CN107135163A - A kind of transfer control method based on unmanned plane wideband data downlink - Google Patents

Abstract

The invention relates to a transmission control method based on the downlink of the broadband data link of the unmanned aerial vehicle, and the method improves the reliability of the data link transmission message under the background. Under the transmission background of the UAV broadband data link downlink, by adding time stamps to the data packets at the sending end in the air, the delay is used to judge the congestion situation, the sending rate is controlled by the window, and the congestion threshold parameter is proposed to Early warning of congestion to avoid packet loss caused by severe link congestion. This approach improves the downlink transmission of the drone's broadband data link and improves safety.

Description

A transmission control method based on the downlink of UAV broadband data link

technical field

The invention discloses a transmission control method based on the downlink of the UAV broadband data link, especially when the downlink of the UAV transmits a large number of data packets, the lack of adjustment of the sending rate leads to an increase in the packet loss rate and a time delay phenomenon. A transmission control method based on the downlink of UAV broadband data link for serious application scenarios.

Background technique

With the development of science and technology, UAVs are used more and more frequently in China, and the available fields are becoming more and more extensive. They can be used for aerial photography, photography, monitoring, transportation, etc. The data link is a data communication system that uses a unified data format and communication protocol to transmit information in real time, accurately and confidentially based on wireless channels.

UAV data link is the core module of UAV technology, and it is also a key research direction in the future. It is the core of sending and receiving information and transmitting data, responsible for controlling the sending of information and receiving of collected data. Therefore, with the development of technology, UAV technology is also constantly upgrading, and the demand is also increasing. Real-time transmission, anti-jamming capability, and accuracy requirements have become key issues in system design. The UAV broadband data link is a data link transmitted on a higher frequency band, which transmits some information data with a large amount of data, which requires high reliability of data link transmission, but the same, it is also One of the problems that needs to be solved.

The data link has a strong asymmetry, that is, the aircraft needs to transmit a large amount of status information to the ground, including the information of the aircraft itself such as attitude, orientation, speed, altitude, temperature, and information of various equipment on board, such as high-definition video information, Laser scanning information, etc., while the information transmitted from the ground to the aircraft is relatively small, including control information, planning information and parameter information. The flight control of the drone itself is difficult, and to complete operations in various harsh environments, it is necessary to ensure communication equipment with strong anti-interference capabilities and data link design standards that can cope with various complex situations.

In the UAV broadband data link system, the flight control data link protocol is one of the core, and the flight control data link can be divided into uplink and downlink. The uplink is the transmission from the ground end to the UAV end. Link; the downlink is the transmission link from the UAV end to the ground end. In the UAV broadband data link, the uplink uploads some control information, etc., and the downlink transmits some UAV information and obtained data, such as images, videos, etc.

Due to the large amount of data transmitted in the downlink of the UAV broadband data link, the transmission protocol is mostly UDP (User Datagram Protocol) transmission protocol. The transmission protocol UDP (User Datagram Protocol) protocol is a connectionless The transport layer protocol, which encapsulates the data transmitted from the application layer in a data packet for transmission, because the UDP protocol (User Datagram Protocol) lacks congestion control, it will not control the sending rate because there are too many or too large data packets , in the application of UDP protocol (User Datagram Protocol), as the transmission data increases, the packet loss rate and delay also increase. If the sending rate is not reduced, packet loss or frame drop will become more and more serious. If there is information loss in the downlink of the drone, this is a fatal problem. So this problem needs to be dealt with.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a method based on downlink transmission control in the UAV broadband data link, and improves the reliability of the data link transmission message under this background.

To achieve the above object, design of the present invention is:

The transmission link of the UAV broadband data link can be divided into uplink and downlink. The uplink mainly uploads some control information parameters, etc., while the data transmitted by the downlink is generally images, videos and other information. For large data, the UDP protocol (User Datagram Protocol) is currently used here, because the UDP protocol (User Datagram Protocol) has a good transmission efficiency compared to the three-way handshake of the TCP protocol (Transmission Control Protocol). , which is very suitable for UAVs with high real-time requirements, but similarly, the UDP protocol (User Datagram Protocol) is a protocol with low reliability.

When the data downloaded by the UAV is only some airborne parameters and sensor information, the amount of data is not large at this time and can be transmitted quickly. When the data transmitted is some video, images, etc. The UDP protocol (User Datagram Protocol) itself does not have any congestion control. The UDP protocol (User Datagram Protocol) will not control the sending rate due to too many or too large data packets. Once congestion occurs, at the moment when the buffer is full The message to be sent is likely to be lost. For the UAV broadband data link system, the data information obtained by the ground terminal will be incomplete, which is a fatal problem.

