KR102305628B1 - 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 proposes a method for removing an interference signal between terminals in a wireless communication system supporting a full-duplex scheme and a method for increasing a downlink diversity gain. A first terminal capable of canceling an interference signal between adjacent terminals according to an embodiment of the present invention, wherein the first terminal obtains interference channel information between the first terminal and an adjacent second terminal, and the interference channel information is singular value decomposed, and when the number of receive antennas of the first terminal is r and the number of transmit antennas is y (y > r), the first matrix from column r+1 to column y in the singular value decomposed right singular vector matrix, or a processor configured to apply precoding in the precoder using the second matrix from row r+1 to row y; and a transmitter configured to transmit the precoding-applied signals in two consecutive time intervals, wherein the processor transmits the interference channel information when the first terminal transmits the same symbol in the two consecutive time intervals It is calculated assuming .

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for removing an interference signal between terminals and increasing a downlink diversity gain in a wireless communication system supporting a full-duplex scheme, and an apparatus for the same. full duplex radio scheme}

The present invention relates to wireless communication, and more particularly, to a method and apparatus therefor for removing an interference signal between terminals and increasing a downlink diversity gain in a wireless communication system supporting a full-duplex scheme.

Full duplex radio (FDR) or full duplex communication (full duplex communication) refers to a communication method that simultaneously supports transmission and reception using the same resource in one terminal. In this case, the same resource means the same time and the same frequency. FDR communication or full duplex communication is called bidirectional communication.

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

Referring to FIG. 1 , three types of interference exist in a network situation supporting FDR. The first is intra-device self-interference. Intra-device self-interference means that a signal transmitted from a transmitting antenna in one base station or a terminal is received by a receiving antenna and acts as interference. The signal transmitted from the transmitting antenna is transmitted with high power, and since the distance between the transmitting antenna and the receiving antenna is short, the transmitted signal is received by the receiving antenna with little attenuation, so that it is received with much greater power than a desired signal. Second, there is interference between terminals (UE to UE inter-link interference). In a network supporting FDR, interference between terminals increases. This means that an uplink signal transmitted by the terminal is received by a terminal located nearby and acts as interference. Third, there is interference between base stations (BS to BS inter-link interference). In a network situation supporting FDR, interference between base stations (BS to BS inter-link interference) increases. This means that a signal transmitted between base stations or between heterogeneous base stations (Pico, femto, relay) in a HetNet situation is received by a receiving antenna of another base station and acts as interference.

As such, in order to improve the communication performance of the terminals when using the FDR scheme, it is necessary to solve the problem of interference between terminals. However, methods for removing interference between terminals in an FDR situation have not yet been specifically studied.

An object of the present invention is to provide a method for a first terminal to cancel an interference signal between adjacent terminals.

Another technical object to be achieved in the present invention is to provide a first terminal capable of canceling an interference signal between adjacent terminals.

The technical problems to be achieved in the present invention are not limited to the above technical problems, and other technical problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description.

In order to achieve the above technical problem, a method for a first terminal to remove an interference signal between adjacent terminals includes: obtaining, by the first terminal, interference channel information between the first terminal and an adjacent second terminal; singular value decomposition of the interference channel information; When the number of receive antennas of the first terminal is r and the number of transmit antennas is y (y>r), the first matrix from the r+1 column to the y column in the singular value decomposed right singular vector matrix or y in the r+1 row applying precoding in the precoder using the second matrix up to the row; and transmitting the precoding-applied 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. do.

In the step of applying the precoding in the precoder, the first matrix is [V _r+1 ^H ... … In the case of V _y ^H ] (where H represents a Hermitian matrix), 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 such as the following Equation A,

[Equation A]

Here, ^* means a complex conjugate, T is a symbol representing a transpose matrix, t is a first time interval, and t+1 is a second time interval continuous with the first time interval am. The matrix of y * r [V _r+1 ... … V _y ], the first precoding matrix corresponding to the partial matrix from the first row to the r row is applied to the symbol transmitted in the first time interval t, and the part from the r+1 row to the y row A second precoding matrix in 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 further includes receiving a reference signal from the second terminal, wherein the interference channel information is obtained based on channel information and channel reciprocity estimated by the reference signal received from the second terminal.

