KR101565707B1 - Method of Data Transmitting/Receiving for Vehicular terminal - Google Patents

Abstract

The present invention relates to a data transmission and reception method of a vehicle terminal wherein when transmitting and receiving data based on the vehicle communications protocol standard IEEE 802.11p/WAVE (Wireless Access Vehicular Environments), if an amount of data to be transmitted by a vehicle terminal is greater than a predetermined amount, data is transmitted and received by being additionally allocated with a TXOP (Transmission Opportunity) limit interval. To this end, by using an Access Category (AC) concept that differentiates data-based priorities and depending on whether each access category-based data is saturated or not, data corresponding to a saturated access category is transmitted and received through an additional TXOP limit interval.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a data transmission /

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a data transmission / reception method of a vehicle terminal, and more particularly, to a vehicular communication system, in which, when data to be transmitted by a vehicle terminal is equal to or greater than a predetermined value during data transmission / reception based on IEEE 802.11p / WAVE TXOP (Transmission Opportunity) Limit section, and transmitting / receiving data. For this purpose, the concept of access category (AC) to distinguish priority by data is utilized. Based on the saturation of data by each access category, data corresponding to a saturated access category is transmitted through an additional TXOP limit section And transmits and receives the data.

Vehicular ad hoc network (VANET) is a type of mobile ad hoc network (MANET) that is a communication technology for application to high-speed moving vehicles. A vehicle ad hoc network is a vehicle-to-vehicle (V2V) communication between a vehicle and a vehicle and a vehicle-to-infrastructure (V2I) But also various infotainment services such as web browsing, media streaming, and real time traffic information. However, in general, a vehicle ad hoc network has a problem in that the moving speed of the on-board unit (OBU) is very fast, the topology changes very frequently, the required communication delay time is short, Wireless communication technologies have limitations in application to vehicle ad hoc networks.

Therefore, the necessity of establishing a new standard for a vehicle ad hoc network has emerged, and the IEEE 802.11p / WAVE (wireless access in vehicular environments) established by the Institute of Electrical and Electronics Engineers (IEEE) is currently used as an international standard for vehicle communication.

IEEE 802.11p / WAVE consists of IEEE 802.11p that defines the physical layer and MAC (medium access control) layer and IEEE 1609 that defines the upper layer. Key features of IEEE 802.11p / WAVE include orthogonal frequency division multiplexing (OFDM) modulation technique to reduce the influence of multipath interference, 7 channels with 10MHz channel bandwidth, WBSS (WAVE with consideration of frequent topology change characteristics) basic Service Set), transmission range of up to 1km considering the moving speed of vehicle terminal, and support of vehicle speed up to 200km / h.

However, despite these advantages, when the number of vehicle terminals on the road increases and the amount of data to be transmitted increases, there is a disadvantage that the collision between data in the network increases, the throughput of the entire network decreases, and the data delay increases. In particular, in the IEEE 802.11p / WAVE system, the minimum contention window (CW _min ) used to avoid data collision between different vehicle terminals is small, There is a high probability. In addition, since the speed of the vehicle terminal is very fast in the vehicle ad hoc network, it is very important to reduce the collision probability because the delay time required to guarantee the safety of the driver is short. Therefore, several studies have tried to mitigate the increase of collision probability between data when the number of vehicles increases in IEEE 802.11p / WAVE standard system.

First, in the existing IEEE 802.11p / WAVE, when the channel access right is obtained, the transmission opportunity (TXOP) technique for continuously transmitting information in the current vehicle terminal is used for a predetermined time. This can reduce the increase of data delay due to the collision because the data can be transmitted immediately without competing in the channel for a certain period of time. However, in the standard, since the time (TXOP limit) that can be continuously transmitted is determined, data can be transmitted for a predetermined time even when there is a lot of information to be transmitted from a specific vehicle terminal.

According to the TXOP scheme, it is possible to mitigate the collision probability between data in the entire system. However, since the data having low importance is continuously transmitted at present, there is a problem that the transmission of data requiring fast transmission is delayed As a result, the transmission of important data between vehicles is delayed.

U.S. Patent No. 7,289,529

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-mentioned problems, and it is an object of the present invention to provide a vehicle terminal that completes data transmission of one access category (AC) during a predetermined time (TXOP limit) If a large amount of data is stored, the new TXOP limit capable of continuously transmitting data of the corresponding AC is reallocated, thereby preventing a channel from being monopolized for data transmission of a specific AC, thereby enabling data transmission / reception of a vehicle terminal Method.

