KR20080113569A - Method for transmitting data in vehicular environment - Google Patents

Abstract

A data communications method in vehicle environment is provided to reduce data service disturbance by data frame transmitted to the user deviating from a service area and to increase the efficiency of data transmission. A wireless access(WAVE) basic service set makes vehicle environment with user(S120). A data request is received from a user(S130). The data request includes on/off information of a WAVE mode. The request data includes transmission rate information about a channel. If there is no data transmitted to the user, ACK(acknowledgement) signal is transmitted.

Description

Method for transmitting data in vehicular environment

1 illustrates a wireless communication system in a vehicle environment.

2 is a flowchart illustrating a data transmission method in a vehicle environment according to an embodiment of the present invention.

3 illustrates a wireless access in vehicular environment (WAVE) declaration frame according to an embodiment of the present invention.

4 illustrates a WAVE poll frame according to an embodiment of the present invention.

5 is a flowchart illustrating a data transmission method in a vehicle environment according to another embodiment of the present invention.

6 is a flowchart illustrating a data transmission method in a vehicle environment according to another embodiment of the present invention.

The present invention relates to a data transmission method in a vehicle environment, and more particularly, to a data transmission method for smoothly providing a data service through efficient channel access in a vehicle moving at a high speed.

Wireless LANs in vehicles moving at high speeds have large channel variations and frequent hand-offs depending on network characteristics. In addition, a hidden node problem frequently occurs due to surrounding buildings or the like.

For example, if a mobile station connected to a fixed station moves to a vehicle, the vehicle may move at a high speed or a slow speed or sometimes stop, causing the channel condition to change as the vehicle speed increases or decreases. Done. The vehicle moving at a high speed enters the service coverage of one fixed station and then quickly exits to enter the service area of another fixed station, thereby making frequent hand-offs.

The channel access mechanism in such a vehicle environment uses enhanced distributed channel access (EDCA) based on competition. In the wireless LAN MAC protocol in a vehicle environment, MAC association and authentication processes are not provided. Thus, even if the mobile station leaves the service area of the fixed station, the fixed station may not be aware of it. In this case, the data signal transmitted to the mobile station out of the service area may result in disturbing the data service to the other mobile station, causing the quality of the data service to be degraded.

An object of the present invention is to provide a data transmission method for smoothly providing a data service through efficient channel access in a vehicle moving at a high speed.

The data transmission method in a vehicle environment according to an embodiment of the present invention comprises the steps of establishing a wireless service in a vehicular environment (WAVE) basic service set with a user, and data from the user. Receiving a request and sending data to the user.

According to another embodiment of the present invention, a method for transmitting data in a vehicle environment includes receiving a WAVE (wireless access in vehicular environments) declaration frame from a provider, forming a WAVE basic service set with the provider, and requesting a data request from the provider Transmitting and receiving data from the provider.

According to another embodiment of the present invention, a method of transmitting data in a vehicle environment of a provider includes transmitting a WAVE declaration frame, receiving a WAVE poll frame for the WAVE declaration frame from a user, and including the WAVE poll frame. Transmitting a first data signal to the user at a rate and a second data signal to a neighboring WAVE provider.

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

1 illustrates a wireless communication system in a vehicle environment.

Referring to FIG. 1, a wireless communication system in a vehicle environment includes at least one basic service set (BSS). The basic service set is a concept including a fixed station and a mobile station connected to the fixed station in the service area of the fixed station. When a wireless connection in a vehicle environment is called a wireless access in vehicular environment (WAVE), the basic service set may be referred to as a WAVES basic service set (WBSS).

The WBSS may include at least one onboard unit (OBU) that moves on a roadway and a roadside unit (RSU) disposed around the road. Alternatively, the WBSS may include two or more OBUs. The OBU can be located inside or outside the vehicle and can communicate with multiple RSUs or other OBUs. The OBU may be referred to in other terms, such as a mobile station (MS), a user terminal (UT), a user equipment (UE), a subscriber station (SS), and a wireless device. RSU is widely deployed in the vicinity of roads for data services such as voice and video. RSUs can communicate with multiple OBUs and other RSUs and are connected to wide area networks (WANs). RSU may be called in other terms, such as fixed station (FS), access point (AP), base station (BS), node-B (node-B), base transceiver system (BTS), etc. have.

