Signal processing device, flying object, earth station, signal processing system, method, and program

Abstract

To provide a signal processing device and the like capable of estimating a data string including a signal of an unknown frequency band from received signals with a low S / N ratio.SOLUTION: A signal processing device 2A includes an AD conversion device 215 that converts signals received by a flying object at different times for a predetermined period of time into time-domain data strings for each time, an FFT processing device 221 that performs FFT processing on the time-domain data strings for each time at a plurality of different fast Fourier transform (FFT) point numbers and outputs frequency-domain FFT result data strings for each FFT point number, a correlation calculation device 222 that calculates the correlation between frequency-domain FFT result data strings for different times at the same FFT point number for each section based on a frequency resolution unit determined by the sampling frequency of the AD conversion device and the FFT point number, the correlation calculation device 222 performing the calculation for each of a plurality of different FFT point numbers, and a data string selection device 223 that selects data strings whose correlation is equal to or greater than a threshold.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a signal processing device, an aircraft, an earth station, a signal processing system, a method, and a program that perform signal processing of observed radio waves. [Background technology]

[0002] Satellite systems have been used to estimate the location of radio wave sources (e.g., Non-Patent Documents 1 and 2). In such conventional satellite systems, multiple satellites collect radio waves in relatively narrow bands, downlink transmit the signals to a ground station, and the ground station processes the signals to estimate the location of the source. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Determining the location of a radio source using Doppler rate change from a single satellite, Fucheng Guo, 'Space Electronic Reconnaissance Localization Theories and Methods' Chapter 6.3 [Non-patent document 2] TDOA-FDOA Location of Radio Sources Using Two Satellites, Fucheng Guo, 'Space Electronic Reconnaissance Localization Theories and Methods' Chapter 5.2 Summary of the Invention [Problem to be solved by the invention]

[0004] When monitoring radio signals or other signals on an aircraft, if an unknown frequency band is to be received, the observation band of the signal must be wide. However, when the observation band is wide, noise increases and the signal-to-noise ratio deteriorates. Therefore, even if the received wide-band signal is converted into a data sequence in the frequency domain, it is not possible to determine where in the data sequence the unknown signal is contained, making it difficult to detect the signal contained in the unknown signal from within the wide-band signal.

[0005] The embodiments of the present invention have been made to solve the above-mentioned problems, and aim to estimate a data sequence including a signal of unknown frequency band from received signals with a low SNR. [Means for solving the problem]

[0006] A signal processing device according to one embodiment of the present invention comprises an AD conversion device that converts signals received for a predetermined period of time by one or more flying objects at different times or positions into time-domain data sequences for each time or position; an FFT processing device that performs FFT processing on the time-domain data sequences for each time or position at a plurality of different FFT points and outputs frequency-domain FFT result data sequences for each FFT point; a correlation calculation device that calculates the correlation between frequency-domain FFT result data sequences for different times or positions at the same FFT point for each division based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device and the same FFT point, the correlation calculation device performing the calculation for each of the plurality of different FFT points; and a data sequence selection device that selects data sequences for which the correlation is equal to or greater than a threshold value.

[0007] The data sequence may be a frequency domain FFT result data sequence at an FFT point number where the correlation is equal to or greater than a threshold value.

[0008] The data sequence may be the time domain data sequence corresponding to the frequency domain FFT result data sequence at the number of FFT points where the correlation is equal to or greater than a threshold value.

[0009] The correlation calculation device may multiply the frequency domain FFT result data sequence for each segment at a first time by a complex conjugate of the frequency domain FFT result data sequence for each segment at a second time for the same number of FFT points, and perform inverse FFT processing on the multiplication result to calculate the correlation.

[0010] The data string selection device may select the data string by performing constant false alarm probability (CFAR) processing on the correlation.

[0011] An aircraft according to one embodiment of the present invention comprises any one of the signal processing devices described above, a memory device for storing the data sequence, and a transmitter for transmitting the data sequence stored in the memory device to an earth station.

[0012] An earth station according to one embodiment of the present invention comprises any one of the signal processing devices described above.

[0013] A signal processing system according to one embodiment of the present invention is a signal processing system including one or more flying objects and an earth station, the signal processing system including: an AD conversion device that converts signals received by the one or more flying objects at different times or positions for a predetermined period of time into time domain data sequences for each time or position; The system comprises an FFT processing device that performs FFT processing on the time domain data sequence at each time or position at a plurality of different FFT points and outputs a frequency domain FFT result data sequence at each FFT point; a correlation calculation device that calculates the correlation between frequency domain FFT result data sequences at different times or positions at the same FFT point for each section based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device and the same FFT point, and that performs the calculation for each of the plurality of different FFT points; and a data sequence selection device that selects data sequences whose correlation is equal to or greater than a threshold.

