Channel reservation method and communications device

The present invention discloses a channel reservation method and a communications device. The method includes: generating, by a first device, a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device; and sending, by the first device, the first indication frame to multiple second devices. In the channel reservation method, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time, which avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

TECHNICAL FIELD

The present invention relates to the communications field, and in particular, to a channel reservation method and a communications device.

BACKGROUND

A WLAN (Wireless Local Area Network) system works on an unlicensed spectrum; therefore, other users may share the spectrum on a channel. If multiple users send data at the same time, the data may interfere with each other, causing a collision. The WLAN system uses a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mode to avoid a collision. Carrier sense CS refers to that any device connected to the channel first senses the channel before preparing to send data. The data may be sent only when it is confirmed that the channel is idle. Multiple access MA refers to that multiple devices may access a channel at the same time, and a data frame sent by one device may be received by multiple devices. A CSMA/CA mechanism resolves a collision problem by means of active collision avoidance instead of passive detection, which can satisfy those demands for which it is not easy to accurately detect whether a collision occurs. A working manner of CSMA is: when a device prepares to send a data frame and senses that a channel is idle, if the device further waits for a random time in which the channel is still idle, the device sends the data frame. However, there is a problem about a hidden node in a WLAN network; and when an access point AP1sends data to a STA (Station), a station or an access point that cannot sense the access point AP1may think that the channel is idle and send the data, which interferes with the receiving device STA. Such a problem about a hidden node cannot be resolved by using a CSMA/CA protocol.

At present, for the problem about a hidden node, the WLAN system protects transmission by using an RTS/CTS (Request to Send/Clear to Send) protocol, where a channel is reserved before a station or an access point sends data. The RTS/CTS protocol specifies: the access point AP1first sends an RTS frame before sending the data, and the STA responds with a CTS frame after receiving the RTS frame. Each of other APs (Access Point) or STAs that receive the RTS or CTS frame sets a NAV (Network Allocation Vector) according to an indication of the received RTS or CTS frame. Within a time corresponding to the NAV, such AP or STA cannot send data on the corresponding channel. After sending the RTS frame and receiving the CTS frame returned by the STA, the AP1obtains a sending opportunity, and if the AP1sends data to the STA within this time period, the AP1is not interfered by a surrounding AP or STA.

However, when APs and STAs are intensively deployed in the WLAN system, a collision probability of RTS frames greatly increases, and a contention window length after a collision doubles; therefore, not only system overheads are relatively high, but also a reduction in system efficiency is caused.

SUMMARY

The present invention provides a channel reservation method and a communications device, which can reduce a collision probability, thereby reducing system overheads.

According to a first aspect, the present invention provides a channel reservation method, including: generating, by a first device, a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device; and sending, by the first device, the first indication frame to multiple second devices.

With reference to the first aspect, in a first implementation manner of the first aspect, the sending, by the first device, the first indication frame to multiple second devices includes: sending, by the first device, the first indication frame to the multiple second devices in a broadcast or multicast manner.

With reference to the first aspect and the foregoing implementation manner thereof, in a second implementation manner of the first aspect, before the generating, by a first device, a first indication frame, the method further includes: acquiring, by the first device, scheduling information; and the sending, by the first device, the first indication frame to multiple second devices includes: sending, by the first device, the first indication frame to the multiple second devices according to the scheduling information.

According to a second aspect, the present invention provides a channel reservation method, including: receiving, by a second device, a first indication frame from a first device, where the first indication frame is used for indicating a sending moment at which the second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device; and determining, by the second device, the sending moment according to the first indication frame, and sending the channel reservation frame at the sending moment.

With reference to the second aspect, in a first implementation manner of the second aspect, the first indication frame includes a random backoff time, and the determining, by the second device, the sending moment according to the first indication frame includes: performing, by the second device, random backoff according to the random backoff time in the first indication frame; and if the channel is idle within the random backoff time, determining, by the second device, that a moment at which the random backoff time expires is the sending moment.

