Helicopter-mounted communication device and communication method for helicopter-mounted communication device

Abstract

To provide a helicopter-mounted communication device and a communication method for the helicopter-mounted communication device, which can shorten the time required to establish a synchronized state with a signal output from an antenna device when switching the antenna device selected from a plurality of antenna devices.SOLUTION: A modulator-demodulator 24 demodulates a first received signal output from a first antenna device 21A and calculates the quality of the first received signal. A demodulator 25 demodulates a second received signal output from a second antenna device 21B and calculates the quality of the second received signal. When the modulator-demodulator 24 is not synchronized with the first received signal, the modulator-demodulator 24 sets the number of forward guard stages of the modulator-demodulator 24 on the basis of the quality of the second received signal. When the demodulator 25 is not synchronized with the second received signal, the demodulator 25 sets the number of forward guard stages of the demodulator 25 on the basis of the quality of the first received signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a helicopter-mounted communication device and a communication method in a helicopter-mounted communication device. [Background technology]

[0002] There is known a helicopter-mounted communication device that is mounted on a helicopter and receives signals transmitted from a ground station via a communication satellite. Communication interruptions can occur when the helicopter's rotor blades or other components cross the propagation path between the communication satellite and the antenna of the helicopter-mounted communication device. To solve this problem, for example, a device described in Patent Document 1 is equipped with multiple antennas and switches between the multiple antennas to receive time diversity signals transmitted from the ground station via the communication satellite. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-24038 Summary of the Invention [Problem to be solved by the invention]

[0004] In the device described in Patent Document 1, for example, if a helicopter turns and blocks the propagation path between the communication satellite and the antenna of the helicopter-mounted communication device, and communication is interrupted, when switching the antenna to be selected from multiple antennas, it takes time to establish a synchronized state with the signal output from the antenna, which can result in the continuity of communication being lost.

[0005] Therefore, an object of the present disclosure is to provide a helicopter-mounted communication device and a communication method for a helicopter-mounted communication device that can shorten the time required to establish a synchronized state with a signal output from an antenna device when switching the antenna device selected from among a plurality of antenna devices. [Means for solving the problem]

[0006] A helicopter-mounted communication device according to the present disclosure includes a first antenna unit installed on the helicopter for receiving a signal, a first demodulator for performing a first demodulation process on a first received signal output from the first antenna unit and calculating the quality of the first received signal, a second antenna unit installed on the helicopter for receiving a signal, and a second demodulator for performing a second demodulation process on a second received signal output from the second antenna unit and calculating the quality of the second received signal. The first demodulation process includes synchronization with the first received signal, and the second demodulation process includes synchronization with the second received signal. When the first demodulator is not synchronized with the first received signal, the first demodulator sets a forward guard stage number based on the quality of the second received signal. When the second demodulator is not synchronized with the second received signal, the second demodulator sets a forward guard stage number based on the quality of the first received signal. [Effects of the Invention]

[0007] According to the present disclosure, when an antenna device is selected from a plurality of antenna devices and switched, the time required to establish a synchronized state with a signal output from the antenna device can be shortened. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a helicopter satellite communication system according to a first embodiment. [Figure 2] FIG. 2 is an external view showing an example of the mounting state of an antenna portion of a communication device mounted on a helicopter. [Figure 3]2 is a diagram showing the configuration of a communication device 34 mounted on a helicopter according to the first embodiment. FIG. [Figure 4] FIG. 2 shows the configuration of a modem 24. [Figure 5] FIG. 2 shows the configuration of a demodulator 25. [Figure 6] FIG. 2 is a diagram showing the frame configurations of a first received signal and a second received signal. [Figure 7] FIG. 2 is a diagram showing state transitions of a modem 24. [Figure 8] FIG. 2 is a diagram showing state transitions of the demodulator 25. [Figure 9] 5 is a flowchart showing a procedure for processing a first received signal according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing the configuration of a helicopter-mounted communication device 34A according to a second embodiment. [Figure 11] 10 is a flowchart showing a procedure for processing a first received signal according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated in principle. Embodiment 1

[0010] Fig. 1 is a diagram showing a helicopter satellite communication system according to the first embodiment. Fig. 2 is an external view showing an example of the state in which an antenna portion of a communication device mounted on a helicopter is mounted. The helicopter satellite communication system includes a ground station 32, a communication satellite 33, and a helicopter 1.

[0011] The helicopter 1 includes a rotor 35 and an on-board communication device 34. The on-board communication device 34 includes a first antenna device 21A provided on the right side of the cockpit and a second antenna device 21B provided on the left side of the cockpit.

[0012] The helicopter-mounted communication device 34 receives audio information, map information, etc. sent from the ground station 32 via the communication satellite 33, and transmits video information, audio information, map information, etc. to the ground station 32 via the communication satellite 33. Note that the helicopter-mounted communication device 34 may also transmit and receive information directly to the ground station 32 without going through the communication satellite 33.

[0013] Depending on the orientation of the communication satellite 33 and the helicopter 1, signals from the communication satellite 33 to the first antenna device 21A or the second antenna device 21B may be blocked by the rotor blades 35 of the helicopter 1 or the body of the helicopter 1. Furthermore, if the orientation of the helicopter 1 changes due to, for example, the turning of the helicopter 1, the blocking area, which is the area in which signals from the communication satellite 33 to the first antenna device 21A or the second antenna device 21B are blocked by the body of the helicopter 1, may change. The helicopter-mounted communication device 34 of the present disclosure can reduce the time required to synchronize with the signal received by the antenna when the blocking area changes due to, for example, the turning and the selected antenna is switched.

[0014] FIG. 3 is a diagram showing the configuration of the helicopter-mounted communication device 34 according to the first embodiment. The helicopter-mounted communication device 34 includes a first antenna unit 21A, a first radio circuit 2A, a modulator-demodulator 24, a second antenna unit 21B, a second radio circuit 2B, a demodulator 25, an antenna control device 22, a switching device 23, an operation panel 27, and a video encoding device 26. The first radio circuit 2A includes a power amplifier 51A and a frequency converter 52A. The second radio circuit 2B includes a power amplifier 51B and a frequency converter 52B.