As an embodiment of the WBSS may be made as WBSS 1 (110), WBSS 2 (120), WBSS 3 (130). WBSS 1 110 includes RSU 1, OBU 1 and OBU 2. In WBSS 1, RSU 1 may provide data services to OBU 1 and OBU 2. OBU 1 and OBU 2 may exchange data with each other via a direct link. Direct link is a method in which two mobile stations on the same network exchange data directly without passing through a fixed station. Alternatively, OBU 1 and OBU 2 may exchange data through RSU 1. That is, WBSS 1 110 is a direct link and a link via the RSU. WBSS 2 120 includes RSU 2 and OBU 3. RSU 2 provides data services to OBU 3. WBSS 3 130 includes OBU 4 and OBU 5. OBU 4 and OBU 5 exchange data with each other over a direct link.

The WAVE declaration frame is used to initialize the WBSS. In order to provide a wireless access service in a vehicle environment, a station for transmitting a WAVE declaration frame is called a provider, and a device for receiving a WAVE declaration frame is called a user. The WAVE declaration frame may be sent by the RSU or OBU. That is, the RSU may be a provider for sending a WAVE declaration frame, and the OBU may be a user for receiving it. Alternatively, the OBU can be a provider and the RSU can be a user. Alternatively, one OBU may be a provider and another OBU may be a user.

Hereinafter, a wireless connection (WAVE) and a data transmission method in a vehicle environment will be described. For convenience of explanation, it is assumed that the provider is an RSU and the user is an OBU. However, this is not a limitation and the provider and the user may be set to either RSU or OBU.

2 is a flowchart illustrating a data transmission method in a vehicle environment according to an embodiment of the present invention.

Referring to FIG. 2, the provider transmits a WAVE announcement frame (S110). The WAVE declaration frame may be transmitted in a broadcast or unicast manner. The WAVE declaration frame may include information on WAVE service.

The provider and the user are switched to the WAVE mode (S120). This means that the provider and the user form a WAVES Basic Service Set (WBSS). The provider and the user each include a station management unit (SME) and a MAC sublayer management entity (MLME). On the user side, upon receiving the WAVE declaration frame, the MLME sends the WAVE declaration information to the SME, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to the WAVE mode. On the provider side, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to the WAVE mode.

The user sends a data request to the provider (S130). The data request may be made as a WAVE-Poll frame. The WAVE Poll frame contains control information from WAVE. Control information in the WAVE includes information on the on / off of the WAVE mode, the transmission rate suitable for the user's channel state. The user can send a WAVE poll frame at a time when the channel condition is good. Alternatively, the user may transmit a WAVE poll frame at any time.

The provider transmits the data frame after a predetermined time interval (S140). At this time, the provider determines the transmission rate of the transmission signal according to the information on the transmission rate. The transmission rate of the transmission signal may be determined by a transmission power level for a data frame, a modulation and coding scheme, and the like. The data frame may be a data frame that is buffered for provision by the provider to the user. If there is no data frame to provide to the user, the provider transmits an ACK signal. Here, the predetermined time interval may be a short interframe space (SIFS). SIFS is a time interval between frames for providing priority to the radio medium access, and may have a fixed value according to a physical layer in consideration of the time from one frame transmission to another frame reception.

On the other hand, HCF Controlled Channel Access (HCCA), which uses contention-based Enhanced Distributed Channel Access (EDCA) and a contention-free channel approach using polling mechanisms, is provided by providers to provide data frames to multiple users. There is). The hybrid coordination function (HCF) includes a media access mechanism for improving the quality of service (QoS) of a wireless LAN and can transmit QoS data in both contention and contention-free cycles. EDCA and HCCA are also compatible with MAC using Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF is a contention-based asynchronous access method, and PCF is a polling-based synchronous access method that polls periodically so that all users can receive data frames. The provider may select a user from among users transmitting the WAVE poll frame in a contention-based or polling manner and transmit the data frame. Preferably, the provider transmits the data frame only to the user sending the WAVE poll frame in a polling manner. The provider selects a user who has a good channel condition among the users who transmit the WAVE poll frame and transmits the data frame.

When the user correctly receives the data frame, the user transmits an ACK signal (S145). After receiving the data frame may have a predetermined time interval to transmit the ACK signal. Here, the predetermined time interval may be SIFS.

If the provider transmits a data frame (S150) and the user does not receive the data frame correctly, the provider transmits a data re-request or a not-acknowledgement (NACK) signal (S160). The data re-request can be made with a WAVE poll frame. After the user receives the data frame, the time interval for transmitting the data re-request signal may be an extended inter frame space (EIFS). EIFS is used to give the receiving station enough time to send an ACK signal when there is an error in frame transmission.

The provider retransmits the data frame after a predetermined time interval (S170). Here, the predetermined time interval may be a short interframe space (SIFS).

