KR101806655B1 - System and method of an efficient time slot acquisition on the hybrid tdma/csma multi-channel mac in vanet - Google Patents

Abstract

The present invention relates to a hybrid TDMA / CSMA multi-channel MAC protocol for VANETs capable of efficiently broadcasting messages and increasing control channels, and, according to one aspect, a method of obtaining a timeslot of a processor implemented at least temporarily by a computer Selecting a random time slot for access in a TDMA-based reservation period, generating an announcement packet ANC including information on neighboring nodes in each time slot corresponding to the selected random time slot, broadcasting an announcement packet, and obtaining a reserved timeslot based on the broadcasting.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a system and a method for effectively obtaining time slots in a hybrid TDMA / CSMA multi-channel MAC in a VANET,

The present invention relates to a hybrid TDMA / CSMA multi-channel MAC protocol capable of efficiently broadcasting messages and increasing control channels in VANETs.

Intelligent Transportation System (ITS) is becoming a major research issue with the development of technologies related to wireless communication, with the aim of constructing a practical and human friendly traffic environment. Research and technical standardization work for the construction of intelligent transportation system such as providing various services through internet access on the road, traffic control for maintaining smooth traffic flow, and development of safety related services that prioritize driver safety are in full swing. In such an intelligent traffic system, a VANET (Vehicular Ad-hoc Network) constitutes a wireless communication environment between vehicles on the road or between a vehicle and a road-side unit (RSU). In the IEEE 1609 WAVE (Wireless Access in Vehicular Environments) standard for ITS construction, the MAC protocol for VANET support applies the DSRC (Dedicated Short Range Communications) standard, which is aimed at fast transmission.

DSRC technology uses a 75MHz bandwidth of 5.9GHz band and is based on IEEE 802.11a to reduce communication overhead and is standardized as IEEE 802.11p. The DSRC defines seven channels in the 75 MHz band, one is defined as CCH (Control Channel) and used for system control and safety related message transmission, and the rest is set up as a Service Channel (SCH) Are used to exchange irrelevant data. Utilizing these channel settings, IEEE 802.11p has been defined as an extended MAC standard for WAVE applications. IEEE 802.11p supports the EDCA (Enhanced Distributed Channel Access) based priority function and has the concept of multi-channel structure. Multichannel support is a mixture of frequency division and time division multiple access.

Korean Patent Publication No. 10-2010-0091456 Korean Patent No. 10-0903431

According to one aspect, a method of obtaining a timeslot of a processor that is at least temporarily implemented by a computer includes the steps of: selecting a random time slot for access in a TDMA-based reservation period; Broadcasting an announcement packet (ANC) containing information about neighboring nodes in each timeslot, and obtaining a reserved timeslot based on the broadcasting.

The announcement packet (ANC) according to an embodiment includes a node ID field, a reserved time slot field, a switched time slot field, a number of time slots a number of time slots field, an IDs of neighbor nodes field, a time slot allocated allocated by neighbor nodes field, and a safety application packet, Field and at least one field from among the fields.

A time slot acquisition method according to an embodiment includes calculating an average number of nodes to acquire a time slot within a sync-interval, and calculating a probability that the calculated nodes acquire time slots within n frames Gt;

The time slot acquisition method according to an embodiment includes calculating a collision probability in a contention period based on the calculated average number and the determined probability.

The time slot acquisition method according to an embodiment further includes checking an announcement packet (ANC) broadcast from a neighboring node after a period of a sync-interval.

The time slot acquisition method according to an exemplary embodiment determines whether or not which time slots can access a TDMA-based reservation period based on an announcement packet (ANC) broadcast from the neighbor node .

A time slot acquisition system according to one aspect comprises: a selector for selecting a random time slot for access in a TDMA-based reservation period; a selector for selecting, in each time slot corresponding to the selected random time slot, A broadcasting section for broadcasting an announcement packet (ANC) including information on the broadcasting time, and an acquiring section for acquiring a reserved time slot based on the broadcasting.

The time slot acquisition system according to one aspect further includes a calculation unit, wherein the calculation unit calculates an average number of nodes to acquire a time slot within a sync-interval, To determine the probability of obtaining a slot.

