KR20160132595A - Apparatus and method for cancelling interference signal between UEs and enhancing downlink diversity gain in wireless communication system supportable full duplex radio scheme - Google Patents

Abstract

The present invention provides a method for removing an interference signal between user equipment in a wireless communication system supporting a full duplex method and a method for enhancing a downlink diversity gain. First user equipment capable of removing an interference signal between adjacent user equipment according to an embodiment of the present invention comprises: a processor configured to, if the first user equipment obtains interference channel information between the first user equipment and second user equipment adjacent to the first user equipment and decomposes the interference channel information into singular values, the number of receiving antennas of the first user equipment is r and the number of transmitting antennas is y (y>r), then apply precoding in a precoder by using a first matrix from an (r+1)^th column to a y^th column or a second matrix from a (r+1)^th row to a y^th row in a right singular vector matrix generated by the singular value decomposition; and a transmitter configured to transmit signals having the precoding applied thereto in two consecutive time sections. The processor calculates the interference channel information while assuming that the first user equipment transmits identical symbols in the two consecutive time sections.

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for canceling interference signals between terminals and increasing a downlink diversity gain in a wireless communication system supporting a full duplex scheme, and a method for improving the downlink diversity gain between UEs and enhancing downlink diversity gain in a wireless communication system full duplex radio scheme}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication, and more particularly, to a method and apparatus for removing an interference signal between terminals and increasing a downlink diversity gain in a wireless communication system supporting a full-duplex scheme.

A full duplex radio (FDR) or full duplex communication scheme refers to a communication scheme that supports transmission and reception simultaneously using the same resources in a single terminal. At this time, the same resource means the same time, same frequency. FDR communication or full duplex communication is called bi-directional communication.

1 is a conceptual diagram of a terminal supporting a FDR and a base station.

Referring to FIG. 1, there are three types of interference in a network environment supporting FDR. First, it is Intra-device self-interference. Intra-device self-interference (SNR) of a terminal means that a signal transmitted from a transmitting antenna at a base station or a terminal is received by a receiving antenna and acts as an interference. Since the signal transmitted from the transmitting antenna is transmitted with a large power and the distance between the transmitting antenna and the receiving antenna is short, the transmitted signal is received by the receiving antenna with almost no attenuation so that it is received at a much higher power than the desired signal. Second, there is UE to UE inter-link interference. In a network supporting FDR, inter-terminal interference increases. It means that the uplink signal transmitted by the terminal is received by the terminal located adjacent thereto and acts as an interference. Third, there is BS to BS inter-link interference. In a network environment supporting FDR, BS to BS inter-link interference increases. This means that the signal transmitted between the base stations or between the heterogeneous base stations (Pico, femto, relay) in the HetNet situation is received by the receiving antenna of the other base station and acts as an interference.

In this way, in order to improve the communication performance of the terminal when using the FDR scheme, it is necessary to solve the interference problem caused between the terminals. However, methods for eliminating interference between terminals in the FDR situation have not yet been specifically studied.

According to an aspect of the present invention, there is provided a method for a first terminal to remove an interference signal between adjacent terminals.

According to another aspect of the present invention, there is provided a first terminal capable of removing an interference signal between adjacent terminals.

The technical problems to be solved by the present invention are not limited to the technical problems and other technical problems which are not mentioned can be understood by those skilled in the art from the following description.

According to another aspect of the present invention, there is provided a method for canceling an interference signal between adjacent terminals of a first terminal, comprising: obtaining interference channel information between a first terminal and a second terminal adjacent to the first terminal; Decomposing the interference channel information into singular values; If the number of reception antennas of the first terminal is r and the number of transmission antennas is y (y > r), then in the singular value decomposed right singular vector matrix, the first matrix from r + Applying precoding in a precoder using a second matrix up to a first row; And transmitting the precoded signals in two consecutive time intervals, wherein the interference channel information is calculated by assuming that the first terminal transmits the same symbol in the two consecutive time intervals do.

Wherein applying the precoding in the precoder comprises: if the first matrix is [V _{r + 1} ^H ... ... V _y ^H ] (where H denotes a Hermitian matrix), and in the precoder [V _{r + 1} ... ... V _y ] matrix is applied. The same symbol transmitted in the two consecutive time intervals is represented by a matrix as shown in the following equation (A)

[Mathematical formula A]

Where ^* is the complex conjugate (complex conjugate) the meaning and, T is the transposed matrix, and a symbol indicating the (transpose matrix), t the first time interval, and t + 1 is the second time interval that is continuous to the first time interval to be. The matrix [V _{r + 1} ... ... Portion of a first precoding matrix for the sub-matrices of the V _y] to the r rows from the first row of the first effect for the symbols transmitted in the first time interval (t), and from r + 1 row to the y line A second precoding matrix to which a complex conjugate operation is applied to a matrix is applied to a symbol transmitted in the second time interval (t + 1).

