KR20200051473A - Method and apparatus for avoiding signal collision by enhanced distributed coordination access in wireless local access network - Google Patents

Abstract

The present invention relates to an operation method a first communication node for transmitting a message in a vehicle to everything (V2X) communication network which includes the steps of: receiving information on a time period including a plurality of transmission slots from a second communication node; selecting one transmission slot included in the time period based on a first index set based on information on the time period; and transmitting a message through the one transmission slot. The information on the time period may include information on the number of the transmission slots included in the time period.

Description

METHOD AND APPARATUS FOR AVOIDING SIGNAL COLLISION BY ENHANCED DISTRIBUTED COORDINATION ACCESS IN WIRELESS LOCAL ACCESS NETWORK}

The present invention relates to a method for transmitting a signal in a WLAN network, and more particularly, to a technique for avoiding collision between signals by performing enhanced distributed coordination access (EDCA) operation based on an index of transmission slots included in a time interval. It is about.

2. Description of the Related Art Recently, as the spread of mobile devices has expanded, wireless LAN technology capable of providing fast wireless Internet services to them has been spotlighted. Wireless LAN technology is a technology that enables mobile devices such as smart phones, smart pads, laptop computers, portable multimedia players, and embedded devices to access the Internet wirelessly based on wireless communication technology at a short distance.

2. Description of the Related Art Recently, as the spread of mobile devices has expanded, wireless LAN technology capable of providing fast wireless Internet services to them has been spotlighted. Wireless LAN technology is a technology that enables mobile devices such as smart phones, smart pads, laptop computers, portable multimedia players, and embedded devices to access the Internet wirelessly based on wireless communication technology at a short distance.

Since the initial wireless LAN technology used the 2.4 GHz frequency through the Institute of Electrical and Electronics Engineers (IEEE) 802.11, it has supported OFDM speeds of 1 to 2 Mbps through frequency hopping, spread spectrum, and infrared communication. (Orthogonal Frequency Division Multiplex) can be applied to support up to 54Mbps. In addition, in IEEE 802.11, quality of service (QoS) is improved, access point (AP) protocol compatibility, security enhancement, radio resource measurement, and wireless access vehicular for vehicle environments Various technology standards such as environment, fast roaming, mesh network, interworking with external network, and wireless network management are being put into practical use or development.

Among IEEE 802.11, IEEE 802.11b supports a communication speed of up to 11 Mbps while using the frequency of the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, used 5GHz bands instead of 2.4GHz bands to reduce the effect of interference compared to the frequencies of the fairly congested 2.4GHz bands, and uses OFDM technology to maximize the communication speed. Improved to 54Mbps. However, IEEE 802.11a has a shorter communication distance than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses a frequency of 2.4 GHz band to realize a communication speed of up to 54 Mbps, and has received considerable attention because it satisfies backward compatibility. Is in the upper hand.

And, there is IEEE 802.11n as a technical standard enacted to overcome the limitation on the communication speed, which has been pointed out as a vulnerability in the wireless LAN. IEEE 802.11n aims to increase the speed and reliability of the network and to extend the operating distance of the wireless network. More specifically, IEEE 802.11n supports high throughput (HT) of which the data processing speed is up to 540 Mbps or higher, and also uses multiple antennas at both ends of the transmitter and receiver to minimize transmission errors and optimize the data rate. It is based on MIMO (Multiple Inputs and Multiple Outputs) technology. In addition, this standard not only uses a coding scheme for transmitting multiple duplicate copies to increase data reliability, but also can use Orthogonal Frequency Division Multiplex (OFDM) to increase the speed.

As the spread of wireless LAN is activated and the applications using it are diversified, recently, there is a need for a new wireless LAN system to support a higher throughput (Very High Throughput, VHT) than the data processing speed supported by IEEE 802.11n. This is emerging. Among them, IEEE 802.11ac supports a wide bandwidth (80 MHz to 160 MHz) at a 5 GHz frequency. The IEEE 802.11ac standard is defined only in the 5 GHz band, but for backward compatibility with existing 2.4 GHz band products, the initial 11ac chipsets will also support operation in the 2.4 GHz band. At this time, 802.11ac supports a bandwidth from 2.4 GHz up to 40 MHz. Theoretically, according to this standard, the wireless LAN speed of multiple terminals is at least 1 Gbps, and the maximum single link speed is at least 500 Mbps. This is done by extending the concept of radio interfaces accepted by 802.11n, including wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high density modulation (up to 256 QAM). In addition, IEEE 802.11ad is a method of transmitting data using a 60 GHz band instead of the existing 2.5 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that provides a speed of up to 7 Gbps using beamforming technology, and is suitable for high bitrate video streaming such as large data or uncompressed HD video. However, the 60 GHz frequency band has a drawback that it is difficult to pass through an obstacle and can only be used between devices in a short distance.

The wireless LAN can use a wide frequency band. In order to use a wide frequency band, before transmitting data, it is checked whether there is a possible band for a certain period of time, and the frequency band is used by concatenating data according to whether a frequency band of an adjacent region is available. For example, if the 20MHz band is the main frequency band (main channel), then 20MHz is available, then 20MHz is unavailable, and then 20MHz is available, the data is transmitted with a total of 40MHz as the transmission band. Since only the contiguous frequency band is used as a data transmission band, there is a problem that it cannot be used even though there is an actual available frequency band. In addition, the conventional wireless access technology only supports one-to-one connection of one transmitting terminal and one receiving terminal in every transmission attempt within the same Basic Service Set (BSS), so it is inefficient because it does not reflect the connection environment of the terminals or the characteristics of the transmitted data. It has.