In order to achieve the above other technical problem, a first terminal capable of canceling an interference signal between adjacent terminals, the first terminal acquires interference channel information between the first terminal and an adjacent second terminal, and the interference channel Singular value decomposition of information, and when the number of receive antennas of the first terminal is r and the number of transmit antennas is y (y>r), the first matrix from column r+1 to column y in the singular value decomposed right singular vector matrix or a processor configured to apply precoding in the precoder using the second matrix from row r+1 to row y; and a transmitter configured to transmit the precoding-applied signals in two consecutive time intervals, wherein the processor transmits the interference channel information when the first terminal transmits the same symbol in the two consecutive time intervals It is calculated assuming . The processor determines that the first matrix is [V _r+1 ^H ... … In the case of V _y ^H ] (where H represents a Hermitian matrix), 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 such as the following Equation A,

[Equation A]

Here, ^* means a complex conjugate, T is a symbol representing a transpose matrix, t is a first time interval, and t+1 is a second time interval continuous with the first time interval am. The processor, the matrix of y * r [V _r+1 ... … V _y ], the first precoding matrix corresponding to the partial matrix from the first row to the r row is applied to the symbol transmitted in the first time interval t, and the part from the r+1 row to the y row A second precoding matrix in which a complex conjugate operation is applied to a matrix is applied to a symbol transmitted in the second time interval (t+1). The first terminal is a receiver for receiving a reference signal from the second terminal It further includes, wherein the processor obtains the interference channel information based on the channel information and the channel reciprocity estimated by the reference signal received from the second terminal.

In the present invention, interference cancellation between terminals is performed by designing a terminal precoder for two frequencies or times. In addition, it is possible to obtain an additional gain in the downlink through the design of the precoder in the base station.

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

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as a part of the detailed description to help the understanding of the present invention, provide embodiments of the present invention, and together with the detailed description, explain the technical spirit of the present invention.
1 shows a conceptual diagram of a terminal and a base station supporting FDR.
2 is a block diagram illustrating the configuration of the base station 105 and the terminal 110 in the wireless communication system 100 .
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 transmission/reception of a control signal when a neighboring terminal requests a downlink while the base station supports uplink.
5 is a diagram illustrating a flow of transmission/reception of a control signal when a neighboring terminal requests an uplink while the base station supports downlink.
6 is a view summarizing the content to be proposed in the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION The detailed description set forth below in conjunction with the appended drawings is intended to describe exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. For example, the following detailed description will be described in detail on the assumption that the mobile communication system is a 3GPP LTE or LTE-A system, but except for the specific details of 3GPP LTE and LTE-A, it is also applied to any other mobile communication system. Applicable.

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

In addition, in the following description, it is assumed that a terminal refers to a mobile or fixed user end device such as a user equipment (UE), a mobile station (MS), and an advanced mobile station (AMS). In addition, it is assumed that the base station collectively refers to an arbitrary node of a network end that communicates with the terminal, such as a Node B, an eNode B, a base station, and an access point (AP). Although this specification is described based on the IEEE 802.16 system, the contents of the present invention are applicable to various other communication systems.

In a mobile communication system, a user equipment may receive information from a base station through a downlink, and the terminal may also transmit information through an uplink. 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 and use.

The following technologies include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. It can be used in various wireless access systems. CDMA is UTRA (Universal Terrestrial Radio Access). It may be implemented with a radio technology such as CDMA2000. TDMA may be implemented with a radio technology such as Global System for Mobile communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented with a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA), and the like. UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3GPP (3rd Generation Partnership Project) long term evolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is an evolved version of 3GPP LTE.

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

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

Although one base station 105 and one terminal 110 (including a D2D terminal) are illustrated to simplify the wireless communication system 100, the wireless communication system 100 includes one or more base stations and/or one or more terminals. It may include a terminal.

