WO2016126077A2 - Wireless communication method and wireless communication terminal using training signal - Google Patents

Abstract

A wireless communication terminal is disclosed. The wireless communication terminal comprises: a transceiver unit for transmitting and receiving a wireless signal; and a processor for controlling an operation of the wireless communication terminal. The transceiver unit receives a training signal from a base wireless communication terminal and receives data from the base wireless communication terminal on the basis of the training signal. The base wireless communication terminal allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals including the wireless communication terminal, and transmits the training signal and the data to the plurality of wireless communication terminals through each of the plurality of sub-frequency bands.

Description

Wireless communication method and wireless communication terminal using training signal

The present invention relates to a wireless communication method and a wireless communication terminal for establishing a broadband link. Specifically, the present invention relates to a wireless communication method and a wireless communication terminal for increasing the data communication bandwidth of the terminal to increase the data communication efficiency.

Recently, with the spread of mobile devices, wireless LAN technology, which can provide fast wireless Internet service to them, is getting much attention. Wireless LAN technology is a technology that enables wireless devices such as smart phones, smart pads, laptop computers, portable multimedia players, and embedded devices to wirelessly access the Internet at home, enterprise, or specific service area based on wireless communication technology at short range. to be.

Since IEEE (Institute of Electrical and Electronics Engineers) 802.11 supports the initial wireless LAN technology using the 2.4GHz frequency, various standards of technology are being put into practice or being developed. First, IEEE 802.11b supports communication speeds up to 11Mbps while using frequencies in the 2.4GHz band. IEEE 802.11a, which has been commercialized after IEEE 802.11b, reduces the influence of interference compared to the frequency of the congested 2.4 GHz band by using the frequency of the 5 GHz band instead of the 2.4 GHz band. Orthogonal Frequency Division Multiplexing, It uses OFDM technology to increase the communication speed up to 54Mbps. However, IEEE 802.11a has a shorter communication distance than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses a frequency of 2.4 GHz band to realize a communication speed of up to 54 Mbps and satisfies backward compatibility, which has received considerable attention. Is in the lead.

In addition, IEEE 802.11n is a technical standard established to overcome the limitation of communication speed, which has been pointed out as a weak point in WLAN. 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 (HT) with data throughput of up to 540 Mbps and also uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. It is based on Multiple Inputs and Multiple Outputs (MIMO) technology. In addition, the specification may use a coding scheme that transmits multiple duplicate copies to increase data reliability.

As the spread of wireless LANs is activated and applications are diversified, there is a need for a new wireless LAN system to support higher throughput (VHT) than the data throughput supported by IEEE 802.11n. It became. Among them, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at 5GHz frequency. The IEEE 802.11ac standard is defined only in the 5GHz band, but for backwards compatibility with existing 2.4GHz band products, early 11ac chipsets will also support operation in the 2.4GHz band. Theoretically, this specification allows multiple stations to have a minimum WLAN speed of 1 Gbps and a maximum single link speed of at least 500 Mbps. This is accomplished by extending the 802.11n concept of wireless interfaces, including wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to eight), multi-user MIMO, and higher density modulation (up to 256 QAM). In addition, IEEE 802.11ad is a method of transmitting data using a 60 GHz band instead of the existing 2.4 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that uses beamforming technology to provide speeds of up to 7Gbps, and is suitable for streaming high bitrate video such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band is difficult to pass through obstacles, and thus can be used only between devices in a short space.

On the other hand, as the next generation wireless LAN standard after 802.11ac and 802.11ad, a discussion for providing a high-efficiency and high-performance wireless LAN communication technology in a high-density environment continues. That is, in a next generation WLAN environment, high frequency efficiency communication should be provided indoors / outdoors in the presence of a high density station and an access point (AP), and various technologies are required to implement this.

In particular, as the number of devices using a wireless LAN increases, it is necessary to efficiently use a predetermined channel. Therefore, there is a need for a technology capable of efficiently using bandwidth by simultaneously transmitting data between a plurality of stations and an AP.

One embodiment of the present invention is to provide an efficient wireless communication method and a wireless communication terminal.

In particular, an embodiment of the present invention is to provide a wireless communication method and a wireless communication terminal using a training signal.

Wireless communication terminal according to an embodiment of the present invention, the base wireless communication terminal is a transceiver for transmitting and receiving a wireless signal; And a processor for controlling an operation of the wireless communication terminal, wherein the transceiver unit allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals, and transmits a training signal and data through each of the plurality of sub-frequency bands. The training signal is used to estimate the channel over which the data is transmitted.

At this time, the transmission and reception unit may start the transmission of the training signal at the same time in each of the plurality of sub-frequency bands, and may terminate the transmission of the training signal at the same time.

In addition, the transceiver unit transmits an equal number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in each of the plurality of sub-frequency bands, and the training signal OFDM symbol includes an OFDM symbol including the training signal. Can be represented.

The transceiver may transmit the training signal based on a frequency band in which the most space-time streams of the plurality of sub-frequency bands are transmitted.

The number of the training signal OFDM symbols required in the corresponding sub-frequency band is greater than the number of the first OFDM symbols, which is the number of the training signal OFDM symbols required in the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. If the number of second OFDM symbols is small, additional training signals may be transmitted in the corresponding band by the difference between the number of first OFDM symbols and the number of second OFDM symbols.

In this case, the additional training signal may be a repetition of the previously transmitted training signal.

The additional training signal may be a cyclic shift of the previously transmitted training signal.

The additional training signal may be a training signal including a subcarrier having a phase pattern for canceling a space-time stream transmitted in a sub-frequency band different from the sub-frequency band in which the additional training signal is transmitted.

The transmitter / receiver is a subcarrier indicated by one row of the number of second OFDM symbols from one row of the N × N orthogonal matrix in an N × N orthogonal matrix applied to the phase of the subcarrier included in the training signal in OFDM symbol units. The training signal may be transmitted to each of the plurality of sub-frequency bands according to a phase of N, and N may represent the number of the first OFDM symbols.

In addition, the transceiver may transmit the training signal based on a frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted.

In this case, the transmission / reception unit performs combined training in a frequency band where the training signal OFDM symbols are required more than the number of the training signal OFDM symbols required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. The signal is transmitted, and the combined training signal may be a training signal combining a plurality of the training signals into one.

A plurality of training signals included in the combined training signal may be combined on a frequency axis.

The combined training signal may be a combination of a plurality of training signals in an orthogonal code axis.

The training signal may transmit a signal on an even subcarrier included in the training signal and may not transmit a signal on an odd subcarrier.

Wireless communication terminal according to an embodiment of the present invention includes a transceiver for transmitting and receiving a wireless signal; And a processor for controlling an operation of the wireless communication terminal, wherein the transceiver receives a training signal from a base wireless communication terminal, receives data from the base wireless communication terminal based on the training signal, and receives the base wireless communication. The terminal allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals including the wireless communication terminal, and signals the training signal and the data to the plurality of wireless communication terminals through each of the plurality of sub frequency bands. Can transmit

In this case, each of the plurality of wireless communication terminals may start receiving the training signal at the same time in each of the plurality of sub-frequency bands and end the reception of the training signal at the same time.

Further, each of the plurality of wireless communication terminals receives an equal number of training signal Orthogonal Frequency Division Multiplexing (OFDM) symbols in each of the plurality of sub-frequency bands, and the training signal OFDM symbol receives the training signal. The OFDM symbol may be included.

The transceiver unit receives the data from the wireless communication terminal by receiving the data than the number of the first OFDM symbol is the number of the training signal OFDM symbols required in the sub-frequency band for transmitting the most space-time stream of the plurality of sub-frequency bands When the number of second OFDM symbols that is the number of the training signal OFDM symbols required in the frequency band is small, the additional training signal may be received by the difference between the number of the first OFDM symbols and the number of the second OFDM symbols.

The transmitter / receiver is a subcarrier indicated by one row of the number of second OFDM symbols from one row of the N × N orthogonal matrix in an N × N orthogonal matrix applied to the phase of the subcarrier included in the training signal in OFDM symbol units. The channel on which the data is transmitted is estimated based on a phase of N, and N may be the number of the first OFDM symbols.

Method of operation of a wireless communication terminal according to an embodiment of the present invention comprises the steps of receiving a training signal from the base wireless communication terminal; And receiving data from the base wireless communication terminal based on the training signal, wherein the base wireless communication terminal allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals including the wireless communication terminal. The training signal and the data may be transmitted to the plurality of wireless communication terminals through each of the plurality of sub frequency bands.

One embodiment of the present invention provides an efficient wireless communication method and a wireless communication terminal.

In particular, an embodiment of the present invention provides a wireless communication method and a wireless communication terminal using the training signal efficiently.

1 illustrates a WLAN system according to an embodiment of the present invention.

2 shows a WLAN system according to another embodiment of the present invention.

3 is a block diagram showing a configuration of a station according to an embodiment of the present invention.

4 is a block diagram illustrating a configuration of an access point according to an embodiment of the present invention.

5 schematically shows a process of establishing a link with an access point by a station according to an embodiment of the present invention.

6 shows channel allocation of a 2.4 GHz band for OFDMA wireless communication according to an embodiment of the present invention.

7 illustrates channel allocation of a 5 GHz band for OFDMA wireless communication according to an embodiment of the present invention.

8 illustrates an OFDMA operating principle of a wireless communication device according to an embodiment of the present invention.

9 shows a format of a physical frame according to an embodiment of the present invention.

10 illustrates a detailed format of a physical frame and a signaling field of a physical frame according to an embodiment of the present invention.

11 shows a specific format of a physical frame according to another embodiment of the present invention.

12 illustrates a method of configuring a physical frame according to whether MU and MIMO are used when OFDMA is not used in an embodiment of the present invention.

FIG. 13 illustrates a method of configuring a physical frame according to whether MU and MIMO are used when OFDMA is used in an embodiment of the present invention.

14 illustrates a method for aligning durations of OFDM symbols in each sub-frequency band in communication using OFDMA according to an embodiment of the present invention.

FIG. 15 shows that a first wireless communication terminal transmits data using a LTF to a plurality of second wireless communication terminals according to an embodiment of the present invention.

FIG. 16 illustrates signal patterns of subcarriers included in an LTF when the LTF is transmitted using 64 FFT, 128 FFT, and 256 FFT according to an embodiment of the present invention.

FIG. 17 illustrates a specific signal pattern of subcarriers included in the LTF described with reference to FIG. 16.

FIG. 18 illustrates a signal pattern of a subcarrier included in an LTF signal for SU using 256 FFTs in a 20 MHz band according to an embodiment of the present invention.

19 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 17 in detail.

20 shows a structure of a physical frame transmitted by a plurality of stations to an AP.

21 shows signal patterns of subcarriers included in an LTF used when 9 stations transmit data to an AP.

FIG. 22 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 21.

FIG. 23 shows signal patterns of subcarriers included in an LTF used when five stations transmit data to an AP.

24 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 23 in detail.

FIG. 25 shows a signal pattern of a subcarrier included in an LTF used when three stations transmit data to an AP.

FIG. 26 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 25 in detail.

27 is a view illustrating a signal pattern of a subcarrier included in an LTF transmitted by a second wireless communication terminal according to one embodiment of the present invention.

FIG. 28 shows signal patterns of subcarriers included in the LTF described with reference to FIG. 27 in detail.

29 illustrates a method of channel estimation using an LTF according to an embodiment of the present invention.

30 shows a method of channel estimation using an LTF according to another embodiment of the present invention.

31 is a matrix illustrating a phase pattern applied in units of OFDM symbols to subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention.

32 is a view illustrating specific values of a phase pattern applied in units of OFDM symbols to subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention.

FIG. 33 is a diagram illustrating an orthogonal pattern applied to a predetermined number of subcarrier units to individual subcarriers included in an LTF used by a wireless communication terminal according to another embodiment of the present invention.

FIG. 34 is a matrix illustrating an orthogonal pattern applied to each subcarrier included in an LTF used by a wireless communication terminal in a predetermined number of subcarriers according to another embodiment of the present invention.

35 is a view illustrating a method of estimating a channel using an orthogonal pattern applied to an individual subcarrier included in an LTF used by a wireless communication terminal according to another embodiment of the present invention.

36 is a detailed operation of estimating a channel based on LTFs including 26 subcarriers using an orthogonal pattern applied to individual subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention. Shows.

FIG. 37 is a view illustrating specific channel estimation based on an LTF including 26 subcarriers using an orthogonal pattern applied to individual subcarriers included in an LTF used by a wireless communication terminal according to another embodiment of the present invention. Show the action.

38 illustrates that a wireless communication terminal according to an embodiment of the present invention applies a first orthogonal pattern to an individual subcarrier included in an LTF and transmits an LTF to which an orthogonal pattern is applied to an individual subcarrier according to a second orthogonal pattern. Shows.

39 illustrates a case in which a wireless communication terminal applies a first orthogonal pattern to an individual subcarrier included in an LTF and transmits an LTF to which an orthogonal pattern is applied to an individual subcarrier according to a second orthogonal pattern according to an embodiment of the present invention; In this case, a method of estimating a channel using the LTF is shown by the wireless communication terminal receiving the same.

40 illustrates a wireless communication terminal applying a first orthogonal pattern having a unit number of 4 to individual subcarriers included in an LTF, and applying a second orthogonal pattern to an LTF to which an orthogonal pattern is applied to individual subcarriers. According to the show to send.

FIG. 41 is a view illustrating a SU-MIMO physical frame transmitted by a wireless communication terminal according to an embodiment of the present invention using various orthogonal patterns described above.

42 illustrates a physical frame transmitted by each of a plurality of stations when a plurality of stations transmit data to the AP through MU-MIMO according to an embodiment of the present invention.

43 is a ladder diagram illustrating operations of a first wireless communication terminal and a second wireless communication terminal according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

This application claims the priority based on the Republic of Korea Patent Application No. 10-2015-0016322, 10-2015-0062806, 10-2015-0064992, and 10-2015-0086024, the basis of the priority Examples and descriptions described in each of the above applications are to be included in the detailed description of the present application.

1 illustrates a WLAN system according to an embodiment of the present invention. The WLAN system includes one or more Basic Service Sets (BSSs), which represent a set of devices that can successfully synchronize and communicate with each other. In general, the BSS may be classified into an infrastructure BSS (Independent BSS) and an Independent BSS (IBSS), and FIG. 1 illustrates an infrastructure BSS.

As shown in FIG. 1, an infrastructure BSS (BSS1, BSS2) is an access point (PCP / AP) that is a station that provides one or more stations (STA1, STA2, STA3, STA_d, STA5), and a distribution service. -1, PCP / AP-2), and a Distribution System (DS) connecting multiple access points (PCP / AP-1, PCP / AP-2).

A station (STA) is any device that includes a medium access control (MAC) compliant with the IEEE 802.11 standard and a physical layer interface to a wireless medium. This includes both access points (APs) as well as non-AP stations. In addition, in the present specification, the term 'terminal' may be used as a concept including both a station and an WLAN communication device such as an AP. The station for wireless communication may include a processor and a transmit / receive unit, and may further include a user interface unit and a display unit according to an embodiment. The processor may generate a frame to be transmitted through the wireless network or process a frame received through the wireless network, and may perform various processing for controlling the station. The transceiver is functionally connected to the processor and transmits and receives a frame through a wireless network for a station.

An access point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for an associated station to the AP. In the infrastructure BSS, communication between non-AP stations is performed via an AP. However, when a direct link is established, direct communication between non-AP stations is possible. Meanwhile, in the present invention, the AP is used as a concept including a personal BSS coordination point (PCP), and is broadly used as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site. It can include all the concepts such as a controller.

The plurality of infrastructure BSSs may be interconnected through a distribution system (DS). At this time, the plurality of BSSs connected through the distribution system is referred to as an extended service set (ESS).

2 illustrates an independent BSS, which is a wireless LAN system according to another embodiment of the present invention. In the embodiment of FIG. 2, the same or corresponding parts as those of the embodiment of FIG. 1 will be omitted.

Since BSS3 shown in FIG. 2 is an independent BSS and does not include an AP, all stations STA6 and STA7 are not connected to the AP. Independent BSSs do not allow access to the distribution system and form a self-contained network. In the independent BSS, the respective stations STA6 and STA7 may be directly connected to each other.

3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention.