The method may further include receiving a reference signal from the second terminal, wherein the interference channel information is obtained based on channel information estimated from the reference signal received from the second terminal and channel reciprocity.

According to another aspect of the present invention, there is provided a first terminal capable of canceling an interference signal between adjacent terminals, the first terminal acquiring interference channel information between the first terminal and a second terminal adjacent to the first terminal, (R + 1) -th row to the y-th column in the singular value decomposed right singular vector matrix when the number r of reception antennas of the first terminal and the number of transmission antennas is y (y> r) Or a precoder in a precoder using a second matrix from row r + 1 to row y; And a transmitter configured to transmit the precoded signals in two consecutive time intervals, wherein the processor transmits the interference channel information to the first terminal when the first terminal transmits the same symbol in the two consecutive time intervals . The processor is characterized in that the first matrix is [V _{r + 1} ^H ... ... V _y ^H ] (where H denotes a Hermitian matrix), and in the precoder [V _{r + 1} ... ... V _y ] matrix. The same symbol transmitted in the two consecutive time intervals is represented by a matrix as shown in the following equation (A)

[Mathematical formula A]

Where ^* is the complex conjugate (complex conjugate) the meaning and, T is the transposed matrix, and a symbol indicating the (transpose matrix), t the first time interval, and t + 1 is the second time interval that is continuous to the first time interval to be. The processor is configured to calculate the matrix [V _{r + 1} ... ... Portion of a first precoding matrix for the sub-matrices of the V _y] to the r rows from the first row of the first effect for the symbols transmitted in the first time interval (t), and from r + 1 row to the y line And applies a second precoding matrix to which a complex conjugate operation is applied to a matrix to a symbol transmitted in the second time interval (t + 1). The first terminal may be a receiver that receives a reference signal from the second terminal Wherein the processor acquires the interference channel information based on the channel information estimated based on the reference signal received from the second terminal and channel reciprocity.

In the present invention, a terminal precoder for two frequencies or time is designed to perform inter-terminal interference cancellation. Further, additional gain in the downlink can be obtained through the precoder design in the base station.

In this proposal, the transmit diversity effect in the downlink can be obtained by using the maximum rate transmission precoder.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
1 is a conceptual diagram of a terminal supporting a FDR and a base station.
2 is a block diagram showing the configuration of the base station 105 and the terminal 110 in the wireless communication system 100. As shown in FIG.
3 is an exemplary diagram for explaining a full-duplex multi-user multi-antenna system including one base station and two terminals.
4 is a diagram illustrating a flow of a control signal transmission / reception in a case where a neighboring terminal in a UL supporting a base station requests a downlink.
5 is a diagram illustrating a flow of a control signal transmission / reception in a case where a neighboring terminal requests downlink support in a downlink of a base station.
FIG. 6 is a diagram summarizing the contents proposed by 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. For example, the following detailed description assumes that a mobile communication system is a 3GPP LTE and an LTE-A system. However, other than specific aspects of 3GPP LTE and LTE-A, Applicable.

In some instances, well-known structures and devices may be omitted or may be shown in block diagram form, centering on the core functionality of each structure and device, 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.

In the following description, it is assumed that the UE collectively refers to a mobile stationary or stationary user equipment such as a UE (User Equipment), an MS (Mobile Station), and an AMS (Advanced Mobile Station). It is also assumed that the base station collectively refers to any node at a network end that communicates with a terminal such as a Node B, an eNode B, a base station, and an access point (AP). Although the present invention is described based on the IEEE 802.16 system, the contents of the present invention are also applicable to various other communication systems.

In a mobile communication system, a user equipment can receive information through a downlink from a base station, and the terminal can also transmit information through an uplink. The information transmitted or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transmitted or received by the terminal.

The following description is to be understood as illustrative and non-limiting, such as 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 And can be used in various wireless access systems. CDMA is Universal Terrestrial Radio Access (UTRA). And can be implemented with a radio technology such as CDMA2000. The 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 in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) is part of E-UMTS (Evolved UMTS) using E-UTRA, adopts OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is an evolved version of 3GPP LTE.

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

2 is a block diagram showing the configuration of the base station 105 and the terminal 110 in the wireless communication system 100. As shown in FIG.

Although one base station 105 and one terminal 110 (including a D2D terminal) are shown for the sake of simplicity of the wireless communication system 100, the wireless communication system 100 may include one or more base stations and / And may include a terminal.