The calculation unit according to an embodiment calculates a collision probability in a contention period based on the calculated average number and the determined probability.

The processing unit may check an announcement packet (ANC) broadcasted from a neighboring node after a period of a sync-interval, and transmit a notification packet ANC, based on the announcement packet, which time slots can access the TDMA-based reservation period.

The program according to an embodiment includes a set of instructions for selecting a random time slot for access in a TDMA-based reservation period, information for neighboring nodes in each timeslot corresponding to the selected random time slot, And a set of instructions for obtaining a reserved timeslot based on the broadcasting.

1 is a diagram illustrating a timeslot acquisition system according to one embodiment.
2 is a diagram illustrating a format of a notification packet according to an exemplary embodiment.
3 is a view for explaining a control channel according to an embodiment.
4 is a view for explaining a time slot acquisition method according to an embodiment.
5 is a view for explaining a method of calculating a collision probability in a contention period.
FIG. 6 is a view for explaining a Marcov chain in the HER-MAC. FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, the scope of the rights is not limited or limited by these embodiments. Like reference symbols in the drawings denote like elements.

The terms used in the following description are chosen to be generic and universal in the art to which they are related, but other terms may exist depending on the development and / or change in technology, customs, preferences of the technician, and the like. Accordingly, the terminology used in the following description should not be construed as limiting the technical thought, but should be understood in the exemplary language used to describe the embodiments.

Also, in certain cases, there may be a term chosen arbitrarily by the applicant, in which case the meaning of the detailed description in the corresponding description section. Therefore, the term used in the following description should be understood based on the meaning of the term, not the name of a simple term, and the contents throughout the specification.

1 is a diagram illustrating a time slot acquisition system 100 in accordance with one embodiment.

The time slot acquisition system 100 may include a selection unit 110, a processing unit 120, an acquisition unit 130, and a calculation unit 140. The time slot acquisition system 100 may be implemented at least temporarily by a computing terminal. The computing terminal includes any type of electronic device such as a personal computer, a medical device, a smart phone, a tablet computer, and a wearable device. The selecting unit 110, the processing unit 120, the obtaining unit 130, and the calculating unit 140 may be physical and / or logical elements included in such electronic devices, respectively. The selecting unit 110, the processing unit 120, the obtaining unit 130, and the calculating unit 140 may be implemented by dedicated hardware or general purpose computing resources controlled by software or an operating system. It is also possible that the selection unit 110, the processing unit 120, the acquisition unit 130, and the calculation unit 140 are implemented together on one chip, And can be changed by design change or design change. Accordingly, it is understood that the functions, operations, and structures of the selector 110, the processor 120, the acquiring unit 130, and the calculator 140 are distinguished from each other, but in some embodiments, such distinctions may be interpreted differently .

Specifically, using the present invention, it is possible to provide a hybrid TDMA / CSMA multi-channel MAC protocol for VANETS capable of efficiently broadcasting messages and increasing control channels. Also, the MAC proposed in the present invention can remove unnecessary control packets such as HELLO and SWITCH packets in the HER-MAC. Finally, the analysis and simulation results using the present invention may indicate that the techniques proposed in the present invention enable faster slot acquisition than HER-MAC.

To this end, the time slot acquisition system 100 includes a selection unit 110, a processing unit 120, an acquisition unit 130, and a calculation unit 140.

First, the selector 110 selects a random time slot for access in a TDMA-based reservation period.

Next, the processing unit 120 broadcasts an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot. At this time, an announcement packet (ANC) may include a field for informing information about the node, and a field for confirming information about the neighbor node.

It can be assumed that each node has one transceiver, and the transceiver at this time can switch between the control channel (CCH) and the service channel (SCH). If the node does not send or receive a packet on the SCH, it performs an operation to broadcast a safety message on the CCH or an exchange of a WSA / RFS message to reserve a time slot in the SCH for non-safety message transmission . For a safety application, each node must acquire an accurate one time slot in a TDMA-based reservation period. Each of these nodes must transmit an announcement packet (ANC) during the reservation period.