Aiming at the situation that congestion will occur in the downlink of the UAV broadband data link, the present invention proposes a transmission control method, which will use three parameters to monitor the congestion status of the UAV downlink transmission process. Judgment, using four different control methods to improve the reliability of the transmission link.

According to above-mentioned inventive concept, the present invention adopts following technical scheme:

The present invention is characterized in that the time delay is used to reflect link congestion, the transmission rate is controlled by the window, and the congestion threshold and the target time delay parameter are added, and the size of the window value is adjusted by judging the time delay and the packet loss situation, and the specific operation Proceed as follows:

1) Set the initial window value, congestion threshold and target delay;

2) Use the timestamp to read the transmission delay;

3) Adjust the window value through the value of delay and packet loss.

The method of setting the initial window value, congestion threshold and target delay in the above step 1) is: set the initial window value, congestion threshold and target delay according to the design requirements of the UAV data link, and the window value is used to control the transmission rate , the initial value can be set larger to quickly increase the link transmission rate; the congestion threshold and target delay are used to avoid entering the congestion state, and the size can be set according to the needs of the link.

The above step 2) The method of using the time stamp to read the transmission delay is: add a time stamp to the data packet of the UAV’s aerial transmitter, and record the sending time. When the data packet is sent to the ground receiving end, by reading the time The absolute transmission delay can be obtained by subtracting the timestamp from the local time.

The method of adjusting the window value in the above step 3) through the value of delay and packet loss is: according to the read delay and packet loss rate, it can be divided into four window control methods. The specific operation steps are as follows :

① When the delay value is less than the difference between the target delay and the congestion threshold, it indicates that the congestion state is good at this time, and the transmission can be accelerated. Returning ACK (confirmation character) indicates that the sending rate can be increased by rapidly expanding the window value;

②When the delay value is greater than the difference between the target delay and the congestion threshold and is less than the target delay value, it indicates that the congestion state is about to be reached at this time, and the transmission rate needs to be controlled. Returning ACK indicates that the method of slowing down and expanding the window value can be used. Slowly increase the sending rate;

③When the delay value is greater than the target delay value, it indicates that it can be judged as a congestion state at this time, and returning ACK indicates that the transmission rate can be reduced by reducing the window value;

④ When packet loss occurs due to unexpected circumstances, returning ACK indicates that the sending rate can be reduced by rapidly reducing the window value.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant technological progress:

This method can effectively improve the transmission reliability of the UAV broadband data link downlink, reduce the probability of data packet loss or the occurrence of frame drop, and improve the transmission efficiency as much as possible under the premise of ensuring reliability. Compared with the downlink transmission control of the traditional UAV data link, this greatly improves the performance of the data link.

Description of drawings

Fig. 1 is a block diagram of the downlink transmission control flow of the UAV broadband data link of the present invention.

Fig. 2 is a conversion diagram of the UAV broadband data link downlink transmission control stage of the present invention.

detailed description

Preferred embodiments of the present invention are described in detail as follows in conjunction with accompanying drawings:

Embodiment one:

Referring to Fig. 1, the transmission control method based on the downlink of the UAV broadband data link is characterized in that the delay is used to reflect the link congestion, the transmission rate is controlled by the window, and the congestion threshold and the target delay parameter are added. Determine the size of the delay and packet loss, and adjust the size of the window value. The specific steps are as follows:

1) Set the initial window value, congestion threshold and target delay;

2) Use the timestamp to read the transmission delay;

3) Adjust the window value through the value of delay and packet loss.

Embodiment two:

This embodiment is basically the same as Embodiment 1, and its special features are as follows:

The feature is that in step 1) the method of setting the initial window value, congestion threshold and target delay is: setting the initial window value, congestion threshold and target delay according to transmission requirements, the window value is used to control the transmission rate, the congestion threshold and The target delay is used to avoid entering a congestion state; the feature is that step 2) uses the time stamp to read the transmission delay method: add a time stamp to the data packet of the aerial sending end of the drone, and when it is sent to the ground receiving end , the transmission delay can be obtained by reading the timestamp; the feature is that step 3) the method of adjusting the window value through the value of the delay and the packet loss situation is: according to the size of the delay and the packet loss rate, It can be divided into four window control methods, and the specific operation steps are as follows:

① When the delay value is less than the difference between the target delay and the congestion threshold, the method of rapidly expanding the window value is adopted to increase the sending rate;

② When the delay value is greater than the difference between the target delay and the congestion threshold and is less than the target delay value, take the method of slowing down the expansion of the window value to increase the sending rate;

③ When the value of time delay is greater than the value of target time delay, take the method of reducing the window value to reduce the sending rate;

④ When packet loss occurs due to unexpected circumstances, the sending rate is reduced by quickly reducing the window value.