With reference to the second aspect and the foregoing implementation manner thereof, in a second implementation manner of the second aspect, the first indication frame includes a channel reservation frame sending rule, and the determining, by the second device, the sending moment according to the first indication frame includes: determining, by the second device, the sending moment according to the channel reservation frame sending rule in the first indication frame.

With reference to the second aspect and the foregoing implementation manners thereof, in a third implementation manner of the second aspect, the sending the channel reservation frame at the sending moment includes: sending the channel reservation frame at the sending moment in a broadcast manner.

According to a third aspect, the present invention provides a channel reservation method, including: generating, by a first device, a second indication frame, where the second indication frame is used for instructing a second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device; and sending, by the first device, the second indication frame to the second device.

With reference to the third aspect, in a first implementation manner of the third aspect, the sending, by the first device, the second indication frame to the second device includes: performing, by the first device, random backoff; and sending, by the first device, the second indication frame to the second device when the channel is idle.

According to a fourth aspect, the present invention provides a channel reservation method, including: receiving, by a second device, a second indication frame from a first device, where the second indication frame is used for instructing the second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device; and sending, by the second device, the channel reservation frame.

With reference to the fourth aspect, in a first implementation manner of the fourth aspect, the sending, by the second device, the channel reservation frame includes: performing, by the second device, random backoff; and if the channel is idle, sending, by the second device, the channel reservation frame.

According to a fifth aspect, the present invention provides a communications device, including: a generation unit, configured to generate a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device sends data to the second device; and a sending unit, configured to send the first indication frame to multiple second devices.

With reference to the fifth aspect, in a first implementation manner of the fifth aspect, the sending unit is specifically configured to send the first indication frame to the multiple second devices in a broadcast or multicast manner.

With reference to the fifth aspect and the foregoing implementation manner thereof, in a second implementation manner of the fifth aspect, the communications device further includes: an acquiring unit, configured to acquire scheduling information, where the sending unit is specifically configured to send the first indication frame to the multiple second devices according to the scheduling information.

According to a sixth aspect, the present invention provides a communications device, including: a receiving unit, configured to receive a first indication frame from a first device, where the first indication frame is used for indicating a sending moment at which the communications device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the communications device; a determining unit, configured to determine the sending moment according to the first indication frame; and a sending unit, configured to send the channel reservation frame at the sending moment.

With reference to the sixth aspect, in a first implementation manner of the sixth aspect, the first indication frame includes a random backoff time, and the communications device further includes: a control unit, configured to control, according to the random backoff time in the first indication frame, the communications device to perform random backoff, where the determining unit is specifically configured to: if the channel is idle within the random backoff time, determine that a moment at which the random backoff time expires is the sending moment.

With reference to the sixth aspect and the foregoing implementation manner thereof, in a second implementation manner of the sixth aspect, the first indication frame includes a channel reservation frame sending rule, and the determining unit is specifically configured to determine the sending moment according to the channel reservation frame sending rule in the first indication frame.

With reference to the sixth aspect and the foregoing implementation manners thereof, in a third implementation manner of the sixth aspect, the sending unit is specifically configured to send the channel reservation frame at the sending moment in a broadcast manner.

According to a seventh aspect, the present invention provides a communications device, including: a generation unit, configured to generate a second indication frame, where the second indication frame is used for instructing a second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device sends data to the second device; and a sending unit, configured to send the second indication frame to the second device.

With reference to the seventh aspect, in a first implementation manner of the seventh aspect, the communications device further includes: a control unit, configured to control the communications device to perform random backoff, where the sending unit is specifically configured to send the second indication frame to the second device when the channel is idle.

According to an eighth aspect, the present invention provides a communications device, including: a receiving unit, configured to receive a second indication frame from a first device, where the second indication frame is used for instructing the communications device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the communications device; and a sending unit, configured to send the channel reservation frame.

With reference to the eighth aspect, in a first implementation manner of the eighth aspect, the communications device further includes: a control unit, configured to control the communications device to perform random backoff, where the sending unit is specifically configured to: if the channel is idle, send the channel reservation frame.

