Anti-multipath fading method and system for wireless data transmission system of unmanned aerial vehicle

Abstract

The invention belongs to the field of wireless communication, and discloses an anti-multipath fading method and system for a wireless data transmission system of an unmanned aerial vehicle, and the method comprises the steps: a main end sends a multipath scanning instruction and a multipath scanning frequency point n of a next time slot in advance at a (k-1) th time slot; the slave end receives the multipath scanning indication and the multipath scanning frequency point of the next time slot in the (k-1) th time slot and stores the multipath scanning indication and the multipath scanning frequency point; in the kth time slot, the master end and the slave end switch own frequency points into multipath scanning frequency points, the master end sends a pilot signal, and the slave end receives the pilot signal and estimates multipath characteristics of the position where the slave end is located, and sends the pilot signal at the sending moment; the master end receives the pilot signal sent by the slave end in the k time slot, and estimates the multipath characteristics of the position of the master end; in the (k + 1) th time slot, the master and slave ends recover the original working frequency point m, and data is transmitted normally; and repeating the steps, and scanning the next frequency point n + 1. In the wireless communication process, the multi-path fading characteristics of each frequency point can be scanned in real time to reasonably select the frequency point.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the field of wireless communication technology, and in particular relates to a method and system for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle. Background Art

[0002] Multipath fading refers to the situation where electromagnetic waves emitted from the same antenna reach the same receiving point along different paths due to the uneven propagation environment. These different paths cause different phase shifts of the electromagnetic field. When the environment changes randomly, the phase shift of the multipath also fluctuates randomly, causing the superposition of the electric fields of each path to fluctuate randomly and strongly over time.

[0003] When current drones transmit wireless data over long distances, as the environment and distance change, they will usually suddenly encounter multipath fading at certain locations. At this time, the channel is severely distorted due to multipath fading and data cannot be transmitted normally.

[0004] General frequency selection equipment will select the appropriate frequency for transmission based on the environmental noise, but multipath fading and environmental noise are not related, and environmental noise cannot be used to characterize multipath fading, making it impossible to reasonably select the frequency under multipath fading.

[0005] In view of the above analysis, the technical problems that need to be solved urgently in the prior art are:

[0006] How to reasonably select the frequency under multipath fading conditions. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a method and system for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle.

[0008] The present invention is implemented as follows: a method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle, characterized in that the method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle specifically comprises:

[0009] S1: The master end sends the multipath scanning indication and multipath scanning frequency point n of the next time slot in advance in the k-1th time slot;

[0010] S2: The slave receives and stores the multipath scanning indication and multipath scanning frequency of the next time slot in the k-1th time slot;

[0011] S3: At the kth time slot, the master and slave switch their own frequencies to multipath scanning frequencies. The master sends a pilot signal. The slave receives the pilot signal and estimates the multipath characteristics of its own location, and then sends the pilot signal at the sending time.

[0012] S4: The master end receives the pilot signal sent by the slave end in the k-th time slot and estimates the multipath characteristics of the location where the master end is located;

[0013] S5: At the (k + 1)-th time slot, the master and slave ends restore the original working frequency point m and normally transmit data;

[0014] S6: Repeat step S1 to scan the next frequency point n + 1.

[0015] Furthermore, the scanning period depends on the frequency and the number of frequency points of the scanning time slots. It scans once every K time slots and there are a total of N frequency points. Therefore, it takes a total of K * N time slots to complete a scan of all frequency points.

[0016] Another object of the present invention is to provide an anti-multipath fading system for an unmanned aerial vehicle wireless data transmission system. This system has 1 master end (remote controller) and 1 slave end (unmanned aerial vehicle), and TDD communication is carried out between the master and slave ends. The frequency is f1~fN, the channel bandwidth is BW, and f1, f2,... fN are adjacent channels, and the bandwidth of each channel is BW.

[0017] Furthermore, in this system, after all devices are powered on, the master end periodically sends a synchronization signal. The slave end synchronizes with the master end and sends its own signal following the signal of the master end, and communicates according to the agreed TDD time slot allocation. The time of one transmission by the master end + one transmission by the slave end is called 1 time slot, and the time slot length is fixed at M seconds. The transmission time of the master end and the transmission time of the slave end are also fixedly allocated.

[0018] Combined with the above technical solutions and the solved technical problems, the advantages and positive effects of the technical solution to be protected by the present invention are as follows:

[0019] The present invention can reasonably select frequency points by real-time scanning the multipath fading characteristics of each frequency point during the wireless communication process.

