio is a radio that can support a plurality of wireless communication methods with the same hardware resources in the radio by switching the execution program of the radio with a software program.

[0004] [Conventional Aircraft Wireless Communication System: FIG. 7] The conventional aircraft wireless communication system will be described with reference to FIG. 7. FIG. 7 is a schematic configuration diagram of the conventional aircraft wireless communication system. As shown in FIG. 7, the conventional aircraft wireless communication system includes a ground control tower device 3, a host device 4, an aircraft-side device 5, and a host terminal 6.

[0005] The ground control tower device 3 is a software radio and includes a high-frequency section 31 and a modulation / demodulation section 32. The modulation / demodulation unit 32 performs modulation / demodulation processing using digital signal processing and includes an interference detection unit 33, a demodulation circuit 34, a modulation circuit 35, and a CPU (Central Processing Unit) 36, all of which are implemented using an FPGA (Field Programmable Gate Array).

[0006] The high-frequency unit 31 performs frequency conversion and amplification associated with the transmission and reception of wireless signals, upconverts the signal for transmission and sends the wireless signal from the antenna, downconverts the wireless signal received by the antenna and branches it, and outputs it to the interference detection unit 33 and the demodulation circuit 34.

[0007] The demodulation circuit 34 demodulates the signal received from the high-frequency section 31 according to the modulation scheme of the transmitting side. The modulation circuit 35 modulates the signal to be transmitted from the host device 4 using a predetermined modulation scheme and outputs it to the high-frequency unit 31.

[0008] The interference detection unit 33 detects whether or not there is interference in the received signal. Specifically, the interference detection unit 33 performs an FFT (Fast Fourier Transform) on the received signal to convert it into a relationship between frequency and level, and then detects the peak of the received signal by comparing it with a threshold value. The interference detection unit 32 determines that there is no interference if there is one peak in the power level, and determines that there is interference if there are multiple peaks, and outputs the determination result as an interference detection signal to the CPU 35.

[0009] The CPU 35 communicates with the host device 4 and outputs the interference detection result to the host device 4. The higher-level device 4 is a control console operated by users such as air traffic controllers in the control tower, and displays the interference detection result on the interference detection display unit 41. The higher-level device 4 also handles audio input and output.

[0010] Furthermore, the aircraft-side device 4 is a software-defined radio and includes a high-frequency unit 51 and a modulation / demodulation unit 52. The high-frequency unit 51 upconverts the transmission signal to transmit the wireless signal from the antenna, and downconverts the wireless signal received by the antenna to output it to the modulation / demodulation unit 52. The modulation / demodulation unit 52 includes, as functions implemented by the FPGA, an A / D conversion unit 53, a band-limiting filter 54, a demodulation circuit 55, and a modulation circuit 56.

[0011] The A / D conversion unit 53 converts the analog signal input from the high-frequency unit 51 into a digital signal. The band-limiting filter 54 is a band-pass filter that allows only audio signals in the audio band to pass through. The demodulation circuit 55 demodulates the bandwidth-limited signal and outputs the audio signal to the higher-level terminal 6. The modulation circuit 56 modulates the audio signal input from the upper terminal 6 in a predetermined manner and outputs it to the high-frequency unit 51.

[0012] The upper-level terminal 6 is a terminal operated by the aircraft pilot and is equipped with a microphone 61 for voice input and a speaker 62 for voice output. Thus, the aircraft-side equipment 4 and the higher-level terminal 6 of the conventional wireless communication system do not have a configuration for detecting interference or indicating that interference is occurring.

[0013] [Conventional interference detection] In conventional aircraft radio communication systems, the control tower-side device 3 detects the presence or absence of interference. When air traffic controllers or others recognize interference based on the display on the interference detection display unit 41, the operator of the higher-level device 6 transmits instructions, such as avoiding landing, via voice to the aircraft-side device 5 to prevent danger. In other words, the aircraft-side device 4 could not immediately confirm whether interference had been detected by the control tower-side device 3, and there was a delay between the detection of interference by the control tower-side device 3 and the notification of the danger to the higher-level terminal 6.