Based on the foregoing technical solutions, in the channel reservation method of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time, which avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It should be understood that, the technical solutions in the embodiments of the present invention may be applied to a communications system using an unlicensed spectrum resource, for example, a WALN system.

It should be further understood that, in the embodiments of the present invention, an access point is a network device providing an access service, for example, an AP in a WALN system. A station is a device on the other end that accesses the access point by using a wireless network to perform communication, for example, user equipment (“UE” for short), which may be referred to as a terminal, a mobile station (“MS” for short), a mobile terminal, or the like, which is not limited in the present invention. However, for ease of description, the following embodiments are described by using the access point AP and the station STA as examples.

FIG. 1is a schematic structural diagram of an applicable communications system according to an embodiment of the present invention. The communications system inFIG. 1is described by using a first AP110awhose coverage area is101aand a second AP110bwhose coverage area is101bas examples. However, a quantity of APs110is not limited in this embodiment of the present invention.

A first STA120aaccesses the first AP110a, a second STA120baccesses the second AP110b, a third STA120caccesses the first AP110a, and the first STA120aand the second STA120bare located in a coverage area102in which101aoverlaps101b.

If transmission protection is performed by using an RTS/CTS protocol, when preparing to send data to the first STA120aand the third STA120c, the AP110amay first send an RTS frame. After receiving the RTS frame, the first STA120aand the third STA120crespond with a CTS frame. After receiving the RTS or the CTS frame, each of the second AP110band the second STA120bsets a NAV, and does not send data on a corresponding channel within a time corresponding to the NAV. After receiving the CTS frame, the first AP110aobtains a sending opportunity, and sends data to the first STA120aand the third STA120c. In this case, the first STA120aand the third STA120care not interfered by a surrounding AP or STA. In this way, transmission protection is performed by using the RTS/CTS protocol, and therefore, relatively high additional overheads are caused. Alternatively, the first AP110asends a CTS-to-self (Clear to send to self) frame and directly sends data, without needing the first STA120aand the third STA120cto make a response. In this way, additional overheads are reduced, but a problem about a hidden node cannot be resolved.

In addition, when APs and STAs are intensively deployed in a WLAN system, a collision probability of RTS frames greatly increases, and a contention window length after a collision doubles; therefore, not only system overheads are relatively high, but also a reduction in system efficiency is caused.

An embodiment of the present invention provides a channel reservation method, which not only can resolve a problem about a hidden node, but also reduces additional system overheads, and can be applied to multiple application scenarios that are based on contention or into which a scheduling mode is introduced.

FIG. 2is a schematic flowchart of a channel reservation method20according to an embodiment of the present invention. A first device executing the method20ofFIG. 2is a sender in a data transmission process, for example, an AP110shown inFIG. 1.

201: The first device generates a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device.

For example, if the second device sends a channel reservation frame to reserve a channel to be used when the first device sends data to the second device, the channel reservation frame is used for informing the first device that the channel may be used to send the data to the second device within a time period specified by the channel reservation frame.

In addition, in addition to the first device, there are also some devices that can sense the channel reservation frame sent by the second device. Therefore, the channel reservation frame may be further used for indicating that all other devices that receive the channel reservation frame except the first device cannot use, within the time period specified by the channel reservation frame, the channel to actively initiate data transmission.

202: The first device sends the first indication frame to multiple second devices.

In the channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is the sender in the data transmission process, and the second device is a receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the second device may determine that the second device is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the first device. Alternatively, in an application scenario into which the scheduling mode is introduced, the second device may determine, after acquiring scheduling information, that the second device is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, the second devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the first device can correctly receive the channel reservation frames that are sent by the multiple second devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, in step202, when the first device sends the first indication frame to multiple second devices, the first device may send the first indication frame to the multiple second devices in a broadcast or multicast manner.

