KR20140119637A - Method and apparatus for opportunistic interference alignment in single-user multi-input multi-output transmission - Google Patents

Abstract

Disclosed are a method and an apparatus for an opportunistic interference alignment in SU-MIMO transmission. The method for opportunistic interference alignment includes the steps of: selecting an interference space; broadcasting information about the selected interference space; selecting a user terminal to give a transmission opportunity for each sub channel based on the information about a leakage of interference (LIF) if a request to send (RTS) message including information about the (LIF) is received from the user terminal; and transmitting data to the selected user terminal.

Description

METHOD AND APPARATUS FOR OPTICAL INTERFERENCE ALIGNMENT IN SINGLE-USER MULTI-INPUT MULTI-OUTPUT TRANSMISSION IN SU-MIMO TRANSMISSION < RTI ID = 0.0 >

The following discussion relates to opportunistic interference alignment methods in WLANs and how to design energy efficient transmission vectors.

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

The configuration of the wireless LAN is made up of an access point (AP) and a user station (STA). An AP is a device that transmits radio waves to wireless LAN users within a transmission distance so that they can use the Internet and the network, and functions as a base station of a cellular phone or a hub of a wired network. In the wireless broadband internet service provided by the ISP (Internet Service Provider), an AP device is already installed in the service area.

The terminal must be equipped with a wireless LAN card 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 the rules for the physical layer and medium access control that make up the wireless LAN.

The medium access control layer efficiently utilizes the capacity of the medium by defining the order and rules to be followed when a terminal or a device using the shared medium accesses / accesses the medium.

The basic building block of the IEEE 802.11 network is a Basic Service Set (BSS). The IEEE 802.11 network includes an independent BSS in which terminals in a BSS communicate directly with each other and an infrastructure BSS in which an AP participates in the process of communicating with terminals inside and outside the BSS, And an extended service set for extending the service area by connecting the BSS.

Generally, a wireless LAN system based on IEEE 802.11 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 is not a method of allocating 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, the channel used in each BSS is likely to be overlapped in a situation where many wireless LAN systems exist. If the channels overlap, interference will occur between adjacent BSSs.

If the WLAN communication devices belonging to the same BSS are communicating in accordance with the rules and the radio wave emitting devices not belonging to the same BSS are emitting radio waves irrespective of the rules at a close enough distance to be sufficiently influential, .

Conventional interference environment In the wireless LAN network, a method of avoiding interference with each other 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.

According to one embodiment, an opportunistic interference alignment method includes: selecting an interference space; Broadcasting information on the selected interference space; Selecting a user terminal to which a transmission opportunity is to be given for each subchannel based on the interference leakage information when receiving an RTS message including interference leakage information from the user terminal; And transmitting data to the selected user terminal.

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

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

The opportunistic interference sorting method according to an exemplary 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 sorting method according to an exemplary embodiment may further include broadcasting information about a selected user terminal for each subchannel when selection of a user terminal for the entire subchannel is completed.

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

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

The opportunistic interference alignment method according to another embodiment is characterized in that when the access point receives a message from the at least one user terminal indicating that the RTS message has been received from the access point during the waiting time, The method comprising the steps of:

An access point according to an exemplary embodiment includes a transmission vector determination unit that determines a transmission vector based on a channel between an access point and at least one user terminal; A user terminal selection unit for selecting a user terminal to which a transmission opportunity is to be given for each subchannel based on the interference leakage information when receiving an RTS message including interference leakage information from the user terminal; And a communication unit for transmitting data to the selected user terminal.

A user terminal according to an exemplary embodiment includes an interference leakage determining unit that determines an interference leak for each subchannel based on information on an interference space received from an access point; A waiting time setting unit for setting a waiting time for transmitting an RTS message based on the determined interference leak; And a communication unit for transmitting the RTS message to the access point if 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 channel use range of an IEEE 802.11ac according to an exemplary embodiment.
3 is a flow diagram illustrating the operation of an opportunistic interference alignment method performed by an access point in accordance with one embodiment.
4 is intended to illustrate the operation in which an AP receives an RTS message for a particular subchannel.
5 is a flow diagram illustrating the operation of an opportunistic interference alignment method performed by a user terminal in accordance with one embodiment.
6 is a diagram illustrating a detailed configuration of an access point according to an embodiment.
7 is a detailed block diagram of a user terminal according to an exemplary embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details.