[0020] In existing industrial applications, the wireless data transmission of unmanned aerial vehicles is significantly affected by multipath fading. Due to the complex flight environment and the existence of obstacles such as buildings and mountains, the traditional fixed frequency point and unidirectional transmission mode are difficult to quickly track the fading characteristics, resulting in a large fluctuation in communication quality and even disconnection. When multiple unmanned aerial vehicles are running simultaneously, the multipath problem is more prominent, often causing technical problems such as low communication efficiency and long transmission delay, and unable to meet the requirements of the industrial field for high-reliability and high-bandwidth transmission.

[0021] To address this issue, the present invention proposes a technical means of using multi-path scanning time slots for pilot signal measurement and bidirectionally obtaining multi-path characteristics between the master end and the slave end. By periodically switching to different scanning frequencies in time slots outside the normal operating frequency points, the present invention can locate and evaluate the depth and delay characteristics of multi-path fading in a short time, thereby providing real-time multi-path environment data for the communication system. Compared with traditional methods that rely on fixed channel parameters or only perform one-way monitoring, the present invention significantly improves the accuracy and frequency flexibility of multi-path measurement.

[0022] In industrial applications, the dynamic scanning and multi-path characteristic acquisition mechanism proposed by the present invention can help the UAV system effectively cope with environmental changes, achieve rapid frequency point switching, waveform adaptive adjustment, and transmit power optimization, etc. On the one hand, it avoids large-scale packet loss and communication interruption caused by multi-path fading, thereby improving the reliability of UAV swarms performing tasks such as inspection, mapping, and logistics in complex environments; on the other hand, by performing multi-path scanning only when needed and switching frequencies only in short time slots, the present invention reduces the occupancy of the normal service bandwidth and achieves a significant improvement in communication robustness at a small system cost.

[0023] Overall, the technological progress achieved by the present invention in multi-path fading suppression lays the foundation for the large-scale application of UAV wireless data transmission in the industrial field. It can not only effectively reduce the costs of hardware transformation and excessive redundant design, but also significantly improve the communication link quality and data throughput efficiency, contributing to the wide application and technological upgrading of UAVs in various scenarios such as smart factories, logistics transportation, and disaster monitoring. These achievements all show that the present invention has significant industry applicability and technological leadership, bringing significant technological improvements and added value to the UAV communication industry. Brief Description of the Drawings

[0024] Figure 1 is a flowchart of the anti-multi-path fading method for the UAV wireless data transmission system provided by an embodiment of the present invention;

[0025] Figure 2 is a block diagram of the anti-multi-path fading system device for the UAV wireless data transmission system provided by an embodiment of the present invention;

[0026] Figure 3 is a schematic diagram of the operation of the anti-multi-path fading system device for the UAV wireless data transmission system provided by an embodiment of the present invention. Detailed Embodiments

[0027] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] As Figure 1 shown, an embodiment of the present invention provides an anti-multipath fading method for an unmanned aerial vehicle (UAV) wireless data transmission system, and the method specifically includes:

[0029] S1: The master end sends the multipath scanning indication and the multipath scanning frequency point n of the next time slot in advance at the (k - 1)-th time slot;

[0030] S2: The slave end receives and stores the multipath scanning indication and the multipath scanning frequency point of the next time slot at the (k - 1)-th time slot;

[0031] S3: When it comes to the k-th time slot, the master end and the slave end switch their own frequency points to the multipath scanning frequency point. The master end sends a pilot signal. At this time, the slave end receives the pilot signal and estimates the multipath characteristics of its own location, and then sends the pilot signal at the transmission moment;

[0032] S4: The master end receives the pilot signal sent by the slave end at the k-th time slot and estimates the multipath characteristics of the master end's location;

[0033] S5: At the (k + 1)-th time slot, the master and slave ends restore their original working frequency point m and normally transmit data;

[0034] S6: Repeat step S1 to scan the next frequency point n + 1.

[0035] The anti-multipath fading method of the present invention mainly coordinates the multipath scanning and the exchange of pilot signals between the master end and the slave end within a specific time slot to effectively identify and compensate for the multipath effect, thereby improving the stability and reliability of the UAV wireless data transmission. The working principle of this method will be elaborated in detail below.