Optionally, as another embodiment, before the first device generates the first indication frame, the first device may acquire scheduling information. In this case, when sending the first indication frame to the multiple second devices, the first device may send the first indication frame to the multiple second devices according to the scheduling information.

For example, in a WLAN into which the scheduling mode is introduced, the first device may be an AP, which determines a receiving device for data transmission according to acquired scheduling information, then generates a first indication frame, and sends the first indication frame to the corresponding receiving device (for example, the second device).

FIG. 3is a schematic flowchart of a channel reservation method30according to another embodiment of the present invention. A second device executing the method30ofFIG. 3is a receiver in a data transmission process, for example, a STA120shown inFIG. 1.

301: The second device receives a first indication frame from a first device, where the first indication frame is used for indicating a sending moment at which the second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device.

For example, if the second device sends a channel reservation frame to reserve a channel to be used when the first device sends data to the second device, the channel reservation frame is used for informing the first device that the channel may be used to send the data to the second device within a time period specified by the channel reservation frame.

In addition, in addition to the first device, there are also some devices that can sense the channel reservation frame sent by the second device. Therefore, the channel reservation frame may be further used for indicating that all other devices that receive the channel reservation frame except the first device cannot use, within the time period specified by the channel reservation frame, the channel to actively initiate data transmission.

302: The second device determines the sending moment according to the first indication frame, and sending the channel reservation frame at the sending moment.

In the channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in the data transmission process, and the second device is the receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the second device may determine that the second device is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the first device. Alternatively, in an application scenario into which the scheduling mode is introduced, the second device may determine, after acquiring scheduling information, that the second device is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, the second devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the first device can correctly receive the channel reservation frames that are sent by the multiple second devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, the first indication frame includes a random backoff time, and in step302, when determining the sending moment according to the first indication frame, the second device may perform random backoff according to the random backoff time in the first indication frame. If the channel is idle within the random backoff time, the second device determines that a moment at which the random backoff time expires is the sending moment.

For example, the first device generates a random number as the random backoff time, and sends the random backoff time to the second device by using the first indication frame. The second device performs random backoff within the random backoff time, and performs channel sensing. If the channel is idle, the second device sends the channel reservation frame at the moment at which the random backoff time expires; otherwise, the channel reservation frame is not sent.

Optionally, as another embodiment, the first indication frame includes a channel reservation frame sending rule, in step302, when determining the sending moment according to the first indication frame, the second device may determine the sending moment according to the channel reservation frame sending rule in the first indication frame.

For example, the channel reservation frame sending rule may be: a working mode is set, and a sending moment of the channel reservation frame in such a working mode is predefined; or an AP in a scheduling system may specify that: when each timeslot ends, stations to be scheduled to a next timeslot send the channel reservation frame on a scheduled channel at the same time. If multiple STAs comply with the rule specified by the AP, the multiple STAs may send channel reservation frames at the same time. For example, all STAs in a scheduling system that are scheduled to a same channel and a same timeslot may send, on the scheduled channel, channel reservation frames at the same time.

Optionally, as another embodiment, when the channel reservation frame is sent at the sending moment, the channel reservation frame may be sent at the sending moment in a broadcast manner.

Optionally, in some application scenarios, for example, in an exclusive area such as a corporate campus, performance of a network deployed by a corporation may need to be ensured, and a network device that is not deployed by the corporation is blocked for this purpose. In this case, some dedicated channel reservation devices may be deployed in the corporate campus, and an AP may instruct these devices to send channel reservation frames, to reserve channels for the network device that is not deployed by the corporation. If a device in a WLAN network deployed by the corporation receives the channel reservation frames sent by these channel reservation devices, a setting of a NAV is not modified. In this way, the network device that is not deployed by the corporation does not affect communication in the network of the corporation.

Optionally, coordinated stations (including an AP and a STA), for example, an AP and all STAs in a BSS based on scheduling transmission, or all APs and a STA in multiple BSSs that may perform joint scheduling, do not contend for a channel by means of contention. If receiving a channel reservation frame sent by another coordinated station, any one of the coordinated stations neither needs to keep silent nor needs to modify a setting of a NAV.