A method for transmitting / receiving data of a vehicle terminal according to an aspect of the present invention includes: transmitting data of a first access category (AC) through a communication channel to a vehicle terminal during a TXOP limit (TXOP limit) period corresponding to the first access category (A) transmitting; When the data transmission is completed during the TXOP limit (TXOP limit) corresponding to the first access category, the amount of data stored in the queue for each access category is detected, and the amount of data stored in the queue for each access category detected (B) selecting a second access category in which the amount of data stored in the queue is equal to or greater than a reference value by discriminating whether each access category is greater than or equal to a reference value; If the second access category is selected through the step (b), transmitting a message indicating that there is data to be transmitted during a subsequent TXOP limit interval; And (d) transmitting data of the second access category during a subsequent TXOP limit interval.

The vehicle terminal can transmit and receive data based on the IEEE 802.11p / WAVVE communication protocol.

The step (b) includes: (b-1) counting a counter for data stored in a queue for each access category; (B-2) calculating an average packet size of each access category using size information of a queue for each access category and the counter information; (B-3) calculating the number of packets that can be transmitted during the TXOP limit period using the calculated average packet size information for each access category; (B-4) determining whether the counter of the data stored in the queue for each access category is equal to or greater than the number of packets that can be transmitted during the TXOP limit interval for each access category; And (b-5) selecting a second access category in which the counter of the data stored in the queue through the step (b-4) is greater than or equal to the number of packets that can be transmitted during the TXOP limit period.

The step (c) may transmit a Ready-to-Send (RTS) message as a message indicating that there is data to be transmitted during a subsequent TXOP limit interval.

At this time, the terminal device receiving the RTS message through step (c) can continuously transmit a clear-to-send (CTS) message at least once.

And (e) when the data transmission of the second access category is completed through the step (d), a competition for acquiring the communication channel is newly performed.

A method of transmitting and receiving data of a vehicle terminal according to a preferred embodiment of the present invention includes transmitting a data of a corresponding access category (AC) during a given TXOP limit period by providing a counter for each access category (AC) When the amount of data currently stored in the queue of the category (AC) is equal to or more than a predetermined value, the TXOP limit section is further allocated and the data of the access category (AC) is transmitted, thereby enabling more flexible data transmission and reception.

Also, as can be seen from the simulation results of the data transmission / reception method according to the present invention, there is an effect of improving the saturation throughput and the access delay performance, as compared with the conventional TXOP technique based on the IEEE 802.11p / WAVE communication standard.

1 illustrates an EDCA (Enhanced Distributed Channel Access) architecture based on the IEEE 802.11p / WAVE communication standard,
2 is a diagram illustrating an EDCA operation based on the IEEE 802.11p / WAVE communication standard,
3 illustrates a TXOP operation based on the IEEE 802.11p / WAVE communication specification,
4 is a diagram illustrating a data transmission / reception method of a vehicle terminal according to an embodiment of the present invention;
Figure 5 illustrates a continuous TXOP scheme in accordance with an embodiment of the present invention;
6A and 6B are graphs showing collision probability and average contention window size according to the number of terminals in a network based on the IEEE 802.11p / WAVE communication standard,
FIG. 7 is a graph illustrating a comparison of the saturation throughput performance of the conventional data transmission / reception technique and the data transmission / reception technique according to the present invention,
FIG. 8 is a graph illustrating comparison of access delay performance between a conventional data transmission / reception technique and a data transmission / reception technique according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It should be understood, however, that it is not intended to be limited to the specific embodiments of the invention but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The IEEE 802.11p MAC uses a competition-based CSMA / CA channel access scheme similar to the existing IEEE 802.11 MAC and uses EDCA (IEEE 802.11e) in order to support quality of service enhanced distributed channel access).

The CSMA / CA is a scheme designed to avoid collisions that may occur when multiple nodes attempt to access the shared radio channel for information transmission. To do this, a specific time interval called an inter-frame space (IFS) is provided between each transmission frame to check the idle state of the channel. A back-off stage counter (BSC) and a back-off counter (BC) are used for channel access. Before each node transmits a frame, BSC initializes it to 0, CW (contention window, contention window size) is CWmin, and BC is any value within [0, CW] range. If the channel is idle during IFS, the value of BC is decremented by 1 and the frame transmission is attempted at the moment of 0. In this case, if the frame transmission fails, the BSC is incremented by 1, the retransmission is attempted while repeating the above procedure, and if the BSC exceeds the threshold value, the transmission is abandoned. The value of CW is changed whenever BSC increases. Therefore, when using the CSMA / CA scheme, collision can be avoided to some extent. However, because the CSMA / CA scheme is a random access scheme, more important information may arrive later than less important information. Therefore, the EDCA method is used to support QoS of the application.