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

The specific terminology used in the following description is provided to aid understanding of the present invention, and the use of such specific terminology may be changed into other forms without departing from the technical idea of the present invention.

In some instances, well-known structures and devices are omitted or shown in block diagram form around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

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 clarity, the following description will focus on the IEEE 802.11 system, but the technical idea of the present invention is not limited thereto.

When Interference Alignment (IA) is used in a WLAN, each receiver of an interference network maps the received interference signals to a space with a limited dimension, thereby generating degrees-of-freedom (DoF) on the entire network Can be increased in proportion to the number of interference access points (APs), and finally, the sum-rate of the network environment can be increased.

The interference alignment can be implemented using various diversity aspects. In Opportunistic Interference Alignment (OIA) method during interference alignment, a method of providing opportunity to transmit a user terminal with the most interference among the many user terminals using multiuser diversity Thereby improving the DoF of the entire network. The opportunistic interference alignment is a method of arranging and transmitting signals of a user terminal having a high priority so that an interference signal of a user terminal having a low priority is not affected. In case of opportunistic interference alignment, interference alignment can be implemented with only a small feedback overhead according to the design method of the protocol since only the user terminal with the best interference can be found.

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

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

(ii) It is assumed that each user terminal that has obtained the transmission opportunity transmits only one message symbol to the AP for one message transmission time. The transmission vector for message transmission can be designed in such a way as to give less influence of interference to each other in consideration of MIMO channel characteristics.

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

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

Represents a noise vector in the AP network g, and E represents 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 a plurality of user terminals wirelessly connected to each AP may have an environment having at least one antenna.

In the case of a wireless LAN user, a plurality of user terminals can access each AP network, and each user terminal can communicate through the AP network to which the user terminal belongs. In this interference environment, each user terminal can perform precoding using multiple antennas in the message symbol transmission process in order to reduce interference influence to other AP networks.

In a wireless interfering channel environment, when a user terminal transmits a signal to an AP network to which the user terminal belongs, a signal received at the AP may be modeled as Equation (2).

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 is the signal vector received at AP g,

AP c and the user terminal

≪ / RTI >

Lt; / RTI &

Of the transmission signal vector,

Lt; / RTI &

Quot; message " Here,

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

Hereinafter, opportunistic interference alignment will be described. Interference Environment When message symbols are transmitted simultaneously in multiple AP networks, the throughput of the entire network may be degraded due to the interference phenomenon. Therefore, it is necessary to control the interference appropriately in order to prevent the throughput degradation due to the interference phenomenon.

In the embodiment, in the case of the communication method using the opportunistic interference alignment, each AP can select a user terminal that has the smallest interference influence to another AP network and communicate with the AP network, thereby preventing a reduction in throughput due to interference. In the opportunistic interference alignment, each AP network can specify the signal space to be decoded by the AP, so that the user terminals can measure the level of leakage of interference (LIF) that can exist on other networks . At this time, the LIF level of each user terminal can be determined based on Equation (3). An interference leak may include information about interference by other user terminals in the service area of the AP and interference by other access points.

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 the user terminal a,

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

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

Is the wireless channel matrix between the xth access point (APx) and the user terminal a, and V _a is the transmission vector. At this time, the LIF level has a smaller value as it is precisely aligned in a space orthogonal to the signal space of the AP which effects each interference. Here, the user terminal can minimize the LIF level that each user terminal can have by adjusting the transmission vector to be transmitted, that is, v _a . The method of designing the transmission vector will be described in detail later.

The planning-based interference-based communication method minimizes the interference effect between each AP network by obtaining the opportunity for the user terminal having the smallest LIF level to transmit the message symbol.

