CN117395764A - Distributed time division multiplexing medium access control system and method for driving safety - Google Patents
Distributed time division multiplexing medium access control system and method for driving safety Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/28—TPC being performed according to specific parameters using user profile, e.g. mobile speed, priority or network state, e.g. standby, idle or non transmission
- H04W52/283—Power depending on the position of the mobile
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/30—Services specially adapted for particular environments, situations or purposes
- H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
- H04W4/46—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for vehicle-to-vehicle communication [V2V]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
- H04W72/044—Wireless resource allocation based on the type of the allocated resource
- H04W72/0446—Resources in time domain, e.g. slots or frames
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Abstract
A distributed time division multiplexing control system and method for driving safety comprises: the invention relates to a driving safety perceived power control module, a lightweight chain structure maintenance module and a conflict-free time slot distribution module, which takes different safety requirements of each vehicle node in a network into consideration, and the core idea of the invention is to match a V2V communication range with the driving safety requirements of vehicles, and only exchange safety messages between vehicles which pay attention to safety mutually, thereby greatly improving the utilization rate of channel resources. Vehicles with mutual safety concerns on the same lane form a flexible and dynamic broadcast chain structure. The invention combines driving safety perceived power control and lightweight dynamic intra-link color switching, and can avoid access conflict and merging conflict in the highly dynamic Internet of vehicles.
Description
Technical Field
The invention relates to a technology in the unmanned field, in particular to a fully distributed time division multiplexing control system and method (BubbleMAC) for driving safety.
Background
The existing broadcast Medium Access Control (MAC) method of the Internet of vehicles design comprises a centralized method and a distributed method, wherein the former strongly depends on a central control node, cannot work without the central control node, and consumes a large amount of channel resources; the latter communication delay cannot be guaranteed, and especially in a scene with high vehicle density, the problem of hidden terminals causes serious delay, and in a scene with high vehicle density, the problem of collision between insufficient allocation of channel resources and mutual transmission of vehicle nodes is faced.
Disclosure of Invention
Aiming at the defects that reliable communication of vehicles is difficult to realize and reliable work is difficult in a high-dynamic and high-density vehicle scene in the prior art, the invention provides a distributed time division multiplexing control system and a distributed time division multiplexing control method for driving safety, and considering that each vehicle node in a network has different safety requirements (for example, a straight-going vehicle is most concerned with a front vehicle and a lane-changing vehicle is concerned with vehicles in front of and behind a target lane), the core idea of the invention is to match a V2V communication range with the driving safety requirements of the vehicles and exchange safety messages only between vehicles which are mutually concerned with safety, thereby greatly improving the utilization rate of channel resources. Vehicles with mutual safety concerns on the same lane form a flexible and dynamic broadcast chain structure. The invention combines driving safety perceived power control and lightweight dynamic intra-link color switching, and can avoid access conflict and merging conflict in the highly dynamic Internet of vehicles.
The invention is realized by the following technical scheme:
the invention relates to a distributed time division multiplexing control system facing driving safety, which comprises: the system comprises a driving safety sensing power control module, a lightweight chain structure maintenance module and a conflict-free time slot distribution module, wherein: the driving safety perceived power control module determines a safety distance according to the vehicle local information and the received neighbor vehicle information, so that communication power control facing mutual safety concern is realized, and channel resources are saved; the lightweight chain structure maintenance module judges and processes the growth and fracture of the chain structure according to whether neighbor vehicle information is received or not, and updates the vehicle roles in real time in a highly dynamic environment; and the conflict-free time slot allocation module allocates mutually disjoint time slot resources to each role according to the vehicle role information in the chain structure, so that time slot allocation without access collision and time slot allocation without merging collision are realized, and reliable and safe broadcasting among vehicles is ensured.
The invention relates to a distributed time division multiplexing medium access control method (BubbleMAC) based on the system, which is characterized in that each vehicle determines the minimum safety distance with a front vehicle according to the driving states of the vehicle and the front vehicle in the initial stage, adaptively adjusts the communication range to cover the front vehicle and the rear vehicle according to the receiving condition of the front vehicle and the rear vehicle, forms a chain structure among vehicles which are mutually communicated and cover, so as to identify the roles of each vehicle in a chain and the information of the chain, updates and maintains the local of each chain member of the chain, and allocates conflict-free time slots to each role in the chain structure.
Technical effects
According to the invention, through quantifying driving safety requirements, vehicles adaptively adjust communication ranges according to the mutual safety requirements, divide channel time slots into disjoint resource pools and construct a dynamic broadcast chain structure, and in the chain structure, the vehicles immediately know and update own roles according to beacon receiving conditions; compared with the prior art, the method has the advantages that the communication range is limited on the premise of ensuring driving safety, the space utilization rate of channel resources is improved, conflict-free time slots are allocated for vehicles with different densities and movement attributes, and the chain structure is maintained in a highly dynamic environment with low communication cost.