[0014] Each of the devices may be provided in either the air vehicle or the earth station.

[0015] The devices may be provided separately in the aircraft and the earth station.

[0016] A signal processing method according to one embodiment of the present invention comprises one or more computers performing AD conversion on signals received by one or more flying objects at different times or positions for a predetermined period of time, respectively, into time-domain data sequences for each time or position, performing FFT processing on the time-domain data sequences for each time or position at a plurality of different FFT points, respectively, outputting frequency-domain FFT result data sequences for each FFT point, calculating the correlation between the frequency-domain FFT result data sequences for different times or positions at the same FFT point for each division based on a frequency resolution unit that is determined by the sampling frequency of the AD conversion device and the same FFT point, performing this calculation for each of the plurality of different FFT points, and selecting data sequences for which the correlation is equal to or greater than a threshold. [Effects of the Invention]

[0017] According to the embodiment of the present invention, it is possible to estimate a data string including a signal of an unknown frequency band from among received signals with a low SNR. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing the configuration of a signal processing system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a detailed configuration of a receiver. [Figure 3] FIG. 1 is a diagram showing the relationship between the motion of an aircraft (small satellite) and data sampling. [Figure 4] FIG. 2 is a diagram illustrating a detailed configuration of a digital signal processing device. [Figure 5] FIG. 2 is a diagram for explaining FFT processing by the FFT processing device. [Figure 6] FIG. 10 is a conceptual diagram of a frequency domain FFT result data string at each FFT point viewed in section units. [Figure 7] FIG. 2 is a diagram for explaining a correlation calculation method of the correlation calculation device. [Figure 8] 10A and 10B are diagrams for explaining a data selection process of the data string selection device; [Figure 9] 3 is an example of an operation flowchart of a signal processing system including the signal processing device of the first embodiment. [Figure 10] FIG. 10 is a diagram showing the configuration of a signal processing system according to a second embodiment. [Figure 11] FIG. 11 is a diagram showing the positional relationship between a plurality of flying objects, earth stations, and transmission sources according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] A signal processing device, an aircraft, an earth station, a signal processing system, a method, and a program according to an embodiment of the present invention will be described with reference to the drawings.

[0020] [1. First embodiment] [1-1.Configuration] FIG. 1 is a diagram showing the configuration of a signal processing system according to a first embodiment. The signal processing system 1 shown in FIG. 1 is a system that receives signals such as radio waves and performs signal processing on the received signals. As will be described below, this signal processing system 1 estimates a data string that includes a signal whose frequency band is unknown from among the received signals. The signal processing system 1 can be used as a radio wave monitoring system.

[0021] The signal processing system 1 includes an air vehicle 2 and an earth station 3. The air vehicle 2 can receive signals such as radio waves and transmit the results of signal processing performed on the received signals to the earth station 3. The air vehicle 2 can be, for example, an artificial satellite or an aircraft. In this specification, the air vehicle 2 is an artificial satellite, and more specifically, a small satellite. The small satellite can be, for example, a CubeSat-standard satellite such as 1U to 6U, a W6U satellite, or a 50 kg-class satellite. 1U is a size defined as 10 cm x 10 cm x 10 cm, and 1U to 6U are 10 cm x 10 cm x (10 cm to 60 cm). W6U is a size defined as 10 cm x 20 cm x 30 cm. A 50 kg-class satellite is a satellite measuring 55 cm x 35 cm x 55 cm. The small satellite can move around the Earth in a satellite orbit. The satellite orbit may be, for example, a low earth orbit (LEO), a middle earth orbit (MEO), or a geostatinary earth orbit (GEO), but is not particularly limited to these.

[0022] The aircraft 2 includes a receiving antenna 20, a receiver 21, a digital signal processing device 22, a storage device 23, a transmitter 24, a transmitting antenna 25, a position information acquisition device 26, a communication antenna 27, a communication transceiver 28, and a control device 29, and may also include other components that realize various functions. These components may include a power supply subsystem that supplies power to each device mounted on the aircraft 2, including solar panels, batteries, etc., an attitude control subsystem that controls the attitude of the aircraft 2, a propulsion subsystem that propels the aircraft 2, a thermal control subsystem that controls the temperature range within the aircraft 2, etc.

[0023] The receiving antenna 20 is an aerial for receiving signals such as radio waves. The radio waves referred to here may be, for example, electromagnetic waves having a frequency of 3 THz or less, but are not limited to this. The receiving antenna 20 receives, for example, radio waves arriving from the Earth. The Earth may refer to, for example, the ground and / or the sea, but the radio waves that the receiving antenna 20 can receive are not limited to these. In other words, radio wave sources may include equipment installed on the ground, mobile objects that can move on the ground, ships on the sea, aircraft above the ground or sea surface, and spacecraft in outer space.

