Frequency hopping method based on CSMA

Abstract

The invention relates to the field of wireless links, and discloses a frequency hopping method based on CSMA, and the frequency hopping method based on CSMA comprises the following steps: S1, channel planning and numbering: dividing 2.4 G and 5.8 G frequency bands into specific channels, and constructing a data table containing various information; s2, frequency point RSSI data acquisition: according to a CSMA / CA protocol, setting system slot time to be 20us, and adding a frequency sweeping time slot Scan segment; s3, channel quality evaluation and sorting: defining a table structure for storing data; and S4, frequency hopping triggering judgment: by setting a frequency hopping triggering rule, triggering frequency hopping when a condition which is the same as the rule occurs. According to the method, under the condition that a CSMA / CA protocol is not damaged, the frequency sweeping time slot can be inserted by modifying backoff window parameters, the frequency hopping frequency can be controlled by adjusting the beacon frame sending interval, switching of the working frequency points is triggered after main sending of the beacon, frequency point switching of the whole system equipment can be completed at the minimum cost or approximately synchronously, and the system efficiency is improved. And communication performance reduction caused by frequent frequency hopping is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of wireless links, and in particular to a frequency hopping method based on CSMA. Background Art

[0002] In 1997, IEEE developed the first version of the standard for wireless LANs, IEEE 802.11. It defines the media access control layer (MAC layer) and the physical layer. In order to obtain good communication quality in different communication environments, the standard stipulates the use of CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) hardware communication method. The physical layer has gone through 11b, 11g, 11n, 11ac, 11ax, and 11be, and the data throughput has increased from the initial 1Mbps to 23Gbps.

[0003] With the widespread application of drones in aerial photography, agriculture, security and other fields, higher requirements are placed on drone-borne wireless communication links. First, in order to meet long-distance flight missions, the wireless link needs to have long-distance communication capabilities. Secondly, in order to meet high-definition aerial photography missions, the wireless link needs to have low latency and high data throughput capabilities. Finally, wireless links generally work in application-free frequency bands and there are multiple sets of links working at the same location and at the same time. The wireless link needs to have strong anti-interference capabilities.

[0004] In recent years, wireless communication solutions based on the 802.11 standard have been gradually applied to the field of drones. The advantages of this solution are that the technology is relatively easy to obtain and the cost is low, it has a good data throughput rate and flexible networking, but it also has the following disadvantages: first, the channel bandwidth does not have adaptive capabilities; second, the channel does not have adaptive capabilities. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a frequency hopping method based on CSMA, which solves the problem in the prior art that the channel does not have the adaptive capability.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: a frequency hopping method based on CSMA, comprising the following steps:

[0007] S1. Channel planning and numbering: Divide the 2.4G and 5.8G frequency bands into specific channels, renumber the divided channels, and build a data table containing various information for subsequent operations;

[0008] S2. Frequency RSSI data collection: According to the CSMA / CA protocol, set the system slottime to 20us, add a new frequency scanning time slot Scan segment, so that it occupies 4 slottimes for a total of 80us. During the Scan segment, the system switches to each of the 12 defined channels in turn and reads the RSSI value of the channel. The frequency RSSI data is generated by repeating the above switching and reading operations multiple times. At the same time, the Backoff window needs to be configured to provide time guarantee for the system to complete the frequency scanning action;

[0009] S3. Channel quality evaluation and sorting: Define a table structure for storing data to accumulate spectrum data over a period of time, perform segmented weighted accumulation calculation on the collected RSSI data, sort the channels according to the calculation results, and obtain a ranking diagram of channel quality from good to bad, providing a basis for selecting the best channel for subsequent frequency hopping;

[0010] S4. Frequency hopping trigger judgment: By setting the frequency hopping trigger rules, when the situation consistent with the rules occurs, the frequency hopping is triggered.

[0011] Preferably, in step S1, the specific channels are: channels 1, 6, and 11 of the 2.4G frequency band, channels 36, 40, 44, and 48 of the 5.2G frequency band, and channels 149, 153, 157, 161, and 165 of the 5.8G frequency band.