[0015] The operation panel 27 sets parameters required for the processing of the modem 24 and demodulator 25 .

[0016] The first antenna device 21A receives a signal transmitted from the earth station 32 via the communication satellite 33 and outputs a first received signal to the first radio circuit 2A. The power amplifier 51A amplifies the first received signal in the RF band received by the first antenna device 21A. The frequency converter 52A converts the frequency of the amplified first received signal in the RF band to the IF band and outputs the amplified and frequency-converted first received signal to the modulator / demodulator 24.

[0017] The modem 24 executes demodulation processing of the first received signal, including synchronization processing with the first received signal. The modem 24 detects a unique word in the frame of the first received signal, thereby becoming synchronized with the first received signal (synchronized state). The modem 24 extracts data in the frame of the first received signal and outputs it to the switching device 23. In this specification, the synchronized state means a state in which the unique word in the frame can be detected multiple times consecutively.

[0018] The modulator-demodulator 24 calculates a reception level CA of the first reception signal as the quality of the first reception signal and sends it to the demodulator 25 via the antenna control device 22. The modulator-demodulator 24 sends a status signal SA indicating the status of the modulator-demodulator 24 to the switching device 23 and the demodulator 25 via the antenna control device 22. Here, the status signal SA is a signal indicating an asynchronous state, a forward protection state, a synchronous state, or a backward protection state, which will be described later.

[0019] The second antenna device 21B receives a signal transmitted from the earth station 32 via the communication satellite 33 and outputs a second received signal to the second radio circuit 2B. The power amplifier 51B amplifies the second received signal in the RF band received by the second antenna device 21B. The frequency converter 52B converts the frequency of the amplified second received signal in the RF band to the IF band and outputs the amplified and frequency-converted second received signal to the demodulator 25.

[0020] The demodulator 25 performs demodulation processing of the second received signal, including processing for synchronization with the second received signal. The demodulator 25 becomes synchronized with the second received signal (synchronized state) by detecting a unique word in the frame of the second received signal. The demodulator 25 extracts data in the frame of the second received signal and outputs it to the switching device 23.

[0021] The demodulator 25 calculates the reception level CB of the second reception signal as the quality of the second reception signal and sends it to the modulator-demodulator 24 via the antenna control device 22. The demodulator 25 sends a status signal SB indicating the status of the demodulator 25 to the switching device 23 and the modulator-demodulator 24 via the antenna control device 22.

[0022] The switching device 23 selects either the data output from the modem 24 or the data output from the demodulator 25 based on whether the modem 24 and the demodulator 25 are synchronized. The switching device 23 selects the data output from the modem 24 when the modem 24 is synchronized with the first received signal and the demodulator 25 is not synchronized with the second received signal. The switching device 23 selects the data output from the demodulator 25 when the modem 24 is not synchronized with the first received signal and the demodulator 25 is synchronized with the second received signal. The switching device 23 arbitrarily selects either the data output from the modem 24 or the data output from the demodulator 25 or selects a predetermined one when the modem 24 is synchronized with the first received signal and the demodulator 25 is synchronized with the second received signal. When the modulator-demodulator 24 is not synchronized with the first received signal and the demodulator 25 is not synchronized with the second received signal, the switching device 23 waits until at least one of the modulator-demodulator 24 and the demodulator 25 is synchronized.

[0023] When the switching device 23 selects the modulator-demodulator 24 and the first antenna device 21A, it outputs to the outside the audio information or map information contained in the data extracted from the first received signal output from the modulator-demodulator 24. When the switching device 23 selects the demodulator 25 and the second antenna device 21B, it outputs to the outside the audio information or map information contained in the data extracted from the second received signal output from the demodulator 25.

[0024] Next, the operation during transmission will be described. The video encoding device 26 encodes the video information and outputs it to the modulator / demodulator 24. The modulator / demodulator 24 modulates the encoded video information.

[0025] The switching device 23 outputs externally input audio information for transmission and map information for transmission to the modem 24. The modem 24 receives the input video information for transmission, audio information for transmission, and map information for transmission, generates a transmission signal from this information, and outputs the transmission signal to the switching device 23. When the first antenna device 21A is selected, the switching device 23 outputs the transmission signal to the frequency conversion device 52A. The frequency conversion device 52A converts the frequency of the IF band transmission signal to the RF band. The power amplification device 51A amplifies the RF band transmission signal and outputs it to the first antenna device 21A. The first antenna device 21A transmits the transmission signal to the earth station 32 via the communication satellite 33. When the second antenna device 21B is selected, the switching device 23 outputs the transmission signal to the frequency conversion device 52B. The frequency conversion device 52B converts the frequency of the transmission signal in the IF band to the RF band. The power amplification device 51B amplifies the transmission signal in the RF band and outputs it to the second antenna device 21B. The second antenna device 21B transmits the transmission signal to the earth station 32 via the communication satellite 33.

[0026] Fig. 4 is a diagram showing the configuration related to the demodulation process of the modem 24. In Fig. 4, the configuration related to the modulation process of the modem 24 is omitted.

[0027] The modulator / demodulator 24 includes a bandpass filter (BPF) 3A, an automatic gain control (AGC) amplifier 4A, a synchronous detection clock generator 5A, a 90-degree phase shifter 7A, a detector 6A, a detector 6B, a low-pass filter 8A, a low-pass filter 8B, an A / D converter 9A, an A / D converter 9B, a low-pass filter (LPF) 10A, a low-pass filter (LPF) 10B, a demodulation circuit 11A, a Viterbi decoding circuit 12A, a frame synchronization circuit 13A, a signal processing circuit 14A, an automatic gain control (AGC) circuit 15A, and a reception level calculation circuit 16A.