WAVE communication is a standard technology defined by IEEE 802.11p and IEEE 1609.x. In the media access control (MAC) layer of WAVE communication, DCF (distribution coordination function) based on carrier sensing medium access / collision avoidance (CSMA / CA) And EDCA (enhanced distributed channel access) is used to support quality of service (QoS). Each channel of the MAC layer may have four access categories (AC) with different EDCA parameters (AIFSN, Cwmin, Cwmax, TXOP) according to data characteristics. In general MAC structure, WAVE communication can support EDCA based on DCF.

However, unlike a typical WLAN communication environment, vehicles are nodes that move along a specific path called a road, and thus, in a region such as a city center and an intersection, a situation in which the density of vehicles increases significantly. V2X traffic may increase due to an increase in the density of a vehicle and a packet according to a V2X service, and a collision problem between radio signals may occur, thereby increasing channel congestion. As a result, packet loss and delay may occur, and it may be difficult to smoothly perform the V2X service.

An object of the present invention for solving the above problems is to perform an enhanced distributed coordination access (EDCA) operation on a transmission slot determined based on index information indicating each transmission slot, to avoid collision between signals. It is to provide a method of operation.

An operation method of a first communication node for transmitting a message in a vehicle to everything (V2X) communication network according to an embodiment of the present invention for achieving the above object is a plurality of transmission slots (transmission slot) from the second communication node Receiving information about a time period comprising: a; Selecting one transmission slot included in the time period based on a first index set based on the information on the time period; And transmitting a message through the one transmission slot, and the information on the time period includes information on the number of the plurality of transmission slots included in the time period.

Here, the number of the plurality of transmission slots included in the time period is at least one of the number of communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message, and the number of messages transmitted during the time period. It is characterized by being set on the basis of one.

Here, the step of receiving the information on the time period from the second communication node, receiving a wireless access for vehicle environment (WSA) service advertisement (WSA) including information on the time period through a control channel (CCH) It is characterized by.

Here, in the step of selecting one transmission slot included in the time period based on the first index, performing a carrier sense multiple access / collision avoidance (CSMA / CA) on a transmission slot indicated by the first index, The method further includes detecting whether there is a collision between messages in a transmission slot indicated by the first index.

Here, the step of selecting one transmission slot included in the time period based on the first index, if the collision is detected as a result of performing the CSMA / CA, resetting the second index excluding the first index Further comprising steps. Here, in the step of selecting one transmission slot included in the time period based on the first index, when the number of times of performing the operation of resetting the second index excluding the first index exceeds a preset threshold, The method further includes changing a channel access mode of the time period.

Here, the step of transmitting a message through the one transmission slot further includes the step of maintaining the first index of the one transmission slot when the message is transmitted through the one transmission slot.

Here, in the step of transmitting a message through the one transmission slot, if the one transmission slot is terminated before the transmission of the message is completed, the message is additionally transmitted through the transmission slot after the one transmission slot. It is characterized by transmitting.

A second communication node for transmitting a message in a vehicle to everything (V2X) communication network according to another embodiment of the present invention for achieving the above object includes a processor; A memory in which at least one instruction executed through the processor is stored; And at least one antenna that performs signal transmission and reception under the control of the processor, and the at least one command generates information on a transmission slot for giving a transmission opportunity to the first communication nodes. and; Generating information on a time period including a plurality of transmission slots based on the information on the transmission slots; And transmitting information on the time period to the first communication nodes, wherein the information on the time period includes information on the number of the plurality of transmission slots included in the time period. .

Here, the second communication node is a road side unit (RSU), and the first communication nodes are characterized by being on board units (OBU).

Here, the number of the plurality of transmission slots included in the time period, the number of first communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message transmitted by the first communication nodes, the It is characterized in that it is set based on at least one of the number of messages transmitted by the first communication nodes during the time period.

Here, the step of transmitting the information on the time period to the first communication node, a wireless access for vehicle environment (WSA) service advertisement (WSA) including information on the time period is transmitted through a control channel (CCH). It is characterized by.

A first communication node for transmitting a message in a vehicle to everything (V2X) communication network according to an embodiment of the present invention for achieving the above object includes a processor; A memory in which at least one instruction executed through the processor is stored; And at least one antenna performing signal transmission and reception under the control of the processor, wherein the at least one command receives information on a time period including a plurality of transmission slots from a second communication node, ; Selecting one transmission slot included in the time period based on a first index set based on the information on the time period; And it is executed to transmit a message through the one transmission slot, and the information on the time period is characterized in that it includes information on the number of the plurality of transmission slots included in the time period.

Here, the number of the plurality of transmission slots included in the time period is at least one of the number of communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message, and the number of messages transmitted during the time period. It is characterized by being set on the basis of one.

Here, the at least one command, when receiving information on the time period from the second communication node, WSA (wireless access for vehicle environment) including information on the time period through a control channel (CCH) service advertisement).

Here, the at least one command, in selecting one transmission slot included in the time period based on the first index, a carrier sense multiple access / collision (CSMA / CA) in a transmission slot indicated by the first index avoidance) to detect whether there is a collision between messages in a transmission slot indicated by the first index.

Here, the at least one command, in selecting one transmission slot included in the time period based on the first index, when the CSMA / CA is performed, detects the collision, excludes the first index It is further executed to reset the second index.

Here, the at least one command, in selecting one transmission slot included in the time period based on the first index, the number of times of performing the operation of resetting the second index excluding the first index is preset When the threshold is exceeded, it is further executed to change the channel access mode of the time period.

