KR101982928B1 - Vehicle communication method and apparatus for wireless access in vehicular environments - Google Patents

Abstract

The present invention relates to a vehicle communication method and apparatus for wireless connection for a vehicle environment, wherein the embodiments of the present invention use a control channel and a service channel simultaneously using a dual transceiver, By transmitting a packet for reservation of a safety packet and a service channel through a channel and transmitting and receiving a data file based on a non-contention reservation through a service channel reservation, a service quality requirement for a safety packet (for example, To-vehicle communication method and apparatus for wireless connection for a vehicle environment capable of satisfying the above-mentioned requirements.

Description

≪ Desc / Clms Page number 1 > Vehicle Communication Method and Apparatus for Wireless Access for Vehicle Environment

The present invention relates to a vehicle communication method and apparatus for wireless access for a vehicle environment, and more particularly to a method and apparatus for vehicle communication that is capable of meeting requirements of quality of service (e.g., a delay of less than 100 ms and a successful delivery probability of at least 98% To a vehicle communication method and apparatus for wireless connection for a vehicle environment.

In recent years, demands for research on wireless access in vehicular environments (WAVE) have arisen not only in academic fields but also in industrial fields. The purpose of WAVE is to provide additional commercial and entertainment services to the driver to ensure comfort and efficient travel, while reducing the cost of mass casualties due to vehicle crashes, by using electronic communication technology in conjunction with automotive communications equipment and road infrastructure. Safety applications help drivers avoid accidents by exchanging emergency packets and state packets between vehicles. Meanwhile, non-secure applications such as Internet access and electronic map updates provide convenience. WAVE will become the core infrastructure of autonomous vehicles that are being actively developed in the industry in recent years.

ITS (Intelligent Transportation Systems) improves the stability and efficiency of transportation systems and reduces traffic accidents and road congestion. ITS enhances driver comfort.

International standard technologies for ITS are as follows.

The IEEE Working Group has introduced a family of IEEE 802.11p and IEEE 1609 standards, called Wireless Access for Vehicle Environment (WAVE), as a new communication standard for vehicle networks. The Technical Committee for Intelligent Transportation Systems (ETSI TC-ITS), operated by the European Telecommunications Standards Institute, also introduced a similar standard, ITS-G5.

There are two types of WAVE devices: OBU (on-board unit) and roadside unit (RSU). The OBU is a vehicle-mounted communication device. The RSU is connected to the wired infrastructure network and is in a fixed position on the road. The IEEE 802.11p and IEEE 1609.4 standards are based on the medium access control (MAC) and physical layer (PHY) protocols for vehicle-to-vehicle communication between OBUs and vehicle-to-infrastructure communication between OBUs and RSUs. . IEEE 802.11p specifies a MAC layer for single channel operation, and IEEE 1609.4 specifies a MAC layer for multi-channel operation. The MAC protocol of the IEEE 802.11p and IEEE 1609.4 standards complies with IEEE 802.11e enhanced distributed channel access (EDCA) by adding channel tuning, which consists of channel routing and channel selectors.

1 is a diagram showing a WAVE equipment and network configuration diagram of the IEEE.

WAVE equipment is divided into on-board unit (OBU) and roadside unit (RSU) as shown in Fig. The OBU is a vehicle-mounted wireless communication device. The RSU is fixed on the road and is responsible for communication with the wired infrastructure network. Communication between OBUs is called vehicle-to-vehicle communication, and communication between OBUs and RSU is called vehicle-to-infrastructure communication (V2I).

The service categories of IEEE WAVE include Safety applications and Non-safety applications. Safety applications help drivers avoid accidents. Non-safety applications provide convenience for drivers, such as Internet access and electronic map updates.

IEEE WAVE quality of service (QoS) requirements are as follows.

The safety application has a condition of delay ≤ 100 msec and a condition of successful delivery probability ≥ 98%. The non-secure application has the condition that the transfer of the large capacity data file is completed within the coverage of the RSU.

2 is a diagram illustrating multi-channel operation of a WAVE system.

The standards related to multi-channel operation are as follows.

IEEE 802.11p / IEEE 1609.4 specifies the MAC protocol for V2V and V2I communication. IEEE 802.11p specifies the MAC protocol for single-channel operation, and IEEE 1609.4 specifies the MAC protocol for multi-channel operation.

For multi-channel operation, the 75 MHz bandwidth in the 5.850 GHz to 5.925 GHz frequency band is divided into seven 10 MHz frequency channels as shown in FIG. One of these seven channels is designated as a control channel (CCH) and the other six channels are used as a service channel (SCH).

3 is a diagram illustrating a channel operation for a single radio.

The OBU may be equipped with a single radio device operating on only one radio channel at a time, or a dual radio device operating concurrently on the control channel and service channel. To operate the MAC protocol with a single radio device capable of listening to safety packets for all vehicles, the channel time must be divided into a fixed-length 100 ms synchronization interval consisting of the CCH interval (CCHI) and the SCH interval (SCHI) Is 50 ms (see FIG. 3). Since an OBU with a single radio unit can only transmit packets on one channel at a time, a continuous transition between CCH and SCH must occur every 50 ms. During CCHI, all OBU radios are tuned to the CCH for the transmission and reception of safety packets. During SCHI, all OBU radios are tuned to one of the six SCHs for the transmission and reception of non-secure messages.

A disadvantage of a single radio unit is that it can not use the SCH during the CCHI, resulting in half the SCH bandwidth being wasted. Studies have reported that reducing the available transmission bandwidth in half does not meet the QoS requirements for safety applications. Due to the cost issues of multiple radio devices, it is assumed that the current IEEE 1609.4 WAVE is equipped with a single radio device in the OBU. In the future, however, advances in wireless technology will dramatically reduce radio costs and allow for consideration of dual radio devices. IEEE 1609.4 refers to the possibility of adopting multiple radio devices at the beginning of the standard. In addition, ITS-G5 considers each OBU to have two radios.

Korean Registered Patent No. 10-1690157 (registered on December 21, 2016)

Embodiments of the present invention use a control channel and a service channel simultaneously using a dual transceiver, transmit a packet for reservation of a secure packet and a service channel through a control channel according to a contention-based distributed channel access method, By transmitting and receiving data files on a non-contention-based reservation basis, it is possible to meet the requirements of quality of service (e.g., a delay of less than 100 ms and a successful delivery probability of at least 98% And a vehicle communication method and apparatus.

According to a first aspect of the present invention, there is provided a vehicle communication method for a wireless connection for a vehicle environment performed by a vehicle communication device, the method comprising: transmitting and receiving a safety packet through a control channel according to a contention- ; Transmitting a request for service packet through a control channel according to a contention-based distributed channel access method to reserve a service channel; And transmitting and receiving a data file based on a non-competition reservation through the reserved service channel.

The transmitting and receiving of the security packet may include checking whether the transmitted safety packet is transmitted according to whether or not an acknowledgment message for the transmitted safety packet is received, It can be confirmed by the successful transmission of the packet.

When the response message is not received, the step of transmitting and receiving the security packet retransmits the safety packet if the retransmission limit is not reached, and the transmission failure of the transmitted safety packet can be confirmed when the retransmission limit is reached.

The step of reserving the service channel may include determining whether the service channel is reserved according to whether the response message to the transmitted service channel reservation packet is received or not, and if receiving the response message, allocating a service channel from the rover device And can confirm that the reservation of the service channel is successful.

The step of reserving the service channel may retransmit the service channel reservation packet if retransmission restriction is not reached when the response message is not received, and may be confirmed as a reservation failure of the service channel upon reaching the retransmission limit.

The transmitting / receiving of the data file may include checking whether the service channel is allocated according to whether the service channel is reserved in the step of reserving the service channel, and if the service channel is reserved, The data file can be transmitted and received.

The step of transmitting / receiving the data file may be confirmed as a failure of transmission / reception of the data file when the reservation of the service channel fails.

The secure packet and the service channel reservation packet may be assigned to first and second access category queues, respectively, and the first access category may have a higher priority than the second access category queue.

The first and second access category queues may compete with each other in the control channel.

According to a second aspect of the present invention, there is provided a method for allocating an input safety packet and a service channel reservation packet to a first queue corresponding to a contention-based control channel, To a second queue corresponding to the MAC layer queue management unit; A first transceiver configured to transmit and receive a secure packet through a control channel according to a contention-based distributed channel access method and transmit a service channel reservation packet through a control channel according to a contention-based distributed channel access method to reserve a service channel; And a second transceiver for transmitting and receiving a data file based on a non-competition reservation through the reserved service channel.

Wherein the first transceiver verifies whether the transmitted safety packet is transmitted according to whether the acknowledgment message for the transmitted safety packet is received or not, and when the response message is received, Success can be confirmed.

If the response message is not received, the first transceiver may retransmit the safety packet if the retransmission limit is not reached, and may confirm transmission failure of the transmitted safety packet when the retransmission limit is reached.

The first transceiver confirms whether a service channel is reserved according to whether the response message to the transmitted service channel reservation packet is received or not. When receiving the response message, the first transceiver allocates a service channel from the sidewalk device, Can be confirmed by the success of the reservation.

When the response message is not received, the first transceiver retransmits the service channel reservation packet if the retransmission limit is not reached. If the first transceiver reaches the retransmission limit, the first transceiver can confirm the reservation failure of the service channel.

Wherein the second transceiver determines whether a service channel is allocated according to whether the service channel is reserved in the step of reserving the service channel, and if the service channel is reserved, Lt; / RTI >

If the reservation of the service channel fails, the second transceiver can confirm transmission / reception failure of the data file.

The secure packet and the service channel reservation packet may be assigned to first and second access category queues, respectively, and the first access category may have a higher priority than the second access category queue.

The first and second access category queues may compete with each other in the control channel.

Embodiments of the present invention use a control channel and a service channel simultaneously using a dual transceiver, transmit a packet for reservation of a secure packet and a service channel through a control channel according to a contention-based distributed channel access method, By transmitting and receiving the data file on a non-contention-based reservation basis, it is possible to satisfy the quality of service requirement for the secure packet (e.g., a delay of less than 100 ms and a successful delivery probability of at least 98%).

Embodiments of the present invention can always transmit and receive a safety message by monitoring the CCH, and can simultaneously transmit and receive a non-secure message through an SCH specified by the RSE among a plurality of SCHs.

Embodiments of the present invention do not require switching between the control channel and the service channel and can utilize the full potential of the channel spectrum.

Embodiments of the present invention allow the RSE to allow acknowledgment of a safety packet to a sender so that a sender can retransmit a SAFE packet when a collision occurs, thereby improving the reliability of the broadcasted packet.

Embodiments of the present invention can increase the probability of transmission of a safety packet by retransmitting a safety packet when a sender collides (i.e., when an ACK message is not received). For example, embodiments of the present invention may deliver a secure packet within 100 ms with a successful delivery probability of 98% or more even if the number of vehicles reaches 150.

Embodiments of the present invention can utilize the CCH more efficiently in a lean environment with fewer vehicles, in addition to the benefits of access delay.