[0036] At the (k - 1)-th time slot, the master end pre-sends the multipath scanning indication of the next time slot (the k-th time slot) and the frequency point n to be scanned. The purpose of this step is to inform the slave end in advance of the upcoming multipath scanning operation, so that the slave end can timely prepare the relevant receiving and processing resources. By transmitting the scanning indication in the previous time slot, the master end ensures that the slave end can synchronously identify the multipath characteristics and avoid synchronization problems caused by time delay.

[0037] After receiving the multipath scanning indication and the frequency point information sent by the master end at the (k - 1)-th time slot, the slave end stores this information. This storage process provides the necessary basic data for the slave end to perform multipath scanning at the k-th time slot. By pre-receiving and storing the scanning indication, the slave end can quickly switch to the specified scanning frequency point n in the next time slot to ensure the accurate capture and subsequent processing of the multipath characteristics.

[0038] In the k-th time slot, the master and the slave simultaneously switch their operating frequencies to the pre-specified multipath scanning frequency point n. At this time, the master sends a pilot signal. After receiving the pilot signal, the slave immediately estimates the multipath characteristics. By analyzing the arrival time and intensity of the pilot signal, the slave can accurately determine its position and the characteristics of the reflection paths in the multipath environment, and then adjust its transmission strategy to reduce the impact of multipath fading.

[0039] In the k-th time slot, after the master receives the pilot signal sent by the slave, it also estimates the multipath characteristics. By analyzing the pilot signal sent by the slave, the master can identify the multipath characteristics of itself in the multipath environment. This estimation process helps the master understand the current multipath condition of the wireless channel, so as to optimize its subsequent data transmission strategy and ensure the stable transmission of signals.

[0040] In the (k + 1)-th time slot, the master and the slave restore their respective frequencies to the original operating frequency m and continue normal data transmission. After completing the multipath scanning and pilot signal exchange, both parties adjust the transmission parameters based on the previously estimated multipath characteristics to offset the impact of the multipath effect. In this way, signal fading and interference during the data transmission process are effectively reduced, improving the reliability and data integrity of the transmission.

[0041] The last step of the method is to repeat steps S1 to S6 after the (k + 1)-th time slot to scan the next frequency point n + 1. This cyclic process ensures that the system can continuously monitor and adapt to the dynamic changes of the wireless channel, and timely adjust the multipath compensation strategy. By periodically performing multipath scanning and characteristic estimation, the system can cope with the wireless channel changes in different flight states of the unmanned aerial vehicle and maintain the efficiency and stability of data transmission.

[0042] Through the coordinated operation of the above six steps, the multipath fading resistance method of the present invention can effectively identify and compensate for the multipath effect in the wireless channel, significantly improving the performance and reliability of the unmanned aerial vehicle wireless data transmission system, and is applicable to various complex flight and communication environments.

[0043] The multipath fading resistance method for an unmanned aerial vehicle wireless data transmission system provided by the embodiment of the present invention aims to obtain the multipath characteristics of all frequencies supported by the device for selecting a reasonable operating frequency.

[0044] The scanning period depends on the frequency and the number of frequency points of the scanning time slots. It scans once every K time slots and there are a total of N frequency points. Therefore, a total of K * N time slots are required to complete a scan of all frequency points.

[0045] As Figure 2As shown in the figure, an anti-multipath fading system for a UAV wireless data transmission system provided by an embodiment of the present invention has 1 master end (remote controller) and 1 slave end (UAV). TDD communication is carried out between the master and the slave, and the frequency is f1~fN. The channel bandwidth is BW, and f1, f2,..., fN are adjacent channels (each channel bandwidth is BW).

[0046] As Figure 3 shown, after all devices are powered on, the master end periodically sends a synchronization signal, and the slave end synchronizes with the master end and sends its own signal following the signal of the master end, and communicates according to the agreed TDD time slot allocation. The time for one transmission of the master end + one transmission of the slave end is called 1 time slot. The time slot length is fixed at M seconds. The transmission time of the master end and the transmission time of the slave end are also fixedly allocated.

[0047] Embodiment 1: UAV wireless data transmission system based on LTE network

[0048] In this embodiment, the system uses the LTE (Long Term Evolution) network as the communication basis. The master end is a ground control station, and the slave end is an LTE communication module carried on the UAV. The system configuration includes an LTE base station device supporting multi-frequency point operation, a pilot signal transmission module, a multipath feature estimation algorithm processing unit, and an LTE receiver, a pilot signal receiving and transmitting module, and a storage unit on the UAV.