As shown, the station 100 according to an embodiment of the present invention may include a processor 110, a transceiver 120, a user interface 140, a display unit 150, and a memory 160. .

First, the transceiver 120 transmits and receives a wireless signal such as a wireless LAN packet, may be provided in the station 100 or externally provided. According to an embodiment, the transceiver 120 may include at least one transceiver module using different frequency bands. For example, the transceiver 120 may include a transceiver module of different frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 may include a transmission / reception module using a frequency band of 6 GHz or more and a transmission / reception module using a frequency band of 6 GHz or less. Each transmit / receive module may perform wireless communication with an AP or an external station according to a wireless LAN standard of a frequency band supported by the corresponding transmit / receive module. The transceiver 120 may operate only one transceiver module at a time or simultaneously operate multiple transceiver modules according to the performance and requirements of the station 100. When the station 100 includes a plurality of transmit / receive modules, each transmit / receive module may be provided in an independent form, or a plurality of modules may be integrated into one chip.

Next, the user interface unit 140 includes various types of input / output means provided in the station 100. That is, the user interface unit 140 may receive a user input by using various input means, and the processor 110 may control the station 100 based on the received user input. In addition, the user interface 140 may perform an output based on a command of the processor 110 using various output means.

Next, the display unit 150 outputs an image on the display screen. The display unit 150 may output various display objects such as contents executed by the processor 110 or a user interface based on a control command of the processor 110. In addition, the memory 160 stores a control program used in the station 100 and various data according thereto. Such a control program may include an access program necessary for the station 100 to perform an access with an AP or an external station.

The processor 110 of the present invention may execute various instructions or programs and process data in the station 100. In addition, the processor 110 may control each unit of the station 100 described above, and may control data transmission and reception between the units. According to an embodiment of the present disclosure, the processor 110 may execute a program for accessing an AP stored in the memory 160 and receive a communication setup message transmitted by the AP. In addition, the processor 110 may read information on the priority condition of the station 100 included in the communication configuration message, and request a connection to the AP based on the information on the priority condition of the station 100. The processor 110 of the present invention may refer to the main control unit of the station 100, and according to an embodiment, a part of the station 100 may be referred to, for example, a control unit for individually controlling the transceiver 120 and the like. You can also point it. The processor 110 controls various operations of the wireless signal transmission and reception of the station 100 according to an embodiment of the present invention. Specific embodiments thereof will be described later.

The station 100 illustrated in FIG. 3 is a block diagram according to an embodiment of the present invention, in which blocks marked separately represent logical elements of devices. Therefore, the elements of the above-described device may be mounted in one chip or in a plurality of chips according to the design of the device. For example, the processor 110 and the transceiver 120 may be integrated into one chip or implemented as a separate chip. In addition, in the embodiment of the present invention, some components of the station 100, such as the user interface unit 140 and the display unit 150, may be selectively provided in the station 100.

4 is a block diagram illustrating a configuration of an AP 200 according to an exemplary embodiment.

As shown, the AP 200 according to an embodiment of the present invention may include a processor 210, a transceiver 220, and a memory 260. In FIG. 4, overlapping descriptions of parts identical or corresponding to those of the station 100 of FIG. 3 will be omitted.

Referring to FIG. 4, the AP 200 according to the present invention includes a transceiver 220 for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the transceiver 220 of the AP 200 may also include a plurality of transceiver modules using different frequency bands. That is, the AP 200 according to the embodiment of the present invention may be provided with two or more transmit / receive modules of different frequency bands, for example, 2.4 GHz, 5 GHz, and 60 GHz. Preferably, the AP 200 may include a transmission / reception module using a frequency band of 6 GHz or more and a transmission / reception module using a frequency band of 6 GHz or less. Each transmit / receive module may perform wireless communication with a station according to a wireless LAN standard of a frequency band supported by the corresponding transmit / receive module. The transceiver 220 may operate only one transceiver module at a time or simultaneously operate multiple transceiver modules according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 and various data according thereto. Such a control program may include an access program for managing a connection of a station. In addition, the processor 210 may control each unit of the AP 200 and may control data transmission and reception between the units. According to an embodiment of the present disclosure, the processor 210 may execute a program for accessing a station stored in the memory 260 and transmit a communication setting message for one or more stations. In this case, the communication setting message may include information on the access priority condition of each station. In addition, the processor 210 performs connection establishment according to a connection request of a station. The processor 210 controls various operations of wireless signal transmission and reception of the AP 200 according to an embodiment of the present invention. Specific embodiments thereof will be described later.

5 schematically illustrates a process in which an STA establishes a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is largely established through three steps of scanning, authentication, and association. First, the scanning step is a step in which the STA 100 obtains access information of a BSS operated by the AP 200. As a method for performing scanning, a passive scanning method for obtaining information by using only a beacon message S101 periodically transmitted by the AP 200, and a STA 100 requests a probe to the AP. There is an active scanning method of transmitting a probe request (S103) and receiving a probe response from the AP (S105) to obtain access information.

The STA 100 that has successfully received the radio access information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs an authentication step. do. After the authentication step is performed, the STA 100 transmits an association request (S109a), receives an association response from the AP 200 (S109b), and performs the association step. In the present specification, the association (association) basically means a wireless coupling, the present invention is not limited to this, the binding in the broad sense may include both wireless coupling and wired coupling.

Meanwhile, the 802.1X based authentication step S111 and the IP address obtaining step S113 through DHCP may be performed. In FIG. 5, the authentication server 300 is a server that processes 802.1X-based authentication with the STA 100 and may be physically coupled to the AP 200 or may exist as a separate server.

When data is transmitted using orthogonal frequency division multiple access (OFDMA) or multi input multi output (MIMO), any one wireless communication terminal may simultaneously transmit data to a plurality of wireless communication terminals. In addition, any one wireless communication terminal can receive data from a plurality of wireless communication terminals at the same time.

For convenience of description, any one wireless communication terminal communicating with a plurality of wireless communication terminals at the same time is referred to as a first wireless communication terminal, and a plurality of wireless communication terminals communicating with the first wireless communication terminal simultaneously with a plurality of second wireless terminals. This is called a communication terminal. The first wireless communication terminal may also be referred to as a base wireless communication terminal. In addition, the first wireless communication terminal may be a wireless communication terminal for allocating and scheduling communication medium resources in communication with the plurality of wireless communication terminals. In more detail, the first wireless communication terminal may function as a cell coordinator. In this case, the first wireless communication terminal may be the access point 200. In addition, the second wireless communication terminal may be a station 100 associated with the access point 200. According to a specific embodiment of the present invention, the first wireless communication terminal may be a wireless communication terminal for allocating communication medium resources and scheduling in an independent network that is not connected to an external distribution service such as an ad-hoc network. In addition, the first wireless communication terminal may be at least one of a base station, an eNB, and a transmission point (TP).

6 to 43, a method in which any one of the first wireless communication terminals communicates with the plurality of second wireless communication terminals will be described. Specifically, a method of using a training signal when any one of the first wireless communication terminals and the plurality of second wireless communication terminals communicates will be described.

6 to 7, a description will be given of a frequency band defined as being used by a wireless communication terminal using wireless LAN communication and a wireless communication terminal using the corresponding frequency band according to an embodiment of the present invention.

6 shows channel allocation of a 2.4 GHz band for OFDMA wireless communication according to an embodiment of the present invention.

An unlicensed frequency band is a frequency band designated for universal use without a specific purpose. Specifically, the 100 MHz frequency band of 2.4 GHz to 2.5 GHz is an unlicensed Industrial Scientific Medical (ISM) frequency band designated for industrial, scientific, and medical use.

A wireless communication terminal for wireless LAN communication in the 100 MHz frequency band of 2.4 GHz to 2.5 GHz may use channels 1 to 13 in 5 MHz units. In this case, the channel number is assigned by the Institute of Electrical and Electronics Engineers (IEEE). Specifically, the center frequency of channel 1 is 2412 MHz, the center frequency of channel 2 is 2417 MHz, and the center frequency of channel 13 is 2472 MHz. In the US, channels 1 through 11 are used, and most countries outside the US use channels 1 through 13.

When the wireless communication terminal uses a 20MHz bandwidth, in order to minimize interference and use a frequency band without overlapping, the wireless communication terminal should use channel 1, channel 5, channel 9, and channel 13. However, in the United States, channels 12 and 13 cannot be used, so the 20MHz frequency band of three channels 1, 6, and 11 is used to minimize the interference between channels.

When the wireless communication terminal uses a 40MHz bandwidth, the existing 802.11n standard specifies that the wireless communication terminal uses a 40MHz frequency band centered on channel 3 or channel 4.

A wireless communication terminal according to an embodiment of the present invention may use a 40 MHz frequency band centering on channel 11 as well as channel 3 and channel 4. In addition, the wireless communication terminal according to an embodiment of the present invention may use the 80MHz frequency band centering on channel 7.

When the first wireless communication terminal communicates with a plurality of second wireless communication terminals through orthogonal frequency-division multiple access (OFDMA) in the 2.4 GHz band, the first wireless communication terminal has a bandwidth of any one of 20 MHz, 40 MHz, and 80 MHz. It is possible to use a frequency band having a.

In this case, each of the plurality of second wireless communication terminals may be allocated a sub-frequency band having any one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, and 20 MHz. In this case, the sub-frequency band is a frequency band included in the entire frequency band and having a bandwidth smaller than that of the entire frequency band. In a specific embodiment, when the first wireless communication terminal communicates with two second wireless communication terminals and uses a 20 MHz frequency band, the first wireless communication terminal has a sub-frequency having a 10 MHz bandwidth in each of the two second wireless communication terminals. Bands can be allocated. In addition, when the first wireless communication terminal communicates with two second wireless communication terminals and uses a 40 MHz frequency band, the first wireless communication terminal may assign a sub-frequency band having a 20 MHz bandwidth to each of the two second wireless communication terminals. Can be assigned. In addition, when the first wireless communication terminal communicates with two second wireless communication terminals and uses an 80 MHz frequency band, the first wireless communication terminal has a sub-frequency band having a 40 MHz bandwidth to each of the two second wireless communication terminals. Can be assigned.

7 illustrates channel allocation of a 5 GHz band for OFDMA wireless communication according to an embodiment of the present invention.

The 665 MHz frequency band from 5.170 GHz to 5.835 GHz is also an unlicensed ISM frequency band designated for industrial, scientific, and medical use. A wireless communication terminal for wireless LAN communication selects and uses various non-overlapping channels in the 5 GHz frequency band.

In the 5 GHz frequency band, the channel number assigned by the IEEE is used in 5 MHz units. At this time, the start frequency of channel 34 is 5170MHZ, the start frequency of channel 35 is 5175MHz. In addition, the center frequency of the channel having a 20 MHz bandwidth combining channels 34 to 37 is the same as the start frequency of channel 36. Accordingly, a channel having a 20 MHz bandwidth combining channels 34 to 37 may be referred to as 36 channel 20 MHz.

The wireless communication terminal can use only non-overlapping 20 MHz channels such as channels 36, 40, and 44 in the 5 GHz frequency band, and overlaps adjacent channels as in the 2.4 GHz band. Cannot be used.

The existing 802.11ac standard stipulates that 20 MHz, 40 MHz, 80 MHz, and 160 MHz bandwidths are available in this 5 GHz band. A wireless communication terminal according to an exemplary embodiment of the present invention may use a channel having a 20 MHz, 40 MHz, 80 MHz, and 160 MHz bandwidth in a 5 GHz band.

Therefore, when the first wireless communication terminal allocates the frequency bandwidth to three or four second wireless communication terminal evenly, the first wireless communication terminal is any of 5MHz, 10MHz, 20MHz, and 40MHz to each of the second wireless communication terminal It is possible to allocate a sub-frequency band having one bandwidth.

In addition, when the first wireless communication terminal allocates the frequency bandwidth to the two second wireless communication terminal evenly, the first wireless communication terminal to the bandwidth of any one of 10MHz, 20MHz, and 40MHz to each of the second wireless communication terminal Can have a sub-frequency band.

When the first wireless communication terminal allocates the frequency bandwidth to each of the second wireless communication terminal unevenly, the first wireless communication terminal may allocate a frequency bandwidth of at least 5MHz to 120MHz to the second wireless communication terminal.

8 illustrates an OFDMA operating principle of a wireless communication device according to an embodiment of the present invention.

According to a specific embodiment, the first wireless communication terminal may transmit data to the plurality of second wireless communication terminals according to the following principle described in FIG.

The first wireless communication terminal can transmit data to up to four second wireless communication terminals at the same time. In the 802.11ac standard and the like defined before the embodiment of the present invention, any one wireless communication terminal can transmit data to four wireless communication terminals through MIMO (Multi-Input Multi-Output). Accordingly, when the first wireless communication terminal transmits data to four second wireless communication terminals, the previously defined signaling field may be used.

In addition, the first wireless communication terminal may allocate frequency bands having uneven bandwidths to each of the plurality of second wireless communication terminals. This is because, when the first wireless communication terminal allocates bandwidths equal to each other to each of the plurality of second wireless communication terminals, an unallocated bandwidth among the frequency bands available to the first wireless communication terminal may occur. In addition, when the first wireless communication terminal allocates an equal bandwidth to each of the plurality of second wireless communication terminals, it may not be possible to transmit data to a specific second wireless communication terminal at one time according to the data distribution for each second wireless communication terminal. Because it can.

In addition, the first wireless communication terminal may transmit a plurality of second radios through the corresponding frequency band only when a primary channel having a minimum unit frequency bandwidth is idle in the frequency band used by the first wireless communication terminal. Data can be transmitted to the communication terminal. In this case, when a physical frame of another BSS is transmitted in a primary channel, the second wireless communication terminal does not need to perform a clear channel assessment (CCA) on a secondary channel of a corresponding frequency band. This is because the first wireless communication terminal always transmits data to the plurality of second wireless communication terminals including the main channel of the corresponding frequency band. Therefore, through this, the first wireless communication terminal can reduce the CCA burden of the second wireless communication terminal. The minimum unit frequency bandwidth may be 20 MHz.

Also, in a specific embodiment, the first wireless communication terminal may perform only a single user (SU) MIMO transmission in the sub-frequency band. This is because the hardware complexity of the first wireless communication terminal may increase if the first wireless communication terminal performs multi-user (MU) MIMO transmission in the sub-frequency band.

According to another specific embodiment, the first wireless communication terminal may transmit data to the plurality of second wireless communication terminals according to the following principle described in FIG. 8 (b).

The first wireless communication terminal can simultaneously transmit data to up to eight second wireless communication terminals. In this case, however, the previously defined signaling field should be modified and used.

In addition, the first wireless communication terminal includes a plurality of second channels through the corresponding frequency band even when a primary channel having a minimum unit frequency bandwidth in the frequency band used by the first wireless communication terminal is not idle. Data can be transmitted to a wireless communication terminal. In this case, however, as described above, the second wireless communication terminal must perform CCA for the secondary channel even when a frame of another BSS is transmitted through the primary channel of the corresponding frequency band. Therefore, the CCA burden on the second wireless communication terminal is increased compared to the above-described embodiment.

Also, in a specific embodiment, the first wireless communication terminal may perform multi-user (MO) MIMO transmission in the sub-frequency band. In this case, hardware complexity of the first wireless communication terminal is increased compared to the above-described embodiment.

However, according to the principle described in FIG. 8B, when transmitting data to a plurality of second wireless communication terminals, frequency resources may be maximized.

The first wireless communication terminal may signal static information about wireless communication through a beacon message. The static information about the wireless communication may include at least one of a wireless bandwidth and a main channel available to the first wireless communication terminal. In addition, the first wireless communication terminal may signal dynamic information about wireless communication through a header of the data frame. The first wireless communication terminal may include at least one of information on a frequency band and a frequency bandwidth allocated to each second wireless communication terminal. This will be described with reference to FIGS. 9 to 11.

9 shows a format of a physical frame according to an embodiment of the present invention.

A physical frame transmitted by a wireless communication terminal according to an embodiment of the present invention includes a legacy preamble 710 signaling information for a wireless communication terminal that does not support an embodiment of the present invention, and a radio supporting an embodiment of the present invention. A non-legacy preamble 720 signaling information for the communication terminal, and a data frame transmitting data.