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

In the case of IEEE 802.11ac, up to 160 MHz can be used. Due to the wide bandwidth, the simultaneous use of all channels by one user terminal may be inefficient due to frequency selectivity. Therefore, it is preferable that the AP divides the entire band into a plurality of subchannels to perform OIA-based adjustment. There are two major advantages when OIA adjustment is performed by dividing the entire frequency band for each subchannel.

First, the effect of multiuser diversity can be obtained. When only one user terminal is reserved and used for the entire frequency band, there may be a frequency interval in which deep fading occurs in a channel between APs communicating with the user terminal. In the frequency domain where deep fading occurs, it may be difficult to expect an overall throughput improvement due to the low SINR. In addition, the frequency interval in which deep fading occurs may also cause a strong interference level in a specific frequency band in terms of an interfering link. In such a case, the throughput may be lowered due to interference transmitted from other networks in a specific frequency band. In implementing the opportunistic interference alignment protocol (OIA protocol), when a user terminal selection is performed for each subchannel by dividing into subchannels, there is a high possibility of preventing a deep fading effect or a strong interference effect depending on the number of user terminals , Which may lead to an increase in overall network throughput.

Second, it has the advantage that it is easy to make opportunistic interference coordination (OIA coordination) while protecting IEEE 802.11a communication in terms of backward compatibility. When opportunistic interference alignment adjustment is performed by dividing the entire frequency band into a plurality of subchannels, it is easy to adjust the opportunistic interference alignment without restrictions on subchannels that are not used by the user terminals of IEEE 802.11a.

In a subchannel in which an existing IEEE 802.11a user terminal communicates, existing IEEE 802.11a user terminals and IEEE 802.11ac user terminals coexist through RTS (request to send) -CTS (clear to send) Can be avoided.

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

In the interference alignment process, the AP searches for a user terminal having the lowest level of LIF and communicates with the corresponding user terminal. Therefore, feedback on the value of the LIF may not be received. Control Message for Data Transmission During the message negotiation process, the LIF can solve the problem by having the smallest user terminal have the highest priority.

3 is a flow diagram illustrating the operation of an opportunistic interference alignment method performed by an access point, in accordance with one embodiment.

In step 310, the AP may select an interference space and broadcast information about the selected interference space. At this time, the AP can broadcast information about the interference space to all user terminals in the AP network. The AP may determine a transmission vector to transmit to the user terminal based on the channel between the access point and the 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. In another example, the AP may calculate a Lagrangian multiplier, calculate a null vector based on the Lagrangian function, and then determine the transmission vector based on the null vector.

In step 320, the AP may wait until it receives an RTS message for a particular 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 an RTS message, the AP may determine in step 340 whether the received RTS message is directed to itself. The AP may determine whether an RTS message has been received through the subchannel assigned to the AP. If the RTS message does not belong to the AP, the AP does not connect to the user terminal that transmitted the RST message, And waits until it receives the RTS message.

If the received RTS message is destined for itself, the AP may select a user terminal to which to send a transmission opportunity for that subchannel and send a response message to the user terminal in step 350. The AP may select a user terminal to grant a transmission opportunity for each subchannel based on the interference leakage information when receiving an RTS message including interference leakage information from at least one user terminal. The AP can select the user terminal having the smallest value of the interference leak as the user terminal to which the transmission opportunity is to be given.

According to an exemplary embodiment, the AP may grant a transmission opportunity for the corresponding subchannel to the user terminal that 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.

At step 360, the AP may determine whether a user terminal has been selected for all subchannels. If the user terminal is not selected in all subchannels, the AP returns to step 320 to select a user terminal for the subchannel for which the user terminal is not selected, and when the RTS message for the other subchannel is received . The AP may perform the operations of steps 320 to 350 for all subchannels of the AP.

If the selection of the user terminal for the entire subchannel is complete, then in step 370 the AP may broadcast information about the selected user terminal for each of the subchannels of the AP. In one embodiment, the message being broadcast may indicate that message negotiation has ended. The AP may broadcast a corresponding message to user terminals connected to each subchannel. At this time, the message may include information about a user terminal selected for each sub-channel. For example, a content including a user terminal's physical or logical address of a user terminal may be included in a certain subchannel.