2, a base station 105 includes a transmit (Tx) data processor 115, a symbol modulator 120, a transmitter 125, a transmit and receive antenna 130, a processor 180, a memory 185, a receiver 190, a symbol demodulator 195, and a receive data processor 197. The terminal 110 includes a transmission (Tx) data processor 165, a symbol modulator 170, a transmitter 175, a transmission / reception antenna 135, a processor 155, a memory 160, a receiver 140, A demodulator 155, and a receive data processor 150. Although the transmission / reception antennas 130 and 135 are shown as one in the base station 105 and the terminal 110, respectively, the base station 105 and the terminal 110 have a plurality of transmission / reception antennas. Therefore, the base station 105 and the terminal 110 according to the present invention support a Multiple Input Multiple Output (MIMO) system. In addition, the base station 105 according to the present invention can support both a Single User-MIMO (SU-MIMO) and a Multi User-MIMO (MIMO) scheme.

On the downlink, the transmit data processor 115 receives traffic data, formats, codes, and interleaves and modulates (or symbol maps) the coded traffic data to generate modulation symbols Symbols "). A symbol modulator 120 receives and processes the data symbols and pilot symbols to provide a stream of symbols.

The symbol modulator 120 multiplexes the data and pilot symbols and transmits it to the transmitter 125. At this time, each transmission symbol may be a data symbol, a pilot symbol, or a signal value of zero. In each symbol period, the pilot symbols may be transmitted continuously. The pilot symbols may be frequency division multiplexed (FDM), orthogonal frequency division multiplexed (OFDM), time division multiplexed (TDM), or code division multiplexed (CDM) symbols.

Transmitter 125 receives the stream of symbols and converts it to one or more analog signals and further modulates (e.g., amplifies, filters, and frequency upconverts) The transmission antenna 130 transmits the generated downlink signal to the mobile station.

In the configuration of the terminal 110, the reception antenna 135 receives the downlink signal from the base station and provides the received signal to the receiver 140. The receiver 140 adjusts (e.g., filters, amplifies, and downconverts) the received signal and digitizes the conditioned signal to obtain samples. The symbol demodulator 145 demodulates the received pilot symbols and provides it to the processor 155 for channel estimation.

Symbol demodulator 145 also receives a frequency response estimate for the downlink from processor 155 and performs data demodulation on the received data symbols to obtain a data symbol estimate (which is estimates of the transmitted data symbols) And provides data symbol estimates to a receive (Rx) data processor 150. [ The receive data processor 150 demodulates (i.e., symbol demaps), deinterleaves, and decodes the data symbol estimates to recover the transmitted traffic data.

The processing by symbol demodulator 145 and received data processor 150 is complementary to processing by symbol modulator 120 and transmit data processor 115 at base station 105, respectively.

On the uplink, the terminal 110 processes the traffic data and provides data symbols. The symbol modulator 170 may receive and multiplex data symbols, perform modulation, and provide a stream of symbols to the transmitter 175. A transmitter 175 receives and processes the stream of symbols to generate an uplink signal. The transmission antenna 135 transmits the generated uplink signal to the base station 105.

In the base station 105, an uplink signal is received from a terminal 110 via a receive antenna 130, and a receiver 190 processes the received uplink signal to obtain samples. The symbol demodulator 195 then processes these samples to provide received pilot symbols and data symbol estimates for the uplink. The receive data processor 197 processes the data symbol estimates to recover the traffic data transmitted from the terminal 110.

The processors 155 and 180 of the terminal 110 and the base station 105 respectively instruct (for example, control, adjust, manage, etc.) the operation in the terminal 110 and the base station 105. Each of the processors 155 and 180 may be coupled with memory units 160 and 185 that store program codes and data. The memories 160 and 185 are connected to the processor 180 to store operating systems, applications, and general files.

The processors 155 and 180 may also be referred to as a controller, a microcontroller, a microprocessor, a microcomputer, or the like. Meanwhile, the processors 155 and 180 may be implemented by hardware or firmware, software, or a combination thereof. (DSP), digital signal processing devices (DSPDs), programmable logic devices (PLDs), and the like may be used to implement embodiments of the present invention using hardware, , FPGAs (field programmable gate arrays), and the like may be provided in the processors 155 and 180.

Meanwhile, when implementing embodiments of the present invention using firmware or software, firmware or software may be configured to include modules, procedures, or functions that perform the functions or operations of the present invention. Firmware or software configured to be stored in the memory 155 may be contained within the processor 155 or 180 or may be stored in the memory 160 or 185 and be driven by the processor 155 or 180. [

Layers of a wireless interface protocol between a terminal and a base station and a wireless communication system (network) are divided into a first layer (L1), a second layer (L2) based on the lower three layers of an open system interconnection ), And a third layer (L3). The physical layer belongs to the first layer and provides an information transmission service through a physical channel. An RRC (Radio Resource Control) layer belongs to the third layer and provides control radio resources between the UE and the network. The UE and the base station can exchange RRC messages through the RRC layer with the wireless communication network.