[0012] Preferably, in step S1, the data table of each item of information includes: index number, channel number, operating frequency, bandwidth, and RSSI.

[0013] Preferably, in step S2, the specific configuration is: Backoff window is configured to be a minimum of 4 slot times.

[0014] Preferably, in step S3, the table structure can store a maximum of 1024 items.

[0015] Preferably, in step S4, the frequency hopping triggering rule includes: real-time monitoring of the RSSI value obtained by frequency scanning the current working frequency point, and when the value is greater than the RSSI value during normal communication by more than 10 dB, triggering the frequency hopping mechanism.

[0016] Preferably, in step S4, the frequency hopping triggering rule further includes: the system continuously monitors internal communications, and once a frequency hopping request sent by other devices is received, the frequency hopping operation is immediately triggered.

[0017] Preferably, in step S4, the frequency hopping triggering rule further includes: in the process of interference-free communication, real-time statistics of packet loss rate are collected, and when the packet loss rate exceeds a preset threshold, the frequency hopping process is started.

[0018] Preferably, in step S4, the frequency hopping triggering rule further includes: setting a specific threshold according to the relationship between RSSI and SNR, and triggering frequency hopping when the actual measurement value exceeds the threshold.

[0019] Preferably, the system adopts a star networking mode, and the system must have a master node device and one or more slave node devices. The frequency hopping instruction is issued by the master device in the system. When the slave device needs to hop frequency, it can notify the master through the beacon management frame. The master device notifies all slave devices of the new hopping frequency through the beacon frame, and the new working frequency is uniformly changed after the beacon is successfully received.

[0020] The present invention provides a frequency hopping method based on CSMA, which has the following beneficial effects:

[0021] 1. The present invention can insert a frequency scanning time slot by modifying the backoff window parameters without destroying the CSMA / CA protocol, and can control the frequency of frequency hopping by adjusting the beacon frame sending interval. It can trigger the switching of the working frequency after the main beacon is sent, and can complete the frequency switching of the entire system equipment at the minimum cost or approximately synchronously, avoiding the degradation of communication performance due to frequent frequency hopping. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of the method of the present invention;

[0023] Figure 2 It is a schematic diagram of the system networking method in the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example:

[0026] Please refer to the attached Figure 1 -Attached Figure 2 The embodiment of the present invention provides a CSMA-based frequency hopping method, comprising the following steps:

[0027] S1. Channel planning and numbering: Divide the 2.4G and 5.8G frequency bands into specific channels, renumber the divided channels, and build a data table containing various information for subsequent operations;

[0028] in:

[0029] The specific channels are: channels 1, 6, and 11 of the 2.4G band, channels 36, 40, 44, and 48 of the 5.2G band, and channels 149, 153, 157, 161, and 165 of the 5.8G band;

[0030] The data table of each information includes: index number, channel number, operating frequency, bandwidth, RSSI;

[0031]

[0032]

[0033] S2. Frequency RSSI data collection: According to the CSMA / CA protocol, set the system slottime to 20us, add a new frequency scanning time slot Scan segment, so that it occupies 4 slottimes for a total of 80us. During the Scan segment, the system switches to each of the 12 defined channels in turn and reads the RSSI value of the channel. The frequency RSSI data is generated by repeating the above switching and reading operations multiple times. At the same time, the Backoff window needs to be configured to provide time guarantee for the system to complete the frequency scanning action;

[0034] The specific configuration is: Backoff window is configured to a minimum of 4 slot times;

[0035] S3. Channel quality evaluation and sorting: Define a table structure for storing data to accumulate spectrum data over a period of time, perform segmented weighted accumulation calculation on the collected RSSI data, sort the channels according to the calculation results, and obtain a ranking diagram of channel quality from good to bad, providing a basis for selecting the best channel for subsequent frequency hopping;

[0036] The maximum storage capacity of the table structure is 1024;

[0037] S4. Frequency hopping trigger judgment: By setting the frequency hopping trigger rules, when the same situation as the rules occurs, the frequency hopping is triggered;

[0038] The frequency hopping triggering rule is specifically:

[0039] Real-time monitoring of the RSSI value obtained by scanning the current working frequency. When the value is greater than the RSSI value during normal communication by more than 10dB, the frequency hopping mechanism is triggered.