The AP receives the RTS message for each subchannel, terminates the RTS negotiation for all the subchannels, broadcasts the information of the selected user terminals, notifies all the message negotiations are completed, and informs all the user terminals .

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

4 is intended to illustrate the operation in which an AP receives an RTS message for a particular subchannel.

The AP may adjust the time the user terminal waits to transmit the control message to be proportional to the LIF level. For example, if the LIF level corresponding to the subchannel f of the user terminal a is LIF _a (f), then the AP waits for the waiting time to transmit an RTS message for subchannel f to be T _c LIF _a (f) . Here, Tc is a preset constant.

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

Each user terminal can set the waiting time to wait for the RTS message to be transmitted for each subchannel to be proportional to the LIF value.

When one of the UEs in the corresponding subchannel transmits the RTS message at the earliest, the AP can estimate that the LIF level of the UE is the smallest. Therefore, when one user terminal transmits an RTS message for the subchannel f, the APs can control the other user terminals not to additionally transmit the RTS message to the AP for the subchannel f.

5 is a flow diagram illustrating the operation of an opportunistic interference alignment method performed by a user terminal, in accordance with one embodiment.

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

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

In step 530, the user terminal may wait for the transmission of an RTS message for a waiting time corresponding to each subchannel. According to one embodiment, the user terminal may mean waiting for a waiting time after receiving information on the interference space selected by the AP from the AP.

When the waiting time has elapsed, the user terminal can transmit an RTS message to the AP, and can determine the operation according to the state of the subchannel to transmit the RTS message, rather than transmitting according to the waiting time.

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

If the received RTS message is received from another user terminal belonging to the AP network, such as the AP network to which the current user terminal belongs, then the user terminal may set the waiting time for that subchannel to be infinite in step 560. If the user terminal receives an RTS message from another user terminal during the waiting time, it can reset the waiting time to infinity. This is for giving the user terminal that has transmitted the RTS message priority to communicate with the AP.

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

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

If the broadcast message has not been received from the AP, the user terminal may transmit an RTS message for the subchannel to the AP in step 580. The RTS message may include level information of interference leakage per subchannel. If the user terminal does not receive feedback information from other user terminals included in the service range of the access point during the waiting time, the user terminal can transmit an RTS message to the AP. According to one embodiment, step 580 may be performed after a determined waiting time based on the LIF value.

As described above, when the waiting time elapses, when the RTS message is transmitted from the user terminal to the AP, when the user terminal receives the RTS message for the corresponding subchannel from another user terminal before the waiting time elapses, Determines whether another user terminal that transmitted 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 Do not.

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

In step 590, the user terminal may communicate with the AP over the subchannel that transmitted the RTS message. The user terminal can send message symbols to the AP.

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

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

According to one embodiment, the transmission vector determination unit 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 determination unit 620 may determine a transmission vector according to a maximum-gain based precoding method. The transmission vector determining unit 620 can determine a vector that can minimize the transmission power while satisfying the target SNR at the receiving end considering the channel between the at least one user terminal and the access point 610. [ When receiving the signal transmitted from the at least one user terminal at the access point 610 and decoding the message symbol, the decoded message symbol can be modeled as Equation (4).

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 received interference vectors.

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

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

Lt; / RTI > therefore,

The value becomes SNR, and the transmission vector v _a , in 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 a signal-to-noise ratio of a received signal excluding an interference component,

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

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

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

Table 1 shows how to define a Lagrangian function derived from the problem for Lagrangian optimization and to calculate a vector satisfying the condition.

The derivation process according to Table 1 is as follows. First, the optimization problem for the Lagrangian optimization is expressed by Equation (6).

The Lagrangian function for solving the problem of Equation (6) can be defined as the following Equation (7).

In order to obtain an optimized transmission vector in Equation (7), the following Equation (8) must be satisfied.