In order to end transmission and reception of data frames between the provider and the user, the user transmits a WAVE mode off signal (S180). The WAVE mode off signal may consist of a WAVE poll frame. At this time, the WAVE mode information in the WAVE poll frame is designated as 'off'.

The provider and the user release the WAVE mode (S190).

As described above, the provider and the user are converted to the WAVE mode by using the WAVE declaration frame, but the process of transmitting the WAVE declaration frame may be omitted. If the process of transmitting the WAVE declaration frame is omitted, the WAVE poll frame serves as a WAVE declaration frame. That is, when the user transmits the WAVE poll frame to the provider, the user and the provider are converted to the WAVE mode to perform data transmission and reception.

In case of providing data on a contention basis for all users who receive the WAVE declaration frame, data transmission efficiency may be reduced because channel variation caused by a vehicle moving at a high speed may not be properly reflected. However, when data is provided on a polling basis for a user who transmits a WAVE poll frame, data transmission efficiency can be improved because a user having a good channel state can be selected to provide data.

3 illustrates a WAVE declaration frame according to an embodiment of the present invention. The WAVE declaration frame contains parameters for configuring WBSS.

Referring to FIG. 3, the WAVE declaration frame includes a category field, an action value field, and a WAVE announcement contents field.

The category field may indicate that the corresponding frame is a frame indicating WAVE (WAVE Service Information) and may have a length of one octet. The action value field is a field indicating an act of the WAVE declaration frame and may have a length of 2 octets. The WAVE Declaration Content field is a field representing information required for the WAVE mode. The WAVE declaration content field may have various lengths according to included information, and may be represented as Table 1 below as an example of included information.

Order Information Element One  Timestamp 2  Capability information 3  SSID 4  Supported Rates 5  EDCA parameter set

The timestamp field indicates a value for synchronizing stations of the same basic service set (BSS). The capability information field includes the number of subfields indicating the capability of the station. The SSID (service set identity) field indicates an ID of a broadcast service set. The supported rates field indicates the specific operating rate of an operational rate set that represents the data rates used for communication between stations in the BSS. An EDCA parameter set is a field indicating a parameter for traffic of user priority, and may be represented as Table 2 below as an example.

AC CWmin CWmax AIFSN TXOP Limit OFDM / CCK-OFDM PHY 0 aCWmin aCWmax 9 0 One (aCWmin + 1) / 2-1 aCWmin 6 0 2 (aCWmin + 1) / 4-1 (aCWmin + 1) / 2-1 3 0 3 (aCWmin + 1) / 4-1 (aCWmin + 1) / 2-1 2 0

By properly setting the value of the EDCA parameter, it is possible to optimize the network performance and obtain the transmission effect by the priority of traffic.

The WAVE declaration frame may be transmitted in a broadcast manner or a unicast manner. The station sending the WAVE declaration frame becomes the provider in WAVE mode, and the station receiving the WAVE declaration frame becomes the user in WAVE mode. However, when sending a WAVE declaration frame to send data from the RSU to the OBU, the neighboring RSU may receive the WAVE declaration frame and enter WAVE mode, in which case the neighboring RSU is another for hand-off. Can be a provider

4 illustrates a WAVE poll frame according to an embodiment of the present invention.

Referring to FIG. 4, a WAVE poll frame includes a frame control (FC) field, a WAVE mode control field, a basic service set identification (BSSID) field, a transmitter address (TA) field, and a frame check (FCS). sequence) field.

The frame control field indicates information such as protocol version, power management, data request, distribution system (DS), etc., and has a length of 2 octets. The WAVE mode control field indicates on / off and rate information of the WAVE mode and has a length of one octet.

The subfield of the WAVE mode control field includes a WAVE mode field and a PHY Tx Rate field. The WAVE mode field has a length of 1 bit. When the bit value is '1', data transmission is performed in the WAVE mode. When the bit value of the WAVE mode is '0', the WAVE mode is released. Alternatively, when the bit value of the WAVE mode field is '1', the WAVE mode may be released. When the bit value of the WAVE mode field is '0', the WAVE mode may be indicated. The rate field has a length of 4 bits and contains information about a rate appropriate for the state of a communication channel. In addition to calculating the appropriate data rate according to the measured channel quality, the data rate field includes the information, as well as signal-to-interference plus noise ratio (SINR), modulation and coding scheme (MCS) level, and reception. Various types of information, such as received signal strength indicators, may be included.

The BSSID field indicates an ID of a basic service set in WAVE and has a length of 6 octets. The TA field indicates the address of the transmitting end of the WAVE poll frame and has a length of 6 octets. The FCS field is a field for determining whether a frame is correctly transmitted and has a length of 4 octets. The FCS field includes 32 bits of cyclic redundancy code (CRC).

