Radio positioning system for unmanned aerial vehicles on mars

Abstract

A radio positioning system applied to a Mars unmanned aerial vehicle belongs to the field of radio positioning in radio technology. The present application aims at the problem that the Mars unmanned aerial vehicle cannot be effectively positioned by external means. Four antennas are arranged at the four corners of the front surface of a square PCB to form a planar pseudo-Doppler antenna circular array; four microwave switches, a baseband circuit and a single-chip microcomputer are arranged on the front surface of the PCB; four-way microstrip radio frequency transmission lines, four sets of TOF ranging chips and peripheral circuits are arranged on the back surface of the PCB; each antenna is connected to a microwave switch, the microwave switch is connected to the starting end of a microstrip radio frequency transmission line, the ending ends of the four-way microstrip radio frequency transmission lines are connected to the baseband circuit after converging at the center point of the square PCB; each set of TOF ranging chip and peripheral circuit is arranged close to an antenna and connected to the antenna through the microwave switch; the microwave switch is controlled by the single-chip microcomputer to position the unmanned aerial vehicle based on signals. The present application is used for radio positioning.

Description

TECHNICAL FIELD

[0001] The present application relates to a radio positioning system applied to a Mars unmanned aerial vehicle, and belongs to the field of radio positioning in radio technology. BACKGROUND

[0002] With the development of space technology, the form of extraterrestrial probes is gradually diversified, from satellite on-orbit observation to landing in-situ probes, and mobile exploration vehicles and aircraft have appeared. Taking Mars as an example, an unmanned aerial vehicle has been successfully launched on Mars. Due to the thin air on Mars, the lift generated by the Mars unmanned aerial vehicle is very limited, so the weight of each subsystem is strictly limited. The distance between Mars and the Earth is too large, and the communication delay is too high, so the probe cannot be remotely controlled in real time on the ground, and therefore all actions such as navigation, guidance and control must be performed autonomously by the on-board computer, which puts higher requirements on the performance of the on-board computer. On the other hand, in order to ensure reliability, the probe usually uses a combined navigation method to correct the cumulative error of inertial navigation, but for the Mars unmanned aerial vehicle, since the global satellite navigation system cannot be used on Mars, the on-board navigation system lacks a reliable positioning reference, which limits its range of activities. Therefore, an external positioning reference is needed to correct the cumulative error of inertial navigation.

[0003] Radio direction finding technology is a technology that uses an antenna array to receive a radio signal and calculates the relative direction (the direction of arrival) between the receiver and the source according to the differences in the signals received by the antenna elements, which is suitable for relatively open scenarios and is currently applied to civil aviation passenger aircraft, ship positioning and other aspects. Through radio direction finding, combined with the distance between the receiver and the source, positioning can be performed, and the measurement result of this positioning method is independent and has no cumulative error. Radio direction finding can usually achieve passive direction finding, which only needs to passively receive the incoming signal, which is beneficial to saving energy. However, existing radio direction finding equipment usually needs a large antenna array and a relatively complex receiving device to achieve high-precision real-time incoming direction estimation.

[0004] In summary, for the Mars unmanned aerial vehicle, there is currently no perfect external positioning method. SUMMARY

[0005] In view of the problem that the Mars unmanned aerial vehicle cannot be effectively positioned by external means, the present application provides a radio positioning system applied to a Mars unmanned aerial vehicle.

[0006] The radio positioning system applied to a Mars unmanned aerial vehicle of the present application comprises: one antenna is arranged at each of the four corners of the front surface of a square PCB, forming a planar pseudo-Doppler antenna circular array; four microwave switches, a baseband circuit and a single-chip microcomputer are further arranged on the front surface of the square PCB; four-way microstrip radio frequency transmission lines, four sets of TOF distance measuring chips and peripheral circuits are arranged on the back surface of the square PCB.

[0007] Each antenna is connected with a microwave switch, and each microwave switch is connected with the head end of a microstrip radio frequency transmission line, and the terminal of the four microstrip radio frequency transmission lines is connected with the baseband circuit after converging to the center point of the square PCB; the microwave switch is controlled by a single-chip microcomputer; each set of TOF ranging chip and peripheral circuit is arranged close to an antenna and connected with the antenna through the corresponding microwave switch;

[0008] The microwave switch is controlled by a single-chip microcomputer to realize direction finding or distance measurement.