1 is a diagram showing a WAVE equipment and network configuration diagram of the IEEE.
2 is a diagram illustrating multi-channel operation of a WAVE system.
3 is a diagram illustrating a channel operation for a single radio.
4 is a diagram illustrating a system configuration to which a vehicle communication apparatus according to an embodiment of the present invention is applied.
5 is a configuration diagram of a vehicle communication apparatus for wireless connection for a vehicle environment according to an embodiment of the present invention.
6 and 7 illustrate channel operations using a dual transceiver according to an embodiment of the present invention.
8 is a diagram illustrating a MAC layer queue management unit of a vehicle communication apparatus according to an embodiment of the present invention.
9 is a diagram illustrating the operation of each packet in a control channel and a service channel in a vehicle communication method according to an embodiment of the present invention.
10 is a flowchart illustrating transmission of a security packet in a vehicle communication method according to an embodiment of the present invention.
11 is a flowchart illustrating transmission of an RFS packet in a vehicle communication method according to an embodiment of the present invention.
12 is a flowchart showing a transmission / reception of a data file in the vehicle communication method according to the embodiment of the present invention.
13 is a diagram illustrating a Markov chain necessary for analyzing performance of a security packet according to an embodiment of the present invention.
14 is a diagram illustrating a Markov chain required for performance analysis of an RFS packet according to an embodiment of the present invention.
15 is a diagram illustrating a probability distribution of a connection delay of a secure packet according to an embodiment of the present invention.
16 is a diagram illustrating a successful delivery probability of a safety packet according to an embodiment of the present invention.
17 is a diagram illustrating a successful delivery probability of an RFS packet according to an embodiment of the present invention.
FIG. 18 is a diagram illustrating a comparison result of the success probability of a secure packet according to an embodiment of the present invention.
FIGS. 19 and 20 are diagrams showing a comparison result between a successful delivery probability and an average access delay of a non-secure packet according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present invention. In describing the embodiments of the present invention, description of technical contents which are well known in the art to which the present invention belongs and which are not directly related to the present invention will be omitted. This is for the sake of clarity of the present invention without omitting the unnecessary explanation.

In describing the constituent elements of the present invention, the same reference numerals may be given to constituent elements having the same name, and the same reference numerals may be given to different drawings. However, even in such a case, it does not mean that the corresponding component has different functions according to the embodiment, or does not mean that it has the same function in different embodiments, and the function of each component is different from that of the corresponding embodiment Based on the description of each component in FIG.

4 is a diagram illustrating a system configuration to which a vehicle communication apparatus according to an embodiment of the present invention is applied.

First, main assumptions in a system configuration to which a vehicle communication apparatus according to an embodiment of the present invention is applied will be described. First, a multi-channel environment is considered. Second, each OBU is equipped with dual transceivers with dual radios. Third, communication infrastructure such as RSU is installed on the road.

To meet QoS requirements for safety packets (i.e., a delay of less than 100 ms and a successful delivery probability of at least 98%), the main assumptions of the present invention are as follows.

It is assumed that all OBUs are equipped with a dual radio unit. Therefore, channel switching between CCH and SCH is not required, and the full potential of the channel spectrum can be used.

Most non-secure applications involve data transfer between the vehicle and the RSU. Therefore, it is assumed that an infrastructure such as an RSU is installed on the road, and a MAC protocol supporting both safety and non-safety applications is considered. A WAVE basic service set (WBSS), which is a communication area covered by one RSU, is considered.

The secure packet is broadcast to the neighboring vehicle, and the broadcasted packet is generally not answered. As a result, the sender can not detect failed transmissions and can not use the binary backoff mechanism for retransmissions. This causes WAVE performance degradation especially in the areas where there is a severe collision and causes serious reliability problems in crash warning devices. Since all OBUs are within the coverage of the RSU, the RSU can receive packets broadcast from the OBU. Therefore, in order to improve the reliability of the broadcasted packet, it is assumed that only the RSU allows the sender to acknowledge the safety packet so that the sender can retransmit the safety packet in the event of a collision. Multi-hop broadcasts for emergency packets are required to support secure applications. In the present invention, an RSU receiving an emergency packet can communicate with a neighboring RSU to forward an emergency packet. The neighboring RSU then broadcasts the forwarded emergency packet to the vehicle within its coverage.

5 is a configuration diagram of a vehicle communication apparatus for wireless connection for a vehicle environment according to an embodiment of the present invention.

5, a vehicle communication apparatus 100 for wireless connection for a vehicle environment according to an embodiment of the present invention includes a MAC layer queue management unit 120, a first transceiver 111 and a second transceiver 112, .

The dual radio device applied to the embodiment of the present invention is expected to be used as a long-term solution in WAVE, and a vehicle equipped with a dual radio device can continuously monitor the safety message through the CCH. Despite these advantages, however, little research has been done on the WAVE MAC protocol using dual radio devices. The present invention relates to a MAC protocol that supports both secure and non-secure applications of WAVE using dual radio devices.

Dual radio devices can send and receive packets over two channels at the same time. One of the dual radios (ie, CCH radio) is used for CCH, and the other radio (ie, SCH radio) is used for simultaneous exchange of data files at the designated SCH. Therefore, using a dual radio device helps solve the problem of inefficient channel usage caused by using a single radio device.

As a MAC protocol of the present invention, a secure packet and a request for service (RFS) packet are transmitted in a high priority order and a low priority order on a CCH using a contention-based EDCA scheme. On the other hand, the SCH uses non-contention through reservation to service non-secure applications such as information and commercial data files.

For the MAC protocol, the present invention proposes a mathematical analysis model and evaluates successful delivery probability and delay of security and RFS packets as key performance indicators. In the mathematical analysis model of the present invention, an approximation method based on the M / M / K / K / N queuing model is presented, and two interacting Markov chains for the safety packet and the RFS packet are constructed.

The performance of the MAC protocol according to an embodiment of the present invention is verified through numerical studies and simulations. The numerical result indicates that the QoS requirement for the safety packet is met. That is, even if the number of vehicles reaches 150, the security packet can be delivered within 100ms with a successful delivery probability of 98% or more. In addition, the non-contention-based reservation scheme of the present invention shows superior performance in terms of access delay of a non-secure packet over a contention-based random selection scheme.

Hereinafter, the MAC protocol of the present invention configured with reservation of contention-based EDCA and SCH on CCH in IEEE 802.11p / 1609.4 WAVE will be described. The safety packet and the RFS packet will be respectively described.

The CCH is a public channel for providing safety related messages and exchanging control packets. A safety packet consists of a status packet and an emergency packet. The status packet includes information about the status of the vehicle, such as location, direction, speed, and acceleration, and every vehicle broadcasts a status packet to the neighboring vehicle every 100ms. Emergency packets are generated when an unexpected event occurs, such as a sudden stop or a car accident, and provide other drivers with advance information about the accident to prevent major accidents.

The SCH is used to transfer data files when a user of the vehicle attempts to upload or download a data file. There are two ways to access the SCH. That is, the two methods are (i) reservation-based method and (ii) random method. That is, (i) each OBU reserves the CCH to access the reserved SCH. (ii) Each OBU randomly selects an SCH, and OBUs that select the same SCH compete with each other to access the SCH. The performance of these two methods is compared in Figures 18, 19 and 20. In the present invention, the following reservation-based method is used. Schedule the SCH first to upload or download the data file. After the reservation, the data file is transmitted / received through the allocated SCH. To reserve the SCH, the OBU sends an RFS packet to the RSU on the CCH using a contention-based EDCA. If the RFS packet has been successfully transmitted and there is an available SCH, the RSU will assign one SCH to the OBU.

The present invention contemplates a MAC protocol that supports both secure and non-secure applications of WAVE. The QoS requirements are determined by the type of application. For safety applications, they have very short delays of less than 100 ms and high delivery probabilities of over 98% as QoS requirements. This is because, if a safety message is lost (or long-term delay), the vehicle may not be provided with a warning message about the danger, leading to a serious accident. For non-secure applications, the transfer time of large data files should be short so that the service can be completed within the RSU coverage. Because of the fast vehicle mobility and the narrow range of RSU coverage, the vehicle passes through the RSU coverage in a short time.

The specific configuration and operation of each component of the vehicle communication device 100 for wireless connection for vehicle environment according to the embodiment of the present invention shown in Fig. 5 will be described below.

The MAC layer queue management unit 120 allocates the input safety packet and the service channel reservation packet to the first queue corresponding to the contention-based control channel, and transmits the input data file to the non- To the second queue.

The first transceiver 111 transmits and receives a secure packet over a control channel according to a contention-based distributed channel access method, and transmits a service channel reservation packet through a control channel according to a contention-based distributed channel access method, Make a reservation. Here, the first transceiver 111 confirms whether or not the transmitted safety packet is transmitted according to whether the acknowledgment message for the transmitted safety packet is received. If the first transceiver 111 receives the response message, As shown in Fig. If the response message is not received, the first transceiver 111 retransmits the safety packet if the retransmission limit is not reached, and confirms transmission failure of the transmitted safety packet when the retransmission limit is reached. The first transceiver 111 confirms whether the service channel is reserved according to whether the response message to the transmitted service channel reservation packet is received or not. When receiving the response message, the first transceiver 111 allocates a service channel from the sidewalk device, As shown in FIG. If the response message is not received, the first transceiver 111 retransmits the service channel reservation packet if the retransmission limit is not reached. If the retransmission limit is reached, the first transceiver 111 confirms the reservation failure of the service channel.

The second transceiver 112 transmits and receives the data file based on the non-contention-based reservation through the first transceiver 111 through the reserved service channel. Herein, the second transceiver 112 checks whether or not the service channel is allocated according to whether or not the service channel is reserved in the step of reserving the service channel. If the service channel is reserved, Send and receive data files. When the reservation of the service channel fails, the second transceiver 112 confirms that the transmission / reception of the data file fails.

The secure packet and the service channel reservation packet are assigned to first and second access category queues, respectively, and the first access category has a higher priority than the second access category queue. The first and second access category queues compete with each other in the control channel.

6 and 7 illustrate channel operations using a dual transceiver according to an embodiment of the present invention.

The present invention relates to an IEEE 802.11p / 1609.4 WAVE MAC protocol that satisfies both the safety applications of ITS services and the quality of service requirements of non-secure applications.

As shown in FIG. 6, the vehicle communication apparatus 100 uses the dual transceiver 110 to simultaneously use the control channel and the service channel. The vehicle communication apparatus 100 according to the embodiment of the present invention may be equipped with a dual transceiver 110 to simultaneously use the CCH and the SCH. The first transceiver 111, i.e., the CCH transceiver 111, can always transmit and receive a safety message by monitoring the CCH. Also, the second transceiver 112, that is, the SCH transceiver 112, can transmit and receive the non-secure message through the SCH specified by the RSU among the six SCHs.

The MAC protocol according to the embodiment of the present invention includes a CCH access method and an SCH access method. A contention-based EDCA method is used for the CCH connection, and a contention-based reservation method is used for the SCH connection.

Also, the way in which the RSU sends an ACK message is also used. When the RSU successfully receives the security packet broadcast by the OBU in the WBSS, it sends an ACK message to the sender as a representative. Therefore, the sender can retransmit the secure packet at the time of collision (i.e., when the ACK message is not received). This makes it possible to increase the probability of successful delivery of the secure packet. IEEE's WAVE is a requirement for quality of service in safety applications requiring a delay of less than 100ms and a successful delivery rate of at least 98%.

The vehicle communication apparatus 100 according to the embodiment of the present invention can use the CCH and SCH at the same time. The CCH performs security message transmission and non-secure message transmission reservation. Safety packets and RFS packets compete with each other in the CCH according to the EDCA protocol. The CCH is unsynchronized. SCH transmits and receives non-secure messages according to the result of reservation using the RFS packet at the CCH. That is, it is a non-competitive method.

8 is a diagram illustrating a MAC layer queue management unit 120 of the vehicle communication apparatus 100 according to an embodiment of the present invention.

