Patent Description:
In an Intelligent Transportation System (Intelligent Transportation System, ITS), various types of information related to transportation are obtained in a timely manner through vehicle to vehicle (Vehicle to Vehicle, V2V) communication, vehicle to infrastructure (Vehicle to Infrastructure, V2I) communication, vehicle-to-pedestrian (Vehicle-to-Pedestrian, V2P) communication, or vehicle-to-network (Vehicle-to-Network, V2N) communication. These communication manners may be collectively referred to as vehicle to X (Vehicle to X, V2X) communication. X is a collective term for vehicles, road infrastructure, pedestrians, and networks.

When a V2X message is transmitted by using a Long Term Evolution (Long Term Evolution, LTE) technology, two user equipments (User Equipment, UE) may be directly connected to each other for communication. When the two UEs are directly connected to each other for communication, an eNB first configures a transmission resource pool for the UE. The UE selects a transmission resource in an idle state from the transmission resource pool in a manner in which a transmission resource is selected after channel sensing is performed. Then, the UE sends the V2X message by using the transmission resource in the idle state. The manner in which a transmission resource is selected after channel sensing is performed is as follows: The UE senses each transmission resource in the transmission resource pool, where a typical value of sensing duration is <NUM>; and then determines the transmission resource in the idle state based on a sensing result.

In the foregoing manner, the transmission resource in the idle state can be selected only after at least <NUM>-ms sensing duration. Therefore, the manner is not applicable to all V2X message sending scenarios. In some specific sending scenarios, for example, after the UE initially obtains configuration information of the transmission resource pool, even though there is a to-be-transmitted V2X message, the UE needs to wait for the <NUM>-ms sensing duration, and then select the transmission resource in the idle state to send the V2X message. Because a transmission delay requirement of the V2X message is <NUM> or <NUM>, the UE may fail to send the V2X message after waiting for the <NUM>-ms sensing duration.

<NPL>, discloses that multiple and different resource pools may be configured for V2V, V2P, V2I and V2N communications, as they may have different service requirement and traffic characteristics. In Rel-<NUM> D2D, different resource pool configurations are used for Mode <NUM> and Mode <NUM> resource allocation. The reason is to avoid the interference from unpredictable Mode <NUM> data transmission to Mode <NUM> data transmission.

Document <CIT> discloses that in a second mode (Mode <NUM>), a UE, on its own, selects resources from resource pool(s) to transmit D2D data and D2D control information. The resource pool(s) are predefined, preconfigured, or fixed. For example, the resource pool(s) can be indicated by a physical D2D synchronization channel (PD2DSCH) that is transmitted by a D2D UE and received by one or more other D2D UEs. The resource pool(s) can also be indicated in system information block from an eNB or a relay node. The resource pool(s) for D2D data and D2D control can be the same or different. The D2D UE selects resources to transmit SA to one or more other D2D UEs, and the SA indicates resources for D2D data. The D2D UE selects resources to transmit D2D data together with control information, where a separate SA used to indicate resources for D2D data may not be necessary.

The present invention is defined by the attached set of independent claims.

According to a first aspect of the embodiments, a V2X message sending method is provided, and the method includes:.

In this design, it can be ensured that the V2X message is normally transmitted in a specific sending scenario when the preset condition is met.

In a possible design, the specific sending scenario is a scenario in which cell handover needs to be performed on the terminal, and the obtaining, by a terminal, first configuration information includes:.

In a possible design, the preset condition includes:
a current moment belongs to a handover time period, a start time of the handover time period is a time at.

To describe the technical solutions in the embodiments more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following descriptions show merely some embodiments, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

To make the objectives, technical solutions, and advantages clearer, the following further describes the embodiments in detail with reference to the accompanying drawings.

A "module" mentioned in this specification is a program or an instruction that is stored in a memory and can implement some functions. A "unit" mentioned in this specification is a functional structure divided based on logic. The "unit" may be implemented by only hardware, or implemented by a combination of software and hardware.

"A plurality" mentioned in this specification means at least two. "And/or" describes an association relationship between associated objects and represents that three relationships may exist. The character "/" usually indicates an "or" relationship between the associated objects.

<FIG> is a schematic structural diagram of a message sending system <NUM> according to an embodiment. The message sending system <NUM> includes at least one terminal <NUM> and at least one access network device <NUM>.