Drawings
FIG. 1 is a schematic diagram of the present invention;
FIG. 2 is a vehicle n 1 Schematic of One Hop Set (OHS) and Two Hop Set (THS) and one access collision;
figures 3 and 4 are diagrams of the present invention,
FIG. 5 is a schematic view of a safe distance;
in the figure: (a) Indicating that n is acquired j Driving state information of vehicle n i Obtaining n i And n j A safe distance requirement between the two; (b) Indicating that when the driving state information of the preceding vehicle cannot be acquired, the vehicle n j It is necessary to calculate the safe distance of the driver assuming that there is a completely stopped vehicle in front;
FIG. 6 is a schematic diagram of a growth process of a chain structure;
In the figure: (a) Representing the proximity of two chains, (b) representing the merging of two chains;
FIG. 7 is a schematic diagram of a chain structure breaking process;
in the figure: (a) Indicating the distance of members in the chain, (b) indicating the disconnection of the chain
FIG. 8 is a schematic diagram of a frame structure according to the present invention;
FIG. 9 is a schematic view of the proximity of two chains on different lanes;
in the figure: (a) Indicating the proximity of the two chains, (b) indicating the intersection of the two chains;
FIG. 10 is a schematic illustration of an example of the present invention in other complex driving scenarios;
in the figure: (a) Representing a lane change scene, n 1 The vehicle waits and turns right while changing the road, (b) represents the scene of the crossing, n 2 Vehicle waiting n 1 Turning right after passing straight;
FIG. 11 is a schematic diagram of a MAC layer packet structure of the present medium access control method;
FIG. 12 is a schematic diagram of road topology in a simulation experiment;
in the figure: (a) is a highway, (b) is a three-way intersection, and (c) is a four-way intersection;
FIG. 13 is a schematic view showing the influence of different vehicle densities on driving safety in a simulation experiment;
in the figure: (a) is a transmission collision rate, (b) is a packet reception rate, and (c) is a necessary packet reception rate;
FIG. 14 is a schematic diagram showing the effect of different road topologies on driving safety in a simulation experiment;
in the figure: (a) is a transmission collision rate, (b) is a packet reception rate, and (c) is a necessary packet reception rate;
FIG. 15 is a schematic view of the impact of an abnormally moving vehicle on driving safety at each vehicle density in a simulation experiment;
in the figure: (a) is low traffic density, (b) is medium traffic density, and (c) is high traffic density;
fig. 16 is a schematic diagram showing the distribution of a set of one-hop distributed timeslots |ohn| and a set of timeslots |chain| in a Chain structure;
in the figure: (a) is an |ohn| distribution and (b) is a Chain distribution.
Detailed Description
As shown in fig. 1, the vehicles adaptively adjust the communication range according to safety concerns of each other, wherein: vehicle n on the same lane 1 (head car), n 2 (intermediate vehicle) and n 3 (rear vehicle) constitutes a chain structure; in the chain structure, each vehicle is allocated a collision-free time slot for sharing and forwarding critical driving state information and decision information. When one chain structure approaches another chain structure in the same driving direction, lightweight negotiation is performed, and the approaching chain structure makes necessary time slot changes to avoid potential merging message collision.
As shown in fig. 3, a distributed time division multiplexing medium access control system for driving safety according to this embodiment includes: the system comprises a driving safety sensing power control module, a lightweight chain structure maintenance module and a conflict-free time slot distribution module, wherein: the driving safety perceived power control module determines a safety distance according to the vehicle local information and the received neighbor vehicle information, so that communication power control facing mutual safety concern is realized, and channel resources are saved; the lightweight chain structure maintenance module judges and processes the growth and fracture of the chain structure according to whether neighbor vehicle information is received or not, and updates the vehicle roles in real time in a highly dynamic environment; and the conflict-free time slot allocation module allocates mutually disjoint time slot resources to each role according to the vehicle role information in the chain structure, so that time slot allocation without access collision and time slot allocation without merging collision are realized, and reliable and safe broadcasting among vehicles is ensured.
The time slot resources refer to: in a time division multiplexing based medium access control Method (MAC), time is divided into a series of frames (frames), each frame consisting of a fixed number of slots (slots). All vehicles synchronize via GPS and assign each vehicle a time slot to transmit messages. Once a vehicle node successfully acquires a time slot, it occupies the same time slot in all subsequent frames until a transmission collision is detected. As shown in FIG. 2, a set of one-hops for a vehicle node is a neighboring vehicle within a certain vehicle communication rangeThe node union of the OHS of each neighbor node in the OHS of the vehicle is the two-hop set (THS) of the vehicle, i.e., U ∈ ->For->When n is 1 And n 2 ∈THS(n 1 ) The same time slot is selected, then at n 5 Where access collisions occur. When the vehicle node n is at a long distance j Joining vehicle node n due to relative movement i When they share the same time slot, a combining conflict occurs.
The chain structure refers to: when two or more vehicles in the same lane are in mutual safety concern, and each vehicle is located at the minimum safety distance d of the following vehicle safe In the inner case, a chain structure is formed in which each vehicle adjusts its communication range to cover the front and rear vehicles.
Due to the lack of centralized coordination, two types of message collisions may occur, namely: access conflicts and merge conflicts. When the vehicle node n i And THS (n) i ) Another vehicle node n of (a) j An access collision occurs when the same time slot is selected in one frame. For example, in FIG. 2, when n 1 And n 6 ∈THS(n 1 ) The same time slot is selected, then at n 5 Access collision occurs at the location; when the vehicle node n is at a long distance j Joining vehicle node n due to relative movement i When they share the same time slot, a combining conflict occurs. To avoid access collisions, each vehicle may include in its beacon information of the neighbor occupancy time slots in the neighbor OHS set. After listening to the channel for one frame, the vehicle may collect information about the time slots occupied by neighbors in its THS and select an available time slot for all subsequent frames. However, merging conflicts in a fully distributed environment is difficult to eliminate due to the diverse mobility of vehicles.
The power control includes:
step a) determining a safe distance: as shown in fig. 5 (a), when the vehicle n i At t beac. Through a security beacon with n for a time interval (e.g., 100 ms) j Exchanging its driving status information. When n is j Suddenly braking with maximum deceleration, n i On receipt of n j The brake is started after the beacon of (c). To avoid collision, n i Should be at least equal to n j Maintaining a safe distance Wherein: v i And v j Respectively n i And n j Is a speed of (2); b i And b j Respectively n i And n j Maximum deceleration of (2); ρ i Is n i The adopted braking coefficient; t (T) reac. Is the human driver reaction time (typically 0.6-0.8 seconds) or the reaction time of an autopilot agent. Consider in the worst case, n as shown in FIG. 5 (b) i When the beacons of other vehicles cannot be heard, it is necessary to assume that there is a completely stationary vehicle in front and calculate the maximum safe distance
Therefore, to ensure driving safety, n i Its transmit power should be controlled to ensure that its communication range is greater than d safe . In addition, when n i When the speed is 0, the safety distance is 0 according to the formula, and n is i Active broadcasting is stopped.