[0024] The receiver 21 performs signal processing on the received signal and converts it into a digital signal that indicates the time-domain waveform of the received signal. The digital signal processing device 22 is configured to include one or more computers and / or one or more processing circuits, and performs signal processing such as Fast Fourier Transform (FFT) on the signal output by the receiver 21 to select a data string. The detailed configurations of the receiver 21 and the digital signal processing device 22 will be described later. The signal processing device 2A of this embodiment can be configured by an AD conversion device 215 of the receiver 21, which will be described later, and the digital signal processing device 22.

[0025] The storage device 23 is configured with a memory and / or storage and stores the data sequence selected by the digital signal processing device 22. The transmitter 24 transmits information including the data sequence stored in the storage device 23 and information about the aircraft 2 to the earth station 3 via the transmitting antenna 26. The information about the aircraft 2 is, for example, satellite information including the position (altitude), velocity, and acceleration of the satellite, and is satellite information at the time corresponding to the selected data sequence. The transmitting antenna 25 is an antenna for transmitting signals including information. The information transmitted by the transmitter 24 and the transmitting antenna 25 is transmitted using a predetermined frequency band. The position information acquisition device 26 acquires position information about the aircraft 2. The position information acquisition device 26 calculates the position (e.g., altitude), velocity, and acceleration of the aircraft 2 based on, for example, signals from a Global Navigation Satellite System (GNSS). The calculated position, velocity, and acceleration can be included in the information about the aircraft 2 transmitted by the transmitter 24 and the transmitting antenna 25.

[0026] The communication antenna 27 is an aerial that receives command signals from the earth station 3 and transmits telemetry signals to the earth station 3. The command signals are signals that include command data for controlling the flying object 2. The command signals are signals that the control device 29 uses to control each component, and are transmitted from the communication transceiver 28 to the control device 29. The telemetry signals are signals that include telemetry data that indicate the status of the flying object 2. The telemetry data may include, for example, the position, velocity, and acceleration of the flying object 2. To avoid interference, the command signals and telemetry signals are communicated using a frequency band different from that of the transmitter 24 and the transmitting antenna 25. The communication transceiver 28 demodulates the command signals received by the communication antenna 27 and outputs the demodulated signals to the control device 29. The communication transceiver 28 modulates the telemetry signals and transmits them to the earth station 3 via the communication antenna 27.

[0027] The control device 29 is configured with one or more computers and / or one or more processing circuits, and performs overall control of the aircraft 2. For example, the control device 29 can control the receiver 21, the digital signal processing device 22, the storage device 23, the position information acquisition device 26, and the communication transceiver 28.

[0028] The earth station 3 is a system that communicates with the flying object 2. The earth station 3 may be fixedly installed on the ground, or may be deployed on a mobile object that can move on the ground, on the sea, or above the ground or sea surface.

[0029] The earth station 3 includes a receiving antenna 30, a receiver 31, a communication antenna 32, a communication transceiver 33, and an information processing device .

[0030] The receiving antenna 30 is an aerial for receiving information transmitted via the transmitter 24 and the transmitting antenna 25. The receiver 31 demodulates the information received by the receiving antenna 30 and outputs the resulting information to the information processing device 34.

[0031] The communication antenna 32 is an aerial for transmitting command signals and receiving telemetry signals. The communication transceiver 33 modulates control signals for the flying object 2 to generate and transmit command signals. The communication transceiver 33 also receives and demodulates telemetry signals and outputs the results to the information processing device 34.

[0032] The information processing device 34 is configured to include an input / output device, and a computer and / or processing circuit, and generates a control signal for the aircraft 2. The information processing device 34 also estimates the position (e.g., latitude, longitude) of the radio wave source based on the information input from the receiver 31 and the Doppler change rate. This position estimation method can be a known method, such as the method described in Non-Patent Document 1. The Doppler change rate can be obtained from a time-domain data sequence at each time. The information processing device 34 of this embodiment has a control function for the aircraft 2 and a position estimation function for the radio wave source, but each function may be configured based on separate hardware configurations.

[0033] 2 is a diagram showing the detailed configuration of a receiver. The receiver 21 may be a heterodyne receiver, a direct sampling receiver, or a direct conversion receiver. The receiver 21 of this embodiment is a direct conversion receiver. The receiver 21 includes a low-noise amplifier 211, an interference wave suppression filter 212, a direct conversion amplifier 213, an alias rejection filter 214, an AD conversion device 215, a local oscillator 216, and a clock generator 217.

