CN111556465B - Distributed Internet of vehicles MAC layer time slot access method and system based on TDMA technology - Google Patents

Distributed Internet of vehicles MAC layer time slot access method and system based on TDMA technology Download PDF

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Publication number
CN111556465B
CN111556465B CN202010363433.9A CN202010363433A CN111556465B CN 111556465 B CN111556465 B CN 111556465B CN 202010363433 A CN202010363433 A CN 202010363433A CN 111556465 B CN111556465 B CN 111556465B
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vehicle
time slot
vehicles
time
information
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CN111556465A (en
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李保珠
侯芬
张霞
张长悦
曹毅
韩士元
陈贞翔
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Beijing Bailong Mayun Technology Co ltd
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Beijing Bailong Mayun Technology Co ltd
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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]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/02—Services making use of location information
    • H04W4/025—Services making use of location information using location based information parameters
    • H04W4/026—Services making use of location information using location based information parameters using orientation information, e.g. compass
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/02—Services making use of location information
    • H04W4/025—Services making use of location information using location based information parameters
    • H04W4/027—Services making use of location information using location based information parameters using movement velocity, acceleration information
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
    • H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
    • H04W74/0816—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA carrier sensing with collision avoidance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
    • H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
    • H04W74/0825—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA carrier sensing with collision detection
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The invention discloses a distributed Internet of vehicles MAC layer time slot access method and system based on a TDMA technology, comprising the following steps: judging whether a new vehicle is added, if so, executing a time slot access algorithm, performing collision detection and collision processing, then judging whether a time slot is obtained, if so, occupying time slot communication, otherwise, continuing executing the time slot access algorithm, and performing the collision detection and collision processing again until the time slot is obtained. The invention does not need the participation of roadside units, and only needs the vehicles to exchange beacon frames. Therefore, the construction cost of roadside infrastructure can be reduced, and the input cost is reduced.

Description

Distributed Internet of vehicles MAC layer time slot access method and system based on TDMA technology
Technical Field
The invention belongs to the technical field of Internet of vehicles, and particularly relates to a distributed Internet of vehicles MAC layer time slot access method based on a TDMA technology.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The existing literature proposes a directional-based distributed TDMA scheduling strategy. In this strategy, vehicles in one direction can only compete for even slots and vehicles in the other direction can only compete for odd slots. This approach can avoid the problem of a merging collision of vehicles traveling in opposite directions. However, this document does not describe how the actual direction of travel of the vehicle is mapped into the protocol.
The prior art proposes a reliable broadcast mechanism based on TDMA. In this document, a frame is divided into three parts: l, R, F. L and R represent the driving direction of the vehicle, respectively, and F is related to RSU.
On this basis, the prior art document further divides L and R into smaller sub-portions. Based on the direction of travel and the lane in which it is located, the vehicle needs to select a time slot in the appropriate set of time slots. When the driving lane changes, the vehicle needs to change its own occupied time slot. This protocol is too complex and may not achieve the desired effect.
The existing literature also provides a centralized internet of vehicles MAC layer combined collision prediction and avoidance method. In the method, each period of the time slot is divided into three parts, wherein the first part is a vehicle node time slot, and the part is further divided into a left-hand driving vehicle node time slot and a right-hand driving vehicle node time slot according to the driving direction of the vehicle; the second part is a relay node time slot; the third part is the RSU slot. The RSU selects a relay node vehicle for the vehicles within the coverage area and allocates a corresponding relay node time slot for it.
The prior art proposes a predictive based TDMA MAC protocol in the internet of vehicles for reducing packet merging collisions. In the above document, when a newly added vehicle is competing for a slot (slot access phase), the vehicle uses the most basic random access mechanism to select one of the available slots to transmit data. In this case, when the available time slots are small, the probability that a plurality of newly joined vehicles select the same time slot to transmit data is large, so that a competitive collision (access collision) is liable to occur. When a collision occurs, all vehicles competing for the time slot need to reselect the time slot until all newly joined vehicles acquire the time slot. Therefore, this method is prone to waste of time slot resources.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a distributed Internet of vehicles MAC layer time slot access method based on a TDMA technology, which can solve the time slot competition problem of newly added vehicles and the processing problem after access collision.
To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:
a distributed Internet of vehicles MAC layer time slot access method based on a TDMA technology comprises the following steps:
judging whether a new vehicle is added, if so, executing a time slot access algorithm, performing collision detection and collision processing, then judging whether a time slot is obtained, if so, occupying time slot communication, otherwise, continuing executing the time slot access algorithm, and performing the collision detection and collision processing again until the time slot is obtained.