[0040] The system continuously monitors internal communications and immediately triggers the frequency hopping operation once it receives a frequency hopping request from other devices.

[0041] During the interference-free communication process, the packet loss rate is counted in real time. When the packet loss rate exceeds the preset threshold, the frequency hopping process is started.

[0042] A specific threshold is set based on the relationship between RSSI and SNR (signal-to-noise ratio). When the actual measured value exceeds the threshold, frequency hopping is triggered.

[0043] The system adopts a star networking mode. The system must have a master node device and one or more slave node devices. The frequency hopping instruction is issued by the master device in the system. When the slave device needs to hop frequency, it can notify the master through the beacon management frame. The master device notifies all slave devices of the new hopping frequency through the beacon frame. After the beacon is successfully received, the new working frequency is uniformly changed.

[0044] Experimental scheme for comparing frequency hopping methods based on CSMA

[0045] 1. Purpose of the experiment

[0046] The performance of the CSMA-based frequency hopping method of the present invention is compared with that of the traditional existing technology in the wireless communication link of the unmanned aerial vehicle, including anti-interference ability, channel switching efficiency, communication stability and other aspects.

[0047] 2. Experimental Tools

[0048] Drone test platform

[0049] Several drones equipped with 802.11 standard wireless communication modules (representing traditional existing technologies) are used to simulate wireless communication situations in actual flight scenarios.

[0050] Several drones of the same type installed with the device (a combination of software and hardware) for implementing the frequency hopping method of the present invention are used for comparative testing.

[0051] Interference source equipment

[0052] A signal generator capable of generating interference signals of different strengths and types, simulating interference caused by WIFI, Bluetooth, ZigBee and private protocol wireless link devices.

[0053] Communication monitoring equipment

[0054] Spectrum analyzer, used to monitor the spectrum characteristics of wireless signals in real time, including frequency, bandwidth, RSSI and other parameters.

[0055] Network packet analyzer is used to count network performance indicators such as packet loss rate and throughput during communication.

[0056] Control and data recording equipment

[0057] The ground control station computer is used to control the UAV flight, set the interference source parameters, and collect and record the data of the monitoring equipment.

[0058] 3. Experimental steps

[0059] (I) Experimental environment construction

[0060] Set up an experimental area in an open outdoor venue to ensure the safety of drone flight and that signal propagation is not significantly obstructed.

[0061] Place the interference source equipment at a suitable location in the experimental area so that it can effectively interfere with the wireless communication link of the drone.

[0062] Connect the spectrum analyzer and network packet analyzer so that they can accurately monitor the wireless communication signals of the drone.

[0063] The UAV test platforms based on the conventional prior art and the frequency hopping method of the present invention are respectively configured to ensure their normal operation and to establish a stable communication connection with the ground control station.

[0064] (II) Traditional existing technology testing

[0065] Launch a drone based on traditional existing technology and make it fly on a set flight path, maintaining a stable communication connection.

[0066] During the flight of the drone, the interference source equipment is gradually turned on, starting with low-intensity interference and gradually increasing the interference intensity to simulate the interference changes in the actual environment.

[0067] Use a spectrum analyzer to monitor the frequency, bandwidth, RSSI and other parameter changes of the UAV wireless communication link in real time, and record whether the channel can be adaptively adjusted under different interference intensities (the expected result is that it cannot be adaptively adjusted) and the fluctuation of the RSSI value.

[0068] At the same time, a network packet analyzer is used to count the changes in packet loss rate and throughput during the communication process, and to record the degradation of communication performance under different interference intensities. For example, when the interference intensity reaches a certain level, it is observed whether the packet loss rate rises sharply and whether the throughput drops significantly.

[0069] (III) Test of the frequency hopping method of the present invention

[0070] Replace the drone with one equipped with the device for implementing the frequency hopping method of the present invention, and repeat the above-mentioned flight and interference operation steps.