An announcement packet (ANC) is described in more detail in FIG.

2 is a view for explaining the format of the announcement packet 200 according to an embodiment.

The announcement packet ANC 200 includes a node ID field, a reserved time slot field, a switched time slot field, a number of time slots field, , An IDs of neighbor nodes field, a time slot allocated allocated by neighbor nodes field, and a safety application packet field. can do.

The Node ID field is a field containing an identifier for the node that transmits the announcement packet (ANC 200), and can uniquely identify the broadcasting node from other nodes.

The reserved time slot field records information about a time slot occupied in a contention period through broadcasting in an announcement period.

The switched time slot field records information on time slots that have changed from reservation to non-reservation or from non-reservation to reservation.

A number of time slots field records information on the number of timeslots included during the current sync interval and an IDs of neighbor nodes field identifies the current node And an identifier for identifying neighboring nodes at the center.

The time slot is allocated by neighbor nodes field includes information on time slots that are allocated to neighbor nodes that are not the current node and can not be occupied during the current sync interval .

The safety application packet field may contain a message for a safe driving application.

The acquiring unit 130 acquires the reserved time slot based on the broadcasting. Specifically, the time slot can be preempted according to the announcement signal broadcasting at present, and the acquiring unit 130 acquires information on the preempted time slot, thereby completing the time slot acquisition.

The calculation unit 140 according to an exemplary embodiment may calculate a collision probability that may occur in the current network.

Specifically, the calculation unit 140 may calculate an average number of nodes to acquire a time slot within a sync-interval, and may determine a probability that the calculated nodes acquire a time slot within n frames . In addition, the calculation unit 140 may calculate the collision probability in the contention period based on the calculated average number and the determined probability.

3 is a view for explaining a control channel according to an embodiment.

The control channel according to an exemplary embodiment may be implemented with a time division structure of a WAVE MAC. The control channel according to an exemplary embodiment divides time into consecutive 100 ms intervals, and the first 50 ms is allocated to the CCH and the second 50 ms is allocated to the SCH for each 100 ms interval. At the beginning of each 50 ms interval, ie, the CCH, a guard interval (GI) of 4 ms is placed, which is for stabilizing channel switching between the CCH and the SCH.

The GI is followed by an announcement period, in which broadcasting for time slot acquisition can be performed. Also, after the announcement period, a contention period may occur. The contention period may include a backoff slot, a WSA / RFS, an ACK, a RES, and a Safe interval for a WAVE Service Advertisement (WSA) message.

An SCH interval after the CCH can be obtained and a contention period can follow the announcement period in the SCH as in the case of the CCH.

Such a channel switching is performed so that even if the WAVE equipment is a single-channel wireless equipment, it is possible to access both the CCH and the SCH channel with a time lag. It reflects that CCH connection is essential for anyone to obtain information for safety.

For example, single-channel radio equipment can accommodate both safety-related and non-safety-related services through channel switching between the CCH and the SCH. In the CCH section, two kinds of messages are transmitted. The first is a message for a safety-related application program, and the second is a WAVE Service Advertisement (WSA) message for notifying a service available on the SCH channel. Safety-related messages are classified into event-based messages related to an unexpected situation and status messages periodically transmitted as basic information for safe operation.

Event-based messages are generated intermittently, priority is applied for fast transmission, and status messages are generated periodically to become the main input information of safety-related applications. All of them have a common characteristic that broadcasting is required due to the characteristics of the message. In the broadcast transmission type, the transmission efficiency according to the traffic load is a main performance index. In this respect, many researches have paid attention to the transmission efficiency of the periodic status message having a larger data amount than the intermittent event based message.

4 is a view for explaining a time slot acquisition method according to an embodiment.

A time slot acquisition method according to an embodiment selects a random time slot for access (step 410) and broadcasts an announcement packet (ANC) (step 420).

The time slot acquisition method acquires a scheduled time slot based on broadcasting (step 430). That is, the corresponding time slot is reserved according to broadcasting.