Further technical scheme, time slot access algorithm: before competing for time slots, a newly added vehicle firstly listens for one frame of time, establishes a one-hop neighbor table, a two-hop neighbor table and a time slot array, and obtains the running state of the neighbor vehicle, the time slot use information and the idle time slot information;
meanwhile, recording the time when the vehicle starts to monitor the time slot, namely the time when the vehicle monitors the first time slot, and calling the time as a competition time stamp;
then, K idle time slots are selected from a frame starting from the competition time stamp in the running direction of the user, and one time slot is randomly selected from the K idle time slots to be used as the transmission time slot of the user;
finally, the vehicle puts the announcement information into the beacon frame, and when the next transmission time slot arrives, the beacon frame is transmitted to announce that the beacon frame will occupy the time slot.
According to the technical scheme, the vehicles executing the time slot access algorithm are provided with the signal receiving and transmitting equipment and the global positioning system, the signal receiving and transmitting equipment receives wireless signals from the neighbor vehicles and can transmit own wireless signals to the neighbor vehicles, but at the same time, the signal receiving and transmitting equipment can only receive or transmit the wireless signals and cannot receive and transmit the wireless signals at the same time.
According to a further technical scheme, a TDMA communication technology is used for realizing the communication of the Internet of vehicles, time is divided into a plurality of repeated frames, and then the frames are divided into a plurality of equal-length time slots.
Further technical scheme, defining a one-hop neighbor set and a two-hop neighbor set;
a one-hop neighbor set refers to a set of all vehicles within a vehicle communication range;
the two-hop neighbor set refers to a set of all vehicles that can be communicated by the vehicles through the relay of the middle one-hop node;
the vehicle sends the beacon frame to the one-hop neighbor, the hop value of the beacon frame is set to 1, when the one-hop neighbor receives the beacon frame, the hop value is reduced by 1 to 0, and the neighbor vehicle discards the beacon frame.
Further technical proposal, defining the running direction of the vehicle, namely the protocol direction, and mapping from the actual running direction of the vehicle;
vehicles traveling in the same direction are divided into one set, and thus the vehicles are divided into two sets, different time slots are allocated according to different traveling directions of the vehicles, and the combined collision between vehicles traveling in opposite directions is eliminated.
According to the further technical scheme, the vehicle needs to collect and update running states and time slot use information of the vehicle and the one-hop neighbor in real time and embed the running states and time slot use information into a beacon frame, and the running state and time slot use information are periodically transmitted to the one-hop neighbor vehicle for completing information exchange;
the running state information includes: position, speed, acceleration and direction of travel; the slot usage information includes: occupying a slot ID and a timestamp when the slot is obtained;
the time slot ID is an integer from 0, the maximum value is the total time slot number of the frame, and if the time slot ID occupied by the vehicle is 0, the vehicle does not compete for the time slot yet; otherwise, the actual time slot occupied by the vehicle is indicated.
According to a further technical scheme, a time slot array is established, the number of elements of the array is the same as the number of time slots of each frame, an array index number is a time slot ID, each element comprises N fields, N is more than or equal to 3, repeated time slot fields indicate whether the time slot is occupied by different vehicles, a value of 1 indicates that at least two vehicles occupy the time slot, and a value of 0 indicates that at most one vehicle occupies the time slot; the other fields are vehicle ID fields used for recording the vehicle ID occupying the time slot, when the vehicle occupies the time slot, the vehicle ID is filled in the fields, and the other fields are filled in NULL.