[0009] When used for direction finding, the four antennas in the planar pseudo-Doppler antenna circular array are controlled by a single-chip microcomputer to be switched on in turn at a frequency of 4 kHz, simulating the state of a single antenna rotating at a frequency of 1 kHz; each antenna receives a plane wave signal generated from a slave end source, and the microwave switch, under the control of a single-chip microcomputer control signal, transmits the plane wave signal received by the corresponding antenna to the baseband circuit through the microstrip radio frequency transmission line to obtain a preprocessed plane wave signal after frequency conversion and filtering, and then transmits the preprocessed plane wave signal to the single-chip microcomputer; the single-chip microcomputer obtains the frequency components corresponding to the frequency shift of the multi-Doppler after FM demodulation of the received signal, and extracts the phase of the preprocessed plane wave signal under the frequency components to obtain the plane wave direction of arrival.

[0010] When used for distance measurement, the single-chip microcomputer controls the corresponding microwave switch to make a selected set of TOF ranging chip and peripheral circuit communicate with the antenna; the selected set of TOF ranging chip and peripheral circuit sends a distance measurement signal to the slave end source through the antenna, and the single-chip microcomputer calculates the distance between the positioning system and the slave end according to the distance measurement response signal of the slave end.

[0011] The slave end is a known slave end.

[0012] According to the direction finding result of the plane wave direction of arrival and the distance measurement result of the distance between the positioning system and the slave end, the Mars unmanned aerial vehicle is positioned.

[0013] According to the radio positioning system applied to the Mars unmanned aerial vehicle, the antenna is an omnidirectional antenna, the coaxial line interface is connected with the microwave switch through the microstrip line, and the microwave switch is close to the coaxial line interface.

[0014] According to the radio positioning system applied to the Mars unmanned aerial vehicle, each antenna, the corresponding microwave switch and the microstrip radio frequency transmission line form a group of signal units, and the four groups of signal units are centrally symmetrically distributed with the center point of the PCB as the center.

[0015] The microwave switch is a reflection type switch adopting a patch type package and working at a 2.4G frequency band, and has a radio frequency signal input port, a control signal port, a signal output port A and a signal output port B.

[0016] For direction finding, the radio frequency signal input port is used for receiving a plane wave signal, and the control signal port is used for receiving a control signal of a single-chip microcomputer; the control signal is a high level signal and a low level signal; the control signal port makes the signal output port A conductive according to the received control signal, and signal transmission is performed, and meanwhile, the other signal output port is not conductive.

[0017] For distance measurement, the direction finding function is closed; the radio frequency signal input port is used for receiving a distance measurement signal sent by a selected set of TOF distance measurement chips and peripheral circuits; the control signal port makes the output port B conductive according to the received control signal of the single-chip microcomputer, so that the distance measurement signal is sent to the antenna through the output port B, and the antenna sends the distance measurement signal to the signal source at the slave end.

[0018] The square PCB has a geometric size of not more than 10*10 cm.

[0019] Each microstrip radio frequency transmission line has an impedance of 50 ohms, and a length of an integer multiple of 1 / 4 lambda, wherein lambda is the wavelength of a 2.4G frequency band signal in the microstrip radio frequency transmission line; when one microstrip radio frequency transmission line transmits a signal, the input impedance of the other three microstrip radio frequency transmission lines is in an open circuit state.

[0020] The terminals of the four microstrip radio frequency transmission lines are connected at the center point of the square PCB and form a cross layout, each microstrip radio frequency transmission line extends in a zigzag manner from the first end to the terminal, and a circular arc is used at the zigzag corner.

[0021] The baseband circuit includes a down-conversion module composed of a radio frequency front end I / Q modulation and demodulation chip and its peripheral circuit, and a differential to single end and low pass filter module composed of a double-channel integrated operational amplifier and its peripheral circuit.

[0022] The plane wave signal transmitted by the microstrip radio frequency transmission line is converted into a differential signal by a balun in the baseband circuit, and then enters the down-conversion module to obtain I\Q two-channel differential signals, and then the differential to single end and low pass filter module outputs low frequency band I\Q two-channel single end signals as preprocessed signals to the single-chip microcomputer.

[0023] The method for FM demodulation of the received signal by the single-chip microcomputer of the radio positioning system applied to the unmanned aerial vehicle of Mars according to the application comprises the following steps:

[0024] Supposing that the plane wave signal generated by the signal source is f(t):

[0025]

[0026] In the formula, f is a carrier frequency, ω is a carrier angular frequency, c is a carrier signal initial phase, and t is time; c

[0027] Four antennas are switched on in turn, and four plane wave signals are integrated in time sequence into one, and the signal S(t) entering the baseband circuit is: n

[0028]

[0029] In the formula, n is the number of the antenna, B n is the amplitude of the plane wave signal received by the nth antenna, is a carrier signal phase, D is the diameter of the pseudo-Doppler antenna circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna when t=0;

[0030] After the signal S n (t) is processed by the baseband circuit, the preprocessed plane wave signal obtained is a low-frequency I\Q two-way single-ended signal;

[0031] The single-chip microcomputer performs an inverse tangent operation on the low-frequency I\Q two-way single-ended signal, and the instantaneous phase φ(t) of the plane wave signal is obtained:

[0032]

[0033] In the formula, Δf is the Doppler frequency shift generated by the switching-on of the four antennas in turn; when the ratio of the horizontal height difference between the signal source and the antenna and the distance from the signal source to the center of the pseudo-Doppler antenna circular array is less than 1 / 10, the elevation angle ε of the plane wave signal is regarded as 0, and cosε is regarded as 1;

[0034] The instantaneous frequency ω(t) of the plane wave signal is obtained by deriving the instantaneous phase φ(t):

[0035]

[0036] Thus, the FM demodulation of the received signal by the single-chip microcomputer is realized.

