KR101714395B1 - Access point apparatus, wireless lan system including the same, and channel sounding method of the same - Google Patents

Abstract

An access point apparatus according to an embodiment of the present invention includes a channel estimator for estimating a coherence time, which is a time at which a channel state of each of a plurality of terminal devices is maintained; And determining a coherence time that maximizes a difference between expected gain and expected loss reflecting data traffic for the plurality of terminal devices among the coherent times as a first sounding period, And a sounding processor for determining whether to perform a multi-user MIMO (MU-MIMO) sounding operation based on the received signal.

Description

TECHNICAL FIELD [0001] The present invention relates to an access point apparatus, a wireless LAN system including the same, and a channel sounding method therefor. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an access point apparatus, a wireless LAN system including the same, and a channel sounding method thereof, and more particularly to an access point apparatus that performs channel sounding based on a substantial gain in consideration of a network environment, A wireless LAN system, and a channel sounding method thereof.

Since the Institute of Electrical and Electronics Engineers (IEEE) 802, a standardization organization of wireless LAN (WLAN) technology, was established in February 1980, many standardization works have been performed. Since the initial WLAN technology supports a speed of 1 ~ 2Mbps through frequency hopping, spread spectrum and infrared communication using 2.4GHz frequency through IEEE 802.11, recently it has applied OFDM (Orthogonal Frequency Division Multiplex) Speed can be supported. In IEEE 802.11, IEEE 802.11 has been improved to improve QoS (Quality of Service), access point protocol compatibility, security enhancement, radio resource measurement, wireless access vehicle environment for vehicle environment, , Fast Roaming, Mesh Network, Interworking with External Network, and Wireless Network Management are being put into practical use or development.

IEEE 802.11ac is a relatively recent technical standard to overcome the limitation of communication speed which is pointed out as a vulnerability in wireless LAN. IEEE 802.11ac supports high bandwidth (80MHz to 160MHz) at 5GHz frequency and 2.4GHz to 40MHz bandwidth for compatibility with 802.11n. Theoretically, according to the IEEE 802.11ac standard, the wireless LAN speed of the multiple terminals can be at least 1 Gbit / s and the maximum single link speed can be at least 500 Mbit / s. It supports a wide range of radio frequency bandwidths (up to 160 MHz), more Multiple Input Multiple Output spatial streams (up to 8), multiple user MIMO QAM) and other wireless interface concepts adopted by 802.11n.

The configuration of the wireless LAN is made up of an access point and a station. The access point is a device that transmits radio waves to enable wireless LAN users within the transmission distance to access the Internet and the network, and functions as a hub of a cellular phone or a hub of a wired network.

In the next generation wireless LAN system, the access point can simultaneously transmit data frames to at least one terminal device that is MIMO-paired. To this end, the access point can acquire information on a channel to be used for data transmission through channel sounding in transmitting a frame to a receiving terminal apparatus. However, time resources are used to perform this channel sounding, and the more frequently the channel sounding is performed, and the more the number of terminals participating in channel sounding, the more the time resources are used. Therefore, if the channel sounding is not efficiently performed, the wireless LAN performance is seriously reduced by consuming most of the time resources used for data packet transmission for channel sounding.

Published Japanese Patent Application No. 10-2014-0071948 (June 14, 2014)

The present invention relates to an access point apparatus capable of efficiently performing channel sounding in consideration of a network environment such as a downlink traffic load, a wireless LAN system including the access point apparatus, and a channel sounding method thereof will be.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

According to an aspect of the present invention, there is provided an access point apparatus including: a plurality of terminal apparatuses each having a plurality of terminal apparatuses, Determining a coherence time that maximizes a difference between expected gain and expected loss reflecting data traffic for terminal equipments to be a first sounding period, and determining an MU-MIMO based on the first sounding period, ) Type sounding operation to be performed.

According to an embodiment, when the expected gain according to the first sounding period is greater than the expected loss, the sounding processor performs the sounding operation of the MU-MIMO scheme according to the first sounding period .

According to an embodiment, the sounding processor may perform the sounding operation of the MU-MIMO scheme for terminal devices whose coherence time is larger than the first sounding period among the plurality of terminal devices have.

According to an embodiment, the sounding processor may perform a sounding operation of a single-user MIMO (SU-MIMO) scheme when the expected gain according to the first sounding period is smaller than the expected loss.

According to an embodiment, the sounding processor may calculate the expected gain based on a probability that a packet to be transmitted to each of the plurality of terminal devices exists in a queue.

According to an embodiment, the expected loss may be the time required for the sounding operation per sounding period.

A channel sounding method according to an embodiment of the present invention is a method for estimating a channel sounding time of a plurality of terminal equipments from data coherence time Determining a coherence time that maximizes a difference between the expected gain and the expected loss to be reflected as a first sounding period and performing a sounding operation of a multi-user MIMO (MU-MIMO) scheme based on the first sounding period And determining whether to perform the operation.

A wireless LAN system according to an embodiment of the present invention includes a plurality of terminal devices and a plurality of terminal devices in a MIMO manner based on channel state information collected through sounding operations with respect to the plurality of terminal devices, Wherein the access point device transmits data for the plurality of terminal devices among the coherence times, which is a time at which a channel state of each of the plurality of terminal devices is maintained, Determining a coherence time that maximizes a difference between expected gain and expected loss reflecting traffic, as a first sounding period, and performing a sounding operation of a multi-user MIMO (MU-MIMO) scheme based on the first sounding period And a sounding processor for determining whether to perform the sounding process.

According to the access point apparatus, the wireless LAN system including the access point apparatus, and the channel and null sounding method according to an embodiment of the present invention, whether to support MU-MIMO considering the degree of channel change of the terminal apparatus and downlink traffic load , The terminal device to participate in the sounding operation, and the sounding period, so that the overhead due to sounding can be maintained at an appropriate level according to the network environment and the data transmission efficiency can be maximized.

1 is a diagram illustrating a wireless LAN system according to an embodiment of the present invention.
2 is a block diagram showing the access point apparatus shown in FIG. 1 in more detail.
3 is a flowchart illustrating a channel sounding method of the access point apparatus shown in FIG.

The technical spirit of the present invention can be applied to various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. in this specification may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like refer to the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. In addition, the suffix "module" and " part "for constituent elements used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of IEEE 802 systems, 3GPP systems, 3GPP LTE and LTE-Advanced (LTE-Advanced) systems and 3GPP2 systems, which are wireless access systems. That is, the steps or portions of the embodiments of the present invention that are not described in order to clearly illustrate the technical idea of the present invention can be supported by the documents. In addition, all terms disclosed in this document may be described by the standard document.

The following description will be made on the assumption that the present invention is applicable to a CDMA system such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), and Single Carrier Frequency Division Multiple Access And can be used in various radio access systems. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). For the sake of clarity, the following description will focus on the IEEE 802.11 ac system, but the technical idea of the present invention is not limited thereto.

1 is a diagram illustrating a wireless LAN system according to an embodiment of the present invention.

Referring to FIG. 1, the WLAN system 10 includes an access point apparatus 100 and at least one terminal apparatus 300-1 to 300-4.

The access point apparatus 100 is a device that transmits radio waves so that users of at least one terminal apparatus 300-1 to 300-4 within a transmission distance can use the Internet connection and the network, and conforms to the IEEE 802.11ac standard. The access point apparatus 100 may be connected to a network outside the wireless LAN system 10 and may function as a base station or a hub for connecting the at least one terminal apparatus 300-1 to 300-4 to the network .

The access point apparatus 100 includes at least one terminal apparatus 300-1 to 300-4 that are paired with at least one terminal apparatus 300-1 to 300-4 and an MU-MIMO (Multi-User Multiple Input Multiple Output) -4) at the same time using multiple antennas. According to an embodiment, the access point 100 may transmit data to at least one terminal device 300-1 through 300-4 using a beamforming technique to improve transmission performance.

To this end, the access point 100 acquires information on a channel to be used for data transmission, that is, channel state information, through a channel sounding operation in transmitting a frame to a reception object terminal device can do.

The access point apparatus 100 estimates a coherence time of at least one of the terminal devices 300-1 to 300-4 and transmits a downlink traffic load and a sounding overhead overhead) to determine which terminal apparatus supports MU-MIMO and sets an optimal sounding period for the selected terminal apparatus.

Herein, the coherence time refers to a time during which the channel state of each of the at least one of the terminal devices 300-1 to 300-4 is kept constant, and at least one of the terminal devices 300-1 to 300-4 The coherence time of the coherence can be different.

Each of at least one of the terminal devices 300-1 to 300-4 transmits the channel status information to the access point 100 through channel sounding and transmits the channel status information to the access point 100 through the allocated channel It can transmit and receive.

2 is a block diagram showing the access point apparatus shown in FIG. 1 in more detail.

1 and 2, the access point apparatus 100 may include a processor 110, a memory 150, and a transceiver 170. [

The processor 110 may control the access point device 100 to perform the channel sounding method according to an embodiment of the present invention.

The processor 110 may include a channel estimation unit 120 and a sounding processing unit 130.

Each of the channel estimation unit 120 and the sounding processing unit 130 may be implemented by software executed in the processor 110 and / or hardware included in the processor 110, but the scope of the present invention is not limited thereto . Although at least one of the terminal devices 300-1 to 300-4 is supposed to have four terminals in FIG. 1, in the following description, at least one terminal device 300-1 to 300-4 (N is an integer of 1 or more) 300-N) is present in the first embodiment.

The channel estimation unit 120 may estimate the coherence time of each of the at least one terminal devices 300-1 to 300-N. That is, the channel estimating unit 120 estimates channel states of the at least one terminal apparatus 300-1 to 300-N based on the channel state information previously transmitted by each of the at least one terminal apparatuses 300-1 to 300-N, The coherence time, which is the time at which the channel state of the channel is maintained.

The sounding processor 130 performs an MU-MIMO sounding operation considering data traffic (downlink traffic load) for a plurality of terminal devices, coherence time and sounding overhead of each terminal device, and the like Or not. In addition, when the sounding processor 130 determines to perform the sounding operation of the MU-MIMO scheme, the sounding processor 130 may determine the sounding periods and the terminals to participate in the sounding operation.

In order for the access point apparatus 100 to simultaneously transmit data to the at least one terminal apparatuses 300-1 to 300-N in the MU-MIMO scheme through a plurality of antennas, the access point apparatus 100 and the at least one terminal Interference between at least one of the terminal devices 300-1 to 300-N should be removed based on channel information between wireless links between the devices 300-1 to 300-N. However, since the propagation environment between the access point 100 and the at least one terminal device 300-1 to 300-N varies with time, the sounding operation for obtaining channel state information is performed sufficiently frequently, The device 100 must obtain accurate channel state information. Therefore, the sounding period should be determined in consideration of the coherence time, which is the time that the channel state information is considered to be constant.

라 하고, 적어도 하나의 단말 장치(300-1~300-N)에 대한 각 가간섭성 시간을

라 한다. 이때, 액세스 포인트 장치(100)가 무선 링크에 대해 정확한 채널 정보를 가질 수 있는 단말은 N개의 단말 장치들 중

의 조건을 만족하는 단말들이 된다. 즉, 액세스 포인트 장치(100)는 상기 조건을 만족하는 단말들에 대해서만 MU-MIMO를 지원할 수 있게 된다.The sounding cycle

, And the respective coherence times for at least one of the terminal devices 300-1 to 300-N

. At this time, the terminal, to which the access point 100 has accurate channel information for the radio link,

Are satisfied. That is, the access point 100 can support MU-MIMO only for terminals satisfying the above conditions.

Hereinafter, an operation of determining whether the access point apparatus 100 determines an optimal sounding period and using the MU-MIMO will be described.

As the sounding cycle becomes smaller, the MU-MIMO can be supported for more terminal apparatuses. Therefore, the gain for MU-MIMO increases but the loss due to the sounding operation increases because more time is required for the sounding operation .

를 다음의 수학식 1에 의해 결정할 수 있다.The access point device 100 may be an optimal sounding period

Can be determined by the following equation (1).

는 MU-MIMO에 의해 단위시간당 발생하는 시간에 대한 기대이득

와 사운딩 동작에 의해 단위시간당 발생하는 시간에 대한 기대손실

간의 차이를 최대로 하는 사운딩 주기를 의미할 수 있다.Here, the optimal sounding cycle

Is the expected gain for the time that occurs per unit time by MU-MIMO

And the expected loss in time per unit time due to the sounding operation

May mean a sounding cycle that maximizes the difference between the two.

일 때, MU-MIMO가 지원될 수 있는 단말들의 집합은 다음의 수학식 2에 의해 결정될 수 있다.On the other hand,

, The set of terminals that can support MU-MIMO may be determined by Equation (2).

는 다음의 수학식 3에 의해 결정될 수 있다.MU-MIMO data transmission according to IEEE 802.11ac is performed by transmitting at least one data packet to the at least one terminal device 300-1 to 300-N at the head of data to be transmitted by the access point apparatus 100, Only when a medium access opportunity is obtained at the time of contention between the terminals 300-1 to 300-N of the terminals 300-1 to 300-N. Therefore,

Can be determined by the following equation (3).

는 다운링크 시간 채널 이용(downlink time channel utilization) 즉, 제i 단말 장치(제i 단말 장치는 MU-MIMO가 지원될 수 있는 단말들 중 어느 하나의 단말장치)가 다운링크 채널을 점유할 확률을 의미하고,

는 액세스 포인트 장치(100)가 제i 단말 장치에 전송할 패킷으로 미디엄 액세스 기회를 얻었을 때의 MU-MIMO에 의한 기대이득을 의미한다.here,

(Downlink time channel utilization), that is, the probability that the ith terminal device occupies the downlink channel (any one of the terminals to which the MU-MIMO can be supported) occupies the downlink channel Meaning,

Denotes an expected gain due to the MU-MIMO when the access point 100 obtains a medium access opportunity as a packet to be transmitted to the ith terminal.

는 다음의 수학식 4에 의해 결정될 수 있다.In addition, when the access point apparatus 100 obtains medium access opportunity as a packet to be transmitted to the ith terminal apparatus, a packet to be transmitted to another terminal apparatus exists in the head of data to be transmitted by the access point apparatus 100 Since only MU-MIMO transmission can be made,

Can be determined by the following equation (4).

는

에서 제i 단말 장치를 제외한 단말들의 집합을 의미하고,

는

의 모든 부분집합의 집합을 의미한다.

는 제i 단말 장치에 전송할 패킷으로 액세스 포인트 장치(100)가 미디엄 액세스 기회를 얻었을 때, 액세스 포인트 장치(100)가 전송할 데이터에 다른 MU-MIMO 지원 가능한 단말 장치들 중 집합

에 속한 단말 장치들에 전송할 패킷이 존재하는 경우에 MU-MIMO에 의한 기대이득을 의미한다.here,

The

Refers to a set of terminals excluding the i < th > terminal apparatus,

The

≪ / RTI >

MIMO) capable of supporting data to be transmitted by the access point apparatus 100 when the access point apparatus 100 acquires a medium access opportunity as a packet to be transmitted to the ith terminal apparatus,

MIMO denotes an expected gain due to the MU-MIMO when there is a packet to be transmitted to the terminals belonging to the MIMO system.

는 위와 같은 경우가 있을 확률로서 다음의 수학식 5와 같이 주어진다.

Is given by the following equation (5).

는 집합

에 속한 단말 장치들 중 어느 하나인 제j 단말 장치에 전송할 패킷이 액세스 포인트 장치(100)가 전송할 데이터(즉, 큐(queue))에 존재할 확률로 제j 단말 장치의 하향링크 트래픽 로드가 클수록 큰 값을 갖게 되며 이는 앞서 언급한 하향링크 트래픽 로드에 해당한다.here,

Is a set

The larger the downlink traffic load of the jth terminal device is, the greater the probability that a packet to be transmitted to the jth terminal device belonging to the access terminal device 100 exists in data (i.e., a queue) to be transmitted by the access point device 100 Value, which corresponds to the downlink traffic load mentioned above.

를 고려하는 이유는 최적의 사운딩 주기와 어느 단말 장치에 대해 MU-MIMO를 지원할지 결정함에 있어서, 보다 합리적인 결정을 위해 가간섭성 시간 외에 하향링크 트래픽 로드를 반영하여 결정하는 것이 필요하기 때문이다.At this time,

Is that it is necessary to determine the optimum sounding period and which terminal device to support MU-MIMO by reflecting the downlink traffic load outside the coherent time for a more rational decision .

It is assumed that the channel of a specific terminal device changes relatively rapidly in an environment where at least one terminal device 300-1 to 300-N exists. In order to support MU-MIMO for the specific terminal device, the channel of the specific terminal device changes rapidly. Therefore, the sounding operation must be performed frequently and a lot of time resources must be allocated to the sounding operation. However, if the downlink traffic load of the specific terminal device is large, the gain generated by supporting MU-MIMO may be larger than the damage caused by the sounding operation, even if a lot of time is used for the sounding operation.

Therefore, in the present invention, the optimal sounding period and the MU-MIMO support for the terminal devices are set considering the downlink traffic load, rather than setting the sounding period only considering the coherence time.

=액세스 포인트 장치(100)의 안테나 수"라 하고,

를 집합

에 속한 단말 중 가장 신호대 잡음비(signal to noise ratio;SNR)가 큰

개의 단말의 집합이라 하면,

는 다음의 수학식 6과 같이 계산될 수 있다.Finally, the number of terminals that can support MU-MIMO is equal to or smaller than the number of antennas of the access point 100, and up to four can be defined in the IEEE 802.11ac standard. "

= The number of antennas of the access point apparatus 100 "

Set

The signal to noise ratio (SNR)

Assuming a set of UEs,

Can be calculated by the following Equation (6).

,

,

,

는 각각 제i 단말 장치의 SNR, 데이터 프레임 간의 시간 간격인 SIFS(short interframe space), 응답 프레임 중 하나인 Block ACK의 전송 시간, 제i 단말 장치의 패킷 전송시간을 의미한다.here,

,

,

,

Denotes the SNR of the i-th terminal, the short interframe space (SIFS) between the data frames, the transmission time of the Block ACK which is one of the response frames, and the packet transmission time of the i-th terminal.

라 가정하면, 이러한 사운딩 주기로 수집되는 채널 상태 정보의 정확도에 의해서는 집합

에 속하는 단말 장치들에 대하여서만 MU-MIMO 지원이 가능하므로, 이 외에 단말들이 사운딩 동작에 참여하는 것은 오버헤드(overhead) 만을 유발하게 된다. 따라서, 사운딩 주기당 한 번의 사운딩 동작에서 발생하는 시간 오버헤드는 다음의 수학식 7과 같이 주어진다.Sounding cycle

Assuming that the channel state information is collected in this sounding period,

The MU-MIMO support is possible only for the terminals belonging to the MIMO system. In addition, participation of the terminals in the sounding operation causes overhead only. Therefore, the time overhead that occurs in one sounding operation per sounding period is given by Equation (7).

,

,

,

은 각각 NDPA 전송 시간, NDP 전송시간, 채널 상태 정보 전송 시간, 폴링 패킷(polling packet) 전송시간을 의미한다. 상기 NDPA는 사운딩 동작을 위한 사운딩 프로토콜의 시작을 알리는 데이터이며, 사운딩 동작의 대상이 되는 단말 장치의 ID(identification) 정보를 포함할 수 있다. 상기 NDP는 채널 상태 정보를 획득하기 위한 사운딩 정보에 대한 데이터이다.here,

,

,

,

Denotes an NDPA transmission time, an NDP transmission time, a channel state information transmission time, and a polling packet transmission time, respectively. The NDPA is data for notifying the start of the sounding protocol for the sounding operation and may include identification information of the terminal device that is the object of the sounding operation. The NDP is data on sounding information for obtaining channel state information.

는 다음의 수학식 8과 같이 나타낼 수 있다.Since the time overhead occurring in one sounding operation per sounding period is as shown in Equation (7), the overhead occurring per unit time, that is, the expected loss due to the sounding operation per unit time

Can be expressed by the following equation (8).

는 0보다 큰 모든 값들을 가질 수 있기 때문에, 수학식 1을 만족하는

를 찾는 것은 쉽지 않다.The sounding processing unit 130 must determine an optimal sounding period in order to determine whether to perform the sounding operation of the MU-MIMO scheme. However, in theory,

Lt; / RTI > can have all values greater than zero, so that < RTI ID = 0.0 >

It is not easy to find.

는 사운딩 주기

와 MU-MIMO가 지원될 수 있는 단말들의 집합

에 대해서만 연관을 갖는다. 따라서, 비록

가 바뀌더라도

가 바뀌지 않으면

는 달라지지 않는다.In Equation 1, the optimal sounding cycle

The sounding cycle

And MU-MIMO can be supported

Lt; / RTI > Therefore,

Even if it changes

If it does not change

Does not change.

에서

의 분자는 마찬가지로

와

에 대해서만 연관을 가지고,

의 분모는

가 커질수록 커진다.

는 앞서 정의한 바와 같이

에 대하여 연관된 단말 장치들의 가간섭성 시간인

을 기준으로 바뀌게 되므로,

에 대하여서만

를 비교하여 가장 크게 만드는 사운딩 주기가 최적 사운딩 주기

가 된다. 이는

를 결정하는 경계 값이

이므로

에 대해서만

를 비교하면 최적 사운딩 주기

를 결정할 수 있기 때문이다.Also,

in

The molecule of

Wow

Only with regard to,

The denominator of

.

As previously defined

The coherence time of the associated terminal devices

. Therefore,

Only about

And the largest sounding cycle is the optimum sounding cycle

. this is

Lt; RTI ID = 0.0 >

Because of

Only for

The optimum sounding cycle

. ≪ / RTI >

와 기대 손실

간의 차이를 최대로하는 최적 사운딩 주기(또는 제1 사운딩 주기)

를 결정한 뒤, 최적 사운딩 주기

에 따른 수학식 1의 기대이득

와 기대 손실

간의 차이가 0보다 큰지 여부에 따라 MU-MIMO 방식의 사운딩 동작을 수행할 지 결정할 수 있다.The sounding processing unit (130)

And expected loss

(Or a first sounding period) that maximizes the difference between the first sounding period and the second sounding period,

The optimum sounding period

Lt; RTI ID = 0.0 > (1) <

And expected loss

MIMO scheme according to whether the difference between the MU-MIMO scheme is greater than zero.

와 기대 손실

간의 차이가 0보다 큰 경우, MU-MIMO에 의해 발생하는 이득이 사운딩 동작에 의해 발생하는 손해보다 크다고 할 수 있으므로 사운딩 처리부(130)는 MU-MIMO 방식의 사운딩 동작을 수행할 수 있다. 이때, 사운딩 처리부(130)는 복수의 단말 장치들(300-1~300-N) 중 가간섭성 시간이 최적 사운딩 주기

보다 큰 단말 장치들에 대해 MU-MIMO 방식의 사운딩 동작을 수행할 수 있다.That is,

And expected loss

The gain generated by the MU-MIMO may be greater than the damage caused by the sounding operation, so that the sounding processor 130 can perform the sounding operation of the MU-MIMO scheme . At this time, the sounding processing unit 130 determines whether the coherence time among the plurality of terminal devices 300-1 to 300-N is an optimal sounding cycle

It is possible to perform the sounding operation of the MU-MIMO scheme for larger terminal devices.

를 사운딩 주기로 하여, MU-MIMO 방식의 사운딩 동작을 수행할 수 있다.In addition, the sounding processing unit 130 may include an optimal sounding cycle

The MU-MIMO system can perform a sounding operation.

에 따른 수학식 1의 기대이득

와 기대 손실

간의 차이가 0보다 작은 경우(음수인 경우), 사운딩 동작에 의해 발생하는 손해가 MU-MIMO에 의해 발생하는 이득보다 크다고 할 수 있으므로, MU-MIMO를 사용하지 않는 것이 바람직하다. 따라서, 사운딩 처리부(130)는 MU-MIMO 방식이 아닌 SU-MIMO(single-user MIMO) 방식의 사운딩 동작을 수행할 수 있다.Optimum Sounding Cycle

Lt; RTI ID = 0.0 > (1) <

And expected loss

It is preferable not to use MU-MIMO because the loss caused by the sounding operation is larger than the gain caused by MU-MIMO. Therefore, the sounding processor 130 can perform a sounding operation of a single-user MIMO (SU-MIMO) scheme instead of the MU-MIMO scheme.

The memory 150 may store a program for performing the channel sounding method according to an embodiment of the present invention, and data generated according to the execution of the program.

The transceiver 170 may transmit or receive a radio signal with at least one of the terminal devices 300-1 to 300-4 or an external network. Transceiver 170 may be configured to function and be operatively coupled to processor 110.

According to the access point apparatus 100 according to the embodiment of the present invention, whether to support MU-MIMO considering the degree of channel change of the terminal apparatus and the downlink traffic load, the terminal apparatuses to participate in the sounding operation and the sounding cycle The overhead due to sounding can be maintained at an appropriate level according to the network environment and the data transmission efficiency can be maximized.

3 is a flowchart illustrating a channel sounding method of the access point apparatus shown in FIG.

1 to 3, the channel estimation unit 120 may estimate the coherence time, which is the time at which the channel state of each of the plurality of terminal devices 300-1 to 300-N is maintained (S10 ).

와 기대 손실

의 차이를 최대로 하는 가간섭성 시간을 최적 사운딩 주기(

;제1 사운딩 주기)로 결정할 수 있다(S20).The sounding processing unit 130 may calculate an expected gain that reflects data traffic for a plurality of terminal devices 300-1 to 300-N among the coherent times

And expected loss

The coherence time that maximizes the difference between the optimum coherence time

(First sounding period) (S20).

)에 따른 기대이득

와 기대 손실

간의 차이가 0보다 큰지 여부에 따라 MU-MIMO 방식의 사운딩 동작을 수행할 지 여부를 결정할 수 있다(S30).The sounding processing unit 130 calculates an optimal sounding period

) Expected benefit

And expected loss

The MU-MIMO system may determine whether to perform the sounding operation according to whether the difference is greater than 0 (S30).

와 기대 손실

간의 차이가 0보다 큰 경우(S30의 Yes 경로), 사운딩 처리부(130)는 MU-MIMO 방식의 사운딩 동작을 수행할 수 있다(S40). 이때, 사운딩 처리부(130)는 복수의 단말 장치들(300-1~300-N) 중 가간섭성 시간이 최적 사운딩 주기

보다 큰 단말 장치들에 대해 MU-MIMO 방식의 사운딩 동작을 수행할 수 있다. 또한, 사운딩 처리부(130)는 최적 사운딩 주기

를 사운딩 주기로 하여, MU-MIMO 방식의 사운딩 동작을 수행할 수 있다.Expected benefit

And expected loss

The sounding processing unit 130 can perform the sounding operation of the MU-MIMO scheme (S40). At this time, the sounding processing unit 130 determines whether the coherence time among the plurality of terminal devices 300-1 to 300-N is an optimal sounding cycle

It is possible to perform the sounding operation of the MU-MIMO scheme for larger terminal devices. In addition, the sounding processing unit 130 may include an optimal sounding cycle

The MU-MIMO system can perform a sounding operation.

와 기대 손실

간의 차이가 음수인 경우(S30의 No 경로), 사운딩 동작에 의해 발생하는 손해가 MU-MIMO에 의해 발생하는 이득보다 크다고 할 수 있으므로, 사운딩 처리부(130)는 MU-MIMO를 사용하지 않는 것이 바람직하다(S50).Expected benefit

And expected loss

MIMO), the sounding processing unit 130 does not use the MU-MIMO because the loss caused by the sounding operation is larger than the gain caused by the MU-MIMO (S50).

The above-described WLAN system 10 is not limited in the configuration and method of the embodiments described above, but the embodiments may be modified so that all or some of the embodiments are selectively And may be configured in combination.

The channel sounding method of the wireless LAN system 10 according to the present invention can be implemented as a computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording media storing data that can be decoded by a computer system. For example, it may be a ROM (Read Only Memory), a RAM (Random Access Memory), a magnetic tape, a magnetic disk, a flash memory, an optical data storage device, or the like. In addition, the computer-readable recording medium may be distributed and executed in a computer system connected to a computer network, and may be stored and executed as a code readable in a distributed manner.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that various modifications and changes may be made.

Wireless LAN system (10)
In the access point apparatus 100,
The processor 110,
Channel estimator 120,
The sounding processor 130,
In memory 150,
The transceiver (170)

Claims (17)

A maximum interference power that maximizes a difference between expected gain and expected loss reflecting data traffic for the plurality of terminal equipments among the coherence times, which is the time when the channel state of each of the plurality of terminal equipments is maintained, Determining a first sounding period as a first sounding period, and determining whether to perform a multi-user MIMO (MU-MIMO) sounding operation based on the first sounding period. The method according to claim 1,
The sounding processor,
And performs the sounding operation of the MU-MIMO scheme according to the first sounding period when the expected gain according to the first sounding period is greater than the expected loss. 3. The method of claim 2,
The sounding processor,
And performs the sounding operation of the MU-MIMO scheme for terminal devices whose coherence time is larger than the first sounding period among the plurality of terminal devices. The method according to claim 1,
The sounding processor,
And performs a sounding operation of a single-user MIMO (SU-MIMO) scheme when the expected gain according to the first sounding period is smaller than the expected loss. The method according to claim 1,
The sounding processor,
Wherein the expected gain is calculated based on a probability that a packet to be transmitted to each of the plurality of terminal devices exists in a queue. The method according to claim 1,
Wherein the expected loss is a time required for the sounding operation per sounding cycle. Wherein the sounding processing unit of the access point apparatus calculates an expected gain and an expected gain reflecting the data traffic for the plurality of terminal equipments among the coherence times (channel coherence times) Determining a coherence time that maximizes a difference in loss as a first sounding period; And
Wherein the sounding processing unit determines whether to perform a multi-user MIMO (MU-MIMO) sounding operation based on the first sounding period. 8. The method of claim 7,
And if the expected gain according to the first sounding period is greater than the expected loss, the sounding processing unit further comprises performing the sounding operation of the MU-MIMO scheme according to the first sounding period Channel sounding method. 9. The method of claim 8,
Wherein the sounding operation of the MU-MIMO scheme is performed for terminal devices whose coherence time is larger than the first sounding period among the plurality of terminal devices. 8. The method of claim 7,
Wherein the sounding processing unit performs a sounding operation in a single-user MIMO (SU-MIMO) mode when the expected gain according to the first sounding period is smaller than the expected loss. Way. 8. The method of claim 7,
Wherein the expected gain is calculated based on a probability that a packet to be transmitted to each of the plurality of terminal devices exists in a queue. 8. The method of claim 7,
Wherein the expected loss is a time required for the sounding operation per sounding period. A plurality of terminal devices; And
And an access point device for communicating with the plurality of terminal devices in a MIMO manner based on channel state information collected through sounding operations on the plurality of terminal devices,
The access point device includes:
The difference between expected gains and expected losses reflecting data traffic for the plurality of terminal equipments among the coherence times, which is the time at which the channel state of each of the plurality of terminal equipments is maintained, Determining a coherence time as a first sounding period and determining whether to perform a multi-user MIMO (MU-MIMO) sounding operation based on the first sounding period. 14. The method of claim 13,
The sounding processor,
And performs the sounding operation of the MU-MIMO scheme according to the first sounding period when the expected gain according to the first sounding period is greater than the expected loss. 15. The method of claim 14,
The sounding processor,
And performs sounding of the MU-MIMO scheme for terminal apparatuses whose coherence time is larger than the first sounding period among the plurality of terminal apparatuses. 14. The method of claim 13,
The sounding processor,
And performs a sounding operation of a single-user MIMO (SU-MIMO) scheme when the expected gain according to the first sounding period is smaller than the expected loss. 14. The method of claim 13,
The sounding processor,
Wherein the expected gain is calculated based on a probability that a packet to be transmitted to each of the plurality of terminal devices exists in a queue.

Images