Time synchronization and distance measurement method for time packet network unmanned aerial vehicle measurement and control system

Abstract

The invention discloses a time synchronization and distance measurement method for a time packet network unmanned aerial vehicle measurement and control system, and the method comprises the following steps: completing the distance measurement between a ground control station and each unmanned aerial vehicle in a first time frame, and obtaining a distance value D1; step 2, in a second time frame, completing time synchronization between the ground control station and each unmanned aerial vehicle according to the distance value D1; 3, in a third time frame, the airborne equipment of the main unmanned aerial vehicle sends the local sending moment t7 of the synchronized standard moment in a framing manner; and recording an inter-UAV distance measurement frame receiving moment t8 from airborne equipment of the unmanned aerial vehicles, and calculating a transmission delay according to t8 and t7 so as to obtain a distance value between the unmanned aerial vehicles. According to the method, the technical complexity of the ranging function can be greatly reduced, time slot division occupied by the ranging function is reduced compared with a non-coherent ranging method for a time-division networking system, and the networking efficiency of the time-division system is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of wireless communication, and relates to a time synchronization and ranging method for a time-division packet network unmanned aerial vehicle measurement and control system. BACKGROUND

[0002] The unmanned aerial vehicle measurement and control system is used for realizing remote control, remote measurement, tracking positioning and information transmission of the unmanned aerial vehicle, and can be divided into a ground control station and a data link, and the data link is used for data interaction between the ground and the airborne. A single center node unmanned aerial vehicle measurement and control system based on a time division duplex (TDD) and a time division multiple access (TDMA) communication system divides a measurement and control communication period into time intervals with different lengths. The ground control station and a plurality of unmanned aerial vehicle groups use the time division duplex method to perform information receiving and sending on the same carrier channel, one party is in a sending state, and the remaining nodes are in a receiving state, so that full duplex communication is realized.

[0003] The time synchronization technology is a key technology for successful networking between the ground control station and the unmanned aerial vehicle groups under the time division system. When the synchronization error is greater than the protection time interval, the ground control station can simultaneously receive a plurality of airborne downlink frames of the same frequency, so that correct synchronization and demodulation cannot be realized. The time error mainly comes from the local clock drift and the error caused by wireless transmission. The main methods for correcting the local clock error to realize time synchronization include a GPS cycle time correction and a round-trip two-way timing synchronization method. The two-way timing synchronization method initiates an uplink frame time synchronization instruction by timing of the ground control station, and each airborne device adjusts the local clock to be synchronized with the standard clock of the ground control station by analyzing the time synchronization instruction.

[0004] The wireless data link positioning is an important part of the measurement and control data link system. At present, the ranging mode mainly adopts a pseudo code ranging system. According to the coherence between the ground station and the airborne device, the ranging mode is divided into coherent ranging and incoherent ranging. The incoherent ranging mode is simpler to realize than the coherent ranging mode, and is more widely applied.

[0005] The incoherent ranging utilizes the autocorrelation of the spread spectrum code, acquires the phase difference of the transceiving code, converts the phase difference into a transmission time delay, and then realizes distance measurement. The mutual transmission and reception between the ranging terminals can be divided into uplink transmission and downlink transmission links. Taking the ranging between the unmanned aerial vehicle and the ground station as an example, the ground station sends the uplink frame to the airborne device by using the spread spectrum system. The airborne device captures, synchronizes, despreads and demodulates the uplink frame, extracts the ranging information such as the uplink frame count and the code phase count, and puts the local ranging information into the downlink frame and transmits the downlink frame to the ground. The ground realizes the ranging function after extracting the ranging information of the downlink frame. The method requires that the clock crystal oscillator of the ranging two terminals has high frequency accuracy and stability. At the same time, the influence of the stability of the local oscillator and other signals in the hardware circuit on the ranging accuracy also needs to be considered. SUMMARY

[0006] The application aims to provide a time synchronization and distance measurement method for a time division packet network unmanned aerial vehicle measurement and control system.