[0014] Furthermore, in a conventional wireless communication system, since the aircraft-side device 4 is notified of the detection of interference and danger avoidance by an operation of an air traffic controller or the like, there is a possibility of human error such that the air traffic controller or the like is delayed in noticing the display of interference detection or does not notice it at all, and such possibility could not be eliminated.

[0015] [Related Art] Incidentally, as a related prior art, there is Japanese Patent No. 6886075 "Air Traffic Control Station Device and Alarm Transmission Method of Air Traffic Control Station Device" (Patent Document 1). In Patent Document 1, an air traffic control station device is shown that improves the reliability of interference detection by determining the presence or absence of simultaneous reception of multiple waves (interference) in real time for a received signal and transmitting an alarm, and transmitting another alarm when the simultaneous transmission of multiple waves ends.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0017] As described above, in a conventional wireless communication system for an aircraft, even if the air traffic control tower-side device detects an interference state, it cannot immediately confirm it with the aircraft-side device, and it takes time until it is notified to the upper terminal on the aircraft side, and there is a problem that there is a risk that aircraft will approach each other.

[0018] Incidentally, Patent Document 1 does not describe a configuration in which when an interference state is detected by the air traffic control tower-side device, an interference detection signal outside the voice band is generated, synthesized with the voice signal, transmitted to the aircraft-side device, and the presence or absence of interference is determined based on the level of the interference detection signal at the aircraft-side device.

[0019] The present invention has been made in view of the above circumstances, and when the control tower side device detects a congestion state, the aircraft side device can immediately confirm the congestion and quickly notify the upper terminal without any artificial operation, so as to avoid the approach of aircraft to each other. The purpose is to provide a wireless communication system for aircraft.

Means for Solving the Problems

[0020] The present invention for solving the problems of the above conventional examples is a wireless communication system for aircraft that performs wireless communication between a control tower side device provided in a control tower and an aircraft side device mounted on an aircraft. When the control tower side device detects the congestion of wireless signals received from a plurality of aircraft, in the transmission signal to the aircraft, a congestion detection signal is generated at a frequency outside the voice band range, synthesized with the voice signal within the voice band range, and transmitted to the aircraft side device. The aircraft side device is characterized by detecting the congestion detection signal from the signal received from the control tower side device and notifying the congestion.

[0021] Further, the present invention is characterized in that, in the above wireless communication system, the aircraft side device branches the signal received from the control tower side device, removes the congestion detection signal from one of the branched signals to obtain a voice signal, and removes the voice signal from the other branched signal to obtain a congestion detection signal.

[0022] Further, the present invention is characterized in that, in the above wireless communication system, the aircraft side device includes a first band-limiting filter that removes the congestion detection signal from one signal to obtain a voice signal, a frequency shift unit that shifts the frequency of the other signal, a second band-limiting filter that removes the voice signal from the frequency-shifted other signal to obtain a congestion detection signal, and a determination unit that compares the level of the obtained congestion detection signal with a threshold value to determine the congestion.

[0023] Further, the present invention is characterized in that, in the above wireless communication system, the aircraft side device varies the threshold value according to the distance between the mounted aircraft and the control tower.

[0024] Furthermore, the present invention is characterized in that, in the above-mentioned wireless communication system, the aircraft-side device notifies of interference by display or sound. [Effects of the Invention]

[0025] According to the present invention, an aircraft wireless communication system is provided that performs wireless communication between a control tower-side device installed in an air traffic control tower and an aircraft-side device mounted on an aircraft. When the control tower-side device detects interference in wireless signals received from multiple aircraft, it generates an interference detection signal at a frequency outside the voice band range in the signal transmitted to the aircraft, synthesizes it with a voice signal within the voice band range, and transmits it to the aircraft-side device. The aircraft-side device detects the interference detection signal from the signal received from the control tower-side device and notifies the system of the interference. As such, when the control tower-side device detects interference, it immediately notifies the aircraft-side device without any manual operation, allowing the aircraft-side device to confirm the interference and quickly notify a higher-level terminal, thus enabling aircraft to avoid approaching each other.