Step b) power control for mutual security concerns: from the safe distance calculation, n i A kind of electronic deviceProportional to the square of the velocity. When a higher speed following vehicle n k Is approaching n i Obviously n k Maximum safe distance +.>Ratio of $ to n i Large. When n is i At n k When in the communication range of (2), n i Can hear n k The transmitted beacons, but not vice versa. In this case, when n i Brake, n k Will not be notified. The invention calls $n i And n k With mutual safety concerns, n i Its communication range should be extended to cover its own d safe And d with a follower car of mutual safety concern safe . For other driving situations, such as lane changing or turning at intersections, it is possible to turn n equivalently i Has been transferred to the target lane to switch to a straight-going scenario.
The maintenance of the lightweight chain structure is as follows: when vehicle n i When the communication link is established with other vehicles with safety concerns on the same lane, a dynamic and flexible communication chain structure is formed. According to n i The two-way links between safety concern neighbors can be established with the front and the rear in two directions, and the vehicles in the chain structure can dynamically switch roles, so that the growth and the fracture of the chain structure are caused, and the growth and the fracture process of the chain structure are light.
The conflict-free time slot allocation refers to: the time slots in each frame are time division multiplexed into mutually exclusive sets for communication of vehicles of different roles. In order to avoid the acquisition conflict, each vehicle node adds the time slot use condition of the node in the OHS set and the time slot use condition of the node of the Chain structure to the data packet as control information, and the node selects an available time slot to use by collecting the time slot information occupied by the neighbor and the node in the Chain in the THS. In order to avoid merging conflicts, during the extension or splitting of the chain structure, when the roles of the vehicles change, the vehicles select a new time slot from the corresponding dedicated time slot set. When two chain structures in different lanes meet, the head vehicle of the adjacent chain structure coordinates the use of the time slots of the members in the chain, and avoids the use of the occupied time slots in the front chain structure.
As shown in fig. 4, this embodiment relates to a fully distributed time division multiplexing control method for driving safety based on the above system, where each vehicle determines a minimum safety distance to be kept by the front vehicle according to its own driving state and the front vehicle at an initial stage, adaptively adjusts a communication range to cover the front vehicle and the rear vehicle according to a receiving condition of the front vehicle and the rear vehicle beacons, and forms a chain structure between vehicles covered by mutual communication to identify roles of each vehicle in a chain and information of the chain, update and maintain the local of each chain member of the chain, and allocate time slots without collision to each role in the chain structure, and specifically includes:
step 1) the vehicle initially broadcasts the local information of the vehicle in a single vehicle state, and determines the vehicle n according to the running state and the braking preference of the vehicle i And hypothetical forward fully stationary vehicle node n j Minimum safe distance d between safe Limiting the communication range by adjusting the transmission power to cover at least a minimum safe distance d safe The method comprises the steps of carrying out a first treatment on the surface of the When the host vehicle n i Receiving front vehicle n j Or receiving the same lane rear vehicle n k At its minimum safe distance d safe In the case of a beacon transmitted in range, host vehicle n i Adjusting the communication range to cover the front vehicle n j Or rear vehicle n k And forming a chain structure;
And 2) carrying out maintenance on the lightweight chain structure in a distributed manner on vehicles in all the chain structures. When a new chain structure or an existing chain structure is generated or broken through a merging mode, each vehicle rapidly deduces the relative position of the vehicle in the chain locally according to a received beacon (beacon) so as to determine the role of the vehicle.
And 3) after determining the roles of the vehicles, each vehicle in the chain structure respectively performs mutually-disjoint time slot resource division according to the roles, and the process mainly comprises time slot allocation without access conflict and time slot reassignment without merging conflict, so that reliable conflict-free safe broadcasting is realized.
The vehicle role includes: isolated vehicles (isolateddevehicles), head vehicles (headvechicles), intermediate vehicles (intermedia vechicles) and tail vehicles (tailvechicles), wherein: an isolated vehicle, i.e. a bicycle, refers to a vehicle that cannot establish a communication link with a neighbor with mutual safety concern on the same lane, meaning that it does not form a chain structure. The head truck (or tail truck) refers to a vehicle that can form a chain structure with a neighbor having mutual safety concern in the front (or rear) direction on the same lane, but cannot form a chain structure with a vehicle in the rear (or front) direction. An intermediate vehicle refers to a vehicle that can establish a two-way communication link on the same lane with a front-to-rear direction neighbor with mutual safety concerns.
The identification of the roles of the respective vehicles in the chain means that: by confirming the host vehicle n i And (3) whether a bidirectional link between a beacon of the same-lane vehicle and a safety concern neighbor can be received and established in a forward and backward bidirectional manner, determining the role of the vehicle and enabling the growth or fracture of a chain structure, wherein: growth of the chain structure, i.e. the process of adding new nodes to the chain, comprises: an isolated vehicle encounters an isolated vehicle, an isolated vehicle encounters a chain structure, a chain structure encounters an isolated vehicle, and a chain structure encounters two chain structures; the breaking of the chain structure means: when the distance between two vehicles in the chain increases gradually due to the speed difference until d of the following vehicle is exceeded safe At this time, the chain structure breaks.