Here, the at least one command is further executed to maintain the first index of the one transmission slot when the message is transmitted through the one transmission slot when transmitting the message through the one transmission slot. do.

Here, the at least one command, in transmitting a message through the one transmission slot, if the one transmission slot is terminated before the transmission of the message is completed, the transmission slot after the one transmission slot It is characterized by further transmitting the message through.

According to the present invention, by selecting one transmission slot among transmission slots included in a sync interval, an on board unit (OBU) attempting channel access based on an index, V2X (vehicle to everything) It has the effect of preventing collisions between messages generated by OBUs in the communication network.

1 is a conceptual diagram showing a first embodiment of a wireless LAN system.
2 is a block diagram showing a first embodiment of a communication node constituting a wireless LAN system.
3 is a flowchart illustrating a procedure for connecting stations in a wireless LAN system.
4 is a timing diagram showing a first embodiment of an operation method of a communication node based on EDCA.
5 is a conceptual diagram illustrating an embodiment of a sync interval in WAVE communication.
6 is a conceptual diagram illustrating an embodiment of a channel access mode of a communication node.
7 is a conceptual diagram illustrating an embodiment of a channel interval including a plurality of transmission slots (transmission slots) in WAVE communication.
8 is a flowchart illustrating an embodiment of a CSMA / CA-based message transmission method in a wireless LAN system.
9 is a flowchart illustrating an embodiment of a method for a communication node of a wireless LAN system to determine a transmission slot for transmitting a message.
10 is a conceptual diagram illustrating a first embodiment of a CSMA / CA-based message transmission result in a wireless LAN system.
11 is a conceptual diagram illustrating a second embodiment of a CSMA / CA-based message transmission result in a wireless LAN system.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component. The term and / or includes a combination of a plurality of related described items or any one of a plurality of related described items.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but there may be other components in between. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the overall understanding in describing the present invention, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

A communication system to which embodiments according to the present invention are applied (for example, a wireless local area network (WLAN) system) will be described. The communication system to which the embodiments according to the present invention are applied is not limited to the contents described below, and the embodiments according to the present invention can be applied to various communication systems. Here, the communication system may be used in the same sense as the communication network.

1 is a conceptual diagram showing a first embodiment of a wireless LAN system.

Referring to FIG. 1, a wireless LAN system may include at least one basic service set (BSS). BSS means a set of stations (STA1, STA2 (AP1), STA3, STA4, STA5 (AP2), STA6, STA7, STA8) that can successfully communicate with each other by synchronizing, and not a concept of a specific area . In the embodiments below, a station performing the function of an access point may be referred to as an "access point (AP)", and a station not performing the function of an access point may be a "non-AP station" or a "station. It may be referred to as ".

The BSS can be divided into an infrastructure BSS (Infrastructure BSS) and an independent BSS (IBSS). Here, BSS1 and BSS2 may mean infrastructure BSS, and BSS3 may mean IBSS. The BSS1 is a first station STA1, a first access point providing a distribution service (STA2 (AP1)), and a distribution connecting a plurality of access points (STA2 (AP1), STA5 (AP2)) It may include a distribution system (DS). In BSS1, the first access point STA2 (AP1) may manage the first station STA1.

BSS2 includes a third station (STA3), a fourth station (STA4), a second access point (STA5 (AP2)) that provides distribution services, and multiple access points (STA2 (AP1), STA5 (AP2)). And a connecting distribution system (DS). In BSS2, the second access point STA5 (AP2) may manage the third station STA3 and the fourth station STA4.

BSS3 may refer to IBSS operating in an ad-hoc mode. In BSS3, an access point that is a centralized management entity may not exist. That is, in BSS3, stations STA6, STA7, and STA8 may be managed in a distributed manner. In BSS3, all stations STA6, STA7, and STA8 may refer to a mobile station, and are not allowed access to the distribution system DS, thus forming a self-contained network.

The access points STA2 (AP1) and STA5 (AP2) may provide access to the distributed system DS through a wireless medium for the stations STA1, STA3, and STA4 coupled to them. Communication between stations (STA1, STA3, STA4) in BSS1 or BSS2 is generally performed through an access point (STA2 (AP1), STA5 (AP2)), but when a direct link is established, the stations ( Direct communication between STA1, STA3, and STA4) is possible.

A plurality of infrastructure BSSs can be interconnected through a distribution system (DS). A plurality of BSSs connected through a distribution system (DS) are called an extended service set (ESS). Communication nodes included in the ESS (STA1, STA2 (AP1), STA3, STA4, STA5 (AP2)) can communicate with each other, any station (STA1, STA3, STA4) in the same ESS without interruption while communicating You can move from one BSS to another.

The distribution system (DS) is a mechanism for one access point to communicate with another access point, whereby the access point transmits a frame for stations coupled to the BSS it manages or moves to another BSS. Frames can be sent for any station. In addition, the access point can transmit and receive frames with an external network, such as a wired network. Such a distribution system (DS) is not necessarily a network, and if it can provide a predetermined distribution service defined in the IEEE 802.11 standard, there is no limitation on its form. For example, the distribution system may be a wireless network, such as a mesh network, or a physical structure that connects access points to each other. Communication nodes included in the WLAN system (STA1, STA2 (AP1), STA3, STA4, STA5 (AP2), STA6, STA7, STA8) may be configured as follows.

2 is a block diagram showing a first embodiment of a communication node constituting a wireless LAN system.

Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to a network to perform communication. The transceiver 230 may be referred to as a transceiver, a radio frequency (RF) unit, an RF module, or the like. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, and the like. Each of the components included in the communication node 200 may be connected by a bus 270 to communicate with each other.

However, each component included in the communication node 200 may be connected through a separate interface or a separate bus centered on the processor 210, not the common bus 270. For example, the processor 210 may be connected to at least one of the memory 220, the transceiver 230, the input interface device 240, the output interface device 250, and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may be configured as at least one of read only memory (ROM) and random access memory (RAM).

Meanwhile, in the wireless LAN system, the connection procedure may be performed as follows.

3 is a flowchart illustrating a procedure for connecting stations in a wireless LAN system.

Referring to FIG. 3, the connection procedure of the station (STA) in the infrastructure BSS is largely a step of detecting an access point (probe step), an authentication step with the detected access point (AP), and authentication It may be divided into an association step (association step) with the access point (AP) that performed the procedure.

The station STA may first detect neighboring access points (APs) using a passive scanning method or an active scanning method. When using the passive scanning method, the station STA may detect neighboring access points APs by overhearing the beacon transmitted by the access points APs. When using the active scanning method, the STA may transmit a probe request frame and receive a probe response frame that is a response to the probe request frame from access points APs. By doing so, it is possible to detect neighboring access points (APs).

When neighboring access points (APs) are detected, the station (STA) may perform an authentication step with the detected access point (AP). In this case, the station STA may perform an authentication step with a plurality of access points APs. The authentication algorithm according to the IEEE 802.11 standard may be divided into an open system algorithm exchanging two authentication frames, a shared key algorithm exchanging four authentication frames, and the like.

The station (STA) may transmit an authentication request frame based on an authentication algorithm according to the IEEE 802.11 standard, and an authentication response frame that is a response to the authentication request frame from the access point (AP). By receiving, authentication with the access point (AP) can be completed.

When the authentication with the access point (AP) is completed, the station (STA) may perform a connection step with the access point (AP). In this case, the station STA may select one of the access points APs that have performed the authentication step with itself, and may perform a connection step with the selected access point AP. That is, the station STA may transmit an association request frame to the selected access point AP, and transmit an association response frame that is a response to the connection request frame from the selected access point AP. By receiving, the connection with the selected access point (AP) can be completed.

On the other hand, communication nodes (for example, access points, stations, etc.) belonging to a wireless LAN system include PCF (point coordination function), HCF (hybrid coordination function), HCCA (HCF controlled channel access), DCF (distributed coordination function), A frame transmission / reception operation may be performed based on EDCA (enhanced distributed channel access).

In a WLAN system, frames may be classified into management frames, control frames, and data frames. The management frame includes an association request frame, a connection response frame, a reassociation request frame, a reconnection response frame, a probe request frame, a probe response frame, a beacon frame, and a connection. It may include a disassociation frame, an authentication frame, a deauthentication frame, an action frame, and the like.

The control frame includes an acknowledgment (ACK) frame, a block ACK request (BAR) frame, a block ACK (BA) frame, a power saving (PS) -Poll frame, a request to send (RTS) frame, and a clear to send (CTS) frame. It can contain. Data frames may be classified into quality of service (QoS) data frames and non-QoS (non-QoS) data frames. The QoS data frame may indicate a data frame that requires transmission according to QoS, and the non-QoS data frame may indicate a data frame that does not require transmission according to QoS.

Meanwhile, in a wireless LAN system, a communication node (eg, access point, station) may operate based on EDCA.

4 is a timing diagram showing a first embodiment of an operation method of a communication node based on EDCA.

Referring to FIG. 4, a communication node that wants to transmit a control frame (or management frame) monitors a channel state during a predetermined period (eg, short interframe space (SIFS), PCF IFS (PIFS)). Control frame (when a channel state is determined to be an idle state during an operation (for example, a carrier sensing operation) and a predetermined period (for example, SIFS, PIFS) Alternatively, a management frame) may be transmitted. For example, the communication node may transmit an ACK frame, BA frame, CTS frame, etc. when the channel state is determined to be idle during SIFS. In addition, the communication node may transmit a beacon frame or the like when the channel state is determined to be idle during PIFS. On the other hand, when the channel state is determined to be busy during a predetermined period (eg, SIFS, PIFS), the communication node may not transmit a control frame (or management frame). Here, the carrier sensing operation may indicate a clear channel assessment (CCA) operation.

A communication node that wants to transmit a non-QoS data frame may perform a channel state monitoring operation (eg, carrier sensing operation) during DIFS (DCF IFS), and when the channel state is determined to be idle during DIFS A random backoff procedure can be performed. For example, the communication node may select a backoff value (eg, a backoff counter) within a contention window according to a random backoff procedure, and an interval corresponding to the selected backoff value (hereinafter “back”) During the off period), a channel state monitoring operation (eg, a carrier sensing operation) may be performed. The communication node may transmit a non-QoS data frame when the channel state is determined to be idle during the backoff period.

A communication node that wants to transmit a QoS data frame can perform a channel state monitoring operation (for example, a carrier sensing operation) during AIFS (arbitration IFS), and random back when the channel state is determined to be idle during AIFS. The off procedure can be performed. AIFS may be set according to an access category (AC) of a data unit (for example, a protocol data unit (PDU)) included in a QoS data frame. AC of the data unit may be as shown in Table 1 below.

