CN111417081B

CN111417081B - Reliable broadcasting method for mixed traffic system with formation as center

Info

Publication number: CN111417081B
Application number: CN202010235874.0A
Authority: CN
Inventors: 王剑; 黄延
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2020-12-29
Anticipated expiration: 2040-03-30
Also published as: CN111417081A

Abstract

The invention relates to the field of communication, in particular to a reliable broadcasting method of a mixed traffic system taking formation as a center. The invention takes unmanned formation as a center to form a wireless basic service set. Where the convoy vehicles use a TDMA protocol and the other vehicles use a CSMA/CA protocol. The invention selects part of formation members as CTS responders in the basic service set, realizes RTS/CTS function for the broadcast communication of free vehicles driven by people, and leads the broadcast communication to have retransmission capability by introducing RTS/CTS mechanism for the broadcast communication, thereby improving the reliability of the broadcast communication. The invention makes full use of the topological structure characteristics in the hybrid traffic system, and can greatly reduce the performance loss caused by collision in wireless communication, thereby improving the network communication efficiency.

Description

Reliable broadcasting method for mixed traffic system with formation as center

Technical Field

The invention relates to the field of communication, in particular to a reliable broadcasting method of a mixed traffic system taking formation as a center.

Background

The unmanned technology is mature continuously, and unmanned vehicles form an unmanned formation to greatly improve the driving passing efficiency and reduce the energy consumption. The spacing between vehicles within a formation can be very short and the topology of the vehicles within the formation can remain stable for a significant period of time. Currently, there are many communication systems specifically designed for such a formation system, and most of them adopt a conflict-free protocol design mode, for example, a Time Division Multiplexing (TDMA) method. In a real application scenario, the unmanned formation will coexist with a conventional manned vehicle. Such a traffic system in which unmanned formation and manned vehicles coexist is called a hybrid traffic system. In hybrid transportation systems, the communication performance of people driven vehicles is often overlooked.

It is anticipated that hybrid traffic systems will be the primary mode of traffic operation for a long period of time in the future. In the hybrid transportation system, since the motion state of the human-driven vehicle is difficult to predict and the topological result thereof is unstable, a competition-based communication protocol is still used in the human-driven vehicle. The current vehicle-to-vehicle communication standard for vehicle networking communication is Wireless Access in Vehicular environment (WAVE). Wherein the data link layer of WAVE uses the carrier sense multiple access/collision avoidance (CSMA/CA) mechanism of the ieee802.11p standard. CSMA/CA does not require workshop synchronization, but in CSMA/CA, each node needs to acquire access to a control channel by way of contention. In a high-density network scenario, the performance loss due to contention may reduce the efficiency and effectiveness of the communication.

In the WAVE protocol, the 75MHz bandwidth is divided into 7 channels, including one control channel and six service channels. The control channel is responsible for transmitting control information and security related information. According to the IEEE1609.4 standard in WAVE, a vehicle's access to a plurality of channels defined in the standard is temporally divided into synchronization intervals of length 100ms, each of which is further divided into control channel intervals and service channel intervals of length 50ms each, for accessing control channels and service channels, respectively. The vehicle access right allocation to the service channel needs to be negotiated on the control channel, so the communication efficiency of the service channel is also limited by the communication performance and reliability of the control channel. Due to the nature of the type of message transmitted, it is typically a multi/broadcast mode on the control channel and a unicast mode on the service channel. In the method, due to the lack of a pre-designated target node, broadcast communication used by a control channel cannot naturally use mechanisms such as ACK and RTS/CTS to ensure the reliability of transmission, but the control channel is specially used for transmitting control and safety related information, and resource scheduling of a service channel is also performed on the control channel. The unreliability of the CSMA mechanism on the control channel can bring great uncertainty to the multi-channel communication performance between vehicles, and even further endanger the driving safety. Designing a reliable broadcast communication protocol for a hybrid transportation system therefore has a very important impact on overall communication performance and robustness.