As shown in FIG. 6, n 1 And n 2 Is the intermediate car and the tail car of the slower chain. n is n 3 And n 4 Is the head car and the middle car of the faster chain. When the faster chain encounters the slower chain, the faster chain obtains the time slot allocation information of the slower chain, and the two chains are combined into a new chain; . As shown in FIG. 6 (a), whenA faster chain i, approaching another slower chain j on the same lane, tail car n of j 2 Head car n which will be located at i 3 Is within a safe distance of (2). In this case, the growth of the chain structure occurs. Specifically, at n 2 Receipt of n 3 Which changes its communication range to cover n 3 And the adjacent vehicle n in front of it 1 . Similarly, at n 3 Receipt of n 2 It will also adjust its communication range to cover n after the beacon of (a) 2 And n 4 . Finally, n 2 And n 3 The role is changed and chain i is incorporated into chain j. N before combining 2 (or n) 3 ) Is an isolated vehicle that will become the lead (or tail) vehicle of chain j. Otherwise, as shown in FIG. 6 (b), n 3 And n 2 All become intermediate vehicle nodes of the chain j, and the time slot occupation is updated according to the condition of the channel resources below.
When the distance between two vehicles in the chain increases gradually due to the speed difference until d of the following vehicle is exceeded safe When the chain structure breaks, the method specifically comprises the following steps: from head car break, from middle car break and from tail car break on the same lane, wherein: under the condition that the head car or the tail car is broken, the head car or the tail car in the original chain is changed into a single car, and the original intermediate car is changed into the head car or the tail car of the new chain; in the event of a break from the intermediate vehicle, the front and rear disconnected vehicle nodes become the front and rear two new chain-structured tail vehicles and head vehicles, respectively. As shown in fig. 7, when the distance between two vehicles in the same chain is gradually increased until the safety distance d of the following vehicle is exceeded safe When the chain structure breaks into two chains;
as shown in FIG. 7 (a), when a pair of members n in chain i 2 And n 3 The distance between them gradually increases until n is exceeded 3 At the maximum safe distance of (2), the chain structure breaks. Specifically, when n 2 Cannot be from n 3 Where it considers chain splitting to occur when a beacon is received. As shown in FIG. 7 (b), n is now 2 Will adjust its communication range to cover only the front vehicle n 1 And changes its role from the intermediate (or head) car node of chain i to the tail car node (or orphan car node) of chain i.
The mutually disjoint time slot resource division refers to: to avoid data transmission collisions, the vehicle selects a time slot according to its role in the chain. As shown in fig. 8, the time slot resources of each frame are divided into three mutually disjoint sets, i.e., L for nodes in the left direction, R for nodes in the right direction, and F for fixed roadside units (RSUs); l and R are further divided into four subsets, H for head nodes, I for intermediate nodes, T for tail nodes, S for isolated nodes, dividing the frame into three mutually disjoint sets of timeslots L, R and F, wherein: f reserves resources for RSU, L and R with left and right road vehicles, respectively. The definition of left and right sides herein is that a road segment extending from north/south to west (east) is considered to be a left or right road segment, as shown in fig. 8. The division of resources into L and R aims to cope with the drastic changes in the relative positions of vehicles on the lanes of opposite directions. To reduce the possible collision caused by the relative position change between co-traveling vehicles, the set of time slot resources L and R are each further divided into H, I & S and T, where: h for head cars in the chain, T for tail cars in the chain, and I & S for intermediate cars and isolated vehicles in the chain.
The time slot allocation without access collision refers to: the access collision and the merging collision in the packet transmission process are eliminated by utilizing disjoint time slot sets and dynamic intra-link angle variation. The vehicle node ni not only broadcasts its own driving status and decisions, but also shares the time slot usage information of the vehicles in the OHS set and the chain structure in which it is located. Vehicles on the road should first listen to the channel (for 1 frame), determine the time slots occupied by their THS nodes and nodes in the belonging chain (when not a bicycle) and determine the unoccupied set of time slots O. The vehicle randomly selects one time slot for access from the intersection set of the available time slot set and the corresponding belonging set. For example, the head car of the left lane should randomly select a time slot from O.U.H.U.L. When a vehicle does not hear any data packets from neighbors on the same lane, it should be an isolated vehicle, when it is on the left (right) lane, it should be on On I&S.andL (or O.andI)&S n R) randomly selects a time slot. Vehicles of different roles never intersectThe time slot is acquired from the time slot resource pool, and the access collision is almost completely eliminated. Only vehicles having the same role may collide when acquiring the same time slot at the same time. In particular, when an isolated vehicle on one lane encounters another isolated vehicle, the probability of selecting the same time slot is limited because they both randomly select the time slot. When there are k available time slots, the probability of using the same time slot in the nth consecutive frame is
The time slot allocation without merging collision comprises the following steps:
a) Scenes on the same lane. The invention takes two chain structures on the same lane as an example. As shown in FIG. 6 n 3 And n 4 Head car and intermediate car of faster chain respectively, n 1 And n 2 The middle car and the tail car of the slower chain respectively. Before the chain structure completes growth, n 3 Always as a head cart, n 2 As the tail car is always used, the time slot sets with different identities are mutually disjoint, and the two time slot sets are necessarily different in time slot, so that the growth process can not generate transmission collision. During the approach, n 3 From n 2 The time slot allocation of the front slower chain is acquired and this information is added as control information to the broadcast packet. Other vehicles in the faster chain adjust own broadcasting time slot according to the occupation condition of the fleet time slot information. The other three growth conditions and the disconnection conditions were also treated in a similar manner.