AC_BK may indicate background data, AC_BE may indicate data transmitted in a best effort method, AC_VI may indicate video data, and AC_VO may be a voice ( voice) can indicate data. For example, the length of AIFS for QoS data frames corresponding to AC_VO and AC_VI, respectively, may be set equal to the length of DIFS. The length of AIFS for QoS data frames corresponding to AC_BE and AC_BK may be set longer than the length of DIFS. Here, the length of AIFS for the QoS data frame corresponding to AC_BK may be set longer than the length of AIFS for the QoS data frame corresponding to AC_BE.

In the random backoff procedure, the communication node may select a backoff value (eg, backoff counter) within the contention window according to AC of the QoS data frame. The competition window according to AC may be as shown in Table 2 below. CW _min may indicate the minimum value of the contention window, CW _max may indicate the maximum value of the contention window, and each of the minimum and maximum values of the contention window may be represented by the number of slots.

The communication node may perform a channel state monitoring operation (eg, a carrier sensing operation) during the backoff period, and transmit a QoS data frame when the channel state is determined to be idle during the backoff period.

Next, WLAN multi-channel operation methods in a communication system will be described. Even when a method (for example, transmission or reception of a signal) performed in the first communication node among the communication nodes is described, the corresponding second communication node corresponds to a method performed in the first communication node (eg For example, the signal may be received or transmitted. That is, when the operation of the terminal is described, the corresponding base station may perform an operation corresponding to the operation of the terminal. Conversely, when the operation of the base station is described, the corresponding terminal may perform an operation corresponding to the operation of the base station.

In the following, a wireless communication network to which embodiments according to the present invention are applied will be described. The wireless communication network to which the embodiments according to the present invention are applied is not limited to the contents described below, and the embodiments according to the present invention can be applied to various wireless communication networks.

5 is a conceptual diagram illustrating an embodiment of a sync interval in WAVE communication.

Referring to FIG. 5, communication nodes using WAVE communication have a mechanism to access one or more channels in a specific time period. For example, the communication node may access one of a control channel (CCH) or a service channel (SCH). The communication node can access by changing the CCH and SCH. The channel operation method according to the change access mode may be operated based on a sync interval, which is a time period synchronized with the standard time used in WAVE communication.

One sync interval may include a CCH interval capable of transmitting and receiving signals through CCH and a SCH interval capable of transmitting and receiving signals through SCH. During the CCH interval, communication nodes can send and receive messages over the CCH. The communication node participating in the application-service may switch the access target channel to the SCH during the SCH interval. During the SCH interval, the communication node can transmit and receive messages with other communication nodes belonging to the V2X communication network through the SCH. Each of the CCH interval and the SCH interval may include a guard interval. Each interval can start with a guard interval. The guard interval may start at each control channel (CCH) interval and service channel (SCH) interval. In the guard interval, the communication node can switch channels and secure synchronization. In the guard interval, a communication node switching a channel may not receive a packet.

As defined in IEEE 1609.4, the CCH interval may be 50 ms, and the service channel (SCH) interval may be 50 ms. In addition, the guard interval included in each interval (CCH interval or SCH interval) may be 4 ms. In each interval (CCH interval or SCH interval), a time during which a communication node can use a channel may be 46 ms, which is a time excluding the guard interval. When the channel access mode is the change access mode, each communication node can synchronize the channel interval and sink interval by standard time, such as universal time coordinated (UTC). The communication node may synchronize the channel interval and the sync interval for each pulse per second (PPS) interval based on UTC.

6 is a conceptual diagram illustrating an embodiment of a channel access mode of a communication node.

Referring to FIG. 6, different MAC layers in one physical layer may divide time to alternately use CCH and different channel access modes. The channel access mode of the communication node of FIG. 7 may be divided into a), b) continuous mode, c) altering mode, d) extended mode, and e) immediate mode.

The continuous mode may be a mode in which each communication node operates regardless of time division criteria such as the time slot / CCH interval / SCH interval of FIG. 6. When the channel access mode is the continuous mode, the communication node can continuously receive the operation information of the channel through the designated CCH or SCH. In addition, the communication node can transmit and receive messages with other communication nodes in the V2X communication system.

When the channel access mode is the change mode, each communication node can receive the operation information of the channel during the CCH interval. In addition, when the channel access mode is a change mode, each communication node can perform a negotiation procedure for transmitting and receiving messages with other communication nodes of the V2X communication system during the CCH interval. When the channel access mode is a change mode, each communication node can transmit and receive a message between a service provider and a user during a SCH interval. When the channel access mode is the change mode, the communication node can alternately communicate through the CCH and SCH during the set CCH interval and SCH interval.

When the channel access mode is the extended mode, the communication node can change the CCH interval and the SCH interval as in the change mode. However, the service / information exchange of the SCH interval may be performed also in the CCH interval. When the channel access mode is the extended mode, the communication node may transmit and receive control information during the CCH interval. In addition, when the communication node enters the SCH interval, the SCH interval may be maintained until message transmission and reception is finished.

When the channel access mode is the immediate mode, the communication node can transmit and receive messages to and from other communication nodes in the V2X communication network as in the change mode or the extended mode. However, if the negotiation for information exchange is completed during the CCH interval, the 있다 communication node may switch the channel to the designated SCH directly instead of waiting for the end of the CCH interval to transmit and receive a message.

7 is a conceptual diagram illustrating an embodiment of a channel interval including a plurality of transmission slots (transmission slots) in WAVE communication.

Referring to FIG. 7, the channel interval (CCH interval or SCH interval) may include a transmission opportunity interval, which is a section excluding the guard interval. The transmission opportunity period may include a plurality of transmission slots. According to the embodiment of FIG. 7, the transmission opportunity period may include 15 transmission slots.