Disclosure of Invention

The invention aims to fill the blank of the prior art and provides a reliable broadcasting method of a mixed traffic system taking formation as a center. The invention makes full use of the topological structure characteristics in the hybrid traffic system, and can greatly reduce the performance loss caused by collision in wireless communication, thereby improving the network communication efficiency. In addition, the invention introduces RTS/CTS mechanism for broadcast communication, thus the broadcast communication can have retransmission capability, and the reliability of the broadcast communication is improved.

The invention provides a reliable broadcasting method of a mixed traffic system taking formation as a center, which is characterized by comprising the following steps:

1) taking an unmanned formation formed by unmanned vehicles and a set formed by one-hop neighbor nodes of the formation as a wireless basic service set P-WBSS taking the formation as a center; wherein the one-hop neighbor node of the formation is a vehicle driven by a person;

in P-WBSS, the inside of the unmanned formation uses a communication protocol based on TDMA, and the vehicles driven by people use CSMA/CA protocol in WAVE standard;

2) the unmanned formation confirms the division mode of the TDMA section and the CSMA section in the control channel access interval;

the specific method comprises the following steps: dividing a control channel interval with the length of 50ms specified in WAVE into a TDMA section used by formation and a CSMA section used by vehicles driven by people, wherein the TDMA section is positioned in front of the CSMA section, and after the formation determines the allocation proportion of the control channel, the TDMA section is sent to other vehicles in the P-WBSS through the periodic broadcast of formation members;

3) determining a CTS responder list in the formation members by the unmanned formation; the method comprises the following specific steps:

3-1) making i ═ 1;

3-2) taking the leading vehicle of the unmanned formation as a CTS responder i and adding the CTS responder i into a CTS responder list;

3-3) the CTS responder i selects the same formation member farthest in the communication range of the responder i as a CTS responder i +1 and joins a CTS responder list;

3-4) making i ═ i + 1; repeating the step 3-3) until the last vehicle at the tail of the formation serves as a CTS responder and is added into a CTS responder list to obtain a final CTS responder list;

4) each member of the unmanned formation periodically transmits a broadcast message on a control channel; adding a CTS response service announcement frame header CTS-RAH in the message when determining each CTS responder broadcast in the responder list in the step 3), wherein the frame header comprises the position and speed information of a sender, the ID of a P-WBSS and a time stamp of sending time;

5) when any one of the driverless vehicles listens for broadcast messages from any one of the driverless formations, the following is determined:

5-1) if the driveable vehicle does not currently belong to any of the P-WBSSs, proceeding to step 5-2); if the drived vehicle currently belongs to any one P-WBSS, entering step 5-3);

5-2) the vehicle driven by the person as a one-hop neighbor node to which the formation of the broadcast messages sent belongs joins the P-WBSS to which the formation belongs; after joining, the current P-WBSS ID of the manned vehicle is set to the P-WBSS ID to which the formation belongs; and the drived vehicle communicates according to the TDMA and CSMA division results confirmed by the driverless formation in the P-WBSS;

5-3) determining whether the broadcast message is from a P-WBSS to which the driveable vehicle currently belongs: if yes, entering step 6); if not, entering the step 5-4);

5-4) if the unmanned formation sending the broadcast message is the formation closest to the front of the same-direction driving of the manned vehicle, emptying the local CTS responder list by the manned vehicle, and then adding the local CTS responder list as a one-hop neighbor node to which the formation sending the broadcast message belongs to the P-WBSS to which the formation belongs; after joining, the current P-WBSS ID of the manned vehicle is set to the P-WBSS ID to which the formation belongs; and the drived vehicle communicates according to the TDMA and CSMA division results confirmed by the driverless formation in the P-WBSS; then entering step 6);

if the unmanned formation that sent the broadcast message is not the nearest formation ahead of the co-current travel of the driveable vehicle, then the driveable vehicle is still in the currently affiliated P-WBSS, and step 10) is entered;

