KR102034530B1 - Method of multiple frame transmission in wireless communication system and transmitter - Google Patents

Abstract

 Provided are a multiple frame transmission method and transmitter in a wireless communication system. The transmitter sends a request to send (RTS) frame having a first bandwidth to the receiver. TXOP (receiving a clear to send (CTS) frame having a second bandwidth from the receiver in response to the RTS frame, indicating that the transmitter has a right to transmit at least one data frame) establish a transmission opportunity. During the TXOP, the transmitter sequentially transmits a plurality of data frames to the receiver.

Description

METHOD OF MULTIPLE FRAME TRANSMISSION IN WIRELESS COMMUNICATION SYSTEM AND TRANSMITTER}

The present invention relates to wireless communication, and more particularly, to a multi-frame transmission method and a transmitter using the same in a wireless communication system.

Recently, with the development of information and communication technology, various wireless communication technologies have been developed. Among them, WLAN (Wireless Local Area Network) is based on radio frequency technology and uses a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), and the like. It is a technology that allows users to access the Internet wirelessly in a business or company or a specific service area.

In order to overcome the limitation of communication speed which has been pointed out as a weak point in WLAN, IEEE (Institute of Electrical and Electronics Engineering) 802.11n is a relatively recent technical standard. IEEE 802.11n aims to increase the speed and reliability of networks and to extend the operating range of wireless networks. More specifically, IEEE 802.11n supports high throughput with data throughput of up to 540 Mbps, and MIMO (multiple antennas on both sides of the transmitter and receiver to minimize transmission errors and optimize data rates). Multiple Inputs and Multiple Outputs) technology. In addition, the standard not only uses a coding scheme for transmitting multiple duplicate copies to increase data reliability, but may also use orthogonal frequency division multiplexing (OFDM) to increase the speed.

The Basic Access Mechanism of IEEE 802.11 Medium Access Control (MAC) is a Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) mechanism combined with binary exponential backoff. The CSMA / CA mechanism is also called the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC. It basically employs a "listen before talk" access mechanism. In this type of connection mechanism, a station (STA) listens to a radio channel or medium prior to starting transmission. As a result of the listening, if it is detected that the medium is not being used, the listening STA starts its own transmission. On the other hand, if the medium is detected to be in use, the station does not start its own transmission and enters a delay period determined by the binary exponential backoff algorithm.

The CSMA / CA mechanism includes virtual carrier sensing in addition to physical carrier sensing in which the STA directly listens to the medium. Virtual carrier sensing is intended to compensate for the limitation of physical carrier sensing such as hidden node problem. For virtual carrier sensing, IEEE 802.11 Medium Access Control (MAC) uses Network Allocation Vector (NAV). The NAV is a value indicative of a time remaining until a medium becomes available by a STA that is currently using or is authorized to use the medium. Therefore, the value set to NAV corresponds to a period in which the use of the medium is scheduled by the STA transmitting the corresponding frame.

One of the procedures for setting the NAV is an exchange procedure of a Request To Send (RTS) frame and a Clear To Send (CTS) frame. The RTS frame and the CTS frame include information that informs the receiving STAs of an upcoming frame transmission, thereby delaying the frame transmission by the receiving STA. The information may be included in, for example, a duration field of the RTS frame and the CTS frame. After the exchange of the RTS frame and the CTS frame, the source STA transmits the actual frame to be sent to the target STA.

TXOP (Transmission Opportunity) is the opposite concept of NAV that prevents frame transmission. TXOP means the time that the STA has a right to transmit a data frame.

Existing IEEE 802.11 systems support either 20 MHz or 40 MHz bandwidth. However, in order to obtain higher yields, supporting bandwidths of 80 MHz or more is required.

The existing CSMA / CA system assumes that the bandwidth set does not change when NAV or TXOP (Transmission Opportunity) is set. However, the entire set band may not always be used within the TXOP set to the wide band.