[0028] The bandpass filter 3A limits the band of the first received signal to remove unnecessary bands from the first received signal. The automatic gain control amplifier 4A keeps the level of the first received signal constant in accordance with the AGC control voltage sent from the automatic gain control (AGC) circuit 15A.

[0029] Synchronous detection clock generator 5A outputs clock CLK1 to detector 6A for frequency conversion to the baseband. 90-degree phase shifter 7A shifts the phase of clock CLK1 by 90 degrees and outputs clock CLK2. Detector 6A converts the first received signal output from automatic control gain amplifier 4A into an I signal of a baseband signal based on clock CLK1. Detector 6B converts the first received signal output from automatic control gain amplifier 4A into a Q signal of a baseband signal based on clock CLK2.

[0030] Low-pass filter 8A removes aliasing signals from the I signal of the baseband signal output from detector 6A. Low-pass filter 8B removes aliasing signals from the Q signal of the baseband signal output from detector 6B. A / D converter 9A converts the output signal of low-pass filter 8A into a digital signal. A / D converter 9B converts the output signal of low-pass filter 8B into a digital signal. Low-pass filter 10A passes only the low-frequency components of the output signal of A / D converter 9A in order to suppress code interference in the output signal of A / D converter 9A. Low-pass filter 10B passes only the low-frequency components of the output signal of A / D converter 9B in order to suppress code interference in the output signal of A / D converter 9B.

[0031] Demodulation circuit 11A demodulates the output signals of low-pass filter 10A and low-pass filter 10B. Viterbi decoding circuit 12A Viterbi-decodes, that is, corrects errors in, the output signal of demodulation circuit 11A.

[0032] The frame synchronization circuit 13A executes processing to establish synchronization with the first received signal of the modulator-demodulator 24 based on the detection of a unique word within the frame of the first received signal output from the Viterbi decoding circuit 12A. The frame synchronization circuit 13A changes the state of the modulator-demodulator 24 based on whether the unique word within the frame of the first received signal was detected, a status signal SB indicating the state of the demodulator 25 sent from the frame synchronization circuit 13B of the demodulator 25, and the reception level CB of the second received signal sent from the reception level calculation circuit 16B of the demodulator 25. The frame synchronization circuit 13A outputs a status signal SA indicating the state of the modulator-demodulator 24 to the switching device 23 and the frame synchronization circuit 13B of the demodulator 25 via the antenna control device 22.

[0033] The signal processing circuit 14A extracts data from the frame of the first received signal and outputs the extracted data to the switching device 23. The automatic gain control circuit 15A generates an AGC control voltage from the output signals of the low-pass filter 10A and the low-pass filter 10B and outputs it to the automatic gain control amplifier 4A.

[0034] The reception level calculation circuit 16A calculates the reception level CA of the first reception signal based on the power of the output signals of the low-pass filter 10A and the low-pass filter 10B, and outputs the reception level CA to the frame synchronization circuit 13B of the demodulator 25 via the antenna control device 22. Note that a control section may be provided in the demodulator 25, and the status signal SA and the reception level CA may be output to the control section of the demodulator 25.

[0035] FIG. 5 is a diagram showing the configuration of demodulator 25. As shown in FIG. The demodulator 25 includes a band-pass filter (BPF) 3B, an automatic gain control amplifier (AGC) 4B, a synchronous detection clock generator 5B, a 90-degree phase shifter 7B, a detector 6C, a detector 6D, a low-pass filter 8C, a low-pass filter 8D, an A / D converter 9C, an A / D converter 9D, a low-pass filter (LPF) 10C, a low-pass filter (LPF) 10D, a demodulation circuit 11B, a Viterbi decoding circuit 12B, a frame synchronization circuit 13B, a signal processing circuit 14B, an automatic gain control (AGC) circuit 15B, and a reception level calculation circuit 16B.

[0036] The bandpass filter 3B limits the band of the second received signal to remove unnecessary bands from the second received signal. The automatic gain control amplifier 4B keeps the level of the second received signal constant in accordance with the AGC control voltage sent from the automatic gain control (AGC) circuit 15B.

[0037] Synchronous detection clock generator 5B outputs clock CLK1, which is used for frequency conversion to the baseband, to detector 6C. 90-degree phase shifter 7B shifts the phase of clock CLK1 by 90 degrees and outputs clock CLK2. Detector 6C converts the second received signal output from automatic control gain amplifier 4B into an I signal of a baseband signal based on clock CLK1. Detector 6D converts the second received signal output from automatic control gain amplifier 4B into a Q signal of a baseband signal based on clock CLK2.

[0038] Low-pass filter 8C removes aliasing signals from the I signal of the baseband signal output from detector 6C. Low-pass filter 8D removes aliasing signals from the Q signal of the baseband signal output from detector 6D. A / D converter 9C converts the output signal of low-pass filter 8C into a digital signal. A / D converter 9D converts the output signal of low-pass filter 8D into a digital signal. Low-pass filter 10C passes only the low-frequency components of the output signal of A / D converter 9C in order to suppress code interference in the output signal of A / D converter 9C. Low-pass filter 10D passes only the low-frequency components of the output signal of A / D converter 9D in order to suppress code interference in the output signal of A / D converter 9D.

[0039] Demodulation circuit 11B demodulates the output signals of low-pass filter 10C and low-pass filter 10D. Viterbi decoding circuit 12B Viterbi-decodes, that is, performs error correction on the output signal of demodulation circuit 11B.

[0040] The frame synchronization circuit 13B executes a process of establishing synchronization with the second received signal of the demodulator 25 based on the detection of a unique word in the frame of the second received signal output from the Viterbi decoding circuit 12B. The frame synchronization circuit 13B changes the state of the demodulator 25 based on whether or not the unique word in the frame of the second received signal has been detected, a status signal SA indicating the state of the modulator-demodulator 24 sent from the frame synchronization circuit 13A of the modulator-demodulator 24, and a reception level CA of the first received signal sent from the reception level calculation circuit 16A of the modulator-demodulator 24. The frame synchronization circuit 13B outputs a status signal SB indicating the state of the demodulator 25 to the switching device 23 and the frame synchronization circuit 13A of the modulator-demodulator 24 via the antenna control device 22.