[0034] The low-noise amplifier 211 amplifies the signal received by the receiving antenna 20 while suppressing noise generation. The interference wave suppression filter 212 is a filter that suppresses interference waves from the signal input from the low-noise amplifier 211. The direct conversion 213 converts the signal input from the interference wave suppression filter 212 to a low frequency and generates I and Q signals. Specifically, the direct conversion 213 mixes the signal input from the interference wave suppression filter 212 with a local oscillation signal from the local oscillator 216 to generate an I signal (in-phase signal) and a Q signal (quadrature-phase signal). The I signal and Q signal are analog signals. The alias removal filters 214 are provided for the I and Q signals, respectively, and are filters that remove aliases from the I and Q signals.

[0035] An AD conversion device 215 is provided for each of the I and Q signals, and converts the analog I and Q signals into digital data streams. Specifically, the AD conversion device 215 generates digital I and Q signals using a sampling clock having a sampling frequency fs from a clock generator 217. That is, the digital I and Q signals are time-domain data streams that have been sampled, quantized, and coded at the sampling frequency fs.

[0036] The local oscillator 216 generates a local oscillator signal and provides it to the direct conversion unit 213. The local oscillator signal is a signal having a local oscillator signal frequency that determines the center frequency fc. The local oscillator 216 can switch the center frequency fc based on a control signal from the control unit 29. The clock generator 217 generates a sampling clock and provides it to the AD conversion unit 215. The sampling clock is a signal having a sampling frequency fs.

[0037] The relationship between radio wave collection and a time-domain data sequence generated from the collected radio wave signal will be described using FIG. 3. FIG. 3 is a diagram illustrating the relationship between the movement of an airborne vehicle 2 (small satellite) and data sampling. As shown in FIG. 3, in one example of radio wave collection, a single airborne vehicle 2 orbits a satellite and receives radio waves at predetermined times starting from different times ti (i is a natural number). For example, the airborne vehicle 2 receives a signal for S seconds at time t1 in an observation band with a center frequency fc and a bandwidth B, and then receives a signal for S seconds at time t2, which is different from time t1, in an observation band with a center frequency fc and a bandwidth B. In this way, radio wave reception can be repeated at different times but in the same observation band. Furthermore, the airborne vehicle 2 can repeatedly receive radio waves at different observation bands by switching the center frequency fc. Multiple observation bands may or may not overlap with adjacent observation bands. Furthermore, the center frequency fc can be switched for each orbit or for each coverage area. Furthermore, radio wave collection may be performed by orbiting the Earth multiple times to receive radio waves over a wide band or to receive radio waves over the entire coverage area.

[0038] The center frequency fc can be determined by the frequency of the local oscillator signal of the local oscillator 216. The bandwidth B is proportional to the sampling frequency fs, and can therefore be determined by the sampling frequency fs of the AD conversion device 215. Therefore, the higher the sampling frequency fs, the wider the bandwidth B can be, making it possible to receive signals in a wider frequency band and making it easier to capture signals with unknown frequency bands.

[0039] In this specification, for convenience, a signal received for S seconds from each time t i is identified as a signal for each time t i. The AD conversion device 215 converts the signal for each time t i into a time-domain data sequence for each time t i. If the number of sample data samples for S seconds at a sampling frequency fs is K, the time-domain data sequence for each time t i is a time-domain digital I, Q signal composed of K pieces of data. Note that the signal for each time t input to the AD conversion device 215 is a signal that has passed through each of the components 211 to 214. In this way, the AD conversion device 215 converts signals received by the aircraft 2 at different times for a predetermined period of time into time-domain data sequences for each time.

[0040] Fig. 4 is a diagram showing a detailed configuration of the digital signal processing device 22. The digital signal processing device 22 includes an FFT processing device 221, a correlation calculation device 222, and a data string selection device 223. Fig. 5 is a diagram for explaining the FFT processing of the FFT processing device.

[0041] As shown in Fig. 5, the FFT processing unit 221 performs FFT processing on the time domain data sequence at each time point at a plurality of different fast Fourier transform (FFT) points, and outputs the frequency domain FFT result data sequence at each FFT point. The FFT points are the number of sampling points, and are 2 N N is a natural number, and can be a natural number equal to or greater than 8, such as 8, 9, 10, . . . , L.