According to a further technical scheme, when a beacon frame of a neighbor is received, the vehicle performs the following two steps:
(1) Updating a neighbor table, the updating of the neighbor table comprising two parts:
a) Updating a one-hop neighbor table, checking the one-hop neighbor table of the communication neighbor, and if the communication neighbor is in the one-hop neighbor table of the communication neighbor, updating the running state and the time slot use information corresponding to the communication neighbor in the neighbor table; otherwise, adding the communication neighbor into a one-hop neighbor table and adding the running state and time slot use information;
b) Updating a two-hop neighbor table, and firstly screening two-hop neighbors: finding out a vehicle of a communication neighbor, which is not a vehicle of a communication neighbor, as a two-hop neighbor of the vehicle, checking a two-hop neighbor table of the vehicle, and if the active two-hop neighbor is in the two-hop neighbor table of the vehicle, updating the running state and the time slot use information corresponding to the active two-hop neighbor in the two-hop neighbor table; otherwise, adding the active two-hop neighbor into the two-hop neighbor table and adding the driving state and the time slot use information;
(2) Updating the time slot array, comparing the time slot occupation condition of the communication neighbor and the one-hop neighbor with the time slot array, updating, adding or deleting the data of the time slot array in real time according to the beacon frame of the communication neighbor, and calculating the time slot occupation ratio R of the vehicle running direction P And R is N Wherein R is P For the forward slot occupancy ratio, R N Is the reverse slot occupancy ratio;
R P ＝N P /N T wherein N is P N is the number of occupied forward time slots T Is the total number of forward time slots; r is R N ＝N N /N T Wherein N is N For the number of negative slots, assume that the total number of positive slots is equal to the total number of negative slotsEtc.
According to a further technical scheme, the competition time stamp is the time when a newly added vehicle listens to the first time slot;
the vehicle density refers to the number of vehicles in the range of two hops in the vehicle traveling direction. After listening for a frame time and executing two steps, the vehicle traverses the slot array, and the number of the vehicle ID fields occupied by the vehicle in each element in the running direction is accumulated, so that the obtained result is the vehicle density;
the declaration information is information transmitted when the vehicle is competing for a slot in the slot access phase. This information includes vehicle ID, competitive time stamp, vehicle density, etc.;
the collision information means that the vehicle cannot correctly analyze the signal content in a certain time slot, and transmits information about the collision time slot in its own time slot, and the collision information includes a collision time slot ID and a collision flag to indicate that a collision occurs in a certain time slot.
According to the further technical scheme, after the declaration information is sent out, the one-hop neighbors of the vehicle can detect the signal, if only the vehicle competes for the time slot, in the next frame, the one-hop neighbors of the vehicle contain the ID (identification) of the competing vehicle and the time slot use information in the beacon information of the vehicle, and the competing time slot is successful;
otherwise, in the case that there are multiple vehicles competing for the same time slot and at least two vehicles are in a two-hop range, the vehicles that sense the declaration signal are classified into two types: one is a vehicle that successfully receives the declaration information, and the other is a vehicle that receives the collision signal.
The one or more of the above technical solutions have the following beneficial effects:
(1) The invention does not need the participation of roadside units, and only needs the vehicles to exchange beacon frames. Therefore, the construction cost of roadside infrastructure can be reduced, and the input cost is reduced.
(2) The invention can increase the success rate of the vehicle access time slot and reduce unnecessary resource waste.
(3) The invention makes an explanation on mapping the actual running direction of the vehicle into the protocol, has stronger practicability and improves the reliability of the algorithm.
(3) In the invention, if a plurality of vehicles collide in competition, one of the vehicles can successfully compete for the time slot by the aid of the neighbor vehicles, and other collision vehicles need to compete for the time slot again. Therefore, the method not only can reduce the access collision probability, but also can effectively utilize the time slot resources and avoid resource waste.
(3) In order to facilitate the inquiry of vehicles to neighbor vehicles using the same time slot, the invention establishes a time slot array. Wherein, the array index is the time slot index; one field of each element indicates whether the time slot is occupied by at least two vehicles; other fields record the vehicle ID occupying the slot. By traversing the array, potential collision vehicles can be quickly found, thereby improving query efficiency.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a schematic diagram of a frame structure according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a direction mapping relationship according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an embodiment of a time slot array;
fig. 4 is a schematic diagram of slot access according to an embodiment of the present invention;
FIG. 5 is a schematic view of a vehicle A, B in an exemplary embodiment of the present invention;
FIG. 6 is a diagram of a vehicle access slot according to an embodiment of the present invention;
fig. 7 is a schematic view of an access collision of a vehicle A, B according to an embodiment of the present invention;
FIG. 8 is a scene diagram of an Internet of vehicles according to an embodiment of the present invention;
FIG. 9 is a flowchart illustrating overall steps of an embodiment of the present invention.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Embodiments of the invention and features of the embodiments may be combined with each other without conflict.
Term interpretation: MAC (Media Access Control, medium access control), RSU (Road-Side Unit), TDMA (Time Division Multiple Access ).