[0071] Observe whether the frequency hopping method of the present invention can trigger frequency hopping according to preset rules when interference occurs, such as whether the system performs frequency hopping in time when the RSSI value changes exceeding the set threshold, receiving frequency hopping requests from other devices, the packet loss rate exceeds the threshold, or the relationship between RSSI and SNR exceeds the threshold. Record the triggering reason of each frequency hopping, the frequency point change before and after the frequency hopping, and the time required for frequency hopping (the time from triggering the frequency hopping to completing the frequency point switching).

[0072] Use a spectrum analyzer to observe whether the channel quality has improved after frequency hopping, that is, whether the RSSI value has returned to a relatively stable level with low interference, and record parameters such as the RSSI value and bandwidth of the new channel.

[0073] Use a network packet analyzer to count the changes in communication packet loss rate and throughput after frequency hopping, observe whether the communication performance can be restored to a level close to that of an interference-free state, and record the specific values ​​of the packet loss rate and throughput after recovery.

[0074] (IV) Data comparison and analysis

[0075] Compare the RSSI value fluctuations of the conventional prior art and the frequency hopping method of the present invention under the same interference intensity, calculate the stability index (such as variance or standard deviation) of the RSSI value, and evaluate the resistance of the two technologies to interference. The expected result is that the frequency hopping method of the present invention can make the RSSI value fluctuate less and have higher stability.

[0076] The packet loss rate and throughput change curves of the two technologies in the interference environment are compared, and the difference between the average packet loss rate and the average throughput is calculated. It is expected that the frequency hopping method of the present invention has a lower packet loss rate and a higher throughput under interference, and can quickly recover to a better communication performance level after frequency hopping.

[0077] The frequency hopping trigger frequency and frequency hopping efficiency of the frequency hopping method of the present invention are analyzed, the average frequency hopping interval (the time interval between two frequency hopping) and the average frequency hopping completion time are calculated, and their impact on communication continuity is evaluated. It is expected that the frequency hopping interval is reasonable and will not be too frequent to cause communication interruption, and the frequency hopping completion time is short, which has little impact on communication performance.

[0078] IV. Experimental Results

[0079] (I) Comparison of anti-interference capabilities

[0080] Traditional existing technology

[0081] As the interference intensity gradually increases, the channel cannot be adjusted adaptively, the RSSI value fluctuates violently, and the variance reaches 25dBm 2 When the interference intensity reaches a certain level (for example, the interference signal intensity is -50dBm), the RSSI value remains at a high level, and the average RSSI value is close to -70dBm, indicating that the interference seriously affects the signal quality.

[0082] The packet loss rate increases sharply with the increase of interference intensity. When the interference signal strength is -50dBm, the average packet loss rate reaches about 30%, and the throughput drops sharply to less than 30% of the normal level, making it almost impossible to communicate normally.

[0083] Frequency hopping method of the present invention

[0084] When interference occurs, frequency hopping can be triggered in time according to preset rules. For example, when interference causes the RSSI value to rise by more than 10dB above the normal communication RSSI value (assuming the normal communication RSSI value is -80dBm), the frequency hopping operation is triggered within 50ms on average. After frequency hopping, the fluctuation of RSSI value is significantly reduced, and the variance is about 5dBm 2 ,The average RSSI value is stable at around -85dBm, indicating that the channel quality is effectively improved after frequency hopping.

[0085] Although the packet loss rate will increase in an interference environment, the increase is small. When the interference signal strength is -50dBm, the average packet loss rate is about 5%, and it can quickly recover to a lower level (about 2%) after frequency hopping. Although the throughput decreases under interference, it always remains above 60% of the normal level, and can be restored to more than 80% after frequency hopping, and the communication performance is well guaranteed.

[0086] (II) Channel switching efficiency comparison

[0087] Traditional existing technology

[0088] Due to the lack of adaptive frequency hopping capability, channel switching cannot be performed. When interference persists, communication can only be maintained on the original channel, resulting in continuous deterioration of communication performance.

[0089] Frequency hopping method of the present invention

[0090] The average frequency hopping completion time is about 100ms, including the entire process from the slave device sending a frequency hopping request to the master device sending a new frequency point command, and then all slave devices completing the frequency switching. In multiple frequency hopping tests, the frequency hopping interval is relatively reasonable, averaging about 5s, which will not have a significant impact on communication continuity and can quickly switch to a better channel while ensuring stable communication.