The processor 155 of the terminal and the processor 180 of the base station in the present specification are not limited to the operation of processing signals and data except for the functions of the terminal 110 and the base station 105 to receive or transmit signals and the storage function, But for the sake of convenience, the processors 155 and 180 are not specifically referred to hereafter. It may be said that a series of operations such as data processing and the like are performed instead of the function of receiving or transmitting a signal even if the processors 155 and 180 are not specifically mentioned.

As described above, a wireless communication system supporting a full-duplex scheme is a system in which a base station or a terminal simultaneously performs transmission and reception. Full-duplex based wireless communication systems can achieve improved spectral-efficiency and higher data rates over conventional half-duplex communication systems. However, unlike a half-duplex multi-user system, in a multi-user system composed of a full-duplex terminal, a problem occurs in that an uplink transmission signal of a specific terminal acts as an interference to a downlink received signal of an adjacent terminal . This is a factor that hinders the performance improvement of the transmission rate of full-duplex multi-user system compared to half-duplex system. Such inter-terminal interference can be eliminated by using a null-space projection (NSP) precoding (or pre-processing) technique proposed in the present invention. The null - space projection preprocessing scheme is a technique for transmitting the signal to the null - space of the interference channel by the interfering terminal and making the intensity of the interference signal received by the neighboring terminal zero. In the present invention, a terminal causing or giving an interference signal to a neighboring terminal is called an interference terminal, and a terminal receiving interference is called a victim terminal. Since neighboring terminals can interfere with each other, each terminal may be an interfering terminal or a interfering terminal depending on the situation.

In order to eliminate the interference through the null-space projection precoder, spatial resources equal to the number of receiving antennas of the interfering terminal are required. Particularly, when the number of transmitting antennas of the interfering terminal is equal to or less than the number of receiving antennas of the interfering terminal It is difficult to acquire null-space of an interference channel using only spatial resources. Therefore, in the present invention, a null space of an effective interference channel is formed by adding two reception signals corresponding to a space and an additional resource (frequency or time) in a reception terminal, and a null precoding based on null projection is designed And to eliminate the inter-terminal interference. The precoder technique according to the present invention can eliminate the inter-terminal interference and gain additional gain in the downlink through the base station linear precoder design. We will also discuss how to exchange channel information for precoder design and how to exchange control signals to inform existing support terminals of the occurrence of additional terminals.

Null-space projection-free coding technique

Let the number of transmit and receive antennas of the terminal be N _t , N _r . At this time, an expression for the singular value decomposition (SVD) of the inter-terminal interference channel H _{I having} the size N _r × N _t ( N _t > N _r ) can be expressed by the following Equation 1.

을 좌측 특이벡터,

를 우측 특이벡터라 하며, 각 행렬을 이루는 벡터들은 직교정규(orthonormal) 벡터들이다. 즉, 서로 다른 두 벡터 u _i 와 u _j , 그리고 v _i 와 v _j 사이에는 다음과 같은 수학식 2가 성립한다.In Equation (1)

The left specific vector,

Are the right singular vectors, and the vectors forming each matrix are orthonormal vectors. That is, between two different vectors u _i and u _j , and v _i and v _j , the following Equation 2 is established.

중 하나 이상의 벡터를 선택하여 프리코더로 사용하면 상기 직교(orthogonal) 성질에 의해 단말 간 간섭 채널을 제거할 수 있다.Therefore, in the transmitting end (for example, transmitting end)

If the vector is used as a precoder, the interference channel can be removed by the orthogonal property.

3 is an exemplary diagram for explaining a full-duplex multi-user multi-antenna system including one base station and two terminals.

3, the channel information for the downlink channel between the BS and the MS 1 can be denoted by H ₁ , and the channel information for the downlink channel between the BS and the MS 2 can be denoted by H ₂ . Signals transmitted from the terminal 1 and the terminal 2 in an environment using a full-duplex scheme can be an interference signal to each other. When a signal transmitted from the transmission antenna of the terminal 1 enters the reception antenna of the terminal 2, the interference channel is denoted by H _{I, 21.} On the contrary, when a signal transmitted from the transmission antenna of the terminal 2 enters the reception antenna of the terminal 1 , And the interference channel therefor can be expressed as H _{I, 12} . In order to eliminate such inter-terminal interference, the terminal 1 applies a matrix of F _{I, UE} 1 at the transmitting end to a precoder and then transmits a signal. At the transmitting end, the terminal 2 calculates a matrix of F _{I and UE} 2, It is necessary to transmit the signal after application. Also, the base station may calculate the F _{k, BS} matrix to increase the transmit diversity _, and transmit the downlink signal after applying it in the precoder.