[0007] The application aims to provide a time synchronization and distance measurement method for a time division packet network unmanned aerial vehicle measurement and control system.

[0008] The application aims to provide a time synchronization and distance measurement method for a time division packet network unmanned aerial vehicle measurement and control system.

[0009] Step one, in the first time frame, distance measurement between the ground control station and each unmanned aerial vehicle is completed, and a distance value D1 is obtained.

[0010] Step two, in the second time frame, time synchronization between the ground control station and each unmanned aerial vehicle is completed according to the distance value D1.

[0011] Step three, in the third time frame, one-way distance measurement between each unmanned aerial vehicle is completed, including:

[0012] Step 31, the airborne equipment of the main unmanned aerial vehicle serves as a distance measurement instruction initiator, initiates an inter-aircraft distance measurement frame in the inter-aircraft distance measurement time slot, and sends a local sending time t7 in a synchronized standard time frame.

[0013] Step 32, after the airborne equipment of the slave unmanned aerial vehicle completes synchronization, demodulation, decoding and frame analysis on the received signal, records the inter-aircraft distance measurement frame receiving time t8 at this moment, and analyzes the sending time t7 in the data frame, and the signal space transmission time delay is recorded as

[0014] ΔT=t8-t7

[0015] According to the electromagnetic wave transmission distance calculation formula, the distance value D2 between the unmanned aerial vehicles is obtained, and D2=ΔT*C, wherein C is the speed of light.

[0016] Preferably, the specific steps of step one are as follows:

[0017] Step 11, according to the time division packet network time slot division, the ground control station serves as a central node, initiates a distance measurement instruction in the distance measurement time slot period, sends an uplink distance measurement frame containing the distance measurement instruction through physical layer encoding and modulation, completes the sending of the uplink distance measurement frame, and records the sending time t1 at this moment.

[0018] Step 12, the airborne equipment on the unmanned aerial vehicle works in a receiving state, the radio frequency signal is down-converted to an intermediate frequency and then enters a digital signal processing module, synchronization, demodulation and decoding of the received signal are completed, after frame analysis, the uplink frame receiving time t2 at this time is recorded; when waiting for a downlink sending time slot, the downlink ranging frame sending time t3 at this moment is recorded, then t2 and t3 are combined as ranging information into the downlink ranging frame, and after physical layer waveform coding and modulation, the downlink ranging frame is sent to a radio frequency channel, and the sending of the downlink ranging frame is completed;

[0019] Step 13, the ground control station completes synchronization, demodulation and decoding of the received signal, and after frame analysis, the downlink ranging frame receiving time t4 is recorded;

[0020] Step 14, the ground control station calculates the transmission time through the ranging information analyzed and the local receiving time t4, and further obtains the distance value D1 between the ground control station and the unmanned aerial vehicle, wherein D1 = TOA * C, and C is the speed of light.

[0021] Preferably, the specific steps of step two are as follows:

[0022] Step 21, first, according to time division network time slot division, the ground control station as a center node combines the sending time t5 at this moment, the ranging result distance value D1 and the transmission time TOA of the last time into the uplink synchronization frame sending according to the time synchronization time slot period initiation time synchronization instruction;

[0023] Step 2, the airborne equipment on the unmanned aerial vehicle completes synchronization, demodulation and decoding of the received signal, and after frame analysis, the uplink synchronization frame receiving time t6 at this moment is recorded, and the time deviation θ is calculated according to the TOA and the sending time t5 obtained by analysis:

[0024] θ = t6-t5-TOA

[0025] After the time deviation is used as a time synchronization result to compensate the local clock, the airborne local timing is continued, and standard time synchronization between the ground control station and the unmanned aerial vehicle is realized.

[0026] Preferably, step two further comprises the following steps:

[0027] Step 3, the airborne equipment frames the time deviation and sends it, the ground control station analyzes the time deviation transmitted by the airborne equipment and compares it with the local standard time, and when the deviation exceeds a threshold value, timely time synchronization correction is performed.