[0026] Furthermore, according to the present invention, the aircraft-side device is a wireless communication system that varies the threshold value according to the distance between the aircraft and the control tower. Therefore, even when the distance to the control tower is large, it is possible to reliably detect the interference detection signal and notify of the interference, which has the effect of prompting attention. [Brief explanation of the drawing]

[0027] [Figure 1] This is a schematic diagram of the system's configuration. [Figure 2] This is an explanatory diagram showing the received signals from the aircraft's equipment. [Figure 3] This is an explanatory diagram showing the signal after passing through a bandwidth-limiting filter. [Figure 4] This is an explanatory diagram showing the operation of the frequency shift section. [Figure 5] This is an explanatory diagram showing the signal after passing through the filter. [Figure 6] This is an explanatory diagram illustrating the general overview of interference detection. [Figure 7]This is a schematic diagram of a conventional aircraft radio communication system. [Modes for carrying out the invention]

[0028] Embodiments of the present invention will be described with reference to the drawings. [Summary of the Embodiment] In the aircraft radio communication system according to an embodiment of the present invention (this system), when the control tower-side equipment detects interference in radio signals received from multiple aircraft, it generates an interference detection signal at a frequency outside the voice band in the signal transmitted to the aircraft, synthesizes the interference detection signal with the voice signal within the voice band, and transmits it to the aircraft-side equipment. The aircraft-side equipment then detects the interference detection signal from the signal received from the control tower-side equipment and notifies the higher-level terminal of the interference. As soon as the control tower-side equipment detects interference, it immediately notifies the aircraft-side equipment of the interference state, which is then reported to the higher-level terminal on the aircraft side. This allows the aircraft pilot to quickly recognize that interference is occurring and take evasive action, thereby preventing dangerous situations such as aircraft approaching each other and improving safety.

[0029] [This system: Figure 1] This system will be explained with reference to Figure 1. Figure 1 is a schematic diagram of the system's configuration. As shown in Figure 1, this device has a control tower-side configuration consisting of a control tower-side device 1 and a higher-level device 4 on the control tower side, and an aircraft-side configuration consisting of an aircraft-side device 2 and a higher-level terminal 6 on the aircraft side, and communicates wirelessly between the control tower-side device 1 and the aircraft-side device 2. Furthermore, since the upper-level device 4 among the above components is the same as before, its explanation will be omitted. Furthermore, the aircraft-side device described in the claim corresponds to a configuration that combines the aircraft-side device 2 and the higher-level terminal 6.

[0030] [Parts of this system: Figure 1] This section will provide a detailed explanation of each part of this system. [Control tower side equipment 1] The control tower-side device 1 is a software-defined radio and has a high-frequency section 11 and a modulation / demodulation section 12. The modulation / demodulation section 12 has the same configuration as conventional systems and includes an interference detection section 13, a demodulation circuit 14, a modulation circuit 15, and a CPU 16. A distinctive feature of this wireless communication system is the inclusion of an out-of-band tone generation section 17 and a combining section 18. The interference detection unit 13, demodulation circuit 14, modulation circuit 15, CPU 16, out-of-band tone generation unit 17, and synthesis unit 18 are all implemented by the FPGA of the modulation / demodulation unit 12.

[0031] Furthermore, the interference detection signal from the interference detection unit 13 is split into two and input not only to the CPU 16 but also to the out-of-band tone generation unit 17. We will omit explanations for parts that are the same as before.

[0032] The out-of-band tone generation unit 17 generates a tone signal (hereinafter referred to as the tone signal) at a frequency outside the audio band when interference is detected. The tone signal corresponds to the interference detection signal described in the claim. Specifically, the out-of-band tone generation unit 17 generates a tone signal at a frequency outside the audio band and outputs it to the synthesis unit 18 when the interference detection signal from the interference detection unit 13 indicates that there is interference.

[0033] The combining unit 18 combines the audio signal from the higher-level device 4, which has been modulated by the modulation circuit 15, with the tone signal from the out-of-band tone generation unit 17, and outputs it to the high-frequency unit 11. As a result, if interference is detected in the control tower-side equipment 1, the voice signal and the tone signal outside the voice band are combined and transmitted wirelessly to the aircraft-side equipment 2.