[0037] The method for obtaining the plane wave direction of arrival of the radio positioning system applied to the unmanned aerial vehicle of Mars according to the application comprises the following steps:​​​

[0038] FFT transform the instantaneous frequency w(t) to get the planar wave signal spectrum diagram; the frequency component corresponding to the antenna rotation contained in the spectrum diagram is the frequency component corresponding to the Doppler shift; the frequency component is expressed as a complex number, and the phase of the complex number frequency component is obtained to get the incoming angle with constant offset

[0039]

[0040] In the formula, θ0 represents the constant offset, and θ is calculated to determine the planar wave incoming direction.

[0041] The beneficial effects of the present application: the system has the characteristics of high integration, small size and low power consumption, and is a narrowband radio positioning system.

[0042] The system adopts PCB technology, and selects a 2.4G frequency band with a shorter wavelength in the signal frequency band, realizes the miniaturization of the antenna array and the integration of the signal processing system, and greatly reduces the volume and weight of the system. In the case of long distance, the signal source signal is considered as a kind of plane wave. The fast switching between the four antenna units is used to simulate the rotation of a single antenna, the radio frequency signal is received, the radio frequency signal is down-converted, filtered, amplified and other processed by the baseband circuit, and finally sent to the single-chip microcomputer for AD sampling. The signal processing is carried out in the single-chip microcomputer, the phase change value of the switching frequency signal is obtained by processing the received signal, and the wave direction of the signal is calculated by using the result. At the same time, the distance is measured based on the slave end set by the TOF distance measuring chip, so as to realize the radio positioning of the Mars unmanned vehicle.

[0043] The system is integrated in a small volume PCB, uses fewer components and materials, occupies smaller volume and weight, realizes radio positioning, and can be applied to radio positioning and autonomous navigation of Mars unmanned vehicles or other space probes with strict weight and volume constraints.

[0044] The system only connects one antenna at the same time, and only uses a single receiver to complete, which can save equipment weight and complexity. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a structure schematic diagram of the radio positioning system applied to the Mars unmanned vehicle according to the present application;

[0046] Figure 2 is a layout schematic diagram of four-way microstrip radio frequency transmission lines on the back of a square PCB;

[0047] Figure 3 is a signal transmission flowchart of the radio positioning system applied to the Mars unmanned vehicle according to the present application;

[0048] Figure 4 is a signal processing flow chart in baseband circuitry;

[0049] Figure 5 is a signal processing flow chart of a single-chip microcomputer;

[0050] Figure 6 is a principle schematic diagram of the system in a ranging state. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0052] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0053] The present application will be further described below in combination with the drawings and specific embodiments, but is not limited to the present application.

[0054] Specific embodiment one, in combination Figures 1 to 3 and Figure 6 As shown in the drawings, the present application provides a radio positioning system applied to a Mars unmanned aerial vehicle, comprising,

[0055] The entire system is distributed on a square PCB board, one antenna 1 is arranged at each of the four corner positions on the front surface of the square PCB board, to form a planar pseudo-Doppler antenna circular array; four microwave switches 3, baseband circuitry 4 and a single-chip microcomputer 5 are further arranged on the front surface of the square PCB board; four-way microstrip radio frequency transmission lines 2, four sets of TOF ranging chips and peripheral circuits are arranged on the back surface of the square PCB board;

[0056] Each antenna is connected to one microwave switch, and the first end of each microwave switch is connected to one way of the microstrip radio frequency transmission line; the terminal ends of the four-way microstrip radio frequency transmission lines are converged to the center point of the square PCB board, and then connected to the baseband circuitry; the microwave switches are controlled by the single-chip microcomputer; each set of TOF ranging chip and peripheral circuit is arranged close to one antenna, and connected to one antenna through the corresponding microwave switch;

[0057] The microwave switches are controlled by the single-chip microcomputer to realize direction finding or ranging:

[0058] For direction finding, four antennas in the planar pseudo-Doppler antenna circular array are switched on by single-chip microcomputer control at a frequency of 4 kHz in turn, simulating the state of a single antenna rotating at a frequency of 1 kHz; each antenna receives a plane wave signal generated from a slave end source, and a microwave switch transmits the plane wave signal received by the corresponding antenna to the baseband circuit through a microstrip radio frequency transmission line under the control of a single-chip microcomputer control signal, and obtains a pre-processed plane wave signal after frequency conversion and filtering, and then transmits the pre-processed plane wave signal to the single-chip microcomputer; the single-chip microcomputer obtains the frequency component corresponding to the frequency shift of the received signal after FM demodulation, and extracts the phase of the pre-processed plane wave signal under the frequency component to obtain the plane wave direction of arrival;

[0059] For ranging, the single-chip microcomputer controls the corresponding microwave switch to make a selected set of TOF ranging chips and peripheral circuits communicate with the antenna; the selected set of TOF ranging chips and peripheral circuits send a ranging signal to the slave end source through the antenna, and the single-chip microcomputer calculates the distance between the positioning system and the slave end according to the ranging response signal of the slave end.

[0060] The slave end is a known and set slave end.

[0061] According to the direction finding result of the plane wave direction of arrival and the ranging result of the distance between the positioning system and the slave end, the Mars unmanned aerial vehicle is positioned.

[0062] The square PCB also integrates a power supply part 6 for supplying power to the baseband circuit 4 and the single-chip microcomputer 5. The square PCB also carries a 422 serial port output interface for outputting the direction finding result to the upper computer through the serial port.

[0063] The positioning system serves as the master end, and the single-chip microcomputer can calculate the distance between the master and the slave according to the time difference between the master sending a ranging signal to the slave and the slave receiving the response signal. In the embodiment, the slave end can send a 2.4 GHz radio frequency signal outward, which can serve as a direction finding signal source or a TOF ranging chip ranging slave.

[0064] The working principle of the system of the application is as follows:

[0065] Suppose a fixed-location beacon transmits a direction-finding signal. Over long distances, this signal can be considered a plane wave. For a plane wave arriving at a pseudo-Doppler antenna array at a certain angle, each antenna element receives a signal that is slightly delayed or advanced relative to other antenna elements. The switching between antenna elements causes a phase step discontinuity in the received signal. This signal, after passing through an FM demodulator, generates pulses. These pulses are essentially sampling points on a continuous sine wave, with a period equal to the time it takes for a single analog antenna to rotate once, which is the time required for all antenna elements to switch once. By employing strict time synchronization control in the program and then performing FM demodulation, the direction of the incoming wave can be extracted.

[0066] In this embodiment, the antenna is an omnidirectional antenna, connected to a microwave switch via a microstrip line using a coaxial cable interface; the microwave switch is located near the coaxial cable interface. The four antennas in the pseudo-Doppler antenna circular array are located on the same plane and are of the same model.

[0067] Each antenna, along with its corresponding microwave switch and microstrip RF transmission line, forms a signal unit. The four signal units are centrally symmetrically distributed around the center point of the PCB board. In this embodiment, the antenna positions, the positions of the microwave switches and peripheral circuit components, and the geometry of the RF transmission line are all strictly centrally symmetrical about the center of the antenna array.

[0068] Furthermore, the microwave switch is a surface-mount packaged reflective switch operating in the 2.4 GHz band, and has an RF signal input port, a control signal port, a signal output port A, and a signal output port B;

[0069] When used for direction finding, the RF signal input port is used to receive plane wave signals, and the control signal port is used to receive control signals from the microcontroller; the control signals are high-level signals and low-level signals; the control signal port turns on signal output port A to transmit signals according to the high or low level of the received control signals, and at the same time turns off the other signal output port; the microcontroller sends control signals through GPIO.

[0070] When used for distance measurement, the direction finding function is closed; the radio frequency signal input port is used to receive the distance measurement signal sent by a selected set of TOF distance measurement chips and peripheral circuits; the control signal port makes the output port B conductive according to the control signal received by the single-chip microcomputer, so that the distance measurement signal is sent to the antenna through the output port B, and the antenna sends the distance measurement signal to the signal source at the slave end. The single-chip microcomputer can control whether the TOF distance measurement chip is connected to the antenna and whether the system enters the distance measurement state by controlling the on-off of the microwave switch. When entering the distance measurement state, the direction finding function is closed, a TOF distance measurement chip is selected by the single-chip microcomputer, and the antenna is connected to the chip. The single-chip microcomputer communicates with the TOF distance measurement chip through the SPI bus, sends the direction finding signal to the slave end, calculates the master-slave distance according to the response signal of the slave, and calculates the position of the slave relative to the master according to the distance measurement result and the direction finding result, thereby realizing the positioning of the master relative to the slave.