The legacy preamble may include at least some information decodable by a wireless communication terminal supporting an embodiment of the present invention. The legacy preamble may include an L-STF field, an L-LTF field, and an L-SIG field. The L-STF field represents a short training signal that can be decoded by both a wireless communication terminal supporting an embodiment of the present invention and a wireless communication terminal not supporting the embodiment of the present invention. The training signal is a signal that assists in demodulation and decoding setup of a wireless communication terminal for receiving a signal to be transmitted after transmission of the training signal. The short training signal is a training signal having a relatively short signal length. In more detail, the wireless communication terminal performs automatic gain control (AGC) on an OFDM symbol including an L-LTF field and an L-SIG field based on a short training signal, performs an OFDM symbol and timing and includes an L-SIG field. Frequency can be synchronized.

The L-LTF field indicates a long training signal that can be decoded by both a wireless communication terminal supporting an embodiment of the present invention and a wireless communication terminal not supporting the embodiment of the present invention. The long training signal is a training signal having a relatively long signal length. In more detail, the wireless communication terminal may estimate a frequency offset and a channel of an OFDM symbol including an L-SIG field based on the long training signal.

The L-SIG field is signaling information that can be decoded by both a wireless communication terminal supporting an embodiment of the present invention and a wireless communication terminal not supporting the embodiment of the present invention. In more detail, the L-SIG field represents information about a data rate and a data length.

10 illustrates a detailed format of a physical frame and a signaling field of a physical frame according to an embodiment of the present invention.

The SIG-A field used in an embodiment of the present invention supports downlink Multi User-Multi Input Multi Output (MU-MIMO). Therefore, the configuration of the SIG-A field varies depending on whether the physical frame is a frame for a single user (SU) or a frame for a multiple user (MU).

10 (a) shows a physical frame for SU according to an embodiment of the present invention.

Physical frames for SU are BW field, STBC field, Goup ID field, NSTS field, Partial AID field, TXOP_PS field, SHORT GI field, GI_NYSM field, Coding field, LDPC extra field, MCS field, Beamformed field, CRC field, and It may include at least one of the tail field.

The BW field represents a bandwidth of a frequency band in which a physical frame is transmitted. In a specific embodiment, the BW field may indicate 20 MHz, 40 MHz, 80 MHz, and 160 MHz.

The STBC field indicates whether space time block coding is applied.

The Group ID field indicates whether it is a physical frame for SU. In more detail, when the value of the Group ID field is a specific value, this may represent a physical frame for SU. In this case, the specific value may be at least one of 0 and 63.

The NSTS field indicates the number of space-time streams to transmit to the second wireless communication terminal. At this time, the number of transmission of the LTF field varies according to the number of space-time streams. This is because when the number of space-time streams is changed, the number of LTF fields required to distinguish the space-time streams is changed. The number of LTF fields required to distinguish the space-time stream may vary depending on at least one of a channel estimation method and a phase pattern applied to a subcarrier included in the LTF field. This will be described later. In an embodiment of the present invention, when the number of space-time streams is 1, 2, 4, 6, and 8, 1, 2, 4, 6, and 8 LTF fields are transmitted, respectively. In addition, when the number of space-time streams is 3, 5, 7, 4, 6, 8 LTF fields are transmitted.

The Partial AID field indicates a partial association ID (AID) of the second wireless communication terminal to receive the frame. The second wireless communication terminal can receive the physical frame based on the Partial AID field. In more detail, when the Partial AID field value indicates the second wireless communication terminal, the second wireless communication terminal may receive a physical frame.

The SHORT GI field indicates whether a data field included in a physical frame has a relatively short GI (Guard Interval) value.

The TXOP_PS field indicates whether a wireless communication terminal other than the wireless communication terminal receiving the frame may enter the power save mode while the physical frame is transmitted by the first wireless communication terminal.

The GI_NYSM field indicates N _SYM value when a short GI is used.

Coding field indicates whether LDPC coding is applied to data.

The LDPC extra field indicates whether LDPC coding is applied to data to include additional OFDM symbols.

The MCS field represents a Modulation & Coding Scheme (MCS) of a signal including data.

The Beamformed field indicates whether beamforming has been applied.

The CRC field indicates whether the SIG-A field contains an error.

The Tail field indicates the end of the SIG-A field.

10 (b) shows a physical frame for an MU according to an embodiment of the present invention.

The physical frame for the MU may include at least one of a BW field, an STBC field, a Goup ID field, a plurality of NSTS fields, a TXOP_PS field, a SHORT G1 field, a GI_NYSM field, a plurality of coding fields, an LDPC extra field, a CRC field, and a tail field. It may include.

The Group ID field indicates a group identifier for identifying a group including a second wireless communication terminal to receive a physical frame. In more detail, the Group ID field may have a value of 1 to 62 instead of 0 or 63. At this time, the value of the Group ID field identifies a group including a plurality of second wireless communication terminals. In this case, the number of the plurality of second wireless communication terminals may be four.

The plurality of NSTS fields indicate the number of space-time streams to transmit to each of the plurality of second wireless communication terminals belonging to the group indicated by the GID. In more detail, the value of the NSTS field is the number of radio streams transmitted to the second radio communication terminal.

 In the case of an MU physical frame, the MCS value of the signal containing the data is signaled by the SIG-B.

The other field may be as described in Physical Frame for SU.

11 shows a specific format of a physical frame according to another embodiment of the present invention.

11 (a) shows a specific format of a physical frame when the HE-SIG-B field is located after the HE-STF and the HE-LTF.

Description of the L-STF, L-LTF, and L-SIG is as described above with reference to FIG.

The HE-SIG-A field signals information that is commonly applied to a plurality of second wireless communication terminals.

The HE-STF field represents a short training signal that can be decoded by a wireless communication terminal supporting an embodiment of the present invention. A wireless communication terminal supporting an embodiment of the present invention provides AGC (Automatic Gain Control) for an OFDM symbol including a HE-LTF field, a HE-SIG-B field, and data included in a payload based on a short training signal. Can be performed. In addition, the wireless communication terminal supporting the embodiment of the present invention is based on the short training signal for the timing and frequency of the OFDM symbol including the HE-LTF field, the HE-SIG-B field, and the data contained in the payload Synchronization can be performed.

The HE-LTF field represents a long training signal that can be decoded by a wireless communication terminal supporting an embodiment of the present invention. A wireless communication terminal supporting an embodiment of the present invention estimates a frequency offset and a channel of an OFDM symbol including a HE-SIG-B field and data included in a payload based on a long training signal. can do. In more detail, a wireless communication terminal supporting an embodiment of the present invention can estimate a channel on which data is transmitted based on a long training signal. In addition, the wireless communication terminal supporting the embodiment of the present invention can estimate the frequency offset of the OFDM symbol based on the long training signal. In the present specification, the term HE-LTF may indicate a long training signal included in the HE-LTF field itself or the HE-LTF field.

The HE-SIG-B field signals information about a plurality of second wireless communication terminals.

The HE-SIG-A field may be represented by an OFDM x symbol and the HE-SIG-B may be represented by a length of an OFDM y symbol. At this time, as the value of x increases, the number of second wireless communication terminals that can transmit data by the first wireless communication terminal increases. In more detail, the number of second wireless communication terminals capable of transmitting data by the first wireless communication terminal according to the value of x may be any one of 4, 8, 12, and 16. In addition, the HE-LTF may be transmitted in a variable number depending on the number of spatial streams of the first wireless communication terminal and the second wireless communication terminal.

In the embodiment of FIG. 11 (a), L-STF, L-LTF, L-SIG, and HE-SIG-A of a physical frame are configured with 64 FFT-based OFDM symbols, and 256 from the HE-STF to the data frame. It is composed of FFT-based OFDM symbols.

Assuming a minimum data rate of 6 Mbps, and the maximum length of the physical frame is 1366 symbols, the total transmission maximum time from the HE-SIG-A field to the data field can be limited to 5.464 ms.

11 (b) shows a specific format of a physical frame when the HE-SIG-B field is located before the HE-STF.

In the embodiment of FIG. 11 (b), L-STF, L-LTF, L-SIG, HE-SIG-A, and HE-SIG-B of a physical frame are configured with 64 FFT-based OFDM symbols, and HE-STF From then on, the data frame is composed of 256 FFT-based OFDM symbols.

In the embodiment of FIG. 11B, the HE-STF is classified into a HE-STF-short and a HE-STF-long according to a purpose. The HE-STF-short may be used in the SU downlink transmission physical frame, the MU downlink transmission physical frame, and the SU uplink transmission physical frame. The HE-STF-short may have a total length of 4.0us in a form in which a signal pattern having a length of 0.8us on the time axis is repeated five times. HE-STF-long may be used in the uplink MU physical frame. The HE-STF-long may have a total length of 8.0us in a form in which a signal pattern having a length of 1.6us is repeated five times.

In the embodiment of Figure 11 (b), HE-LTF is divided into HE-LTF-short and HE-LTF-long according to the purpose. HE-LTF-short may be used in indoor communication. The HE-LTF-short may have a length equal to the sum of 6.4us and the guard interval length. HE-LTF-long may be used in outdoor communication. The HE-LTF-long may have a length equal to the sum of 12.8us and the guard interval length.

In the embodiment of FIG. 11B, the physical frame includes a HE-SIG-C field. The HE-SIG-C field may be used in MU-MIMO transmission. In more detail, the HE-SIG-C field may indicate at least one of MCS and data length for each second wireless communication terminal. The HE-SIG-C field may have a variable length. However, according to a specific embodiment, without the HE-SIG-C field, the HE-SIG-B field may indicate at least one of MCS and data length for each second wireless communication terminal.

As described above, the number of LTFs varies according to the number of space-time streams. Specifically, as the number of space-time streams increases, the number of LTFs required for estimating the frequency offset and the channel of each space-time stream increases. In addition, in order to estimate a frequency offset and a channel of each space-time stream, a phase pattern applied to the entire subcarrier included in each of the plurality of LTFs transmitted in the same frequency band may be an orthogonal pattern. Since the number of radio streams transmitted for each sub-frequency band is different in the communication using OFDMA, the number of HE-LTFs transmitted for each sub-frequency band may vary. 12 to 15 illustrate a method of determining the number of HE-LTFs transmitted for each sub-frequency band when OFDMA is applied. In this case, the number of HE-LTFs may indicate the number of OFDM symbols including the HE-LTF.

12 illustrates a method of configuring a physical frame according to whether MU and MIMO are used when OFDMA is not used in an embodiment of the present invention.

12 (a) shows the configuration of a physical frame in Single User-Single Input Single Output (SU-SISO) when OFDMA is not used in an embodiment of the present invention. In FIG. 12 (a), the AP transmits data to the first station STA_a using twice the bandwidth of the minimum unit bandwidth. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a receives L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having a 20 MHz bandwidth. In addition, the first station STA_a receives the same L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having an extended 20 MHz bandwidth. The first station STA_a receives one space-time stream from the AP. Accordingly, the first station STA_a receives one HE-LTF from the first wireless communication terminal.

12 (b) shows the configuration of a physical frame in a single user-multiple input multiple output (SU-MIMO) when no OFDMA is used in an embodiment of the present invention. In FIG. 12B, the AP transmits data to the first station STA_a using twice the bandwidth of the minimum unit bandwidth. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a receives L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having a 20 MHz bandwidth. In addition, the first station STA_a receives the same L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having an extended 20 MHz bandwidth. The first station STA_a receives two space-time streams from the AP. Accordingly, the first station STA_a receives two HE-LTFs from the AP.

12 (c) shows the configuration of a physical frame in a multiple user-multiple input multiple output (MU-MIMO) when no OFDMA is used in an embodiment of the present invention. In FIG. 12C, the AP transmits data to the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d using twice the bandwidth of the minimum unit bandwidth. send. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a receives L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having a 20 MHz bandwidth. In addition, the first station STA_a receives the same L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the first wireless communication terminal through a frequency band having an extended 20 MHz bandwidth. The first station STA_a receives two space-time streams from the AP, the second station STA_b receives one space-time stream from the AP, and the third station STA_c receives three space-time streams from the AP. , And the fourth station STA_d receive two space-time streams from the AP. Therefore, two HE-LTFs in the frequency band corresponding to the first station STA_a are two, and one HE-LTF in the frequency band corresponding to the second station STA_b is one. The HE-LTFs of the frequency band corresponding to the third station STA_c are four. There are two HE-LTFs in the frequency band corresponding to the fourth station STA_d.

In FIG. 12C, the data transmission is indicated by a dotted line to indicate that data is transmitted through MU-MIMO to a plurality of wireless communication devices without using OFDMA in the corresponding frequency band. Subsequently, when data is transmitted to a plurality of wireless communication devices using OFDMA in the corresponding frequency band, data transmission is indicated by a solid line to distinguish it from transmission using MU-MIMO.

FIG. 13 illustrates a method of configuring a physical frame according to whether MU and MIMO are used when OFDMA is used in an embodiment of the present invention.

FIG. 13 (a) shows the configuration of a physical frame in a single user-single input single output (SU-SISO) when OFDMA is used in an embodiment of the present invention. In FIG. 13A, the AP transmits data to the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d using twice the bandwidth of the minimum unit bandwidth. send. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d are L-STF, L-LTF, and L-SIG from the AP through a frequency band having a 20 MHz bandwidth. , And HE-SIG-A fields. In addition, the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d are the same L-STF, L- from the AP through a frequency band having an extended 20 MHz bandwidth. Receive the LTF, L-SIG, and HE-SIG-A fields. Each of the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d receives one space-time stream on a sub-frequency band allocated to each. Accordingly, each of the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d receives one HE-LTF from the AP.

FIG. 13 (b) shows the configuration of a physical frame in a single user-multiple input multiple output (SU-SISO) when OFDMA is used in an embodiment of the present invention. In FIG. 13B, the AP transmits data to the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d using twice the bandwidth of the minimum unit bandwidth. send. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d are L-STF, L-LTF, and L-SIG from the AP through a frequency band having a 20 MHz bandwidth. , And HE-SIG-A fields. In addition, the first station STA_a, the second station STA_b, the third station STA_c, and the fourth station STA_d are the same L-STF, L- from the AP through a frequency band having an extended 20 MHz bandwidth. Receive the LTF, L-SIG, and HE-SIG-A fields. The first station STA_a receives two space-time streams from the AP through a sub-frequency band allocated to the first station STA_a. The second station STA_b receives one space-time stream from the AP through the sub-frequency band allocated to the second station STA_b. The third station STA_c receives three space-time streams from the AP through the sub-frequency band allocated to the third station STA_c. The fourth station STA_d receives two space-time streams from the AP through a frequency band allocated to the fourth station STA_d. Accordingly, the first station STA_a receives two HE-LTFs. In addition, the second station STA_b receives one HE-LTF. In addition, the third station STA_c receives four HE-LTFs. In addition, the fourth station STA_d receives two HE-LTFs.

FIG. 13 (c) shows the configuration of a physical frame in Multiple User-Multiple Input Multiple Output (MU-MIMO) when OFDMA is used in an embodiment of the present invention. In FIG. 13 (c), the AP uses a bandwidth twice the minimum unit bandwidth, and thus, the first station STA_a, the second station STA_b, the third station STA_c, the fourth station STA_d, and the fifth station. Data is transmitted to STA_e, the sixth station STA_f, and the seventh station STA_g. Specifically, the AP transmits data using the MU-MIMO to the first station STA_a and the fifth station STA_e through the first sub-frequency band. In addition, the AP transmits data using the MU-MIMO to the second station STA_b and the sixth station STA_f through the second sub-frequency band. In addition, the AP transmits data using the MU-MIMO to the third station STA_a and the seventh station STA_g through the third sub-frequency band. In addition, the AP transmits data using the SU-SISO to the fourth station STA_d through the fourth sub-frequency band. At this time, it is assumed that the minimum unit bandwidth is 20MHz. The first station STA_a to the seventh station STA_e receive the L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having a 20 MHz bandwidth. In addition, the first station STA_a to the seventh station STA_e receive the same L-STF, L-LTF, L-SIG, and HE-SIG-A fields from the AP through a frequency band having an extended 20 MHz bandwidth. do. The first station STA_a receives two space-time streams from the AP on the first sub-frequency band. In addition, the fifth station STA_e receives one space-time stream from the AP through the first frequency band. In addition, the second station STA_b receives one space-time stream from the AP through the second sub-frequency band. In addition, the sixth station STA_f receives two space-time streams from the AP through the second sub-frequency band. In addition, the third station STA_c receives three space-time streams from the AP through the third frequency band. In addition, the seventh station STA_g receives one space-time stream from the AP through the third sub-frequency band. In addition, the fourth station STA_d receives two space-time streams from the AP through the fourth sub-frequency band. Therefore, the AP transmits three HE-LTFs on the first sub-frequency band. The AP then transmits three HE-LTFs on the second sub-frequency band. The AP transmits five HE-LTFs through the third sub-frequency band. The AP transmits two HE-LTFs through the fourth sub-frequency band.