Traffic generated in each vehicle communication apparatus 100 is classified into a safety packet, an RFS packet, and a data file.

A safety packet is a packet associated with the IEEE WAVE safety application. For example, a status packet and an emergency packet are included.

A packet for service channel reservation (RFS packet) is a packet used for reserving an SCH necessary for the following data file transmission.

A data file is a packet associated with a non-safety application of IEEE WAVE. For example, Internet access and electronic-map updates.

The channel usage and access method according to the traffic type are shown in Table 1 below.

Channel type CCH SCH Traffic type Safety packets, RFS packets Data file Connection method EDCA (Competitive Method) Reservation (non-competition)

The vehicle communication apparatus 100 according to the embodiment of the present invention accesses one control channel by using a contention-based enhanced distributed channel access (EDCA) method, - Connect using a contention-free reservation method.

Types of packets transmitted through the control channel include a safety packet and an RFS packet.

Types of packets transmitted over the service channel include packets associated with non-secure applications such as map downloads and commercial advertisements.

The control channel access method classifies the safety packet into a high priority AC ₁ (Access Category 1), classifies the RFS packet into a low priority AC ₂ (Access Category 2), and connects the control channel to the contention based EDCA.

The service channel access method reserves a service channel by transmitting an RFS packet to a control channel whenever a non-secure application is used. That is, a non-competitive reservation method is used.

AIFS[2], CW_min[1]

CW_min[2] 및 CW_max[1]

CW_max[2]를 만족하도록 설정한다.Looking at the access category 1 (AC [1]) and the access category 2 (AC [2]) in the EDCA on the CCH, each OBU divides the traffic sent on the CCH into two categories of access. AC [1] has a high priority and AC [2] has a low priority. The security packet corresponds to AC [1], and the RFS packet corresponds to AC [2]. Here, the EDCA parameter is AIFS [1]

AIFS [2], CW _min [1]

CW _min [2] and CW _max [1]

CW _max [2] is satisfied.

9 is a diagram illustrating the operation of each packet in a control channel and a service channel in a vehicle communication method according to an embodiment of the present invention.

When the RFS packet is successfully transmitted over the CCH, the ACK packet is transmitted after the SIFS has elapsed. Here, since SCH1, SCH2, SCH3, and SCH6 are in use in the example of FIG. 9, the available idle SCHs are SCH4 and SCH5. The ACK packet is transmitted to the OBU that successfully transmitted the RFS packet including information indicating that the data file can be transmitted / received during the TXOP using SCH4. The OBU adjusts the SCH radio to SCH4 and transmits / receives the data file during the TXOP. After the ACK packet is transmitted, the non-empty AC [1] and AC [2] wait for AIFS [1] and AIFS [2], respectively, and then restart the backoff procedure. AC [1] The OBU that has reached the back-off counter value 0 transmits a safety packet on the CCH. At this time, in the example of FIG. 9, the AC [2] backoff counter value of the other OBU also reaches 0, and the RFS packet is transmitted on the CCH. Thus, the two packets collide with each other.

All non-empty ACs [1] wait for AIFS [1] after detecting a collision and resume the backoff procedure. All non-empty ACs [2] also wait for AIFS [2] after detecting a collision and then restart the backoff procedure. AC [1] The OBU that has reached the back-off counter value 0 transmits a safety packet on the CCH. At this time, in the example of FIG. 9, since all the AC [2] are waiting for AIFS [2], the OBU successfully transmits the safety packet.

After that, the OBU that has reached the AC [2] backoff counter value of 0 transmits the RFS packet on the CCH. The RFS packet is successfully delivered and the ACK packet is delivered after the SIFS has elapsed. Here, since SCH1, SCH2, SCH4, and SCH6 are in use in the example of FIG. 9, the available idle SCHs are SCH3 and SCH5. The ACK packet is transmitted to the OBU that has transmitted the RFS packet including information indicating that the data file can be transmitted / received during TXOP using SCH5. The OBU adjusts the SCH radio to SCH5 to transmit / receive a data file during the TXOP.

10 is a flowchart illustrating transmission of a security packet in a vehicle communication method according to an embodiment of the present invention.

The vehicle communication apparatus 100 confirms whether there is a safety packet to be transmitted (S101).

As a result of the check (S101), if there is a safety packet to be transmitted, the vehicle communication apparatus 100 tries to transmit the safety packet using the EDCA (S102). On the other hand, if it is determined in step S101 that there is no safety packet to be transmitted, the vehicle communication apparatus 100 performs step S101 again to check whether there is a safety packet.

Then, the vehicle communication apparatus 100 confirms whether an ACK message is received (S103).

As a result of the check (S103), when the ACK message is received, the vehicle communication apparatus 100 determines that the transmission of the safety packet is successful (S104).

On the other hand, if the ACK message is not received (S103), the vehicle communication apparatus 100 confirms whether the retransmission limit is reached (S105).

If the retransmission limit is not reached (S105), the vehicle communication apparatus 100 performs the transmission of the safety packet using the EDCA from step S102.

On the other hand, when the confirmation result (S105) is reached and the retransmission limit is reached, the vehicle communication apparatus 100 determines that transmission of the safety packet is unsuccessful (S106).

11 is a flowchart illustrating transmission of an RFS packet in a vehicle communication method according to an embodiment of the present invention.

The vehicle communication apparatus 100 confirms whether there is an RFS packet to be transmitted (S201).

As a result of the check (S201), if there is an RFS packet to be transmitted, the vehicle communication apparatus 100 tries to transmit the RFS packet using the EDCA (S202). On the other hand, if it is determined in step S201 that there is no RFS packet to be transmitted, the vehicle communication apparatus 100 performs step S201 again to check whether there is an RFS packet.

Then, the vehicle communication apparatus 100 confirms whether an ACK message is received (S203).

As a result of the check (S203), when the ACK message is received, the vehicle communication apparatus 100 confirms whether the SCH has been allocated from the RSU (S204).

As a result of the check (S204), when the SCH is allocated from the RSU, the vehicle communication apparatus 100 determines that the transmission of the RFS packet is successful (S205). On the other hand, if the SCH is not allocated from the RSU (S204), the vehicle communication apparatus 100 determines that the transmission of the RFS packet has failed (S207).

On the other hand, if the ACK message is not received (S203), the vehicle communication apparatus 100 confirms whether the retransmission limit is reached (S206).

As a result of the check (S206), if the retransmission limit is not reached, the vehicle communication apparatus 100 performs the process from S202 in which the transmission of the RFS packet is attempted using the EDCA.

On the other hand, when the retransmission limit is reached (S206), the vehicle communication apparatus 100 determines that the transmission of the RFS packet has failed (S207).

12 is a flowchart showing a transmission / reception of a data file in the vehicle communication method according to the embodiment of the present invention.

The vehicle communication apparatus 100 confirms whether there is a data file to be transmitted or received (S301).

As a result of the check (S301), if there is a data file to be transmitted or received, the vehicle communication apparatus 100 generates an RFS packet and reserves the SCH using the generated RFS packet (S302). On the other hand, if it is determined in step S301 that there is no data file to be transmitted or received, the vehicle communication apparatus 100 performs step S301 again to check whether there is a data file.

Then, the vehicle communication apparatus 100 confirms whether the reservation of the SCH is successful (S303).

If the reservation of the SCH is successful (S303), the vehicle communication apparatus 100 transmits / receives the data file for the transmission opportunity (TXOP) through the reserved SCH (S304).

Then, the vehicle communication apparatus 100 determines that the transmission / reception of the data file is successful (S305).

On the other hand, if the reservation of the SCH is not successful (S303), the vehicle communication apparatus 100 determines that transmission / reception of the data file has failed (S306).

Meanwhile, a vehicle communication method according to an embodiment of the present invention relates to a MAC protocol configured by reserving EDCA and SCH for CCH.

Hereinafter, the MAC protocol according to the embodiment of the present invention configured with reservation of contention-based EDCA and SCH on CCH in IEEE 802.11p / 1609.4 WAVE will be described in detail.

Let's look at access category 1 (AC ₁ ) and access category 2 (AC ₂ ). Two access category AC ₁ and AC ₂ queues are present in the MAC layer of each OBU to store the secure packet and the RFS packet, respectively. The AC ₁ and AC ₂ queues are serviced on the CCH.

A state packet is generated every 100 ms, and an emergency packet is generated as an event driven event. The state packet and the emergency packet correspond to the safety packet. Once a secure packet is generated, it is stored in the AC ₁ queue. Because the newly created safety packet has the most up-to-date information, the old safety packet is replaced with the newly created safety packet. That is, when a safety packet is newly generated, if a previous safety packet in the AC ₁ queue is not transmitted, the old packet is old and replaced with a newly generated packet. Therefore, each OBU has zero or one safety packets in the AC ₁ queue at all times, and safety packets sent to the vehicle always have up-to-date information. The RFS packet is generated whenever a user of the vehicle attempts to upload or download a data file. The generated RFS packet is stored in the AC ₂ queue to reserve the SCH. The data file is transmitted and received on the SCH allocated after the handshake negotiation of the RFS packet.

Meanwhile, a case where the first packet is transmitted without a backoff procedure will be described.

큐에 도착한 첫 번째 패킷은 CCH가 DIFS 기간 동안 유휴 상태로 감지되면 백 오프 절차없이 즉시 전송된다. CCH가 DIFS 기간 동안 사용 중으로 감지되면,

는 감지를 중지하고 매체의 사용이 끝날 때까지 대기한다. 대기 후

는 패킷 전송을 위해 백 오프 절차를 수행한다. 반면, 비어있지 않은

큐에 도착한 패킷은 백 오프 절차를 거쳐 전송되어야 한다.emptied

The first packet arriving at the queue is immediately transmitted without a backoff procedure if the CCH is detected to be idle during the DIFS period. If the CCH is detected as busy during the DIFS period,

Stops the detection and waits until the use of the medium is finished. After waiting

Performs a backoff procedure for packet transmission. On the other hand,

Packets arriving at the queue must be transmitted through a backoff procedure.

Let's look at the CCH access protocol. Describes how secure packets and RFS packets access the CCH. Adopts the EDCA mechanism of the IEEE 802.11e standard to give high priority to safety packets versus RFS packets. EDCA provides differentiated access to priority packets by setting different channel access parameter values, such as arbitration inter frame space (AIFS) and contention window (CW) size, for each AC. To avoid accidents, the security packets are given a high priority, while the RFS packets are given low priority. Accordingly, in the present invention, the channel access parameter values for the access categories AC ₁ and AC ₂ are set as follows.

에 대한 AIFS 값을

라 하자.

대비

에 높은 우선 순위를 부여하기 위해

를 만족하도록

를 설정한다.

는 패킷(즉,

내의 안전 패킷 또는

내의 RFS 패킷)을 전송하기 전에 먼저

기간 동안 연속적으로 CCH를 감지한다.

기간 동안 CCH가 유휴 상태임을 감지하면,

는 패킷을 전송한다. 그렇지 않으면(즉, CCH가 사용 중임을 감지하면),

는

범위에서 백 오프 카운터 값을 랜덤하게 선택하여, CCH가 사용 중으로 감지된 후 즉시 백 오프 절차를 수행한다. 여기서

는

에 대한 최소 CW 크기를 나타낸다.

대비

에 높은 우선 순위를 부여하기 위해

를 만족하도록

를 설정한다.

는 CCH가 유휴 상태임을 감지할 때마다 백 오프 카운터 값을 감소시키고, CCH가 사용 중임을 감지하면 백 오프 카운터 값을 고정시킨다. 백 오프 카운터 값이 0에 도달하면

는 패킷을 전송한다.