Transmit diversity - Alamouti technique

Spatial diversity is an effect that can be obtained by transmitting the same symbol on multiple links in a multi-antenna system, and it is possible to cope with fading by utilizing the fact that the probability of deep fading occurring at the same time on at least one link is very low Thereby securing the stability of data transmission. The diversity order can be obtained by an approximation in the high signal-to-noise ratio (SNR) domain for the average symbol error probability, which is the average error in the high signal- Means the slope of the probability curve. The Alamouti scheme is a typical scheme for obtaining transmit diversity and can be applied to a multi-antenna system environment having two transmit antennas. For example, if two reception antennas are assumed, the channel H between the transmitting and receiving antennas is expressed by the following equation (3).

Two transmission symbols s ₁ and s ₂ are allocated to two different resources (frequency and / or time resources) and transmitted as follows. Here, ^* denotes a complex conjugate.

Accumulating the two received signal vectors y ( t ) and y ( t + 1) according to each transmission signal forms an effective channel H _eff as shown in Equation (4).

Where N _tx is the number of transmit antennas. Since the effective channel ( H _eff ) has an orthogonal property, detection is possible for each stream through a simple reception filter such as maximal-ratio combining (MRC), and a diversity order Can be obtained.

In the full-duplex multi-user system, all the uplink / downlink signals use the same time and / or frequency band, so that the uplink transmission signal of the terminal may interfere with the downlink received signal of the neighboring terminal. The null-space projection technique for eliminating the inter-terminal interference is a technique in which the interfering terminal transmits a signal to the null-space of the interfering channel to zero the interfering signal of the interfering terminal. When the null-space projection precoder is used, since the spatial resources are consumed by the number of receiving antennas of the interfering terminal, the transmission rate of the uplink signal is greatly reduced. In order to design a null-space projection precoder, it is assumed that the number of transmit antennas of the interference user terminal is greater than the number of receive antennas of the interfering user terminal, and when the above condition is not satisfied, It is impossible to obtain space. Therefore, the technique proposed by the present invention proposes a null-space based precoder utilizing additional resources (frequency or time).

In order to design the precoder, the scheme proposed in the present invention requires downlink channel information at the base station and information about the inter-terminal interference channel at the interfering terminal. In addition, each of the terminals needs to grasp information about the surrounding interference and existence of the interfering terminal, and also whether or not to apply the precoder technique proposed in the present invention based on information on the presence or absence of the interference and the interfering terminal You need to decide. Accordingly, the present invention proposes a control signal transmission algorithm for exchanging base station-to-terminal downlink channel information and inter-terminal interference channel information, and a series of control signal transmission algorithms for exchanging information necessary for performing interference cancellation in the terminal.

The present invention proposes a technique for eliminating interference between terminals using two resources in a multi-user multi-antenna (MU-MIMO) wireless communication system in which both base stations and two terminals operate in a full duplex manner. For convenience of explanation of the inter-terminal interference cancellation technique, two time resources (or time intervals) (for example, symbols in the LTE / LTE-A system, time slot units, subframe units, etc.) I suppose. The base station fully knows the information on the downlink channel and assumes that the channel does not change during the two time periods (e.g., time slots). It is assumed that the number of transmission antennas of the base station is four and the number of transmission and reception antennas of the terminal is two. Since both the terminal 1 and the terminal 2 communicate with each other in a full duplex manner, they simultaneously function as an interference / interference interfering terminal. However, when the base station supports the downlink to the terminal 1 for convenience, the terminal 2 transmitting the uplink signal acts as an interference user terminal Will be analyzed and explained.

Acquisition of channel state information at transmitter (CSIT) at base station and terminal and feedback algorithm for operation of proposed method

In the precoder design process of the terminal and the base station, downlink channel information at the base station and inter-terminal interference channel information at the interfering terminal are required. In addition, the terminal must determine an operation algorithm according to whether inter-terminal interference occurs. An algorithm for exchanging the control signal is shown in FIG.

4 is a diagram illustrating a flow of a control signal transmission / reception in a case where a neighboring terminal in a UL supporting a base station requests a downlink.

Referring to FIG. 4, in a state where the terminal 2 is transmitting an uplink signal to the base station (S310), the terminal 1 corresponding to the terminal adjacent to the terminal 2 requests downlink support to the base station (S320). The base station notifies the terminal 2 that a downlink supporting terminal (terminal 1 in FIG. 3) adjacent to the terminal 2 is added (S330), transmits a downlink grant signal to the terminal 1, And may request the downlink channel information (S340). The terminal 1 transmits a reference signal to the base station (S345), and the base station can acquire the downlink channel information or the downlink channel state through the reference signal received from the terminal 1 (S350).

At this time, since the reference signal transmitted by the terminal 1 is also received by the adjacent terminal 2, the terminal 2 can acquire the channel information between the terminal 1 and the terminal 2 based on the reference signal received from the terminal 1, Interference channel information between the terminals (between the terminal 1 and the terminal 2) can be obtained using channel reciprocity (S355). On the other hand, the base station calculates a downlink channel gain value necessary for the reception signal processing for eliminating inter-terminal interference to the terminal 1 based on the downlink channel state information with the acquired terminal 1 (S360) .