In each transmission slot, the communication node performs channel access. The communication node may select any transmission slot included in the transmission section. Each transmission slot can be indicated by a slot index. The communication node may select any number of indexes of available transmission slots included in the transmission opportunity period. For example, the communication node can select any number from 1 to 15.

The communication node may perform channel access in a transmission slot having a random number selected as a slot index. All terminals in the communication network can perform synchronization at the guard interval and simultaneously check the start time of the transmission slot. Therefore, communication nodes of the communication network can attempt to access the channel at the same time. When the channel sensed by the communication node is in the idle state, simply transmitting a signal after the DIFS has passed may cause a collision with a signal transmitted by another communication node. Therefore, terminals attempting to transmit at the start time of the transmission slot can perform random backoff after DIFS and transmit data. Communication nodes that transmit signals after the start of the transmission slot can operate according to the idle state of the channel, such as accessing a wireless LAN channel.

The operation of the present embodiment can be applied to a case in which data generated during use by switching to another channel needs to be switched and transmitted to this channel. For example, when data to be transmitted through the CCH is generated during the time of operation with the SCH interval, the communication node may switch to the CCH interval and transmit the data at the time of operation. That is, if the time when the communication node generates data corresponds to the transmission slot number 12 of the SCH interval, the communication node may perform transmission in the transmission slot 12 after switching to the CCH interval.

8 is a flowchart illustrating an embodiment of a CSMA / CA-based message transmission method in a wireless LAN system.

Referring to FIG. 8, the V2X communication system may include a road side unit (RSU) 810 and an on board unit (OBU) 820. Although only one OBU 820 is illustrated in FIG. 8, the V2X communication system may further include a plurality of OBUs.

The RSU 810 may generate information on transmission slots included in the sync interval (S810). For example, the RSU 810 may set the number of transmission slots included in the sync interval in S810. First, the size of each transmission slot for transmitting a message may be set according to Equation 1 based on the OFDM PHY parameter.

As defined in IEEE 1609.4, the CCH interval and the SCH interval may be 50 ms, respectively, and the guard interval may be 4 ms. Therefore, the time time for actually transmitting a message may be 46 ms. The number of transmission slots included in the sync interval may be calculated by Equation 2 below.

는 AC에 따른 AIFS 값일 수 있고,

은 AC에 따른 백오프 타임의 최대 값을 지시할 수 있다. AC에 따른

및

은 아래의 표 3에 따라 정의될 수 있다. In Equation 2

May be an AIFS value according to AC,

Can indicate the maximum value of the backoff time according to AC. According to AC

And

Can be defined according to Table 3 below.

, 각각의 통신 노드들이 송수신하는 메시지의 전송율(Tx rate) 및 통신 노드들이 송수신하는 메시지의 수

에 관한 정보를 추가로 반영하여 싱크 인터벌에 포함되는 전송 슬롯의 개수를 최적화할 수 있다. Referring to Equations 1 to 2, the RSU 810 may determine the number of transmission slots included in the sync interval based on the OFDM parameter and the EDCA parameter. In addition, the RSU 810 may further reflect characteristics of the V2X network to determine the optimal number of transmission slots included in the sync interval. For example, the RSU 810 is the number of OBUs located within a preset range from the RSU 810.

, Tx rate of messages transmitted and received by each communication node and number of messages transmitted and received by communication nodes

The number of transmission slots included in the sync interval may be optimized by additionally reflecting the information on.

The RSU 810 may transmit a message including information on transmission slots included in the generated sync interval to the OBU 820 (S820). The RSU 810 may transmit a message including information on transmission slots to the OBU 820 through a control channel (CCH) included in the sync interval (820). The message including information on the transmission slots may be a message in the form of a wireless access for vehicle environment (WSA) service advertisement (WSA). The OBU 820 may receive a message including information on transmission slots included in the sync interval from the RSU 810 (S820). The OBU 820 may obtain information on transmission slots included in the sync interval from the received message.

The OBU 820 may set one index based on the information on the transmission slots included in the obtained sync interval (S830). For example, the OBU 820 may acquire information N regarding the number of transmission slots included in the sync interval. In addition, the OBU 820 may set an integer of 1 or more and N or less as an index. One index set by the OBU 820 may indicate one of the transport slots included in the sync interval, and the OBU 820 may attempt channel access through the transport slot indicated by the index. have.

The OBU 820 may determine one transmission slot to transmit a message among the transmission slots included in the sync interval based on one set index. The operation of determining one transmission slot by the OBU 820 may include the following operations.

9 is a flowchart illustrating an embodiment of a method for a communication node of a wireless LAN system to determine a transmission slot for transmitting a message.

Referring to FIG. 9, the OBU 820 may set one index in S830, and may perform DCF in a transmission slot indicated by one set index. Specifically, the OBU 820 may perform CSMA / CA in a transmission slot indicated by one index set in S830 (S841).

The OBU 820 may determine whether there is a collision between messages in a transmission slot indicated by the index based on the CSMA / CA result in S841 (S842). The OBU 820 may determine whether to change the index based on whether a collision occurs in the transmission slot. For example, when there is no collision between messages in the transmission slot indicated by the index, the OBU 820 may maintain the index determined in S830 (S843-1).

On the other hand, when a collision occurs between messages in a transmission slot indicated by the index, the OBU 820 may determine that another communication node transmits the message through the transmission slot. In addition, the OBU 820 may reset the index determined in S830 (S843-2). For example, the OBU 820 may reset an integer of 1 or more and N or less to an index. However, the OBU 820 performing the index reset operation may reset the index among values excluding the index value set in S830 (S843-2).