[0049] First, in the (k - 1)th time slot, the ground control station sends a multipath scanning instruction to the UAV through the LTE base station and specifies the scanning frequency point n (for example, 1800 MHz). After receiving the instruction, the UAV stores the information of the scanning frequency point n in the internal storage unit and prepares to perform a multipath scanning operation in the kth time slot.

[0050] Next, in the kth time slot, the ground control station and the UAV simultaneously switch their working frequency points to the specified scanning frequency point n. The ground control station sends a pilot signal. After receiving the pilot signal, the UAV estimates its own multipath characteristics using the received signal characteristics and sends a pilot signal back to the ground control station within the same time slot.

[0051] After the ground control station receives the pilot signal sent by the UAV in the kth time slot, it analyzes the arrival time and intensity of the signal, thereby estimating its own characteristics in the multipath environment. Through this two-way pilot signal exchange, the master end and the slave end can accurately identify their respective multipath path characteristics, and then adjust the transmission strategy to reduce the impact of multipath fading.

[0052] In the (k + 1)-th time slot, the ground control station and the UAV restore the frequency band to the original working frequency band m (e.g., 1900 MHz) and start normal data transmission. Based on the previous multipath feature estimation, the system dynamically adjusts transmission parameters such as power control and modulation mode to ensure the stability and reliability of data transmission.

[0053] Finally, after the (k + 1)-th time slot, the system repeats steps S1 to S6 to scan the next frequency band n + 1 (e.g., 2100 MHz). By periodically performing multipath scanning and feature estimation, the system can continuously adapt to the dynamic changes of the wireless channel and ensure that the data transmission performance of the UAV in a complex environment always remains at a high level.

[0054] Embodiment 2: High-speed UAV data transmission system based on 5G network

[0055] In this embodiment, the system uses a 5G network as the communication platform. The master end is the ground control station, and the slave end is the 5G communication module carried on the UAV. The system configuration includes 5G base station equipment supporting Sub-6 GHz and millimeter-wave frequency band operations, a high-precision pilot signal transmission module, a multipath feature estimation algorithm processing unit, and a 5G receiver, a pilot signal receiving and transmitting module, and a high-performance processor on the UAV.

[0056] In the (k - 1)-th time slot, the ground control station sends a multipath scanning instruction to the UAV through the 5G base station and specifies the scanning frequency band n (e.g., 28 GHz millimeter-wave frequency band). After receiving the instruction, the UAV stores the information of the scanning frequency band n in the internal storage unit and prepares for the multipath scanning operation in the k-th time slot.

[0057] Subsequently, in the k-th time slot, the ground control station and the UAV simultaneously switch their working frequency bands to the specified scanning frequency band n (28 GHz). The ground control station sends a high-precision pilot signal. After receiving the signal, the UAV quickly estimates its own multipath features using the high bandwidth and low latency characteristics of 5G and sends a pilot signal back to the ground control station within the same time slot.

[0058] After receiving the pilot signal sent by the UAV in the k-th time slot, the ground control station analyzes the multipath characteristics of the signal using the high-precision positioning function of the 5G network and estimates its own path characteristics in the multipath environment. Through this two-way pilot signal exchange, the master end and the slave end can accurately identify their respective multipath path characteristics and optimize transmission parameters to reduce the impact of multipath fading.

[0059] In the (k + 1)-th time slot, the ground control station and the UAV restore the frequency point to the original working frequency point m (for example, 3.5 GHz in the Sub-6 GHz band), and start high-speed data transmission. Based on the previous multipath feature estimation, the system dynamically adjusts transmission parameters such as beamforming and power control to ensure the efficiency and reliability of data transmission.

[0060] Finally, after the (k + 1)-th time slot, the system repeats steps S1 to S6, and scans the next frequency point n + 1 (for example, 39 GHz in the millimeter wave band). Through continuous multipath scanning and feature estimation, the system can quickly respond to changes in the wireless channel, ensuring that the data transmission of the UAV always maintains high performance and stability during high-speed flight and in complex terrains.