[0071] As an example, the geometric size of the square PCB board does not exceed 10*10 cm, and a 6-layer stacking scheme is adopted. The stacking structure from top to bottom is non-radio frequency circuit layer L1, power supply layer L2, signal layer L3, ground layer L4, ground layer L5, and signal layer L6. The microstrip radio frequency transmission line is located in the L6 layer.

[0072] In this embodiment, the microstrip radio frequency transmission line is 4 microstrip lines on the PCB board, each line starts from the microwave switch near each antenna port and converges at the center, and then changes from 4 paths to 1 path into the baseband circuit. The impedance of each microstrip radio frequency transmission line is 50 ohms; in order to prevent mutual interference between the four antennas, since the microwave switch is selected to be reflective, combined with the 1 / 4 wavelength impedance transformation property of the transmission line, the length of each microstrip radio frequency transmission line is controlled to be an integer multiple of 1 / 4λ, where λ is the wavelength of the 2.4G frequency band signal propagating in the microstrip radio frequency transmission line; when one microstrip radio frequency transmission line transmits a signal, from the perspective of the convergence point as an input port, the input impedance of the other three microstrip radio frequency transmission lines is in an open circuit state.

[0073] As an example, considering the layout of components, system weight, etc., the length of the microstrip radio frequency transmission line is selected to be 5 / 4λ.

[0074] In combination with Figure 2 As shown in the figure, the terminals of the four microstrip radio frequency transmission lines are connected at the center point of the square PCB board and form a cross layout, and each microstrip radio frequency transmission line extends in a zigzag shape from the first end to the terminal. In order to reduce signal reflection, a circular arc is used at the zigzag corner.

[0075] The microstrip radio frequency transmission line transmits the signal of the antenna array to the baseband circuit, and at the same time avoids interference between the four microstrip lines of the microstrip radio frequency transmission line by controlling the length.

[0076] Furthermore, in combination withFigure 4 The baseband circuit includes a down-conversion module composed of a zero intermediate frequency architecture radio frequency front end I / Q modulation and demodulation chip and its peripheral circuit operating at 2.4G frequency band and a differential to single end and low pass filter module composed of a double path integrated operational amplifier and its peripheral circuit;

[0077] The planar wave signal (single end signal) transmitted by the microstrip radio frequency transmission line is converted into a differential signal by a balun in the baseband circuit, and then enters the down-conversion module to obtain the I / Q two-way differential signal at zero intermediate frequency. Then the differential to single end and low pass filter module outputs the I / Q two-way single end signal at a low frequency band (about 10 kHz) as the pre-processed signal to the single chip microcomputer AD sampling port. The baseband circuit is only responsible for the analog signal processing from the radio frequency signal to the baseband signal.

[0078] The LO oscillation frequency inside the I / Q modulation and demodulation chip can be changed by modifying the internal register, and the register can be modified by SPI. In the system, the SPI communication interface is reserved for the single chip microcomputer 5 and the I / Q modulation and demodulation chip, and the register of the I / Q modulation and demodulation chip can be modified by the single chip microcomputer 5. By default, the LO frequency f LO is 2436.999512 MHz. The I / Q modulation and demodulation chip down-converts the radio frequency signal with a carrier frequency f c to a baseband signal with a frequency f IF = f LO- f c . For example, when a signal with a carrier frequency f c of 2436.99 MHz needs to be received, the signal is first down-converted to f IF = 2436.999512-2436.99 = 0.009512 MHz = 9.512 kHz in the I / Q modulation and demodulation chip, and then the high frequency components such as image frequency are filtered out by a low pass filter, and finally the I / Q orthogonal two-way baseband signal with an intermediate frequency of 9.512 kHz is output for the next processing stage.

[0079] In order to avoid high frequency signal interference and increase the signal amplitude for sampling, the signal is sent to a low pass filter composed of an operational amplifier after passing through the I / Q modulation and demodulation chip, and the cutoff frequency of the low pass filter is about 24 kHz. Since the signal output by the I / Q modulation and demodulation chip is a differential signal, it also needs to be converted to a single end signal at the filter. The I / Q two-way signal output by the low pass filter is sent to the single chip microcomputer for sampling.

[0080] The power supply section 6 includes multiple low-dropout linear regulators (LDOs) and DC-DC circuits, distributed at different locations on the PCB. The system's total power input is 5V, which is then supplied to each LDO. The LDO output voltages include 3.3V and 2.85V, supplying power to the microcontroller and I / Q modem chips. The DC-DC output is ±5V, used to power the operational amplifiers.

[0081] In this embodiment, the microcontroller mainly undertakes the functions of microwave switch switching control, direction finding signal acquisition and processing, direction finding result output, and system status indication. A serial port and a program debugging port are reserved for external access.