The OBU 820 may measure the number of index reset operations. In addition, the OBU 820 may compare the number of index reset operations with a preset threshold (S844). The OBU 820 may determine whether to change the channel access mode based on the comparison result in S844. The channel access mode may be one of continuous mode, change mode, extended mode and immediate mode, as shown in FIG. 7. For example, the channel access mode can be set to a change mode.

In S844, the OBU 820, which determines that the number of preset index reset operations is small, may maintain the channel access mode. In addition, in S844, the OBU 820, which determines that the number of index reset operations is greater than the preset number, may change the channel access mode. For example, the OBU 820 may change the channel access mode from the change mode to the immediate mode.

When the index reset and the channel access mode change are completed, the OBU 820 may perform CSMA / CA operation in the transmission slot indicated by the reset index. If a collision is not detected in a transmission slot indicated by the reset index, the OBU 820 may maintain the reset index. On the other hand, if a collision is detected in a transmission slot indicated by the reset index, the OBU 820 may reset the index.

Referring to FIG. 8 again, the OBU 820 may select one transmission slot based on the index information set in S830 (S840). The index set in S830 and the index of one selected transmission slot may be the same, but may be different. The OBU 820 may transmit a message to other communication nodes in the V2X communication network through one transmission slot determined in S840 (S850).

10 is a conceptual diagram illustrating a first embodiment of a CSMA / CA-based message transmission result in a wireless LAN system.

Referring to FIG. 10, the sync interval may include a first time slot and a second time slot. The first time slot may include a CCH interval, and the second time slot may include a SCH interval. The first time slot may include a plurality of transmission slots, and the second time slot may also include a plurality of transmission slots. An index may be set in each of the plurality of transmission slots included in the second time slot.

The V2X communication system may include an RSU and an OBU, and the RSU may transmit a WSA including information on the transmission slots of the sync interval in the first time slot to the OBU through the CCH. The OBU may determine one index n as illustrated in FIGS. 9 to 10. Specifically, the OBU may set a range of an index based on information on transmission slots of a sync interval (for example, information on the number of transmission slots, etc.), and one integer among the integers included in the set range of the index. Can be determined by index n.

The OBU may attempt to transmit a message through one transmission slot indicated by index n determined among transmission slots included in the second time slot of the sync interval. The OBU may perform a CSMA / CA operation to prevent collision with a message transmitted by another OBU in the n-th transmission slot. If a collision does not occur as a result of CSMA / CA, the OBU may transmit a message through the n th transmission slot.

According to FIG. 10, when a plurality of OBUs attempt to access a channel in a second time slot, each OBU may attempt to access the channel based on a randomly determined index. Accordingly, the CSMA / CA-based message transmission method according to an embodiment of the present invention can reduce contention for channel access between OBUs.

11 is a conceptual diagram illustrating a second embodiment of a CSMA / CA-based message transmission result in a V2X communication system.

Referring to FIG. 11, different OBUs may transmit a message through transmission slots included in one time slot (second time slot of FIG. 11). Each OBU may set an arbitrary index. For example, the first OBU may set n to an arbitrary index, the second OBU may set n to an arbitrary index, and the third OBU may set n + 1 to an arbitrary index.

Each OBU can select a transmission slot to transmit a message based on the set index. For example, the first OBU may perform a CSMA / CA operation on the nth transmission slot, and the second OBU may perform a CSMA / CA operation on the nth transmission slot. The EDCA parameter of the first OBU and the EDCA parameter of the second OBU may be set differently from each other. Accordingly, the message transmission priority between the first OBU and the second OBU may be different from each other. Referring to FIG. 12, the first OBU may have a higher priority than the second OBU, and thus, the first OBU may transmit a message through the n th transmission slot.

The second OBU may perform CSMA / CA in the n-th transmission slot. If the nth transmission slot remains idle during AIFS after the message transmission of the first OBU is completed, the second OBU may transmit a message through the nth transmission slot. However, the second OBU may transmit a message using only a part of the n-th transmission slot, and thus the second OBU may transmit only a part of the message through the n-th transmission slot. If the n-th transmission slot is ended before transmission of the message is completed, the second OBU may additionally transmit the message through the transmission slot after the n-th transmission slot. For example, the second OBU may transmit a part of the message through the nth transmission slot, and may transmit the remaining part of the message through the n + 1th transmission slot.

The third OBU may perform CSMA / CA in the n + 1 th transmission slot. When the second OBU transmits a message through the n + 1 th transmission slot, the third OBU may not detect a collision in the n + 1 th transmission slot and perform a signal transmission operation. If the n + 1 th transmission slot remains idle during AIFS after the second OBU message transmission is completed, the third OBU may transmit a message through the n + 1 th transmission slot. The third OBU may transmit a message using only some of the n + 1 th transmission slots.

Alternatively, the third OBU may transmit only part of the message through the n + 1 th transmission slot. If the n th transmission slot is ended before the transmission of the message is completed, the third OBU may transmit a part of the message through the n + 1 th transmission slot, and the remaining part of the message through the n + 2 th transmission slot I can send it.

The methods according to the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer readable medium. Computer-readable media may include program instructions, data files, data structures, or the like alone or in combination. The program instructions recorded on the computer-readable medium may be specially designed and configured for the present invention or may be known and usable by those skilled in computer software.