[0042] Here, the number of sample data K in the time domain data sequence at each time is assumed to be greater than the number of FFT points. For example, K=2 M where M is a natural number that satisfies M>N. The FFT processing unit 221 processes the time domain data sequence at each time point by FFT points 2 N Divide into K / 2 N Specifically, the FFT processing unit 221 performs FFT processing twice on the time domain data sequence at each time point. N The number of data is K / 2 NThe data is divided into sets, and FFT processing is performed on each set to obtain an FFT result (i.e., a frequency-domain data sequence) for each set. The FFT results for each set are then added together, and the addition result is output as a frequency-domain FFT result data sequence. As shown in FIG. 5, the FFT processing unit 221 performs FFT processing on the time-domain data sequence at each time using multiple different N (i.e., multiple different FFT points), and outputs multiple frequency-domain FFT result data sequences for the time-domain data sequence at time t1. For example, by performing FFT processing on the time-domain data sequence at time t1, the FFT processing unit 221 outputs frequency-domain FFT result data sequences for N=8, 9, 10, etc. As shown in FIG. 5, the multiple frequency-domain FFT result data sequences with different FFT points are derived from the time-domain data sequence at time t1. Therefore, the multiple frequency-domain FFT result data sequences can be labeled with time t1 and the FFT point number (N).

[0043] The correlation calculation device 222 calculates the correlation between frequency domain FFT result data strings at different times for the same FFT point number for each section based on the frequency resolution unit. The correlation calculation device 222 then performs this calculation for each of a plurality of different FFT points. Here, the frequency resolution unit Δf is the ratio of the sampling frequency fs of the AD conversion device 215 to the frequency resolution unit Δf for the same FFT point number 2. N Here, Δf=fs / 2 N Since fs is constant, the larger N, the smaller the frequency resolution unit Δf. Figure 6 is a conceptual diagram of the frequency domain FFT result data sequence at each FFT point, viewed in units of sections. The example in Figure 6 shows the frequency domain FFT result data sequence at time ti where N = 8, 9, 10... As shown in Figure 6, the frequency domain FFT result data sequence has smaller sections, i.e., smaller frequency resolution units Δf, as N increases. In other words, by varying the number of FFT points, signal processing can be performed with a variety of frequency resolutions, enabling signal processing that matches the frequency of the radio waves from the radio wave transmission source.

[0044] Fig. 7 is a diagram for explaining a correlation calculation method of the correlation calculation device. As shown in Fig. 7, in this embodiment, in a frequency domain FFT result data sequence for each section Δf at time ti with the same number of FFT points, the correlation calculation device 222 multiplies the frequency domain FFT result data sequence for each section Δf at time tj by the complex conjugate of the frequency domain FFT result data sequence for each section Δf at time tj different from time ti, and calculates the correlation by performing inverse FFT processing on the multiplication result.

[0045] Specifically, the frequency domain FFT result data sequence for each section with the same FFT points is divided into FFT results k (k=0, 1, . . . , 2 N -1), the frequency domain FFT result data sequence at each time is divided into multiple FFT results k (k=0, 1, . . . , 2 N For example, the first section of the frequency domain FFT result data string at each time is FFT result 0, and the second section is FFT result 1. The correlation calculation device 222 calculates (FFT result k) at time ti × (FFT result l) at time tj. * Calculate (k, l=0,1,··,2 N -1) The correlation is obtained by performing inverse FFT on each multiplication result. The correlation is obtained for each section. Correlation C in Figure 7 is composed of correlations for each section.

[0046] The data string selection device 223 selects data strings whose correlation is equal to or greater than a threshold. FIG. 8 is a diagram illustrating the data selection process of the data string selection device. As shown in FIG. 8, the data string selection device 223 of this embodiment performs constant false alarm rate (CFAR) processing on the calculated correlation to perform signal detection. If a signal is detected, that is, if the correlation is equal to or greater than a threshold, it means that the signal matches the received signal band (frequency band of radio waves) and there is an integral effect. While FIG. 8 shows an example in which one frequency band is detected, multiple bands can be detected for one data string. In this case, the presence of multiple radio wave sources is estimated by detecting multiple bands. The CFAR processing can be well-known and publicly known processing such as cell average CFAR or Weibull CFAR.

[0047] The data string selection device 223 can store data strings whose correlation is greater than or equal to a threshold in the storage device 23. That is, the data string selection device 223 selects data strings to be stored in the storage device 23 from a large number of data strings based on the presence or absence of correlation. The data string to be stored may be a frequency-domain FFT result data string at an FFT point where the correlation is greater than or equal to a threshold, or a time-domain data string corresponding to the frequency-domain FFT result data string at an FFT point where the correlation is greater than or equal to a threshold. Because the correlation is the result between data strings at different times, the data string to be stored may be a pair of data strings at different times. In one example, the data selection device 223 stores in the storage device 23 data strings at times t1 and t2, which are frequency-domain FFT result data strings at the same FFT point where the correlation is greater than or equal to a threshold. In another example, the data selection device 223 stores in the storage device 23 data strings at times t1 and t2, which are time-domain data strings whose correlation is greater than or equal to a threshold and correspond to the frequency-domain FFT result data string at the same FFT point where the correlation is greater than or equal to a threshold. The threshold value can be set appropriately.