FIG. 1 illustrates an EDCA (Enhanced Distributed Channel Access) structure based on the IEEE 802.11p / WAVE communication standard. FIG. 2 illustrates an EDCA operation based on the IEEE 802.11p / WAVE communication standard. FIG. 3 is a diagram illustrating a TXOP operation based on a communication standard. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an EDCA technique will be described in detail with reference to FIGS.

According to the EDCA technique, different types of ACs are allocated according to the QoS of data as shown in FIG. 1, and different arbitration inter frame spacing (AIFS), minimum contention window, and maximum contention window (CW _min ) are allocated. In this case, the numbers of 3, 2, 1, and 0 are assigned to each of the ACs AC_VO (Voice), AC_VI (Video), AC_BE (Best Effect), and AC_BK Mark as shown.

Therefore, when the EDCA technique is used, as shown in FIG. 2, when the channel is accessed for transmission, the higher the priority, the lower the waiting time. Also, the higher the priority, the smaller the minimum contention window and the maximum contention window, so that the value of the backoff counter also becomes smaller on average, and the possibility of sending the data with a shorter delay time than the data of the lower priority AC becomes larger.

Also, as shown in FIG. 3, by assigning a time to transmit a plurality of frames to a specific vehicle terminal and allocating a TXOP limit, which is a period in which data in the same AC can be continuously transmitted within that time, stochastically important information is more stable To be transmitted quickly.

The present invention has been proposed to solve the problem that can occur as the data traffic increases when the number of the vehicle terminals to transmit information within the transmission range of the specific vehicle network under the conventional vehicle network environment increases. To this end, the present invention proposes a continuous TXOP scheme that improves the existing TXOP scheme that continuously transmits only the same AC data within a predetermined TXOP interval so that the vehicle terminal can transmit data of another AC among data to be transmitted.

In order to realize this, the present invention has a separate counter for counting the number of data to be transmitted for each AC. The counter is a means for considering the number of data in a queue of each AC. When the queuing delay of a high priority AC increases, data corresponding to the corresponding AC can be continuously transmitted through an additional TXOP limit interval .

In an embodiment of the present invention, a counter for counting the number of data packets in a queue of an access category corresponding to AC_VO (voice) and AC_VI (video) is provided. This is because the IEEE 802.11p standard supports the TXOP scheme only in the access category of AC_VO and AC_VI as shown in Table 1 below in order to guarantee the QoS. It should be noted that the above embodiments are described only to be specific to the present IEEE 802.11p standard. According to the application example, a separate counter may be additionally provided in the queue of the access category corresponding to AC_BE and AC_BK to be. The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. However, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. It can be understood that

AC_VO AC_VI AC_BE AC_BK TXOP limit 1.504 ms 3.008 ms - -

FIG. 4 illustrates a method of transmitting and receiving data of a vehicle terminal according to an embodiment of the present invention. Referring to FIG. 4, the technical features of the present invention will be described in detail.

First, the vehicle terminal receives a communication channel through competition based on the IEEE 802.11p / WAVE communication standard, and transmits data of the first access category (AC) through the communication channel (S410). In this case, the transmission of data may mean data transmission to a specific destination terminal or may mean broadcasting data to a plurality of terminals.

In step S410, the data of the first access category AC is transmitted only during the TXOP limit interval determined according to the IEEE 802.11p / WAVE communication standard. For example, according to the type of the first access category AC, data can be transmitted only for a predetermined time as shown in Table 1 above.

When the transmission of the data corresponding to the first AC is completed through step S410, the amount of data stored in the queues for each access category (AC) is detected. If the amount of data stored in the queues for each access category exceeds the reference value 2 access category (S420). The concrete method for this is as follows.

First, a counter is counted for data stored in queues for each access category (AC). For convenience of explanation, the numbers of counters for AC_VO and AC_VI are N ₁ and N ₂ , respectively.