Referring to FIG. 2 , the base station 105 includes a transmit (Tx) data processor 115 , a symbol modulator 120 , a transmitter 125 , a transmit/receive antenna 130 , a processor 180 , a memory 185 , and a receiver ( 190 ), a symbol demodulator 195 , and a receive data processor 197 . In addition, the terminal 110 includes a transmit (Tx) data processor 165 , a symbol modulator 170 , a transmitter 175 , a transmit/receive antenna 135 , a processor 155 , a memory 160 , a receiver 140 , and a symbol. It may include a demodulator 155 and a receive data processor 150 . Although the transmit/receive 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 are provided with a plurality of transmit/receive antennas. Accordingly, 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 single user-MIMO (SU-MIMO) and multi-user-MIMO (MU-MIMO) schemes.

On the downlink, transmit data processor 115 receives traffic data, formats and codes the received traffic data, interleaves and modulates (or symbol maps) the coded traffic data, and generates modulation symbols (“data symbols"). A symbol modulator 120 receives and processes these data symbols and pilot symbols and provides a stream of symbols.

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

Transmitter 125 receives a stream of symbols and converts them to one or more analog signals, and further modulates (eg, amplifies, filters, and frequency upconverts) the analog signals to create a wireless channel Generates a downlink signal suitable for transmission through the transmission antenna 130 then transmits the generated downlink signal to the terminal.

In the configuration of the terminal 110 , the reception antenna 135 receives a downlink signal from the base station and provides the received signal to the receiver 140 . Receiver 140 modulates (eg, filters, amplifies, and frequency downconverts) the received signal and digitizes the modulated signal to obtain samples. A symbol demodulator 145 demodulates the received pilot symbols and provides them to a processor 155 for channel estimation.

A symbol demodulator 145 also receives a frequency response estimate for the downlink from the processor 155, performs data demodulation on the received data symbols, and generates a data symbol estimate (which is an estimate of the transmitted data symbols). and provides the data symbol estimates to a receive (Rx) data processor 150 . Receive data processor 150 demodulates (ie, symbol de-maps) the data symbol estimates, deinterleaves, and decodes the data symbol estimates to recover the transmitted traffic data.

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

The terminal 110 processes the traffic data on the uplink, and the transmission data processor 165 provides data symbols. A symbol modulator 170 may receive and multiplex the data symbols, perform modulation, and provide a stream of symbols to a transmitter 175 . A transmitter 175 receives and processes the stream of symbols to generate an uplink signal. In addition, the transmit antenna 135 transmits the generated uplink signal to the base station 105 .

In the base station 105, an uplink signal is received from the terminal 110 through the reception antenna 130, and the receiver 190 processes the received uplink signal to obtain samples. A symbol demodulator 195 then processes these samples and provides received pilot symbols and data symbol estimates for the uplink. The receive data processor 197 processes the data symbol estimate 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 (eg, control, coordinate, manage, etc.) operations in the terminal 110 and the base station 105 , respectively. Each of the processors 155 and 180 may be connected to memory units 160 and 185 that store program codes and data. The memories 160 and 185 are connected to the processor 180 to store an operating system, applications, and general files.

The processors 155 and 180 may also be referred to as controllers, microcontrollers, microprocessors, microcomputers, or the like. Meanwhile, the processors 155 and 180 may be implemented by hardware, firmware, software, or a combination thereof. When implementing the embodiment of the present invention using hardware, ASICs (application specific integrated circuits) or DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices) configured to carry out the present invention , field programmable gate arrays (FPGAs), etc. may be provided in the processors 155 and 180 .

On the other hand, when the embodiments of the present invention are implemented using firmware or software, the firmware or software may be configured to include a module, procedure, or function that performs the functions or operations of the present invention, and Firmware or software configured so as to be provided in the processors 155 and 180 or stored in the memories 160 and 185 may be driven by the processors 155 and 180 .