The terminal <NUM> is a terminal in the Internet of Vehicles. Optionally, the terminal <NUM> is at least one of a communications device disposed in a vehicle, a communications device disposed in roadside infrastructure, or a communications device used by a pedestrian. Specifically, the terminal <NUM> may be a device such as a personal communications service (PCS, Personal Communications Service) phone, a cordless telephone set, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL, Wireless Local Loop) station, or a personal digital assistant (PDA, Personal Digital Assistant). The terminal may also be referred to as a system, a subscriber unit (Subscriber Unit), a subscriber station (Subscriber Station), a mobile station (Mobile Station), a mobile (Mobile), a remote station (Remote Station), an access point (Access Point), a remote terminal (Remote Terminal), an access terminal (Access Terminal), a user terminal (User Terminal), a user agent (User Agent), a user device (User Device), or user equipment (User Equipment).

The terminal <NUM> communicates with one or more access network devices <NUM> by using a radio access network (Radio Access Network, RAN).

The access network device <NUM> may be a base station, and serves as a router between the terminal <NUM> and a remaining part of the access network, and the remaining part of the access network may include an Internet Protocol (Internet Protocol, IP) network. The base station may further coordinate attribute management of an air interface. For example, the base station may be a base transceiver station (BTS, Base Transceiver Station) in GSM or CDMA, or may be a NodeB (NodeB) in WCDMA, or may be an evolved NodeB (eNB or e-NodeB, evolutional NodeB) in LTE. This is not limited in this application. An example in which the access network device <NUM> is the eNB is used for description in the following embodiment.

When V2X communication is implemented between two terminals <NUM>, a first communication manner is as follows:
A V2X message sent by one terminal <NUM> is sent to the other terminal <NUM> through forwarding by the access network device <NUM>; and a second communication manner is as follows: The two terminals <NUM> are directly connected to each other for communication. In this embodiment, a case in which the two terminals <NUM> are directly connected to each other for communication is mainly involved.

When the two terminals <NUM> are directly connected to each other for communication, the access network device <NUM> needs to preconfigure a transmission resource pool for the terminal <NUM>; and the terminal <NUM> selects a transmission resource in an idle state from the transmission resource pool, and sends the V2X message by using the transmission resource in the idle state.

The V2X message includes at least one of a V2V message, a V2I message, a V2P message, or a V2N message. Optionally, the V2X message is a message carrying V2X data, or the V2X message is V2X data.

<FIG> is a method flowchart of a message sending method according to an embodiment. An example in which the message sending method is applied to the terminal <NUM> shown in <FIG> is used for description in this embodiment.

Step <NUM>: Obtain first configuration information, where the first configuration information is used for determining a first transmission resource pool.

Optionally, the first configuration information is configured by an access network device for the terminal. That is, the terminal receives RRC dedicated signaling sent by the access network device, and obtains the first configuration information from the RRC dedicated signaling; or the terminal receives system information sent by the access network device, and obtains the first configuration information from the system information. The system information is broadcast information sent by the access network device.

Optionally, the first configuration information is the preconfigured first configuration information. To be specific, the first configuration information is configuration information that is pre-specified according to a communications protocol related to LTE and that is pre-stored in the terminal. When the first configuration information is the preconfigured first configuration information, the terminal reads the first configuration information stored in the terminal.

Step <NUM>: Determine the first transmission resource pool based on the first configuration information.

Step <NUM>: When a preset condition is met, select a first transmission resource from the first transmission resource pool in a first transmission resource obtaining manner.

Optionally, the preset condition is a condition set based on a specific sending scenario. The specific sending scenario is a scenario in which a transmission resource is selected in a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2 (where a typical value is <NUM>); and consequently, V2X message sending fails, or a transmission delay requirement cannot be met.

Optionally, a time spent in selecting the transmission resource in the first transmission resource obtaining manner is less than a transmission delay requirement value of a V2X message. Optionally, the transmission delay requirement value is <NUM> or <NUM>.

The first transmission resource obtaining manner includes any one of the following three manners:.

Step <NUM>: Send a V2X message by using the first transmission resource.

In conclusion, the transmission resource is fast selected in the first transmission resource obtaining manner. Therefore, when the preset condition is met, the first transmission resource is selected from the first transmission resource pool in the first transmission resource obtaining manner, and the V2X message is sent by using the first transmission resource, so as to ensure that the V2X message can be normally transmitted in a specific sending scenario when the preset condition is met.