The average packet size of each access category is calculated by using the counter information and the size information of each access category queue. AC_VO, and AC_VI are respectively defined as Q ₁ and Q ₂ , the average packet size (L _i ) for each access category (AC) can be calculated as shown in Equation (1) below.

The number of packets that can be transmitted during the TXOP limit period is calculated using the average packet size information of each access category (AC) calculated through the above method.

For example, if the current rates of AC_VO and AC_VI are defined as R ₁ and R ₂ , respectively, and T _ACK is defined as the time taken to send an ACK (acknowledge) message, the time required to transmit one data within each TXOP limit is (2) " (2) "

Here, T _tri-1 and T _tri-2 represent the time taken to transmit one data within the TXOP limit of AC_VO and AC_VI, respectively.

Since the TXOP limit value corresponding to each access category can be known through Table 1, if the channel access right is obtained by dividing T _tri-i by the corresponding TXOP limit value, the number of packets that can be transmitted in the TXOP limiter Can be obtained by the following equation (3).

Where T _TXOP-1 and T _TXOP-2 represent the TXOP limit values of AC_VO and AC_VI, and n ₁ and n ₂ represent the number of packets that can be transmitted within the TXOP limit of AC_VO and AC_VI.

The counter of the data stored in the queue for each access category (AC) using the number of packets that can be transmitted during the TXOP limit period calculated through the above method is used for the transmission of the packets that can be transmitted during the TXOP limit interval for each access category Or more. Accordingly, even if the vehicle terminal obtains the data transmission right through the subsequent channel competition, it is determined whether or not enough data that can not be transmitted during the given TXOP interval is stored in the current queue.

The vehicle terminal that has acquired the channel use right through channel competition transmits data corresponding to the first access category (AC) during the predetermined TXOP limit, and transmits the data corresponding to the first access category (AC) Detects the amount of data currently stored in each queue of the access category and determines a second access category (AC), where the amount of duplicate data is greater than or equal to a certain amount (more than the maximum amount that can be transmitted for all of the TXOP limit periods corresponding to each access category) . At this time, if there are a plurality of access categories in which the amount of data currently stored in the queue is equal to or more than a certain level, the access category AC having a higher priority can be selected as the second access category AC.

If the second access category (AC) is selected, it sends a message that there is data to transmit during the subsequent TXOP limit interval. This will be described in detail with reference to FIG.

5 is a diagram illustrating a continuous TXOP scheme according to an embodiment of the present invention.

As shown in FIG. 5, it is possible to transmit a Ready-to-Send (RTS) message with a message that there is data to be transmitted during a subsequent TXOP limit interval.

At this time, when there are a plurality of destinations for the data to be transmitted, the CTS (Clear-to-Send) message for the RTS message can be transmitted twice consecutively only at the destination vehicle terminal. This is because it can not be received at the vehicle terminal near the destination and thus reduces transmission attempts during the next TXOP limit.

Alternatively, in the case of data to be broadcasted, a service provider providing a road infrastructure or service may send a CTS message for an RTS message to prevent transmission from attempting to be transmitted to another vehicle terminal around the next TXOP limit . This allows you to cope with dynamic topology changes.

When the vehicle terminal completes the data transmission of the second access category through the above-described method, the vehicle terminal newly performs competition for acquiring the communication channel. That is, when data transmission for a given TXOP limit interval is completed for the second access category, the data transmission is terminated regardless of the counter value for each access category, and separate channel competition is performed for data transmission thereafter. This is to prevent an increase in access delay of data of other vehicle terminals due to a longer time for one vehicle terminal to use the channel.

Hereinafter, the characteristics of the data transmission and reception method of the vehicle terminal according to the present invention will be described in detail with reference to simulation results and a detailed description thereof.

In order to compare the network performance according to the simulation, simulation was performed based on the MAC parameters as shown in Table 2 below.

Parameter Value AC_VO's average data number (n ₁ ) 4 AC_VI's average data number (n ₂ ) 6 AC_VO's average data size (L ₁ ) 300 bytes AC_VI's average data size (L ₂ ) 400 bytes AC_BK's average data size (L ₃ ) 450 bytes AC_BE's average data size (L ₄ ) 450 bytes Data rate (R) 16 Mbps Time period for PHY / MAC header (T _h ) 20 us Time period for ACK message (T _ACK ) 50 us Propagation delay (T _prop ) 1 us Slot time (T _slot ) 13 us Time period for RTS message (T _RTS ) 120 us Time period for CTS message (T _CTS ) 120 us SIFS 39 us DIFS 65 us

6A and 6B are graphs showing collision probability and average contention window size according to the number of terminals in a network based on the IEEE 802.11p / WAVE communication standard. 6A and 6B are graphs showing how the values of the collision probability c and the average contention window size W _avg increase as the number of terminals increases in the network based on the IEEE 802.11p / WAVE EDCA standard. As can be seen from the graph, it can be seen that the collision probability in the network increases as the number of terminals attempting to transmit under the saturated network environment increases. As the collision increases, the number of retransmissions increases and the size of the average contention window also increases.