Meanwhile, an announcement packet (ANC) broadcast from a neighboring node can be received. In this case, it is necessary to confirm which slot the neighboring node is to reserve. Accordingly, the time slot acquisition method checks an announcement packet (ANC) broadcasted from a neighboring node through step 440.

That is, in step 440, after a period of the sync-interval, an announcement packet (ANC) broadcasted from a neighboring node can be checked. Next, the time slot acquisition method determines which time slots are accessible to a TDMA-based reservation period (step 450).

On the other hand, when the nodes receive the ANC packet from the neighboring nodes, each node learns information related to the neighboring node. After a period of synchronization interval (50 milliseconds), each node checks the announcement packet (ANC) by the neighboring node. Thereafter, all neighbor nodes broadcast an ANC packet containing information in the neighbor information field to obtain a successfully reserved time slot.

For example, if a new node desires access to a timeslot, it may send an announcement packet (ANC) for one cycle of the synchronization interval, e.g., 50 milliseconds, for announcement packets (ANC) ).

Upon receipt of an announcement packet (ANC), the new node has information about the entire neighbor. Based on the received information, the new node may determine which timeslots are accessible to the TDMA based reservation period. In the protocol according to the present invention, in order to save the reservation period to a minimum length, the switched node may broadcast an announcement packet (ANC) including a TDMA-based reservation period.

At this time, the collision probability that can occur in the contention period can not be ignored.

Specifically, in the HER-MAC, a switched node broadcasts a SWITCH packet including a new time slot in a contention period. At this time, if there are many nodes broadcasting the safety messages in the contention period, there is a high possibility of collision.

5 is a view for explaining a method of calculating a collision probability in a contention period.

In order to provide adequate and effective safety applications, the MAC (Medium Access Control) protocol requires efficient broadcast services for safety messages. In addition, the multi-channel MAC protocol can improve the transmission reliability of safety messages by inserting CCH and SCH operations and priority access parameters. The MAC proposed in the present invention enables effective broadcasting of a message and increase of throughput of a control channel.

The present invention is a description of multi-channel MACs in vehicular ad hoc networks (VANETs), providing a new MAC protocol that can increase the throughput of control channels and the broadcasting of efficient messages. The MAC to be provided removes unnecessary control packets such as HELLO and SWITCH packets in the HER-MAC. To this end, the present invention designs an equation for determining the average number of nodes to acquire time slots within a sync interval and the probability that all modes acquire time slots within n frames.

First, in the method of FIG. 5, the average number of nodes is first calculated (step 510) and the probability of obtaining a timeslot may be determined (step 520).

Finally, in the method of FIG. 5, a collision probability at a contention period may be calculated based on the calculated average number and the determined probability (step 530).

Specifically, the average number of nodes that will acquire time slots within the synchronization interval using the Marquee chain of FIG. 6 and the formula for the probability that all nodes will acquire time slots for all nodes within n frames in the HER- You can decide.

Figure 6 shows an embodiment 600 illustrating a marc band in a HER-MAC.

From the Markov chain shown in FIG. 6, the possibility that a node may transmit a HELLO or safety application in any time slot

Lt; / RTI > becomes clear.

Can be expressed as: " (1) "

[Equation 1]

When two or more nodes are transmitted in a single time slot,

Can be defined as the probability of collision,

Can be expressed by Equation (2), and the variable

Wow

A solution can be found in the following numerical range.

&Quot; (2) "

,

,

In FIG. 6, agreements in all time slots in the HELLO interval indicate the possibility

Lt; / RTI > therefore,

Can be calculated through Equation (3).

&Quot; (3) "

For reference, in p-persistent CSMA / CA, the backoff interval is the probability

And the geometric distribution.

Based on the Bernoulli implementation, X can be defined as the number of successful nodes participating in the competing window size.

(4), p (X = i) can be calculated in a single frame.

&Quot; (4) "

On the basis of the Bernoulli trial, x can be calculated through Equation (5).

&Quot; (5) "

In each frame, E [X _i ] and p _{i, suc} can be calculated together with the parameters of the unsuccessful node in the i ^th frame that replaces K in the node's parameter that failed in the (i-1) ^th frame.