Specifically, whether a channel reservation frame is from a coordinated station may be determined by using the following method: each station saves addresses of APs in all coordinated BSSs or a network address of multiple coordinated BSSs. If a receiver address domain (for example, an RA domain in CTS-to-self frames) in the channel reservation frame is one of a list of coordinated APs, or is the network address of the multiple coordinated BSSs, it may be determined that the channel reservation frame is from the coordinated station.

FIG. 4is a schematic flowchart of a channel reservation method40according to another embodiment of the present invention. A first device executing the method40ofFIG. 4is a sender in a data transmission process, for example, an AP110or a STA120shown inFIG. 1.

401: The first device generates a second indication frame, where the second indication frame is used for instructing a second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device.

402: The first device sends the second indication frame to the second device.

In the channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which provides an implementable manner to resolve a problem about a hidden node.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is the sender in the data transmission process, and the second device is a receiver in the data transmission process. The second device may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, in step402, when the first device sends the second indication frame to the second device, the first device may first perform random backoff, and then the first device sends the second indication frame to the second device when the channel is idle. In this way, a collision probability can be further reduced, so that system overheads are reduced.

FIG. 5is a schematic flowchart of a channel reservation method50according to another embodiment of the present invention. A second device executing the method50ofFIG. 5is a receiver in a data transmission process, for example, an AP110or a STA120shown inFIG. 1.

501: The second device receives a second indication frame from a first device, where the second indication frame is used for instructing the second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the second device.

502: The second device sends the channel reservation frame.

In the channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which provides an implementable manner to resolve a problem about a hidden node.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in the data transmission process, and the second device is the receiver in the data transmission process. The second device may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, in step502, when the second device sends the channel reservation frame, the second device may first perform random backoff, and if the channel is idle, the second device then sends the channel reservation frame.

FIG. 6is a schematic block diagram of a communications device60according to an embodiment of the present invention. The communications device60inFIG. 6includes a generation unit610and a sending unit620. For example, the communications device60may be an AP110shown inFIG. 1.

The generation unit610is configured to generate a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device60sends data to the second device.

The sending unit620is configured to send the first indication frame to multiple second devices.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the communications device60is a sender in a data transmission process, and the second device is a receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the second device may determine that the second device is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the communications device60. Alternatively, in an application scenario into which the scheduling mode is introduced, the second device may determine, after acquiring scheduling information, that the second device is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, the second devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the communications device can correctly receive the channel reservation frames that are sent by the multiple second devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address, receiver address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, the sending unit620is specifically configured to send the first indication frame to the multiple second devices in a broadcast or multicast manner.

Optionally, as another embodiment, the communications device60further includes an acquiring unit630. The acquiring unit630is configured to acquire scheduling information. In this case, the sending unit620is specifically configured to send the first indication frame to the multiple second devices according to the scheduling information.

FIG. 7is a schematic block diagram of a communications device70according to another embodiment of the present invention. The communications device70inFIG. 7includes a receiving unit710, a determining unit720, and a sending unit730. For example, the communications device70may be a STA120shown inFIG. 1.

The receiving unit710is configured to receive a first indication frame from a first device, where the first indication frame is used for indicating a sending moment at which the communications device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the communications device.

The determining unit720is configured to determine the sending moment according to the first indication frame.

The sending unit730is configured to send the channel reservation frame at the sending moment.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in a data transmission process, and the communications device70is a receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the communications device70may determine that the communications device70is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the first device. Alternatively, in an application scenario into which the scheduling mode is introduced, the communications device70may determine, after acquiring scheduling information, that the communications device70is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set, basic service set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, communications devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the first device can correctly receive the channel reservation frames that are sent by the multiple communications devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, the first indication frame includes a random backoff time, and the communications device70further includes a control unit740. The control unit740is configured to control, according to the random backoff time in the first indication frame, the communications device to perform random backoff. In this case, the determining unit720is specifically configured to: if the channel is idle within the random backoff time, determine that a moment at which the random backoff time expires is the sending moment.