[0048] [1-2. Operation] Fig. 9 is an example of an operational flowchart of a signal processing system including a signal processing device of this embodiment. As shown in Fig. 9, an aircraft 2 receives radio waves multiple times (S01: multiple radio wave reception). For example, the aircraft 2, which is an artificial satellite, receives radio waves for S seconds from discrete times ti (i is a natural number) in an observation band with a center frequency fc and a bandwidth B while orbiting a satellite. In this embodiment, the received signal undergoes various processes by components 211 to 214, 216 of the receiver 21.

[0049] Next, the AD conversion device 215 performs AD conversion processing on each signal in S01 at a sampling frequency fs to generate a time domain data sequence at each time ti (S02: AD conversion processing). In one example, the number of sample data K in the time domain data sequence at each time is 2 M is.

[0050] The FFT processing unit 221 performs FFT processing on the time domain data sequence at each time using a plurality of different FFT points, and generates frequency domain FFT result data sequences with the time and the FFT points as parameters (S03: FFT processing). Specifically, the FFT processing unit 221 processes the time domain data sequence at each time using FFT points 2 N FFT processing is performed sequentially for each K / 2 N In other words, the time domain data sequence for each time is N If the number of data is one set, the time domain data sequence for each time is K / 2 N It is a collection of sets, and FFT processing is performed on each set. For example, when M=14 and N=8, 2 14 / 2 8 Since there are 64 sets, FFT processing is performed 64 times. The horizontal axis of the FFT result for each set is frequency, and the FFT processing device 221 adds up the FFT results for each set at each time, and the sum is used as a frequency domain FFT result data string for each time. In this way, in S03, a frequency domain FFT result data string with a plurality of different FFT points is obtained for each time.

[0051] The correlation calculation device 222 performs correlation calculation processing (S04: correlation calculation processing). That is, the correlation calculation processing is a processing in which the correlation between frequency domain FFT result data strings at different times with the same FFT point number is calculated for each section, and the calculation is performed for each of a plurality of different FFT points. The section is a frequency resolution unit Δf, where Δf = sampling frequency fs / FFT point number 2 N Since fs is constant, the larger N is, the smaller Δf is. The frequency domain FFT result data sequence for each section is FFT result k (k=0, 1, . . . , 2 N −1), the correlation calculation device 222 calculates (FFT result k) at time ti×(FFT result l) at time tj. * Calculate (k, l=0,1,··,2 N -1) The correlation is obtained by performing inverse FFT on each multiplication result.

[0052] The data selection device 223 performs a data string selection process to select data strings based on the correlation obtained in S04 (S05: data string selection process). Here, the data selection device 223 selects data strings whose correlation is equal to or greater than a threshold as data strings to be stored in the storage device 23, and selects data strings whose correlation is less than the threshold as data strings not to be stored in the storage device 23.

[0053] The data strings whose correlation is equal to or greater than the threshold are stored in the storage device 23 (S06: storage process). Then, the transmitter 24 reads out the data strings whose correlation is equal to or greater than the threshold from the storage device 23, modulates the data strings, and transmits them to the earth station 3 via the transmitting antenna 25 (S07: transmission process). The transmitter 24 transmits to the earth station 3 status information of the flying object 2 at the time corresponding to the data strings (e.g., the position, speed, and acceleration of the flying object 2). This transmission may be performed together with the transmission of the data strings, or may be performed separately.

[0054] At the earth station 3, the transmitted data sequence and the status information of the aircraft 2 are received by the receiver 31 via the receiving antenna 30 (S08: receiving processing), and the information processing device 34 performs source position estimation processing to estimate the position of the radio wave source based on the data sequence, the status information of the aircraft 2, and the Doppler change rate (S09: source position estimation processing).

[0055] As described above, by performing FFT processing with multiple different FFT points, the frequency domain data sequence can be diversified, and correlations can be obtained at various frequency resolution units Δf. This makes it possible to select the data sequence necessary for analyzing location estimation even when the frequency band is unknown. The correlation calculation process and data sequence selection process can be collectively referred to as the matching band detection process.

[0056] [1-3. Actions and Effects] (1) The signal processing device 2A of this embodiment includes an AD conversion device 215 that converts signals received by the aircraft at different times for a predetermined period of time into time-domain data sequences for each time, an FFT processing device 221 that performs FFT processing on the time-domain data sequences for each time using a plurality of different fast Fourier transform (FFT) points and outputs frequency-domain FFT result data sequences for each FFT point, a correlation calculation device 222 that calculates the correlation between frequency-domain FFT result data sequences for different times at the same FFT point for each section based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device 215 and the same FFT point, and performs the calculation for each of a plurality of different FFT points, and a data sequence selection device 223 that selects data sequences whose correlation is equal to or greater than a threshold.