Example 1
The embodiment discloses a distributed internet of vehicles MAC layer time slot access method based on a TDMA technology, the whole steps are shown in figure 9, whether a new vehicle is added or not is judged, if yes, a time slot access algorithm is executed, collision detection and collision processing are carried out, then whether a time slot is obtained or not is judged, if yes, time slot communication is occupied, otherwise, the time slot access algorithm is continuously executed, and the collision detection and the collision processing are carried out again until the time slot is obtained.
In a specific embodiment, referring to fig. 8, each vehicle is equipped with a signal transceiver device and a global positioning system (GPS, beidou navigation system, etc.). The signal transceiver device may receive wireless signals from the neighboring vehicles and may also transmit own wireless signals to the neighboring vehicles, but at the same time, the signal transceiver device may only receive or transmit wireless signals and cannot transmit and receive simultaneously. The present application uses TDMA communication technology for enabling internet of vehicles communications. In common practice, the present application divides the Time into a plurality of repeated frames (frames, each of about 100 ms), and then divides the frames into a plurality of equal-length Time slots (Time slots). For example, as shown in fig. 1, two consecutive frames are given, wherein each frame is equally divided into 14 slots. The vehicle first competes for the time slot. If successful, it uses this time slot to transmit wireless signals until a collision occurs or itself gives up. Because each vehicle needs to broadcast its own time slot information and the time slot information of one-hop neighbor nodes, the vehicle knows which time slots are available in its own two-hop range. With technology upgrade, each vehicle can accurately acquire own position, speed, acceleration, running direction and time synchronization information through a global positioning system.
In a specific embodiment, the communication range of the vehicle is a one-hop range, that is, a communication range that the vehicle can reach after one hop. The two-hop range is a communication range that the vehicle can reach by requiring one-hop neighbor node relay.
In order to implement the invention, two sets are also defined, respectively: a one-hop neighbor set and a two-hop neighbor set. A one-hop neighbor set refers to a set of all vehicles within a vehicle communication range; a two-hop neighbor set refers to a set of all vehicles that a vehicle can communicate with through an intermediate one-hop node relay. Because of the problems of space multiplexing technology and hidden terminals, vehicles in one-hop and two-hop neighbor sets cannot use the same time slot, otherwise signal collision occurs, and information cannot be received; while vehicles outside the two-hop neighbors may use the same time slot. Thus, when a competing time slot is newly added to a vehicle, a collision occurs if at least two vehicles within a two-hop range select the same time slot at the same time. In general, the Collision in this case is called an Access Collision (Access Collision) or a contention Collision (Competing Collision)
To prevent broadcast storm problems, the vehicle only needs to send a beacon frame to one-hop neighbors, thus setting the hop count value of the beacon frame to 1. When a hop neighbor receives a beacon frame, the hop count value minus 1 becomes 0, and the neighbor vehicle discards the beacon frame.
Protocol direction and frame structure: in view of the fact that vehicles traveling in opposite directions are extremely liable to cause a merging collision problem, first, a traveling direction of the vehicle in the present invention, i.e., a protocol direction, is defined, which is mapped from an actual traveling direction of the vehicle (a direction in the global positioning system). As shown in FIG. 2, the directions of the vertical stripes and the solid lines are mappedThe direction of the horizontal stripes and the broken lines is mapped to the other direction (reverse direction). Vehicles traveling in the same direction are divided into one set, and thus the vehicles can be divided into two sets (set D P And set D N ) Different time slots are allocated according to the direction of travel of the vehicle. The purpose of this is to: the merging collision between vehicles traveling in opposite directions is eliminated. This is a direction-based time slot division method. As shown in fig. 1, the frame is divided into front and rear portions, and the front portion is allocated to a vehicle traveling in the forward direction (set D P ) The latter part is assigned to vehicles traveling in reverse (set D N )。
Neighbor table and slot array: in order to better perceive the surrounding environment, implement TDMA technology for ad hoc networks, and support security-related applications, vehicles need to collect and update their own and one-hop neighbor driving states and time slot usage information in real time and embed them in beacon frames, and periodically transmit them to one-hop neighbor vehicles for completing information exchange. The running state information includes: position, speed, acceleration and direction of travel; the slot usage information includes: occupy slot ID and timestamp when slot is obtained. The slot ID is an integer starting from 0, and the maximum value is the total number of slots of a frame. If the time slot ID occupied by the vehicle is 0, indicating that the vehicle has not contended for the time slot; otherwise, the actual time slot occupied by the vehicle is indicated.