Optionally, as another embodiment, the first indication frame includes a channel reservation frame sending rule. In this case, the determining unit720is specifically configured to determine the sending moment according to the channel reservation frame sending rule in the first indication frame.

Optionally, as another embodiment, the sending unit730is specifically configured to send the channel reservation frame at the sending moment in a broadcast manner.

FIG. 8is a schematic block diagram of a communications device80according to another embodiment of the present invention. The communications device80inFIG. 8includes a generation unit810and a sending unit820. For example, the communications device80may be an AP110or a STA120shown inFIG. 1.

The generation unit810is configured to generate a second indication frame, where the second indication frame is used for instructing a second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device80sends data to the second device.

The sending unit820is configured to send the second indication frame to the second device.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also reduces additional system overheads.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the communications device80is a sender in a data transmission process, and the second device is a receiver in the data transmission process. The second device may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, the communications device80further includes a control unit830. The control unit830is configured to control the communications device to perform random backoff. In this case, the sending unit820is specifically configured to send the second indication frame to the second device when the channel is idle. In this way, a collision probability can be further reduced, so that system overheads are reduced.

FIG. 9is a schematic block diagram of a communications device90according to another embodiment of the present invention. The communications device90inFIG. 9includes a receiving unit910and a sending unit920. For example, the communications device90may be an AP110or a STA120shown inFIG. 1.

The receiving unit910is configured to receive a second indication frame from a first device, where the second indication frame is used for instructing the communications device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the communications device.

The sending unit920is configured to send the channel reservation frame.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also reduces additional system overheads.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in a data transmission process, and the communications device90is a receiver in the data transmission process. The communications device90may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, the communications device90further includes a control unit930. The control unit930is configured to control the communications device to perform random backoff. In this case, the sending unit920is specifically configured to: if the channel is idle, send the channel reservation frame. In this way, a collision probability can be further reduced, so that system overheads are reduced.

FIG. 10is a schematic block diagram of a communications device100according to another embodiment of the present invention.

The communications device100inFIG. 10may be configured to implement steps and methods in the foregoing method embodiments. In the embodiment ofFIG. 10, the communications device100includes an antenna1010, a transmitter1020, a receiver1030, a processor1040, and a memory1050. The processor1040controls an operation of the communications device100, and may be configured to process a signal. The memory1050may include a read-only memory and a random access memory, and provide an instruction and data to the processor1040. The transmitter1020and the receiver1030may be coupled to the antenna1010. Components of the communications device100are coupled together by using a bus system1060, where the bus system1060includes not only a data bus, but also a power bus, a control bus, and a status signal bus. However, for a clear description, various buses are marked as the bus system1060in the figure. The communications device100is a sender in a data transmission process, for example, may be an AP110shown inFIG. 1.

Specifically, the memory1050may store an instruction for executing the following process: the processor1040generates a first indication frame, where the first indication frame is used for indicating a moment at which a second device sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device sends data to the second device; and the transmitter1020sends the first indication frame to multiple second devices.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the communications device is the sender in the data transmission process, and the second device is a receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the second device may determine that the second device is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the communications device. Alternatively, in an application scenario into which the scheduling mode is introduced, the second device may determine, after acquiring scheduling information, that the second device is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, the second devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the communications device can correctly receive the channel reservation frames that are sent by the multiple second devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, the memory1050may further store an instruction for executing the following process: when sending the first indication frame to the multiple second devices, the transmitter1020may send the first indication frame to the multiple second devices in a broadcast or multicast manner.

Optionally, as an embodiment, the memory1050may further store an instruction for executing the following process: before the first indication frame is generated, the processor1040acquires scheduling information; in this case, the transmitter1020sends the first indication frame to the multiple second devices according to the scheduling information.

FIG. 11is a schematic block diagram of a communications device according to another embodiment of the present invention.