[0082] In this embodiment, a circular array of pseudo-Doppler antennas receives 2.4G direction-finding signals from a source. The signals from each antenna are combined into a single serial signal according to their conduction timing. The signals received by the antennas are down-converted and filtered in the baseband circuit before entering the microcontroller. The microcontroller receives both I and Q signals and stores the corresponding signals received by each antenna in its memory according to the antenna switching time. The direction-finding result is obtained by using the microcontroller to extract the phase of each antenna signal, compare the phases, and take the average value.

[0083] Example:

[0084] Assuming the signal source is a 2436.99MHz signal generated by a radio signal source, the system described in this invention is applicable to all signals in the 2.4GHz band under the ISM band.

[0085] Combination Figure 3 As shown, the microcontroller 5 sends a control signal to the microwave switch group to control the antenna elements in the planar four-antenna circular array to turn on in turn to receive the direction finding signal. Then the signal first enters the baseband circuit 4 for down-conversion and filtering, and then is sent to the microcontroller 5.

[0086] Combination Figure 5 As shown, after the microcontroller 5 receives the signal from the baseband circuit 4, it first passes through a digital low-pass filter, which further removes most of the noise outside the target received signal; then it performs FM demodulation, and then uses FFT transformation to find the frequency component corresponding to the antenna rotation, extracts the signal phase under this component, and finally obtains the direction of arrival.

[0087] Combination Figure 5 As shown, the methods for FM demodulation of received signals by a microcontroller include:

[0088] When the signal source is far enough away from the antenna array, the incoming wave can be considered a plane wave. The antenna array radius is r, and the angle between the incoming wave and the antenna at t=0 is θ. Consider the case where the antenna rotates one revolution, that is, the four antennas are turned on in turn once:

[0089] Assume that the plane wave signal generated by the signal source is f(t):

[0090]

[0091] where f c is the carrier frequency, ω c is the carrier angular frequency, is the initial phase of the carrier signal, and t is time;

[0092] The four antennas are switched on in turn, and the four plane wave signals are integrated in time sequence into one, and the signal entering the baseband circuit is S n (t):

[0093]

[0094] where n is the number of antennas, B n is the amplitude of the plane wave signal received by the nth antenna, is the phase of the carrier signal, D is the diameter of the pseudo-Doppler antenna circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna at t=0;

[0095] After the signal S n (t) is processed by the baseband circuit, it is down-converted and quadrature-decomposed in the I / Q modulation and demodulation chip to obtain a pre-processed plane wave signal in the low-frequency I / Q two-way single-ended signal; the signal is output to the single-chip microcomputer 5, sampled by the ADC of the single-chip microcomputer 5, and stored in the on-chip memory. Subsequent signal processing is performed in the single-chip microcomputer 5.

[0096] The single-chip microcomputer performs arctangent operation on the low-frequency I / Q two-way single-ended signal to obtain the instantaneous phase φ(t) of the plane wave signal:

[0097]

[0098] where is the Doppler frequency shift generated by the rotation of the antenna, which is a single-frequency sine signal, and the carrier frequency is the rotation frequency of the single antenna, is the phase change due to carrier modulation. For this embodiment, the carrier is not modulated, so this item can be ignored. When the ratio of the horizontal height difference between the signal source and the antenna to the distance from the signal source to the center of the pseudo-Doppler antenna circular array is less than 1 / 10, that is, the horizontal height difference between the signal source and the antenna is much smaller than the distance from the signal source to the center of the pseudo-Doppler antenna circular array, the elevation angle ε of the plane wave signal is considered to be 0, coSε and 1.

[0099] The derivative of the instantaneous phase φ(t) is calculated, and the difference operation is performed on the discrete signal collected by the single-chip microcomputer to obtain the instantaneous frequency ω(t) of the plane wave signal.

[0100]

[0101] Thus, the single-chip microcomputer realizes FM demodulation of the received signal.

[0102] The method for obtaining the direction of arrival of the plane wave is as follows:

[0103] The FFT transform is performed on the instantaneous frequency ω(t) to obtain a spectrum diagram of the plane wave signal; the frequency component corresponding to the rotation of the antenna in the spectrum diagram is the frequency component corresponding to the Doppler shift; due to the existence of noise in the actual system and the influence of the high-order harmonic, noise components and high-order harmonic components exist in the spectrum diagram, but the signal corresponding to the above formula is the fundamental wave, and the amplitude is the largest in the spectrum diagram, so only the component corresponding to the largest amplitude in the spectrum diagram is the component corresponding to the instantaneous frequency ω(t). The frequency component is stored in the single-chip microcomputer in the form of a complex number, and the phase of the complex number frequency component is obtained to obtain the direction of arrival with a constant offset

[0104]

[0105] In the formula, θ0 represents the constant offset, and θ is calculated to determine the direction of arrival of the plane wave.

[0106] In the above formula, represents the direction of arrival of the output before calibration, and the constant offset θ0 can be determined through experimental calibration.