[0034] [Operation of control tower-side device 1: Figure 1] Let me briefly explain the operation of control tower-side device 1. In the control tower-side device 1, the interference detection unit 13 detects the presence or absence of interference, and an interference detection signal indicating the detection result is input to the CPU 16 and the out-of-band tone generation unit 17. The CPU 16 then notifies the higher-level device 4 of the interference detection result (interference present / absent), as in the conventional system.

[0035] Furthermore, if the interference detection signal indicates interference, the out-of-band tone generation unit 17 generates an out-of-band tone signal and outputs it to the synthesis unit 18. The synthesis unit 18 then combines the audio signal from the host device 4 with the generated tone signal, and the high-frequency unit 11 converts it to a radio frequency and transmits it wirelessly to the aircraft-side device 2.

[0036] Thus, when the control tower-side device 1 of this wireless communication system detects interference, it can quickly notify the aircraft-side device 2 that interference is occurring without the need for an operator to intervene. Furthermore, this eliminates the need for notification from the higher-level device 4 to the aircraft-side device 2, thus eliminating human error. Furthermore, in addition to transmitting a tone signal when interference is detected, the operator may also provide an audible notification from the higher-level device 4, as in the conventional system, thereby ensuring that aircraft pilots and others can reliably avoid danger.

[0037] [Aircraft side device 2] The aircraft-side device 2 is a software-defined radio and has a high-frequency section 21 and a modulation / demodulation section 22. The modulation / demodulation section 22 has the same configuration as conventional systems and includes an A / D conversion section 23, a band-limiting filter 24, a demodulation circuit 25, and a modulation circuit 26. A distinctive feature of this wireless communication system is the inclusion of a frequency shift section 27, a filter 28, a level calculation section 29, and a threshold comparison section 30.

[0038] The A / D conversion unit 23, the band-limiting filter 24, the demodulation circuit 25, the modulation circuit 26, the frequency shift unit 27, the filter 28, the level calculation unit 29, and the threshold comparison unit 30 are all implemented by the FPGA of the modulation / demodulation unit 22.

[0039] Furthermore, the output from the A / D conversion unit 23 is split into two and input to the band-limiting filter 24 and the frequency shift unit 27. Furthermore, the same band-limiting filter 24 and demodulation circuit 25 as in the conventional design will be collectively referred to as the demodulation section, and their operation will be described later.

[0040] The frequency shifting unit 27, for example, consists of a numerically controlled oscillator and a mixer, and shifts the frequency of the entire input signal so that the tone signal generated as a signal outside the audio band is within the frequency range of the audio band. Specifically, the frequency is converted so that the center frequency of the tone signal (interference frequency) becomes the center frequency of the audio band. As a result, tone signals that were outside the audio band become tone signals within the audio band, and synthesized audio signals become signals outside the audio band.

[0041] Filter 28 is similar to the band-limiting filter 24 and allows signals within the audio band to pass through. In other words, filter 28 allows frequency-shifted tone signals to pass through but does not allow frequency-shifted audio signals to pass through. The level calculation unit 29 calculates the level of the tone signal that has passed through the filter 28.

[0042] The threshold comparison unit 30 compares the level of the tone signal calculated by the level calculation unit 29 with a threshold value to determine whether interference is present and outputs the result to the upper terminal 6. In this case, if the detected signal level is greater than the threshold (i.e., an interference detection signal is detected), it is determined that there is interference; if it is below the threshold (i.e., no interference is detected), it is determined that there is no interference. The threshold comparison unit 30 corresponds to the determination unit described in the claim. The configuration comprising the frequency shift unit 27, filter 28, level calculation unit 29, and threshold comparison unit 30 is referred to as the interference detection circuit, and its operation will be described later.

[0043] The upper-level terminal 6 is equipped with a microphone 61, a speaker 62, and an interference detection unit 63. The interference detection unit 63 is equipped with, for example, an LED lamp, and if the determination result from the threshold comparison unit 30 indicates interference (interference detection), the LED lamp is turned on (or blinks) to notify the aircraft pilot that interference is occurring. Alternatively, the interference detection unit 63 may output an alarm sound from the speaker 63 when interference is detected.

[0044] [Signal processing in aircraft-side equipment: Figures 2-5] Next, we will explain the signal processing of the aircraft-side device 2 of this wireless communication system in the event of interference, using Figures 2 to 5, while illustrating the operation of each part. The numbers shown in the upper left of Figures 2 to 6 correspond to the numbers circled in Figure 1, schematically indicating the signal state at the numbered location.