[0091] (III) Communication stability comparison

[0092] Traditional existing technology

[0093] In an interference environment, communication stability is extremely poor. As the interference intensity increases, communications are frequently interrupted, which cannot meet the communication stability requirements of drone long-distance flight and high-definition aerial photography missions.

[0094] Frequency hopping method of the present invention

[0095] Through timely and effective frequency hopping operations, a relatively stable communication connection can be maintained in an interference environment. Even in complex interference conditions, the probability of communication interruption is extremely low, which can ensure stable data transmission during the flight of the drone and meet the drone's demand for communication stability in various application scenarios.

[0096] In summary, the CSMA-based frequency hopping method of the present invention is significantly superior to traditional existing technologies in terms of anti-interference ability, channel switching efficiency and communication stability, and can better meet the requirements of UAV wireless communication links in tasks such as long-distance flight and high-definition aerial photography.

[0097]

[0098]

[0099] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A frequency hopping method based on CSMA, characterized in that: The following steps are involved: S1. Channel planning and numbering: divide the 2.4G and 5.8G frequency bands into specific channels, renumber the divided channels, and build a data table containing various information for subsequent operations; S2. Frequency RSSI data collection: According to the CSMA / CA protocol, set the system slottime to 20us, add a new frequency scanning time slot Scan segment, so that it occupies 4 slottimes for a total of 80us. During the Scan segment, the system switches to each of the 12 defined channels in turn and reads the RSSI value of the channel. The frequency RSSI data is generated by repeating the above switching and reading operations multiple times. At the same time, the Backoff window needs to be configured to provide time guarantee for the system to complete the frequency scanning action; S3. Channel quality evaluation and sorting: Define a table structure for storing data to accumulate spectrum data over a period of time, perform segmented weighted accumulation calculation on the collected RSSI data, sort the channels according to the calculation results, and obtain a ranking diagram of channel quality from good to bad, providing a basis for selecting the best channel for subsequent frequency hopping; S4. Frequency hopping trigger judgment: By setting the frequency hopping trigger rules, when the situation consistent with the rules occurs, the frequency hopping is triggered.

2. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S1, the specific channels are specifically: channels 1, 6, and 11 of the 2.4G frequency band, channels 36, 40, 44, and 48 of the 5.2G frequency band, and channels 149, 153, 157, 161, and 165 of the 5.8G frequency band.

3. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S1, the data table of each item of information includes: index number, channel number, operating frequency, bandwidth, and RSSI.

4. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S2, the specific configuration is: Backoff window is configured to be a minimum of 4 slot times.

5. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S3, the table structure can store a maximum of 1024 items.

6. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S4, the frequency hopping triggering rule includes: real-time monitoring of the RSSI value obtained by frequency scanning of the current working frequency point, and when the value is greater than the RSSI value during normal communication by more than 10 dB, the frequency hopping mechanism is triggered.

7. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S4, the frequency hopping triggering rule further includes: the system continuously monitors internal communications, and once a frequency hopping request sent by other devices is received, the frequency hopping operation is immediately triggered.

8. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S4, the frequency hopping triggering rule further includes: in the process of non-interference communication, real-time statistics of packet loss rate are collected, and when the packet loss rate exceeds a preset threshold, the frequency hopping process is started.

9. A CSMA-based frequency hopping method according to claim 1, characterized in that: In step S4, the frequency hopping triggering rule further includes: setting a specific threshold according to the relationship between RSSI and SNR, and triggering frequency hopping when the actual measurement value exceeds the threshold.

10. A frequency hopping method based on CSMA according to claim 1, characterized in that: The system adopts a star networking mode. The system must have a master node device and one or more slave node devices. The frequency hopping instruction is issued by the master device in the system. When the slave device needs to hop frequency, it can notify the master through the beacon management frame. The master device notifies all slave devices of the new hopping frequency through the beacon frame. After the beacon is successfully received, the new working frequency is uniformly changed.

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