In the embodiment of FIG. 13 (b) and the embodiment of FIG. 13 (c), the number of spatiotemporal streams received for each second wireless communication terminal is different so that the number of HE-LTFs transmitted for each sub-frequency band is different. Accordingly, the first wireless communication terminal transmits data to one wireless communication terminal and a HE-LTF to another terminal in a specific time interval. When the first wireless communication terminal transmits data, various types of guard intervals such as 0.8us, 1.6us, and 3.2us may be used. However, the guard interval of the HE-STF and HE-LTF is fixed. Accordingly, when data, HE-STF, and HE-LTF are simultaneously transmitted in communication using OFDMA, the guard interval may vary for each sub-frequency band of the entire frequency band to which OFDMA is applied. In this case, the transmission and reception complexity increases. Therefore, in OFDMA communication, it is necessary to align OFDM symbols between sub-frequency bands. This will be described with reference to FIG. 14.

14 illustrates a method for aligning durations of OFDM symbols in each sub-frequency band in communication using OFDMA according to an embodiment of the present invention.

As described above, in order to reduce transmission and reception complexity, the first wireless communication terminal may align the duration of OFDM symbols in each sub-frequency band when communicating with OFDMA. In detail, the first wireless communication terminal may start transmitting the HE-LTF to the second wireless communication terminal at the same time and stop the HE-LTF transmission at the same time. In this case, the second wireless communication terminal may start receiving the HE-LTF at the same time from the first wireless communication terminal and stop receiving the HE-LTF at the same time. To this end, in an embodiment of the present invention, the first wireless communication terminal may use only SISO when communicating using OFDMA. In this case, the number of space-time streams transmitted through each sub-frequency band is one. Therefore, the first wireless communication terminal starts the HE-LTF transmission to the second wireless communication terminal at the same time and stops the HE-LTF transmission at the same time.

In another specific embodiment, the first wireless communication terminal may transmit the same number of space-time streams through each sub-frequency band in communication using OFDMA. In this case, the first wireless communication terminal transmits the same number of HE-LTFs through each sub-frequency band.

In another specific embodiment, the first wireless communication terminal may transmit the same number of HE-LTFs through each sub-frequency band when communicating using OFDMA. At this time, the second wireless communication terminal receives the same number of HE-LTFs as other second wireless communication terminals. In this case, the number of HE-LTFs may indicate the number of OFDM symbols including the HE-LTF. In this case, the first wireless communication terminal can align OFDM symbols even using MU-MIMO in the sub-frequency band. In more detail, the first wireless communication terminal may transmit the HE-LTF based on the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. For example, the first wireless communication terminal may transmit as many HE-LTFs as the number of HE-LTFs required by the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted in each sub-frequency band. To this end, the first wireless communication terminal can transmit the additional HE-LTF in the sub-frequency band smaller than the number of HE-LTF required in the sub-frequency band to which the space-time stream is transmitted. In this case, the number of HE-LTFs required by the sub-frequency band through which the space-time stream is transmitted may be the number of HE-LTFs required to distinguish the space-time stream as described above. In addition, the number of HE-LTFs required to distinguish the spatiotemporal stream may vary depending on at least one of a channel estimation method and a phase pattern applied to a subcarrier included in the LTF field. This will be described later.

In addition, the first wireless communication terminal may signal the number of HE-LTFs required by the sub-frequency band to which the largest space-time stream of the plurality of sub-frequency bands is transmitted to the second wireless communication terminal. In more detail, the first wireless communication terminal may include the HE-SIG-A field described above for the number of HE-LTFs required by the sub-frequency band for transmitting the most space-time streams among the plurality of sub-frequency bands to the second wireless communication terminal. Signaling may be performed through the HE-SIG-B field. The second wireless communication terminal can obtain the number of HE-LTFs required by the sub-frequency band to which the largest space-time stream of the plurality of sub-frequency bands is transmitted from the signaling information received from the first wireless communication terminal. The second wireless communication terminal may receive data based on the number of HE-LTFs obtained. In more detail, the second wireless communication terminal may acquire the number of HE-LTFs required by the sub-frequency band based on the HE-SIG-A field.

In more detail, the first wireless communication terminal may repeatedly transmit the HE-LTF transmitted before the sub-frequency band in which the number of HE-LTFs corresponding to the space-time stream is smaller than the HE-LTF required by the space-time stream. In another specific embodiment, the first wireless communication terminal cycles a pattern of HE-LTFs to be originally transmitted in a sub-frequency band in which the number of HE-LTFs required by the space-time stream is smaller than the HE-LTF to be transmitted. The HE-LTF of the shifted pattern may be transmitted. In another specific embodiment, the first wireless communication terminal transmits to the second wireless communication terminal different in the same sub-frequency band in a sub-frequency band in which the number of HE-LTFs required by the space-time stream is smaller than the HE-LTF to be transmitted. A HE-LTF including a subcarrier having a phase pattern for canceling a space-time stream may be transmitted.

Also, in a specific embodiment, the first wireless communication terminal is space-time of the second wireless communication terminal different in different sub-frequency bands in a sub-frequency band in which the number of HE-LTFs required by the space-time stream is smaller than the HE-LTF to be transmitted. A HE-LTF including a subcarrier having a phase pattern for canceling the stream may be transmitted. In more detail, the first wireless communication terminal may use an N × N orthogonal matrix applied in OFDM symbol units to the phase of the subcarrier included in the HE-LTF. In this case, N is the number of HE-LTFs required by the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. In this case, the number of HE-LTFs may be the number of OFDM symbols including the HE-LTF as described above. The second wireless communication terminal can receive data from the first wireless communication terminal based on the N × N orthogonal matrix. In more detail, the second wireless communication terminal can estimate a channel through which data transmitted by the first wireless communication terminal passes based on the N × N orthogonal matrix. A detailed form of the N × N orthogonal matrix will be described later with reference to FIG. 31.

In addition, the first wireless communication terminal transmits the HE-LTF to each of the plurality of sub-frequency bands according to the phase of the subcarrier indicated by the number of rows required by the corresponding sub-frequency band from one row in the N × N orthogonal matrix. Can be. The second wireless communication terminal can estimate a channel through which data transmitted by the first wireless communication terminal passes based on the number of rows required by the corresponding sub-frequency band from one row in the N × N orthogonal matrix. For example, in the embodiment of 13 (b), the first wireless communication terminal may transmit the HE-LTF for each sub-frequency band according to a phase pattern having a 4 × 4 matrix. The number of HE-LTFs required by the largest number of space-time streams transmitted for each sub-frequency band is four. Therefore, the first wireless communication terminal uses a phase pattern having a 4 x 4 matrix. In addition, since the number of space-time streams are two in the first sub-frequency band, the first wireless communication terminal transmits the HE-LTF according to the pattern of the first row and the second row of the 4 × 4 matrix. In this case, the second wireless communication terminal that receives data through the first sub-frequency band estimates a channel through which data transmitted by the first wireless communication terminal passes based on a pattern of rows 1 and 2 of the 4 × 4 matrix. do. In addition, since the number of space-time streams is one in the second sub-frequency band, the first wireless communication terminal transmits the HE-LTF according to the pattern of one row of the 4 × 4 matrix. In this case, the second wireless communication terminal receiving data through the second sub-frequency band estimates a channel through which data transmitted by the first wireless communication terminal passes based on a pattern of one row of a 4 × 4 matrix. In addition, since the number of space-time streams is three in the third sub-frequency band, the first wireless communication terminal transmits the HE-LTF according to the pattern of rows 1 to 4 of the 4 × 4 matrix. In this case, the second wireless communication terminal that receives data through the third sub-frequency band estimates a channel through which data transmitted by the first wireless communication terminal passes based on a pattern of rows 1 to 4 of the 4 × 4 matrix. do. In addition, since the number of space-time streams is two in the fourth sub-frequency band, the first wireless communication terminal transmits the HE-LTF according to the pattern of the first row and the second row of the 4 × 4 matrix. In this case, the second wireless communication terminal that receives data through the fourth sub-frequency band estimates a channel through which data transmitted by the first wireless communication terminal passes based on a pattern of rows 1 and 2 of the 4 × 4 matrix. do.

In another specific embodiment, the second wireless communication terminal may transmit the HE-LTF based on the sub-frequency band required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. Specifically, the second wireless communication terminal is multiplexed to a frequency band requiring more training signals than the number of training signals required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. -LTF can be sent Binding HE-LTF represents an LTF combining a plurality of HE-LTFs into one. In more detail, the combined HE-LTF may be a combination of a plurality of LTFs on a frequency axis. In another specific embodiment, the combined HE-LTF may be a combination of a plurality of LTFs in an orthogonal code axis. In this case, the second wireless communication terminal may estimate a channel through which data transmitted by the first wireless communication terminal passes based on the combined HE-LTF. In detail, the second wireless communication terminal can estimate a channel through which data transmitted by the first wireless communication terminal passes by demultiplexing the combined HE-LTF.

According to another specific embodiment, the first wireless communication terminal may change the guard interval value of the preamble transmitted before data transmission to maintain the same as the guard interval of data transmitted in another sub-frequency band. In more detail, the first wireless communication terminal may change the guard interval of at least one of the HE-STF, the HE-LTF, and the HE-SIG-B.

FIG. 15 shows that a first wireless communication terminal transmits data using a LTF to a plurality of second wireless communication terminals according to an embodiment of the present invention.

As described above, when communicating using OFDMA, the first wireless communication terminal may transmit the same number of HE-LTFs through each sub-frequency band. In more detail, the first wireless communication terminal may transmit the HE-LTF based on the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. This will be described in detail once again through the embodiment of FIG. 15.

In the embodiment of FIG. 15A, the first wireless communication terminal transmits data to four second wireless communication terminals. Specifically, the first wireless communication terminal transmits data to each of the four second wireless communication terminals through each of the four sub-frequency bands. Specifically, the first wireless communication terminal transmits two space-time streams in the first sub-frequency band. The first wireless communication terminal also transmits one space-time stream in the second sub-frequency band. The first wireless communication terminal also transmits three space-time streams in the third sub-frequency band. The first wireless communication terminal also transmits two space-time streams in the fourth sub-frequency band.

In this case, two HE-LTFs are required in the first sub-frequency band. In addition, one HE-LTF is required in the second sub-frequency band. In addition, four HE-LTFs are required in the third sub-frequency band. In addition, two HE-LTFs are required in the fourth sub-frequency band. Accordingly, the first wireless communication terminal transmits a total of four HE-LTFs including two additional HE-LTFs in the first sub-frequency band. In addition, the first wireless communication terminal transmits a total of four HE-LTFs including three additional HE-LTFs in the second sub-frequency band. In addition, the first wireless communication terminal transmits a total of four HE-LTFs without an additional HE-LTF in the third sub-frequency band. In addition, the first wireless communication terminal transmits a total of four HE-LTFs including two additional HE-LTFs in the fourth sub-frequency band. In this case, the additional HE-LTF may be transmitted according to various embodiments described above.

In the embodiment of FIG. 15B, the first wireless communication terminal transmits data to seven second wireless communication terminals. Specifically, the first wireless communication terminal transmits data to eight second wireless communication terminals through four sub-frequency bands. Specifically, the first wireless communication terminal transmits two and one space-time stream to each of the two second wireless communication terminals in the first sub-frequency band. In addition, the first wireless communication terminal transmits one and two space-time streams to each of the two second wireless communication terminals in the second sub-frequency band. The first wireless communication terminal also transmits three and one space-time streams to each of the two second wireless communication terminals in the third sub-frequency band. The first wireless communication terminal also transmits two space-time streams in the fourth sub-frequency band.

In this case, three HE-LTFs are required in the first sub-frequency band. In addition, three HE-LTFs are required in the second sub-frequency band. In addition, five HE-LTFs are required in the third sub-frequency band. In addition, two HE-LTFs are required in the fourth sub-frequency band. Accordingly, the first wireless communication terminal transmits a total of five HE-LTFs including two additional HE-LTFs in the first sub-frequency band. In addition, the first wireless communication terminal transmits a total of five HE-LTFs including two additional HE-LTFs in the second sub-frequency band. In addition, the first wireless communication terminal transmits a total of five HE-LTFs without an additional HE-LTF in the third sub-frequency band. In addition, the first wireless communication terminal transmits a total of five HE-LTFs including three additional HE-LTFs in the fourth sub-frequency band. In this case, the additional HE-LTF may be transmitted according to various embodiments described above.

In the embodiment of FIG. 15A and the embodiment of FIG. 15B, the second wireless communication terminal starts receiving the HE-LTF at the same time from the first wireless communication terminal and stops receiving the HE-LTF at the same time. can do. In addition, as described above, the second wireless communication terminal requires that the second wireless communication terminal requires a sub-frequency band for transmitting the most space-time streams among the plurality of sub-frequency bands from the signaling information received from the first wireless communication terminal. The number of HE-LTFs can be obtained. The second wireless communication terminal may receive data based on the number of HE-LTFs obtained. In more detail, the second wireless communication terminal may acquire the number of HE-LTFs required by the sub-frequency band based on the HE-SIG-A field.

A detailed pattern of the LTF according to an embodiment of the present invention will be described with reference to FIGS. 16 to 28.

FIG. 16 illustrates signal patterns of subcarriers included in an LTF when the LTF is transmitted using 64 FFT, 128 FFT, and 256 FFT according to an embodiment of the present invention. FIG. 16 shows specific signal patterns of subcarriers included in the LTF described with reference to FIG. 15.

FIG. 16 (a) shows a subcarrier signal pattern included in the L-LTF transmitted using 64 FFTs according to an embodiment of the present invention, and FIG. 17 (a) shows the L-LTF described in FIG. 16 (a). Shows a subcarrier specific signal pattern included.

When transmitting an L-LTF using a 64 FFT, the L-LTF includes 64 subcarriers in the 20 MHz band. At this time, the spacing between subcarriers is 312.5 KHz. The wireless communication terminal may transmit data through the left 26 and the right 26 subcarriers except the subcarriers belonging to the left 6 and the right 5 guard bands of the 64 subcarriers.

At this time, the signal pattern of the subcarrier included in the L-LTF is as follows. {L-LTF _ (-26,26)} = {1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 0, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, 1, 1}

The wireless communication terminal transmits a total of 52 signal values and modulates the corresponding signal in the form of BPSK. At this time, the {LTF_L} pattern and the {LTF_R} pattern around the direct current (DC) band of the frequency center may be defined as follows.

 {LTF_L} = {1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1,- 1, 1, -1, 1, 1, 1, 1}

 {LTF_R} = {1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1,- 1, 1, -1, 1, -1, 1, 1, 1, 1}

 Using the {LTF_L} pattern and the {LTF_R} pattern, the signal pattern of the subcarrier that the L-LTF contains is shortened to {L-LTF _ (-26,26)} = {{LTF_L}, 0, {LTF_R}}. Can be represented.

FIG. 16 (b) shows a subcarrier signal pattern included in the HT / VHT-LTF transmitted using 64 FFT according to an embodiment of the present invention, and FIG. 17 (b) shows the HT described in FIG. 16 (b). Shows the subcarrier specific signal pattern included in / VHT-LTF.

When transmitting HT / VHT-LTF using 64 FFT, HT / VHT-LTF includes 64 subcarriers in the 20 MHz band. At this time, the spacing between subcarriers is 312.5 KHz. The wireless communication terminal may transmit data through the left 28 and right 28 subcarriers except the subcarriers belonging to the left 4 and right 3 guard bands of the 64 subcarriers.

{HT / VHT-LTF _ (-28,28)} = {1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1 , 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 0, 1, -1, -1, 1, 1, -1, 1, -1 , 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, 1, 1, -1,- One}

 This is the value of {1, 1} and {-1, -1} in the subcarriers located at {-28, -27} and {27, 28} of the signal pattern of the subcarrier included in the L-LTF described above. Is an additional assignment.