First, summarizing the first condition, it can be expressed as the following Equation (9).

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 the expression (9)

The determinant must be zero. When the determinant is 0, there is always a null vector, and this null vector is given as a vector space that can minimize the 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 the Lagrangian multiplier zero, can be transformed into an eigenvalue problem. If the number of access points is larger 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,

, And the determinant condition can be transformed into the following equation (10).

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

In the form of the inverse of the positive eigenvalue of Eq.

의 형태, 즉 diagonal term들의 합으로 나타낸다.The positive eigenvalues are

, That is, the sum of 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 above matrix

For term, rank is given as 1. therefore,

Is also less than 1, indicating that the positive eigenvalue is less than or equal to 1 and the remaining eigenvalue is zero. Therefore, it can be intuitively understood that the sum of the total eigenvalues is a unique positive eigenvalue. The sum of eigenvalues can be found as the sum of the diagonal terms of the matrix traces. Thus, for a unique positive eigenvalue,

.

After calculating the Lagrangian multiplier, the null vector of the differential form of the above-mentioned Lagrangian function can be calculated based on the following equation (11).

The null vector calculated based on Equation (11) is given as a vector space capable of minimizing the LIF, and finally, the transmission vector can be calculated according to the SNR constraint.

The communication unit 640 may broadcast information on the selected interference space. The communication unit 640 can 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. The RTS message may be divided according to the subchannel.

When receiving the RTS message including the interference leakage information from at least one user terminal, the user terminal selection unit 630 can select a user terminal to which to give a transmission opportunity for each sub-channel based on the interference leakage information . The user terminal selection unit 630 may select the user terminal having the smallest value of the interference leakage as the user terminal to which the transmission opportunity is to be given.

According to one embodiment, the user terminal selection unit 630 may grant a transmission opportunity for the corresponding subchannel to the user terminal that 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 is selected for all subchannels. If a user terminal is not selected in all subchannels, the user terminal selection unit 630 can select a user terminal based on the RTS message for other subchannels.

When the selection of the user terminal for the entire subchannel is completed, the communication unit 640 may broadcast information about the selected user terminal for each of the subchannels. In one embodiment, the message being broadcast may indicate that the message negotiation is terminated. The communication unit 640 may broadcast the message to the user terminals connected to the respective subchannels. At this time, the message may include information about a user terminal selected for each sub-channel. For example, a content including a user terminal's physical or logical address of a user terminal may be included in a certain subchannel.

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

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

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

When the interference leak determining unit 720 receives information on the interference space from the AP, it can determine an interference leak for each sub-channel. The user terminal 710 can determine interference leakage for each sub-channel based on the information on the interference space received from the AP. Here, the method of calculating the interference leakage may refer to the description of Equation (3).

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

The waiting time setting unit 730 can determine whether the RTS message is received from another user terminal. If the user terminal 710 receives the RTS message transmitted from another user terminal, the waiting time setting unit 730 sets the received RTS message to the same AP network as the AP network to which the current user terminal 710 belongs It can be judged whether or not it 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 710 belongs, the waiting time setting unit 730 sets the waiting time for the corresponding subchannel to infinity . When the RTS message is received from another user terminal during the waiting time, the waiting time setting unit 730 can reset the waiting time to infinity.

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

The communication unit 740 can communicate with the AP through the subchannel on which the RTS message is transmitted. The communication unit 740 can transmit a message symbol to the AP. When the communication unit 740 does not receive the feedback information from other user terminals included in the service range of the AP during the waiting time, the communication unit 740 may transmit the RTS message to the AP. The RTS message may include level information of interference leakage per subchannel.

The communication method of the present invention has an advantage that it is not necessary to receive LIF feedback from all user terminals by identifying the user terminal having the smallest LIF level through the RTS scheduling using the LIF level. In addition, it can maximize multi-user diversity by managing the opportunistic interference alignment for each sub-channel, and has an advantage of easily protecting the communication of the existing IEEE 802.11a terminal. Also, the precoding method proposed in the present invention can obtain an improved sum-rate while using less transmission power as compared with the conventional method. As a result, the battery life of the user terminal can be increased and the influence on other networks can be reduced.