Embodiment three:

The transmission control method based on the UAV broadband data link downlink is described in detail in conjunction with Figure 1 as follows:

This embodiment uses the time delay to reflect the link congestion situation, controls the sending rate with the window, and adds the congestion threshold and the target time delay parameter, and adjusts the size of the window value by judging the size of the time delay and the packet loss situation, and the specific operation steps as follows:

1) Set the initial window value, congestion threshold and target delay;

2) Use the timestamp to read the transmission delay;

3) Adjust the window value through the value of delay and packet loss.

Step 1) is to set the initial window value, congestion threshold and target delay according to the design requirements of the UAV data link. The window value is used to control the transmission rate. The initial test value can be set larger to quickly increase the link transmission rate ; Congestion threshold and target delay are used to avoid entering the congestion state, and the size can be set according to the requirements of the link.

Step 2) is to add a timestamp to the data packet of the UAV’s air transmitter, and record the sending time. When the data packet is sent to the ground receiver, by reading the timestamp and subtracting the timestamp from the local time, we can get Absolute transmission delay.

Step 3) can be divided into four window control methods according to the read delay and packet loss rate. The specific operation steps are as follows:

① When the delay value is less than the difference between the target delay and the congestion threshold, it indicates that the congestion state is good at this time, and the transmission can be accelerated. Returning ACK (confirmation character) indicates that the sending rate can be increased by rapidly expanding the window value;

②When the delay value is greater than the difference between the target delay and the congestion threshold and is less than the target delay value, it indicates that the congestion state is about to be reached at this time, and the transmission rate needs to be controlled. Returning ACK (confirmation character) indicates that the window can be expanded by slowing down Value way to slowly increase the sending rate;

③When the delay value is greater than the target delay value, it indicates that it can be judged as a congestion state at this time, and returning ACK (confirmation character) indicates that the sending rate can be reduced by reducing the window value;

④ When packet loss occurs due to unexpected circumstances, returning ACK (confirmation character) indicates that the sending rate can be reduced by rapidly reducing the window value.

The four window controls of the above process 4 can be expressed as:

Where W(t+1) is the value of the next window, W(t) is the value of the current window, T is the target delay, c is the absolute delay, q is the congestion threshold, P is the gain factor, where P1, P2 , P3 is related to the maximum message unit, and if P1>>P2, P3 is a negative value, and P4 is related to the packet loss rate.

The control phase can be divided into an initial phase, a steady phase, a pre-congestion phase, and a congestion phase according to the formula and illustrated in FIG. 2 with reference to the accompanying drawings. From the initial stage, the sending window has been expanded until the time delay is equal to the difference between the target delay and the congestion threshold and enters the second stage of steady state. As the window continues to expand, it enters the pre-congestion stage at this time, and the window value will continue to increase, but The increase range begins to decrease, and when the delay reaches the target time delay, it enters the congestion stage and begins to reduce the window value.

Claims (4)

1. A transmission control method based on the downlink of the UAV broadband data link, characterized in that it utilizes time delay to respond to link congestion, controls the transmission rate with a window, and adds congestion threshold and target time delay parameters, through judging The size of the delay and the packet loss situation, adjust the size of the window value, the specific operation steps are as follows: 1) Set the initial window value, congestion threshold and target delay; 2) Use the timestamp to read the transmission delay; 3) Adjust the window value through the value of delay and packet loss. 2. The transmission control method based on the UAV broadband data link downlink according to claim 1, characterized in that the method of setting the initial window value, congestion threshold and target time delay in the step 1) is: according to the transmission It is required to set the initial window value, congestion threshold and target delay. The window value is used to control the transmission rate, and the congestion threshold and target delay are used to avoid entering the congestion state. 3. The transmission control method based on the UAV broadband data link downlink according to claim 1, characterized in that the step 2) uses the time stamp to read the transmission delay method: in the air of the UAV A time stamp is added to the data packet at the sending end, and when it is sent to the receiving end on the ground, the transmission delay can be obtained by reading the time stamp. 4. The transmission control method based on the UAV broadband data link downlink according to claim 1, characterized in that said step 3) the method for adjusting the window value through the numerical value of the delay and the packet loss situation is: According to the size of the delay and the packet loss rate, it can be divided into four window control methods. The specific operation steps are as follows: ① When the delay value is less than the difference between the target delay and the congestion threshold, the method of rapidly expanding the window value is adopted to increase the sending rate; ② When the delay value is greater than the difference between the target delay and the congestion threshold and is less than the target delay value, take the method of slowing down the expansion of the window value to increase the sending rate; ③ When the value of time delay is greater than the value of target time delay, take the method of reducing the window value to reduce the sending rate; ④ When packet loss occurs due to unexpected circumstances, the sending rate is reduced by quickly reducing the window value.