4, the base station and the two terminals proposed in the present invention perform the proposed technique and remove interference between the terminals through the reception signal processing at the base station and the terminal and the downlink terminal. The base station supports the downlink to the terminal 1 in step S365. The terminal 2 transmits the uplink signal using the NSP scheme in step S370, and the base station detects the y (t) signal in step S375. The terminal 1 detects a signal y (t) + y (t + 1) from the terminal 2 and multiplies the received signal of the time interval t + 1 by a complex conjugate operation and a rotation matrix in order to eliminate inter- Can perform operations. Details of application of the NSP scheme of the UE 2 and interference cancellation of the UE 1 will be described later.

5 is a diagram illustrating a flow of a control signal transmission / reception in a case where a neighboring terminal requests downlink support in a downlink of a base station.

Referring to FIG. 5, the base station supports the downlink of the subscriber station 1 (i.e., it is transmitting a downlink signal to the subscriber station 1) (S405). At this time, the subscriber station 2 requests the base station for uplink support S410). The base station informs the terminal 1 of the occurrence of inter-terminal interference, and requests the terminal 1 for the downlink channel information necessary for the precoder design (S415). The base station transmits a signal informing the terminal 2 of approval of the uplink (S420).

The terminal 1 transmits a reference signal to the base station (S425), and the base station acquires downlink channel information (or downlink channel state information) based on the reference signal received from the terminal 1 (S430). The reference signal is also received in the adjacent uplink terminal 2, and the terminal 2 can acquire the inter-terminal interference channel information using the channel reciprocity (S435). The base station calculates the downlink channel gain value necessary for the reception signal processing for canceling the inter-terminal interference to the terminal 1 based on the downlink channel information with the acquired terminal 1, and transmits the calculated downlink channel gain value to the terminal 1 (S440).

Hereinafter, the base station and the two terminals perform the inter-terminal interference cancellation technique according to the present invention, and can eliminate the inter-terminal interference through the reception signal processing at the base station and the terminal and the downlink terminal.

Terminal precoder design for eliminating inter-terminal interference

In FIG. 5, the terminal 2 repeatedly transmits the same symbol for two consecutive time intervals (for example, symbols in LTE / LTE-A, time slot units, subframe units, etc.) 1 time interval, and t + 1 is a second time interval continuous in the first time interval). As a result, it is possible to form an effective channel in the space-time domain with respect to the inter-user interference channel, and obtain null space for interference cancellation. For example, the transmission signal vector of the terminal 2 for the two time intervals t and t + 1 is assumed as shown in the following equation.

Here, ^* denotes a complex conjugate.

At this time, the reception interference signal of the terminal 1 for two consecutive time intervals can be expressed by the following Equation (6).

은 단말 2에 의한 단말 1의 간섭 채널을 나타내는 간섭 채널 행렬이다. 상술한 바와 같이, 단말 2에 의한 단말 1의 간섭 채널은 단말 1의 기준신호가 단말 2에 수신된 경우에 획득한 채널 정보에 대해 채널 상호성에 이용하여 획득한 채널 정보이다. 단말 1에서는 단말 2의 상향링크 신호로부터 유발되는 단말 간 간섭을 제거하기 위하여 시간 구간 t+1의 수신 신호에 복소 켤레 연산 적용 및 회전 행렬을 곱해주는 연산을 수행한다. 시간 구간 t의 수신 신호와 상기 연산 결과를 더해주는 수신 신호 연산 과정은 다음 수학식 7과 같다.here

Is an interference channel matrix representing the interference channel of the terminal 1 by the terminal 2. As described above, the interference channel of the terminal 1 by the terminal 2 is channel information obtained by using the channel information obtained when the reference signal of the terminal 1 is received by the terminal 2, in channel reciprocity. The terminal 1 performs a complex conjugate operation and a rotation matrix multiplication operation on the reception signal of the time interval t + 1 to eliminate inter-terminal interference caused by the uplink signal of the terminal 2. The reception signal calculation process for adding the reception signal of the time interval t and the calculation result is shown in Equation (7).

와

는 각각 y _I (t+1)의 첫 번째 및 두 번째 성분의 복소 켤레(complex conjugate)를 의미한다. 상기 수학식 7에서 단말 간 간섭에 대한 유효 채널을 H _I,eff 라 하자. 그러면, H _I,eff 는 다음 수학식과 같이 나타낼 수 있다.here

Wow

Denotes a complex conjugate of the first and second components of y _I ( t +1), respectively. In Equation (7), an effective channel for inter-terminal interference is denoted by H _{I, eff} Let's say. Then, H _{I, eff} Can be expressed by the following equation.