[0107] In the ranging state, the single-chip microcomputer controls four sets of TOF ranging chips and peripheral circuits carried by the system through the SPI bus, selects one set to activate, and enters the ranging working mode. The master sends a ranging request signal to the slave and starts timing, and the slave records the signal processing time after receiving the signal, and then sends a response signal, which contains the signal processing time t r ; the master stops timing after receiving the response signal, and obtains the time difference t0; the slave processing signal time t r is read from the response signal, and the actual signal flight time is t=t0-t r ; according to the time t, combined with the radio wave propagation speed c, the distance d between the master and the slave can be obtained, and the ranging is completed.

[0108] The angle information between the master and the slave is obtained by direction finding, and the distance information between the master and the slave is obtained by ranging, so that the position of the master relative to the slave can be obtained, and the positioning effect is realized.

[0109] CombinedFigure 6 As shown, the system of the application has two working states: direction finding state and communication state, and the two states will not occur simultaneously due to the multiplexing design of the antenna.

[0110] When the system works in the direction finding state, the single-chip microcomputer controls the microwave switch to select the antenna in turn, and the direction finding signals received by the antenna are transmitted to the radio frequency front end in turn.

[0111] When the system works in the communication state, the single-chip microcomputer controls the microwave switch to connect one of the antennas to a group of TOF ranging chip communication channels for TOF ranging chip communication and ranging.

[0112] In summary, the application uses high-speed switching among the four antenna units to receive the direction finding signals, and uses the single-chip microcomputer 5 to extract the pseudo-Doppler characteristics of the incoming wave signals and obtain the three-dimensional spatial wave direction of the direction finding signals.

[0113] Although the application has been described herein with reference to particular embodiments thereof, it will be understood that these embodiments are merely examples of the principles and application of the application. It will be understood that many modifications can be made to the example embodiments, and that other arrangements can be devised without departing from the spirit and scope of the application as defined by the appended claims. It will be understood that different dependent claims and features described herein can be combined with each other in ways other than those described in the original claims. It will also be understood that features described in connection with individual embodiments can be used in other described embodiments.

Claims

1. A radio positioning system for application to a Mars unmanned aerial vehicle, characterized in that, Comprising, Four antennas are arranged at the four corners of the front surface of the square PCB board to form a planar pseudo-Doppler antenna circular array; four microwave switches, a baseband circuit and a single-chip microcomputer are arranged on the front surface of the square PCB board; four microstrip radio frequency transmission lines, four sets of TOF ranging chips and peripheral circuits are arranged on the back surface of the square PCB board; Each antenna is connected to a microwave switch, and the first end of each microwave switch is connected to a microstrip radio frequency transmission line; the terminal ends of the four microstrip radio frequency transmission lines converge at the center point of the square PCB board and are connected to the baseband circuit; the microwave switches are controlled by the single-chip microcomputer; each set of TOF ranging chip and peripheral circuit is arranged close to an antenna and is connected to the antenna through the corresponding microwave switch; The on-off of the microwave switch is controlled by the single-chip microcomputer to realize direction finding or distance measurement: When used for direction finding, the four antennas in the planar pseudo-Doppler antenna circular array are controlled by the single-chip microcomputer to be switched on in turn at a frequency of 4kHz, simulating the state of a single antenna rotating at a frequency of 1kHz; each antenna receives a plane wave signal generated from a slave end signal source; under the control of the single-chip microcomputer control signal, the microwave switch transmits the plane wave signal received by the corresponding antenna to the baseband circuit through the microstrip radio frequency transmission line for frequency conversion and filtering to obtain a preprocessed plane wave signal which is transmitted to the single-chip microcomputer; The single-chip microcomputer demodulates the received signal by FM, then uses FFT transformation to obtain the frequency component corresponding to the frequency shift of the Doppler, extracts the phase of the preprocessed plane wave signal under the frequency component to obtain the plane wave direction of arrival; When used for distance measurement, the single-chip microcomputer controls the corresponding microwave switch to make a selected set of TOF ranging chip and peripheral circuit communicate with the antenna; the selected set of TOF ranging chip and peripheral circuit sends a distance measurement signal to the signal source at the slave end through the antenna; the single-chip microcomputer calculates the distance between the positioning system and the slave end according to the distance measurement response signal from the slave end; The slave end is a known slave end; According to the direction finding result of the plane wave direction of arrival and the distance measurement result of the distance between the positioning system and the slave end, the Mars unmanned aerial vehicle is positioned.

2. The radio positioning system applied to the Mars unmanned aerial vehicle according to claim 1, characterized in that: The antenna is an omnidirectional antenna, and a coaxial line interface is used to connect the microwave switch through a microstrip line; the microwave switch is close to the coaxial line interface.