b) Scenes on different lanes. Vehicles on different lanes cannot form a chain structure, nor can they merge as in the above scenario. The present invention uses a lightweight negotiation mechanism to eliminate the combined transmission conflicts caused by the relative movement of vehicles on different lanes. As shown in fig. 9, n 3 And n 4 Is the head car and the middle car of the faster chain. n is n 1 And n 2 Is the intermediate car and the tail car of the slower chain. When a faster chain i intersects another chain j on a different lane, it does not change the respective chain structure. However, head car n of chain i 3 Responsible for time of day according to channel use condition of chain jThe slots are reassigned. Specifically, when n 3 Tail car n receiving chain j 2 When a beacon is transmitted, it chains all members in j and the time slots used by them. Similar to the chain merging case on the same lane, n 3 And coordinating all members in the chain i, and selecting the time slot unoccupied by the members in the chain j. For example, n 4 Informed, another unoccupied time slot is selected to avoid association with n in chain j 1 A collision occurs.
c) Intersection scenarios. For the MAC control method, the intersection is a challenging intersection because of the high density of vehicles and the inability of vehicles in different directions to negotiate. The invention adjusts the broadcasting behavior according to the traffic signal lamp, and eliminates the merging collision at the intersection. Specifically, at the intersection, when an isolated vehicle or head car stops, it should turn off its radio and notify the following vehicles. Even if it does not broadcast, the following vehicle is calculating d safe While still there is a stationary vehicle. For example, when a north-south green light is on and an east-west red light is on, the behavior of a straight-going vehicle is the same as a non-intersection scenario of a different lane. At this time, stationary vehicles on lane 1 and lane 5 turn off the radio to avoid interfering with the broadcasting of vehicles in the north-south direction. When the vehicles on the right-turn lanes of the lane 1 and the lane 5 want to turn right at this time, the vehicles are added as isolated vehicles to the main road traffic, that is, the situation that the isolated vehicles encounter a chain structure or the isolated vehicles encounter the isolated vehicles is converted.
As shown in FIG. 10 (a), when n 1 When the lane change is intended to the right lane, n1 can hear n 2 The transmitted beacon can calculate n according to the current driving state of the neighbor node 1 Whether or not to n 2 Is safe. When it is, then n 1 The right of way of changing is obtained, and action is taken accordingly to obtain new roles and time slots on the target lane; otherwise, n 1 One must wait for a suitable opportunity (e.g., to accelerate to a safe distance d 2). Another example is shown in fig. 10 (b), a right-turn vehicle n 2 Gifts a straight vehicle n 1 . Although they all select one slot from the R set, no merge collision occurs because when n 2 When stopping at the intersection, the speed of the vehicle is 0, and the vehicle stops broadcasting due to the power control perceived by the safety of the vehicle. However, due to n 2 Still listening to the channel, it can determine when it can safely turn right and get a new character and time slot on the target road segment. Therefore, as vehicles strictly adhere to traffic regulations and do not physically collide, vehicles that broadcast by the present medium access control method do not collide with messages.
As shown in fig. 11, the data packet (MSDU) includes: an 802.11MAC header and a MAC layer data unit MAC service data unit, wherein: the first byte represents host n 1 One-hop aggregation of (2)Is followed by each member inThe vehicle ID and the acquired time slot; the next byte represents the size of chain i, followed by the vehicle ID and the acquired time slot for each member in chain i; the other fields are the current lane number, speed, longitude, latitude, maximum deceleration and other movement information and driving decision information.
The simulation is performed on a track-based (tracedriver), that is, the vehicle track under various scenes is generated using SUMO, and the simulation of different control methods is performed using a verus simulator. Consider three typical cases, namely, a highway, a three-way junction, and a four-way junction, each of which is a road with a length of 4 km in two-way eight lanes, as shown in fig. 12. The speed limit of four lanes in the same direction is 60km/h,80km/h,100km/h and 120km/h respectively. Each intersection had a traffic light with a green light duration of 20 seconds. Vehicles having ten different movement parameters, including acceleration capacity (from 1m/s 2 To 5m/s 2 ) Ability to decelerate (from 3 m/s) 2 To 10m/s 2 ) And maximum speed (from 80km/h to 240 km/h). To simulate different traffic conditions in a day, different traffic flows are set, such as high-density traffic flow (10 vehicles are added per minute per lane), medium-density traffic flow (5 vehicles are added per minute per lane) and low-density traffic flow Amount (3 vehicles added per lane per minute). Each vehicle randomly selects a destination and route when entering the road and drives under a Krauss vehicle following model and an LC2013 lane change model. The maximum communication range is set to 300 meters because an on-board unit compatible with 802.11p can reliably transmit data within 300 meters. For each round of simulation, a trajectory 100 seconds long after the steady traffic was formed was selected. Then, an interactive simulation function of a verus simulator (the verus simulator can make the decision information source of the vehicle come from the internet of vehicles communication data packet only) is used, in the expressway scene of the same experimental parameters, the set vehicle motion is dynamically changed according to the communication result, and 5%,10% and 15% of emergency braking vehicles which are decelerated at the maximum deceleration speed are set therein, so as to examine the effect of the present invention on enhancing driving safety in the extreme scene. Furthermore, the evaluation was also performed on the real world dataset HighD dataset, which was collected on german highways using unmanned aerial vehicles, recording track data of more than 110,500 vehicles.
In a communication simulation experiment of a real road data set, the communication performance indexes of the method comprise: the method comprises the steps of carrying out a first treatment on the surface of the Transmission collision rate (MessageCollisionRate, MCR)): the number of transmission collisions per frame per vehicle is averaged. The method comprises the steps of carrying out a first treatment on the surface of the Packet reception rate (BeaconReceptionRatio, BRR): the average number of actual packets per frame per vehicle divided by the number of packets that should be received. The method comprises the steps of carrying out a first treatment on the surface of the Necessary packet acceptance rate (UtilityofSafetyBeacons, USB): the average number of the mutual security concern packets actually received by each vehicle per frame is divided by the number of the mutual security concern packets to be received. The method comprises the steps of carrying out a first treatment on the surface of the Number of collision accidents: number of collision incidents that occurred during simulation. In the process of using VENUS interactive simulation, the invention considers the influence of different control methods on safe driving and mainly considers the number of accidents (NumberofCrasses), namely the number of traffic accidents.