The provider sends data to the user upon receiving the WAVE poll frame. If the WAVE poll frame is not received from the user, the data is transmitted to another user who sends the WAVE poll frame without transmitting the data. When multiple users transmit WAVE poll frame at the same time, it is possible to check data rate information included in WAVE poll frame to allocate channel and transmit data to users with good transmission rate, thereby improving data transmission efficiency.

When an OBU that has been receiving data service by accessing one RSU enters the service area of a new RSU, it must disconnect from the previous RSU and receive data service from the new RSU. However, there is a case in which a contention-based access method does not immediately connect to a new RSU, which prevents data from being continuously serviced. In particular, when the OBU moves at high speed, the time given for handoff between the service area of one RSU and the service area of another RSU is shortened.

Hereinafter, a handoff method capable of continuously receiving data from WAVE will be described. The provider that transmits the current data to the user is called a serving provider, and the provider that is the target of the handoff is called an adjacency provider.

5 is a flowchart illustrating a data transmission method in a vehicle environment according to another embodiment of the present invention.

Referring to FIG. 5, the service provider transmits a WAVE declaration frame (S210). The WAVE declaration frame may be transmitted in a broadcast manner and may be received by the user and the neighbor provider.

The service provider, the neighbor provider and the user are switched to the WAVE mode (S220). That is, a service provider, a neighboring provider, and a user form a WAVE Basic Service Set (WBSS). On the user side, upon receiving the WAVE declaration frame, the MLME sends the WAVE declaration information to the SME, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to the WAVE mode. At each service provider and neighbor provider, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to WAVE mode.

The user sends a data request to the provider (S230). The data request may be made with a WAVE poll frame. The WAVE Poll frame contains information about the WAVE mode on / off and the appropriate bit rate for the channel. The process of transmitting a WAVE declaration frame (S210) may be omitted, in which case the WAVE poll frame serves as a WAVE declaration frame. That is, when a user transmits a WAVE poll frame to a service provider and a neighbor provider, the user, service provider, and neighbor provider are converted to the WAVE mode.

The service provider transmits a data frame to the user (S240). At this time, the service provider transmits the data frame after a predetermined time interval after receiving the WAVE poll frame. The predetermined time interval may be short interframe space (SIFS). Here, the service provider may select a user having a good channel state, that is, a high data rate, from among a plurality of users who have transmitted the WAVE poll frame, and transmit the data frame.

The service provider pre-forwards the data frame to be provided to the user in advance (S245). In order to continuously transmit data frames to the user when the user hands off to the service area of the neighbor provider, the data frame to be provided to the user is cached in advance to the neighbor provider. The data transmitted to the neighbor provider may be part of the data that the service provider will provide to the user.

For example, it is assumed that there are 10 data frames provided to the user by the service provider from the first frame to the tenth frame, and five data frames are transmitted to the neighboring provider. The data frame transmitted to the neighbor provider may be five data frames from the second frame to the sixth frame to be provided to the user except for the first frame transmitted to the user. The second to sixth frames are sequentially transmitted to neighboring providers. In order to reduce the data buffering burden of the neighbor provider, the number of data frames transmitted to the neighbor provider is limited. The limit of the number of data frames transmitted to the neighbor provider may be determined at a predetermined threshold or may be determined according to the data buffering environment of the neighbor provider.

When the user receives the data frame, the user transmits an ACK signal to the service provider (S250). In this case, a time interval between receiving a data frame and transmitting an ACK signal may be SIFS.

The service provider transmits a data frame of the next order to the user (S260), and the user who transmits the data frame transmits an ACK signal to the service provider (S270).

When the service provider transmits a data frame of the next order to the user, the service provider updates the data frame previously transmitted to the neighboring provider (S265). That is, the service provider transmits a seventh frame to the neighbor provider, and the neighbor provider discards the second frame and buffers the seventh frame according to a first in first out (FIFO) scheme. Therefore, the number of data frames buffered by the neighboring provider is maintained at five.

During transmission and reception of data frames between the service provider and the user, the user may move to the service area of the neighboring provider and the provider may be changed (S280). That is, the user receives data from a service provider and then data from a neighboring provider.

The user transmits a data request to the neighbor provider (S290). The data request may be made with a WAVE poll frame.

The neighbor provider transmits the buffered data frame to the user (S295). The time interval at which the neighbor provider transmits a data frame after receiving a data request from the user may be SIFS. The neighboring provider transmits a data frame to the user according to a first in, first out method, and the user receives a data frame consecutive to the data frame received from the service provider. For example, when the user receives the second frame from the service provider, the adjacent service provider transmits the third frame to the user while being buffered from the third frame to the seventh frame.