[0028] The present application has the following beneficial effects:

[0029] For example, Figure 5 , Figure 6The shown is the ranging model comparison under the condition of 4-unit network state, under the non-coherent ranging model, the inquiry end machine and the response end machine carry out one two-way communication to complete the non-coherent ranging, and the inquiry end machine still needs to send the ranging result to the response end machine, so 3 times of sending and receiving processes are needed, and a total of 3*6=18 times of sending and receiving processes are needed, the one-way ranging process only needs to send once for each end machine, and the relative ranging result can be obtained by the remaining end machines in the network, so a total of 4 times of sending and receiving processes are needed.

[0030] Therefore, under the condition of N-unit network, the traditional non-coherent ranging method needs to communicate at least 3 times between each aircraft, and the inquiry machine and the response machine can obtain the distance information of each other, and the complexity is 3N*(N-1) / 2. The present application only needs to send once the ranging frame containing the ranging information of each aircraft under the premise of completing the standard time synchronization, so as to obtain the distance information between each other, and the complexity is N. The method can greatly reduce the technical complexity of the ranging function, and for the time division network system, the time slot occupied by the ranging function is reduced compared with the non-coherent ranging method, and the network efficiency of the time division system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The ranging principle diagram between the ground control station and the unmanned aerial vehicle.

[0032] Figure 2 The time synchronization principle diagram between the ground control station and the unmanned aerial vehicle.

[0033] Figure 3 The ranging principle diagram between the unmanned aerial vehicles.

[0034] Figure 4 The non-coherent ranging model diagram between the unmanned aerial vehicles.

[0035] Figure 5 The one-way ranging model diagram between the unmanned aerial vehicles.

[0036] Figure 6 The time slot division diagram of the ranging period. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below in combination with the drawings and examples.

[0038] The time division system requires high time synchronization for data link networking, and non-coherent ranging is carried out by spread spectrum link data transmission, and the ranging function is realized by using the autocorrelation of the pseudo code, and the uplink and downlink communication is required to complete the calculation of the distance value of both sides once, and because of the non-coherence with the local time, the clock stability of the device and the stability of the radio frequency channel are required to be high. Therefore, the present application is suitable for the time division network unmanned aerial vehicle measurement and control system, and the local time calibration and synchronization between the ground station and the unmanned aerial vehicle are completed by the time synchronization mode, and based on the same time standard, the ranging and positioning between the unmanned aerial vehicles are realized, so that the mutual ranging process between the non-central nodes only needs one-way communication, reduces the technical complexity, and optimizes the time slot division efficiency under the time division system.

[0039] A time division network unmanned aerial vehicle measurement and control system time synchronization and ranging method, comprising ranging between a ground control station and an unmanned aerial vehicle, time synchronization and mutual ranging between multiple unmanned aerial vehicle networks. The ranging between the ground control station and the unmanned aerial vehicle, and the time synchronization process utilizes the electromagnetic wave TOA (time of arrival) ranging principle, considers that the delay interval of the unmanned aerial vehicle receiving and transmitting is usually about 10ms, and combines the actual flight speed of the small and medium-sized unmanned aerial vehicle which is about 100m / s, and can be considered that the error between the uplink transmission distance D1 and the downlink transmission distance D2 is small, and can be regarded as the same ranging value D and transmission time TOA. The specific steps are as follows:

[0040] Step one, in the first time frame, ranging between the ground control station and the unmanned aerial vehicle is completed, and the distance value D1 is obtained.

[0041] The ranging method between the ground control station and the unmanned aerial vehicle is shown in Figure 1 The ground control station sends the uplink frame in the ground sending time slot, the airborne device receiver obtains the ranging instruction after synchronization and demodulation, modulates and sends the downlink frame recording the airborne ranging time information in the airborne sending time slot, and the ground device calculates the air interface transmission delay by analyzing the airborne ranging time information and combining the ground ranging time information.