Interference effective channels H _{I, eff} between terminals Can be expressed by Equation (8). &Quot; (8) " In Equation (8), it is assumed that the number of transmission antennas of the terminal 2 is four and the number of reception antennas is two.

Therefore, when a valid channel is constructed using two consecutive time intervals, a null space for an interference channel is formed. In this case, if F _{I, eff} = [ v ₃ v ₄ ] is used as a precoder of the terminal 2, 1, the effect of removing the interference signal can be obtained. Using the precoder F _{I, eff} = [ v ₃ v ₄ ], the reception signal operation at the terminal 1 can be expressed by the following equation (9).

Here, v _{3, i} , v _{4, j} ( i = 1, ..., 4, j = 1, ..., 4) represent components of v ₃ and v ₄ , respectively. If the transmission signal of the interfering terminal (terminal 2) is [ x ₁ x ₂ ] ^T through Equation 9, using the precoder as shown in Equation (10), the interference signal is removed through signal processing at the interfering terminal .

이며 피간섭 단말(도 5에서는 단말 1)에서 다음 수학식 11과 같은 수신 신호에 대한 연산을 수행함을 고려하면,If the transmitted signal of the interfering terminal for time interval t , t + 1 is x ( t ) = [ x ₁ x ₂ ] ^T ,

Considering that the interfering terminal (terminal 1 in FIG. 5) performs an operation on the received signal as shown in Equation (11) below,

The precoders F _I ( t ) and F _I ( t + 1) in the terminal 2 can be finally expressed by the following equations (12) and (13).

Pre-coder design of base station to obtain transmit diversity

In the present invention, additional gains in the downlink can be obtained through a general codebook type precoder design in the base station. For example, the base station can acquire spatial diversity in the downlink using a maximum rate transmission precoder. Under the above assumption, the base station can orthogonalize the downlink channel by transmitting a transmission signal vector such as Equation (14) at two consecutive time intervals t and t + 1.

At this time, the downlink signal received by the terminal 1 for two consecutive time intervals can be expressed by Equation (15).

은 기지국과 단말 1 간의 하향링크 채널을 나타내는 채널 행렬이다. 하향링크의 유효 채널을 직교화하기 위하여 단말 1은 회전 행렬

을 이용하여, 다음 수학식 16과 같은 수신 신호 연산을 수행한다.here

Is a channel matrix representing a downlink channel between the BS and the MS 1. [ In order to orthogonalize the effective channel of the downlink,

To perform the reception signal calculation as shown in the following Equation (16).

In Equation (16), the DL effective channel can be expressed by Equation (17).

( k ₁ 는 상수)를 만족하게 된다. 또한, Penrose 역행렬의 정의에 의하여 다음 수학식 18이 성립한다.Here, since H _eff satisfies the orthogonal property,

( k ₁ is a constant). Also, according to the definition of the Penrose inverse matrix, the following equation (18) holds.

를 적용하면 수학식 16을 다음 수학식 19와 같이 나타낼 수 있다.Therefore, it can be seen that the maximum ratio transmission precoder is in conformity with the zero-forcing precoder in consideration of the conditions for the transmission power. The maximum rate transmit precoder for H _eff

The equation (16) can be expressed by the following equation (19).

Let H ( t ) and H _eff ( t +1) denote the portions corresponding to the time intervals t and t + 1 of the components of the DL effective channel, respectively. As in (19), the transmission signal of the base station s = [s ₁ s _2] assuming a time interval ^T t, t +1 at each (H (t)) and ^H (H _eff (t +1) ) ^H It can be seen that transmit diversity can be obtained.

이며 피간섭 단말(도 4에서의 단말 1)에서 다음 수학식 20과 같은 수신 신호 연산을 수행한다. S ( t ) = [ s ₁ s ₂ ] ^T , the transmission signal of the base station with respect to the time interval t , t +1,

And performs a reception signal operation as shown in the following Equation (20) at the interfering terminal (terminal 1 in FIG. 4).

The base station precoders F ( t ) and F ( t + 1) for the time intervals t and t + 1 can be finally expressed by the following equations (21) and (22).

Where N _{tx and BS} are the number of transmit antennas of each base station supporting the terminal.

Using the precoder of the base station and the terminal 2, the received signal at the terminal 1 can be expressed by the following Equation (23).

As can be seen from Equation (23), when the base station and the terminal 2 apply the precoder according to the present invention, the received inter-terminal interference signal is removed from the terminal 1, and the transmit diversity is improved.

FIG. 6 is a diagram summarizing the contents proposed by the present invention.

Due to the ease of reception of the downlink signal at the interfering terminal, the transmitting terminal can remove the interfering signal of the interfering terminal using the null-space projection precoder obtained by Equations (12) and (13). That is, since the interfering terminal only receives the downlink signal, a separate technique such as a post-processor design for eliminating inter-terminal interference at the receiving end is not required.