For example, as muti-user (MU-MIMO) -MIMO is introduced, data for a plurality of STAs may be transmitted as one aggregated MAC protocol data unit (A-MPDU). As the number of STAs within the configured TXOP is reduced, the size of the A-MPDU may be reduced, and thus the required bandwidth may be reduced.

There is a need for a technique that can dynamically allocate bandwidth and adjust dynamically.

The present invention provides a multi-frame transmission method for dynamically adjusting the bandwidth.

The present invention also provides a transmitter that dynamically adjusts bandwidth.

In one aspect, a multi-frame transmission method in a wireless communication system includes a transmitter transmitting a request to send (RTS) frame having a first bandwidth to a receiver, wherein the transmitter has a CTS having a second bandwidth in response to the RTS frame. (clear to send) receiving a frame from the receiver, establishing a transmission opportunity (TXOP) indicating a time at which the transmitter has the right to transmit at least one data frame, and wherein the transmitter has a plurality of Sequentially transmitting the data frames to the receiver. The bandwidth of each data frame is equal to or less than the second bandwidth, and the bandwidth of subsequent data frames is less than or equal to the bandwidth of the last data frame transmitted last before the subsequent data frame.

The second bandwidth may be less than or equal to the first bandwidth.

The first bandwidth may be one of 40 MHz, 80 MHz, and 160 MHz, and the second bandwidth may be one of 20 MHz, 40 MHz, 80 MHz, and 160 MHz.

The RTS frame may be repeatedly transmitted for each 20MHz of the first bandwidth.

The CTS frame may be repeatedly transmitted for each 20 MHz of the second bandwidth.

In another aspect, a transmitter for multi-frame transmission in a wireless communication system sends a request to send (RTS) frame having a first bandwidth to a receiver and clear to send having a second bandwidth in response to the RTS frame. Receive a frame from the receiver, establish a transmission opportunity (TXOP) indicating the time at which the transmitter has the right to transmit at least one data frame, and sequentially receive the plurality of data frames during the TXOP. It includes a processor to transmit to. The bandwidth of the data frame is equal to or less than the second bandwidth, and the bandwidth of the subsequent data frame is less than or equal to the bandwidth of the last data frame transmitted last before the subsequent data frame.

Bandwidth can be dynamically adjusted during the RTS-CTS process. In addition, the bandwidth of the data frame can be adjusted during TXOP, so that another STA can utilize the idle subchannel.

1 illustrates a configuration of an example of a WLAN system to which an embodiment of the present invention can be applied.
2 is an exemplary view illustrating a multiple frame transmission method according to an embodiment of the present invention.
3 is a flowchart illustrating a multiple frame transmission method according to an embodiment of the present invention.
4 is a flowchart illustrating a method of transmitting bandwidth information in a sounding procedure.
5 is a block diagram illustrating a transmitter in which an embodiment of the present invention is implemented.

1 illustrates a configuration of an example of a WLAN system to which an embodiment of the present invention can be applied.

A wireless local area network (WLAN) system includes one or more basic service sets (BSSs). The BSS is a set of stations (STAs) that can successfully synchronize and communicate with each other, and is not a concept indicating a specific area. In addition, a BSS that supports ultra-high speed data processing of 1 GHz or more is called a VHT (Very High Throughput) BSS.

A VHT system that includes one or more VHT BSSs may use 80 MHz channel bandwidth, which is exemplary. For example, the VHT system may use 20 MHz, 40 MHz, 80 MHz, 160 MHz, or more channel bandwidths. As such, the VHT system has a multi-channel environment in which a plurality of subchannels having a channel bandwidth of a predetermined size, for example, 20 MHz is included.

Subchannels may be classified into primary channels and secondary channels. The primary channel is designated among the subchannels, and the secondary channel is a non-primary channel.