The AIFS value for

Let's say.

prepare

To give a higher priority to

To satisfy

.

(I.e.,

Within a secure packet or

Before transmitting the RFS packet

CCH is continuously detected during the period.

If it detects that the CCH is idle for a period of time,

Transmits a packet. Otherwise (that is, it detects that the CCH is in use)

The

Randomly selects a backoff counter value in the range, and performs the backoff procedure immediately after the CCH is detected as being in use. here

The

Gt; CW < / RTI >

prepare

To give a higher priority to

To satisfy

.

Decrements the backoff counter value whenever it detects that the CCH is idle, and fixes the backoff counter value when it detects that the CCH is in use. When the backoff counter value reaches 0

Transmits a packet.

과

가 CCH에서 서로 경쟁하고 있다. 하나의 OBU에 있는

백 오프 카운터와

백 오프 카운터가 동시에 0에 도달하면 내부 충돌(internal collision)이 발생한다. 내부 충돌을 피하기 위해 우선 순위가 높은

은 안전 패킷을 전송하는 반면, 우선 순위가 낮은

는 충돌 발생으로 간주하고 CW 크기를 두 배로 늘려 CCH 액세스에 대한 백 오프 절차를 재개한다. 따라서

패킷은 다른 OBU들의

패킷 및

패킷과 충돌할 수 있다. 반면

패킷은 다른 OBU들의

패킷 및

패킷, 또는 자체 OBU의

패킷과 충돌할 수 있다. 충돌이 발생할 때마다, 각

는 최대 값

까지 CW 크기를 두 배로 늘린다.

의 최대 백 오프 단계가

인 경우

는 아래와 같이 결정된다.Since each OBU generates safety packets and RFS packets and several vehicles are within the coverage of a single RSU,

and

Are competing with each other in the CCH. In one OBU

Back off counter

When the backoff counter reaches 0 at the same time, an internal collision occurs. In order to avoid internal collisions,

Lt; RTI ID = 0.0 > a < / RTI > low priority

Consider the occurrence of a collision and double the CW size to resume the backoff procedure for CCH access. therefore

The packet is sent to other OBUs

Packets and

It may collide with a packet. On the other hand

The packet is sent to other OBUs

Packets and

Packet, or self-OBU

It may collide with a packet. Each time a collision occurs,

Is the maximum value

To twice the size of the CW.

The maximum backoff step of

If

Is determined as follows.

(

)까지 유지된다. 그러므로

에 대한

번째 CW 크기는 다음과 같이 주어진다.The maximum CW size is the retransmission limit

(

). therefore

For

The second CW size is given by

에 도달할 때까지 성공적으로 전송되지 못한 패킷은

에서 폐기된다. 본 발명의 분석에서는

및

로 설정하였다. 그러나, 본 발명의 분석은 일반적인 경우로 쉽게 확장될 수 있다.Retransmission Restrictions

Packets that were not successfully transmitted until

. In the analysis of the present invention

And

Respectively. However, the analysis of the present invention can be easily extended to a general case.

For security services, all OBUs broadcast security packets on the CCH. In order to guarantee a successful delivery probability of at least 98%, which is the QoS requirement for the safety packet, the RSU sends an ACK message to the sender as a representative when the RSU successfully receives the safety packet broadcast by the OBU in the WBSS. Therefore, the sender can retransmit if there is a collided packet.

Let's look at the SCH access protocol. Describes how the OBU sends and receives data files on the SCH. The OBU that wants to upload / download the data file must first transmit the RFS packet to the RSU through the CCH according to the contention-based EDCA method described above. After successfully receiving the RFS packet, the RSU accepts or rejects the service request based on the current SCH availability. If there is at least one available idle SCH, the service request is accepted and the RSU sends an ACK packet to the OBU requesting the service. The ACK packet includes information on the SCH ID to be used and the transmission opportunity (TXOP). The transmission opportunity is the time interval during which the OBU can send and receive data files exclusively. The OBU switches the SCH radio to the designated SCH after a successful handshake with the RSU according to the contention-based EDCA on the CCH, and then uses it to transmit / receive the entire data file at one time during the TXOP. If the RSU successfully receives an RFS packet and there is no idle SCH available at that moment, the service request is rejected and the RSU sends a NAK packet to the OBU requesting the service. The OBU then abandons sending and receiving data files and discards RFS packets.

Meanwhile, the mathematical analysis model and technique of the present invention will be described.

의 확률적 변화를 모델링하는 것이다. 네트워크에 N 개의 차량과 K 개의 서비스 채널(

이 있다고 하자. 각 OBU는 안전 패킷 및 RFS 패킷을 생성한다. 따라서 N 개의 AC₁ 큐와 N 개의 AC₂ 큐는 CCH에서 서로 경쟁한다. 본 발명의 분석 모델에 사용되는 주요 가정은 다음과 같다. 실제적인 상황을 반영하기 위해 불포화 조건(즉, 큐가 비어있는 경우도 있음)을 다룬다. 안전 패킷은 모수가

인 포아송 과정에 따라 생성된다. 또한 OBU는 데이터 파일의 송/수신이 완료될 때까지 새로운 RFS 패킷을 생성하지 않으며, RFS 패킷은 데이터 파일의 송/수신이 완료된 후, 기댓값이

인 지수 분포를 따라 생성된다. 데이터 파일의 크기는 기댓값이

인 기하 분포를 따른다. 분석의 용이성을 위해

로 설정한다. The analytical technique of the present invention is based on the use of an embedded discrete time Markov chain

Is modeled. N vehicles in the network and K service channels (

Let's say. Each OBU generates a secure packet and an RFS packet. Thus, N AC ₁ queues and N AC ₂ queues compete on the CCH. The main assumptions used in the analysis model of the present invention are as follows. It deals with unsatisfying conditions (that is, the queue may be empty) to reflect the actual situation. The safety packet is a parameter

In Poisson process. Also, the OBU does not generate a new RFS packet until the transmission / reception of the data file is completed, and after the transmission / reception of the data file of the RFS packet is completed,

Lt; / RTI > The size of the data file is

As shown in Fig. For ease of analysis

.

인 기본 백 오프 슬롯, (ii) 길이가

인

패킷의 성공적인 전송 슬롯, (iii) 길이가

인

패킷의 성공적인 전송 슬롯, (iv) 길이가

인

패킷만으로 인한 충돌 슬롯, (v) 길이가

인

패킷만으로 인한 충돌 슬롯으로 분류될 수 있다. 본 발명에서는 슬롯의 경계를 임베디드 포인트로 설정한다. 두 개의 임의의 연속된 임베디드 포인트 사이의 구간을 일반 슬롯이라고 한다. 분석의 용이성을 위해 관례대로

라 가정한다. 따라서 일반 슬롯은 길이가

인 유휴 슬롯이거나 아니면 길이가

인 사용중인 슬롯이 된다.In the analytical model of the present invention, the time axis is discretized into slots, each slot having (i)

A basic backoff slot, (ii) a length

sign

A successful transmission slot of the packet, (iii)

sign

A successful transmission slot of the packet, (iv)

sign

Collision slots due to packet only, (v)

sign

It can be classified as a collision slot due to only a packet. In the present invention, the boundary of a slot is set as an embedded point. The interval between two arbitrary consecutive embedded points is referred to as a general slot. As is customary for ease of analysis

. Therefore,

Idle slot, or

Lt; / RTI > in use.

는

가 일반 슬롯에서 패킷 전송을 시도할 확률을 나타낸다. 조건부 충돌 확률

는

가 패킷 전송을 시도한다는 가정하에, 전송된

패킷이 충돌을 겪을 확률을 나타낸다. 전송 확률

및 조건부 충돌 확률

는 채널 상태 및 백 오프 이력에 관계없이 일정하다고 가정된다. 상기 파라미터를 찾기 위해 비앙키(Bianchi) 형 마르코프 체인(Markov chain)과 갱신 보상 과정이 주로 사용된다. 본 발명에서는 비앙키 형 마르코프 체인 방법을 이용한다. The main parameters used in the analysis of the present invention are the transmission probability and the conditional collision probability. Transmission probability

The

Indicates the probability of attempting to transmit a packet in a normal slot. Conditional collision probability

The

Lt; / RTI > attempts to transmit a packet,

Indicates the probability that a packet will experience a collision. Transmission probability

And conditional collision probability

Is assumed to be constant regardless of the channel state and back-off history. A Bianchi Markov chain and an update compensation process are mainly used to find the above parameters. In the present invention, a Bianchi type Markov chain method is used.

13 is a diagram illustrating a Markov chain necessary for analyzing performance of a security packet according to an embodiment of the present invention.

Let's look at performance analysis of safety packets. We analyze the delay and successful delivery probability of the safety packet in AC ₁ queue. To do this, we consider arbitrary AC ₁ as tagged AC ₁ and observe stochastic changes in AC ₁ tagged at each embedded point.

를

번째(

) 임베디드 포인트에서 태그된 AC₁의 상태를 나타내는 확률 변수라 하자. 태그된 AC₁은 (i) 백 오프 상태, (ii) 유휴 상태, (iii) 캐리어 감지 상태 중 하나의 상태를 취할 수 있다. AC₁이

번째 슬롯 동안 백 오프 절차를 수행하는 경우, AC₁은

번째 임베디드 포인트에서 백 오프 상태가 된다. 백 오프 상태는 다음과 같이 표시된다.Let's look at Markov chain modeling for tagged AC ₁ .

To

th(

) Let be a random variable representing the state of AC ₁ tagged at the embedded point. The tagged AC1 may take _one of (i) a back off state, (ii) an idle state, and (iii) a carrier sense state. AC ₁ is

Lt; th > slot, AC < _{RTI ID} = 0.0 &_gt; _{1 <}

Lt; th > embedded point. The back off state is displayed as follows.

및

은 태그된 AC₁의 백 오프 단계와 백 오프 카운터 값을 각각 나타내고

이다. 태그된 AC₁은 자신의 큐가 비어있는 경우 유휴 상태가 된다. 유휴 상태는 다음과 같이 표시된다.here

And

Represents the backoff step of the tagged AC ₁ and the backoff counter value, respectively

to be. The tagged AC ₁ is idle if its queue is empty. The idle state is displayed as follows.

기간 동안 CCH를 감지한다. 상기 캐리어 감지 상태는 다음과 같이 표시된다.A non-alternate safety packet may be generated when the tagged AC ₁ is idle or only during a successful transmission of a previous safety packet. If the CCH is not in use when a safety packet is generated at the tagged AC ₁ that is idle, the tagged AC ₁ will remain in use until the CCH is found in use

CCH is detected during the period. The carrier sensing state is indicated as follows.

는

을 유휴 슬롯 단위로 환산한 값이며,

는 태그된 AC₁이 (

기간 전부터

번째 임베디드 포인트까지 줄곧 CCH가 유휴 상태였음을 감지하는 것을 나타낸다.here

The

In the idle slot unit,

Lt; _{RTI ID =} 0.0 _> AC1 &

Before the period

Lt; RTI ID = 0.0 > CCH < / RTI >

는 이산 시간 마르코프 체인을 형성하며, 도 13에 도시된 천이 다이어그램을 갖는다. 도 13에 도시된 천이 확률은 각각 다음과 같이 계산된다. 표기법을 간소화하기 위해 아래의 기호를 사용한다.Embedded Process

Form a discrete-time Markov chain and have the transition diagram shown in Fig. The transition probabilities shown in Fig. 13 are calculated as follows. Use the following symbols to simplify the notation.