 Using the {LTF_L} pattern and the {LTF_R} pattern, it is simplified to {HT / VHT-LTF _ (-28,28)} = {1, 1, {LTF_L}, 0, {LTF_R}, -1, -1} Can be represented.

At this time, the VHT-LTF includes a subcarrier that serves as a pilot signal for phase and frequency tracking. Specifically, the subcarriers located at {-21, -7, 7, 21} of the VHT-LTF are not affected by the phase pattern applied to the signals of the subcarriers according to the number of space-time streams. Specifically, the subcarriers located at {-21, -7, 7, 21} are not multiplied by the value of the phase pattern. Therefore, the subcarriers located at {-21, -7, 7, 21} are not used for channel estimation. In addition, in the description of the present specification, applying the phase pattern to the subcarriers included in the LTF may be interpreted to mean applying the phase pattern to the phases of the remaining subcarriers except for the subcarriers serving as pilot signals.

FIG. 16 (c) shows a subcarrier signal pattern included in the HT / VHT-LTF transmitted using 128 FFTs according to an embodiment of the present invention, and FIG. 17 (c) shows the HT described in FIG. 16 (c). Shows the subcarrier specific signal pattern included in / VHT-LTF.

Signal patterns of subcarriers included in HT / VHT-LTF transmitted using 128FFT in 40MHz band are as follows.

 {HT / VHT-LTF _ (-58, 58)} = {{LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1}, {0, 0, 0}, j * {{ -1, 1, 1, -1}, {LTF_L}, 1, {LTF_R}}}

 In this case, it can be seen that the signal pattern of the subcarrier included in the 20MHz L-LTF described above is repeatedly transmitted for each 20MHz in the signal pattern of the subcarrier included in the 40MHz HT / VHT-LTF. In addition, in the case of the signal pattern of the subcarrier included in the 40 MHz HT / VHT-LTF, the subcarriers at positions corresponding to the direct current (DC) subcarriers of the L-LTF are 1, respectively. Signal patterns {-1, -1, -1, 1}, {-1, 1, 1, -1} are transmitted to the eight newly extended subcarriers to the left and right of the 40 MHz DC subcarrier. Can be. This is to minimize the Peak to Average Power Ratio (PAPR) of the subcarriers included in the LTF. In addition, the phase change of j in the signals of the positive 20 MHz band is also to minimize the PAPR of the subcarrier included in the LTF. Further, the positions of the subcarriers serving as pilot signals in {VHT-LTF _ (-58, 58)} are {-53, -25, -11, 11, 25, 53}.

FIG. 16 (d) shows a signal pattern of a subcarrier included in a VHT-LTF transmitted using 256 FFTs in an 80 MHz band according to an embodiment of the present invention, and FIG. 17 (d) shows in FIG. 16 (d). The specific signal pattern of the subcarrier included in the described VHT-LTF is shown.

According to an embodiment of the present invention, a signal pattern of a subcarrier included in a VHT-LTF transmitted using 256 FFTs in an 80 MHz band is as follows.

 {VHT-LTF _ (-122, 122)} = {{LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1, 1}, (-1) * {{-1, 1, -1, 1, 1, -1}, {LTF_L}, 1, {LTF_R}, {1, -1, 1, -1} {0, 0, 0}, {1, -1, -1, 1 }, {LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1}, {1, -1, 1}, {-1, 1, 1, -1}, {LTF_L}, 1, {LTF_R}}}

 In this case, it can be seen that the signal pattern of the subcarrier included in the 20MHz L-LTF described above is repeatedly transmitted by 20MHz in the signal pattern of the subcarrier included in the VHT-LTF transmitted using 256 FFT in the 80MHz band. -1 to the signal pattern of the subcarrier containing 20 MHz L-LTF in the second, third, and fourth 20 MHz bands of the subcarrier signal pattern included in the VHT-LTF transmitted using 256 FFT in the 80 MHz band. It can be seen that the phase has been multiplied by this. This is to reduce the PAPR of the subcarrier included in the LTF. At this time, it can be seen that the signal pattern of the subcarrier included in the VHT-LTF of the 40MHz band described above is repeatedly transmitted every 40MHz at 80MHz.

{1, -1, 1} is transmitted to a position corresponding to the direct current (DC) subcarrier of the 40 MHz VHT-LTF. The eight newly expanded subcarriers to the left and right of the 80 MHz direct current (DC) subcarrier include {1, -1, 1, -1}, {1, -1, -1, 1, which are signal patterns that minimize PAPR of the subcarrier, respectively. } Is sent. In addition, it can be seen that the subcarrier at the {-64 to 122} position is multiplied by -1 to change the phase. This is to reduce the PAPR of the subcarrier included in the LTF. A subcarrier serving as a pilot signal in {VHT-LTF _ (-122, 122)} is located at {-103, -75, -39, -11, 11, 39, 75, 103}.

FIG. 16 (e) shows a signal pattern of a subcarrier included in an LTF transmitted using 32 FFTs in a 1 MHz band according to an embodiment of the present invention, and FIG. 17 (e) shows the LTF described in FIG. 16 (e). Shows a specific signal pattern of the subcarrier that includes.

Specifically, the LTF is as follows.

{S1G-LTF _ (-13, 13)} = {1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, 0, -1,- 1, -1, 1, -1, -1, -1, 1, -1, 1, 1, 1, -1}

 In this case, the {S-LTF_L} pattern and the {S-LTF_R} pattern may be defined based on the direct current (DC) band of the frequency center.

 {S-LTF_L} = {1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1}

 {S-LTF_R} = {-1, -1, -1, 1, -1, -1, -1, 1, -1, 1, 1, 1, -1}

 Using the {S-LTF_L} pattern and the {S-LTF_R} pattern, the {S1G-LTF _ (-13,13)} = {{S signal pattern of the subcarrier included in the LTF transmitted using 32 FFT in the 1 MHz band is used. -LTF_L}, 0, {S-LTF_R}} can be represented briefly.

FIG. 18 illustrates a signal pattern of a subcarrier included in an LTF signal for SU using 256 FFTs in a 20 MHz band according to an embodiment of the present invention. 19 illustrates a signal pattern of a subcarrier included in the LTF signal described with reference to FIG. 18 in detail.

The short LTF indicates an LTF transmitting a signal only to an even subcarrier among subcarriers included in the LTF. The long LTF is used to contrast with the short LTF and indicates an LTF that transmits a signal regardless of whether the subcarriers included in the LTF are even or odd.

18 (a) and 19 (a) show signal patterns of subcarriers included in a short LTF signal for SU using 256 FFTs in a 20 MHz band according to an embodiment of the present invention.

Since 256FFT is used in the 20 MHz band, the LTF described with reference to FIGS. 18 through 19 uses four times as many subcarriers as the LTF of the 20 MHz band described with reference to FIGS. 16 through 17. Therefore, according to an embodiment of the present invention, the signal pattern of the subcarrier included in the short LTF signal for SU using 256 FFT in the 20 MHz band may be as follows.

{HE-LTF-SU-short _ (-122,122) _even} = {{LTF_L_e}, 1, {LTF_R_e}, {A1}, {A2}, {0}, {B1}, {B2}, {LTF_L_e}, 1, {LTF_R_e}}

{HE-LTF-SU-short _ (-122,122) _odd} = {all 0}

In this case, the {LTF_L_e} pattern and the {LTF_R_e} pattern transmit only the even subcarriers in the {LTF-L} and {LTF-R} signal patterns described with reference to FIGS. 16 to 17, and the odd subcarriers Signal pattern of subcarrier with 0 inserted. Accordingly, in the {LTF_L_e} pattern and the {LTF_R_e} pattern, a continuous signal is repeated on the time axis, thereby reducing the reception time by half compared to when receiving the LTF of another embodiment. In this case, the patterns of the {A1} and {B1} signals may be defined as follows in consideration of the PAPR of the subcarrier included in the LTF.

{A1} = {-1, -1, -1, 1}

{B1} = {-1, 1, 1, -1}

In addition, the pattern of the {A2} and {B2} signal may be further defined in consideration of the PAPR of the subcarrier included in the LTF.

FIG. 18B illustrates a signal pattern of a subcarrier included in a long LTF signal for SU using 256 FFTs in a 20 MHz band according to an embodiment of the present invention. According to an embodiment of the present invention, a signal pattern of a subcarrier included in a long LTF signal for SU using 256 FFTs in a 20 MHz band may be as follows.

{HE-STF-SU-long _ (-122,122)} = {{LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1}, {1, -1, 1}, {-1 , 1, 1, -1}, {LTF_L}, 1, {LTF_R}, {1, -1, 1, -1} {0, 0, 0}, {1, -1, -1, 1}, {LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1}, {1, -1, 1}, {-1, 1, 1, -1}, {LTF_L}, 1, {LTF_R}}}

In addition, in order to lower the PAPR of the subcarrier included in the LTF, the wireless communication terminal may transmit the following subcarriers by multiplying (−1) similarly to the 80 MHz VHT-LTF pattern described with reference to FIGS. 16 to 18.

{HE-STF-SU-long _ (-122,122)} = {{LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1, 1}, (-1) * {{-1, 1, -1, 1, 1, -1}, {LTF_L}, 1, {LTF_R}, {1, -1, 1, -1} {0, 0, 0}, {1, -1, -1 , 1}, {LTF_L}, 1, {LTF_R}, {-1, -1, -1, 1}, {1, -1, 1}, {-1, 1, 1, -1}, {LTF_L }, 1, {LTF_R}}}

As described above, when the short LTF is used, the length of the LTF can be reduced by half. However, when the wireless communication terminal uses the short LTF, the channel measurement performance of the wireless communication terminal is lower than when the long LTF having a duration twice as long as the short LTF is used. Therefore, the wireless communication terminal can selectively use the short LTF and the long LTF in the communication environment. Specifically, the wireless communication terminal may use a short LTF indoors and a long LTF outdoors. In another specific embodiment, the wireless communication terminal may use a long LTF when an error of a predetermined criterion or more occurs. The wireless communication terminal may selectively transmit the long LTF and the short LTF even in a single PPDU.

20 shows a structure of a physical frame transmitted by a plurality of stations to an AP.

In the embodiment of FIG. 20, a first station STA_a, a second station STA_b, a third station STA_c, a fourth station STA_d, a fifth station STA_e, a sixth station STA_f, and The seventh station STA_g simultaneously transmits data to the AP. In more detail, the first station STA_a to the seventh station STA_g transmit data to the AP through OFDMA. In addition, the first station STA_a to the seventh station STA_g transmit data to the AP through SU-MIMO. The first station STA_a uses two space-time streams. In addition, the second station STA_b uses one space-time stream. In addition, the third station STA_c uses three space-time streams. In addition, the fourth station STA_d uses two space-time streams. In addition, the fifth station STA_e uses one space-time stream. In addition, the sixth station STA_f uses two space-time streams. In addition, the seventh station STA_g uses one space-time stream. Accordingly, the first station STA_a transmits two HE-LTFs. In addition, the second station STA_b transmits one LTF signal. In addition, the third station STA_c transmits four HE-LTFs. In addition, the fourth station STA_d transmits two HE-LTFs. In addition, the fifth station STA_e transmits one HE-LTF. In addition, the sixth station STA_f transmits two HE-LTFs. In addition, the seventh station STA_g transmits one HE-LTF.

In the case of the embodiment of FIG. 20, duration alignment between OFDM symbols in a plurality of sub-frequency bands is not correct. In detail, since the number of HE-LTFs transmitted in each of the plurality of sub-frequency bands is different, the HE-LTF is transmitted in another sub-frequency band when data is transmitted in one sub-frequency band. When the interval alignment between symbols is not correct as in the embodiment of FIG. 20, the communication complexity of the first wireless communication terminal increases, and the first wireless communication terminal must perform a complicated operation. Therefore, even when a plurality of second wireless communication terminals transmit data to the first wireless communication terminal, it is necessary to align the symbols.

To this end, the plurality of second wireless communication terminals may start the HE-LTF transmission to the first wireless communication terminal at the same time and stop the HE-LTF transmission at the same time. In another specific embodiment, the first wireless communication terminal is space-time of a second wireless communication terminal different in different sub-frequency bands in a sub-frequency band in which the number of HE-LTFs required by the space-time stream is smaller than the HE-LTF to be transmitted. A HE-LTF including a subcarrier having a phase pattern for canceling the stream may be transmitted. In more detail, the first wireless communication terminal may use an N × N orthogonal matrix applied in OFDM symbol units to the phase of the subcarrier included in the HE-LTF. In this case, N is the number of HE-LTFs required by the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. In this case, the number of HE-LTFs may be the number of OFDM symbols including the HE-LTF as described above. In more detail, the first wireless communication terminal transmits the HE-LTF to each of the plurality of sub-frequency bands according to the phase of the subcarrier indicated by the number of rows required by the corresponding sub-frequency band from the first row in the N × N orthogonal matrix. Can be. In another specific embodiment, the additional HE-LTF may be simply repeated transmission of the previously transmitted HE-LTF. In addition, the additional HE-LTF may be a cyclic shift of the previously transmitted HE-LTF.

In another specific embodiment, the second wireless communication terminal may transmit the HE-LTF based on the sub-frequency band required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. In more detail, the second wireless communication terminal is coupled to a frequency band in which a greater number of HE-LTF signals are required than the number of HE-LTFs required in a sub-frequency band in which the smallest number of space-time streams of a plurality of sub-frequency bands are transmitted. HE-LTF may be transmitted. As described above, the combined HE-LTF represents an LTF in which a plurality of HE-LTFs are combined into one. In more detail, the combined HE-LTF may be a combination of a plurality of LTFs on a frequency axis. In another specific embodiment, the combined HE-LTF may be a combination of a plurality of LTFs in an orthogonal code axis.

In this case, the second wireless communication terminal may transmit the HE-LTF described with reference to FIGS. 18 through 19 according to the size of the frequency band allocated by the second wireless communication terminal. This will be described with reference to FIGS. 21 through 26. In addition, the second wireless communication terminal may transmit a separate HE-LTF corresponding to the size of the frequency band allocated by the second wireless communication terminal other than the HE-LTF described with reference to FIGS. 17 to 18. This will be described with reference to FIGS. 27 to 28.

21 shows signal patterns of subcarriers included in an LTF used when 9 stations transmit data to an AP. FIG. 22 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 21.

The second wireless communication terminal can transmit a subcarrier included in the LTF corresponding to the frequency band allocated by the second wireless communication terminal in the above-described LTF. However, when the second wireless communication terminal matches the allocated frequency band and the subcarrier included in the LTF, there may exist a subcarrier that is not allocated to any second wireless communication terminal. The second wireless communication terminal may not transmit a subcarrier that is not assigned to any second wireless communication terminal. In another specific embodiment, any one of a subcarrier not assigned to any second wireless communication terminal, a second wireless communication terminal allocated with a subcarrier closest to the left, and a second wireless communication terminal assigned with a subcarrier closest to the right One second wireless communication terminal may transmit the corresponding subcarrier. In another specific embodiment, any one of a subcarrier not assigned to any second wireless communication terminal, a second wireless communication terminal allocated with a subcarrier closest to the left, and a second wireless communication terminal assigned with a subcarrier closest to the right One second wireless communication terminal can alternately transmit the corresponding subcarrier. In addition, the plurality of second wireless communication terminals may transmit a subcarrier that is not assigned to any second wireless communication terminal while lowering the transmission power. In addition, a subcarrier not allocated to any second wireless communication terminal may be used as a pilot signal. According to a specific embodiment, the first wireless communication terminal may signal at least one of a subcarrier transmission method and a transmission subject that are not assigned to any second wireless communication terminal.

In the embodiment of FIGS. 21 and 22, nine stations divide and transmit the short HE-LTF and the long HE-LTF described with reference to FIGS. 17 and 18. 21 and 22, the subcarriers located at {-96, -42, 42, 96} of the short HE-LTF and {-96, -69, -42, -15, 15, 42, of the long HE-LTF; 69, 96} has not been assigned to any station. Therefore, subcarriers not allocated to any of these stations may be transmitted according to the above-described embodiments. 21 and 22, each of the nine stations may transmit 13 subcarriers of the subcarriers included in the short HE-LTF. In addition, each of the nine stations may transmit 26 subcarriers among the subcarriers included in the long HE-LTF.

FIG. 23 shows signal patterns of subcarriers included in an LTF used when five stations transmit data to an AP. 24 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 23 in detail.