[0041] Signal processing circuit 14B extracts data from the frame of the second received signal and outputs the extracted data to switching device 23. Automatic gain control circuit 15B generates an AGC control voltage from the output signals of low-pass filter 10C and low-pass filter 10D and outputs it to automatic gain control amplifier 4B.

[0042] The reception level calculation circuit 16B calculates the reception level CB of the second reception signal based on the power of the output signals of the low-pass filters 10C and 10D, and outputs the reception level CB to the frame synchronization circuit 13A of the modem 24 via the antenna control device 22. Note that a control section may be provided in the modem 24, and the status signal SB and the reception level CB may be output to the control section of the modem 24.

[0043] FIG. 6 is a diagram showing the frame configurations of the first received signal and the second received signal. One multiframe is made up of N frames, where N is, for example, 8. The first frame of the multiframe includes a first unique word UW1 placed at the beginning and data. The remaining (N-1) frames of the multiframe include a second unique word UW2 placed at the beginning and data.

[0044] FIG. 7 is a diagram showing state transitions of the modem 24. As shown in FIG. When the quality of the first received signal is low, noise may cause bit errors, or information that matches or is similar to UW1 or UW2 may be mixed in the data. As a result, erroneous detection or non-detection of UW1 and UW2 may occur. Therefore, if the modulator-demodulator 24 detects UW1 and (N-1) UW2s once while in a state asynchronous with the first received signal, the modulator-demodulator 24 transitions to the forward protection state rather than to the state synchronized with the first received signal.

[0045] When the modulator-demodulator 24 detects UW1 and (N-1) UW2s consecutively (XA-1) times in the forward protection state, the modulator-demodulator 24 transitions to a state synchronized with the first received signal. When the modulator-demodulator 24 does not detect UW1 and (N-1) UW2s in the forward protection state, the modulator-demodulator 24 transitions to a state asynchronous with the first received signal. XA represents the number of forward protection stages of the modulator-demodulator 24. Note that when the modulator-demodulator 24 does not detect UW1 and (N-1) UW2s consecutively (XA-1) times in the forward protection state, the modulator-demodulator 24 may also transition to a state asynchronous with the first received signal.

[0046] If the modem 24 does not detect UW1 and (N-1) UW2s when in the synchronized state, the modem 24 transitions to the backward protection state.

[0047] When the modulator-demodulator 24 detects UW1 and (N-1) UW2s in the backward protection state, the modulator-demodulator 24 transitions to a state synchronized with the first received signal. When the modulator-demodulator 24 fails to detect UW1 and (N-1) UW2s in the backward protection state for (YA-1) consecutive times, the modulator-demodulator 24 transitions to a state asynchronous with the first received signal, where YA represents the number of backward protection stages of the modulator-demodulator 24.

[0048] Normally, XA and YA are set to, for example, a default value of 3. The default value can be set by the user via the operation panel 27.

[0049] FIG. 8 is a diagram showing the state transition of the demodulator 25. When the quality of the second received signal is low, noise can cause bit errors, or the data can contain information that matches or is similar to UW1 or UW2. As a result, erroneous detection or non-detection of UW1 and UW2 can occur. Therefore, if demodulator 25 detects UW1 and (N-1) UW2s once while in a state asynchronous with the second received signal, demodulator 25 transitions to the forward protection state rather than to the synchronized state with the second received signal.

[0050] When the demodulator 25 detects UW1 and (N-1) UW2s consecutively (XB-1) times in the forward protection state, the demodulator 25 transitions to a state synchronized with the second received signal. When the demodulator 25 does not detect UW1 and (N-1) UW2s in the forward protection state, the demodulator 25 transitions to a state asynchronous with the second received signal. XB represents the number of forward protection stages of the demodulator 25. Note that when the demodulator 25 does not detect UW1 and (N-1) UW2s consecutively (XB-1) times in the forward protection state, the demodulator 25 may transition to a state asynchronous with the second received signal.

[0051] When the demodulator 25 is in a synchronized state with the second received signal and does not detect UW1 and (N-1) UW2s, the demodulator 25 transitions to a backward protection state.

[0052] When the demodulator 25 detects UW1 and (N-1) UW2s in the backward protection state, the demodulator 25 transitions to a state synchronized with the second received signal. When the demodulator 25 fails to detect UW1 and (N-1) UW2s in the backward protection state (YB-1) times in succession, the demodulator 25 transitions to a state asynchronous with the second received signal. YB represents the number of backward protection stages of the demodulator 25.

[0053] Normally, XB and YB are set to, for example, a default value of 3. The default value can be set by the user via the operation panel 27.

[0054] The minimum time Tmin [sec] required for each of the modem 24 and demodulator 25 to transition to a synchronized state with the received signal is expressed by equation (1) using the multiframe length L, transmission rate α, and the number of forward protection stages A.

number

[0055] In the case of a helicopter communication system, the minimum time Tmin is long because the transmission rate α is small and the multiframe length L is long. Changing the transmission rate α or the multiframe length L could be considered to shorten the minimum time Tmin, but changing these would have a significant impact on the entire helicopter communication system.

[0056] On the other hand, the forward guard stage number A is a parameter used inside the modulator-demodulator 24 and the demodulator 25, so changing the forward guard stage number A has little effect on the entire helicopter communication system. By reducing the forward guard stage number A, the time required to transition to a synchronized state with the received signal is shortened.