및

인

에 대해

인 경우를 고려한다. 이 경우 AC₁은 다음 임베디드 포인트에서 백 오프 카운터 값을 1 씩 감소시킨다. 따라서 상태

로부터의 천이 확률은 다음과 같다. The present invention first

And

sign

About

. In this case, AC ₁ decrements the backoff counter value by 1 at the next embedded point. Therefore,

The transition probability from

), 태그된 AC₁은 안전 패킷을 전송한다. 안전 패킷이 전송되는 동안 태그된 AC₁에서 다른 안전 패킷이 새로 생성될 확률을

라 하면 다음과 같이 계산된다.Thereafter, when the backoff counter value reaches 0 (that is,

), And the tagged AC ₁ transmits a safety packet. While the safety packet is being transmitted, the probability that another safety packet will be generated in the tagged AC ₁

Is calculated as follows.

으로부터의 천이 확률은

에 대해 다음의 [수학식 1]과 같이 구해진다. Then,

The transition probability from

Is obtained by the following equation (1).

은 하기의 [수학식2]에 의해 주어진 조건부 충돌 확률이다.here

Is the conditional collision probability given by < EMI ID = 2.0 >

이면 천이 확률은 다음의 [수학식 3]과 같다.if

The transition probability is expressed by the following equation (3).

번째 슬롯에서 전송된 안전 패킷에 충돌이 발생하면, AC₁은 [수학식 1] 및 [수학식 3]의 마지막 항에 반영되는 백 오프 절차를 반복한다.Here, the first and second terms of [Equation 1] and [Equation 3] represent an event that AC ₁ successfully transmits a safety packet. The first term expresses the case where no other safety packet is generated in the tagged AC ₁ while the safety packet is successfully transmitted (AC ₁ therefore transitions to the idle state). The second term represents a case where another safety packet is newly generated in the tagged AC ₁ while the safety packet is successfully transmitted (AC ₁ therefore transitions to the back-off state where the backoff step is 0).

Th slot, AC ₁ repeats the backoff procedure reflected in the last term of Equation (1) and Equation (3).

인 경우를 고려하자. 이러한 조건하에

번째 슬롯이 유휴 슬롯이며,

번째 슬롯 동안 태그된 AC₁에서 안전 패킷이 생성될 확률을

로 정의하자. 반면

번째 슬롯이 사용중인 슬롯이며,

번째 슬롯 동안 태그된 AC₁에서 안전 패킷이 생성될 확률을

로 정의하자. 모수가

인 포아송 과정에 따라 안전 패킷이 생성되는 경우, 상기 확률

,

는 하기의 [수학식 4] 및 [수학식 5]와 같이 계산된다. to the next,

. Under these conditions

Th slot is an idle slot,

Lt; RTI ID = 0.0 > AC1 &_lt; / RTI >

. On the other hand

Th slot is in use,

Lt; RTI ID = 0.0 > AC1 &_lt; / RTI >

. The parameter

When a secure packet is generated according to the Poisson process, the probability

,

Is calculated as shown in the following equations (4) and (5).

은 태그된 AC₁이 안전 패킷을 전송하는 상태가 아니라는 가정하에 유휴 슬롯을 관찰할 조건부 확률을 나타내며 하기의 [수학식 6]에 의해 주어진다.here

Denotes a conditional probability of observing an idle slot under the assumption that the tagged AC ₁ is not in a state of transmitting a safety packet, and is given by Equation (6) below.

로부터의 천이 확률은 다음과 같다. Therefore,

The transition probability from

번째 슬롯 동안 태그된 AC₁에서 안전 패킷이 생성되는 사건을 나타낸다.

번째 슬롯 동안 안전 패킷이 생성되지 않으면 AC₁은 유휴 상태로 유지된다. Here, the first and second terms

AC ₁ in the tag during the second slot shows the case where the safety packet is generated.

If the slot for the second security packet is not generated AC ₁ is maintained at the idle state.

인 경우를 고려한다. 먼저

인 경우를 살펴보자.

번째 슬롯이 유휴 상태이면 태그된 AC₁은 CCH를 계속 감지한다.

번째 슬롯이 유휴 상태가 아니면 태그된 AC₁은 CCH 감지를 중지하고 백 오프 단계가 0인 백 오프 상태로 천이한다. 따라서

인 상태

로부터의 천이 확률은 다음과 같다. Finally,

. first

Let's take a look at the case.

Th slot is idle, the tagged AC ₁ continues to sense the CCH.

Th slot is not in the idle state, the tagged AC ₁ stops detecting the CCH and transitions to the back-off state where the back-off step is zero. therefore

In state

The transition probability from

인 경우를 살펴보자.

이면 AC₁은

번째 슬롯 동안 안전 패킷을 전송한다. 이 경우 AC₁은

번째 임베디드 포인트에서 유휴 상태로 천이되거나 백 오프 단계가 0인 백 오프 상태로 천이된다. 유휴 상태로 천이되기 위해서는

번째 슬롯 동안 안전 패킷이 성공적으로 전송되어야 하며 패킷 전송 중에 다른 안전 패킷이 새로 생성되지 않아야 한다. 따라서 상태

으로부터의 천이 확률은 다음과 같다.

Let's take a look at the case.

If AC ₁ is

Th slot. In this case, AC ₁

Th < / RTI > embedded point to an idle state or a backoff state where the backoff step is zero. To be idle,

During the sec- ond slot, the secure packet shall be transmitted successfully and no other safety packet shall be generated during the packet transmission. Therefore,

The probability of transition from

의 정상 상태 확률을 살펴보기로 한다. 정상 상태 확률을 나타내기 위해 아래의 [수학식 7]의 기호를 사용한다. On the other hand,

Let's look at the steady-state probability of. To represent the steady-state probability, the symbol of the following formula (7) is used.

이다. 정상 상태 확률을 구하기 위해, 도 13에 도시된 천이 다이어그램을 기반으로 하는 균형 방정식을 이용한다. 균형 방정식의 근본적인 원리는, 마르코프 체인

의 상태 공간 S의 임의의 부분 집합 E에 대해 하기의 [수학식 8]이 성립된다는 것이다.here,

to be. To obtain the steady state probability, a balance equation based on the transition diagram shown in FIG. 13 is used. The fundamental principle of the equilibrium equation is that the Markov chain

(8) < / RTI > for an arbitrary subset E of the state space S of Eq.

및

를 다음의 [수학식 9] 및 [수학식 10]과 같이

의 상수배로 나타낼 수 있다.By applying an appropriate subset E to Equation (8), the steady-state probability

And

As shown in the following equations (9) and (10)

Can be represented by a constant multiple of.

및

는 다음과 같이 주어진다. Here,

And

Is given as follows.

은 하기의 정규화 조건을 이용하여 구할 수 있다. percentage

Can be obtained by using the following normalization condition.

the results are as follow.

의 정상 분포를 이용하여 전송 확률

를 다음의 [수학식 11]과 같이 표현할 수 있다.Now Markov Chain

The probability of transmission

Can be expressed as the following Equation (11).

과

의 함수가 된다. 특히, 상수

및

은 각각 [수학식 2], [수학식 4], [수학식 5], [수학식 6]에 보인 바와 같이 미지수

과

를 포함한다.

과

를 구하려면, 관계식 1개가 더 필요하며, 이것은 RFS 패킷의 성능 분석을 통해 유도된다([수학식 26] 참조).Given a system parameter value, Equation (11)

and

. In particular,

And

As shown in [Equation 2], [Equation 4], [Equation 5] and [Equation 6]

and

.

and

, One more relational expression is required, which is derived through performance analysis of the RFS packet (see Equation 26).

Meanwhile, the delay of the safety packet and the probability of successful delivery will be described.

로 표시하자.

은 안전 패킷이 생성된 순간부터 안전 패킷이 성공적으로 전송 완료된 시점까지의 경과 시간으로 정의된다. 전술한 바와 같이, 대체가 아닌 안전 패킷은 태그된 AC₁이 유휴 상태일 때 생성되거나 또는 이전 안전 패킷이 성공적으로 전송되는 동안만 생성될 수 있다. 따라서 지연

은 하기의

,

,

및

중 하나에 해당된다. Delay the safety packet

.

Is defined as the elapsed time from the moment the safety packet is generated to the time point at which the safety packet is successfully transmitted. As described above, a non-alternate safety packet may be generated when the tagged AC ₁ is idle or only during a successful transmission of the previous safety packet. Therefore,

The following

,

,

And

.

을 살펴보면, 안전 패킷이 유휴 상태에서 생성되고 연속적으로

에서

까지의 캐리어 감지 상태

를 통과한다는 가정하에, 상기 안전 패킷이 상태

에서 전송되는 경우 지연을 나타낸다(이때 성공적으로 또는 충돌이 발생한 전송을 모두 포함한다).

, A safety packet is generated in an idle state,

in

Carrier sensing state up to

It is assumed that the safety packet is in a state

Lt; / RTI > (including all transmissions that have occurred successfully or have occurred).

을 살펴보면, 안전 패킷이 유휴 상태에서 생성되고

에서

까지의 캐리어 감지 상태

를 통과하지만 상태

에 도달하지 않는다는 가정하에, 상기 안전 패킷이 상태

에서 전송되는 경우 지연을 나타낸다(이때 성공적으로 또는 충돌이 발생한 전송을 모두 포함한다).

, A safety packet is generated in the idle state

in

Carrier sensing state up to

, But the state

Lt; / RTI > is not reached,

Lt; / RTI > (including all transmissions that have occurred successfully or have occurred).

을 살펴보면, 안전 패킷이 유휴 상태에서 생성되고 어떤 캐리어 감지 상태도 거치지 않는다는 가정하에, 상기 안전 패킷이 상태

에서 전송되는 경우 지연을 나타낸다(이때 성공적으로 또는 충돌이 발생한 전송을 모두 포함한다).

It is assumed that the safety packet is generated in the idle state and does not go through any carrier sensing state,

Lt; / RTI > (including all transmissions that have occurred successfully or have occurred).

을 살펴보면, 안전 패킷이 이전의 안전 패킷이 성공적으로 전송되는 동안 생성되었다는 가정하에, 상기 안전 패킷이 상태

에서 전송되는 경우 지연을 나타낸다(이때 성공적으로 또는 충돌이 발생한 전송을 모두 포함한다).

It is assumed that the secure packet has been generated during the successful transmission of the previous secure packet,

Lt; / RTI > (including all transmissions that have occurred successfully or have occurred).

및

에 대한 표현식을 도출한다. 달리 언급되지 않는 한, 지연과 관련된 모든 측정 항목은 유휴 슬롯 단위로 표시된다. AC₁의

번째 백 오프 단계에서 소비된 지연을

이라 하자.

의 확률 생성 함수(PGF)는 다음의 [수학식 12]와 같다.to the next,

And

To derive an expression for. Unless otherwise noted, all metrics associated with delay are displayed in idle slot units. AC ₁ of

Lt; RTI ID = 0.0 > backoff < / RTI &

.

(PGF) is expressed by the following equation (12).

는 안전 패킷의 전송 시간을 나타낸다.

을 이용하여

를 다음의 [수학식 13]과 같이 표현할 수 있다.here

Represents the transmission time of the safety packet.

Using

Can be expressed as the following equation (13).