Since the service provider transmits the data frame to the neighbor provider in advance, it is possible to continuously provide the data frame even at the time of handoff of the fast moving user.

6 is a flowchart illustrating a data transmission method in a vehicle environment according to another embodiment of the present invention.

Referring to FIG. 6, the service provider transmits a WAVE declaration frame (S310). The WAVE declaration frame can be sent to the user in a unicast fashion.

The service provider and the user are switched to the WAVE mode (S315). That is, the service provider and the user make up the WBSS. On the user side, upon receiving the WAVE declaration frame, the MLME sends the WAVE declaration information to the SME, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to the WAVE mode. At the service provider, the SME makes a connection request to the MLME, and the MLME accepts the connection request and switches to the WAVE mode.

The user sends a data request to the service provider (S320). The data request may be made with a WAVE poll frame. The WAVE poll frame contains information about WAVE mode on / off and the appropriate bit rate for the channel. The process of transmitting the WAVE declaration frame (S310) may be omitted, in which case the WAVE poll frame serves as a WAVE declaration frame. That is, when the user sends the WAVE poll frame to the service provider, the user and the service provider are converted to the WAVE mode.

When the service provider receives the data request from the user, the service provider transmits a WAVE poll frame to the neighbor provider (S325).

The neighbor provider receiving the WAVE poll frame is converted to the WAVE mode (S330). That is, the neighbor provider is included in the service provider and the user's WBSS.

The service provider transmits a data frame to the user (S340). At this time, the service provider transmits the data frame after a predetermined time interval after receiving the WAVE poll frame. The certain time interval may be SIFS.

The service provider pre-forwards the data frame to be provided to the user in advance (S345). The data transmitted to the neighbor provider may be part of the data that the service provider will provide to the user.

When the user receives the data frame, the user transmits an ACK signal to the service provider (S350). In this case, a time interval between receiving a data frame and transmitting an ACK signal may be SIFS.

The service provider transmits a data frame of the next order to the user (S360), and the user who transmits the data frame transmits an ACK signal to the service provider (S370).

The service provider updates the data frame previously transmitted to the neighboring provider (S365). The neighbor provider updates the buffered data frames according to the first in, first out method.

During the transmission and reception of data frames between the service provider and the user, the user may move to the service area of the neighboring provider and the provider may be changed (S380). That is, the user receives data from a service provider and then data from a neighboring provider.

The user transmits a data request to the neighbor provider (S390). The data request may be made of a WAVE poll frame (S390).

The neighbor provider transmits the buffered data frame to the user (S395). The time interval for transmitting a data frame after the neighbor provider receives the data request may be SIFS. The neighboring provider transmits a data frame to the user according to a first in, first out method, and the user receives a data frame consecutive to the data frame received from the service provider.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

As described above, according to the present invention, since the data service is provided to the user who transmits the WAVE poll frame, the data service disturbance caused by the data frame transmitted to the user out of the service area can be reduced, and the channel state in the WAVE poll frame It is possible to improve data transmission efficiency by selecting a good user and provide data to neighboring providers in advance so that data can be continuously provided even during handoff.

Claims (11)

Establishing a wireless service in vehicular environments (WAVE) basic service set with a user; Receiving a data request from the user; And And transmitting the data to the user. 2. The method of claim 1, further comprising retransmitting the data upon receiving a retransmission request of the data from the user. The method of claim 1, wherein an acknowledgment (ACK) signal is transmitted when there is no data to be transmitted to the user. The method of claim 1, wherein the data request includes data rate information for a channel. The method of claim 1, wherein the data request includes on / off information of a WAVE mode. Receiving a wireless access in vehicular environments (WAVE) declaration frame from a provider; Establishing a WAVE basic service set with the provider; Sending a data request to the provider; And Receiving data from the provider. 7. The method of claim 6, wherein the data request includes rate information on a channel and on / off information of a WAVE mode. In the data transmission method of the vehicle environment of the provider, Transmitting a WAVE declaration frame; Receiving a WAVE poll frame for the WAVE declaration frame from a user; Transmitting a first data signal to the user at a transmission rate included in the WAVE poll frame; And Transmitting a second data signal to a neighboring WAVE provider. 10. The method of claim 8, wherein the second data signal is part of the first data signal within a range determined by a threshold. The method of claim 8, wherein when the WAVE provider for the user is changed to the neighboring WAVE provider, the second data signal is transmitted from the neighboring WAVE provider to the user. 10. The method of claim 8, wherein the WAVE poll frame received from the user is transmitted to the neighboring WAVE provider.

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