[0057] Reducing the number of forward protection stages A requires a low probability of erroneous detection or non-detection of UW1 or UW2. Erroneous detection or non-detection of UW1 or UW2 occurs when the quality of the received signal is low. This is because when the quality of the received signal is low, bit errors can occur due to noise, or information similar to UW1 or UW2 can be mixed into the data. When the quality of the received signal is high, erroneous detection or non-detection of UW1 or UW2 is less likely to occur, making it possible to reduce the number of forward protection stages A. Next, the quality of the received signal will be described. The quality R of the received signal is the ratio of the received level C to the level of the system noise N, and is expressed by equation (2).

number

[0058] The system noise N is expressed by the following formula (3): T [K] is the system noise temperature, k [J / K] is the Boltzmann constant (1.38 × 10 -23 ), and B [Hz] is the bandwidth of the modulator-demodulator 24 and the demodulator 25.

number

[0059] Since the system noise N input to the modulator-demodulator 24 and the demodulator 25 is almost equal, the quality R of the received signal can be evaluated based on the value of the reception level C.

[0060] The reception level calculation circuit 16A of the modulator / demodulator 24 calculates the reception level CA of the first reception signal according to equation (4) using the amplitude IA of the I signal of the baseband signal output from the low-pass filter 10A to the demodulation circuit 11A and the amplitude QA of the Q signal of the baseband signal output from the low-pass filter 10B to the demodulation circuit 11A. The reception level calculation circuit 16A outputs the calculated reception level CA to the demodulator 25.

number

[0061] The reception level calculation circuit 16B of the demodulator 25 calculates the reception level CB of the second reception signal according to equation (5) using the amplitude IB of the I signal of the baseband signals output from the low-pass filter 10C to the demodulation circuit 11B and the amplitude QB of the Q signal of the baseband signals output from the low-pass filter 10D to the demodulation circuit 11B. The reception level calculation circuit 16B outputs the calculated reception level CB to the modem 24.

number

[0062] When the modulator-demodulator 24 is not synchronized with the first received signal and the demodulator 25 is synchronized with the second received signal, if the reception level CB of the second received signal is equal to or greater than a predetermined reference value, the modulator-demodulator 24 reduces the number of forward protection stages XA of the modulator-demodulator 24. This reduces the time it takes for the modulator-demodulator 24 to transition to a synchronized state with the first received signal.

[0063] When the demodulator 25 is not synchronized with the second received signal and the modem 24 is synchronized with the first received signal, if the reception level CA of the first received signal is equal to or greater than a predetermined reference value, the demodulator 25 reduces the number of forward protection stages YA of the demodulator 25. This reduces the time it takes for the demodulator 25 to transition to a synchronized state with the second received signal.

[0064] 9 is a flowchart showing a procedure for processing the first received signal according to Embodiment 1. The procedure for processing the first received signal will be described with reference to FIG.

[0065] In step S101, the first antenna device 21A receives a signal from the earth station 32 and outputs a first received signal to the first radio circuit 2A. The first radio circuit 2A amplifies and frequency-converts the first received signal.

[0066] In step S102, the modem 24 demodulates the first received signal received from the first radio circuit 2 A. The modem 24 calculates the reception level CA of the first received signal.

[0067] In step S103, the modem 24 notifies the demodulator 25 via the antenna control device 22 of the reception level CA of the first reception signal.

[0068] In step S104, the modulator-demodulator 24 receives the reception level CB of the second reception signal calculated by the demodulator 25 and the status signal SB indicating the status of the demodulator 25 from the demodulator 25 via the antenna control device 22.

[0069] In step S105, the modulator-demodulator 24 determines whether the modulator-demodulator 24 is not synchronized with the first received signal (is in an asynchronous state or backward protection state) and the demodulator 25 is synchronized with the second received signal. If the modulator-demodulator 24 is not synchronized with the first received signal (is in an asynchronous state or backward protection state) and the demodulator 25 is synchronized with the second received signal, the process proceeds to step S106; if not, the process proceeds to step S108.

[0070] In step S106, the modem 24 determines whether the reception level CB of the second received signal is equal to or greater than the reference value TH. If the reception level CB of the second received signal is equal to or greater than the reference value TH, the process proceeds to step S107. If the reception level CB of the second received signal is less than the reference value TH, the process proceeds to step S108.

[0071] In step S107, the modem 24 decreases the number of forward protection stages XA. For example, the modem 24 decreases the number of forward protection stages XA from the default value "3" by "1".

[0072] In step S108, the modem 24 executes a process of detecting the unique word UW1 and (N-1) UW2s in the frame of the first received signal.

[0073] In step S109, the modem 24 refers to the state transition diagram of Fig. 7 and determines whether a state transition of the modem 24 is necessary. If a state transition of the modem 24 is necessary, the process proceeds to step S110.

[0074] In step S110, the modem 24 transitions between states in accordance with the state transition diagram of FIG.

[0075] In step S111, the modem 24 notifies the demodulator 25 via the antenna control device 22 of a status signal SA indicating the status of the modem 24.

[0076] Next, the procedure for processing the second received signal will be described. The procedure for processing the second received signal by demodulator 25 is similar to the procedure for processing the first received signal by modulator-demodulator 24, so the description will be omitted. The processing by modulator-demodulator 24 and demodulator 25 is performed simultaneously in parallel.

[0077] According to this embodiment, even when the antenna is switched due to a change in the blocking area caused by, for example, the rotation of the helicopter 1, a mechanism is provided in which a synchronized demodulator notifies an unsynchronized demodulator of the reception level of the synchronized demodulator, so that the unsynchronized demodulator can know the quality of the received signal in advance. This allows the number of forward guard stages, which is a parameter for preventing erroneous detection of the unique word in the frame of the received signal, to be set to an appropriate value in advance, thereby shortening the time required to synchronize with the received signal.

[0078] According to this embodiment, the number of forward protection stages, which is a parameter for synchronization processing, can be set to an appropriate value using a simple mechanism, so that design changes to existing helicopter-mounted communication devices can be minimized and increases in costs due to design changes, etc. can be suppressed.