Comparing the invention with IEEE802.11p, veMAC, SCMAC, the broadcast frequency of all control methods is set to 10Hz according to the application requirement of safe driving, namely 10 times per second.
The simulation experiment firstly evaluates the influence of the traffic flow density of the vehicle on the performances of different control methods. Specifically, on a bidirectional 8-lane highway with a length of 4 km, three different densities are used in generating the vehicle traffic flow, namely high density (10 vehicles/min/lane), medium density (5 vehicles/min/lane) and low density (3 vehicles/min/lane). The speed limit of four lanes in each direction on the highway is 120, 100, 80 and 60 km/h, respectively. For each traffic flow density, the experiment was repeated 20 times with the average result calculated.
As shown in fig. 13, the MCR of the present method is very low, 0.005, 0.027 and 0.061 collisions/frames/cars, respectively, for low, medium and high traffic densities. All collisions are random collisions that occur when an isolated vehicle is engaged. In contrast, veMAC cannot avoid a merge collision, while SCMAC and 802.11p cannot avoid an access and merge collision, resulting in a significant increase in MCR. For example, for low, medium and high traffic densities, the number of beacon collisions by VeMAC is 168, 74 and 120 times higher than the present method. Further, for high traffic densities, the BRR of the present method, veMAC, SCMAC and 802.11p are 98.9%, 81.3%, 68.6% and 47.9%, respectively, and USB is 98.9%, 83.7%, 68.0% and 63.9%, respectively.
The simulation experiment then evaluates the effect of the road topology. This experiment tested the robustness of the method on a real vehicle trajectory highD and three typical road topologies, including: a bi-directional 8-lane highway with a length of four kilometers, a three-way junction, and a four-way junction. The phase duration of the traffic signal is fixed at 20 seconds. This experiment produced a medium traffic density vehicle and maintained other experimental setups similar to those described above.
As shown in fig. 14, in all road topologies, the average MCR of VeMAC, SCMAC and 802.11p is very high as more vehicles with conflicting timeslots are gathered at the intersection. In contrast, the present method maintains very low MCR in the highway, trifurcate, quadbate, and highD data sets of 0.027, 0.006, 0.004, and 0.017 collisions/frames/vehicles, respectively. In addition, the method has the highest BRR and USB among all road topologies. For example, for the four intersections, the BRR of the present method, veMAC, SCMAC, and 802.11p are 99.3%, 63.9%, 49.8%, and 62.1%, respectively, while the USB is 99.7%, 77.8%, 67.2%, and 76.8%, respectively. In contrast, the time slot access mechanism of the present invention ensures collision-free performance, making it a control method suitable for various topologies.
And finally, simulating influence of driving safety. Whether the experimental study can only rely on the received beacon as an information source to control the vehicle so as to realize driving safety. In particular, the present experiment generated three vehicles of different traffic densities in the highway road topology, consistent with the experiment 5.5.2 setting. In addition, the present experiment randomly selects 5% to 15% of abnormal vehicles, continues to brake at the maximum deceleration and accelerate to its maximum speed throughout the simulation, and then checks whether a vehicle collision is caused due to an unaware neighbor vehicle motion change. For each simulation setup, the experiment was repeated twenty times.
Fig. 15 plots the average number of crash incidents when different media access control methods are used. Since the present method enables almost collision-free safe beacon broadcasting in various cases, no accident occurs in all simulations. VeMAC, SCMAC and 802.11p can cause a significant number of collision accidents even at medium traffic densities. From a combination of the above observations, all control methods reduce vehicle collisions to some extent. The invention performs best in all scenarios and achieves zero collision. The present invention can avoid collision by reliable communication with a nearby vehicle even if an abnormal vehicle exists.
In contrast to 802.11p, the primary communication overhead of VeMAC and the present invention is the control information required to coordinate medium access, including the vehicle IDs of neighboring vehicles in the OHS set and the corresponding time slot index. Note that |ohn|max is the maximum number of vehicles that can exist in the OHS set of vehicles. The number of bits required to express the vehicle ID in its THS isWherein the symbols areRepresenting an upper rounding function. To identify a specific time slot among s time slots, it is necessary +.>Bits. Thus, the communication overhead (in bits) common to VeMAC and the present invention is +.>The method comprises the following steps: />
Further, the vehicle of the present invention needs to include the chain configuration information in the data packet. Similarly, when the number of vehicle nodes in the Chain is |Chain| max The overhead required for maintaining the time slot usage information of the chain structure is:
thus, the total coordination overhead of the present invention is:
fig. 16 (a) shows the distribution of the OHN's for the different control methods. From this, it can be estimated that the cost of VeMACAbout 150 bytes. The->The overhead is about 95 bytes. Fig. 16 (b) shows the distribution of |chain| in the present invention. From this, it can be estimated that +.>The overhead is about 32.5 bytes. Since the application data size of the secure application broadcast in the internet of vehicles is typically small, about 200-500 bytes, it is acceptable to add an additional 100 bytes of coordination data to the broadcast data packet, since the total data packet size is much smaller than the size of the MAC layer control method data unit.
Compared with the prior art, the method successfully limits the V2V communication between vehicles with mutual safety concern, and avoids the communication problems such as merging conflict and the like which cannot be solved by the prior method through reallocating time slots. Therefore, the method can meet the driving safety requirement and simultaneously improve the channel utilization rate and the road space utilization rate to the greatest extent. A prototype system was realized and a number of trajectory-based simulation experiments were performed. The invention has simple realization and low hardware requirement. Furthermore, in all settings, the medium access control method of the present invention achieves almost zero collision rate messaging.