In order to predict a possible collision more quickly and accurately, a time slot array is established. The number of elements of the array is the same as the number of time slots of each frame, and the array index number is the time slot ID. Each element comprises N fields (N is more than or equal to 3), a repeated time slot field (Boolean type) indicates whether the time slot is occupied by different vehicles, a value of 1 indicates that at least two vehicles occupy the time slot, and a value of 0 indicates that at most one vehicle occupies the time slot; the other fields are vehicle ID fields (integer type) for recording the vehicle ID occupying the time slot, and when the vehicle occupies the time slot, the vehicle ID is filled in the field, and the other fields are filled in NULL. For example, as shown in FIG. 3, the array has 14 slots in total, and the numbers in the first row of dashed boxes represent the array index; a second action repetition time slot field; third, four behavior vehicle ID field, where letter N represents NULL value and other numbers represent vehicle ID. Wherein, the 2 nd, 8 th and 12 th time slots are occupied by two vehicles, the 5 th, 7 th, 10 th, 13 th and 14 th time slots are not used, and the rest time slots are occupied by one vehicle.
"two steps":
when a beacon frame of a neighbor is received (this neighbor is called a communication neighbor), the vehicle performs the following two steps: (1) updating a neighbor table. The updating of the neighbor table comprises two parts, a) updating a one-hop neighbor table. Checking a self one-hop neighbor table, and if the communication neighbor is in the self one-hop neighbor table, updating the running state and the time slot use information corresponding to the communication neighbor in the neighbor table; otherwise, the communication neighbor is added into the one-hop neighbor table and the driving state and the time slot use information are added. b) And updating the two-hop neighbor table. First, two-hop neighbors are screened: vehicles that find one-hop neighbors of the communication neighbors, rather than their own one-hop neighbors, are their own two-hop neighbors (these two-hop neighbors are referred to as active two-hop neighbors). Then, checking the two-hop neighbor list of the user, and if the active two-hop neighbor is in the two-hop neighbor list of the user, updating the running state and the time slot use information corresponding to the active two-hop neighbor in the two-hop neighbor list; otherwise, the active two-hop neighbors are added into the two-hop neighbor list and the driving state and the time slot use information are added. (2) updating the slot array. Comparing the time slot occupation condition of the communication neighbor and the one-hop neighbor with the time slot array, updating, adding or deleting the data of the time slot array in real time according to the beacon frame of the communication neighbor, and calculating the time slot occupation ratio R of the vehicle running direction P And R is N Wherein R is P For the forward slot occupancy ratio, R N Is the reverse slot occupancy ratio. R is R P ＝N P /N T Wherein N is P N is the number of occupied forward time slots T Is the total number of forward time slots. R is R N ＝N N /N T Wherein N is N The number of occupied slots for negative going. We assume that the total number of positive slots and the total number of negative slots are equal.
Competitive timestamp, vehicle density, declaration information, and collision information:
the contention timestamp is the time when the newly joining vehicle listens to the first slot.
The vehicle density refers to the number of vehicles in the range of two hops in the vehicle traveling direction. After listening for a frame time and executing the two steps, the vehicle traverses the slot array, and the number of the vehicle ID fields occupied by the vehicle in each element in the running direction is accumulated, so that the obtained result is the vehicle density.
The declaration information is information transmitted when the vehicle is competing for a slot in the slot access phase. This information includes vehicle ID, competitive time stamp, vehicle density, and the like.
Collision information means that a vehicle cannot accurately analyze the signal content in a certain time slot, and transmits information about the collision time slot in its own time slot. The collision information includes a collision slot ID and a collision flag to indicate that a collision has occurred in a certain slot.
Protocol procedure
Time slot access algorithm: before competing for time slots, a newly added vehicle firstly listens for one frame of time, and performs two steps to establish a one-hop neighbor list, a two-hop neighbor list and a time slot array, so as to obtain the running state of the neighbor vehicle, the time slot use information and the idle time slot information. At the same time, the time when the vehicle starts to listen to the time slot, i.e. the time when it listens to the first time slot, is recorded, and this time is called the contention timestamp. Then, K free slots are selected from one frame (and in the own traveling direction) starting from the contention timestamp, and one slot is randomly selected from the K free slots as the own transmission slot. Finally, the vehicle puts the announcement information into the beacon frame, and when the next transmission time slot arrives, the beacon frame is transmitted to announce that the beacon frame will occupy the time slot. As shown in fig. 4, the vehicle starts to listen to the channel at Ta, listens for a frame time, and then ends at Tb. During this frame time, the vehicle performs "two steps" to obtain one-hop and two-hop neighbor information. The Ta time is the timestamp of the vehicle. Then, the vehicle randomly selects one of the K free slots from Tb as its own transmission slot, which must be the own slot (if the vehicle is traveling in the forward direction, it needs to be from D P Time slots are selected; if the vehicle is travelling in the negative directionIt needs to be taken from D N A time slot is selected). If the vehicle selects slot 10 as its own transmit slot, it will transmit announcement information at the location shown (slot 10).