[0045] [Signal processing in the demodulation section: Figures 2 and 3] First, the signal processing of the demodulation section, which is the same as in the conventional system, will be explained using Figures 2 and 3. Figure 2 is an explanatory diagram showing the received signal from the aircraft-side equipment, and Figure 3 is an explanatory diagram showing the signal after passing through the band-limiting filter. As described above, when interference is detected in the control tower-side device 1, an out-of-band tone generation unit 17 generates an out-of-band tone signal (interference detection signal), which is then combined with the voice signal and transmitted.

[0046] As shown in Figure 2, the signal output from the A / D converter 23 of the aircraft-side device 2 is a signal in which an audio signal within the audio band (audio signal from the higher-level device 4) and a tone signal outside the audio band (interference detection signal) are superimposed. The center frequency of the tone signal is shown as the interference frequency. Furthermore, if we represent the center frequency of the audio bandwidth as 0, the range of frequencies from -f to +f becomes the audio bandwidth.

[0047] Here, the frequency of the tone signal is set to a frequency even higher than the high-frequency side +f of the audio band. In order to reliably separate the audio signal and the tone signal in the processing described later, it is desirable that the frequency of the tone signal (interference frequency) be at least 2f away from the center frequency of the audio band. Furthermore, although the tone signal was generated on the high-frequency side here, it may also be generated at a frequency of -2f or less, so as to be at least 2f away from the low-frequency side.

[0048] Then, as shown in Figure 3, when the signal in Figure 2 passes through the band-limiting filter 24, only the audio band signal passes through, and the tone signal outside the audio band is removed. The signal is then demodulated by the demodulation circuit 25, and the audio is output from the speaker 62 of the upper-level terminal 6. The trapezoidal shape in Figure 3 indicates the range of signals that can pass through the band-limiting filter 24. This allows audio from the host device 4 to be output to the speaker 62 without interference, even when a tone signal indicating interference detection is superimposed.

[0049] [Signal processing of interference detection circuit: Figures 4-6] Next, the signal processing in the interference detection unit will be explained using Figures 4 to 6. Figure 4 is an explanatory diagram showing the operation of the frequency shift unit, Figure 5 is an explanatory diagram showing the signal after passing through the filter, and Figure 6 is an explanatory diagram showing an overview of interference determination. As mentioned above, the interference detection unit consists of a frequency shift unit 27, a filter 28, a level calculation unit 29, and a threshold comparison unit 30.

[0050] As shown in Figure 4, the signal input from the A / D conversion unit 23 is shifted to a lower frequency side in the frequency shifting unit 27, and the tone signal is converted to a frequency within the audio band. In this case, the frequency of the tone signal (interference frequency) is set to the higher frequency side of the audio band, so the frequency shift unit 27 shifts the frequency of the input signal to the lower frequency side. However, if the interference frequency is set to a lower frequency side than the audio band, the entire input signal, including the lower frequency tone signal, is shifted to the higher frequency side.

[0051] Next, the frequency-shifted signal is bandwidth-limited by filter 28, and as shown in Figure 5, filter 28 outputs a signal containing only tone signals that are within the audio band, while audio signals that are outside the audio band are removed.

[0052] Then, the signal after passing through the filter 28 has its signal level calculated in the level calculation unit 29, and as shown in Figure 6, the signal level is compared with a predetermined threshold in the threshold comparison unit 30 to determine whether or not interference is present. As described above, interference is detected if the tone signal level is greater than the threshold, and if it is below the threshold, interference is detected. The result is then output to the interference detection unit 63 of the higher-level terminal 6.

[0053] As a result, when interference is detected by the control tower-side device 1, the aircraft-side device 2 can immediately confirm the interference without waiting for instructions from the air traffic controller, and quickly notify the higher-level terminal 6 of the interference, thereby avoiding dangers such as aircraft approaching each other.