The foregoing embodiments may be partially modified in numerous ways by those skilled in the art without departing from the principles and spirit of the invention, the scope of which is defined in the claims and not by the foregoing embodiments, and all such implementations are within the scope of the invention.
Claims (10)
1. A distributed time division multiplexing control system for driving safety, comprising: the system comprises a driving safety sensing power control module, a lightweight chain structure maintenance module and a conflict-free time slot distribution module, wherein: the driving safety perceived power control module determines a safety distance according to the vehicle local information and the received neighbor vehicle information, so that communication power control facing mutual safety concern is realized, and channel resources are saved; the lightweight chain structure maintenance module judges and processes the growth and fracture of the chain structure according to whether neighbor vehicle information is received or not, and updates the vehicle roles in real time in a highly dynamic environment; the collision-free time slot allocation module allocates mutually-disjoint time slot resources to each role according to the vehicle role information in the chain structure, so that time slot allocation without access collision and time slot allocation without merging collision are realized, and reliable and safe broadcasting among vehicles is ensured;
The chain structure refers to: when two or more vehicles in the same lane are in mutual safety concern, and each vehicle is located at the minimum safety distance d of the following vehicle safe In the inner case, a chain structure is formed in which each vehicle adjusts its communication range to cover the front and rear vehicles.
2. The traffic safety oriented distributed time division multiplexing control system of claim 1, wherein said power control comprises:
step a) determining a safe distance: when vehicle n i At t beac. Through the time interval of the security beacon and n j Exchange driving state information thereof, when n j Suddenly braking with maximum deceleration, n i On receipt of n j To avoid collision, n i Should be at least equal to n j Maintaining a safe distanceWherein: v i And v j Respectively n i And n j Is a speed of (2); b i And b j Respectively n i And n j Maximum deceleration of (2); ρ i Is n i The adopted braking coefficient; t (T) reac. Is the human driver reaction time (typically 0.6-0.8 seconds) or the reaction time of an autopilot agent, consider n in the worst case i When the beacons of other vehicles cannot be heard, it is necessary to assume that there is a completely stationary vehicle in front and calculate the maximum safe distancen i Its transmit power should be controlled to ensure that its communication range is greater than d safe In addition, when n i When the speed is 0, the safety distance is 0 according to the formula, and n is i Stopping active broadcasting;
step b) power control for mutual security concerns: from the safe distance calculation, n i A kind of electronic deviceIn proportion to the square of the speed, when a higher speed follower vehicle n k Is approaching n i Obviously n k Maximum safe distance +.>Ratio n i Large, when n i At n k When in the communication range of (2), n i Hearing n k The transmitted beacons, but not vice versa, in which case when n i Brake, n k Will not be notified, i.e. $n i And n k With mutual safety concerns, n i Its communication range should be extended to cover its own d safe And d with a follower car of mutual safety concern safe For other driving situations, such as lane changing or turning at intersections, by equivalently turning n i Has been transferred to the target lane to switch to a straight-going scenario.
3. The running safety oriented distributed time division multiplexing control system according to claim 1, wherein the lightweight chain structure maintenance means: when vehicle n i When the communication link is established with other vehicles with safety concern on the same lane, a dynamic and flexible communication chain structure is formed, according to n i The two-way links between safety concern neighbors can be established with the front and the rear in two directions, and the vehicles in the chain structure can dynamically switch roles, so that the growth and the fracture of the chain structure are caused, and the growth and the fracture process of the chain structure are light.
4. The traffic safety oriented distributed time division multiplexing control system according to claim 1, wherein the collision-free time slot allocation means: the time slots in each frame are divided into mutually disjoint sets for communication of vehicles with different roles, each vehicle node adds the time slot use condition of a node in the OHS set and the time slot use condition of a node of a Chain structure to be affiliated to the node as control information into a data packet, the node selects available time slots for use by collecting time slot information occupied by neighbors and nodes in the Chain in the THS, in order to avoid merging conflicts, when the roles of the vehicles change in the extending or splitting process of the Chain structures, the vehicles can select a new time slot from the corresponding special time slot set, when two Chain structures in different lanes meet, the adjacent Chain structure head vehicles can coordinate the time slot use of members in the Chain, and the occupied time slots in the front Chain structure are avoided.
5. A distributed time division multiplexing medium access control method based on the system of any one of claims 1-4, wherein each vehicle determines the minimum safety distance to be kept by the front vehicle according to the driving state of itself and the front vehicle at the initial stage, adjusts the communication range adaptively according to the receiving condition of the front and rear vehicle beacons to cover the front and rear vehicles, and forms a chain structure by communicating the covered vehicles with each other so as to identify the roles of each vehicle in the chain and the information of the chain, updates and maintains the local of each chain member of the chain and allocates time slots without collision to each role in the chain structure.