Collision detection: after the declaration information is sent out, the one-hop neighbors of the vehicle can detect the signal. If only the vehicle contends for the time slot, in the next frame, its one-hop neighbor includes the ID of the competing vehicle and the time slot usage information in its own beacon information, and the competing time slot is successful. Otherwise, in the case where there are multiple vehicles competing for the same time slot (and at least two vehicles are within two hops), the vehicles listening for the declaration signal are classified into two categories: one is a vehicle that successfully receives the declaration information, and the other is a vehicle that receives the collision signal. As shown in fig. 5, the vehicle a and the vehicle B have an access collision, and the broken circles represent the communication ranges of the vehicle a and the vehicle B, respectively. Vehicle C, D, E, F is within communication range of vehicle a and vehicle C, H, G, I is within communication range of vehicle B. Vehicle A and vehicle B compete for the same time slot i at the same time, and vehicle C is in the communication range of A and B at the same time, so that C cannot correctly receive the declaration information; vehicle D, E, F can correctly receive the declaration information of vehicle a, and vehicle H, G, I can correctly receive the declaration information of vehicle B.
Collision processing algorithm: in the next frame time, the vehicles C, D, E, F, H, G, I transmit the contention slots with respect to the vehicle A, B in the own transmission slots in the slot order, respectively. In principle, since vehicle C does not normally receive information, it puts collision information into a beacon frame to a one-hop neighbor to indicate that slot i has collided; vehicle D, E, F sends declaration information about vehicle a to the one-hop neighbor; vehicle H, G, I sends declaration information about vehicle B to the one-hop neighbor. However, since each vehicle has a different transmission slot, the declaration information they transmit may also vary. Depending on the transmission time slot of the vehicle and the timestamp size of the vehicle A, B, the time-stamped vehicle takes precedence to acquire the time slot. For example, as shown in fig. 6, the vehicle obtains its own time slot. In time slot 10, the vehicle A, B has sent its own announcement information at the same time, which is intercepted by surrounding neighbors. The problem is described by taking examples of different time stamps of the vehicles A, B, respectively.
Assuming that the timestamp of vehicle A is greater than the timestamp of vehicle B, i.e. TS A ＞TS B . First, in slot 12, vehicle D sends a statement that vehicle a occupies slot 10, which is sensed by its one-hop neighbor A, E, F, C, G. The vehicle A, E, F, C, G then compares the information stored by itself with the information sent by D. The vehicle A, E, F finds that the information is the same and does not update at all; the vehicle C finds that the information is different from the information of the vehicle A and the vehicle A occupies the time slot 10, and updates the information of the vehicle C to the time slot 10 occupied by the vehicle A; if the vehicle G finds that the time stamp of the vehicle a is larger than the time stamp of the vehicle B, the vehicle G updates the own information to the time slot 10 occupied by the vehicle a. Then, in slot 1, vehicle G sends a statement that vehicle a occupies slot 10, which is sensed by its one-hop neighbor B, C, D, H, I. Next, the vehicle B, C, D, H, I compares the information stored by itself with the information transmitted by G. The vehicle C, D finds that the information is the same and does not update at all; the vehicle B, H, I finds that the time stamp of the vehicle a is larger than the time stamp of the vehicle B, and updates the own information to the time slot 10 occupied by the vehicle a. Next, in slot 2, vehicle H sends a statement that vehicle a occupies slot 10, which is sensed by its one-hop neighbor B, C, E, G, I. Next, the vehicle B, C, E, G, I compares the information stored by itself with the information transmitted by H. The vehicle B, C, E, G, I finds that the information is the same and does not make any updates. This process continues until slot 9 ends. Vehicle a acquires slot 10 while vehicle B continues to compete for the slot. In each slot, the vehicle puts in the travel state and slot usage information of other vehicles in addition to the declaration information of the competing vehicles A, B for the slot 10 in the beacon frame. For emphasis and simplicity of discussion, only a portion of the competing time slots of the vehicle A, B are described.