[0042] The specific steps are as follows:

[0043] Step 11, first, according to the time division network time slot division, the ground control station as the central node initiates the ranging instruction in the ranging time slot period, the uplink ranging frame containing the ranging instruction is sent out after physical layer coding and modulation, the sending time t1 at this moment is recorded.

[0044] Step 12, the airborne equipment on the UAV works in a receiving state, the radio frequency signal is down-converted to an intermediate frequency and then enters a digital signal processing module, synchronization, demodulation, decoding of the received signal are completed, after frame analysis, the uplink frame receiving time t2 at this time is recorded. When waiting for the downlink sending time slot, the downlink ranging frame sending time t3 at this moment is recorded, then t2 and t3 are combined as ranging information into the downlink ranging frame, and after physical layer waveform coding and modulation, the downlink ranging frame is sent to the radio frequency channel, and the sending of the downlink ranging frame is completed.

[0045] Step 13, the ground control station completes synchronization, demodulation, decoding of the received signal, after frame analysis, the downlink frame receiving time t4 is recorded, and the ranging information AT contained in the downlink ranging frame is extracted.

[0046] Step 14, the ground control station calculates the transmission time by the parsed ranging information AT and the local receiving time t4, and then obtains the ranging result,

[0047] 2TOA+t3-t2+t1=t4

[0048] It can be obtained that:

[0049] TOA=(t4-t1-t3+t2) / 2

[0050] According to the electromagnetic wave transmission distance calculation formula, the distance value D1 between the ground control station and the UAV is obtained, that is, TOA*C, wherein C is the speed of light.

[0051] Step two, in the second time frame, the time synchronization between the ground control station and each UAV is completed according to the distance value D1.

[0052] The time synchronization method between the ground control station and the UAV is as shown in Figure 2 Due to local clock drift and other reasons, the airborne time and the ground control station standard time may deviate, the ground control station uses a clock crystal oscillator with high time accuracy and stability as a reference standard clock, the ground control station periodically sends a time synchronization instruction, the instruction content contains the frame sending time and the latest ranging result, the airborne equipment analyzes the time synchronization instruction, and adjusts the timing clock to eliminate the time deviation.

[0053] The specific steps are as follows:

[0054] Step 21, first, according to the time division group network time slot division, the ground control station as a center node sends a time synchronization instruction at the initiation time of the time synchronization time slot, combines the sending time t5 at this moment and the latest ranging result distance value D1, transmission time TOA into the uplink synchronization frame, and predicts the time deviation by the transmission delay obtained by ranging.

[0055] Step 22, the airborne equipment on the unmanned aerial vehicle completes synchronization, demodulation, decoding and frame analysis on the received signal, records the uplink synchronization frame receiving time t6 at this time, and adjusts the local clock according to the TOA obtained by analysis and the sending time t5. Assuming that the airborne time is offset from the ground standard time by θ, then

[0056] t6=t5+TOA+θ

[0057] That is, the actual uplink frame receiving time is

[0058] t6 ′ =TOA+t5-θ

[0059] The time deviation θ=t6-t5-TOA, and the local clock is compensated after the result is taken as the time synchronization result, and the airborne end local timing is continued, so that the standard time synchronization between the ground control station and the unmanned aerial vehicle is realized.

[0060] Step 23, the airborne equipment frames the time deviation and sends it down, the ground analyzes the time deviation transmitted by the airborne equipment, and compares it with the local standard time. When the deviation is large, timely time synchronization and deviation correction are performed.

[0061] Step three, in the third time frame, one-way ranging between unmanned aerial vehicles is completed.

[0062] The ranging between unmanned aerial vehicles requires that each unmanned aerial vehicle has the same time standard, that is, after the time synchronization between the ground control station and each unmanned aerial vehicle is completed, accurate inter-unmanned aerial vehicle ranging results can be obtained.