6. The method according to claim 5, characterized in that it comprises in particular:
step 1) the vehicle initially broadcasts the local information of the vehicle in a single vehicle state, and determines the vehicle n according to the running state and the braking preference of the vehicle i And hypothetical forward fully stationary vehicle node n j Minimum safe distance d between safe Limiting the communication range by adjusting the transmission power to cover at least a minimum safe distance d safe The method comprises the steps of carrying out a first treatment on the surface of the When the host vehicle n i Receiving front vehicle n j Or receiving the same lane rear vehicle n k At its minimum safe distance d safe In the case of a beacon transmitted in range, host vehicle n i Adjusting the communication range to cover the front vehicle n j Or rear vehicle n k And forming a chain structure;
step 2) carrying out maintenance on the lightweight chain structure in a distributed manner on vehicles in all chain structures, and when a new chain structure is generated or an existing chain structure is broken in a merging manner, rapidly deducing the relative position of each vehicle in a chain according to a received beacon (beacon) locally so as to determine the role of the vehicle;
step 3) after determining the roles of the vehicles, each vehicle in the chain structure respectively carries out mutually-disjoint time slot resource division according to the roles, and the process mainly comprises time slot allocation without access conflict and time slot reassignment without merging conflict, so that reliable conflict-free safe broadcasting is realized;
the vehicle role includes: isolated vehicles, head vehicles, intermediate vehicles and tail vehicles, wherein: an isolated vehicle, i.e., a single vehicle, refers to a vehicle that cannot establish a communication link with a neighbor with mutual safety concern on the same lane, meaning that it does not form a chain structure, a head vehicle (or tail vehicle) refers to a vehicle that forms a chain structure with a neighbor with mutual safety concern in the front (or rear) direction on the same lane, but cannot form a chain structure with a vehicle in the rear (or front) direction, and an intermediate vehicle refers to a vehicle that establishes a bidirectional communication link with a neighbor with mutual safety concern in the front-rear direction on the same lane;
The data packet (MSDU) includes: an 802.11MAC header and a MAC layer data unit MAC service data unit, wherein: the first byte represents host n 1 One-hop aggregation of (2)Is followed by each member +.>The vehicle ID and the acquired time slot; the next byte represents the size of chain i, followed by the vehicle ID and the acquired time slot for each member in chain i; the remaining fields are the current lane number, speed, longitude, latitude, maximum deceleration and driving decision information.
7. The method of claim 5, wherein said identifying the role of the respective vehicle in the chain is: by confirming the host vehicle n i And (3) whether a bidirectional link between a beacon of the same-lane vehicle and a safety concern neighbor can be received and established in a forward and backward bidirectional manner, determining the role of the vehicle and enabling the growth or fracture of a chain structure, wherein: growth of the chain structure, i.e. the process of adding new nodes to the chain, comprises: an isolated vehicle encounters an isolated vehicle, an isolated vehicle encountersThe chain structure, the meeting of the chain structure with an isolated vehicle and the two chain structures; the breaking of the chain structure means: when the distance between two vehicles in the chain increases gradually due to the speed difference until d of the following vehicle is exceeded safe At this time, the chain structure breaks.
8. The method of claim 6 wherein the mutually exclusive time slot resource partitions are: in order to avoid data transmission conflict, the vehicle selects a time slot according to the roles of the vehicle in the chain structure, and the time slot resources of each frame are divided into three mutually disjoint sets, namely L is used for nodes in the left direction, R is used for nodes in the right direction, and T is used for fixed roadside units; l and R are further divided into four subsets, H for head nodes, I for intermediate nodes, T for tail nodes, S for isolated nodes, dividing the frame into three mutually disjoint sets of timeslots L, R and F, wherein: f reserves resources used by RSU, L and R are respectively used by left and right road vehicles;
to reduce the possible collision caused by the relative position change between co-traveling vehicles, the set of time slot resources L and R are each further divided into H, I & S and T, where: h for head cars in the chain, T for tail cars in the chain, and I & S for intermediate cars and isolated vehicles in the chain.
9. The method of claim 6, wherein the time slot allocation without access collision means: eliminating access collisions and merge collisions during packet transmission using disjoint sets of time slots and dynamic intra-link angle variations, vehicle node n i Broadcasting the driving state and decision of the vehicle, sharing the time slot use information of the vehicles in the OHS set and the chain structure where the vehicles are located, firstly monitoring channels by the vehicles on the road, determining the time slots occupied by the THS nodes and the nodes in the chain structure where the vehicles belong, determining an unoccupied time slot set O, and randomly selecting one time slot from the intersection of the available time slot set and the corresponding set to be accessed by the vehicles;
when an isolated vehicle on one lane encounters another isolated vehicleWhen there are k available time slots, the probability of using the same time slot in the nth consecutive frame is
10. The method of claim 6, wherein said time slot allocation without merge collision comprises:
a) Scene on the same lane: before the chain structure completes growth, n 3 Always as a head cart, n 2 Always used as a tail car, because the time slot sets with different identities are mutually disjoint and the two time slot sets are necessarily used with different time slots, the growth process can not generate transmission collision, and in the approaching process, n 3 From n 2 Acquiring time slot allocation of a front slower chain, adding the information into a broadcast data packet as control information, and adjusting own broadcast time slots by other vehicles in the faster chain according to the occupation condition of the time slot information of a motorcade, wherein the other three growth conditions and disconnection conditions are processed according to similar processes;
b) Scene on different lanes: when the faster chain i intersects another chain j on a different lane, it will not change the respective chain structure, when n 3 Tail car n receiving chain j 2 When transmitting a beacon, it will know all members in chain j and their time slots, similar to the chain merge case on the same lane, n 3 Coordinating all members in chain i, selecting an unoccupied time slot for a member in chain j, and selecting another unoccupied time slot to avoid association with n in chain j 1 A conflict occurs;
c) Intersection scenario: an isolated vehicle or head-mounted vehicle is stopped, which should turn off its radio and notify the following vehicle that it is calculating d even if it is not broadcasting safe When there is still a stationary vehicle, when the green light is on in the north-south direction and the red light is on in the east-west direction, the stationary vehicles on lane 1 and lane 5 turn off the radio to avoid the situation of the non-intersection of different lanesThe broadcasting of vehicles in the north-south direction is not interfered, and when the vehicles on the right-turning lanes of the lane 1 and the lane 5 want to turn right at the moment, the vehicles are added into main road traffic as isolated vehicles, namely, the situation that the isolated vehicles meet a chain structure or meet an isolated vehicle is converted.
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