A communications device110inFIG. 11may be configured to implement steps and methods in the foregoing method embodiments. In the embodiment ofFIG. 11, the communications device110includes an antenna1110, a transmitter1120, a receiver1130, a processor1140, and a memory1150. The processor1140controls an operation of the communications device110, and may be configured to process a signal. The memory1150may include a read-only memory and a random access memory, and provide an instruction and data to the processor1140. The transmitter1120and the receiver1130may be coupled to the antenna1110. Components of the communications device110are coupled together by using a bus system1160, where the bus system1160includes not only a data bus, but also a power bus, a control bus, and a status signal bus. However, for a clear description, various buses are marked as the bus system1160in the figure. The communications device110is a receiver in a data transmission process, for example, may be a STA120shown inFIG. 1.

Specifically, the memory1150may store an instruction for executing the following process: the receiver1130receives a first indication frame from a first device, where the first indication frame is used for indicating a sending moment at which the communications device110sends a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device110sends data to the first device; the processor1140determines the sending moment according to the first indication frame; and the transmitter1120sends the channel reservation frame at the sending moment.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process indicates a moment at which a receiver device sends a channel reservation frame, so that multiple receiver devices in the data transmission process send channel reservation frames at the same time. In this case, after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which not only resolves a problem about a hidden node, but also avoids contention between the receiver devices in current data transmission, thereby reducing a collision probability, and reducing system overheads.

In addition, when transmission protection is performed according to this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in the data transmission process, and the communications device is the receiver in the data transmission process. In an application scenario of an unscheduled mode, for example, in a contention mode, the communications device may determine that the communications device is the receiver in the data transmission process when receiving the first indication frame or by receiving another information frame sent by the first device. Alternatively, in an application scenario into which the scheduling mode is introduced, the communications device may determine, after acquiring scheduling information, that the communications device is the receiver of the data in a corresponding timeslot on the corresponding channel, so that a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

For example, when multiple BSSs (Basic Service Set, basic service set) based on the scheduling mode coexist, APs of the multiple BSSs may contend for a channel by using a method of controlling STAs to send channel reservation frames. An AP of each BSS may instruct a scheduled STA to send, on a scheduled channel, a channel reservation frame according to a random backoff time generated by the AP. All STAs on a same channel in a same BSS send channel reservation frames at the same time, and contend with other BSSs for a channel, which not only avoids contention between the STAs in this BSS, but also reduces a collision probability.

For another example, communications devices uniformly send channel reservation frames by means of OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing). Physical layer data, physical layer parameters, and encoding manners of the channel reservation frames are completely the same, so as to ensure that the first device can correctly receive the channel reservation frames that are sent by the multiple communications devices at the same time, and therefore, obtain a transmission opportunity. Using a CTS-to-self frame as an example, to ensure that CTS-to-self frames sent by all the STAs are identical, structures of the CTS-to-self frames need to be modified, where RA (Receiver Address, receiver address) domains in the CTS-to-self frames no longer indicate address information of the CTS-to-self frames, but indicate a same address, for example, an address of the AP, or a network address preset by multiple coordinated BSSs.

Optionally, as an embodiment, the memory1150may further store an instruction for executing the following process: the first indication frame includes a random backoff time; in this case, when determining the sending moment according to the first indication frame, the processor1140may first control the communications device110to perform random backoff according to the random backoff time in the first indication frame; and if the channel is idle within the random backoff time, the processor1140then determines that a moment at which the random backoff time expires is the sending moment.

Optionally, as an embodiment, the memory1150may further store an instruction for executing the following process: the first indication frame includes a channel reservation frame sending rule; in this case, when determining the sending moment according to the first indication frame, the processor1140may determine the sending moment according to the channel reservation frame sending rule in the first indication frame.

Optionally, as an embodiment, the memory1150may further store an instruction for executing the following process: when sending the channel reservation frame at the sending moment, the transmitter1120sends the channel reservation frame at the sending moment in a broadcast manner.