[0063] The specific steps are as follows:

[0064] Step 31, the airborne equipment of the main unmanned aerial vehicle serves as the ranging instruction initiation end, initiates inter-unmanned aerial vehicle ranging frames in the inter-unmanned aerial vehicle ranging time slot, and sends the local sending time t7 of the synchronized standard time.

[0065] Step 32, the airborne equipment of the slave unmanned aerial vehicle completes synchronization, demodulation, decoding and frame analysis on the received signal, records the inter-unmanned aerial vehicle ranging frame receiving time t8 at this time, and analyzes the sending time t7 in the data frame, so that the signal space transmission time delay can be recorded as

[0066] ΔT=t8-t7

[0067] According to the electromagnetic wave transmission distance calculation formula, the distance D2 between the unmanned aerial vehicles is obtained, where C is the speed of light.

[0068] Taking the ground control station as the center node and the time division group network system of three unmanned aerial vehicles as an example, the time synchronization and ranging method proposed in the application is described. As Figure 6As shown, first according to the functional design, the time when a single device in the time division system sends a signal is called a time slot, the time when all devices send data once is called a time frame, in the case of one ground station and three aircrafts, one time frame contains four time slots: one ground station sending time slot and three aircraft sending time slots. The entire ranging only needs three time frames to complete the mutual ranging function between all devices.

[0069] The first time frame completes the ranging between the ground station and the unmanned aerial vehicle. The ground control station as the center node, taking airborne 1 as an example, first initiates an uplink ranging frame at t1 time of time frame 1 time slot 1, after unmanned aerial vehicle 1 receives the uplink ranging instruction, combines the uplink ranging frame receiving time t2 and the downlink ranging frame sending time t3 into a downlink ranging frame, and sends it in the unmanned aerial vehicle 1 sending time slot. After the ground control station receives the downlink ranging frame at t4 time, it calculates the ranging result, taking t1 = 30s, t2 = 30.08s, t3 = 30.11s, t4 = 30.19s as an example to calculate the ranging result, according to

[0070] TOA = (t4-t1-t3+t2) / 2

[0071] The air transmission delay is 0.08s, then the distance between the ground station and unmanned aerial vehicle 1 is

[0072] D1 = TOA*C = 0.02*3E8 = 24km

[0073] Similarly, unmanned aerial vehicle 2 and unmanned aerial vehicle 3 send downlink frames in the aircraft sending time slot, that is, the ranging between the ground station and the unmanned aerial vehicle is completed.

[0074] The second time frame carries out time synchronization between the ground station and the unmanned aerial vehicle. The ground station combines the ranging result DOA and the uplink synchronization frame sending time t5 into an uplink synchronization frame, initiates the uplink synchronization frame in the ground station sending time slot, unmanned aerial vehicle 1 records the receiving time t6 after receiving the uplink synchronization frame, and updates the local standard time according to the content in the uplink synchronization frame, taking t5 = 30.2s, t6 = 30.29s, TOA = 0.08s as an example to calculate the time deviation

[0075] θ = t6-t5-TOA = 0.01s

[0076] The third time frame completes the ranging between the unmanned aerial vehicles. After completing the time synchronization, it is considered that all nodes in the system have the same standard time, unmanned aerial vehicle 1, unmanned aerial vehicle 2 and unmanned aerial vehicle 3 initiate the one-way inter-aircraft ranging in the respective sending time slot, taking unmanned aerial vehicle 1 initiating the ranging frame and unmanned aerial vehicle 2 receiving the ranging frame as an example, initiating the ranging frame containing the sending time at t7 time, after unmanned aerial vehicle 2 receives the ranging frame, records the receiving time t8, and analyzes the ranging frame to obtain the distance between unmanned aerial vehicle 1, taking t7 = 30.4s, t8 = 30.42s as an example to calculate the inter-aircraft distance of unmanned aerial vehicles

[0077] ΔT = t8 - t7 = 0.02 s

[0078] D2 = ΔT * C = 0.02 * 3E8 = 6 km

[0079] The UAV 2 obtains the distance from the UAV 1, and the UAV 3 also obtains the distance from the UAV 1. After sequentially initiating the ranging frames, all the UAVs in the system obtain the inter-UAV distance information.