[0061] It is necessary to address the multipath fading problem caused by factors such as reflection and diffraction from the ground and obstacles during the complex flight of the UAV. By actively performing "multipath scanning" at different frequency points during the idle or handover time slots of data transmission, the multipath characteristics of each terminal device at its location during flight can be obtained in a timely manner, including information such as multipath delay, phase, and amplitude. Using these scanning results, the master and slave ends can dynamically adjust the transmission and reception strategies according to the multipath conditions in the current environment during subsequent data transmission, thereby effectively reducing the impact of multipath fading on communication quality without significantly increasing the system overhead.

[0062] In specific implementation, the master end (such as the ground station or the mother aircraft) will send the indication information for multipath scanning required in the next time slot and the specified multipath scanning frequency point n to the slave end in advance at the (k - 1)-th time slot. After receiving and storing these scanning instructions and frequency point information in the (k - 1)-th time slot, the slave end (such as the slave aircraft or other UAV nodes) can automatically switch to the corresponding frequency point in the next time slot and wait for scanning. The advantage of this design is that: when performing multipath scanning formally, the master and slave ends have completed frequency point matching in advance, and can enter the pilot signal transmission and reception stage in an extremely short time, reducing the additional overhead of time slot switching and synchronization.

[0063] When the k-th time slot starts, both the master and slave ends switch to the specified multipath scanning frequency point n and sequentially send pilot signals for measuring the multipath characteristics of the environment. First, the master end sends a pilot signal, and the slave end receives and estimates the multipath characteristics of its own location at this scanning frequency point, such as the number of reflection paths, delay characteristics, and received signal strength distribution; then the slave end sends back its own pilot signal in the same time slot, and the master end receives this pilot signal and simultaneously obtains the multipath characteristics of the master end's location. By completing "two-way" pilot measurement in one time slot, the system not only grasps the instantaneous multipath conditions between the master and slave ends, but also provides a necessary basis for equalization, power control, or adaptive modulation during subsequent normal data transmission.

[0064] After completing the multipath scanning in the k-th time slot, the system will resume to the normal operating frequency point m in the (k + 1)-th time slot and continue to perform the regular data transmission tasks. This process repeats cyclically. When the next scanning period starts, the master end will send a new scanning instruction and a new scanning frequency point n + 1 again. During the entire flight process, through the periodically or on-demand triggered multipath scanning mechanism, the system can comprehensively monitor the multipath fading conditions at different frequency points, and then perform corresponding switching and compensation between the frequency points or time slots where severe fading may occur, thereby significantly improving the stability and anti-fading ability of the UAV wireless data transmission system in complex environments.

[0065] The following combines two different usage scenarios to give specific embodiments of the "Method for Anti-Multipath Fading in UAV Wireless Data Transmission System" of the present invention, for illustrating the application process and technical advantages of the method described in the present invention. It should be emphasized that the examples given below are only for illustrative purposes, and the relevant parameter settings and implementation processes can be adjusted according to actual requirements and environmental constraints.

[0066] Embodiment 1: Low-altitude data transmission between a single UAV and a ground base station

[0067] In this example, the ground base station (as the master end) needs to maintain stable data communication with a low-altitude flying UAV (as the slave end). Due to the low flying altitude of the UAV and the presence of buildings and other obstacles near the flight path, the signal received by the ground base station shows obvious multipath fading phenomenon, resulting in a decrease in communication reliability.

[0068] System parameter settings:

[0069] 1. Divide the communication process into consecutive time slots of equal duration, and a complete transceiver operation can be performed within each time slot.

[0070] 2. The master end and the slave end pre-define a scanning period in the communication protocol, including the set of frequency points to be scanned within each period; assume that a total of 5 candidate operating frequency points are prepared and scanned sequentially in each period.

[0071] 3. When the scanning time slot is approaching (assuming that every 10 time slots is a scan), the master end will send a "next time slot scanning instruction" and the corresponding "multipath scanning frequency point n" to the slave end through the current operating frequency point m in the (k - 1)-th time slot. For example, n is 1 at this time.

[0072] Operation process:

[0073] 1) In the (k - 1)-th time slot, the slave end receives the scanning instruction and records the information of "switching to frequency point n = 1 and performing multipath scanning in the next time slot".

[0074] 2) At the k-th time slot, both the master and slave ends simultaneously switch the transmit / receive frequency points to the scanning frequency point n = 1. The master end first sends a pilot signal, and the slave end receives and measures the multipath characteristics (such as delay, fading depth, etc.) at frequency point 1; subsequently, the slave end also sends a pilot signal, and the master end receives and records the multipath condition of the environment where the master end is located at frequency point 1.