FIG. 12is a schematic block diagram of a communications device according to another embodiment of the present invention.

A communications device120inFIG. 12may be configured to implement steps and methods in the foregoing method embodiments. In the embodiment ofFIG. 12, the communications device120includes an antenna1210, a transmitter1220, a receiver1230, a processor1240, and a memory1250. The processor1240controls an operation of the communications device120, and may be configured to process a signal. The memory1250may include a read-only memory and a random access memory, and provide an instruction and data to the processor1240. The transmitter1220and the receiver1230may be coupled to the antenna1210. Components of the communications device120are coupled together by using a bus system1260, where the bus system1260includes not only a data bus, but also a power bus, a control bus, and a status signal bus. However, for a clear description, various buses are marked as the bus system1260in the figure. The communications device120is a sender in a data transmission process, for example, may be an AP110or a STA120shown inFIG. 1.

Specifically, the memory1250may store an instruction for executing the following process: the processor1240generates a second indication frame, where the second indication frame is used for instructing a second device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the communications device sends data to the second device; and the transmitter1220sends the second indication frame to the second device.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which provides an implementable manner to resolve a problem about a hidden node.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the communications device is the sender in the data transmission process, and the second device is a receiver in the data transmission process. The second device may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, the memory1250may further store an instruction for executing the following process: when the transmitter1220sends the second indication frame to the second device, the processor1240may first control the communications device to perform random backoff; and then the transmitter1220sends the second indication frame to the second device when the channel is idle.

In this way, a collision probability can be further reduced, so that system overheads are reduced.

FIG. 13is a schematic block diagram of a communications device according to another embodiment of the present invention.

A communications device130inFIG. 13may be configured to implement steps and methods in the foregoing method embodiments. In the embodiment ofFIG. 13, the communications device130includes an antenna1310, a transmitter1320, a receiver1330, a processor1340, and a memory1350. The processor1340controls an operation of the communications device130, and may be configured to process a signal. The memory1350may include a read-only memory and a random access memory, and provide an instruction and data to the processor1340. The transmitter1320and the receiver1330may be coupled to the antenna1310. Components of the communications device130are coupled together by using a bus system1360, where the bus system1360includes not only a data bus, but also a power bus, a control bus, and a status signal bus. However, for a clear description, various buses are marked as the bus system1360in the figure. The communications device130is a receiver in a data transmission process, for example, may be an AP110or a STA120shown inFIG. 1.

Specifically, the memory1350may store an instruction for executing the following process: the receiver1330receives a second indication frame from a first device, where the second indication frame is used for instructing the communications device to send a channel reservation frame, and the channel reservation frame is used for reserving a channel to be used when the first device sends data to the communications device; and the transmitter1320sends the channel reservation frame.

In a channel reservation method in this embodiment of the present invention, a sender device in a data transmission process instructs a receiver device to send a channel reservation frame, and after the sender device receives the channel reservation frame, it is considered that current channel reservation is successful, and a transmission opportunity is obtained. The receiver devices send the channel reservation frame, to contend for a channel, and the sender device does not need to send an additional frame responding to the channel reservation frame, which provides an implementable manner to resolve a problem about a hidden node.

In addition, when transmission protection is performed according to the channel reservation method in this embodiment of the present invention, the channel reservation method is not limited by an application scenario, for example, a contention working mode, a scheduling mode, or a mode in which contention and scheduling are integrated. Therefore, this embodiment of the present invention has a wider application scope.

It should be understood that, the first device is a sender in the data transmission process, and the communications device is the receiver in the data transmission process. The communications device may send the channel reservation frame when receiving the second indication frame; therefore, a receiver in a data transmission process can send a channel reservation frame, thereby resolving a problem about a hidden node.

Optionally, as an embodiment, the memory1350may further store an instruction for executing the following process when the transmitter1320sends the channel reservation frame, the processor1340may first control the communications device to perform random backoff; and if the channel is idle, the transmitter1320then sends the channel reservation frame.