이다. [수학식 13]의 첫 번째 항은 안전 패킷이 상태

에서 성공적으로 전송되는 경우를 나타낸다. 그렇지 않은 경우, [수학식 13]의 두 번째 항에서 표현된 바와 같이, 안전 패킷은 성공적으로 전송될 때까지

회(

) 재전송된다.here,

to be. The first term in Equation (13)

Lt; / RTI > Otherwise, as represented in the second term of Equation (13), the safety packet is transmitted until successfully transmitted

time(

) Is retransmitted.

까지 지속되지 않는다는 가정하에, 캐리어 감지 상태에서 소비된 지연을

이라 하자.

의 PGF는 다음과 같다.Carrier detect is in a state

, The delay that is spent in the carrier sensing state

.

Of PGF is as follows.

을 이용하여

를 다음의 [수학식 14]와 같이 표현할 수 있다.

Using

Can be expressed as the following equation (14).

은 안전 패킷이 성공적으로 전송될 때까지의 총 재전송 횟수를 나타낸다. 위와 마찬가지로

를 다음의 [수학식 15]와 같이 표현할 수 있다.here

Represents the total number of retransmissions until a safety packet is successfully transmitted. As above

Can be expressed as the following equation (15).

이다. 안전 패킷이 이전 안전 패킷의 성공적인 전송 기간 중에 생성되면, AC₁은 캐리어 감지 상태를 거치지 않고 백 오프 상태로 진입한다. 따라서,

는 다음의 [수학식 16]과 같이

와 동일한 분포를 가진다.here,

to be. If the SAFE packet is generated during the successful transmission of the previous SAFE packet, AC ₁ enters the back-off state without going through the carrier sense state. therefore,

Is expressed by the following equation (16)

.

이다. [수학식 13], [수학식 14], [수학식 15] 및 [수학식 16]을 각각 이용하면

,

,

및

의 PGF를 구할 수 있다.

의 PGF는 다음과 같이 유도된다.here,

to be. Using Equation (13), Equation (14), Equation (15) and Equation (16)

,

,

And

Of PGF can be obtained.

Of PGF is induced as follows.

및

는 다음과 같다. here,

And

Is as follows.

의 확률 분포 함수는 PGF

로부터 구할 수 있다.Finally a delay

The probability distribution function of PGF

.

로 설정 했으므로, 안전 패킷은 전달 마감 기한이 만료되기 전에 전달되면 성공적으로 전달된 것으로 간주된다. 따라서 안전 패킷의 성공적인 전달 확률

은

의 확률 분포 로부터 다음과 같이 구해진다.Each security packet must be sent to the neighboring vehicle within the delivery deadline L (= 100ms). The retransmission limit for AC ₁ is

, The security packet is considered to have been successfully delivered if it is delivered before the delivery deadline expires. Therefore, the probability of successful delivery of a secure packet

silver

Is obtained from the probability distribution of

FIG. 14 is a schematic diagram of an RFS FIG. 4 is a diagram illustrating a Markov chain necessary for performance analysis of a packet. FIG.

Let's look at performance analysis of RFS packet. Analyze the delay and successful delivery probability of RFS packets in the AC ₂ queue. To do this, we consider arbitrary AC ₂ as tagged AC ₂ and observe stochastic changes in AC ₂ tagged at each embedded point. Performance analysis method of RFS packet is similar to performance analysis method of safety packet. Therefore, only the differences will be emphasized here to simplify the explanation.

Let's look at Markov chain modeling for tagged AC ₂ .

를

번째 임베디드 포인트에서 태그된 AC₂의 상태를 나타내는 확률 변수라 하자. 태그된 AC₂는 (i) 백 오프 상태, (ii) SCH 상으로 데이터 파일을 전송하는 상태, (iii) 유휴 상태, (iv) 캐리어 감지 상태 중 하나의 상태를 취할 수 있다. 태그된 AC₂가 백 오프 상태이면 하기와 같이 표시된다.

To

Let be a random variable representing the state of AC ₂ tagged at the ith embedded point. The tagged AC ₂ may take one of the following states: (i) a backoff state, (ii) a state in which a data file is transmitted over an SCH, (iii) an idle state, and (iv) a carrier sensing state. If the tagged AC ₂ is in the back-off state, it is displayed as follows.

,

및

이다. 태그된 AC₂가 RFS 패킷을 성공적으로 전송하고 사용 가능한 SCH가 있으면, 그 중 하나의 SCH를 할당받는다. 태그된 AC₂는 할당된 SCH를 통해 데이터 파일을 송수신한다. 이 경우,

는 하기와 같이 표시된다.here

,

And

to be. If the tagged AC ₂ successfully transmits an RFS packet and there is an available SCH, one of them is allocated. The tagged AC ₂ transmits and receives the data file via the assigned SCH. in this case,

Is expressed as follows.

The tagged AC ₂ is idle if its queue is empty. The idle state is displayed as follows.

The RFS packet can only be generated when the tagged AC ₂ is idle. If the CCH is not in use when an RFS packet is being generated, AC ₂ is in the carrier sense state and is indicated as follows:

는 이산 시간 마르코프 체인을 형성하며, 도 14에 도시된 천이 다이어그램을 갖는다. 도 14에 도시된 천이 확률은 각각 다음과 같이 계산된다. 표기법을 간소화하기 위해 아래의 기호를 사용한다.Embedded Process

Forms a discrete-time Markov chain and has the transition diagram shown in Fig. The transition probabilities shown in Fig. 14 are calculated as follows. Use the following symbols to simplify the notation.

(단,

및

) 로부터의 천이 확률은 다음과 같다.First,

(only,

And

) Is the following.

), 태그된 AC₂는 RFS 패킷을 전송한다. 태그된 AC₂가 RFS 패킷을 성공적으로 전송한 직후 모든

개의 SCH가 사용중일 확률을

이라 하자. 그러면, 상태

으로부터의 천이 확률은

에 대해 다음의 [수학식 17]과 같이 유도된다.When the backoff counter value reaches 0 (that is,

), And the tagged AC ₂ transmits an RFS packet. Immediately after the tagged AC ₂ successfully transmits the RFS packet

Probability that the SCHs are in use

. Then,

The transition probability from

As shown in the following Equation (17).

는 하기의 [수학식 18]에 의해 주어진 조건부 충돌 확률이다.here

Is the conditional collision probability given by < EMI ID = 18.0 >

이면 천이 확률은 다음의 [수학식 19]와 같다.if

The transition probability is expressed by the following equation (19).

개의 모든 SCH가 사용 중이거나, RFS 패킷이 충돌된 후 재전송 제한에 도달한 경우(

인 경우 가능) 발생한다. RFS 패킷에 충돌이 발생하였으나 재전송 제한에 도달하지 않은 경우, AC₂는 [수학식 17]의 마지막 항에 반영되는 백 오프 절차를 반복한다.Here, the first term of Equation (17) and Equation (19) represents an event assigned to the AC ₂ tagged with the SCH after successful transmission of the RFS packet. The second term of Equation (17) and Equation (19) represents the event that the tagged AC ₂ discards the RFS packet. This event can occur immediately after an RFS packet is successfully transmitted

All SCHs are in use, or the retransmission limit is reached after an RFS packet collision (

If possible). If a collision occurs in the RFS packet but the retransmission limit is not reached, AC ₂ repeats the backoff procedure reflected in the last term of Equation (17).

인 경우(즉, 태그된 AC₂가

번째 임베디드 포인트에서 SCH상으로 데이터 파일을 전송하는 상태)를 고려하자. 태그된 AC₂의 파일 전송이

번째 임베디드 포인트까지 계속될 확률을

라 하자. 데이터 파일의 크기가 기댓값이

인 기하 분포를 따르면, 파일 전송 시간은 기댓값이 (

인 기하 분포를 따르게 된다. 여기서

은 데이터 속도이다. 따라서, 확률

는 하기의 [수학식 20]과 같다.to the next,

(I.e., the tagged AC ₂

Lt; th > embedded point to the SCH). Tagged file transfer of AC ₂

Probability of continuing to the next embedded point

Let's say. If the size of the data file is

According to the geometric distribution, the file transfer time is expressed as (

As shown in Fig. here

Is the data rate. Therefore,

Is expressed by the following equation (20).

은 태그된 AC₂가 RFS 패킷을 전송하는 상태가 아니라는 가정하에 유휴 슬롯을 관찰할 조건부 확률을 나타내며 하기의 [수학식 21]에 의해 주어진다.here

Denotes a conditional probability of observing an idle slot under the assumption that the tagged AC ₂ is not in the state of transmitting an RFS packet, and is given by: " (21) "

로부터의 천이 확률은 다음과 같다.Therefore,

The transition probability from

이라고 가정하자. 이러한 조건하에

번째 슬롯이 유휴 슬롯이며,

번째 슬롯 동안 태그된 AC₂에서 RFS 패킷이 생성될 확률을

로 정의하자. 반면

번째 슬롯이 사용중인 슬롯이며,

번째 슬롯 동안 태그된 AC₂에서 RFS 패킷이 생성될 확률을

로 정의하자. 모수가

인 포아송 과정에 따라 데이터 파일이 생성되는 경우, 상기 확률

및

는 다음의 [수학식 22] 및 [수학식 23]과 같이 계산된다.

. Under these conditions

Th slot is an idle slot,

Lt; RTI ID = 0.0 &_gt; AC2 < / RTI >

. On the other hand

Th slot is in use,

Lt; RTI ID = 0.0 &_gt; AC2 < / RTI >

. The parameter

When a data file is generated according to the Poisson process, the probability

And

Is calculated according to the following equations (22) and (23).

로부터의 천이 확률은 AC₁의 천이 확률에서

를 각각

로 대체함으로써 아래와 같이 구할 수 있다. 유사성 때문에 자세한 설명은 생략한다. condition

The probability of transition from AC ₁ to AC ₁ is

Respectively

Can be obtained as follows. Because of similarity, detailed explanation is omitted.

인 상태

로부터의 천이 확률은 다음과 같다.

In state

The transition probability from

일 때, 태그된 AC₂는

인 상태

과 같은 방식으로 동작한다. 그러므로 [수학식 17]을 적용함으로써 상태

으로부터의 천이 확률이 다음과 같이 구해진다.

, The tagged AC ₂ is

In state

. ≪ / RTI > Therefore, by applying Equation (17)

The transition probability is obtained as follows.

을 구하는 과정을 살펴보면 다음과 같다. Meanwhile,

The following is the process of obtaining.

에 대한 정확한 공식은 네트워크 내의 모든 AC₂들의 상태를 추적하는

-차원 마르코프 체인을 사용하여 도출할 수 있다. 그러나, 이 기법은 큰 값을 가지는

에 대해 계산 복잡성을 수반한다. 복잡성 문제를 피하기 위해,

개의 유한 소스를 갖는 M/M/K/K/N 큐잉 모델에 기반하여

에 대한 근사 공식을 제시한다. Engset 모델로 알려진 M/M/K/K/N 시스템은

개의 서버와

개의 유한 소스로 구성된다. 모든

개의 서버가 사용중인 경우, 도착 고객은 시스템에 진입하지 못하고 지수 분포를 따르는 랜덤 시간 후에 재진입을 시도한다. 도착 고객이

개의 서버가 모두 사용 중인 것을 발견할 확률(즉, Engset 손실 공식)은 다음의 [수학식 24]와 같다.

The exact formula for this is to track the state of all AC ₂ 's in the network

- can be derived using a 2D Markov chain. This technique, however,

Lt; RTI ID = 0.0 > complexity. ≪ / RTI > To avoid complexity problems,

Based on the M / M / K / K / N queuing model with finite sources

The approximate formula for The M / M / K / K / N system, known as the Engset model,

Servers and

Of finite sources. all

If two servers are in use, the arriving customer fails to enter the system and attempts reentry after a random time following the exponential distribution. Arriving customers

(I. E., The " Engset loss formula ") is found by the following equation (24).