[0079] Embodiment 2 FIG. 10 is a diagram showing the configuration of a helicopter-mounted communication device 34A according to the second embodiment. A helicopter-mounted communication device 34A of the second embodiment differs from the helicopter-mounted communication device 34 of the first embodiment in that the helicopter-mounted communication device 34A of the second embodiment includes a first antenna device 21C, a second antenna device 21D, a modulator-demodulator 24A, and a demodulator 25A instead of the first antenna device 21A, the second antenna device 21B, the modulator-demodulator 24, and the demodulator 25. Note that a description of the configuration and processing procedures described in the first embodiment will be omitted.

[0080] The first antenna device 21C detects the azimuth angle AZA of the antenna and the altitude angle ELA of the antenna according to the orientation of the antenna mounted on the first antenna device 21C, and outputs the azimuth angle AZA of the antenna and the altitude angle ELA of the antenna to the modem 24A via the antenna control device 22. Here, the azimuth angle AZA of the antenna and the altitude angle ELA of the antenna are examples of a first azimuth angle and a first altitude angle, respectively, that represent the orientation of the antenna.

[0081] The second antenna device 21D detects the azimuth angle AZB of the antenna and the altitude angle ELB of the antenna according to the orientation of the antenna mounted on the second antenna device 21D, and outputs the azimuth angle AZB of the antenna and the altitude angle ELB of the antenna to the demodulator 25A via the antenna control device 22. Here, the azimuth angle AZB of the antenna and the altitude angle ELB of the antenna are examples of a second azimuth angle and a second altitude angle, respectively, that represent the orientation of the antenna.

[0082] The antenna control device 22 determines whether a signal from the ground station 32 to the first antenna device 21C via the communication satellite 33 is in a first airframe block state, in which the signal is blocked by the helicopter 1, based on the azimuth angle AZA and altitude angle ELA of the antenna of the first antenna device 21C, and notifies the modem 24A of the first airframe block state. Note that the modem 24A may determine whether the first airframe block state is in place based on the azimuth angle AZA and altitude angle ELA of the antenna of the first antenna device 21C.

[0083] The modem 24A sets the number of forward protection stages of the modem 24A based on the reception level CB of the second reception signal when the modem 24A is not synchronized with the first reception signal, the demodulator 25A is synchronized with the second reception signal, and the signal to the first antenna device 21C is not in the first aircraft block state.

[0084] The antenna control device 22 determines whether or not a second airframe block state has occurred, in which a signal from the ground station 32 to the second antenna device 21D via the communication satellite 33 is blocked by the helicopter 1, based on the azimuth angle AZB and altitude angle ELB of the antenna of the second antenna device 21D, and notifies the demodulator 25A of the second airframe block state. Note that the demodulator 25A may determine whether or not a second airframe block state has occurred based on the azimuth angle AZB and altitude angle ELB of the antenna of the second antenna device 21D.

[0085] The demodulator 25A sets the number of forward protection stages of the demodulator 25A based on the reception level CA of the first reception signal when the demodulator 25A is not synchronized with the second reception signal, the modulator-demodulator 24A is synchronized with the first reception signal, and the signal to the second antenna device 21D is not in the second aircraft block state.

[0086] 11 is a flowchart showing a procedure for processing the first received signal according to Embodiment 2. The procedure for processing the first received signal will be described with reference to FIG.

[0087] In step S301, the first antenna device 21C receives a signal from the ground station 32 and outputs a first received signal to the first radio circuit 2A. The first radio circuit 2A amplifies and frequency-converts the first received signal. The first antenna device 21C detects an azimuth angle AZA and an altitude angle ELA that indicate the orientation of the antenna mounted on the first antenna device 21C, and outputs the azimuth angle AZA and the altitude angle ELA to the modem 24A via the antenna control device 22.

[0088] In step S302, the modem 24A demodulates the first received signal received from the first radio circuit 2A, and calculates the reception level CA of the first received signal.

[0089] In step S303, the modem 24A notifies the demodulator 25A via the antenna control device 22 of the reception level CA of the first reception signal.

[0090] In step S304, the modulator-demodulator 24A receives the reception level CB of the second reception signal calculated by the demodulator 25A and the status signal SB indicating the status of the demodulator 25 from the demodulator 25A via the antenna control device 22.

[0091] In step S305, the antenna control device 22 determines, based on the azimuth angle AZA and altitude angle ELA of the antenna of the first antenna device 21C, whether or not the signal from the ground station 32 to the first antenna device 21C is in a first airframe blocked state, in which the signal is blocked by the airframe of the helicopter 1. For example, if the azimuth angle AZA of the antenna of the first antenna device 21C is within a predetermined first range and the altitude angle ELA is within a predetermined second range, the modem 24A determines that the signal to the first antenna device 21C is in a first airframe blocked state.

[0092] In step S306, the modulator-demodulator 24A determines whether the modulator-demodulator 24A is not synchronized with the first received signal (in an asynchronous state or backward protection state) and the demodulator 25A is synchronized with the second received signal. If the modulator-demodulator 24A is not synchronized with the first received signal (in an asynchronous state or backward protection state) and the demodulator 25A is synchronized with the second received signal, the process proceeds to step S307; if not, the process proceeds to step S310.

[0093] In step S307, the modem 24A determines whether the reception level CB of the second received signal is equal to or greater than the reference value TH. If the reception level CB of the second received signal is equal to or greater than the reference value TH, the process proceeds to step S308. If the reception level CB of the second received signal is less than the reference value TH, the process proceeds to step S310.

[0094] In step S308, the modem 24A determines whether the signal to the first antenna device 21C is in the first airframe block state. If the signal to the first antenna device 21C is not in the first airframe block state, the process proceeds to step S309.

[0095] In step S309, the modem 24A decreases the number of forward protection stages XA. For example, the modem 24A decreases the number of forward protection stages XA from the default value "3" by "1."

[0096] In step S310, the modem 24A executes a process of detecting the unique word UW1 and (N-1) UW2s in the frame of the first received signal.