[0075] 3) At the (k + 1)-th time slot, both sides resume to their original working frequency point m and continue to transmit conventional data.

[0076] 4. When the next scanning period (such as the (k + 9)-th time slot) arrives, the master end notifies the slave end again in its previous time slot (k + 8) to switch to the next preset scanning frequency point n + 1 (if n = 1 last time, then n = 2 this time), and continue to perform similar operations. Through periodic scanning and recording, the ground base station can timely master the multipath fading conditions of different frequency points in the low-altitude flight environment, and can dynamically select the optimal working frequency point or perform anti-fading processing according to the multipath analysis results.

[0077] (4) Technical advantages

[0078] The periodic scanning mechanism can continuously monitor the multipath fading caused by environmental changes without significantly occupying the service bandwidth.

[0079] The scanning instruction is notified to the slave end one time slot in advance to ensure that it can quickly switch to the specified frequency point and complete the two-way pilot measurement within the scanning time slot, without the need for temporary negotiation, significantly reducing the time slot overhead.

[0080] Comprehensively evaluating the multipath characteristics in multiple frequency bands can significantly improve the frequency diversity and anti-fading ability of communication.

[0081] Embodiment 2: Communication between multiple UAV clusters and a ground mobile receiving station

[0082] In this example, it is assumed that multiple UAVs (slave end 1, slave end 2, slave end 3, etc.) form a formation flight and perform high-bandwidth data backhaul with a mobile ground receiving vehicle (master end). The UAV formation is in the suburban-rural fringe area, where the surrounding terrain undulates and the vegetation and building distributions are diverse, resulting in a complex and ever-changing multipath environment; if the communication frequency point fails to be adapted in time, multipath fading will lead to frequent communication interruptions or data retransmissions.

[0083] 1. Each UAV maintains an independent docking time slot with the master end, or the system communicates with different UAVs in turn through a time-division method.

[0084] 2. When the master end is performing normal data transmission, it needs to perform multipath scanning at intervals of several time slots, so that the master end can respectively obtain the multipath conditions of different UAVs. It is assumed that within a relatively large scanning period of the system, 8 alternative frequency points need to be scanned in sequence.

[0085] 3. After each scanning cycle is completed, the master end can decide which optimal frequency point each subsequent drone uses based on the multipath distribution of different drones, and even support different drones to use different frequencies to complete independent communication in the same period of time.

[0086] Operation process:

[0087] 1) Instruction issuance: In the last regular time slot before data transmission for a certain drone (such as slave 1), the master sends a "multipath scan in the next time slot" instruction to slave 1, including the number of the scanning frequency point to be switched (for example, n=3). If other drones are not assigned to scan at the moment, they continue to maintain the current working frequency point to perform their respective tasks.

[0088] 2) Scanning in time slot: When the scanning time slot arrives, slave 1 and master synchronously switch to the designated scanning frequency n=3 to perform pilot bidirectional measurement. At the same time, if the master and other drones (slave 2 and slave 3) do not need to scan temporarily, they can continue to perform their own data transmission at the original frequency to achieve parallel resource utilization.

[0089] 3) Data return: The master end continues to transmit data with slave end 1 at the initial working frequency m in the next time slot, but at this time the master end already knows the multipath situation of slave end 1 to frequency 3 at this specific flight position, and can further optimize the frequency configuration or transmission waveform. For other drones, the scanning command can also be activated in sequence or on demand and the scanning results can be recorded.

[0090] 4) Frequency switching: When the entire scanning cycle ends (i.e., all 8 preset frequency points have been scanned in turn), the master end forms a complete table of "multipath conditions in the current area and frequency point matching". If a certain frequency point has the best anti-multipath performance for a certain drone, it will be scheduled for this drone first in the subsequent time slot to significantly reduce the link quality fluctuation caused by multipath fading.

[0091] (4)Technological advantages

[0092] In formation communication where multiple drones coexist, the method of the present invention can realize time-sharing scanning and on-demand scanning, which not only avoids the conflict of multiple drones occupying the same scanning time slot, but also can flexibly allocate bandwidth and scanning resources among the drones.

[0093] By combining frequency division with time division, the master end can take into account both normal data transmission and multipath environment update measurement at the same time, reducing the extra burden of occupying public spectrum or time slots.

[0094] The master end can integrate the multipath scanning results of different drones to provide precise support for subsequent dynamic frequency switching, beamforming or adaptive modulation and coding decisions, thereby ensuring the reliability of group drone-to-ground communications.