The BSS may be classified into an infrastructure BSS (Independent BSS) and an Independent BSS (IBSS). The infrastructure BSS is illustrated in FIG. 1. The infrastructure BSS (BSS1, BSS2) connects one or more STAs (STA1, STA3, STA4), an access point (AP) that is a STA that provides a distribution service, and a plurality of APs (AP1, AP2). Distribution system (DS). On the other hand, since the IBSS does not include an AP, all STAs are configured as mobile stations, and thus access to the DS is not allowed, thereby forming a self-contained network.

A STA is any functional medium that includes a Medium Access Control (MAC) layer conforming to the IEEE 802.11 standard and a Physical Layer (PHY) interface to a wireless medium. Broadly speaking, an AP and a Non-AP Station Includes all of them. In addition, a STA that supports ultra-high speed data processing of 1 GHz or more in a multi-channel environment, which will be described later, is referred to as a VHT STA.

Among the STAs, the portable terminal operated by the user is a non-AP STA (STA1, STA3, STA4), which may simply refer to a non-AP STA. The non-AP STA may be a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, or a mobile subscriber unit. It may also be called another name (Mobile Subscriber Unit). In addition, a non-AP STA supporting ultra-high speed data processing of 1 GHz or more in a multi-channel environment as described below is referred to as a non-AP VHT STA.

The APs AP1 and AP2 are functional entities that provide access to the DS via a wireless medium for an associated station (STA) associated therewith. In an infrastructure BSS including an AP, communication between non-AP STAs is performed via an AP. However, when a direct link is established, direct communication between non-AP STAs is possible. The AP may be called a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller. In addition, an AP supporting ultra-fast data processing of 1 GHz or more in a multi-channel environment, which will be described later, is referred to as a VHT AP.

The plurality of infrastructure BSSs may be interconnected through a distribution system (DS). A plurality of BSSs connected through a DS is called an extended service set (ESS). STAs included in the ESS may communicate with each other, and a non-AP STA may move from one BSS to another BSS while seamlessly communicating within the same ESS.

The DS is a mechanism for one AP to communicate with another AP, which means that an AP transmits a frame for STAs coupled to a BSS managed by the AP or if one STA moves to another BSS. Frames can be delivered with external networks, such as wired networks. This DS does not necessarily need to be a network, and there is no limitation on its form as long as it can provide certain distribution services defined in IEEE 802.11. For example, the DS may be a wireless network such as a mesh network or a physical structure that connects APs to each other.

The embodiments described below assume a WLAN system using a multi-channel comprising four contiguous subchannels with a channel bandwidth of 20 MHz, but this is merely exemplary. There is no limit to the number of subchannels or channel bandwidth. For example, the bandwidth of the subchannel may be 5 MHz, 10 MHz, 40 MHz or 80 MHz. The multi-channel can include non-adjacent channels. For example, 80 + 80 MHz means that a multi-channel is composed of two non-contiguous channels having an 80 MHz bandwidth.

2 is an exemplary view illustrating a multiple frame transmission method according to an embodiment of the present invention.

The RTS frame and the CTS frame are transmitted in subchannel units. When the bandwidth of the subchannel is 20 MHz, four RTS frames are repeatedly transmitted in the 80 MHz bandwidth. Similarly, three CTS frames may be transmitted redundantly in a 60 MHz bandwidth.

This subchannel frame transmission allows the transmitter to easily negotiate the available bandwidth when there are a plurality of subchannels. For example, if a full 160 MHz bandwidth is available, but an idle channel is an 80 MHz bandwidth, the transmitter transmits an RTS frame in an idle 80 MHz bandwidth. The receiver receiving the RTS frame transmits the CTS frame in the idle 60MHz bandwidth. The transmitter transmits the data frame in the 60 MHz bandwidth in which the CTS frame was received.

The data frame may be transmitted using SU-MIMO or MU-MIMO.

Subchannels used by the RTS frame, the CTS frame, and the data frame may be contiguous.

Data frames are transmitted at bandwidths equal to or less than the bandwidth of the CTS frame. A plurality of data frames may be transmitted. The bandwidth of the subsequent data frame may be less than or equal to the bandwidth of the previous data frame.