[0097] In step S311, the modem 24A determines whether a state transition of the modem 24A is necessary, with reference to the state transition diagram of Fig. 7. If a state transition of the modem 24A is necessary, the process proceeds to step S312.

[0098] In step S312, the modem 24A transitions the state of the modem 24A in accordance with the state transition diagram of FIG.

[0099] In step S313, the modulator-demodulator 24A notifies the demodulator 25A via the switching device 23 of a status signal SA indicating the status of the modulator-demodulator 24A.

[0100] Next, the procedure for processing the second received signal will be described. The procedure for processing the second received signal by demodulator 25A is the same as the procedure for processing the first received signal by modulator-demodulator 24A, so the description will be omitted. The processing by modulator-demodulator 24A and demodulator 25A is performed simultaneously in parallel. Variant. The present invention is not limited to the above-described embodiment, and includes the following modifications, for example.

[0101] (1) Number of forward protection stages In the above embodiment, the helicopter-mounted communication device 34 reduces the number of forward protection steps XB from the default value when the reception level CA is equal to or greater than the reference value TH, and reduces the number of forward protection steps XA from the default value when the reception level CB is equal to or greater than the reference value TH. However, this is not limiting. The helicopter-mounted communication device 34 may set the number of forward protection steps XB according to the magnitude of the reception level CA, and set the number of forward protection steps XA according to the magnitude of the reception level CB. For example, the helicopter-mounted communication device 34 may set the number of forward protection steps XB and XA to a first level when the reception levels CA and CB are in a first range, set the number of forward protection steps XB and XA to a second level when the reception levels CA and CB are in a second range, and set the number of forward protection steps XB and XA to a third level when the reception levels CA and CB are in a third range.

[0102] (2) Received signal quality In the above embodiment, the reception level of the received signal is used as the quality of the received signal, but this is not limited to this. The ratio of the reception level C to the level of the system noise N may also be used as the quality of the received signal.

[0103] (3) Conditions for changing the number of forward protection stages In the above embodiment, in step S105 of FIG. 9 and step S306 of FIG. 11, when the modem 24, 24A is not synchronized with the first received signal (is in an asynchronous state or backward protection state) and the demodulator 25, 25A is synchronized with the second received signal, the processing proceeds to steps S106 and S307, but this is not limited to this. In addition to the asynchronous state or backward protection state, a forward protection state may be added as a state in which the modems 24, 24A are not synchronized with the first received signal. The condition that the demodulators 25, 25A are synchronized with the second received signal may be omitted. This is because, when the demodulators 25, 25A are synchronized with the second received signal, it may be possible to assume that the reception level CB of the second received signal is equal to or greater than the reference value TH in steps S106 and S306 described below.

[0104] (4) Conditions for changing the number of forward protection stages in the second embodiment In the second embodiment, in order to determine whether or not to change the number of forward protection stages, in addition to whether or not the signal to the first antenna device 21C or the signal to the second antenna device 21D is in an aircraft block state, the states of the modem 24 and the demodulator 25, the reception level CA of the first received signal, and the reception level CB of the second received signal are also referenced, as in the first embodiment, but these do not have to be used. That is, steps S306 and S307 in the flowchart of FIG. 11 may be omitted, and the number of forward protection stages XA may be changed based only on whether or not the signal to the first antenna device 21A indicates the first airframe block state (S308).

[0105] (5) Helicopter-mounted communication device and communication method In the above-described embodiments, examples of a communication device mounted on a helicopter and a communication method for a communication device mounted on a helicopter are shown, but the present disclosure is not limited to this. The present disclosure may be applied to a communication device and a communication method mounted on any rotorcraft, whether manned or unmanned, as long as the rotorcraft is a rotorcraft.

[0106] (6) Transmission method of status signals SA, SB and reception levels CA, CB In the above embodiment, the modulator-demodulator 24 sends a status signal SA to the switching device 23 and the demodulator 25 via the antenna control device 22. The modulator-demodulator 24 sends a reception level CA to the demodulator 25 via the antenna control device 22. The demodulator 25 also sends a status signal SB to the switching device 23 and the modulator-demodulator 24 via the antenna control device 22. While the example in which the demodulator 25 sends a reception level CB to the modulator-demodulator 24 via the antenna control device 22 has been described, the present invention is not limited to this. That is, the modulator-demodulator 24 and the demodulator 25 may transmit signals without going through the antenna control device 22. For example, the modulator-demodulator 24 may directly transmit a status signal SA to the switching device 23 and the demodulator 25. The modulator-demodulator 24 may directly transmit a reception level CA to the demodulator 25. The demodulator 25 may also directly transmit a status signal SB to the switching device 23 and the modulator-demodulator 24. The demodulator 25 may directly transmit the reception level CB to the modem 24 .

[0107] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0108] 1 helicopter, 2A first radio circuit, 2B second radio circuit, 3A, 3B band-pass filter, 4A, 4B automatic control gain amplifier, 5A, 5B clock generator for synchronous detection, 6A, 6B, 6C, 6D detector, 7A, 7B 90-degree phase shifter, 8A, 8B, 8C, 8D, 10A, 10B, 10C, 10D low-pass filter, 9A, 9B, 9C, 9D A / D converter, 11A, 11B demodulation circuit, 12A, 12B Viterbi decoding circuit, 13A, 13B frame synchronization circuit, 14A, 14B signal processing circuit, 15A, 15B automatic gain control circuit, 16A, 16B reception level calculation circuit, 21A, 21C first antenna device, 21B, 21D second antenna device, 22 antenna control device, 23 Switching device, 24, 24A Modulator-demodulator, 25, 25A Demodulator, 26 Video coding device, 27 Control panel, 32 Ground station, 33 Communications satellite, 34, 34A Helicopter-mounted communications device, 35 Rotor, 51A, 51B Power amplifier, 52A, 52B Frequency converter.