As described with reference to FIGS. 22 through 23, each of the five stations transmits a subcarrier of the LTF corresponding to the frequency band allocated thereto. Subcarrier at {-70, -16, 16, 70} of the short HE-LTF and subcarrier at {-70, -69, -16, -15, 15, 16, 69, 70} of the long HE-LTF The carrier has not been assigned to any station. Therefore, subcarriers not allocated to any of these stations may be transmitted according to the above-described embodiments. As the number of second wireless communication terminals and the frequency bands allocated to each of the second wireless communication terminals are changed, the subcarriers of the LTFs transmitted by the second wireless communication terminals are also changed. In the embodiments of FIGS. 23 and 24, each of five stations may transmit 26 subcarriers among the subcarriers included in the short HE-LTF. In addition, each of the five stations may transmit 52 subcarriers among the subcarriers included in the long HE-LTF.

FIG. 25 shows a signal pattern of a subcarrier included in an LTF used when three stations transmit data to an AP. FIG. 26 illustrates a signal pattern of a subcarrier included in the LTF described with reference to FIG. 25 in detail.

As described with reference to FIGS. 22 to 24, each of the three stations transmits a subcarrier of the LTF corresponding to the frequency band allocated thereto. Subcarriers not assigned to any station may be transmitted according to the embodiments described above. As the number of second wireless communication terminals and the frequency bands allocated to each of the second wireless communication terminals are changed, the subcarriers of the LTFs transmitted by the second wireless communication terminals are also changed. In the embodiments of FIGS. 25 and 26, each of the three stations may transmit 53 or 54 subcarriers among the subcarriers included in the short HE-LTF. In addition, each of the three stations may transmit 106 or 108 subcarriers among the subcarriers included in the long HE-LTF.

As described above, the second wireless communication terminal may divide and transmit LTFs transmitted when the first wireless communication terminal transmits data to the plurality of second wireless communication terminals. In this case, however, the PAPR of the LTF transmitted by the individual second wireless communication terminal may not have an optimal value. Accordingly, the second wireless communication terminal may determine the LTF in consideration of only the frequency bandwidth allocated to the second wireless communication terminal and transmit the determined LTF.

27 is a view illustrating a signal pattern of a subcarrier included in an LTF transmitted by a second wireless communication terminal according to one embodiment of the present invention. FIG. 28 shows signal patterns of subcarriers included in the LTF described with reference to FIG. 27 in detail.

{LTF-26-short} = {S-LTF_L} or {S-LTF_R}

{LTF-26-short} represents a short LTF including 26 subcarriers. {LTF-26-short} may follow the subcarrier signal pattern of any one of {S-LTF_L} or {S-LTF_R} described with reference to FIGS. 16 and 17.

{LTF-26-long} = {S-LTF_L, S-LTF_R}

{LTF-26-long} represents a long LTF containing 26 subcarriers. {LTF-26-long} may be a signal pattern of a subcarrier from which a direct current (DC) subcarrier is deleted from a signal pattern of a subcarrier of {S1G-LTF} described with reference to FIGS. 16 and 17.

{LTF-52-short} = {S-LTF_L_e, S-LTF_R_e}

{LTF-52-short} represents a short LTF including 26 subcarriers. {LTF-52-short} is a signal of a subcarrier in which 26 subcarriers excluding a DC subcarrier are transmitted only in an even number subcarrier among 52 subcarriers in {S1G-LTF} described with reference to FIGS. 16 and 17. It may be a pattern.

{LTF-52-long} = {LTF_L, LTF_R}

{LTF-52-long} represents a long LTF including 52 subcarriers.

{LTF-52-long} may be signal patterns of 52 subcarriers excluding a DC subcarrier in {L-LTF} described with reference to FIGS. 16 and 17.

{LTF-106-short} = {LTF_L_e, 1, LTF_R_e}

{LTF-106-short} represents a short LTF including 106 subcarriers. {LTF-106-short} is an even-numbered subcarrier in all 106 subcarriers of 53 subcarriers in which a direct current (DC) subcarrier is changed to {1} in the {L-LTF} signal patterns described with reference to FIGS. 16 and 17. It may be a signal pattern of a subcarrier transmitting a signal only to an even subcarrier.

{LTF-106-long} = {LTF_L, 1, LTF_R, LTF_L, 1, LTF_R}

{LTF-106-long} represents a long LTF including 106 subcarriers. {LTF-106-long} is a signal pattern of a subcarrier that repeatedly transmits 53 subcarriers in which the direct current (DC) subcarrier is changed to {1} twice in {L-LTF} described with reference to FIGS. 16 and 17. Can be.

{LTF-108-short} = {LTF_L_e, 1, 1, LTF_R_e}

{LTF-108-short} represents a short LTF including 108 subcarriers. {LTF-108-short} inserts {1} into 53 subcarriers in which the direct current (DC) subcarrier is changed to {1} in the {L-LTF} signal pattern described with reference to FIGS. 16 and 17. It may be a signal pattern of a subcarrier transmitting a signal only to 54 even subcarriers in 108 subcarriers.

{LTF-108-long} = {LTF_L, 1, LTF_R, x, y, LTF_L, 1, LTF_R}

{LTF-108-long} represents a long LTF including 108 subcarriers. {LTF-108-long} repeats 53 subcarriers with the DC subcarrier changed to {1} twice in {L-LTF} described with reference to FIGS. 16 and 17, and the PAPR of all subcarriers in the center is repeated. It may be a signal pattern of a subcarrier transmitting two subcarriers, {x, y}, to minimize.

29 is a view illustrating a method for estimating a channel using an LTF by a wireless communication terminal according to an embodiment of the present invention.

In the embodiment of FIG. 29, it is assumed that a wireless communication terminal having two antennas communicates with each other. For convenience of description, a wireless communication terminal for transmitting an LTF is called a transmission station (TX STA), and a wireless communication terminal for receiving data is called a reception station (RX STA). The transmission station TX STA transmits the LTF through the transmission antennas x1 and x2. The receiving station RX STA receives the LTF through the receiving antennas y1 and y2.

The TX station transmits the first OFDM symbol including the LTF signal on the time axis at the first time point t1 and the second OFDM symbol at the second time point t2. In this case, a signal received in each k th subcarrier may be represented as shown in FIG. 29 (b). In this case, h _ba denotes a radio channel passing before the signal transmitted from the a-th transmit antenna xa is received by the b-th receive antenna yb. z represents white Gaussian noise. At this time, the signal pattern of the subcarrier included in the LTF transmitted from the X1 antenna at the time of transmitting the second OFDM symbol is multiplied by (-1). A phase shift of 1 or -1 multiplied by the signal pattern of the subcarrier included in the LTF in each transmit antenna at each LTF symbol transmission time may be defined as a separate matrix. This matrix will be described in detail later with reference to FIG. 31.

When the h term and the exponent term of the equations developed in FIG. 29 (b) are combined and expressed as h ^ {~}, the equation of FIG. 29 (c) is obtained.

When the receiving station RX STA adds or subtracts the equation of FIG. 29 (c), each of the h_ {11}, h_ {12}, h_ {21}, h_ {22}, and LTF, as shown in 29 (d), respectively. A channel estimation equation for each subcarrier can be obtained.

A wireless communication terminal using a plurality of antennas may separate LTFs into a plurality and transmit each of the plurality of separated signals through each of the plurality of antennas. In more detail, when using two antennas, the wireless communication terminal may transmit even-numbered carriers of the LTF through one antenna and transmit odd-numbered carriers of the LTF through the other antenna. In this case, the LTF signal is transmitted in a repetitive pattern on the time axis. Therefore, this can reduce the time for the wireless communication terminal to transmit and receive the LTF. This will be described in detail with reference to FIG. 30.

30 is a view illustrating a method for estimating a channel using an LTF by a wireless communication terminal according to another embodiment of the present invention.

In the embodiment of FIG. 30, it is assumed that a wireless communication terminal having two antennas communicates with each other. For convenience of description, a wireless communication terminal for transmitting an LTF is called a transmission station (TX STA), and a wireless communication terminal for receiving data is called a reception station (RX STA). The transmission station TX STA transmits the LTF through the transmission antennas x1 and x2. The receiving station RX STA receives the LTF through the receiving antennas y1 and y2.

In this case, the TX station transmits only half of the LTF signal (for example, even subcarriers) through the X1 antenna and only the other half of the LTF signal (for example, odd subcarriers) through the X2 antenna. . The division pattern applied to the first time point t1 may be reversely applied at the second time point t2. As described above, since the transmission station (TX STA) uses only half of the subcarriers, performing an Inverse Fast Fourier Transform (IFFT) generates signal patterns of subcarriers included in repetitive LTFs in the entire LTF symbol time. The TX station can reduce the time required for LTF transmission by transmitting only a non-repetitive pattern among these.

The transmitting station TX STA transmits the first OFDM symbol including the LTF at the first time point t1 and the second OFDM symbol at the second time point t2 on the time axis. At this time, the signal received in each k-th subcarrier is displayed as shown in FIG. 30 (b). In this case, the wireless channel passing before the signal transmitted from the xa antenna is received by the yb antenna is denoted by h _ba . z represents white Gaussian noise. The TX station transmits the signal pattern of the subcarrier included in the LTF transmitted from the X1 antenna when the second LTF symbol is transmitted by multiplying (-1). A phase shift of 1 or -1 multiplied by the signal pattern of the subcarrier included in the LTF at each transmit antenna at the time of transmission of the OFDM symbol including the LTF may be defined as a separate matrix. This matrix will be described in detail later with reference to FIG. 31.

The sum of the h term and the exponent term of the equations developed in FIG. 30 (b) is represented by h ^ {~}, and is equal to the equation of FIG. 29 (c).

When the receiving station RX STA adds or subtracts the equation of FIG. 30 (c), h_ {11} ^ {k_even}, h_ {12} ^ {k_odd}, and h_ {21} ^ { k_even}, h_ {22} ^ {k_odd} and a channel estimation equation for each subcarrier included in the LTF can be obtained. This is a result of channel estimation of only half of the total subcarriers for each antenna channel. However, the RX STA may perform channel estimation on the remaining signals by performing interpolation using information of both channels on the frequency axis.

As described above, the wireless communication terminal can change the phase while transmitting the LTF to enable channel estimation of the corresponding wireless stream. In this case, a phase pattern that changes every time the LTF is transmitted may be represented by a matrix. This will be described with reference to FIGS. 31 to 42.

31 is a matrix illustrating a phase pattern applied in units of OFDM symbols to subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention.

For convenience of description, in the embodiment of FIG. 31, a phase pattern applied in units of OFDM symbols to a subcarrier included in an LTF used by a wireless communication terminal according to an embodiment of the present invention is referred to as C-orthogonal. The wireless communication terminal according to an embodiment of the present invention multiplies the same LTF by the value corresponding to the C-orthogonal in the same frequency band and transmits each time-space stream. In detail, each ellipse illustrated in FIG. 31 represents a phase change value used when transmitting n space-time streams and the number of OFDM symbols used to transmit LTFs.

For example, when the wireless communication terminal transmits two space-time streams, the wireless communication terminal may select C ₁ (1) * LTF and C ₁ (2) * LTF in each of the two space-time streams in the first OFDM symbol including the LTF. Send it through. Thereafter, the wireless communication terminal transmits C ₂ (1) * LTF and C ₂ (2) * LTF in each of two space-time streams in the second OFDM symbol including the LTF.

In another specific embodiment, when the wireless communication terminal transmits eight space-time streams, the wireless communication terminal is C ₁ (1) * LTF, C ₁ (2) * LTF, C in the first OFDM symbol including the LTF ₁ (3) * LTF, C ₁ (4) * LTF, C ₁ (5) * LTF, C ₁ (6) * LTF, C ₁ (7) * LTF, and C ₁ (8) * LTF Transmit through each of the space-time streams. Then, the wireless communication terminal is C ₂ (1) * LTF, C ₂ (2) * LTF, C ₂ (3) * LTF, C ₂ (4) * LTF, C ₂ (in the second OFDM symbol including the LTF) 5) * LTF, C ₂ (6) * LTF, C ₂ (7) * LTF, and C ₂ (8) * LTF are transmitted on each of the eight space-time streams.

32 is a view illustrating specific values of a phase pattern applied in units of OFDM symbols to subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention.

For convenience of description, specific values included in the C-orthogonal are referred to as C-codes. P _4x4 of FIG. 32 (a) shows a C-code value used when transmitting LTFs supporting 1 to 4 space-time streams. In addition, P _6x6 of FIG. 31 (b) shows a C-code value used when transmitting LTFs supporting 5 to 6 spatiotemporal streams. In addition, P _8x8 of FIG. 32 (c) shows a value of C-code used when transmitting LTFs supporting 7 to 8 space-time streams. The code of FIG. 32 (a) is referred to as 4C-code, the code of FIG. 32 (b) is referred to as 6C-code, and the code of FIG. 32 (c) is referred to as 8C-code.

The wireless communication terminal may transmit the LTF according to this C-orthogonal. The wireless communication terminal receiving the LTF may estimate the channels of all subcarriers included in the LTF in the order described above with reference to FIG. 29. However, if C-orthogonal is used, the number of times the LTF should be sent increases as the number of space-time streams increases.

The wireless communication terminal transmitting the LTF may transmit the subcarriers included in the LTF orthogonally in a predetermined number of units instead of being orthogonal to the entire subcarriers included in the LTF in different space-time streams. In this case, the wireless communication terminal receiving the LTF may extract a signal average value transmitted by a predetermined number of subcarriers and estimate the channel based on the extracted average value. Accordingly, even if the number of space-time streams increases, the wireless communication terminal receiving the LTF may perform channel estimation without receiving additional LTFs. To this end, a wireless communication terminal transmitting an LTF must repeatedly apply a phase pattern to a predetermined number of subcarriers for each subcarrier included in the LTF for each space-time radio stream. This will be described with reference to FIGS. 33 to 35.

FIG. 33 is a diagram illustrating an orthogonal pattern applied to a predetermined number of subcarrier units to individual subcarriers included in an LTF used by a wireless communication terminal according to another embodiment of the present invention. FIG. 34 is a matrix illustrating an orthogonal pattern applied to each subcarrier included in an LTF used by a wireless communication terminal in a predetermined number of subcarriers according to another embodiment of the present invention.

Applying an orthogonal pattern to this specification means transmitting a subcarrier based on the phase indicated by the orthogonal pattern. Specifically, applying the orthogonal pattern may represent multiplying a subcarrier by a phase represented by the orthogonal pattern.

A wireless communication terminal according to an exemplary embodiment of the present invention repeatedly multiplies an orthogonal pattern by a predetermined number of subcarriers to each subcarrier included in the LTF for each space-time radio stream. In more detail, the wireless communication terminal can determine the number of units of subcarriers to which the orthogonal pattern is applied according to the number of space-time streams.

Specifically, if the number of space-time streams is 1 to 4, the pattern to be applied to individual subcarriers is a 4 x 4 orthogonal matrix. In this case, the wireless communication terminal may repeatedly apply each row of the 4 × 4 orthogonal matrix in units of four subcarriers for each space-time stream. Also, if the number of space-time streams is 5 to 6, the pattern to apply to the individual subcarriers is a 6 x 6 orthogonal matrix. In this case, the wireless communication terminal may repeatedly apply each row of the 6 × 6 orthogonal matrix in units of six subcarriers for each space-time stream. Also, if the number of space-time streams is 7 to 8, the pattern to apply to the individual subcarriers is an 8 x 8 orthogonal matrix. In this case, the wireless communication terminal may repeatedly apply each row of the 8x8 orthogonal matrix in units of eight subcarriers for each space-time stream.

For convenience of description, when the orthogonal pattern is repeatedly applied to a certain number of subcarriers, the number of constant subcarriers is referred to as a unit number.

In this case, when the number of subcarriers included in the LTF is not a multiple of the number of units of the subcarrier to which the orthogonal pattern is applied, the wireless communication terminal applies the orthogonal pattern and applies a part of the orthogonal-pattern to the remaining subcarriers in order. .

For convenience of description, the n th subcarrier included in the LTF is represented by L _n , and the value of an orthogonal pattern applied to the n th subcarrier in the i th spatiotemporal stream is denoted by S _n (i). For convenience of explanation, a collection of values generated by multiplying orthogonal patterns by individual subcarriers included in the LTF is referred to as an S-orthogonal LTF, and an S-orthogonal LTF corresponding to the i th spatiotemporal stream is denoted by LTF (i). .

In the embodiment of FIG. 33A, the wireless communication terminal transmits four space-time streams. The wireless communication terminal transmits one OFDM symbol including the LTF on each of four space-time streams. In this case, the orthogonal sequence applied to the subcarriers included in each of the four space-time streams may be a P _4x4 matrix of FIG. 34 (a). Specifically, in the embodiment of FIG. 34 (a), the wireless communication terminal repeatedly applies each row of the P _4x4 matrix to each of four space-time streams in units of four subcarriers.

In addition, in the embodiment of FIG. 33B, the wireless communication terminal transmits six space-time streams. The wireless communication terminal transmits one OFDM symbol including the LTF on each of six space-time streams. In this case, the orthogonal sequence applied to the subcarriers included in each of the six space-time streams may be a P _6x6 matrix of FIG. 34 (b). Specifically, in the embodiment of FIG. 34A, the wireless communication terminal repeatedly applies each row of the P _6x6 matrix to each of six space-time streams in units of six subcarriers.

In addition, in the embodiment of FIG. 33C, the wireless communication terminal transmits eight space-time streams. The wireless communication terminal transmits one OFDM symbol including the LTF on each of the eight space-time streams. In this case, the orthogonal sequence applied to the subcarriers included in each of the eight space-time streams may be a P _8x8 matrix of FIG. 34 (c). Specifically, each row of the P _8x8 matrix of FIG. 34C is repeatedly applied to each subcarrier.

The orthogonal pattern used to generate the S-orthogonal LTF is called 4S-code, 6S-code, and 8S-code depending on the number of subcarriers to which the orthogonal pattern is applied. Therefore, P _4x4 of FIG. 34 (a) is 4S-code, P _6x6 of 34 (b) is 6S-code P _8x8 of 34 (c) is Referred to as 8S-code.

In addition, S-orthogonal LTF is an embodiment of the combined LTF described above.

35 is a view illustrating a method of estimating a channel using an orthogonal pattern applied to an individual subcarrier included in an LTF used by a wireless communication terminal according to another embodiment of the present invention.

In the embodiment of FIG. 35, it is assumed that a wireless communication terminal having two antennas communicates with each other. For convenience of description, a wireless communication terminal for transmitting an LTF is called a transmission station (TX STA), and a wireless communication terminal for receiving data is called a reception station (RX STA). The transmission station TX STA transmits the LTF through the transmission antennas x1 and x2. The receiving station RX STA receives the LTF through the receiving antennas y1 and y2.

The transmitting station TX STA transmits the first OFDM symbol including the LTF signal on the time axis at a first time point t1. In this case, a signal received in each k th subcarrier may be represented as shown in FIG. 35 (b). In this case, h _ba denotes a radio channel passing before the signal transmitted from the a-th transmit antenna xa is received by the b-th receive antenna yb. z represents white Gaussian noise. In this case, a phase change pattern applied to individual subcarriers included in the LTF in each transmit antenna may be defined as a separate orthogonal matrix. Such a matrix may be the S code of FIG. 31 described above.

When the receiving station (RX STA) multiplies each S-orthogonal LTF sequence by both sides of the equation of FIG. 35 (b), it may obtain a value as shown in FIG. 35 (c) due to the orthogonality of the S-orthogonal LTF sequence.

Sub-carrier channel estimation equations included by h_ {11}, h_ {12}, h_ {21}, h_ {22} and LTF are added or subtracted by the receiving station (RX STA) from FIG. 35 (c). Can be obtained. However, the channel estimation equation obtained by the receiving station RX STA is an average of a plurality of subcarriers. In detail, the estimation equation obtained by the reception station RX STA is an average of a plurality of subcarriers by the number of units. This will be described in detail with reference to FIGS. 36 to 37.

36 is a detailed operation of estimating a channel based on LTFs including 26 subcarriers using an orthogonal pattern applied to individual subcarriers included in an LTF used by a wireless communication terminal according to an embodiment of the present invention. Shows.

As described above, the wireless communication terminal according to an embodiment of the present invention receives an LTF including individual subcarriers to which an orthogonal pattern is applied. At this time, the wireless communication terminal multiplies the orthogonal pattern by the unit of a certain number of subcarriers. In more detail, the wireless communication terminal may move the subcarriers included in the LTF one by one and multiply the orthogonal pattern by the number of predetermined subcarriers. Through this, the wireless communication terminal can obtain a channel estimation value in units of a certain number of subcarriers.

In the embodiment of FIG. 36A, the long LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is four. In the equation of FIG. 35, the value of t increases by 1, s is 4, and l = 1. Therefore, the wireless communication terminal multiplies the orthogonal pattern by the first to fourth subcarriers included in the LTF. Thereafter, the wireless communication terminal multiplies the orthogonal pattern by the second to fifth subcarriers included in the LTF. The wireless communication terminal thus moves the subcarriers one by one and multiplies the orthogonal pattern. Finally, the wireless communication terminal multiplies the orthogonal pattern by the twenty third subcarrier to the twenty sixth subcarrier. Through this, channel estimation values can be obtained in units of four subcarriers. In the case of the first three subcarriers and the last three subcarriers, the channel estimation accuracy is lower than that of the other subcarriers, because the channel estimation values are smaller than those of the other subcarriers.

In the embodiment of FIG. 36B, the LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is 6. 35, the value of t increases by 1, s is 6, and l = 1. Therefore, the wireless communication terminal multiplies the number of units of the orthogonal pattern by the first to sixth subcarriers included in the LTF. Thereafter, the wireless communication terminal multiplies the second to seventh subcarriers included in the LTF by the number of units of the orthogonal pattern. The wireless communication terminal moves the subcarriers one by one and multiplies the number of units of the orthogonal pattern. Finally, the wireless communication terminal multiplies the number of units of the orthogonal pattern by the twenty-first subcarrier to the twenty-sixth subcarrier. Through this, a channel estimation value can be obtained in units of six subcarriers. In the case of the first five subcarriers and the last five subcarriers, the channel estimation accuracy is lower than that of other subcarriers, and thus the channel estimation accuracy may be lower than that of other subcarriers.

In the embodiment of FIG. 36C, the LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is eight. In the equation of FIG. 35, the value of t is increased by 1, s is 8, and l = 1. Therefore, the wireless communication terminal multiplies the number of units of the orthogonal pattern by the first to eighth subcarriers included in the LTF. Thereafter, the wireless communication terminal multiplies the second subcarrier included in the LTF by the number of units of the orthogonal pattern. The wireless communication terminal moves the subcarriers one by one and multiplies the number of units of the orthogonal pattern. Finally, the wireless communication terminal multiplies the nineteenth subcarrier to the twenty sixth subcarrier by the number of units of the orthogonal pattern. Through this, a channel estimation value can be obtained in units of six subcarriers. In the case of the first seven subcarriers and the last seven subcarriers, the channel estimation accuracy is lower than that of the other subcarriers, because the channel estimation values are smaller than those of the other subcarriers.

FIG. 37 is a view illustrating specific channel estimation based on an LTF including 26 subcarriers using an orthogonal pattern applied to individual subcarriers included in an LTF used by a wireless communication terminal according to another embodiment of the present invention. Show the action.

As described with reference to FIG. 36, the wireless communication terminal can move the subcarriers included in the LTF one by one and multiply the orthogonal patterns. In another specific embodiment, the wireless communication terminal may move the subcarriers by two and multiply the orthogonal patterns.

For example, in the embodiment of FIG. 37A, the long LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is four. 35, the value of t increases by 2, s is 4, and l = 1. Therefore, the wireless communication terminal multiplies the orthogonal pattern by the first to fourth subcarriers included in the LTF. Thereafter, the wireless communication terminal multiplies the orthogonal pattern by the third to sixth subcarriers included in the LTF. The wireless communication terminal moves the subcarriers by two and multiplies the orthogonal pattern in this manner. Finally, the wireless communication terminal multiplies the orthogonal pattern by the twenty third subcarrier to the twenty sixth subcarrier. Through this, channel estimation values can be obtained in units of four subcarriers. This embodiment has an advantage that the operation speed is faster than moving by one subcarrier and multiplying the orthogonal pattern. However, when the wireless communication terminal moves two subcarriers, at most two channel estimations are performed on one subcarrier, and when the wireless communication terminal moves by one subcarrier, at most two channel estimations are performed. Therefore, when the wireless communication terminal moves two subcarriers, the accuracy of channel estimation may be lower than when the wireless communication terminal moves by one subcarrier.

In addition, the wireless communication terminal may further transmit a subcarrier in a frequency band corresponding to the guard band. Through this, the wireless communication terminal can increase the channel estimation accuracy of the subcarrier adjacent to the guard band.

For example, in the embodiment of FIG. 37B, the long LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is four. In the equation of FIG. 35, the value of t increases from -1 to 25 by 1, s is 4, and l = 1. In addition, in the embodiment of FIG. 37C, the subcarrier is included, and the number of units of the orthogonal pattern is four. 34, the value of t increases from 0 to 1 by 24, s is 4, and l = 1. The wireless communication terminal can improve the channel estimation accuracy of subcarriers adjacent to the guard band through this.

In addition, when the LTF is a short LTF transmitting a signal only to even-numbered subcarriers, the wireless communication terminal may multiply orthogonal patterns only to even-numbered subcarriers.

For example, in the embodiment of FIG. 37D, the short LTF includes 26 subcarriers, and the number of units of the orthogonal pattern is four. 34, the value of t increases from 2 to 20 by 2, s is 4, and l = 1. Through this, the wireless communication terminal estimates the channel of the even subcarrier. The wireless communication terminal then estimates the channel of the adjacent odd subcarrier based on the estimation of the channel of the even subcarrier. Therefore, when the wireless communication terminal estimates a channel based on the short LTF, the channel estimation accuracy may be lower than when the wireless communication terminal estimates the channel based on the long LTF.

The wireless communication terminal may apply the first orthogonal pattern to individual subcarriers included in the LTF, and transmit the LTF to which the orthogonal pattern is applied to the individual subcarriers according to the second orthogonal pattern. Specifically, C-orthogonal and S-orthogonal LTF described above may be used together. Through this, the wireless communication terminal can estimate the channel even through a small number of LTFs. This will be described with reference to FIGS. 38 to 42.

38 illustrates that a wireless communication terminal according to an embodiment of the present invention applies a first orthogonal pattern to an individual subcarrier included in an LTF and transmits an LTF to which an orthogonal pattern is applied to an individual subcarrier according to a second orthogonal pattern. Shows.

In this case, transmitting the LTF to which the orthogonal pattern is applied to the individual subcarriers according to the second orthogonal pattern may represent applying the second orthogonal pattern to the subcarriers included in the LTF in OFDM symbol units.

In more detail, as in the embodiment of 38 (a), the wireless communication terminal can transmit the aforementioned S-orthogonal LTF according to the C-orthogonal.

According to a specific embodiment, when the wireless communication terminal transmits one space-time stream, the wireless communication terminal may transmit one S-orthogonal LTF (LTF (1)). However, in order to estimate a center frequency offset (CFO), the wireless communication terminal can transmit the same S-orthogonal LTF twice. 38 (b) shows this embodiment.

In another specific embodiment, when a wireless communication terminal transmits two space-time streams, the wireless communication terminal may simultaneously transmit two different S-orthogonal LTFs (LTF (1) and LTF (2)). 37 (C) shows this example.

In addition, the wireless communication terminal may transmit two different S-orthogonal LTFs (LTF (1), LTF (2)) twice based on C-orthogonal. The wireless communication terminal can estimate the CFO through this. 38 (d) shows this embodiment.

In another specific embodiment, when the wireless communication terminal transmits four space-time streams, the wireless communication terminal may include four different S-orthogonal LTFs (LTF (1), LTF (2), LTF (3), and LTF (4)). )) Can be sent at the same time. 37 (e) shows this embodiment.

In addition, the wireless communication terminal may transmit four different S-orthogonal LTFs (LTF (1), LTF (2), LTF (3), LTF (4)) twice or four times, respectively, based on C-orthogonal. have. The wireless communication terminal can estimate the CFO or perform other functions through this. 38 (f) and 38 (g) illustrate this embodiment.

39 illustrates a case in which a wireless communication terminal applies a first orthogonal pattern to an individual subcarrier included in an LTF and transmits an LTF to which an orthogonal pattern is applied to an individual subcarrier according to a second orthogonal pattern according to an embodiment of the present invention; In this case, a method of estimating a channel using the LTF is shown by the wireless communication terminal receiving the same.

In the embodiment of FIG. 39, it is assumed that a wireless communication terminal having two antennas communicates with each other. For convenience of description, a wireless communication terminal for transmitting an LTF is called a transmission station (TX STA), and a wireless communication terminal for receiving data is called a reception station (RX STA). The transmission station TX STA transmits the LTF through the transmission antennas x1 and x2. The receiving station RX STA receives the LTF through the receiving antennas y1 and y2.

The TX station transmits the first OFDM symbol including the LTF signal on the time axis at the first time point t1 and the second OFDM symbol at the second time point t2. In this case, a signal received in each k th subcarrier may be represented as shown in FIG. 39 (b). In this case, h _ba denotes a radio channel passing before the signal transmitted from the a-th transmit antenna xa is received by the b-th receive antenna yb. z represents white Gaussian noise. In this case, the first orthogonal pattern is applied to the individual subcarriers included in the LTF, and the LTF to which the first orthogonal pattern is applied to the individual subcarriers is transmitted based on the second orthogonal pattern. The LTF to which the first orthogonal pattern is applied to each subcarrier may be the S-orthogonal LTF described above. Also, the second orthogonal pattern may be C-orthogonal described above.

The receiving station RX STA may obtain the equation of FIG. 39C by multiplying the equation of FIG. 39B by the LTF to which the first orthogonal pattern is applied to each subcarrier.

The receiving station RX STA adds or subtracts the equation of FIG. 39 (c) to include h_ {11}, h_ {12}, h_ {21}, h_ {22} and LTF as shown in 39 (d), respectively. A channel estimation equation for each subcarrier can be obtained.

40 illustrates a wireless communication terminal applying a first orthogonal pattern having a unit number of 4 to individual subcarriers included in an LTF, and applying a second orthogonal pattern to an LTF to which an orthogonal pattern is applied to individual subcarriers. According to the show to send.

When the wireless communication terminal according to an embodiment of the present invention applies a first orthogonal pattern having four units to individual sub-channels included in the space-time stream, the wireless communication terminal may simultaneously transmit four space-time streams. In this case, when the wireless communication terminal transmits the LTF to which the orthogonal pattern is applied to the individual subcarriers according to the second orthogonal pattern, the wireless communication terminal may simultaneously transmit seven space-time streams.

In the embodiment of FIG. 40A, the wireless communication terminal transmits five space-time streams. In this case, the wireless communication terminal includes five LTFs (LTF (1), LTF (2), LTF (3), C ₁ (1) * LTF (4), and C ₁ (2) * LTF (4)). Transmit through an OFDM symbol. Thereafter, the wireless communication terminal uses five LTFs (LTF (1), LTF (2), LTF (3), C ₂ (1) * LTF (4), and C ₂ (2) * LTF (4)). Transmit through an OFDM symbol. Through this, the wireless communication terminal receiving the LTF can distinguish three space-time radio streams through S-code and two space-time streams through C-code.

In the embodiment of FIG. 40B, the wireless communication terminal transmits six space-time streams. At this time, the wireless communication terminal is six LTF (LTF (1), LTF (2), LTF (3), C ₁ (1) * LTF (4), C ₁ (2) * LTF (4), C ₁ ( 3) * LTF (4)) is transmitted through one OFDM symbol. Thereafter, the wireless communication terminal further transmits six LTFs through three OFDM symbols. Through this, the wireless communication terminal receiving the LTF can distinguish three space-time radio streams through S-code and three space-time streams through C-code.

In the embodiment of FIG. 40C, the wireless communication terminal transmits seven space-time streams. In this case, the wireless communication terminal includes seven LTFs (LTF (1), LTF (2), LTF (3), C ₁ (1) * LTF (4), C ₁ (2) * LTF (4), C ₁ ( 3) * LTF (4) .C ₁ (4) * LTF (4)) is transmitted through one OFDM symbol. Thereafter, the wireless communication terminal further transmits 7 LTFs through 3 OFDM symbols. Through this, the wireless communication terminal receiving the LTF can distinguish three space-time radio streams through S-code and four space-time streams through C-code.

40 (a) to 40 (c), the wireless communication terminal used an orthogonal pattern having a unit number of four. However, in a specific embodiment, the wireless communication terminal may use an orthogonal pattern of 6 or 8 units. In this case, the wireless communication terminal can reduce the use of the C-code. Therefore, the wireless communication terminal can reduce the time required to transmit the LTF. However, the channel estimation accuracy of the wireless communication terminal when using the orthogonal pattern of 6 or 8 units can be reduced than when using the orthogonal pattern of 4 units.

FIG. 41 is a view illustrating a SU-MIMO physical frame transmitted by a wireless communication terminal according to an embodiment of the present invention using various orthogonal patterns described above.

FIG. 41 (a) shows that when a wireless communication terminal transmits seven space-time streams, the wireless communication terminal transmits an LTF using 8C-code. In detail, FIG. 41 (a) -1 shows that the wireless communication terminal transmits a long LTF, and FIG. 41 (a) -2 shows that the wireless communication terminal transmits a short LTF. When the short LTF is used, the wireless communication terminal can perform channel estimation in a relatively fast time. However, when the short LTF is used, the accuracy of the wireless communication terminal can be reduced. Therefore, the wireless communication stage can selectively use the short LTF. In particular, the wireless communication terminal may use the short LTF in an environment where radio wave interference is relatively low, such as indoors.

41 (b) shows that when a wireless communication terminal transmits seven space-time streams, the wireless communication terminal transmits an LTF using any one of 4S-code, 6S-code, and 8s-code. In detail, FIG. 41 (b) -1 shows that the wireless communication terminal transmits an LTF using 4S-code. In this case, the wireless communication terminal transmits the first space time radio stream to the fourth space time radio stream in the first OFDM symbol including the LTF, and the fifth space time radio stream to the seventh space time radio stream in the second OFDM symbol including the LTF. Send it. In addition, FIG. 41 (b) -2 shows that the wireless communication terminal transmits the LTF using 6S-code. In this case, the wireless communication terminal transmits the first space time radio stream to the sixth space time radio stream in the first OFDM symbol including the LTF, and the seven space time radio stream in the second OFDM symbol including the LTF. 41 (b) -3 shows that the wireless communication terminal transmits the LTF using 8S-code. In this case, the wireless communication terminal transmits the first space time radio stream to the seventh space time radio stream in the first OFDM symbol including the LTF.

FIG. 41 (c) shows that the wireless communication terminal uses S-code and C-code when the wireless communication terminal transmits seven space-time streams. In the embodiment of FIG. 41 (c)-1, the wireless communication terminal transmits four OFDM symbols including an LTF using 4S-code and 4C-code. At this time, the wireless communication terminal receiving the LTF distinguishes the first space time stream to the third space time stream through 4S-code, and the fourth space time stream to the seventh space time stream through 4C-code. In the embodiment of FIG. 41 (c)-2, the wireless communication terminal transmits three OFDM symbols including an LTF using 6S-code and 4C-code. At this time, the wireless communication terminal receiving the LTF distinguishes the first space time stream to the fifth space time stream through 6S-code, and the fifth space time stream to the seventh space time stream through 4C-code. In the embodiment of FIG. 41 (c) -3, the wireless communication terminal transmits one OFDM symbol including an LTF using 8S-code. In this case, the wireless communication terminal receiving the LTF distinguishes the first space time stream to the seventh space time stream through 8S-code. In the embodiment of FIG. 41 (c)-4, the wireless communication terminal transmits 8 OFDM symbols including the LTF using 8S-code and 8C-code. At this time, the wireless communication terminal receiving the LTF distinguishes the first space time stream to the seventh space time stream through 8S-code and 8C-code.

The wireless communication terminal may selectively use the various LTF transmission methods described above in consideration of at least one of the number of space-time streams to be transmitted, channel estimation performance, CFO estimation performance, and minimization of OFDM symbols for transmitting LTFs.

42 illustrates a physical frame transmitted by each of a plurality of stations when a plurality of stations transmit data to the AP through MU-MIMO according to an embodiment of the present invention.

In FIG. 42, the first station STA_a transmits two space-time streams to the AP, the second station STA_b transmits three space-time streams to the AP, and the third station STA_c transmits one space-time stream to the AP. Is transmitted, and the fourth station STA_d transmits one space-time stream.

In the embodiment of FIG. 42A, the first station STA_a to the fourth station STA_d transmit LTFs using 8S-code and 8C-code. Accordingly, the first station STA_a to the fourth station STA_d transmit LTFs through eight OFDM symbols. The AP distinguishes eight space-time streams through 8S-code and 8C-code.

In the embodiment of FIG. 42B, the first station STA_a to the fourth station STA_d transmit LTFs using 4S-code and 4C-code. Accordingly, the first station STA_a to the fourth station STA_d transmit LTFs through eight OFDM symbols. The AP distinguishes eight space-time streams through 8S-code and 8C-code. At this time, the AP divides the upper three spatiotemporal streams into 4S-codes and the lower four S-temporal streams into C-codes.

The first wireless communication terminal applies a C-code and an S-code according to the number of space-time streams transmitted by each of the plurality of second wireless communication terminals so that the space-time streams of the same second wireless communication terminal are distinguished in the same manner. Can be adjusted. In addition, the wireless communication terminal selectively selects the above-described C-code and S-code in consideration of at least one of the number of space-time streams to be transmitted, channel estimation performance, CFO estimation performance, and minimization of OFDM symbols for transmitting LTFs. Can be used.

43 is a ladder diagram illustrating operations of a first wireless communication terminal and a second wireless communication terminal according to an embodiment of the present invention.

The first wireless communication terminal 400 allocates a plurality of sub-frequency bands to the plurality of second wireless communication terminals 500 (S4301).

The first wireless communication terminal 400 transmits training signals and data to the plurality of second wireless communication terminals 500 through the plurality of sub-frequency bands (S4303). In this case, the training signal is used by the second wireless communication terminal 500 to estimate a channel through which data is transmitted. In more detail, the training signal may be a training signal transmitted through the HE-LTF described with reference to FIGS. 6 to 42. According to a specific embodiment, signal patterns of subcarriers included in the LTF described with reference to FIGS. 16 through 28 may be used.

In addition, the first wireless communication terminal may start transmitting the training signal at the same time in each of the plurality of sub-frequency bands and terminate the transmission of the training signal at the same time. In more detail, the first wireless communication terminal may transmit the same number of training signal OFDM symbols in each of a plurality of sub-frequency bands, and the training signal OFDM symbol may represent an OFDM symbol including a training signal. In this case, the first wireless communication terminal may transmit a training signal based on a frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted.

In more detail, the first wireless communication terminal 400 includes a plurality of training signal OFDM symbols less than the number of training signal OFDM symbols required in a frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. In addition, the additional training signal may be transmitted by a difference between the number of training signal OFDM symbols required in the sub-frequency band where the largest space-time stream is transmitted and the number of training signal OFDM symbols required in the corresponding sub-frequency band. The number of training signals required by the sub-frequency band through which the space-time stream is transmitted may be the number of training signals required to distinguish the space-time stream as described above. In addition, the number of training signals required to distinguish the space-time stream may vary depending on at least one of a channel estimation method and a phase pattern applied to a subcarrier included in the training signal.

The additional training signal may be a repeat of the previously transmitted training signal. In another specific embodiment, the additional training signal may be a cyclic shift of the previously transmitted training signal. In another specific embodiment, the additional training signal includes a subcarrier having a phase pattern for canceling a space-time stream transmitted to a different wireless communication terminal in a different sub-frequency band from which the additional training signal is transmitted. It may be a training signal. In the N × N orthogonal matrix applied to the phase of the subcarrier included in the training signal in the training signal unit, the first wireless communication terminal 400 requires the corresponding sub-frequency band starting from the first row of the N × N orthogonal matrix. The training signal is transmitted to each of the plurality of sub-frequency bands according to the phase of the subcarrier indicated by the number of rows of signal OFDM symbols, and N is a frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. It may be the number of training signal OFDM symbols required for.

In another specific embodiment, the first wireless communication terminal 400 may transmit a training signal based on a frequency band in which the smallest number of space-time streams of a plurality of sub-frequency bands are transmitted. In more detail, the first wireless communication terminal 400 includes a frequency band in which more training signal OFDM symbols are required than the number of training signal OFDM symbols required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. The combined training signal may be transmitted. In this case, the combined training signal may be a training signal in which a plurality of training signals are combined into one. In more detail, the combined training signal may be a combination of a plurality of training signals on a frequency axis. In more detail, the combined training signal may be a combination of a plurality of training signals in an orthogonal code axis.

In addition, as described above, the first wireless communication terminal 400 may transmit a signal to an even subcarrier included in a training signal and may not transmit a signal to an odd subcarrier. Through this, the first wireless communication terminal 400 can shorten the transmission time of the training signal. This training signal may be the short-HE-LTF described above. As described above, the first wireless communication terminal 400 may transmit a signal to an even subcarrier and determine whether to transmit a signal to an odd subcarrier according to a communication environment.

In addition, the first wireless communication terminal 400 may apply an orthogonal pattern in which the phase of the subcarrier included in the training signal is changed in units of OFDM symbols. In another specific embodiment, the first wireless communication terminal 400 may apply an orthogonal pattern in units of a certain number of subcarriers to individual subcarriers included in the training signal. According to another specific embodiment, the first wireless communication terminal 400 may apply a first orthogonal pattern to individual subcarriers included in the LTF and transmit the LTF to which the orthogonal pattern is applied to the individual subcarriers according to the second orthogonal pattern. . In more detail, the first wireless communication terminal 400 may transmit a training signal through various embodiments described with reference to FIGS. 29 to 41.

The second wireless communication terminal 500 obtains data based on the training signal (S4305). In detail, the second wireless communication terminal 500 may estimate a channel through which the first wireless communication terminal transmits data through the training signal. In addition, the second wireless communication terminal 500 may estimate the CFO based on the training signal. The second wireless communication terminal 500 may receive data based on at least one of the estimated channel and the CFO.

As described above, the first wireless communication terminal 400 receives data from the first row of the N x N orthogonal matrix in the N x N orthogonal matrix applied to the phase of the subcarrier included in the training signal. A channel on which the data is transmitted can be estimated based on the phase of the subcarrier indicated by the number of rows of the training signal OFDM symbols required by the sub-frequency band. In this case, N may be the number of the training signal OFDM symbols required in the frequency band for transmitting the most space-time stream of the plurality of sub-frequency bands.

Although the present invention has been described using the WLAN communication as an example, the present invention is not limited thereto and may be equally applicable to other communication systems such as cellular communication. In addition, while the methods, apparatus, and systems of the present invention have been described in connection with specific embodiments, some or all of the components, operations of the present invention may be implemented using computer systems having a general purpose hardware architecture.

Features, structures, effects, and the like described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, contents related to such combinations and modifications should be construed as being included in the scope of the present invention.

Although the above description has been made with reference to the embodiments, these are merely examples and are not intended to limit the present invention. Those skilled in the art to which the present invention pertains are not illustrated above without departing from the essential characteristics of the present embodiments. It will be appreciated that many variations and applications are possible. For example, each component specifically shown in the embodiment can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

Claims (20)

In the base wireless communication terminal, Transmitting and receiving unit for transmitting and receiving a wireless signal; And A processor for controlling an operation of the wireless communication terminal, The transceiver unit Allocating a plurality of sub-frequency bands to a plurality of wireless communication terminals, transmitting a training signal and data through each of the plurality of sub-frequency bands, wherein the training signal is used to estimate a channel through which the data is transmitted. Base wireless communication terminal. In claim 1, Starting transmission of the training signal at the same time and ending transmission of the training signal at the same time in each of the plurality of sub-frequency bands. Base wireless communication terminal. In claim 2, The transceiver unit Transmit the same number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in each of the plurality of sub-frequency bands; The training signal OFDM symbol represents an OFDM symbol including the training signal. Base wireless communication terminal. In claim 3, The transceiver unit The training signal is transmitted based on a frequency band in which the most space-time streams of the plurality of sub-frequency bands are transmitted. Base wireless communication terminal. In claim 4, The transceiver unit The number of the training signal OFDM symbols required in the corresponding sub-frequency band is greater than the number of the first OFDM symbols, which is the number of the training signal OFDM symbols required in the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. If the number of second OFDM symbols, which is the number, is small, an additional training signal is transmitted by a difference between the number of first OFDM symbols and the number of second OFDM symbols in a corresponding band. Base wireless communication terminal. In claim 5, The additional training signal Is a repetition of the previous training signal Base wireless communication terminal. In claim 5, The additional training signal Is a cyclic shift of the previously transmitted training signal Base wireless communication terminal. In claim 5, The additional training signal A training signal comprising a subcarrier having a phase pattern for canceling a space-time stream transmitted in a sub-frequency band different from the sub-frequency band in which the additional training signal is transmitted; Base wireless communication terminal. In claim 8, The transceiver unit In an N × N orthogonal matrix applied in units of OFDM symbols to the phase of a subcarrier included in the training signal, the phase of the subcarrier represented by one row of the number of the second OFDM symbols from one row of the N × N orthogonal matrix Transmit the training signal to each of the plurality of sub-frequency bands accordingly, N represents the number of the first OFDM symbols Base wireless communication terminal. In claim 3, The transceiver unit The training signal is transmitted based on a frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted. Base wireless communication terminal. In claim 10, The transceiver unit Transmitting a combined training signal to a frequency band in which the training signal OFDM symbol is required more than the number of the training signal OFDM symbol required in the frequency band in which the smallest number of space-time streams of the plurality of sub-frequency bands are transmitted, The combined training signal is a training signal combining a plurality of the training signals into one. Base wireless communication terminal. In claim 11, Combining a plurality of training signals included in the combined training signal on a frequency axis Base wireless communication terminal. In claim 11, The combined training signal is a combination of a plurality of training signals in an orthogonal code axis. Base wireless communication terminal. In claim 1, The training signal Transmit a signal to an even subcarrier included in the training signal, and do not transmit a signal to an odd subcarrier Base wireless communication terminal. In the wireless communication terminal, Transmitting and receiving unit for transmitting and receiving a wireless signal; And A processor for controlling an operation of the wireless communication terminal, The transceiver unit Receiving a training signal from a base wireless communication terminal, receiving data from the base wireless communication terminal based on the training signal, The base wireless communication terminal allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals including the wireless communication terminal, and transmits the training signal and the training signal to the plurality of wireless communication terminals through each of the plurality of sub frequency bands. To transmit data Wireless communication terminal. The method of claim 15, Each of the plurality of wireless communication terminals Starting reception of the training signal at the same time in each of the plurality of sub-frequency bands and ending reception of the training signal at the same time; Wireless communication terminal. The method of claim 16, Each of the plurality of wireless communication terminals Receive an equal number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in each of the plurality of sub-frequency bands, The training signal OFDM symbol represents an OFDM symbol including the training signal. Wireless communication terminal. The method of claim 17, The transceiver unit A sub-frequency band in which the wireless communication terminal receives the data than the number of first OFDM symbols, which is the number of the training signal OFDM symbols required in the sub-frequency band in which the largest space-time stream of the plurality of sub-frequency bands is transmitted. Receiving the additional training signal by the difference between the number of the first OFDM symbol and the number of the second OFDM symbol when the number of the second OFDM symbol, which is the number of the training signal OFDM symbols required at Wireless communication terminal. The method of claim 18, The transceiver unit In an N × N orthogonal matrix applied in units of OFDM symbols to the phase of a subcarrier included in the training signal, the phase of the subcarrier represented by one row of the number of the second OFDM symbols from one row of the N × N orthogonal matrix Estimate a channel on which the data is transmitted, N is the number of the first OFDM symbols Wireless communication terminal. In the operation method of the wireless communication terminal, Receiving a training signal from a base wireless communication terminal; And receiving data from the base wireless communication terminal based on the training signal. The base wireless communication terminal allocates a plurality of sub-frequency bands to a plurality of wireless communication terminals including the wireless communication terminal, and transmits the training signal and the training signal to the plurality of wireless communication terminals through each of the plurality of sub frequency bands. To transmit data How it works.

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