[0095] In summary, through the method of the present invention, the system can not only complete data transmission between the UAV and the ground master end within the normal time slots, but also arrange multi-path feature scans at different frequency points in appropriate time slots. On the one hand, it will not cause excessive waste of system resources; on the other hand, it provides key environmental parameter support for subsequent frequency point selection and adaptive optimization of the transmission waveform, thereby effectively improving the reliability and anti-fading ability of the UAV wireless data transmission link in a complex multi-path environment.

[0096] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated designed hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable logic devices such as field programmable gate arrays, or can be implemented by software executed by various types of processors, or can be implemented by a combination of the above hardware circuits and software such as firmware.

[0097] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention by those skilled in the art within the disclosed technical scope of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for resisting multipath fading in a wireless data transmission system of an unmanned aerial vehicle, characterized in that: The method specifically includes: 1) In the k-1th time slot, the master end sends the multipath scanning indication and multipath scanning frequency of the next time slot in advance; 2) The slave terminal receives and stores the multipath scanning indication and the multipath scanning frequency point in the k-1th time slot; 3) At the kth time slot, both the master end and the slave end switch to the multipath scanning frequency point, the master end sends a pilot signal, the slave end receives and estimates the multipath characteristics of its own location, and sends a pilot signal to the master end at its sending time; 4) The master end receives the pilot signal of the slave end in the kth time slot and estimates the multipath characteristics of the master end's location; 5) At the k+1th time slot, the master and slave ends return to their original working frequencies to continue normal data transmission; 6) Repeat step 1) and scan the next multipath scanning frequency point until all the frequencies to be scanned are completed.

2. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to claim 1, characterized in that: The scanning cycle is determined by the frequency of the scanning time slots and the number of frequency points required to be scanned. A scan is triggered every time a preset number of time slots pass, and a complete scanning cycle is completed after all the candidate frequency points are traversed in sequence.

3. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to any one of claims 1 or 2, characterized in that: The multipath scanning instruction includes a specific time for switching to a multipath scanning frequency point, an identifier of the frequency point and a corresponding pilot transmission sequence, so that the master end and the slave end can synchronously switch to the designated scanning frequency point within a predetermined time slot and complete the two-way pilot measurement.

4. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to claim 1, characterized in that: The multipath characteristics include parameters such as delay, amplitude, phase or number of arrival paths of the multipath signal, which are used for subsequent frequency selection, power control or channel equalization by the master end and the slave end.

5. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to claim 4, characterized in that: The master end generates a multipath environment feature database based on the received multipath scanning results, and switches the working frequency used by the drone or adaptively adjusts the modulation method based on the database in subsequent time slots to improve communication reliability and anti-fading capability.

6. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to claim 5, characterized in that: This method is suitable for the communication between multiple UAVs and the same ground base station. The master end uses time division or frequency division scheduling to send multipath scanning instructions to multiple slave ends respectively. Each slave end performs multipath scanning in its own designated time slot and transmits frequency information back to the master end to realize dynamic monitoring of the multipath environment of multiple UAVs.

7. The method for resisting multipath fading for a wireless data transmission system of an unmanned aerial vehicle according to claim 6, characterized in that: After completing the multipath scanning, when the master end or the slave end returns to the regular working frequency for normal data transmission, the rate, adaptive modulation and transmission power are adjusted in real time according to the multipath characteristic parameters obtained in the aforementioned scanning process, thereby reducing the signal interference and transmission interruption probability caused by multipath fading.

8. An anti-multipath fading system for a wireless data transmission system of an unmanned aerial vehicle according to claims 1-2, characterized in that: The system has one master and one slave. The master and the slave perform TDD communication with frequencies of f1 to fN and a channel bandwidth of BW. f1, f2, ..., fN are adjacent channels, and the bandwidth of each channel is BW.

9. The anti-multipath fading system for the wireless data transmission system of an unmanned aerial vehicle according to claim 8, characterized in that: In the system, after all devices are turned on, the master end periodically sends a synchronization signal, the slave end synchronizes with the master end, sends its own signal following the signal of the master end, and communicates according to the agreed TDD time slot allocation. The time of one transmission by the master end + one transmission by the slave end is called a time slot, and the time slot length is fixed to M seconds. The sending time of the master end and the sending time of the slave end are also fixedly allocated.

Images