[0057] This allows us to estimate a data sequence containing a signal in an unknown frequency band from received signals with a low SNR, and this estimated data sequence can be used to estimate the location (e.g., latitude and longitude) of the source of the unknown signal.

[0058] (2) The aircraft 2 of this embodiment is equipped with a signal processing device 2A, a memory device 23 that stores a data string, and a transmitter 24 that transmits the data string stored in the memory device 23 to a ground station.

[0059] This allows only the data sequence necessary for detecting an unknown signal to be provided to the earth station 3. This eliminates the need for large-capacity storage devices and data lines compared to storing all data sequences of received signals and transmitting them to the earth station 3. In particular, even small satellites with limited payload capacity can be used to detect unknown signals. In general, to capture signals from unknown sources, it is necessary to sample the received signal over a wide bandwidth, which requires increasing the sampling frequency of the AD converter. However, small satellites have limitations on the storage capacity for storing sampled data and the amount of data downlinked to the ground station, making it difficult to increase the sampling frequency. On the other hand, this embodiment provides only the data sequence necessary for signal detection to the earth station 3, thereby eliminating the above-mentioned limitations.

[0060] [2. Second Embodiment] The second embodiment will be described. Only the configuration that differs from the first embodiment will be described, and a description of the same configuration will be omitted. In the second embodiment, the digital signal processing performed in the first embodiment is performed in the earth station 3.

[0061] Fig. 10 is a diagram showing the configuration of a signal processing system according to the second embodiment. As shown in Fig. 10, in the second embodiment, a digital signal processing device 22 is provided in an earth station 3 instead of an aircraft 2. Therefore, in the aircraft 2, digital I and Q signals from a receiver 21 are stored in a storage device 23, and the signals are transmitted to the earth station 3 via a transmitter 24 and a transmitting antenna 25.

[0062] In the earth station 3, the digital I and Q signals from the flying object 2 are received by a receiving antenna 30 and a receiver 31, and the received signals are input to an information processing device 34. The information processing device 34 of this embodiment is equipped with a digital signal processing device 22, and performs FFT processing, correlation calculation processing, data selection processing, and source position estimation processing, as in the first embodiment.

[0063] 3. Third Embodiment The third embodiment will be described. Only the configurations that are different from the second embodiment will be described, and the same configurations will not be described. Unlike the first and second embodiments, the third embodiment receives radio waves using multiple flying objects 2.

[0064] 11 is a diagram showing the relative positions of multiple flying objects, earth stations, and transmission sources according to the third embodiment. The signal processing system 1 of this embodiment comprises two flying objects 2, one of which is a primary satellite and the other a secondary satellite. Each flying object 2 simultaneously receives radio waves, and digital I and Q signals that have been AD converted at the same sampling frequency fs in each receiver 21 are stored in a storage device 23. These signals are then transmitted to the earth station 3 via each transmitter 24 and transmitting antenna 25.

[0065] In the earth station 3, the digital I and Q signals from the flying object 2 are received by the receiving antenna 30 and receiver 31, and the received signals are input to an information processing device 34. The digital signal processing device 22 of the information processing device 34 performs FFT processing, correlation calculation processing, data selection processing, and source position estimation processing, as in the first and second embodiments. However, the source position estimation processing takes into account the data delay and Doppler correlation of the downlinked data from the primary and secondary satellites.

[0066] In the second embodiment, correlations were calculated between different times for a single flying vehicle 2, whereas in the third embodiment, correlations are calculated between different positions using signals received at the same time by the primary satellite and secondary satellite. That is, the time domain data sequence at each time and the frequency domain FFT result data sequence at each time in the second embodiment are replaced with the time domain data sequence at each position and the frequency domain FFT result data sequence at each position in this embodiment.

[0067] 4. Other Embodiments Another embodiment will be described. Only the configurations that are different from the above embodiment will be described, and the description of the same configurations will be omitted.

[0068] In other embodiments, the configuration of the receiver 21 and the configuration of the digital signal processing device 22 may be provided in either the aircraft 2 or the earth station 3, or may be provided separately in the aircraft 2 and the earth station 3. In other words, the AD conversion device 215, the FFT processing device 221, the correlation calculation device 222, and the data string selection device 223 may be provided in either the aircraft 2 or the earth station 3, respectively.

[0069] The signal processing device according to the embodiment of the present invention only needs to include at least the digital signal processing device 22, and may not include the AD conversion device 215, unlike the signal processing device 2A of the first embodiment.