The foregoing specific sending scenario includes at least two types of scenarios. The following describes an implementation in a first type of scenario in the embodiments with reference to <FIG> and <FIG>, and describes an implementation in a second type of scenario in the embodiments with reference to <FIG> and <FIG>.

Referring to <FIG>, an access network device <NUM> configures a first transmission resource pool <NUM> and a second transmission resource pool <NUM> for a terminal <NUM>. In a first type of specific sending scenario, the terminal <NUM> sends a V2X message by using a transmission resource in the first transmission resource pool <NUM>, and a first transmission resource obtaining manner with a relatively fast selection speed is used in the first transmission resource pool <NUM>. In a common sending scenario, the terminal <NUM> sends a V2X message by using a transmission resource in the second transmission resource pool <NUM>, and a conventional second transmission resource obtaining manner, namely, a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2, is used in the second transmission resource pool <NUM>. Optionally, T2 = <NUM>.

In this case, a first condition includes: No valid sensing result is obtained from the second transmission resource pool.

<FIG> is a flowchart of a message sending method according to an embodiment. An example in which the method is applied to the message sending system shown in <FIG> is used for description in this embodiment.

Step <NUM>: An access network device sends first configuration information and second configuration information to a terminal.

The first configuration information is used for determining a first transmission resource pool, and a manner of obtaining a transmission resource from the first transmission resource pool is a first transmission resource obtaining manner. The first transmission resource obtaining manner is a random selection manner, a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T1, or a CSMA/CA manner.

The second configuration information is used for determining a second transmission resource pool, and a manner of obtaining a transmission resource from the second transmission resource pool is a second transmission resource obtaining manner. The second transmission resource pool obtaining manner is a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2.

A selection speed of selecting a resource in the first transmission resource obtaining manner is greater than a selection speed of selecting a resource in the second transmission resource obtaining manner.

Optionally, the access network device simultaneously sends the first configuration information and the second configuration information to the terminal; or the access network device first sends the first configuration information to the terminal, and then sends the second configuration information to the terminal; or the access network device first sends the second configuration information to the terminal, and then sends the first configuration information to the terminal.

Optionally, the access network device sends the first configuration information and/or the second configuration information to the terminal by using radio resource control (Radio Resource Control, RRC for short) dedicated signaling; or the access network device sends the first configuration information and/or the second configuration information to the terminal by using a system information block (System Information Block, SIB) in system information; or the access network device sends the first configuration information and/or the second configuration information to the terminal in a semi-static configuration manner, and the semi-static configuration manner is a configuration manner in which one configuration is valid until next configuration is performed.

Optionally, this step may be omitted when both the access network device and the terminal abide by configuration information that is pre-specified in a communications protocol. The terminal reads an internal memory, and obtains the preconfigured first configuration information and/or the preconfigured second configuration information. Correspondingly, the terminal receives the first configuration information and the second configuration information sent by the access network device.

Step <NUM>: The terminal determines a first transmission resource pool based on the first configuration information, and determines a second transmission resource pool based on the second configuration information.

Optionally, transmission resources in the first transmission resource pool are completely different from transmission resources in the second transmission resource pool; or transmission resources in the first transmission resource pool are partially the same as and partially different from transmission resources in the second transmission resource pool; or transmission resources in the first transmission resource pool are completely the same as transmission resources in the second transmission resource pool.

When the transmission resources in the first transmission resource pool are completely the same as the transmission resources in the second transmission resource pool, the first configuration information and the second configuration information are same configuration information. Therefore, the access network device needs to send only one piece of configuration information to the terminal. In addition, the first transmission resource pool and the second transmission resource pool are essentially a same transmission resource pool. "First" and "second" are used for description, and are merely used to indicate that different transmission resource obtaining manners are used.

An example in which the transmission resources in the first transmission resource pool are completely different from the transmission resources in the second transmission resource pool is used for description in this embodiment. Optionally, after determining the second transmission resource pool based on the second configuration information, the terminal starts to continuously sense the transmission resource in the second transmission resource pool.

Step <NUM>: When determining that a preset condition is met, the terminal selects a first transmission resource from the first transmission resource pool in a first transmission resource obtaining manner.

Optionally, the preset condition includes at least one of the following conditions.

When sensing duration of the terminal in the second transmission resource pool reaches <NUM>, if all transmission resources are in a busy state, there is no transmission resource in an idle state.