3. The radio positioning system for use in a Mars drone according to claim 2, characterized in that, Each antenna, the corresponding microwave switch and the microstrip radio frequency transmission line form a group of signal units, and the four groups of signal units are centrally symmetrically distributed with the center point of the PCB board as the center.

4. The radio positioning system applied to the Mars unmanned aerial vehicle according to claim 3, characterized in that: The microwave switch is a reflective switch working at a 2.4G frequency band and adopting a patch type package, and has a radio frequency signal input port, a control signal port, a signal output port A and a signal output port B; When used for direction finding, the radio frequency signal input port is used to receive a plane wave signal, and the control signal port is used to receive a control signal of the single-chip microcomputer; the control signal is a high-level signal and a low-level signal; the control signal port makes the signal output port A conductive to transmit signals according to the received control signal, and simultaneously makes the other signal output port non-conductive. When used for ranging, the direction finding function is closed; the radio frequency signal input port is used for receiving the ranging signal sent by a selected set of TOF ranging chips and peripheral circuits; the control signal port makes the output port B conductive according to the control signal received by the single-chip microcomputer, so that the ranging signal is sent to the antenna through the output port B, and the antenna sends the ranging signal to the signal source at the slave end.

5. The radio positioning system for a Mars drone according to claim 4, wherein The geometric size of the square PCB board is not more than 10*10 cm.

6. The radio positioning system for a Mars drone according to claim 5, wherein The impedance of each microstrip radio frequency transmission line is 50 ohms; the length of each microstrip radio frequency transmission line is an integer multiple of 1 / 4λ, where λ is the wavelength of a 2.4G frequency band signal propagating in the microstrip radio frequency transmission line; when one microstrip radio frequency transmission line transmits a signal, the input impedance of the other three microstrip radio frequency transmission lines is in an open circuit state.

7. The radio positioning system for a Mars drone according to claim 6, wherein The terminals of the four microstrip radio frequency transmission lines are connected at the center point of the square PCB board and form a cross layout; each microstrip radio frequency transmission line extends in a zigzag shape from the head end to the terminal, and a circular arc is used at the zigzag corner.

8. The radio positioning system for a Mars drone according to claim 7, wherein The baseband circuit includes a down-conversion module composed of a radio frequency front-end I / Q modulation and demodulation chip and its peripheral circuit, and a differential-to-single-end and low-pass filtering module composed of a double-channel integrated operational amplifier and its peripheral circuit; After the planar wave signal transmitted by the microstrip radio frequency transmission line is converted into a differential signal by a balun in the baseband circuit, the I\Q two-channel differential signals are obtained in the down-conversion module, and then the low-frequency band I\Q two-channel single-end signals are outputted through the differential-to-single-end and low-pass filtering module as preprocessed signals to the single-chip microcomputer.

9. The radio positioning system for a Mars drone according to claim 8, wherein The method for the single-chip microcomputer to perform FM demodulation on the received signal includes: Assuming that the planar wave signal generated by the signal source is f(t): where f c is the carrier frequency, ω c is the carrier angular frequency, is the initial phase of the carrier signal, and t is time. Four antennas are turned on in turn, and four ways of plane wave signals are integrated into one way in time sequence. The signal into the baseband circuit is S n (t): where n is the number of the antenna, B n is the amplitude of the plane wave signal received by the nth antenna, is the phase of the carrier signal, D is the diameter of the pseudo-Doppler circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna at t = 0. Signal S n (t) After being processed by the baseband circuit, the obtained preprocessed plane wave signal is a low-frequency I\Q two-way single-end signal; The single-chip microcomputer performs an inverse tangent operation on the low-frequency band I\Q two-channel single-end signals to obtain the instantaneous phase φ(t) of the planar wave signal: wherein The Doppler shift generated by the four antennas switching in turn is conducted. When the ratio of the difference between the height of the signal source and the antenna and the distance from the signal source to the center of the pseudo-Doppler circular array is less than 1 / 10, the elevation angle ε of the plane wave signal is considered as 0, and cosε is considered as 1. The derivative of the instantaneous phase φ(t) is obtained to obtain the instantaneous frequency ω(t) of the planar wave signal: Thus, the single-chip microcomputer realizes FM demodulation on the received signal.

10. The radio positioning system for a Mars drone according to claim 9, wherein The method for obtaining the planar wave direction of arrival is: FFT transforming the instantaneous frequency ω(t) to obtain a planar wave signal spectrum diagram; the frequency component corresponding to the antenna rotation in the spectrum diagram is the frequency component corresponding to the Doppler shift; the frequency component is expressed as a complex number, and the phase of the complex number is obtained to obtain the incoming wave angle with a constant offset where θ0 represents a constant offset, and θ is calculated to determine the planar wave direction of arrival.

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