The bandwidth of the data frame may be reduced, but cannot be greater than the bandwidth of the previous data frame. This has the advantage of allocating unused bandwidth to other STAs. In other words, the first data frame is transmitted with a bandwidth of 60MHz, the next data frame is transmitted with a bandwidth of 40MHz. In this case, the unused subchannel may determine that the other STA is idle to start the RTS-CTS process. Subchannels through which data frames are transmitted may be continuous.

The RTS frame includes a transmitter address field indicating an address of a transmitter transmitting the RTS frame, a receiver field indicating an address of a receiver, and a duration field. The interval field indicates a time required for transmitting a pending data frame, a CTS frame, an ACK frame, and a plurality of short interframe space (SIFS) intervals.

The CTS frame includes an address field and a duration field indicating the transmitter indicated in the transmitter address field of the RTS frame. The interval field represents a time obtained by excluding the CTS frame and the SIFS interval from the value obtained from the interval field of the RTS frame.

The RTS frame and the CTS frame are MAC frames generated at the MAC layer. How the transmitter will inform the receiver of the bandwidth over which the RTS frame is transmitted (this is called the first bandwidth) or how the receiver will inform the transmitter about the bandwidth over which the CTS frame is transmitted (this is called the second bandwidth).

According to the proposed embodiment, the first bandwidth and the second bandwidth may be included in a Physical Layer Convergence Procedure (PLCP) header of a PLC Protocol Protocol Data Unit (PPDU) including a corresponding MAC frame. The PLCP header may include an indicator indicating that the bandwidth may be dynamically changed in the RTS-CTS process.

3 is a flowchart illustrating a multiple frame transmission method according to an embodiment of the present invention. This describes the embodiment of FIG. 2 in more detail in chronological order.

STA1 transmits the RTS frame 310 and performs the function of a transmitter. STA2 transmits the CTS frame 320 in response to the RTS frame 310, and performs the function of the receiver.

STA1 transmits the RTS frame 310 to STA2 through four subchannels. STA2 transmits the CTS frame 320 to STA1. Thus, STA1 acquires TXOP. The bandwidth for the TXOP is equal to the bandwidth of the CTS frame 320. The bandwidth of the CTS frame 320 is less than or equal to the bandwidth of the RTS frame 310.

STA3 located near STA1 listens to the RTS frame 310 and sets the NAV 315. STA3 sets the NAV 315 based on the value obtained in the interval field of the RTS frame 310.

STA4 located near STA2 listens to the CTS frame 320 and sets the NAV 325. The STA4 sets the NAV 325 based on the value obtained in the interval field of the CTS frame 320.

During the TXOP, the STA1 sequentially transmits the first data frame 330 and the second data frame 340 to the STA2. The bandwidth of the first data frame 330 is less than or equal to the bandwidth of the CTS frame 320. Subsequent data frames have a bandwidth equal to or less than the previously transmitted data frame. This embodiment shows that the first data frame 330 has a 60 MHz bandwidth, and the second data frame 340 has a 40 MHz bandwidth.

After receiving the data frames 330 and 340, the STA2 transmits the ACK frame 350 to the STA1 as a reception acknowledgment for the data frames 330 and 340.

The RTS-CTS frame may be applied to MU-MIMO. The transmitter transmits an RTS frame to a plurality of receivers. A representative receiver of the plurality of receivers may transmit a CTS frame to the transmitter. The representative receiver may transmit the CTS frame within the maximum bandwidth that the plurality of receivers can commonly support.

Information about the available subchannels or the available bandwidth may be transmitted through a sounding frame. The sounding frame may be transmitted before or after the RTS-CTS exchange procedure.

4 is a flowchart illustrating a method of transmitting bandwidth information in a sounding procedure.