When determining that any one of the foregoing preset conditions is met, the terminal selects the first transmission resource from the first transmission resource pool in the first transmission resource obtaining manner.

Step <NUM>: The terminal sends a V2X message by using the first transmission resource.

Step <NUM>: When obtaining a valid sensing result from the second transmission resource pool, the terminal selects a second transmission resource from the second transmission resource pool in a second transmission resource obtaining manner.

The second transmission resource obtaining manner is a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2.

Step <NUM>: The terminal sends a V2X message by using the second transmission resource.

It should be noted that step <NUM> and step <NUM> are parallel with step <NUM> and step <NUM>. When the terminal performs step <NUM> and step <NUM>, step <NUM> and step <NUM> may not be performed. When the terminal performs step <NUM> and step <NUM>, step <NUM> and step <NUM> may not be performed. Optionally, step <NUM> and step <NUM> may be performed before step <NUM> and step <NUM>. This is not limited in this embodiment.

In conclusion, according to the message sending method provided in this embodiment, when a transmission resource is selected, a selection speed in the first transmission resource obtaining manner is faster than a selection speed in the second transmission resource obtaining manner. When the preset condition is met, the first transmission resource is selected from the first transmission resource pool in the first transmission resource obtaining manner, and the V2X message is sent by using the first transmission resource. Therefore, it can be ensured that the V2X message can be normally transmitted in a scenario in which no valid sensing result is obtained from the second transmission resource pool.

Referring to <FIG>, when a terminal is in a second type of specific sending scenario (a cell handover scenario), the terminal selects a first transmission resource from a first transmission resource pool in a first transmission resource obtaining manner. It is assumed that when the terminal <NUM> needs to be handed over from a cell provided by a first access network device <NUM> to a cell provided by a second access network device <NUM>, the second access network device <NUM> configures a first transmission resource pool <NUM> for the terminal. In a cell handover process, the terminal sends a V2X message by using a first transmission resource in the first transmission resource pool <NUM>.

<FIG> is a flowchart of a message sending method according to another embodiment.

Step <NUM>: When cell handover needs to be performed, a first access network device sends a handover request message to a second access network device.

When a terminal is in an RRC_CONNECTED mode (RRC_CONNECTED), the terminal sends a measurement report of a current cell to the first access network device. The first access network device is an access network device corresponding to a source cell before the handover. The first access network device determines, based on the measurement report sent by the terminal, whether cell handover needs to be performed on the terminal.

When cell handover needs to be performed on the terminal, the first access network device sends a handover request (Handover Request) message to the second access network device. The second access network device is an access network device corresponding to a target cell after the handover.

Correspondingly, the second access network device receives the handover request message sent by the first access network device.

Optionally, the handover request message may correspond to different signaling names in different communications systems.

Step <NUM>: The second access network device generates a handover request acknowledgement message based on the handover request message.

When receiving the handover request message, the second access network device determines, depending on a current running status, whether to allow the current cell handover. If the current cell handover is allowed, the second access network device reserves a necessary resource, for example, a bearer resource established between the second access network device and a mobility management entity (Mobility Management Entity, MME for short).

After reserving the necessary resource, the second access network device generates the handover request acknowledgement (Handover Request Acknowledgement) message, and the handover request acknowledgement message includes cell handover configuration information and first configuration information.

The cell handover configuration information is configuration information related to a current cell handover process, and includes but is not limited to: a physical identifier of the target cell, a cell radio network temporary identifier (Cell Radio Network Temporary Identifier, C-RNTI for short) of the terminal in the target cell, a dedicated preamble sequence for accessing the target cell, and a security algorithm of the target cell.

The first configuration information is used for determining a first transmission resource pool, and a manner of obtaining a transmission resource from the first transmission resource pool is a first transmission resource obtaining manner. Optionally, a time spent in selecting a transmission resource in the first transmission resource obtaining manner is less than a transmission delay requirement value of a V2X message.

Optionally, the first transmission resource obtaining manner is a random selection manner, a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T1, or a CSMA/CA manner.

Optionally, the first configuration information may be included in the cell handover configuration information, or the first configuration information and the cell handover configuration information are included in parallel in the handover request acknowledgement message. An inclusion relationship between the first configuration information and the cell handover configuration information is not limited.

Step <NUM>: The second access network device sends the handover request acknowledgement message to the first access network device.

The handover request acknowledgement message carries the cell handover configuration information and the first configuration information.