Examples of computer-readable media include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language codes that can be executed by a computer using an interpreter, etc., as well as machine language codes such as those produced by a compiler. The above-described hardware device may be configured to operate with at least one software module to perform the operation of the present invention, and vice versa.

Although described with reference to the above embodiments, those skilled in the art understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. Will be able to.

Claims (20)

As a method of operation of the first communication node for transmitting a message in a vehicle to everything (V2X) communication network,
Receiving information on a time period including a plurality of transmission slots from a second communication node;
Selecting one transmission slot included in the time period based on a first index set based on the information on the time period; And
And transmitting a message through the one transmission slot.
Information about the time period,
And information about the number of the plurality of transmission slots included in the time period. The method according to claim 1,
The number of the plurality of transmission slots included in the time period,
Operation of the first communication node, characterized in that it is set based on at least one of the number of communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message, and the number of messages transmitted during the time period. Way. The method according to claim 1,
The step of receiving information about the time period from the second communication node,
A method of operating a first communication node, characterized by receiving a wireless access for vehicle environment (WSA) service advertisement (WSA) including information on the time period through a control channel (CCH). The method according to claim 1,
The step of selecting one transmission slot included in the time period based on the first index,
And performing a carrier sense multiple access / collision avoidance (CSMA / CA) on the transmission slot indicated by the first index to detect whether there is a collision between messages in the transmission slot indicated by the first index. 1 Method of operation of communication node. The method according to claim 4,
The step of selecting one transmission slot included in the time period based on the first index,
If the collision is detected as a result of performing the CSMA / CA, further comprising resetting the second index excluding the first index, the operation method of the first communication node. The method according to claim 5,
The step of selecting one transmission slot included in the time period based on the first index,
If the number of times of performing the operation of resetting the second index excluding the first index exceeds a preset threshold, further comprising changing a channel access mode of the time period. How nodes work. The method according to claim 1,
Transmitting a message through the one transmission slot,
And when the message is transmitted through the one transmission slot, maintaining the first index of the one transmission slot. The method according to claim 1,
Transmitting a message through the one transmission slot,
If the one transmission slot is terminated before the transmission of the message is completed, the method of operating the first communication node, characterized in that further transmitting the message through the transmission slot after the one transmission slot. As a second communication node for transmitting a message in a vehicle to everything (V2X) communication network,
A processor;
A memory in which at least one instruction executed through the processor is stored; And
It includes at least one antenna for performing signal transmission and reception according to the control of the processor,
The at least one command,
Generating information about a transmission slot for giving a transmission opportunity to the first communication nodes;
Generating information on a time period including a plurality of transmission slots based on the information on the transmission slots; And
And transmitting information regarding the time period to the first communication nodes,
Information about the time period,
And a second communication node comprising information on the number of the plurality of transmission slots included in the time period. The method according to claim 9,
The second communication node is a road side unit (RSU),
The first communication node is a second communication node, characterized in that on board unit (OBU). The method according to claim 9,
The number of the plurality of transmission slots included in the time period,
Among the number of first communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message transmitted by the first communication nodes, and the number of messages transmitted by the first communication nodes during the time period A second communication node, characterized in that it is set based on at least one. The method according to claim 9,
The step of transmitting information on the time period to the first communication nodes,
A second communication node, characterized by transmitting a wireless access for vehicle environment (WSA) service advertisement (WSA) including information on the time period through a control channel (CCH). As a first communication node for transmitting a message in a vehicle to everything (V2X) communication network,
A processor;
A memory in which at least one instruction executed through the processor is stored; And
It includes at least one antenna for performing signal transmission and reception according to the control of the processor,
The at least one command,
Receiving information on a time period including a plurality of transmission slots from a second communication node;
Selecting one transmission slot included in the time period based on a first index set based on the information on the time period; And
Is executed to transmit a message through the one transmission slot,
Information about the time period,
A first communication node comprising information on the number of the plurality of transmission slots included in the time period. The method according to claim 13,
The number of the plurality of transmission slots included in the time period,
The first communication node, characterized in that is set based on at least one of the number of communication nodes located within a predetermined distance from the second communication node, the data transmission rate of the message, and the number of messages transmitted during the time period. The method according to claim 13,
The at least one command,
In receiving information about the time period from the second communication node,
A first communication node that is executed to receive a wireless access for vehicle environment (WSA) service advertisement (WSA) including information on the time period through a control channel (CCH). The method according to claim 13,
The at least one command,
In selecting one transmission slot included in the time period based on the first index,
The first communication further performed to detect whether there is a collision between messages in the transmission slot indicated by the first index by performing carrier sense multiple access / collision avoidance (CSMA / CA) on the transmission slot indicated by the first index. Node. The method according to claim 16,
The at least one command,
In selecting one transmission slot included in the time period based on the first index,
As a result of performing the CSMA / CA, when the collision is detected, a first communication node further executed to reset a second index other than the first index. The method according to claim 17,
The at least one command,
In selecting one transmission slot included in the time period based on the first index,
A first communication node further executed to change a channel access mode of the time period when the number of times of performing the operation of resetting the second index excluding the first index exceeds a preset threshold. The method according to claim 13,
The at least one command,
In transmitting a message through the one transmission slot,
When the message is transmitted through the one transmission slot, the first communication node further executed to maintain the first index of the one transmission slot. The method according to claim 13,
The at least one command,
In transmitting a message through the one transmission slot,
If the one transmission slot is terminated before the transmission of the message is completed, the first communication node, characterized in that further transmitting the message through the transmission slot after the one transmission slot.

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