The method according to an embodiment may be implemented in the form of a program command 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 to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (20)

In an opportunistic interference alignment method performed by an access point,
Selecting an interference space;
Broadcasting information on the selected interference space;
The method of claim 1, further comprising: when receiving a request to send (RTS) message including leakage of interference (LIF) information from at least one user terminal, Selecting a terminal; And
Transmitting data to the selected user terminal
/ RTI > The method according to claim 1,
Wherein the step of selecting the interference space comprises:
Determining a transmission vector to transmit to the user terminal based on the channel between the access point and the at least one user terminal
/ RTI > 3. The method of claim 2,
Wherein the determining comprises:
Determining a transmission vector based on a signal-to-noise ratio (SNR) of a signal received from the at least one user terminal
/ RTI > 3. The method of claim 2,
Wherein the determining comprises:
Calculating a Lagrangian multiplier;
Calculating a null vector based on the Lagrangian function; And
Determining a transmission vector based on the null vector
/ RTI > The method according to claim 1,
Wherein the selecting the user terminal comprises:
Selecting a user terminal having the smallest interference leak value as a user terminal to which a transmission opportunity is to be granted
/ RTI > The method according to claim 1,
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 when receiving the RTS message;
Further comprising the steps of: The method according to claim 1,
When the selection of the user terminal for the entire subchannel is completed, broadcasting the information about the selected user terminal for each of the subchannels
Further comprising the steps of: An opportunistic interference alignment method performed by a user terminal,
Determining interference leakage for each subchannel based on information on the interference space received from the access point;
Setting a waiting time for transmitting an RTS message based on the determined interference leak; And
Transmitting the RTS message to the access point if feedback information is not received from another user terminal included in the service range of the access point during the waiting time
/ RTI > 9. The method of claim 8,
The step of setting the waiting time includes:
Setting the wait time to be proportional to the level of the interference leakage
/ RTI > 9. The method of claim 8,
When the RTS message is received from the other user terminal during the waiting time, resetting the waiting time to infinity
Further comprising the steps of: 9. The method of claim 8,
Resetting the waiting time to infinity when the access point receives a message from the at least one user terminal indicating that the RTS message has been received from the access point during the waiting time
Further comprising the steps of: 9. The method of claim 8,
The RTS message includes:
And level information of interference leakage for each subchannel. A transmission vector determination unit that determines a transmission vector based on a channel between the access point and at least one user terminal;
The method of claim 1, further comprising: when receiving a request to send (RTS) message including leakage of interference (LIF) information from at least one user terminal, A user terminal selection unit for selecting a terminal; And
A communication unit for transmitting data to the selected user terminal
. 14. The method of claim 13,
Wherein the transmission vector determination unit determines,
Wherein the transmission vector is determined based on a signal-to-noise ratio (SNR) of a signal received from the at least one user terminal. 14. The method of claim 13,
Wherein the transmission vector determination unit determines,
Calculates a Lagrangian multiplier, calculates a null vector based on the Lagrangian function, and then determines a transmission vector based on the null vector. 14. The method of claim 13,
Wherein the user terminal selection unit comprises:
And selects a user terminal having the smallest interference leak value as a user terminal to which a transmission opportunity is to be given. An interference leakage determining unit that determines an interference leak 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 an RTS message (request to send) based on the determined interference leak; And
And transmitting the RTS message to the access point when the feedback information is not received from another user terminal included in the service range of the access point during the waiting time,
Lt; / RTI > 18. The method of claim 17,
The waiting time setting unit may set,
And setting the wait time to be proportional to the level of the interference leakage. 18. The method of claim 17,
The waiting time setting unit may set,
And when the feedback information is received from the another user terminal during the waiting time, resets the waiting time to infinity. 18. The method of claim 17,
The waiting time setting unit may set,
And resets the waiting time to infinity when the access point receives a message from the at least one user terminal indicating that the RTS message has been received from the access point during the waiting time.

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