Correspondingly, the first access network device receives the handover request acknowledgement message sent by the second access network device.

Optionally, the handover request acknowledgement message may correspond to different signaling names in different communications systems. Optionally, the first access network device communicates with the second access network device by using an X2 interface.

Step <NUM>: The first access network device sends RRC dedicated signaling to a terminal, where the RRC dedicated signaling carries cell handover configuration information and first configuration information.

Optionally, the RRC dedicated signaling is RRC connection reconfiguration (RRC Connection Reconfiguration) signaling.

Optionally, the RRC dedicated signaling includes the cell handover configuration information, and the cell handover configuration information includes the first configuration information. That is, the first configuration information is used as a sub-information entry in the cell handover configuration information.

Optionally, the RRC dedicated signaling includes the cell handover configuration information and the first configuration information, and the cell handover configuration information is parallel with the first configuration information.

Correspondingly, the terminal receives the RRC dedicated signaling sent by the first access network device, and obtains the cell handover configuration information and the first configuration information from the RRC dedicated signaling.

Optionally, the first configuration information may be included in the cell handover configuration information, or the first configuration information and the cell handover configuration information are included in parallel in the RRC dedicated signaling. An inclusion relationship between the first configuration information and the cell handover configuration information is not limited.

Optionally, when the terminal receives the RRC dedicated signaling, a T304 timer starts.

Step <NUM>: Perform cell handover on the terminal based on the cell handover configuration information.

Optionally, after the terminal is successfully handed over to the target cell, the T304 timer stops.

Step <NUM>: The terminal determines a first transmission resource pool based on the first configuration information. Step <NUM>: When a current moment belongs to a handover time period, the terminal selects a first transmission resource from the first transmission resource pool in a first transmission resource obtaining manner.

Optionally, a preset condition includes: The current moment belongs to the handover time period, a start time of the handover time period is a time at which the RRC dedicated signaling is received, and an end time of the handover time period is a time at which the terminal is handed over to the second access network device.

Optionally, the end time of the handover time period is a time at which a cell handover timer stops. For example, the cell handover timer is the T304 timer.

The handover time period may also be considered as a running time period of the cell handover timer.

When determining that the preset condition is met, the terminal selects the first transmission resource from the first transmission resource pool in the first transmission resource obtaining manner.

The first transmission resource obtaining manner is a random selection manner, a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T1, or a CSMA/CA manner.

It should be noted that there is no necessary sequence between step <NUM> and step <NUM>. In this embodiment, an example in which step <NUM> is performed before step <NUM> is used only for description. Alternatively, step <NUM> may be performed after step <NUM>, or step <NUM> and step <NUM> are simultaneously performed. This is not limited in this embodiment.

In conclusion, according to the message sending method provided in this embodiment, when a transmission resource is selected, a selection speed in the first transmission resource obtaining manner is relatively fast. When the preset condition is met, the first transmission resource is selected from the first transmission resource pool in the first transmission resource obtaining manner, and the V2X message is sent by using the first transmission resource. Therefore, it can be ensured that the V2X message can be normally transmitted in a cell handover scenario of the terminal.

In an optional implementation provided based on the embodiment of <FIG>, the first access network device sends second configuration information to the terminal. The terminal determines a second transmission resource pool based on the second configuration information. When cell handover does not need to be performed, the terminal obtains a second transmission resource from the second transmission resource pool in a second transmission resource obtaining manner, and sends the V2X message by using the second transmission resource.

In an optional implementation provided based on the embodiment of <FIG>, the terminal reads an internal memory, and obtains preconfigured second configuration information. The terminal determines a second transmission resource pool based on the second configuration information. When cell handover does not need to be performed, the terminal obtains a second transmission resource from the second transmission resource pool in a second transmission resource obtaining manner, and sends the V2X message by using the second transmission resource.

With reference to the foregoing method embodiments:
Optionally, the random selection manner is as follows: The terminal randomly selects some transmission resources from n transmission resources in the first transmission resource pool as the first transmission resources. Optionally, a specific quantity of some transmission resources is dynamically determined by a data volume of a to-be-sent V2X message.

Optionally, the manner in which a transmission resource is selected after channel sensing is performed for sensing duration T1 is as follows: The terminal continuously senses n transmission resources in the second transmission resource pool, and duration of the continuous sensing is at least T1; and the terminal determines, based on a result of the continuous sensing, a transmission resource in an idle state.