6) determining whether the message heard in step 5) was sent by a CTS responder to the unmanned formation: if so, the vehicle driven by the person adds the CTS responder and the timestamp of the message into a local CTS responder list, and updates the local CTS responder list; if not, not updating the local CTS responder list;

when the vehicle driven by the person continues to monitor the broadcast message periodically sent on the control channel by the members in the current belonging P-WBSS, if the broadcast message is sent by the CTS responders in the unmanned formation, the vehicle driven by the person adds the CTS responders and the time stamp of the message into a local CTS responder list, and updates the local CTS responder list;

7) when the vehicle driven by the person prepares to send the broadcast message on the control channel, checking a local CTS responder list, finding out all time stamps with the difference value between the current moment of sending the message and the time stamp within the time difference threshold value according to the time stamp of each responder sending the message in the local CTS responder list as available time stamps, using CTS responders corresponding to the available time stamps as current available CTS responders, and forming the current available CTS responder list by all the current available CTS responders;

if the current available CTS responder list is not empty, finding out the current available CTS responder closest to the drived vehicle as a target CTS responder according to the relative position of the drived vehicle and each current available CTS responder, and entering the step (8);

if the current available CTS responder list is empty, the vehicle driven by the person directly sends a broadcast message, and then step 10) is entered;

8) the driveable vehicle sending an RTS request to a target CTS responder;

when other vehicles as non-target CTS responders monitor the RTS request, the non-target CTS responders correspondingly update own network allocation vectors;

when a target CTS responder receives an RTS request, checking the local network allocation vector state and judging whether to send a CTS response or not;

9) if the vehicle sending the RTS request receives a CTS response sent by a target CTS responder, a broadcast message is sent to the target CTS responder; other vehicles which monitor the CTS response update own network allocation vector correspondingly; then entering step 10);

if the vehicle sending the RTS request does not receive the CTS response sent by the target CTS responder after the time threshold of the CTS request is exceeded, the vehicle returns to the step 7) after carrying out the index back-off rule of CSMA/CA, and the local CTS responder list is rechecked;

10) determining a state of the driven vehicle:

10-1) if the driverless vehicle monitors the broadcast message from the formation in the currently affiliated P-WBSS within the set broadcast time threshold, the driverless vehicle continues to remain in the currently affiliated P-WBSS; when the vehicle driven by the person receives the broadcast message from any formation, returning to the step 5);

10-2) if the manned vehicle does not hear the broadcast message from the formation within the currently affiliated P-WBSS after exceeding the set broadcast time threshold, the manned vehicle leaves the currently affiliated P-WBSS and clears the local CTS responder list; and returning to step 5) again until the manned vehicle receives the broadcast message from any one of the fleets.

The invention has the characteristics and beneficial effects that:

1. the method is suitable for the workshop communication scene of the hybrid traffic system, can improve the reliability of workshop communication in the hybrid traffic system, and improves the overall throughput efficiency.

2. The invention takes unmanned formation as a center to form a wireless basic service set. Where the convoy vehicles use a TDMA protocol and the other vehicles use a CSMA/CA protocol. The invention selects part of formation members as CTS responders in the basic service set, and realizes RTS/CTS function for the broadcast communication of free vehicles driven by people.

3. The invention can reduce the broadcast communication conflict overhead in the hybrid traffic system and improve the broadcast efficiency and the throughput rate. In addition, the introduction of the RTS/CTS mechanism for broadcasting can add retransmission capability to the broadcast communication, thereby greatly improving the reliability of the broadcast communication.

Drawings

FIG. 1 is an overall flow diagram of the method of the present invention.

Fig. 2 is a system model diagram of a formation-centric wireless infrastructure service set in accordance with the present invention.

Detailed Description

The invention provides a reliable broadcasting method of a hybrid traffic system taking formation as a center, and the invention is further described in detail below by combining the accompanying drawings and specific embodiments.