FIG. 7 is a graph illustrating a comparison of saturation throughput performance of a conventional data transmission / reception technique and a data transmission / reception technique according to the present invention.

FIG. 7 shows a result of comparing the saturation throughput of the conventional TXOP scheme and the data transmission / reception scheme proposed in the present invention when the number of terminals increases. As can be seen from the graph of FIG. 8, the saturation throughput of the proposed data transmission / reception method is higher than that of the conventional TXOP technique. This is because the data transmission / reception method proposed by the present invention can increase the time that can be transmitted without competition in the network, so that the collision due to competition can be reduced.

The markers in the graph of FIG. 7 also show the result of verifying the mathematical model in the NS-3 network simulator using the parameters in Table 2. Computer simulation results show that the proposed data transmission / reception method is superior to the conventional TXOP method in terms of saturation throughput. However, where the mathematical model and the reasons seems little difference between computer simulated mathematical model which always assumes that the W _avg value constant at all terminals because it keeps the BSC value in contrast to the mathematical model, the network simulator before Sinc (syncronization) section This is because there are fewer conflicts due to competition. The reason that the saturation throughput decreases dramatically when the number of terminals is between 20 ~ 60 is because the data generation rate in each AC is assumed to be the same. Therefore, the data in AC_VO and AC_VI, Because the collision increases rapidly.

FIG. 8 is a graph illustrating comparison of access delay performance between a conventional data transmission / reception technique and a data transmission / reception technique according to the present invention.

FIG. 8 shows a comparison of the two schemes in terms of access delay performance when the number of terminals increases. As can be seen from the graph, the data transmission / reception method according to the present invention has better access delay performance than the conventional TXOP technique in both mathematical modeling and computer simulation. However, the reason why the existing TXOP scheme has a shorter access between 20 and 60 terminals is because the delay due to the RTS / CTS message is larger than the delay due to collision reduction when the number of terminals is small.

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (6)

(A) transmitting data of a first access category (AC) through a communication channel to a vehicle terminal during a TXOP limit (TXOP limit) period corresponding to the first access category;
When the data transmission is completed during the TXOP limit (TXOP limit) corresponding to the first access category, the amount of data stored in the queue for each access category is detected, and the amount of data stored in the queue for each access category detected (B) selecting a second access category in which the amount of data stored in the queue is equal to or greater than a reference value by discriminating whether each access category is greater than or equal to a reference value;
If the second access category is selected through the step (b), transmitting a message indicating that there is data to be transmitted during a subsequent TXOP limit interval; And
(D) transmitting data of the second access category during a subsequent TXOP limit interval.
The method according to claim 1,
The vehicle terminal,
And transmitting and receiving data based on the IEEE 802.11p / WAVVE communication protocol.
The method according to claim 1,
The step (b)
(B-1) counting a counter for data stored in a queue for each access category;
(B-2) calculating an average packet size of each access category using size information of a queue for each access category and the counter information;
(B-3) calculating the number of packets that can be transmitted during the TXOP limit period using the calculated average packet size information for each access category;
(B-4) determining whether the counter of the data stored in the queue for each access category is equal to or greater than the number of packets that can be transmitted during the TXOP limit interval for each access category; And
And (b-5) selecting a second access category in which a counter of data stored in the queue through the step (b-4) is greater than or equal to the number of packets that can be transmitted during a TXOP limit period .
The method according to claim 1,
The step (c)
And transmitting a Ready-to-Send (RTS) message as a message that there is data to be transmitted during a subsequent TXOP limit interval.
5. The method of claim 4,
The terminal having received the RTS message through step (c)
And transmitting a clear-to-send (CTS) message one or more times in response thereto.
The method according to claim 1,
Further comprising: (e) performing competition for acquiring the communication channel when data transmission of the second access category is completed through step (d).

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