[0054] [When varying the threshold] Furthermore, in the example described above, the threshold value for interference detection in the threshold comparison unit 30 was set to a specific value, but the threshold value may be varied for the determination. In this case, the threshold comparison unit 30 stores multiple threshold values ​​and determines whether or not interference is present using an appropriate threshold value according to the distance to the control tower-side device 1 calculated from GPS information.

[0055] If the control tower-side device 1 and the aircraft-side device 2 are close together, the signal level received by the aircraft-side device 2 will be high; if they are far apart, the signal level will be low. Therefore, when the distance to the control tower-side device 1 is long, the threshold value is set to a small value, and as the approach to the control tower-side device 1 increases, the threshold value is gradually increased. The threshold comparison unit 3 stores in advance the correspondence between distance and appropriate threshold values. This allows for a more accurate determination of interference based on the distance between the aircraft and the control tower. In particular, even when the aircraft is far from the control tower, interference can be reliably detected and reported to the higher-level terminal 6, allowing for an earlier warning.

[0056] [Effects of the embodiment] According to this system, when the control tower-side device 1 detects interference in radio signals received from multiple aircraft, it generates a tone signal at a frequency outside the voice band in the signal transmitted to the aircraft, synthesizes the tone signal with the voice signal within the voice band, and transmits it to the aircraft-side device 2. The aircraft-side device 2 extracts the tone signal from the signal received from the control tower-side device 1, and if the tone signal level is above a threshold, it notifies the higher-level terminal 6 installed on the aircraft of the interference. Therefore, when the control tower-side device 1 detects interference, it immediately notifies the aircraft-side device 2 with a tone signal without any operation by air traffic controllers, and notifies the higher-level terminal 6 on the aircraft. This allows the aircraft pilot to quickly recognize that interference is occurring and take evasive action, preventing dangerous situations such as aircraft approaching each other and improving safety. [Industrial applicability]

[0057] The present invention is suitable for an aircraft radio communication system that, when interference is detected by the control tower equipment, can immediately be confirmed by the aircraft equipment, and promptly notify a higher-level terminal to avoid aircraft approaching each other. [Explanation of Symbols]

[0058] 1,3…Control tower equipment, 2,5…Aircraft equipment, 4…Higher-level equipment, 6…Higher-level terminal, 11,21,31,51…High-frequency section, 12,22,32,52…Modulation / demodulation section, 13,33…Interference detection section, 14,34…Demodulation circuit, 15,35…Modulation circuit, 16,36…CPU, 17…Out-of-band tone signal generation section, 18…Combination section, 23,53…A / D conversion section, 24,54…Band limiting filter, 25,55…Demodulation circuit, 26,56…Modulation circuit, 27…Frequency shift section, 28…Filter, 29…Level calculation section, 30…Threshold comparison section, 41,63…Interference confirmation section, 61…Microphone, 62…Speaker

Claims

1. An aircraft radio communication system that communicates wirelessly between control tower equipment installed in the control tower and aircraft equipment mounted on the aircraft, When the control tower-side equipment detects interference in radio signals received from multiple aircraft, it generates an interference detection signal at a frequency outside the voice band in the transmission signal to the aircraft, synthesizes it with the voice signal within the voice band, and transmits it to the aircraft-side equipment. The aforementioned aircraft-side device is a wireless communication system characterized by detecting the interference detection signal from the signal received from the control tower-side device and reporting the interference.

2. The wireless communication system according to claim 1, characterized in that the aircraft-side device branches the signal received from the control tower-side device, removes the interference detection signal from one of the branched signals to obtain the voice signal, and removes the voice signal from the other branched signal to obtain the interference detection signal.

3. The wireless communication system according to claim 2, characterized in that the aircraft-side device includes a first band-limiting filter that removes the interference detection signal from one of the signals to obtain the voice signal, a frequency shifting unit that shifts the frequency of the other signal, a second band-limiting filter that removes the voice signal from the other signal whose frequency has been shifted to obtain the interference detection signal, and a determination unit that compares the level of the obtained interference detection signal with a threshold value to determine interference.

4. The wireless communication system according to claim 3, characterized in that the aircraft-side device varies a threshold value according to the distance between the aircraft on which it is installed and the control tower.

5. The wireless communication system according to any one of claims 1 to 4, characterized in that the aircraft-side device notifies of interference by display or sound.

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