The invention provides a reliable broadcasting method of a hybrid traffic system taking formation as a center, wherein the hybrid traffic system consists of unmanned formation and free vehicles driven by people, the overall flow of the method is shown as a figure 1, and the method comprises the following steps:

1) taking an unmanned formation formed by automatic driving vehicles and a Set formed by one-hop neighbor nodes to which the formation belongs as a Wireless Basic Service Set (P-WBSS) taking the formation as a center; wherein the one-hop neighbor node to which the formation belongs is a vehicle driven by a person; a schematic diagram of a system model of a formation-centric wireless basic service set according to the present invention is shown in fig. 2. In fig. 2, the vehicle forward direction is from top left to bottom right. The vehicles on the rightmost lane in the advancing direction are driverless formation comprising formation 1 and formation 2, and the vehicles on the other lanes are free vehicles driven by people. The black lines represent that the free vehicles are able to receive the broadcast message from the formation. The formation 1 and the formation 2 respectively form a P-WBSS 1 and a P-WBSS 2 with one-hop neighbor nodes to which the formation 1 and the formation 2 belong. For vehicles capable of communicating with both convoy 1 and convoy 2, such as vehicle a in the circle, these vehicles always join by selecting the P-WBSS belonging to the convoy located closest to the convoy in front of the ride. In FIG. 2, A chooses to join the P-WBSS 2 front.

In P-WBSS, the unmanned formation uses TDMA-based communication protocols internally, and the manned vehicles continue to use CSMA/CA protocols in the WAVE standard.

2) The unmanned formation confirms the division of the TDMA and CSMA segments in the control channel access interval.

To avoid collisions of CSMA/CA and TDMA, the present invention divides the control channel interval specified in WAVE to be 50ms in length into a TDMA segment for use by formation and a CSMA segment for use by a human driven vehicle, with the TDMA segment preceding the CSMA segment. The distribution ratio of the two periods of time can be dynamically adjusted according to the network load and the vehicle distribution, and the ratio is specified by the formation and is sent to other vehicles in the P-WBSS through the periodic broadcast of the formation members.

3) The unmanned formation determines a CTS responder list among the formation members. The method for determining the CTS responder is that starting from a leading vehicle of a formation, successively selecting the formation member farthest in the communication range as the CTS responder and adding the CTS responder to a responder list. For example: firstly, using a formation leading vehicle as a CTS responder and adding the CTS responder into a responder list, selecting the vehicle which is farthest in the communication range of the formation leading vehicle as A, selecting the vehicle A as the CTS responder and adding the CTS responder list, selecting the vehicle B which is farthest in the communication range of the vehicle A towards the tail of the formation in the communication range of the vehicle A as the CTS responder and adding the CTS responder list, repeating the steps until the tail of the formation, using the last vehicle at the tail of the formation as a CTS responder and adding the CTS responder list to obtain a final CTS responder list.

4) Each member of the unmanned formation periodically transmits a broadcast message on the control channel (the broadcast message need not specify a recipient and can be received by all nodes within communication range). ). Wherein, each CTS responder in the CTS responder list determined in step 3) needs to add a CTS response service announcement frame header (CTS-RAH) to the message during broadcasting, where the frame header includes the location and speed information of the sender, the ID of the P-WBSS, and a timestamp of the sending time.

if the unmanned formation sending the broadcast message is the formation closest to the front of the autonomous vehicle in the same direction, the autonomous vehicle clears the local CTS responder list and then joins the P-WBSS to which the formation belongs as a one-hop neighbor node to which the formation sending the broadcast message belongs; after joining, the current P-WBSS ID of the manned vehicle is set to the P-WBSS ID to which the formation belongs; and the drived vehicle communicates according to the TDMA and CSMA division results confirmed by the driverless formation in the P-WBSS; then entering step 6);