Optionally, the manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2 is as follows: The terminal continuously senses n transmission resources in the first transmission resource pool, and duration of the continuous sensing is at least T2; and the terminal determines, based on a result of the continuous sensing, a transmission resource in an idle state. For example, T2 is less than T1.

Optionally, the continuous sensing is as follows: The terminal detects signal energy received on the n transmission resources; and when the signal energy is greater than a threshold, determines that the transmission resource is in a busy state; or when the signal energy is less than a threshold, determines that the transmission resource is in an idle state. Alternatively, the continuous sensing is as follows: The terminal decodes a signal that is received on the n transmission resources; and when valid information is obtained through decoding, determines that the transmission resource is in a busy state; or when no valid information is obtained through decoding, determines that the transmission resource is in an idle state. Optionally, transmission resources are divided in a unit of a resource block; or divided in a unit of a subframe; or divided in a unit of m symbols, where m = <NUM>, <NUM>, <NUM>, or <NUM>.

Optionally, for the CSMA/CA manner, refer to the <NUM> protocol standard formulated by the Institute of Electrical and Electronics Engineers (Institute of Electrical and Electronics Engineers, IEEE for short).

Optionally, the transmission resource in the foregoing embodiments is also referred to as a time-frequency resource. The time-frequency resource includes a time domain resource and a frequency domain resource.

Optionally, for a manner in which a transmission resource is selected after channel sensing is performed for sensing duration T1 or T2, a transmission resource is selected from a transmission resource pool based on service priority information. Specifically, when the V2X message enters a logical channel of an access layer, the logical channel has a corresponding service priority. The service priority may be obtained by using a corresponding primitive of the V2X message, or may be obtained through configuration or preconfiguration by a base station. Optionally, V2X messages with different service priorities may enter different logical channels. A media access control (Medium Access Control, MAC for short) layer determines a first transmission priority based on a service priority of a logical channel having a V2X service, and notifies a physical layer of the first transmission priority. The physical layer determines a valid transmission resource set based on the first transmission priority and the result of the continuous sensing, and notifies the MAC layer of the valid transmission resource set, so that the MAC layer determines, based on the valid transmission resource set, a transmission resource used for sending the V2X service.

Optionally, when the V2X service is transmitted, a MAC layer of a sending terminal sends, to a physical layer, a second transmission priority and a media access control protocol data unit (Medium Access Control Protocol Data Unit, MAC PDU for short) in which the V2X service is encapsulated, so that the physical layer encapsulates the second transmission priority in an SA (Scheduling Assignment, scheduling assignment) corresponding to the MAC PDU and sends the SA. After receiving the SA, a physical layer of a nearby receiving terminal determines a service priority of the MAC PDU based on the second transmission priority obtained through decoding. Optionally, the second transmission priority is a highest service priority in service priorities corresponding to all logical channel data encapsulated in the MAC PDU.

Optionally, for the sending terminal, the first transmission priority is equal to the second transmission priority.

Optionally, the MAC PDU used for transmitting the V2X service on a direct link uses a first transmission format. Specifically, a header of the MAC PDU carries a source address and a target address. A length of bits occupied by the source address of the MAC PDU is equal to a length of bits occupied by the target address of the MAC PDU. Typically, the bits are <NUM> bits. Optionally, the MAC PDU needs to carry first format indication information. The first format indication information is used to notify the receiving terminal that the MAC PDU uses the first transmission format. Optionally, the SA used for transmitting the V2X service on a direct link uses a second transmission format. Specifically, the SA does not carry a truncated destination address. Optionally, the SA needs to carry second format indication information. The second format indication information is used to notify the receiving terminal that the SA uses the second transmission format.

Optionally, the time domain resource is a symbol (symbol), a symbol group (symbol group), a timeslot (slot), or a subframe (subframe). The timeslot is a <NUM>-ms timeslot in an LTE system with <NUM>-kHz subcarrier spacing, or a timeslot in a communications system with larger subcarrier spacing. The subframe is a <NUM>-ms subframe in an LTE system with <NUM>-kHz subcarrier spacing, or a subframe in a communications system with larger subcarrier spacing.