Therefore, the average number of nodes that acquire time slots within n frames can be calculated by Equation (6).

&Quot; (6) "

Finally, the likelihood that all the nodes will acquire time slots within n frames can be calculated by Equation (7).

&Quot; (7) "

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the apparatus and components described in the embodiments may be implemented within a computer system, such as, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA) A programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For ease of understanding, the processing apparatus may be described as being used singly, but those skilled in the art will recognize that the processing apparatus may have a plurality of processing elements and / As shown in FIG. For example, the processing unit may comprise a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as a parallel processor.

The software may include a computer program, code, instructions, or a combination of one or more of the foregoing, and may be configured to configure the processing device to operate as desired or to process it collectively or collectively Device can be commanded. The software and / or data may be in the form of any type of machine, component, physical device, virtual equipment, computer storage media, or device , Or may be permanently or temporarily embodied in a transmitted signal wave. The software may be distributed over a networked computer system and stored or executed in a distributed manner. The software and data may be stored on one or more computer readable recording media.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (11)

CLAIMS What is claimed is: 1. A method for obtaining a timeslot of a processor that is at least temporarily implemented by a computer,
Selecting a random time slot for access in a TDMA-based reservation period;
Broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot;
Calculating an average number of nodes to acquire a time slot within a sync-interval;
Determining a probability that the calculated nodes will acquire time slots within n frames; And
Acquiring a scheduled time slot based on the broadcasting;
/ RTI >
CLAIMS What is claimed is: 1. A method for obtaining a timeslot of a processor that is at least temporarily implemented by a computer,
Selecting a random time slot for access in a TDMA-based reservation period;
Broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot; And
And obtaining a reserved timeslot based on the broadcasting,
The announcement packet (ANC)
A reserved time slot field, a switched time slot field, a number of time slots field, an identifier (IDs) for a neighboring node, a node ID field, a reserved time slot field, a switched time slot field, a neighbor field, a neighbor node field, a time slot allocated by neighbor nodes field, and a safety application packet field.
delete The method according to claim 1,
Calculating a collision probability in a contention period based on the calculated average number and the determined probability;
/ RTI >
CLAIMS What is claimed is: 1. A method for obtaining a timeslot of a processor that is at least temporarily implemented by a computer,
Selecting a random time slot for access in a TDMA-based reservation period;
Broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot; And
And obtaining a reserved timeslot based on the broadcasting,
Checking a announcement packet (ANC) broadcast from a neighboring node after a period of a sync-interval,
≪ / RTI >
6. The method of claim 5,
Determining which time slots are accessible to a TDMA-based reservation period based on an announcement packet (ANC) broadcast from the neighbor node,
≪ / RTI >
Implemented at least temporarily by the computer:
In a TDMA-based reservation period, a selection unit selects a random time slot for access;
A processing unit broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot;
A calculation unit calculating an average number of nodes to acquire time slots within a sync-interval and determining a probability that the calculated nodes acquire time slots within n frames; And
Based on the broadcasting, an acquiring unit
Gt; time slot < / RTI >
delete 8. The method of claim 7,
Wherein the calculation unit calculates a collision probability in a contention period based on the calculated average number and the determined probability.
Implemented at least temporarily by the computer:
In a TDMA-based reservation period, a selection unit selects a random time slot for access;
A processing unit broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot; And
Based on the broadcasting, an acquiring unit
Lt; / RTI >
Wherein,
After a period of a sync-interval, an announcement packet (ANC) broadcast from a neighboring node is checked, and based on an announcement packet (ANC) broadcasted from the neighboring node, And determining if the slots can access a TDMA-based reservation period.
In combination with the hardware, selecting a random time slot for access in a TDMA-based reservation period;
Broadcasting an announcement packet (ANC) including information on neighboring nodes in each time slot corresponding to the selected random time slot;
Calculating an average number of nodes to acquire a time slot within a sync-interval;
Determining a probability that the calculated nodes will acquire time slots within n frames; And
Acquiring a scheduled time slot based on the broadcasting;
Readable recording medium.

Images