The sounding process is a procedure for determining channel status for SU-MIMO or MU-MIMO transmission. The STA1 becomes a beamformer to perform MU-MIMO transmission, and the STA2 and STA3 become beamformees that receive the beamformed data frame.

STA1 transmits a Null Data Packet Announcement (NDPA) frame 410. The NDPA frame 410 includes STA information for each beamformee. The STA information includes an identifier of a corresponding STA, a feedback type indicating a SU or MU, and an index indicating the number of spatial streams requested. Here, the NDPA frame 410 is said to include the first STA information for STA2 and the second STA information for STA3 sequentially.

After transmitting the NDAP frame 410, the STA1 transmits a null data packet (NDP) frame 420. The NDP frame is used by STA2 and STA3 to measure channel conditions.

STA2 corresponding to the first STA information among the STAs receiving the NDPA frame 410 transmits a feedback frame 430 to STA1. The feedback frame 430 includes channel state information regarding the number of spatial streams, the channel bandwidth on which the measurement was performed, the feedback type, and the beamforming feedback matrix. The feedback type is set to the same value as the feedback type of the corresponding STA information.

The channel state information includes feedback information in angular form representing the beamforming feedback matrix used by the beamformer to determine the steering matrix. The feedback information includes matrix matrix elements indexed by matrix angles in the order shown in the first predetermined table, and data subcarriers indexed from the lowest frequency to the highest frequency. In addition, the channel state information includes signal-to-noise ratio (SNR) information for each space-time stream and average SNR information for the entire space-time stream.

STA1 transmits a poll frame 440 to STA3. The poll frame 440 is a frame for requesting feedback from STA3.

STA3 transmits a feedback frame 450 to STA1.

5 is a block diagram illustrating a transmitter in which an embodiment of the present invention is implemented. 2 to 4 may be implemented by a transmitter.

The transmitter 10 includes a processor 11 and a memory 12. The processor 11 implements the functionality of a transmitter, beamformer or beamformer in the embodiment of FIGS. 2 and 4. The processor 11 may transmit an RTS frame and transmit at least one data frame. The memory 12 stores parameters for the operation of the processor 11.

The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

Claims (12)