와

는 각각 Engset 모델에서 소스의 도착률과 서버의 서비스 율을 나타낸다.here

Wow

Represent the arrival rate of the source and the service rate of the server in the Engset model, respectively.

개의 서버와

개의 유한 소스를 각각

개의 SCH와

개의 AC₂로 간주한다. 또한 도착 간격 및 서비스 시간과 비교할 때, 백 오프 절차에서의 경쟁 시간은 무시할 정도로 작기 때문에 0으로 근사한다. 그러면, 각 RFS 패킷은 모수가

인 포아송 과정에 따라 AC₂에서 생성되기 때문에

가 된다. 또한, SCH상의 파일 전송 시간은 기댓값이

인 기하 분포를 따르기 때문에

가 된다. 따라서 [수학식 24]의 Engset 손실 공식으로부터 하기와 같이

에 대한 근사 공식이 구해진다.In the Engset model,

Servers and

The finite sources of

With SCH

AC ₂ < / RTI > Also, when compared with the arrival interval and the service time, the competition time in the backoff procedure is negligibly small, so it is approximated to zero. Then, each RFS packet has a parameter

Is generated in AC ₂ according to the Poisson process

. In addition, the file transfer time on the SCH is the expected value

Because it follows the geometric distribution of

. Therefore, from the Engset loss formula of (Equation 24)

Is approximated.

Numerical studies and simulations are used to verify the accuracy of the approximation (see FIG. 15).

의 정상 상태 확률을 구한다.The steady-state probability will be examined. The Markov chain < RTI ID = 0.0 >

Of the steady-state probability.

,

이다. 균형 방정식 [수학식 8]에 적절한 부분 집합 E를 적용함으로써, 정상 분포

,

,

각각을 다음과 같이

의 상수배로 나타낼 수 있다.here,

,

to be. By applying an appropriate subset E to the equilibrium equation [Equation 8], the normal distribution

,

,

Each as follows

Can be represented by a constant multiple of.

,

및

는 다음과 같이 주어진다.Here,

,

And

Is given as follows.

은 하기의 정규화 조건을 이용하여 구할 수 있다.percentage

Can be obtained by using the following normalization condition.

the results are as follow.

의 정상 상태 확률을 이용하여 전송 확률

를 다음의 [수학식 26]과 같이 표현할 수 있다.Now Markov Chain

And the probability of transmission

Can be expressed as the following equation (26).

과

의 함수가 된다. 특히, 상수

및

는 각각 [수학식 22], [수학식 23], [수학식 21], [수학식 18], [수학식 20]에 보인 바와 같이 미지수

과

를 포함한다. [수학식 11]과 [수학식 26]을 연립하여 풀면

과

를 구할 수 있다. Given a system parameter value, < RTI ID = 0.0 > [26]

and

. In particular,

And

As shown in [Expression 22], [Expression 23], [Expression 21], [Expression 18], [Expression 20]

and

. If we solved and solved the equations (11) and (26)

and

Can be obtained.

Meanwhile, the delay and successful delivery probability of the RFS packet will be described.

로 표시하자.

는 태그된 AC₂가 RFS 패킷을 생성한 순간부터 SCH를 할당받거나(즉, RFS 패킷이 성공적으로 전달됨), RFS 패킷을 폐기하는(재전송 제한 또는 SCH의 비가용성으로 인해) 시점까지의 경과 시간으로 정의된다. 따라서 지연

는 하기의

,

및

중 하나에 해당된다.Delay the RFS packet

.

Is the elapsed time from the moment the tagged AC ₂ generates the RFS packet to the point at which the SCH is allocated (i.e., the RFS packet is successfully delivered) and the RFS packet is discarded (due to retransmission restriction or SCH non-availability) Is defined. Therefore,

The following

,

And

.

는 연속적으로

에서

까지의 캐리어 감지 상태

를 거친 후, 상태

에서 전송되는 RFS 패킷의 지연을 나타낸다.

Continuously

in

Carrier sensing state up to

, The state

Lt; RTI ID = 0.0 > RFS < / RTI >

는

에서

까지의 캐리어 감지 상태

를 거친 후(그러나 상태

에 도달하지 않음) 상태

에서 전송되는 RFS 패킷의 지연을 나타낸다.

The

in

Carrier sensing state up to

(But not in state

≪ / RTI > does not reach)

Lt; RTI ID = 0.0 > RFS < / RTI >

는 어떤 캐리어 감지 상태를 거치지 않고, 상태

에서 전송되는 RFS 패킷의 지연을 나타낸다.

Lt; / RTI > does not go through any carrier sensing state,

Lt; RTI ID = 0.0 > RFS < / RTI >

및

의 표현식은 각각 [수학식 27], [수학식 28] 및 [수학식 29]와 같다.

And

Are expressed by Equation (27), (28) and (29), respectively.

는 AC₂의

번째 백 오프 단계에서 소비된 지연이고

의 PGF는 하기와 같이 주어진다.here,

Of AC ₂

Lt; RTI ID = 0.0 > backoff < / RTI &

Of PGF is given as follows.

는 캐리어 감지가 상태

까지 지속되지 않는다는 가정하에, 캐리어 감지 상태에서 소비된 지연을 나타내고,

의 PGF는 하기와 같다.Also

Lt; RTI ID = 0.0 >

Lt; RTI ID = 0.0 > a < / RTI > carrier sensing state,

Of PGF is as follows.

,

및

의 PGF를 구할 수 있다.

의 PGF는 다음과 같이 주어진다.Using Equation (27), Equation (28) and Equation (29), respectively,

,

And

Of PGF can be obtained.

Of PGF is given as follows.

및

는 다음과 같다. here,

And

Is as follows.

의 확률 분포 함수는 PGF

로부터 구할 수 있다.Finally a delay

The probability distribution function of PGF

.

The RFS packet is successfully delivered or discarded. In order for the RFS packet to be successfully transmitted, the SCH must be assigned to AC ₂ after successful transmission of the RFS packet. If the RFS packet was successfully transmitted but there is no available SCH, the present invention discards the RFS packet and regards it as a failed transmission. Therefore, considering the three possible cases mentioned above, the probability of successful delivery of RFS packets can be obtained as follows.

Meanwhile, the accuracy of the analysis is verified and the numerical results and the simulation results are compared to evaluate the MAC protocol performance of the present invention. Let's look at simulation settings and parameters.

The present invention developed an event-driven simulator using Matlab and performed a Monte Carlo simulation to obtain simulation results. To investigate the effect of node density, we change the number of vehicles from 50 to 200 and assume an ideal wireless channel with no fading and no shadowing. Packets are therefore lost due to MAC layer problems such as long access delays (for secure packets), collisions or non-availability of SCHs (for RFS packets). The simulations were run for 60 minutes and the simulation results for the first minute were omitted to obtain steady-state results. 1000 simulations were run using random seeds and the arithmetic mean was calculated for the results.

및

를 만족시키는 백 오프 파라미터

,

를 선택한다. 각 파라미터 세트에 대해 Matlab을 사용하여 [수학식 11]과 [수학식 26]을 연립하여 풀고, 안전 패킷 및 RFS 패킷의 지연 분포와 성공적인 전달 확률을 구한다.The present invention adopts the EDCA parameter defined in the IEEE 802.11p standard (see Table 2). It is assumed that the state packet is generated every 100 ms and the emergency packet is included in the safety packet, so that the safety packet occurs on average every 50 ms. According to the standard, the data rate is supported up to 27Mbps. The default value is 6Mbps, so R = 6Mbps for numerical study. As shown in [Table 2], the present invention provides a method for providing a higher priority to a safety packet versus an RFS packet

And

Lt; RTI ID = 0.0 >

,

. Equation (11) and (Equation (26)) are solved and solved by using Matlab for each parameter set, and the delay distribution and the successful delivery probability of the safety packet and the RFS packet are obtained.

parameter  value

 20 packets / sec

 0.003 packets / sec

 3

 4

 5

 64

 120 Bytes

 120 Bytes

 5 MBytes

 6 Mbps

12

sec

36

sec

32

sec

64

sec

15 is a diagram illustrating a probability distribution of a connection delay of a secure packet according to an embodiment of the present invention.

의 확률분포

(

: 서비스 채널의 수,

: 차량의 수)가 나타나 있다. 즉,

와 같다. 차량 수가

이고

인 경우, 도 15는 안전 패킷의 액세스 지연 분포에 관한 분석 결과와 시뮬레이션 결과를 보여준다. 도 15에 사용된 백 오프 파라미터는

및 (

이다. 성능 검증을 위해 개발한 수학적 모델의 정확성을 살펴보기로 한다. 이를 위해, 먼저 분석 결과와 시뮬레이션 결과를 비교하여 수학적 분석의 정확성을 검증한다. 도 15에서 시뮬레이션(Simulation)은 몬테카를로 컴퓨터 시뮬레이션 결과를 나타내며, 분석(Analysis)은 수학적 모델을 이용하여 유도한 이론적 결과를 나타낸다. 도 15에 도시된 결과를 살펴보면, 시뮬레이션 결과와 분석 결과가 일치한다. 즉, 개발한 수학적 모델의 정확성이 확인된다. As shown in FIG. 15, among the MAC protocol capabilities, an access delay of a secure packet,

Probability distribution of

(

: Number of service channels,

: Number of vehicles). In other words,

. Number of vehicles

ego

15 shows an analysis result and a simulation result of the access delay distribution of the safety packet. The backoff parameter used in FIG.

And (

to be. Let's look at the accuracy of the mathematical model developed for performance verification. To do this, we first verify the accuracy of the mathematical analysis by comparing the analysis results with the simulation results. In FIG. 15, the simulation shows the results of Monte Carlo computer simulation, and the analysis shows the theoretical results derived using the mathematical model. Referring to the results shown in Fig. 15, the simulation result and the analysis result coincide with each other. That is, the accuracy of the developed mathematical model is confirmed.

은 하기와 같이 주어진다.A safety packet with an access delay longer than 100 ms is considered lost because the delay of the safety packet must be less than 100 ms, depending on the QoS requirements. That is, the probability of successful delivery of a secure packet

Is given as follows.

이 커질수록 안전 패킷의 액세스 지연은 길어진다. 또한, 도 15는

인 경우, 안전 패킷의 액세스 지연이 거의 100% 성공적인 전달 확률과 함께 각각 5ms, 10ms 미만인 것을 나타낸다. 한편, 도 15에서

인 경우

의 값을 정확히 알기 어렵기 때문에, 도 16을 제공하여

인 경우 각각

및

임을 확인한다. 상기 결과는 차량의 수가 150을 초과하지 않으면 안전 서비스에 대한 QoS 요구 사항(즉, 100ms 이내의 지연과 최소 98%의 성공적인 전달 확률)이 충족됨을 나타낸다.As shown in Fig. 15,

The greater the access delay of the secure packet. 15,

, It indicates that the access delay of the secure packet is less than 5 ms and 10 ms, respectively, with almost 100% successful delivery probability. On the other hand,

If

, It is difficult to know the value of "

Respectively.

And

. The result indicates that QoS requirements for safety services (i.e., a delay of less than 100 ms and a successful delivery probability of at least 98%) are met if the number of vehicles does not exceed 150.

16 is a diagram illustrating a successful delivery probability of a safety packet according to an embodiment of the present invention.