Optionally, the frequency domain resource is a PRB, a physical resource block group (Physical Resource Block Group, RBG for short), a virtual resource block (Virtual Resource Block, VRB), a subcarrier, or a subcarrier group. The PRB and the VRB are basic units for resource allocation in different meanings. The PRB is <NUM> consecutive subcarriers in frequency domain and resources of one timeslot in time domain. A definition of the VRB is the same as a definition of the PRB during centralized resource allocation, and the VRB corresponds to the PRB during distributed resource allocation. A PRB index is a PRB index, and a VRB index is a VRB index. Therefore, the PRB index may be different from the VRB index. The RBG may include a plurality of PRBs, and a quantity of PRBs included in the RBG is determined based on bandwidth of the terminal, or is obtained based on an indication of a network device. The PRB index may be a PRB number, an RBG index may be an RBG number, the VRB index may be a VRB number, a subcarrier index may be a subcarrier number, and a subcarrier group index may be a subcarrier group number. The subcarrier group includes at least one subcarrier.

<FIG> is a block diagram of a message sending apparatus according to an embodiment. The message sending apparatus may be implemented as all or a part of a terminal by using a dedicated hardware circuit or a combination of software and hardware. The message sending apparatus includes a receiving unit <NUM>, a processing unit <NUM>, and a sending unit <NUM>.

The processing unit <NUM> is configured to obtain first configuration information, where the first configuration information is used for determining a first transmission resource pool.

The processing unit <NUM> is configured to determine the first transmission resource pool based on the first configuration information.

The processing unit <NUM> is configured to select a first transmission resource from the first transmission resource pool in a first transmission resource obtaining manner when determining that a preset condition is met.

The sending unit <NUM> is configured to send the V2X message by using the first transmission resource.

In an optional embodiment, the receiving unit <NUM> is configured to receive RRC dedicated signaling sent by a first access network device; the processing unit <NUM> is configured to obtain cell handover configuration information and first configuration information from the RRC dedicated signaling, where the cell handover configuration information and the first configuration information are configured by a second access network device; and the processing unit <NUM> is further configured to hand over the apparatus from a source cell to a target cell based on the cell handover configuration information.

The first access network device is an access network device corresponding to the source cell, and the second access network device is an access network device corresponding to the target cell.

Optionally, the preset condition includes:
a current moment belongs to a handover time period, a start time of the handover time period is a time at which the RRC dedicated signaling is received, and an end time of the handover time period is a time at which the apparatus is handed over to the target cell.

In another optional embodiment, the processing unit <NUM> is further configured to obtain second configuration information, where the second configuration information is used for determining a second transmission resource pool, a manner of obtaining a transmission resource from the second transmission resource pool is a second transmission resource obtaining manner, and the second transmission resource obtaining manner is a transmission resource obtaining manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2; and the processing unit <NUM> is further configured to determine the second transmission resource pool based on the second configuration information.

Optionally, the preset condition includes at least one of the following conditions:.

In an optional embodiment, the first transmission resource pool and the second transmission resource pool are a same resource pool, and the first transmission resource obtaining manner is different from the second transmission resource obtaining manner.

In an optional embodiment, the processing unit <NUM> is configured to obtain the preconfigured first configuration information; or the receiving unit <NUM> is configured to receive radio resource control RRC dedicated signaling sent by the access network device, and the processing unit is configured to obtain the first configuration information from the RRC dedicated signaling; or the receiving unit <NUM> is configured to receive system information sent by the access network device, and the processing unit is configured to obtain the first configuration information from the system information.

According to the invention, the first transmission resource obtaining manner is a random selection manner.

For related details, refer to the method embodiment described in <FIG>, <FIG>, or <FIG>.

It should be noted that the receiving unit <NUM> may be implemented by a receiver, or implemented by a combination of a processor and a receiver. The processing unit <NUM> may be implemented by a processor. The sending unit <NUM> may be implemented by a transmitter, or implemented by a combination of a processor and a transmitter.

<FIG> is a block diagram of a message sending apparatus according to another embodiment. The message sending apparatus may be implemented as all or a part of an access network terminal or a first access network device by using a dedicated hardware circuit or a combination of software and hardware. The message sending apparatus includes a sending unit <NUM>, a processing unit <NUM>, and a receiving unit <NUM>.

The processing unit <NUM> is configured to generate first configuration information.

The sending unit <NUM> is configured to send the first configuration information to a terminal, where the first configuration information is used for determining a first transmission resource pool.

The terminal is configured to: determine the first transmission resource pool based on the first configuration information; when determining that a preset condition is met, select a first transmission resource from the first transmission resource pool in a first transmission resource obtaining manner; and send the V2X message by using the first transmission resource.