Assuming that the timestamp of vehicle A is less than the timestamp of vehicle B, i.e. TS A ＜TS B . First, in slot 12, vehicle D sends a statement that vehicle a occupies slot 10, which is sensed by its one-hop neighbor A, E, F, C, G. Next, the process is carried outThe vehicle A, E, F, C, G compares the information stored by itself with the information transmitted by D. The vehicle A, E, F finds that the information is the same and does not update at all; the vehicle C finds that the information is different from the information of the vehicle A and the vehicle A occupies the time slot 10, and updates the information of the vehicle C to the time slot 10 occupied by the vehicle A; the vehicle G finds that the information is different from the own information and the time stamp of the vehicle a is smaller than that of the vehicle B, and does not make any update. Then, in slot 1, vehicle G sends a statement that vehicle B occupies slot 10, which is sensed by its one-hop neighbor B, C, D, H, I. Next, the vehicle B, C, D, H, I compares the information stored by itself with the information transmitted by G. The vehicle B, H, I finds that the information is the same and does not update at all; the vehicle C, D finds that the time stamp of the vehicle a is smaller than the time stamp of the vehicle B, and updates the own information to the time slot 10 occupied by the vehicle B. Next, in slot 2, vehicle H sends a statement that vehicle B occupies slot 10, which is sensed by its one-hop neighbor B, C, E, G, I. Next, the vehicle B, C, E, G, I compares the information stored by itself with the information transmitted by H. The vehicle B, C, G, I finds that the information is the same and does not make any updates. If the vehicle E finds that the time stamp of the vehicle a is smaller than the time stamp of the vehicle B, the vehicle E updates the own information to the time slot 10 occupied by the vehicle B. Next, in slot 4, vehicle C sends a statement that vehicle B occupies slot 10, which is sensed by its one-hop neighbor B, A, E, G, D, H. Next, the vehicle B, A, E, G, D, H compares the information stored by itself with the information transmitted by C. The vehicle B, E, G, D, H finds that the information is the same and does not make any updates. When the vehicle a finds that the time stamp of the vehicle a is smaller than the time stamp of the vehicle B, the vehicle a updates the own information to the time slot 10 occupied by the vehicle B. This process continues until slot 9 ends. Vehicle B acquires slot 10 while vehicle a continues to contend for the slot.
If the time stamps of the vehicle A and the vehicle B are equal, the vehicle with the large density preferentially obtains the time slot by using the density of the vehicles as a judging condition.
If the vehicle density is small, there is only a vehicle in the common coverage of the vehicles A, B, and there is no vehicle in the other coverage of the vehicle A, B, as shown in fig. 7. In this case, no redundant vehicle assistance determination is made as to the attribution of the slot, and only the vehicle C transmits collision information in its own slot. After receiving the collision information of the vehicle C, the vehicle A, B continues to execute the slot access algorithm to obtain its own transmission slot.
If there are no vehicles within the common coverage of the vehicles A, B, they will not cause a slot collision even if they are within two hops of each other. Thus, in this case, the vehicle A, B can use the same time slot. If the same time slot is used by the vehicles A, B in this case, one of the vehicles will change time slots in time.
Example two
An object of the present embodiment is to provide a distributed internet of vehicles MAC layer time slot access system based on TDMA technology, including: an information transceiving device mounted on a vehicle, the information transceiving device being configured to perform the steps of a TDMA technology-based distributed internet of vehicles MAC layer time slot access method:
judging whether a new vehicle is added, if so, executing a time slot access algorithm, performing collision detection and collision processing, then judging whether a time slot is obtained, if so, occupying time slot communication, otherwise, continuing executing the time slot access algorithm, and performing the collision detection and collision processing again until the time slot is obtained.
It will be appreciated by those skilled in the art that the modules or steps of the invention described above may be implemented by general-purpose computer means, alternatively they may be implemented by program code executable by computing means, whereby they may be stored in storage means for execution by computing means, or they may be made into individual integrated circuit modules separately, or a plurality of modules or steps in them may be made into a single integrated circuit module. The present invention is not limited to any specific combination of hardware and software.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.