: 서비스 채널의 수)이 도 16에 나타나 있다. 본 발명의 실시 예에 따른 차량 통신 방법의 효과에 대해서 살펴보기로 한다. 안전 패킷의 성능 검증과 관련하여, 도 16은 안전 패킷을 100ms 이내에 전달할 확률을 보여준다. 즉, 성공적인 전달 확률이 나타나 있다. 차량 수가 150대에 도달하더라도 성공적인 전달 확률이 98% 이상이 된다. 즉, 제안한 MAC 프로토콜은 안전 패킷에 대한 QoS 요구 사항을 만족시킨다. 도 16에서, 성공적인 전달 확률은

값에 의해 거의 영향을 받지 않는다. 이 결과는 RSU와 예약 협상 시점에서

개의 모든 SCH가 사용 중인 경우 RFS 패킷이 폐기되기 때문에 발생한다.The probability of successfully delivering a secure packet within 100ms (

: Number of service channels) is shown in Fig. The effect of the vehicle communication method according to the embodiment of the present invention will be described. Regarding performance verification of the safety packet, FIG. 16 shows the probability of delivering the safety packet within 100 ms. That is, a successful delivery probability is shown. Even if the number of vehicles reaches 150, the probability of successful delivery is more than 98%. That is, the proposed MAC protocol satisfies the QoS requirements for the secure packet. In Figure 16, the successful delivery probability is

It is hardly affected by the value. The result is that at the time of reservation negotiation with the RSU

This is because the RFS packet is discarded if all SCHs are in use.

17 is a diagram illustrating a successful delivery probability of an RFS packet according to an embodiment of the present invention.

이 나타나 있다. 본 발명은 도 17에서 AC₂ 패킷의 성능을 보여준다. 도 17의 왼쪽 도면은

및

에 대해 차량의 수

이 50에서 200까지 변화될 때, RFS 패킷의 성공적인 전달 확률

를 나타낸다. 성공적인 전달 확률은 사용 가능한 SCH의 수에 크게 영향을 받는다는 것을 알 수 있다. 특히, 도 17의 오른쪽 도면은 RFS 패킷의 성공적인 전달 확률이

일 때

에 대해 92% 이상임을 보여준다. 또한 도 17의 오른쪽 도면은 분석 결과가 시뮬레이션 결과와 잘 일치 함을 보여 주며,

에 대한 근사가 정확함을 나타낸다.Figure 17 shows the success probability of successful delivery of an RFS packet

. The present invention shows the performance of AC ₂ packets in FIG. 17,

And

The number of vehicles

Is changed from 50 to 200, the successful delivery probability of the RFS packet

. It can be seen that the probability of successful delivery is greatly influenced by the number of available SCHs. In particular, the right diagram of FIG. 17 shows that the successful delivery probability of an RFS packet is

when

Gt; 92% < / RTI > Also, the right drawing of FIG. 17 shows that the analysis result is in good agreement with the simulation result,

Lt; / RTI >

Meanwhile, performance comparison will be described. In the MAC protocol of the present invention, a reservation-based scheme is used to access the SCH, so that each OBU can access the reserved SCH in a non-contention manner. For performance comparisons, we consider competition-based methods, which are the opposite of non-competitive methods. A random selection scheme is considered as a competition based method, and the MAC protocol and the performance of the present invention are compared. The random selection scheme operates as follows. Each OBU arbitrarily selects one of the SCHs to transmit a non-secure packet. Then, to access the selected SCH, each OBU competes with IEEE 802.11 DCF with other OBUs that have selected the same SCH. On the other hand, in order to transmit the safety packet, each OBU compete with the IEEE 802.11 DCF to access the CCH. Like the protocol of the present invention, the RSU sends an ACK message to the broadcasted secure packet. Unless otherwise noted, parameters in [Table 2] are used.

FIG. 18 is a diagram illustrating a comparison result of the success probability of a secure packet according to an embodiment of the present invention.

및

Mbps인 경우 안전 패킷의 성공적인 전달 확률

의 비교 결과가 나타나 있다. 본 발명의 MAC 프로토콜과 랜덤 선택 기법은 안전 패킷의 성공적인 전달 확률에 대해 거의 동일한 성능을 보인다. 본 발명의 MAC 프로토콜에서는 CCH가 안전 패킷 및 RFS 패킷에 의해 공유되는 반면, 랜덤 선택 기법에서는 CCH가 안전 패킷에 의해서만 사용된다. 그럼에도 불구하고 상기와 같이 동일한 성능을 보이는 이유는, 안전 패킷이 높은 우선 순위를 가지며 RFS 패킷이 안전 패킷에 비해 드물게 생성되기 때문이다.18,

And

Mbps, the probability of successful delivery of a secure packet

Are shown in Fig. The MAC protocol and the random selection scheme of the present invention show almost the same performance with respect to the successful transmission probability of a secure packet. In the MAC protocol of the present invention, the CCH is shared by the secure packet and the RFS packet, whereas in the random selection scheme, the CCH is used only by the secure packet. Nevertheless, the reason for the same performance as described above is that the safety packet has a high priority and the RFS packet is rarely generated in comparison with the safety packet.

FIGS. 19 and 20 are diagrams showing a comparison result between a successful delivery probability and an average access delay of a non-secure packet according to an embodiment of the present invention.

및

Mbps인 경우 비-안전 패킷의 성공적인 전달 확률

와 평균 액세스 지연

의 비교 결과가 각각 나타나 있다.

Mbps인 경우, 랜덤 선택 기법은 본 발명의 MAC 프로토콜보다 높은 성공적인 전달 확률을 보인다. 그러나 평균 액세스 지연과 관련하여, 본 발명의 MAC 프로토콜은 랜덤 선택 기법보다 우수한 성능을 보인다.

Mbps인 경우, 본 발명의 MAC 프로토콜과 랜덤 선택 기법은

에 대해 99% 이상의 성공적인 전달 확률을 달성한다. 액세스 지연과 관련하여, 본 발명의 MAC 프로토콜은 랜덤 선택 기법보다 우수한 성능을 보인다. 액세스 지연에 대한 이점 외에도, 본 발명의 MAC 프로토콜은 차량이 적은 희박한 도로 환경에서 CCH의 보다 효율적인 활용을 제공할 수 있다.19 and 20

And

Mbps, the probability of successful delivery of non-secure packets

And average access latency

Respectively.

Mbps, the random selection scheme exhibits a higher probability of successful delivery than the MAC protocol of the present invention. However, with respect to the average access delay, the MAC protocol of the present invention shows better performance than the random selection technique.

Mbps, the MAC protocol and random selection scheme of the present invention

≪ / RTI > over 99%. Regarding access delays, the MAC protocol of the present invention outperforms the random selection scheme. In addition to the benefits of access delay, the MAC protocol of the present invention can provide more efficient utilization of the CCH in less sparse road environments where the vehicle is small.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100: vehicle communication device
110: Dual Transceiver
111: CCH transceiver
112: SCH transceiver
120: MAC layer queue manager

Claims (18)

A vehicle communication method for a wireless connection for a vehicle environment performed by a vehicle communication device,
Transmitting and receiving a safety packet through a control channel according to a contention-based distributed channel access method;
Transmitting a request for service packet through a control channel according to a contention-based distributed channel access method to reserve a service channel; And
Transmitting and receiving a data file based on a non-contention reservation through the reserved service channel;
Lt; / RTI >
Wherein the safety packet includes a state packet including information on a state of the vehicle and an emergency packet including an advance information on an accident situation. The method according to claim 1,
The transmitting and receiving of the secure packet includes:
The method comprising: confirming whether the transmitted safety packet is transmitted according to whether or not an acknowledgment message for the transmitted safety packet is received, and, when receiving the response message, A method of communicating a vehicle for wireless connection. 3. The method of claim 2,
The transmitting and receiving of the secure packet includes:
If the response message is not received, retransmits the safety packet if the retransmission limit is not reached, and confirms transmission failure of the transmitted safety packet when the retransmission limit is reached. The method according to claim 1,
Wherein the step of reserving the service channel comprises:
And checks whether the service channel is reserved according to whether the response message to the transmitted service channel reservation packet is received. If the response message is received, the service channel is allocated from the sidewalk device and confirmed as a reservation of the service channel Vehicle communication method for wireless connection for vehicle environment. 5. The method of claim 4,
Wherein the step of reserving the service channel comprises:
And if the response message is not received, resends the service channel reservation packet if the retransmission limit is not reached, and confirms that the reservation of the service channel fails when the retransmission limit is reached. The method according to claim 1,
The transmitting and receiving of the data file comprises:
The method comprising the steps of: determining whether a service channel is allocated according to whether a service channel is reserved in the step of reserving the service channel; if the service channel is reserved, transmitting and receiving a data file through a reserved service channel A vehicle communication method for wireless connection. The method according to claim 6,
The transmitting and receiving of the data file comprises:
And if the reservation of the service channel fails, confirming that transmission / reception of the data file is unsuccessful. The method according to claim 1,
Wherein the secure packet and the service channel reservation packet are assigned to first and second access category queues, respectively, wherein the first access category is a vehicle for radio access for vehicle environment having a higher priority than the second access category queue Communication method. 9. The method of claim 8,
Wherein the first and second access category queues comprise:
And compete with each other in the control channel. A MAC layer for allocating an input safety packet and a service channel reservation packet to a first queue corresponding to a contention-based control channel and allocating an input data file to a second queue corresponding to a non- A queue manager;
A first transceiver configured to transmit and receive a secure packet through a control channel according to a contention-based distributed channel access method and transmit a service channel reservation packet through a control channel according to a contention-based distributed channel access method to reserve a service channel; And
A second transceiver for transmitting and receiving a data file based on a non-contention reservation through the reserved service channel;
Lt; / RTI >
Wherein the safety packet includes a state packet including information on a state of the vehicle and an emergency packet including advance information on an accident situation. 11. The method of claim 10,
The first transceiver comprising:
The method comprising: confirming whether the transmitted safety packet is transmitted according to whether or not an acknowledgment message for the transmitted safety packet is received, and, when receiving the response message, ≪ / RTI > 12. The method of claim 11,
The first transceiver comprising:
If the response message is not received, retransmits the safety packet if the retransmission limit is not reached, and confirms transmission failure of the transmitted safety packet upon reaching the retransmission limit. 11. The method of claim 10,
The first transceiver comprising:
And checks whether the service channel is reserved according to whether the response message to the transmitted service channel reservation packet is received. If the response message is received, the service channel is allocated from the sidewalk device and confirmed as a reservation of the service channel Vehicle communication device for wireless connection for vehicle environment. 14. The method of claim 13,
The first transceiver comprising:
Wherein the control unit retransmits the packet for the service channel reservation when the retransmission limit is not reached when the response message is not received and confirms the reservation failure of the service channel when the retransmission limit is reached. 11. The method of claim 10,
The second transceiver comprising:
The method comprising the steps of: determining whether a service channel is allocated according to whether a service channel is reserved in the step of reserving the service channel; if the service channel is reserved, transmitting and receiving a data file through a reserved service channel A vehicle communication device for wireless connection. 16. The method of claim 15,
The second transceiver comprising:
And when the reservation of the service channel fails, the transmission / reception of the data file is confirmed as a failure. 11. The method of claim 10,
Wherein the secure packet and the service channel reservation packet are assigned to first and second access category queues, respectively, wherein the first access category is a vehicle for radio access for vehicle environment having a higher priority than the second access category queue Communication device. 18. The method of claim 17,
Wherein the first and second access category queues comprise:
And wherein the control channel is configured to compete with each other in the control channel.

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