[0070] In other embodiments of the present invention, the present invention may be a program that realizes the functions of the embodiments of the present invention described above and the processes shown in the flowcharts, or a computer-readable storage medium that stores the program.In still other embodiments, the present invention may be a method that realizes the functions of the embodiments of the present invention described above and the processes shown in the flowcharts.In still other embodiments, the present invention may be a server that can supply a program that realizes the functions of the embodiments of the present invention described above and the processes shown in the flowcharts to a computer.In still other embodiments, the present invention may be a virtual machine that realizes the functions of the embodiments of the present invention described above and the processes shown in the flowcharts.

[0071] In the processes or operations described above, the processes or operations can be freely changed as long as no inconsistencies in the processes or operations occur, such as the use of data that should not yet be available in a certain step. Furthermore, the embodiments described above are merely examples for explaining the present invention, and the present invention is not limited to these examples. The present invention can be embodied in various forms without departing from the spirit of the invention. [Explanation of symbols]

[0072] 1. Signal Processing System 2. Aircraft 20 receiving antenna 21 Receiver 211 Low Noise Amplifier 212 Interference suppression filter 213 Direct Conversion 214 Anti-aliasing filter 215 AD conversion device 216 Local Oscillator 217 Clock Generator 22 Digital Signal Processing Device 23 Storage device 24 Transmitter 25 transmitting antennas 26 Location information acquisition device 26 27 Communication antenna 28 Communication transceiver 28 29 Control Device 3 earth station 30 receiving antenna 31 Receiver 32 Communication antenna 33 Communication Transceiver 34 Information processing equipment

Claims

1. an AD converter that converts signals received by one or more aircraft at different times or positions for a predetermined period of time into time domain data sequences for each time or position; an FFT processing device that performs a Fast Fourier Transform (FFT) process on the time domain data sequence at each time or position at a plurality of different FFT points, and outputs a frequency domain FFT result data sequence at each FFT point; a correlation calculation device that calculates a correlation between frequency domain FFT result data strings at different times or positions with the same FFT point number for each section based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device and the same FFT point number, and that performs the calculation for each of the plurality of different FFT point numbers; a data string selection device that selects data strings whose correlation is equal to or greater than a threshold; A signal processing device comprising:

2. The data sequence is a frequency domain FFT result data sequence at an FFT point where the correlation is equal to or greater than a threshold. The signal processing device according to claim 1 .

3. The data sequence is the time domain data sequence corresponding to the frequency domain FFT result data sequence at the FFT point number where the correlation is equal to or greater than a threshold. The signal processing device according to claim 1 .

4. the correlation calculation device multiplies the frequency domain FFT result data sequence for each section at a first time by a complex conjugate of the frequency domain FFT result data sequence for each section at a second time for the same number of FFT points, and performs an inverse FFT process on the multiplication result to calculate the correlation; The signal processing device according to claim 1 .

5. the data string selection device selects the data string by performing a constant false alarm rate (CFAR) process on the correlation; The signal processing device according to claim 1 .

6. the signals include signals received at the one or more air vehicles at different center frequencies; The signal processing device according to claim 1 .

7. A signal processing device according to any one of claims 1 to 6; a storage device that stores the data string; a transmitter for transmitting the data stream stored in the storage device to an earth terminal; An aircraft equipped with the above.

8. An earth station comprising the signal processing device according to any one of claims 1 to 6.

9. 1. A signal processing system comprising one or more air vehicles and an earth station, an AD converter that converts signals received by the one or more flying objects for a predetermined period of time at different times or positions into time domain data sequences for each time or position; an FFT processing device that performs a Fast Fourier Transform (FFT) process on the time domain data sequence at each time or position at a plurality of different FFT points, and outputs a frequency domain FFT result data sequence at each FFT point; a correlation calculation device that calculates a correlation between frequency domain FFT result data strings at different times or positions with the same FFT point number for each section based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device and the same FFT point number, and that performs the calculation for each of the plurality of different FFT point numbers; a data string selection device that selects data strings whose correlation is equal to or greater than a threshold; A signal processing system comprising:

10. The devices are provided in either the aircraft or the earth station.

10. The signal processing system of claim 9.

11. The devices are provided in a distributed manner in the aircraft and the earth station.

10. The signal processing system of claim 9.

12. 1. A method of signal processing, comprising: One or more computers A signal received by one or more aircraft at different times or positions for a predetermined period of time is converted into a time domain data sequence for each time or position by A / D conversion; performing a Fast Fourier Transform (FFT) on the time domain data sequence at each time or position at a plurality of different FFT points, and outputting frequency domain FFT result data sequences at each FFT point; calculating a correlation between frequency domain FFT result data sequences at different times or positions for the same FFT point number for each section based on a frequency resolution unit that is based on the sampling frequency of the AD conversion device and the same FFT point number, and performing the calculation for each of the plurality of different FFT point numbers; selecting a data sequence whose correlation is equal to or greater than a threshold value; method.

13. A program that causes one or more computers to carry out the method of claim 12.

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