[0080] It can be understood that, for those skilled in the art, equivalent replacements or changes can be made according to the technical solutions and the inventive concept of the present application, and all the changes or replacements shall belong to the protection scope of the appended claims of the present application.

Claims

1. A time synchronization and ranging method for a time-group network UAV telemetry and control system, characterized in that... Includes the following steps: Step 1: Within the first time frame, complete the distance measurement between the ground control station and each UAV to obtain the distance value D1; Step 2: In the second time frame, complete the time synchronization between the ground control station and each UAV based on the distance value D1; Step 3: Within the third time frame, complete one-way ranging between the drones, including: Step 31: The onboard equipment of the main UAV acts as the ranging command initiator, and initiates the inter-machine ranging frame in the inter-machine ranging time slot, sending the local transmission time t7 group frame that has been synchronized with the standard time. Step 32: After the UAV's onboard equipment completes the synchronization, demodulation, decoding, and frame parsing of the received signal, it records the inter-device ranging frame reception time as t8. Simultaneously, it parses the transmission time t7 from the data frame. The signal spatial transmission delay is then recorded as ΔT = t8 - t7. According to the formula for calculating the distance of electromagnetic wave transmission, the distance between drones is D2 = ΔT * C, where C is the speed of light.

2. The time synchronization and ranging method of a time-group network UAV telemetry and control system according to claim 1, characterized in that... The specific steps for Step One are as follows: Step 11: According to the time slot division of the time group network, the ground control station, as the central node, initiates the ranging command during the ranging time slot period. The uplink ranging frame containing the ranging command is sent after being encoded and modulated by the physical layer, and the transmission of the uplink ranging frame is completed. The transmission time t1 at this moment is recorded. Step 12: The onboard equipment on the UAV operates in receiving mode. The radio frequency signal is down-converted to intermediate frequency and then enters the digital signal processing module to complete the synchronization, demodulation, decoding, and frame parsing of the received signal. The uplink frame reception time is recorded as t2. While waiting for the downlink transmission time slot, the downlink ranging frame transmission time is recorded as t3. Then, t2 and t3 are combined as ranging information into the downlink ranging frame and transmitted to the radio frequency channel after being encoded and modulated by the physical layer waveform, thus completing the transmission of the downlink ranging frame. Step 13: After the ground control station completes the synchronization, demodulation, decoding, and frame parsing of the received signal, it records the downlink ranging frame reception time as t4. Step 14: The ground control station calculates the transmission time using the parsed ranging information and the local reception time t4, and then obtains the distance value D1 = TOA * C between the ground control station and the UAV, where C is the speed of light.

3. The time synchronization and ranging method of a time-group network UAV telemetry and control system according to claim 1, characterized in that... The specific steps for step two are as follows: Step 21: First, according to the time slot division of the time group network, the ground control station, as the central node, initiates a time synchronization command during the time synchronization time slot period, and combines the current transmission time t5, the distance value D1 of the most recent ranging result, and the transmission time TOA into an uplink synchronization frame for transmission. Step 2: The onboard equipment on the UAV completes the synchronization, demodulation, and decoding of the received signal. After frame parsing, the uplink synchronization frame reception time is recorded as t6. The time deviation θ is calculated based on the TOA obtained from the parsing and the transmission time t5. θ = t6 - t5 - TOA After compensating the local clock for the time deviation as the time synchronization result, the airborne terminal continues local timing to achieve standard time synchronization between the ground control station and the UAV.

4. The time synchronization and ranging method of a time-group network UAV telemetry and control system according to claim 3, characterized in that... Step two also includes the following steps: Step 3: The airborne equipment sends out time deviation frames, the ground analyzes the time deviation transmitted by the airborne equipment and compares it with the local standard time. When the deviation exceeds the threshold, timely time synchronization correction is performed.

Images