1.6) determining whether the message heard in step 5) was sent by a CTS responder of the unmanned formation (determined by whether the message carries a CTS-RAH): if so, the vehicle driven by the person should add the CTS responder and the timestamp of the message to a local CTS responder list, and update the local CTS responder list; if not, not updating the local CTS responder list;

when the driverless vehicle continues to monitor the broadcast message periodically sent on the control channel by the members (not all members, but the members located in the communication range of the driverless vehicle) in the current belonging P-WBSS, if the broadcast message is sent by the CTS responders in the driverless formation, the driverless vehicle adds the CTS responders and the time stamps of the message into a local CTS responder list, and updates the local CTS responder list;

7) when the driverless vehicle is ready to send broadcast messages on the control channel, the local CTS responder list is checked, and the currently available CTS responder list is found out based on the timestamp of each responder message in the local CTS responder list (in the present invention, the difference between the current time when the driverless vehicle sends a message and the timestamp of each responder in the local CTS responder list is considered available within a set time difference threshold, which is generally set to an integer multiple of the synchronization interval).

8) the driveable vehicle sends an RTS request to the target CTS responder.

2) When other vehicles (any vehicle, which may not belong to the formation) as non-target CTS responders hear the RTS request, the non-target CTS responders update their own network allocation vectors regardless of whether they subsequently hear the corresponding CTS responses (the RTC/CTS technology is IEEE802.11 standard, and the update method is defined in the standard).

When a target CTS responder in the formation receives an RTS request sent to the target CTS responder, the local network allocation vector state is checked, and whether a CTS response is sent or not is judged. (RTC/CTS technology is IEEE802.11 standard, and whether CTS response should be sent out is also defined by the standard);

9) if the vehicle driven by the person sending the RTS request receives the CTS response sent by the target CTS responder, the real broadcast message content is sent to the target CTS responder (the broadcast message does not designate a receiver); other vehicles (any vehicle, which may not belong to the formation) which hear the CTS response also update their own network allocation vectors (which are IEEE802.11 standard content) accordingly; then step 10) is entered.

3) If the vehicle sending the RTS request does not receive the CTS response sent by the target CTS responder after exceeding the set CTS request time threshold (the RTS/CTS interaction process follows the IEEE802.11 standard, and the CTS request time threshold is also specified by the standard), the vehicle returns to step 7 again after performing the CSMA/CA exponential back-off rule, and rechecks the local CTS responder column.

10) Determining a state of the driven vehicle:

10-2) if the manned vehicle does not hear the formation broadcast message from the currently affiliated P-WBSS after exceeding the set broadcast time threshold, the manned vehicle leaves the currently affiliated P-WBSS and clears the local CTS responder list; and returning to step 5) again until the manned vehicle receives a broadcast message from either formation.

The broadcast time threshold is typically set to an integer multiple of the length of the synchronization interval, and may be set to 500ms or 1 s. When set to 500ms, meaning that the free vehicle will leave the P-WBSS if no message from the formation in the same P-WBSS was received in the past five synchronization intervals).

Claims

1. A method for reliable broadcast of a fleet-centric hybrid transportation system, comprising the steps of:

3-1) making i ═ 1;

5-2) the vehicle driven by the person as a one-hop neighbor node to which the formation of the broadcast messages sent belongs joins the P-WBSS to which the formation belongs; after joining, the current P-WBSSID of the manned vehicle is set to the P-WBSSID to which the formation belongs; and the drived vehicle communicates according to the TDMA and CSMA division results confirmed by the driverless formation in the P-WBSS;

5-4) if the unmanned formation sending the broadcast message is the formation closest to the front of the same-direction driving of the manned vehicle, emptying the local CTS responder list by the manned vehicle, and then adding the local CTS responder list as a one-hop neighbor node to which the formation sending the broadcast message belongs to the P-WBSS to which the formation belongs; after joining, the current P-WBSSID of the manned vehicle is set to the P-WBSSID to which the formation belongs; and the drived vehicle communicates according to the TDMA and CSMA division results confirmed by the driverless formation in the P-WBSS; then entering step 6);

8) the driveable vehicle sending an RTS request to a target CTS responder;

10) determining a state of the driven vehicle: