KR102236286B1 - Method and apparatus for opportunistic interference alignment in single-user multi-input multi-output transmission - Google Patents

Abstract

Disclosed is a method and apparatus for opportunistic interference alignment in SU-MIMO transmission. The opportunistic indirect alignment method includes selecting an interference space, broadcasting information on the selected interference space, and RTS including leakage of interference (LIF) information from a user terminal. When receiving a (request to send) message, selecting a user terminal to be given a transmission opportunity for each sub-channel based on the interference leakage information, and transmitting data to the selected user terminal. I can.

Description

Opportunistic interference alignment method and apparatus in SU-MIMO transmission {METHOD AND APPARATUS FOR OPPORTUNISTIC INTERFERENCE ALIGNMENT IN SINGLE-USER MULTI-INPUT MULTI-OUTPUT TRANSMISSION}

The following description relates to a method for aligning opportunistic interference in a WLAN and a method for designing an energy efficient transmission vector.

Local area network (LAN), which is a local area network, is largely divided into wired LAN and wireless LAN. Wireless LAN is a method of performing communication on a network using radio waves without using a cable. The emergence of wireless LAN has emerged as an alternative to solve the difficulty of installation, maintenance, and movement due to cabling, and the need for it is increasing due to the increase of mobile users.

The configuration of the wireless LAN consists of an access point ("AP") and a user terminal (Station, STA). The AP is an equipment that transmits radio waves so that wireless LAN users within the transmission distance can access the Internet and use the network, and acts as a base station of a mobile phone or a hub of a wired network. In the wireless high-speed Internet service provided by ISP (Internet Service Provider), the AP is already installed in the service area.

The terminal must be equipped with a wireless LAN card or the like in order to perform wireless network communication, and may include a PC (including a laptop), a cellular phone, or a PDA.

The most widely used wireless LAN standard today is IEEE 802.11, and the IEEE 802.11 standard defines regulations on the physical layer and medium access control constituting the wireless LAN.

The media access control layer makes efficient use of media capacity by defining an order and rules to be followed when a terminal or device using a shared media uses/accesses the media.

The basic building block of the IEEE 802.11 network is a basic service set (hereinafter referred to as "BSS"). The IEEE 802.11 network includes an independent BSS, in which terminals in the BSS directly communicate with each other, and an infrastructure network (Infrastructure BSS) and BSS in which an AP intervenes in the process of communicating with terminals within and outside the BSS. There is an extended service set that extends the service area by connecting the BSS.

In general, an IEEE 802.11 based wireless LAN system accesses a medium based on a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) method, and each AP (Access Point) operates independently of each other. That is, the wireless LAN system does not allocate a channel by a separate device, and each AP independently selects a channel by an operator or a channel allocation algorithm when the AP is powered on. Therefore, in a situation where there are many wireless LAN systems, there is a high possibility that the channels used by each BSS will overlap. If the channels overlap, interference occurs between adjacent BSSs.

If WLAN communication devices belonging to the same BSS are communicating according to the rules and radiating radio waves irrespective of the rules at a short distance where radio wave emitting devices that do not belong to the same BSS can sufficiently affect, WLAN communication devices will interfere with communication. You will receive.

In the existing interference environment WLAN network, a method of avoiding mutual interference by using CSMA is applied. However, in the CSMA protocol, the degrees-of-freedom (DoF) of the entire network is limited to the number of antennas of the AP.

An opportunistic interference alignment method according to an embodiment includes: selecting an interference space; Broadcasting information on the selected interference space; When receiving an RTS message including interference leakage information from a user terminal, selecting a user terminal to be given a transmission opportunity for each sub-channel based on the interference leakage information; And transmitting data to the selected user terminal.

In the opportunistic interference alignment method according to an embodiment, the selecting of the interference space may include determining a transmission vector to be transmitted to the user terminal based on a channel between the access point and the user terminal.

In the opportunistic interference alignment method according to an embodiment, the determining may include determining the transmission vector based on a signal-to-noise ratio of a signal received from the user terminal.

The opportunistic interference alignment method according to an embodiment may further include, when receiving the RTS message, transmitting a CTS message or an ACK message corresponding to the received RTS message to a user terminal that has transmitted the RTS message. have.

The opportunistic interference alignment method according to an embodiment may further include broadcasting information on the selected user terminal for each sub-channel when the selection of the user terminal for all sub-channels is completed.

An opportunistic interference alignment method according to another embodiment includes: determining interference leakage for each subchannel based on information on an interference space received from an access point; Setting a waiting time for transmitting the RTS message based on the determined interference leakage; And when feedback information is not received from another user terminal included in the service range of the access point during the waiting time, transmitting the RTS message to the access point.

The opportunistic interference alignment method according to another embodiment may further include resetting the waiting time to infinity when feedback information is received from the other user terminal during the waiting time.

In the opportunistic interference alignment method according to another embodiment, when a message indicating that the access point has received an RTS message from at least one user terminal is received from the access point during the waiting time, the waiting time is reset to infinity. It may further include the step of.

An access point according to an embodiment includes: a transmission vector determining unit configured to determine a transmission vector based on a channel between the access point and at least one user terminal; When receiving an RTS message including interference leakage information from a user terminal, a user terminal selection unit for selecting a user terminal to be given a transmission opportunity for each sub-channel based on the interference leakage information; And a communication unit for transmitting data to the selected user terminal.

According to an embodiment, a user terminal includes: an interference leakage determining unit configured to determine interference leakage for each sub-channel based on information on an interference space received from an access point; A waiting time setting unit for setting a waiting time for transmitting the RTS message based on the determined interference leakage; And a communication unit for transmitting the RTS message to the access point when feedback information is not received from another user terminal included in the service range of the access point during the waiting time.

1 is a diagram illustrating an example of an interference environment of a wireless LAN according to an embodiment.
2 is a diagram illustrating a range of use of an IEEE 802.11ac channel according to an embodiment.
3 is a flowchart illustrating an operation of an opportunistic interference alignment method performed by an access point according to an embodiment.
4 is for explaining an operation of an AP receiving an RTS message for a specific subchannel.
5 is a flowchart illustrating an operation of an opportunistic interference alignment method performed by a user terminal according to an embodiment.
6 is a diagram showing a detailed configuration of an access point according to an embodiment.
7 is a diagram showing a detailed configuration of a user terminal according to an embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION The detailed description to be disclosed below together with the accompanying drawings is intended to describe exemplary embodiments of the present invention, and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the invention may be practiced without these specific details.

The following embodiments are a combination of components and features of the present invention in a predetermined form. Each component or feature may be considered as optional unless explicitly stated otherwise. Each component or feature may be implemented in a form that is not combined with other components or features. In addition, some components and/or features may be combined to constitute an embodiment of the present invention. The order of operations described in the embodiments of the present invention may be changed. Some configurations or features of one embodiment may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments.

Specific terms used in the following description are provided to aid understanding of the present invention, and the use of these specific terms may be changed in other forms without departing from the technical spirit of the present invention.

In some cases, in order to avoid obscuring the concept of the present invention, well-known structures and devices are omitted, or are shown in block diagram form centering on core functions of each structure and device. In addition, the same components will be described using the same reference numerals throughout the present specification.

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

The following technologies include Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), etc. It can be used in a variety of wireless access systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with a radio 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 with a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). For clarity, the following description focuses on the IEEE 802.11 system, but the technical idea of the present invention is not limited thereto.

In the case of using Interference Alignment (IA) in WLAN, the degrees-of-freedom (DoF) over the entire network is achieved by mapping the interference signals received by each receiving end of the interfering network into a space having a limited dimension. It can be increased in proportion to the number of interfering access points (APs), and finally, the sum-rate of the network environment can be increased.

Interference alignment can be implemented using various aspects of diversity. In the Opportunistic Interference Alignment (OIA) method of interference alignment, the use of multiuser diversity is used to provide an opportunity for transmission to the user terminal with the best interference alignment among many user terminals. Thus, the DoF of the entire network can be improved. Opportunistic interference alignment is a method of aligning and transmitting a signal of a user terminal having a high priority so that an interference signal of a user terminal having a low priority does not affect the signal. In the case of opportunistic interference alignment, since only user terminals with the best interference alignment need to be found, interference alignment can be implemented with only a small feedback overhead according to a protocol design method.

Hereinafter, for convenience of explanation, the following matters are assumed. However, the scope of the present invention should not be construed as being limited by the following assumptions.

(i) It is assumed that the channel between an access point (AP) and a user terminal (or a station (STA)) is the same for uplink and downlink. That is, it is assumed that there is channel reciprocity.

(ii) It is assumed that each user terminal having a transmission opportunity transmits only one message symbol to the AP during one message transmission time. The transmission vector for message transmission may be designed in a direction that has less interference effect on each other network in consideration of the characteristics of the MIMO channel.

(iii) It is assumed that noise variance follows Equation 1 below.

는 AP 네트워크 g에서의 노이즈 벡터(noise vector)를 나타내고, E는 에너지를 나타낸다.
In Equation 1,

Denotes a noise vector in the AP network g, and E denotes energy.

1 is a diagram illustrating an example of an interference environment of a wireless LAN according to an embodiment.

Each AP has multiple antennas, and even in the case of a plurality of user terminals wirelessly connected to each AP, an environment having at least one antenna may be assumed.

In the case of a wireless LAN user, several user terminals can access each AP network, and each user terminal can communicate through the AP network to which it belongs. In such an interference environment, each user terminal may perform precoding using multiple antennas in a message symbol transmission process in order to reduce an interference effect on other AP networks.

When a user terminal transmits a signal to an AP network to which it belongs in a radio interference channel environment, a signal received from the AP may be modeled as shown in Equation 2 below.

는 AP c와 사용자 단말

간의 무선 채널 행렬을 나타낸다.

는 사용자 단말

의 송신 신호 벡터를 나타내고,

는 사용자 단말

의 메시지 심볼을 의미한다. 여기서, 사용자 단말

는 AP x의 네트워크에서 전송 기회를 얻은 사용자 단말을 의미한다. n_g는 AP g에서의 노이즈 벡터를 의미하고, K는 AP들의 개수를 나타낸다.In the above equation, r _g means a signal vector received from AP g,

AP c and user terminal

Represents the radio channel matrix between.

Is the user terminal

Represents the transmission signal vector of,

Is the user terminal

Means the message symbol of. Here, the user terminal

Denotes a user terminal that has obtained a transmission opportunity in the network of AP x. n _g denotes a noise vector in AP g, and K denotes the number of APs.

Hereinafter, opportunistic interference alignment will be described. Interference Environment When message symbol transmission occurs at the same time in each of the multi-AP networks, throughput of the entire network may be degraded due to interference. Therefore, in order to prevent a decrease in throughput due to an interference phenomenon, appropriate interference control is required.

In an embodiment, in the case of a communication method using opportunistic interference alignment, each AP selects and communicates with a user terminal having the smallest interference effect on another AP network, thereby preventing a decrease in throughput due to interference. In opportunistic interference alignment, a signal space to be decoded by the AP can be specified for each AP network, and accordingly, user terminals can measure the level of leakage of interference (LIF) that may affect other networks. . In this case, the LIF level of each user terminal may be determined based on Equation 3 below. The interference leakage may include information about interference by other user terminals and interference by other access points in the service area of the AP.

는 AP 네트워크 g에 속한 사용자 단말의 집합을 나타낸다. K는 액세스 포인트의 수이고,

는 AP x의 채널 매트릭스 H에 대한 수신 벡터이고,

는 x번째 액세스 포인트(AP x)와 사용자 단말 a 간의 무선 채널 매트릭스이고, V_a는 전송벡터를 의미한다. 이때, LIF 레벨은 각 간섭 영향을 미치는 AP의 시그널 스페이스에 직교하는 공간에 정확하게 나란할수록 작은 값을 가지게 된다. 여기서, 사용자 단말은 송신하는 전송 벡터, 즉 v_a를 조정하여 각 사용자 단말이 가질 수 있는 LIF 레벨을 최소화 할 수 있다. 전송 벡터의 설계 방법에 대해서는 이후 자세히 설명하도록 한다.In Equation 3, LIF _a is the LIF for user terminal a,

Denotes a set of user terminals belonging to the AP network g. K is the number of access points,

Is the received vector for the channel matrix H of AP x,

Is a radio channel matrix between the x-th access point (AP x) and user terminal a, and V _a represents a transmission vector. In this case, the LIF level has a smaller value as it is precisely aligned in a space orthogonal to the signal space of the APs that affect each interference. Here, the user terminal may minimize the LIF level that each user terminal may have by adjusting the transmission vector, that is, v _a. The transmission vector design method will be described in detail later.

The communication method based on planned interference alignment can minimize the influence of interference between each AP network by obtaining an opportunity for a user terminal having the smallest LIF level to transmit a message symbol.

2 is a diagram illustrating a range of use of an IEEE 802.11ac channel according to an embodiment.

In the case of IEEE 802.11ac, up to 160MHz can be used, and due to a wide bandwidth, it may be inefficient for one user terminal to simultaneously use all channels due to frequency selectivity. Therefore, it is preferable that the AP divides the entire band into several sub-channels and performs OIA-based adjustment. There are two main advantages when OIA is adjusted by dividing the entire frequency band for each sub-channel.

First, the effect of multiuser diversity can be obtained. When the entire frequency band is secured and used by only one user terminal, in general, there may be a frequency section in which deep fading occurs in a channel between the user terminal and an AP communicating with the user terminal. In a frequency section where deep fading occurs, it may be difficult to expect an overall throughput improvement due to low SINR. In addition, a frequency section in which deep fading occurs may cause a strong interference level in a specific frequency band in terms of an interfering link. In this case, throughput may be degraded due to interference transmitted from other networks in a specific frequency band. In implementing the opportunistic interference alignment protocol (OIA protocol), when selecting a user terminal for each sub-channel by dividing it into sub-channels, the possibility of preventing a deep fading effect or a strong interference effect is increased depending on the number of user terminals. , This can lead to an increase in the throughput of the overall network.

Second, it has the advantage that it is easy to perform opportunistic interference alignment adjustment (OIA coordination) at the same time while protecting the communication of IEEE 802.11a in terms of backward compatibility. In the case of performing opportunistic interference alignment adjustment by dividing the entire frequency band into a plurality of subchannels, it is easy to adjust the opportunistic interference alignment without any restrictions in a subchannel that is not used by user terminals of IEEE 802.11a.

In the sub-channel where the existing IEEE 802.11a user terminal communicates, the existing IEEE 802.11a user terminal and the IEEE 802.11ac user terminal coexist with each other through the RTS (request to send)-CTS (clear to send) exchange method. Can be avoided.

The AP may include a meaning for a base station. In addition, the AP must designate a signal vector to be decoded by itself, and the user terminal must be able to calculate the LIF level and inform the AP. In addition, the AP must be able to select a user terminal to be given a transmission opportunity to each subchannel according to the LIF level of the user terminal. In an embodiment, in order to allocate a transmission opportunity to a user terminal for each sub-channel, it is necessary to separate and transmit the RTS message for each sub-channel.

In the interference alignment process, the AP finds a user terminal with the lowest LIF level and communicates with the user terminal. Therefore, feedback may not be received for the LIF value. In the process of negotiating a control message for data transmission, the problem can be solved by allowing the user terminal with the smallest LIF to have the highest priority.

3 is a flowchart illustrating an operation of an opportunistic interference alignment method performed by an access point according to an embodiment.

In step 310, the AP may select an interference space and broadcast information on the selected interference space. In this case, the AP may broadcast information on the interference space to all user terminals in the AP network. The AP may determine a transmission vector to be transmitted to the user terminal based on a channel between the access point and at least one user terminal. For example, the AP may determine a transmission vector based on a signal-to-noise ratio of a signal received from at least one user terminal. As another example, the AP may calculate a Lagrangian multiplier, calculate a null vector based on a Lagrangian function, and then determine a transmission vector based on the null vector.

In step 320, the AP may wait until receiving an RTS message for a specific subchannel from at least one user terminal.

In step 330, the AP may receive an RTS message from at least one user terminal.

When receiving the RTS message, in step 340, the AP may determine whether the received RTS message is transmitted to the target itself. The AP may determine whether the RTS message has been received through the subchannel assigned to the AP, and if the RTS message does not belong to the AP, it does not connect to the user terminal that transmitted the RST message, and step 320 again. You can go back to and wait for the RTS message to be received.

If the received RTS message is transmitted to the target itself, in step 350, the AP may select a user terminal to which a transmission opportunity for the corresponding subchannel is to be given, and transmit a response message to the user terminal. When the AP receives an RTS message including interference leakage information from at least one user terminal, the AP may select a user terminal to be given a transmission opportunity for each subchannel based on the interference leakage information. The AP may select a user terminal having the smallest interference leakage value as a user terminal to be given a transmission opportunity.

According to an embodiment, the AP may grant a transmission opportunity for a corresponding subchannel to a user terminal that has transmitted the RTS message. When receiving the RTS message, the AP may transmit a CTS message or an ACK message corresponding to the received RTS message to the user terminal that has transmitted the RTS message.

In step 360, the AP may determine whether a user terminal has been selected for all sub-channels. If the user terminal is not selected in all sub-channels, the AP returns to step 320 to select a user terminal for a sub-channel in which the user terminal is not selected, and when an RTS message for another sub-channel is received. You can wait until. The AP may perform the embodiments of steps 320 to 350 for all sub-channels of the AP.

When the selection of the user terminal for all sub-channels is completed, in step 370, the AP may broadcast information on the selected user terminal for each sub-channel of the AP. In one embodiment, the broadcast message may indicate that message negotiation has ended. The AP may broadcast a corresponding message to user terminals connected to each subchannel. In this case, the message may include information on the user terminal selected for each sub-channel. For example, content including a physical or logical address of a user terminal and a user terminal connected to a sub-channel may be included.

The AP receives the RTS message for each sub-channel, finishes RTS negotiation on all sub-channels, and broadcasts the information of the selected user terminals. Can inform.

When the connection between the AP and the user terminal is completed, in step 380, the AP can communicate with the user terminal and transmit a message symbol to the user terminal. The AP may communicate with a user terminal selected for a specific subchannel. The AP may transmit data to the user terminal selected for each sub-channel.

4 is for explaining an operation of an AP receiving an RTS message for a specific subchannel.

The AP may adjust the amount of time the user terminal waits for the user terminal to transmit the control message in proportion to the LIF level. For example, if the LIF level corresponding to the subchannel f of the user terminal a is LIF _a (f), the AP waits to transmit the RTS message for the subchannel f T _c LIF _a (f) Can be determined by Here, Tc is a preset constant.

If other user terminals belonging to the same network do not transmit the RTS message for the subchannel f during the time of _{T c} LIF _{a (f), the user terminal a may transmit the RTS message for the subchannel f to the AP.} After receiving the RTS message corresponding to the subchannel f, the AP may transmit a CTS or ACK message for the corresponding subchannel. When other user terminals belonging to the same network receive an RTS, an ACK message, or a CTS, the RTS message may not be transmitted for a corresponding subchannel during a communication period between the AP and the user terminal a. The CTS or ACK message may include a field for transmitting radio resource block and AP address information.

Each user terminal may set the waiting time for each sub-channel to wait until the RTS message is transmitted in proportion to the LIF value.

When any one user terminal transmits the RTS message fastest in the corresponding sub-channel, the AP may estimate that the LIF level of the user terminal is the lowest. Accordingly, when one user terminal transmits an RTS message for the subchannel f, the user terminals on the same network can control other user terminals not to additionally transmit the RTS message to the AP for the subchannel f.

5 is a flowchart illustrating an operation of an opportunistic interference alignment method performed by a user terminal according to an embodiment.

In step 510, the user terminal may wait to receive information on the interference space from the AP.

Upon receiving information on the interference space from the AP, in step 520, the user terminal may calculate an interference leak (LIF) for each sub-channel and a waiting time for transmission of an RTS message. The user terminal may determine the interference leakage for each sub-channel based on the information on the interference space received from the AP. Here, a method of calculating the interference leakage may refer to the description of Equation 3 above. The user terminal may set a waiting time for transmitting the RTS message based on the determined interference leak. For example, the user terminal may set the waiting time to be proportional to the level of interference leakage.

In step 530, the user terminal may wait for transmission of the RTS message during a waiting time corresponding to each sub-channel. According to an embodiment, it may mean that the user terminal waits for a waiting time after receiving information on an interference space selected by the AP from the AP.

When the waiting time elapses, the user terminal may transmit the RTS message to the AP. Instead of transmitting according to the waiting time, the user terminal may determine the operation according to the state of the subchannel to which the RTS message is to be transmitted.

In step 540, the user terminal may determine whether the RTS message has been received from another user terminal. If the user terminal receives an RTS message transmitted from another user terminal, step 550 may determine whether the received RTS message belongs to the same AP network as the AP network to which the user terminal currently belongs.

If the received RTS message is received from another user terminal belonging to the same AP network as the AP network to which the current user terminal belongs, in step 560, the user terminal may set the waiting time for the corresponding subchannel to infinity. When the user terminal receives an RTS message from another user terminal during the waiting time, the waiting time may be reset to infinity. This is to give priority to communicate with the AP to the user terminal that has transmitted the RTS message first.

As another example, when the user terminal receives a message indicating that the AP has received an RTS message from at least one user terminal from the AP during the waiting time, the user terminal may reset the waiting time to infinity.

Returning to step 540, if the user terminal has not received an RTS message transmitted from another user terminal, in step 570, the user terminal may determine whether or not a broadcast message has been received from the AP. In step 570, the broadcast message may be a message indicating that message negotiation for the corresponding AP has ended.

If the broadcast message is not received from the AP, in step 580, the user terminal may transmit an RTS message for a corresponding subchannel to the AP. The RTS message may include level information of interference leakage for each sub-channel. When the user terminal does not receive feedback information from another user terminal included in the service range of the access point during the waiting time, the user terminal may transmit an RTS message to the AP. According to an embodiment, step 580 may be performed after the waiting time determined based on the LIF value has elapsed.

As described above, when the RTS message is transmitted from the user terminal to the AP when the waiting time elapses, when the user terminal receives the RTS message for the corresponding subchannel from another user terminal before the waiting time elapses, the RTS It is determined whether the other user terminal that sent the message belongs to the same network as the user terminal, and if the other user terminal belongs to the same network as the user terminal, the user terminal does not transmit the RTS message for the corresponding subchannel to the access point. Does not.

After the user terminal transmits the RTS message, the user terminal may wait until a CTS message or an ACK message is received from the AP.

In step 590, the user terminal may communicate with the AP through a subchannel through which the RTS message is transmitted. The user terminal can transmit a message symbol to the AP.

6 is a diagram showing a detailed configuration of an access point 610 according to an embodiment.

Referring to FIG. 6, the access point 610 may include a transmission vector determination unit 620, a user terminal selection unit 630, and a communication unit 640.

The transmission vector determiner 620 may select an interference space to be used by the user terminal. The transmission vector determiner 620 may determine a transmission vector to be transmitted to the user terminal based on a channel between the access point 610 and at least one user terminal and a channel between access points affected by interference. The transmission vector determiner 620 may minimize the LIF level by using a transmission vector based on a channel state between the access point 610 and at least one user terminal.

According to an embodiment, the transmission vector determiner 620 may determine a transmission vector based on a signal-to-noise ratio of a signal received from at least one user terminal. The transmission vector determiner 620 may determine a transmission vector according to a maximum-gain based precoding method. The transmission vector determiner 620 may determine a vector capable of minimizing transmission power while satisfying a target SNR at the receiving end in consideration of a channel between at least one user terminal and the access point 610. When the access point 610 receives a signal transmitted from at least one user terminal and decodes the message symbol, the decoded message symbol may be modeled as shown in Equation 4 below.

는 채널 매트릭스 H에 대한 액세스 포인트 a의 전송 벡터이고,

는 액세스 포인트 g와 사용자 단말 a 간의 무선 채널 매트릭스이다. v_a는 전송 벡터이다. 이때 수신된 신호의 SNR (interference 성분 제외)는

으로 주어질 수 있다. 따라서,

값이 SNR이 되고, 전송 전력이 최소화 될 수 있는 전송 벡터 v_a는 수학식 5와 같이 주어진다.Equation 4 means the sum of all the received interference vectors.

Is the transmission vector of the access point a for the channel matrix H,

Is the radio channel matrix between the access point g and the user terminal a. v _a is the transfer vector. At this time, the SNR (excluding interference component) of the received signal is

Can be given as therefore,

The value becomes SNR, and the transmission vector v _a for which the transmission power can be minimized is given by Equation 5.

는 채널 매트릭스 H에 대한 액세스 포인트 a의 전송 벡터이며,

는 액세스 포인트 g와 사용자 단말 a 간의 무선 채널 매트릭스이다.Here, SNR is the signal-to-noise ratio of the received signal excluding interference components,

Is the transmission vector of the access point a for the channel matrix H,

Is the radio channel matrix between the access point g and the user terminal a.

As another example, the transmission vector determiner 620 may use a precoding technique using Lagrangian-based optimization. The transmission vector determiner 620 may calculate a Lagrangian multiplier, calculate a null vector based on a Lagrangian function, and then determine a transmission vector based on the null vector.

Table 1 shows a method for defining a Lagrangian function derived from a problem for Lagrangian optimization, and calculating a vector that satisfies the condition.

The induction process according to Table 1 is as follows. First, an optimization problem for Lagrangian optimization is shown in Equation 6 below.

The Lagrangian function for solving the problem of Equation 6 above can be defined as in Equation 7 below.

In order to obtain an optimized transmission vector in Equation 7, it is necessary to satisfy the condition of Equation 8 below.

First, if the first condition is summarized, it can be expressed as Equation 9 below.

은 반드시 determinant가 0이 되어야 한다. determinant가 0이 될 경우, 반드시 널 벡터가 존재하게 되며, 이 널 벡터가 LIF를 최소화시킬 수 있는 벡터 공간으로 주어진다.In order to satisfy the condition of Equation 9

Must have a determinant of 0. When determinant is 0, a null vector must exist, and this null vector is given as a vector space that can minimize LIF.

의 determinant가 0이 되도록 만들어주는 Lagrangian 멀티플라이어는 고유값 문제(eigenvalue problem)으로 변형하여 계산할 수 있다. 액세스 포인트의 개수가 액세스 포인트의 안테나의 개수보다 큰 경우, colored noise의 공분산 매트릭스(covariance matrix)인

은 full rank를 갖는 정방행렬로 주어진다. 따라서,

의 역행렬이 존재할 수 있고, determinant 조건은 다음의 수학식 10으로 변형될 수 있다.

The Lagrangian multiplier, which makes the determinant of 0, can be computed by transforming it into an eigenvalue problem. When the number of access points is greater than the number of antennas of the access point, the covariance matrix of colored noise

Is given as a square matrix with full rank. therefore,

There may be an inverse matrix of, and the determinant condition may be modified by Equation 10 below.

의 positive 고유값의 inverse의 형태로 주어지게 된다.So, for the Lagrangian multiplier,

It is given in the form of the inverse of the positive eigenvalue of.

의 형태, 즉 diagonal term들의 합으로 나타낸다.The positive eigenvalue is

It is expressed as the sum of the diagonal terms.

term의 경우, rank는 1로 주어진다. 따라서,

의 rank 역시 1 이하이며, 이는 전체 고유값들 중 positive 고유값이 1개 이하이고, 나머지 고유값은 0임을 나타낸다. 따라서, 전체 고유값의 합은 유일한 positive 고유값임을 직관적으로 알 수 있다. 고유값들의 합은 행렬의 trace, 즉 diagonal term들의 합으로 구할 수 있다. 따라서, 유일한 positive 고유값의 경우,

임을 알 수 있다.In the matrix above

For term, rank is given by 1. therefore,

The rank of is also 1 or less, indicating that among all the eigenvalues, there are 1 or less positive eigenvalues, and the remaining eigenvalues are 0. Therefore, it can be intuitively seen that the sum of all eigenvalues is the only positive eigenvalue. The sum of the eigenvalues can be obtained as a trace of the matrix, that is, the sum of the diagonal terms. So, for the only positive eigenvalue,

It can be seen that.

After calculating the Lagrangian multiplier, the null vector of the differential form of the Lagrangian function mentioned above may be calculated again based on Equation 11 below.

A null vector calculated based on Equation 11 above is given as a vector space capable of minimizing LIF, and finally, a transmission vector may be calculated according to an SNR constraint.

The communication unit 640 may broadcast information on the selected interference space. The communication unit 640 may transmit the transmission vector determined by the transmission vector determination unit 620 to the user terminal. The communication unit 640 may receive an RTS message including interference leakage information from at least one user terminal. RTS messages can be classified according to sub-channels.

When receiving an RTS message including interference leakage information from at least one user terminal, the user terminal selection unit 630 may select a user terminal to be given a transmission opportunity for each subchannel based on the interference leakage information. . The user terminal selection unit 630 may select a user terminal having the lowest interference leakage value as a user terminal to be given a transmission opportunity.

According to an embodiment, the user terminal selection unit 630 may grant a transmission opportunity for a corresponding subchannel to a user terminal that has transmitted the RTS message. When receiving the RTS message, the communication unit 640 may transmit a CTS message or an ACK message corresponding to the received RTS message to the user terminal that has transmitted the RTS message.

The user terminal selection unit 630 may determine whether a user terminal has been selected for all sub-channels. If a user terminal is not selected from all sub-channels, the user terminal selection unit 630 may select a user terminal for other sub-channels based on the RTS message.

When the selection of the user terminal for all sub-channels is completed, the communication unit 640 may broadcast information on the selected user terminal for each sub-channel. In one embodiment, the broadcast message may indicate that message negotiation has ended. The communication unit 640 may broadcast a corresponding message to user terminals connected to each sub-channel. In this case, the message may include information on the user terminal selected for each sub-channel. For example, content including a physical or logical address of a user terminal and a user terminal connected to a sub-channel may be included.

When the connection between the access point 610 and the user terminal is completed in this way, the communication unit 640 can communicate with the user terminal and transmit a message symbol to the user terminal. The communication unit 640 may transmit data to a user terminal selected for each sub-channel.

7 is a diagram showing a detailed configuration of a user terminal 710 according to an embodiment.

Referring to FIG. 7, the user terminal 710 may include an interference leak determining unit 720, a waiting time setting unit 730, and a communication unit 740.

When the interference leakage determiner 720 receives information on the interference space from the AP, the interference leakage determination unit 720 may determine interference leakage for each subchannel. The user terminal 710 may determine interference leakage for each sub-channel based on information on the interference space received from the AP. Here, a method of calculating the interference leakage may refer to the description of Equation 3 above.

The waiting time setting unit 730 may set a waiting time for transmitting the RTS message based on the determined interference leakage. For example, the waiting time setting unit 730 may set the waiting time to be proportional to the level of interference leakage.

The waiting time setting unit 730 may determine whether an RTS message has been received from another user terminal. If the user terminal 710 receives an RTS message transmitted from another user terminal, the waiting time setting unit 730 may transmit the received RTS message to the same AP network as the AP network to which the user terminal 710 belongs. You can determine if you belong. If the received RTS message is received from another user terminal belonging to the same AP network as the AP network to which the current user terminal 710 belongs, the waiting time setting unit 730 sets the waiting time for the corresponding sub-channel to infinity. I can. When receiving the RTS message from another user terminal during the waiting time, the waiting time setting unit 730 may reset the waiting time to infinity.

As another example, when the AP receives a message indicating that the AP has received an RTS message from at least one user terminal during the waiting time, the waiting time setting unit 730 may reset the waiting time to infinity.

The communication unit 740 may communicate with the AP through a subchannel through which the RTS message is transmitted. The communication unit 740 may transmit a message symbol to the AP. The communication unit 740 may transmit an RTS message to the AP when feedback information is not received from another user terminal included in the service range of the AP during the waiting time. The RTS message may include level information of interference leakage for each sub-channel.

In the case of the communication method proposed in the present invention, the user terminal having the smallest LIF level is identified through RTS scheduling using the LIF level, thereby having the advantage that there is no need to receive LIF feedback from all user terminals. In addition, it is possible to maximize multi-user diversity by managing opportunistic interference alignment for each sub-channel, and has the advantage of easily protecting the communication of the existing IEEE 802.11a terminal. In addition, the precoding method proposed in the present invention can obtain an improved sum-rate while using less transmission power than the conventional method. Accordingly, it is possible to increase the battery life of the user terminal and reduce the influence on other networks.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiment, or may be known and usable to those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic media such as floptical disks. -A hardware device specially configured to store and execute program instructions such as magneto-optical media, and ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operation of the embodiment, and vice versa.

As described above, although the embodiments have been described by the limited embodiments and drawings, various modifications and variations are possible from the above description to those of ordinary skill in the art. For example, the described techniques are performed in a different order from the described method, and/or components such as systems, structures, devices, circuits, etc. described are combined or combined in a form different from the described method, or other components Alternatively, even if substituted or substituted by an equivalent, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and those equivalent to the claims also fall within the scope of the claims to be described later.

Claims (20)

In the opportunistic interference alignment method performed by an access point,
Selecting an interference space;
Broadcasting information on the selected interference space;
When receiving a request to send (RTS) message including leakage of interference (LIF) information from at least one user terminal, a user who will be given a transmission opportunity for each subchannel based on the interference leakage information Selecting a terminal;
Transmitting data to the selected user terminal; And
When the selection of the user terminal for the sub-channel is completed, the selection of the user terminal is completed by transmitting information on the selected user terminal for each of the sub-channels, and the communication step is entered. Including the step of notifying all of the user terminals,
When the user terminal receives an RTS message from another user terminal included in the service range of the access point during a waiting time, the opportunistic interference alignment method resets the waiting time to infinity. The method of claim 1,
Selecting the interference space,
Determining a transmission vector to be transmitted to a user terminal based on a channel between the access point and the at least one user terminal
Opportunistic interference alignment method comprising a. The method of claim 2,
The determining step,
Determining the transmission vector based on a signal-to-noise ratio (SNR) of a signal received from the at least one user terminal
Opportunistic interference alignment method comprising a. The method of claim 2,
The determining step,
Calculating a Lagrangian multiplier;
Calculating a null vector based on a Lagrangian function; And
Determining a transmission vector based on the null vector
Opportunistic interference alignment method comprising a. The method of claim 1,
The step of selecting the user terminal,
Selecting a user terminal with the smallest interference leakage value as a user terminal to be given a transmission opportunity
Opportunistic interference alignment method comprising a. The method of claim 1,
When receiving the RTS message, transmitting a clear to send (CTS) message or an acknowledgment (ACK) message corresponding to the received RTS message to a user terminal that has transmitted the RTS message
Opportunistic interference alignment method further comprising. delete In the opportunistic interference alignment method performed by a user terminal,
Determining interference leakage for each sub-channel based on information on the interference space received from the access point;
Setting a waiting time for transmitting the RTS message to be proportional to the level of the interference leakage;
Transmitting the RTS message to the access point when feedback information is not received from another user terminal included in the service range of the access point during the waiting time; And
When receiving an RTS message from the other user terminal during the waiting time, resetting the waiting time to infinity
Opportunistic interference alignment method comprising a. delete delete In the opportunistic interference alignment method performed by a user terminal,
Determining interference leakage for each sub-channel based on information on the interference space received from the access point;
Setting a waiting time for transmitting the RTS message to be proportional to the level of the interference leakage;
Transmitting the RTS message to the access point when feedback information is not received from another user terminal included in the service range of the access point during the waiting time; And
When receiving a message indicating that the access point has received an RTS message from at least one user terminal from the access point during the waiting time, resetting the waiting time to infinity
Opportunistic interference alignment method comprising a. The method of claim 11,
The RTS message,
Opportunistic interference alignment method comprising the level information of the interference leakage for each sub-channel. A transmission vector determination unit determining a transmission vector based on a channel between the access point and at least one user terminal;
When receiving a request to send (RTS) message including leakage of interference (LIF) information from at least one user terminal, a user who will be given a transmission opportunity for each subchannel based on the interference leakage information A user terminal selection unit for selecting a terminal; And
Including a communication unit for transmitting data to the selected user terminal,
When the selection of the user terminal for the sub-channel is completed, the communication unit completes the selection of the user terminal by transmitting information on the selected user terminal for each of the sub-channels, and a communication step. It is characterized in that it notifies all of the user terminals that it has collapsed,
When the user terminal receives an RTS message from another user terminal included in the service range of the access point during a waiting time, the access point resets the waiting time to infinity. The method of claim 13,
The transmission vector determination unit,
And determining the transmission vector based on a signal-to-noise ratio (SNR) of a signal received from the at least one user terminal. The method of claim 13,
The transmission vector determination unit,
An access point, comprising: calculating a Lagrangian multiplier, calculating a null vector based on a Lagrangian function, and determining a transmission vector based on the null vector. The method of claim 13,
The user terminal selection unit,
An access point, characterized in that the user terminal having the smallest interference leakage value is selected as a user terminal to be given a transmission opportunity. An interference leakage determination unit configured to determine interference leakage for each sub-channel based on information on the interference space received from the access point;
A waiting time setting unit configured to set a waiting time for transmitting an RTS message (request to send) in proportion to the level of the interference leakage; And
When the feedback information is not received from another user terminal included in the service range of the access point during the waiting time, including a communication unit for transmitting the RTS message to the access point,
The waiting time setting unit,
When the feedback information is received from the other user terminal during the waiting time, the waiting time is reset to infinity. delete delete An interference leakage determination unit configured to determine interference leakage for each sub-channel based on information on the interference space received from the access point;
A waiting time setting unit configured to set a waiting time for transmitting an RTS message (request to send) in proportion to the level of the interference leakage; And
When the feedback information is not received from another user terminal included in the service range of the access point during the waiting time, including a communication unit for transmitting the RTS message to the access point,
The waiting time setting unit,
When a message indicating that the access point has received an RTS message from at least one user terminal is received from the access point during the waiting time, the waiting time is reset to infinity.

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