In an optional embodiment, the sending unit <NUM> is configured to: when cell handover needs to be performed on the terminal, send a handover request message to a second access network device, where the second access network device is an access network device corresponding to a target cell; the receiving unit <NUM> is configured to receive a handover acknowledgement message sent by the second access network device, where the handover acknowledgement message includes cell handover configuration information and the first configuration information; the processing unit <NUM> is configured to generate RRC dedicated signaling based on the handover acknowledgement message; the sending unit <NUM> is configured to send the RRC dedicated signaling to the terminal, where the RRC dedicated signaling includes the cell handover configuration information and the first configuration information, and the terminal is configured to: be handed over from a source cell to the target cell based on the cell handover configuration information, select the first transmission resource from the first transmission resource pool in the first transmission resource obtaining manner within a handover time period, and send the V2X message by using the first transmission resource.

In an optional embodiment, the processing unit <NUM> is configured to generate second configuration information; the sending unit <NUM> is configured to send the second configuration information to the terminal, where the second configuration information is used for determining a second transmission resource pool, a manner of obtaining a transmission resource from the second transmission resource pool is a second transmission resource obtaining manner, and the second transmission resource obtaining manner is a transmission resource obtaining manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2.

In an optional embodiment, the sending unit <NUM> is configured to send radio resource control RRC dedicated signaling to the terminal, where the RRC dedicated signaling carries the first configuration information; or
the sending unit <NUM> is configured to send system information to the terminal, where the system information carries the first configuration information.

For related details, refer to the method embodiment described in <FIG> or <FIG>.

It should be noted that the sending unit <NUM> may be implemented by a transmitter, or implemented by a combination of a processor and a transmitter. The processing unit <NUM> may be implemented by a processor. The receiving unit <NUM> may be implemented by a receiver Rx, or implemented by a combination of a processor and a receiver.

<FIG> is a block diagram of a message sending apparatus according to another embodiment. The message sending apparatus may be implemented as all or a part of a second access network device by using a dedicated hardware circuit or a combination of software and hardware. The message sending apparatus includes a receiving unit <NUM>, a processing unit <NUM>, and a sending unit <NUM>.

The receiving unit <NUM> is configured to receive a handover request message sent by a first access network device, where the handover request message is sent by the first access network device when cell handover needs to be performed on a terminal, and the first access network device is an access network device corresponding to a source cell.

The processing unit <NUM> is configured to generate a handover request response message based on the handover request message.

The sending unit <NUM> is configured to send the handover request response message to the first access network device, where the handover request response message carries cell handover configuration information and first configuration information, and the first configuration information is used for determining a first transmission resource pool.

The first access network device is configured to send radio resource control RRC dedicated signaling to the terminal, where the RRC dedicated signaling includes the cell handover configuration information and the first configuration information; and the terminal is configured to: be handed over from the source cell to a target cell based on the cell handover configuration information, select a first transmission resource from the first transmission resource pool in the first transmission resource obtaining manner within a handover time period, and send the V2X message by using the first transmission resource.

For related details, refer to the method embodiment described in <FIG>.

A person of ordinary skill in the art may understand that all or some of the steps of the embodiments may be implemented by hardware or a program instructing related hardware. The program may be stored in a computer-readable storage medium. The storage medium may include a read-only memory, a magnetic disk, an optical disc, or the like.

Claim 1:
A communication method, comprising:
obtaining (<NUM>), by a terminal device (<NUM>), first configuration information and second configuration information, wherein the first configuration information is for determining a first transmission resource pool, the second configuration information is for determining a second transmission resource pool, a manner of obtaining a transmission resource from the first transmission resource pool is a first transmission resource obtaining manner, the first transmission resource obtaining manner is a random selection manner, a manner of obtaining a transmission resource from the second transmission resource pool is a second transmission resource obtaining manner, and the second transmission resource obtaining manner is a transmission resource obtaining manner in which a transmission resource is selected after channel sensing is performed for sensing duration T2;
selecting (<NUM>), by the terminal device (<NUM>), a first transmission resource from the first transmission resource pool in the first transmission resource obtaining manner when a valid sensing result is not obtained from the second transmission resource pool; and
sending (<NUM>), by the terminal device (<NUM>), a vehicle to X, V2X, message on the first transmission resource.