Claims

1. a first antenna device mounted on the helicopter for receiving signals; a first demodulator that performs a first demodulation process on a first received signal output from the first antenna device and calculates quality of the first received signal; a second antenna device mounted on the helicopter to receive the signal; a second demodulator that performs second demodulation processing on a second received signal output from the second antenna device and calculates quality of the second received signal, the first demodulation process includes a synchronization process with the first received signal, and the second demodulation process includes a synchronization process with the second received signal; a first demodulator that sets a forward guard stage number of the first demodulator based on a quality of the second received signal when the first demodulator is not synchronized with the first received signal, and a second demodulator that sets a forward guard stage number of the second demodulator based on the quality of the first received signal when the second demodulator is not synchronized with the second received signal.

2. the quality of the first received signal is a reception level of the first received signal; 2. The helicopter-mounted communication device according to claim 1, wherein the quality of the second received signal is a reception level of the second received signal.

3. 3. A helicopter-mounted communication device according to claim 2, wherein the first demodulator decreases a number of forward guard stages when the first demodulator is not synchronized with the first received signal and when the reception level of the second received signal is equal to or higher than a predetermined reference value, and the second demodulator decreases a number of forward guard stages when the second demodulator is not synchronized with the second received signal and when the reception level of the first received signal is equal to or higher than a predetermined reference value.

4. 4. The helicopter-mounted communication device according to claim 3, wherein the first demodulator sets a forward guard stage number of the first demodulator based on a reception level of the second reception signal when the first demodulator is not synchronized with the first reception signal and the second demodulator is synchronized with the second reception signal, and the second demodulator sets a forward guard stage number of the second demodulator based on a reception level of the first reception signal when the second demodulator is not synchronized with the second reception signal and the first demodulator is synchronized with the first reception signal.

5. the first antenna device detects a first azimuth angle and a first altitude angle that represent the orientation of an antenna mounted thereon; the second antenna device detects a second azimuth angle and a second altitude angle that represent the orientation of the antenna mounted thereon; the first demodulator determines whether the signal to the first antenna device is in a first airframe block state in which the signal is blocked by the airframe of the helicopter, based on the first azimuth angle and the first altitude angle; the first demodulator sets a forward protection stage number of the first demodulator based on a reception level of the second reception signal when the first demodulator is not synchronized with the first reception signal, the second demodulator is synchronized with the second reception signal, and the signal to the first antenna device is not in the first airframe block state; the second demodulator determines whether the signal to the second antenna device is in a second airframe block state, in which the signal is blocked by the airframe of the helicopter, based on the second azimuth angle and the second altitude angle; 5. The helicopter-mounted communication device according to claim 4, wherein the second demodulator sets a forward guard stage number of the second demodulator based on a reception level of the first reception signal when the second demodulator is not synchronized with the second reception signal, the first demodulator is synchronized with the first reception signal, and the signal to the second antenna device is not in the second airframe block state.

6. further comprising an antenna control device that controls the first antenna device and the second antenna device; the first antenna device detects a first azimuth angle and a first altitude angle that represent the orientation of an antenna mounted thereon; the second antenna device detects a second azimuth angle and a second altitude angle that represent the orientation of the antenna mounted thereon; the antenna control device determines whether or not a first airframe block state occurs, in which the signal to the first antenna device is blocked by the airframe of the helicopter, based on the first azimuth angle and the first altitude angle, and notifies the first demodulator of the first airframe block state; the first demodulator sets a forward protection stage number of the first demodulator based on a reception level of the second reception signal when the first demodulator is not synchronized with the first reception signal, the second demodulator is synchronized with the second reception signal, and the signal to the first antenna device is not in the first airframe block state; the antenna control device determines whether or not a second airframe block state occurs, in which the signal to the second antenna device is blocked by the airframe of the helicopter, based on the second azimuth angle and the second altitude angle, and notifies the second demodulator of the second airframe block state; 5. The helicopter-mounted communication device according to claim 4, wherein the second demodulator sets a forward guard stage number of the second demodulator based on a reception level of the first reception signal when the second demodulator is not synchronized with the second reception signal, the first demodulator is synchronized with the first reception signal, and the signal to the second antenna device is not in the second airframe block state.

7. a first antenna device installed on the helicopter for detecting the azimuth angle and altitude angle of the antenna; a first demodulator that performs a first demodulation process on a first reception signal output from the first antenna device; a second antenna device installed on the helicopter for detecting the azimuth angle and altitude angle of the antenna mounted thereon; a second demodulator that performs second demodulation processing on the second received signal output from the second antenna device, the first demodulation process includes a synchronization process with the first received signal, and the second demodulation process includes a synchronization process with the second received signal; a first demodulator that sets a forward guard stage number of the first demodulator based on an azimuth angle and an altitude angle of the first antenna device when the first demodulator is not synchronized with the first received signal, and a second demodulator that sets a forward guard stage number of the second demodulator based on an azimuth angle and an altitude angle of the second antenna device when the second demodulator is not synchronized with the second received signal.

8. 8. A helicopter-mounted communication device according to claim 1, further comprising a switching device that outputs to an external device either the data output from the first demodulator or the data output from the second demodulator, based on whether the first demodulator is synchronized with the first received signal and whether the second demodulator is synchronized with the second received signal.

9. A communication method for a helicopter-mounted communication device including a first antenna device and a second antenna device installed on a helicopter, comprising: the first antenna device receiving a signal; the second antenna device receiving a signal; a first demodulator performing demodulation processing of the first received signal output from the first antenna device, including synchronization processing with the first received signal; the first demodulator calculating a quality of the first received signal; a second demodulator performing demodulation processing of the second received signal output from the second antenna device, including synchronization processing with the second received signal; the second demodulator calculating a quality of the second received signal; setting a forward guard stage number of the first demodulator based on a quality of the second received signal when the first demodulator is not synchronized with the first received signal; and setting a forward guard stage number of the second demodulator based on quality of the first received signal when the second demodulator is not synchronized with the second received signal.

Images