In the wireless communication method,
Transmitting, by the first STA, a Null Data Packet Announcement (NDPA) frame to the second STA;
Transmitting, by the first STA, a null data packet (NDP) to a second STA;
The first STA receiving feedback from the second STA, the feedback comprising a beamforming feedback matrix calculated by the second STA based on the NDP;
Transmitting, by the first STA, a request to send (RTS) frame to the second STA through each of a plurality of channels;
Receiving, by the first STA, a Clear To Send (CTS) frame through one or more channels of a plurality of channels, respectively, wherein one or more channels of the plurality of channels are selected by the second STA; And
And transmitting, by the first STA, data to the second STA through one or more channels of the plurality of channels based on the feedback.
Wherein the number of the plurality of channels through which the RTS frame is transmitted is greater than the number of one or more channels among the plurality of channels through which the CTS frame is received.
The method of claim 1,
The Physical Layer Convergence Procedure (PLCP) header of the RTS frame transmitted through each of the plurality of channels includes a first indicator indicating a first bandwidth of the plurality of channels,
The PLCP header of the CTS frame received on one or more channels of the plurality of channels includes a second indicator indicating a second bandwidth of one or more channels of the plurality of channels. Communication method.
The method of claim 2,
A third indicator indicating whether or not the PLCP header of the RTS frame is capable of receiving a number of CTS frames different from the number of the RTS frames transmitted by the first STA; Further comprising).
In the wireless communication method,
Receiving, by the first STA, a Null Data Packet Announcement (NDPA) frame from the second STA;
Receiving, by the first STA, a null data packet (NDP) from the second STA;
Calculating, by the first STA, a beamforming feedback matrix based on the NDP;
Transmitting, by the first STA, feedback including the beamforming feedback matrix to the second STA;
Receiving, by the first STA, a Request To Send (RTS) frame from the second STA through each of a plurality of channels;
The first STA selecting one or more channels but not all of the plurality of channels;
Transmitting, by the first STA, a clear to send (CTS) frame to the second STA through the selected one or more channels; And
And receiving, by the first STA, data from the second STA through the selected one or more channels based on the feedback.
The data is transmitted from the second STA based on the feedback.
And the number of the plurality of channels through which the RTS frame is received is greater than the number of one or more channels among the plurality of channels through which the CTS frame is transmitted.
The method of claim 4, wherein
The Physical Layer Convergence Procedure (PLCP) header of the RTS frame transmitted through each of the plurality of channels includes a first indicator indicating a first bandwidth of the plurality of channels,
The PLCP header of the CTS frame received on the selected one or more channels includes a second indicator indicating a second bandwidth of the selected one or more channels.
The method of claim 5,
A third indicator indicating whether or not the PLCP header of the RTS frame is capable of receiving a number of CTS frames different from the number of the RTS frames transmitted by the first STA; Further comprising).
In a wireless communication device,
Memory;
At least one processor connected to the memory; including,
When the at least one processor performs a program operation stored in the memory, the at least one processor,
Allow the device to send a NDPA (Null Data Packet Announcement) frame to another device,
Let the device send a NDP (Null Data Packet) to the other device,
Cause the device to receive feedback from the other device, the feedback comprising a beamforming feedback matrix calculated by the other device based on the NDP,
Allow the device to transmit a Request To Send (RTS) frame to each other device through a plurality of channels;
Allow the device to receive a Clear To Send (CTS) frame through one or more of a plurality of channels, respectively, wherein one or more channels of the plurality of channels are selected by the other device, and
Allow the device to send data to the other device over one or more of the plurality of channels based on the feedback;
And the number of the plurality of channels through which the RTS frame is transmitted is greater than the number of one or more channels among the plurality of channels through which the CTS frame is received.
The method of claim 7, wherein
The Physical Layer Convergence Procedure (PLCP) header of the RTS frame transmitted through each of the plurality of channels includes a first indicator indicating a first bandwidth of the plurality of channels,
The PLCP header of the CTS frame received on one or more of the plurality of channels includes a second indicator indicating a second bandwidth of one or more of the plurality of channels. Communication device.
The method of claim 8,
The PLCP header of the RTS frame is a third indicator indicating whether a first STA is capable of receiving a number of CTS frames different from the number of the RTS frames transmitted by the first STA. The wireless communication device further comprises.
In a wireless communication device,
Memory;
At least one processor connected to the memory; including,
When the at least one processor performs a program operation stored in the memory, the at least one processor,
Have the device receive a Null Data Packet Announcement (NDPA) frame from another device,
Allow the device to receive NDP (Null Data Packet) from the other device,
Calculate a beamforming feedback matrix based on the NDP,
Allow the device to send feedback including the beamforming feedback matrix to the other device,
Allow the device to receive a request to send (RTS) frame from the other device through a plurality of channels,
Select one or more channels, but not all of the plurality of channels,
Allow the device to send a Clear To Send (CTS) frame to the other device over the selected one or more channels,
Allow the device to receive data from the other device over the selected one or more channels based on the feedback,
The data is transmitted from the other device based on the feedback,
And the number of the plurality of channels through which the RTS frame is received is greater than the number of one or more channels among the plurality of channels through which the CTS frame is transmitted.
The method of claim 10,
The Physical Layer Convergence Procedure (PLCP) header of the RTS frame transmitted through each of the plurality of channels includes a first indicator indicating a first bandwidth of the plurality of channels,
The PLCP header of the CTS frame received on one or more channels of the plurality of channels includes a second indicator indicating a second bandwidth of one or more channels of the plurality of channels. Communication device.
The method of claim 11,
The PLCP header of the RTS frame is a third indicator indicating whether a first STA is capable of receiving a number of CTS frames different from the number of the RTS frames transmitted by the first STA. The wireless communication device further comprises.

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