Also, the UE repeatedly transmits the same symbol using additional resources other than the space resource. As a result, it is possible to generate the null space of the effective interfering channel and to eliminate the interference between the terminals. However, since the base station also has to transmit the same symbol using additional resources, there is a problem that the spatial multiplexing gain can not be obtained in the downlink signal. Therefore, in order to compensate for this loss, the diversity in the downlink can be increased by using the maximum rate transmission base station precoder designed according to Equations (21) and (22).

As can be seen from Equation (23), in the context of the UE 1, the inter-UE interference cancellation through the received signal sum of two time intervals (for example, two time slots) and the diversity of the downlink signal are improved .

The embodiments described above are those in which the elements and features of the present invention are combined in a predetermined form. Each component or feature shall 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. It is also possible to construct embodiments of the present invention by combining some of the elements and / or features. 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. It is clear that the claims that are not expressly cited in the claims may be combined to form an embodiment or be included in a new claim by an amendment after the application.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Claims (10)

A method for a first terminal to remove an interference signal between adjacent terminals,
Acquiring interference channel information between the first terminal and a second terminal adjacent to the first terminal;
Decomposing the interference channel information into singular values;
If the number of reception antennas of the first terminal is r and the number of transmission antennas is y (y > r), then in the singular value decomposed right singular vector matrix, the first matrix from r + Applying precoding in a precoder using a second matrix up to a first row; And
And transmitting the precoded signals in two consecutive time intervals,
Wherein the interference channel information is calculated assuming that the first terminal transmits the same symbol in the two consecutive time intervals. The method according to claim 1,
Wherein applying precoding in the precoder comprises:
If the first matrix is [V _{r + 1} ^H ... ... V _y ^H ] (where H denotes a Hermitian matrix), and in the precoder [V _{r + 1} ... ... V _y ] matrix is applied. 3. The method according to claim 1 or 2,
The same symbol transmitted in the two consecutive time intervals is represented by a matrix as shown in the following equation (A)
[Mathematical formula A]

Where ^* is the complex conjugate (complex conjugate) the meaning and, T is the transposed matrix, and a symbol indicating the (transpose matrix), t the first time interval, and t + 1 is the second time interval that is continuous to the first time interval In-interference. The method of claim 3,
The matrix [V _{r + 1} ... ... Portion of a first precoding matrix for the sub-matrices of the V _y] to the r rows from the first row of the first effect for the symbols transmitted in the first time interval (t), and from r + 1 row to the y line Wherein a second precoding matrix to which a complex conjugate operation is applied to a matrix is applied to a symbol transmitted in the second time interval (t + 1). The method according to claim 1,
Further comprising receiving a reference signal from the second terminal,
Wherein the interference channel information is obtained based on channel information and channel reciprocity estimated from the reference signal received from the second terminal. 1. A first terminal capable of removing an interference signal between adjacent terminals,
The first terminal acquires interference channel information between the first terminal and a second terminal adjacent to the first terminal,
Decomposes the interference channel information into singular values,
If the number of reception antennas of the first terminal is r and the number of transmission antennas is y (y > r), then in the singular value decomposed right singular vector matrix, the first matrix from r + A processor configured to apply precoding in a precoder using a second matrix up to a row; And
And a transmitter configured to transmit the precoded signals in two consecutive time intervals,
Wherein the processor calculates the interference channel information assuming that the first terminal transmits the same symbol in the two consecutive time intervals. The method according to claim 6,
The processor comprising:
If the first matrix is [V _{r + 1} ^H ... ... V _y ^H ] (where H denotes a Hermitian matrix), and in the precoder [V _{r + 1} ... ... V _y ] matrix. 8. The method according to claim 6 or 7,
The same symbol transmitted in the two consecutive time intervals is represented by a matrix as shown in the following equation (A)
[Mathematical formula A]

Where ^* is the complex conjugate (complex conjugate) the meaning and, T is the transposed matrix, and a symbol indicating the (transpose matrix), t the first time interval, and t + 1 is the second time interval that is continuous to the first time interval The first terminal. 9. The method of claim 8,
The processor is configured to calculate the matrix [V _{r + 1} ... ... Portion of a first precoding matrix for the sub-matrices of the V _y] to the r rows from the first row of the first effect for the symbols transmitted in the first time interval (t), and from r + 1 row to the y line And applies a second precoding matrix applying a complex conjugate operation to a matrix for a symbol transmitted in the second time interval (t + 1). The method according to claim 6,
Further comprising a receiver for receiving a reference signal from the second terminal,
Wherein the processor acquires the interference channel information based on the channel information estimated with the reference signal received from the second terminal and the channel reciprocity.

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