Claims (7)

1. A time slot access method of a distributed Internet of vehicles MAC layer based on a TDMA technology is characterized by comprising the following steps:
judging whether a new vehicle is added, if yes, executing a time slot access algorithm, performing collision detection and collision processing, then judging whether a time slot is obtained, if yes, occupying time slot communication, otherwise, continuing executing the time slot access algorithm, and performing the collision detection and collision processing again until the time slot is obtained;
the time slot access algorithm: before competing for time slots, a newly added vehicle firstly listens for one frame of time, establishes a one-hop neighbor table, a two-hop neighbor table and a time slot array, and obtains the running state of the neighbor vehicle, the time slot use information and the idle time slot information;
defining a one-hop neighbor set and a two-hop neighbor set;
a one-hop neighbor set refers to a set of all vehicles within a vehicle communication range;
the two-hop neighbor set refers to a set of all vehicles that can be communicated by the vehicles through the relay of the middle one-hop node;
meanwhile, recording the time when the vehicle starts to monitor the time slot, namely the time when the vehicle monitors the first time slot, and calling the time as a competition time stamp;
then, K idle time slots are selected from a frame starting from the competition time stamp in the running direction of the user, and one time slot is randomly selected from the K idle time slots to be used as the transmission time slot of the user;
finally, the vehicle puts the declaration information into a beacon frame, and when the next sending time slot arrives, the beacon frame is sent out to declare that the vehicle will occupy the time slot; when receiving the beacon frame of the neighbor, the vehicle performs the following two steps:
s1, updating a neighbor table, wherein the updating of the neighbor table comprises two parts: updating a one-hop neighbor table and updating a two-hop neighbor table;
s2, updating a time slot array, comparing the time slot occupation condition of the communication neighbor and the one-hop neighbor with the time slot array, updating, adding or deleting the data of the time slot array in real time according to the beacon frame of the communication neighbor, and calculating the time slot occupation ratio R of the vehicle running direction P And R is N Wherein R is P For the forward slot occupancy ratio, R N Is the reverse slot occupancy ratio;
the collision treatment specifically comprises the following steps: if the competing time stamp of the vehicle 1 is greater than that of the vehicle 2, the vehicle 1 will acquire the time slot, otherwise the vehicle 2 acquires the time slot, and the vehicle 2 or the vehicle 1 colliding with the time slot will continue competing for the time slot until the time slot is acquired; if the competing time stamps of the vehicles 1 and 2 are equal, taking their vehicle densities as a condition for judging whether time slots can be obtained, the vehicles with large densities will obtain the time slots, wherein, the competing time stamps and the vehicle densities are both in the declaration information of the vehicles;
the vehicle density refers to the number of vehicles in the two-hop range of the vehicle in the running direction of the vehicle;
the declaration information is information transmitted when the vehicle is competing for a slot in the slot access phase.
2. The TDMA-based distributed internet of vehicles MAC layer time slot access method according to claim 1, wherein the vehicles performing the time slot access algorithm are equipped with a signal transceiver and a global positioning system, and the signal transceiver receives wireless signals from neighboring vehicles and can transmit own wireless signals to the neighboring vehicles, but at the same time, the signal transceiver can only receive or transmit wireless signals but cannot transmit and receive simultaneously.
3. A TDMA-based distributed internet of vehicles MAC layer time slot access method according to claim 1 wherein TDMA communication technology is used to effect internet of vehicles communication, wherein time is divided into a plurality of repeated frames, and then the frames are divided into a plurality of equal length time slots.
4. A TDMA-based distributed internet of vehicles MAC layer time slot access method according to claim 1, wherein the vehicle transmits a beacon frame to a one-hop neighbor, sets the hop count of the beacon frame to 1, and when the one-hop neighbor receives the beacon frame, the hop count decreases by 1 to 0, and the neighbor vehicle discards the beacon frame.
5. The TDMA-based distributed internet of vehicles MAC layer time slot access method of claim 1, wherein a driving direction of the vehicle, i.e., a protocol direction, is defined, mapped from an actual driving direction of the vehicle;
vehicles traveling in the same direction are divided into one set, and thus the vehicles are divided into two sets, different time slots are allocated according to different traveling directions of the vehicles, and the combined collision between vehicles traveling in opposite directions is eliminated.
6. A TDMA-based distributed internet of vehicles MAC layer time slot access method according to claim 3, wherein the vehicles need to collect and update their own and one-hop neighbor driving status and time slot usage information in real time, and embed the information into a beacon frame, and periodically transmit the information to the one-hop neighbor vehicles for completing information exchange.
7. A distributed internet of vehicles MAC layer slot access system based on TDMA technology, comprising: an information transceiving device installed on a vehicle, said information transceiving device being configured to perform the steps of a distributed internet of vehicles MAC layer time slot access method based on TDMA technology as claimed in any of claims 1-6.
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