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

In this specification, the processor 155 of the terminal and the processor 180 of the base station process signals and data except for the terminal 110 and the base station 105 receiving or transmitting a signal and a storage function, respectively. However, for convenience of description, the processors 155 and 180 are not specifically referred to below. Even if there is no mention of the processors 155 and 180 in particular, it can be said that a series of operations such as data processing are performed rather than a function of receiving or transmitting a signal.

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. The full-duplex-based wireless communication system can obtain improved spectral-efficiency and high data rate compared to the existing half-duplex communication system. However, unlike a half-duplex multi-user system, in a multi-user system composed of a full-duplex type terminal, an uplink transmission signal of a specific terminal acts as interference to a downlink reception signal of an adjacent terminal. . This acts as a factor hindering the improvement of the data rate summing performance of the full-duplex multi-user system compared to the half-duplex system. Such inter-terminal interference can be removed by using a null-space projection (NSP) precoding (or pre-processing) technique proposed in the present invention. The null-space projection preprocessing technique is a technique in which an interfering terminal transmits a signal in the null-space of an interference channel to make the intensity of an interference signal received by an adjacent terminal 0. In the present invention, a terminal that induces or gives an interference signal to an adjacent terminal is referred to as an interfering terminal, and a terminal subjected to interference is referred to as a victim terminal. Since adjacent terminals may interfere with each other, each terminal may be an interfering terminal or an interfering terminal depending on circumstances.

In order to remove interference through a null-space projection precoder, a space resource equal to the number of receiving antennas of the interfering terminal is required. It is difficult to obtain the null-space of the interference channel using only spatial resources. Therefore, in the present invention, a null-space of an effective interference channel is formed by adding two received signals corresponding to a space and an additional resource (frequency or time) in a receiving terminal, and a null-space projection-based terminal precoder is designed. Therefore, we would like to propose a technique for removing interference between terminals. The precoder technique according to the present invention can eliminate inter-terminal interference and at the same time obtain an additional gain in downlink through a base station linear precoder design. A method of exchanging channel information for designing a precoder and exchanging a control signal informing an existing supporting terminal whether an additional terminal is generated will also be described.

Null-space projection precoding technique

The number of transmit and receive antennas of the terminal is N _t , N _{r respectively} let's say In this case, the equation for singular value decomposition (SVD) of the interference channel H _I between terminals having a size of N _r × N _t ( N _t > N _{r ) may be expressed as in Equation 1 below.}

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 above

is the left singular vector,

is called a right singular vector, and the vectors constituting each matrix are orthonormal vectors. That is, the following Equation 2 holds between two different vectors u _i and u _j , and v _i and v _{j .}

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

When one or more vectors are selected and used as a precoder, an inter-terminal interference channel can be removed due to 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.

Referring to FIG. 3 , channel information on a downlink channel between a base station and terminal 1 may be represented by H ₁ , and channel information on a downlink channel between the base station and terminal 2 may be represented by H _{2 .} In an environment using the full-duplex method, signals transmitted by UE 1 and UE 2 may become interference signals to each other. When a signal transmitted from the transmit antenna of terminal 1 enters the receive antenna of terminal 2, the interference channel is indicated by H _I,21 , and conversely, when a signal transmitted from the transmit antenna of terminal 2 enters the receive antenna of terminal 1 , the interference channel for this can be expressed as H _{I,12 .} In order to eliminate such inter-terminal interference, the terminal 1, after applying the matrix of F _{I, UE1} from the transmission terminal to the precoder, and sends a signal, the terminal 2 is the pre-coder to produce a matrix of F _{I, UE2} at the transmitting end After application, it is necessary to transmit a signal. In addition, the base station may calculate the F _{k and BS} matrix to increase transmit diversity, apply it in the precoder, and then transmit the downlink signal.

transmit diversity - Alamouti technique

Spatial diversity is an effect that can be obtained by transmitting the same symbol to multiple links in a multiple antenna system. It is a method to ensure the stability of data transmission. The diversity order can be obtained through an approximation equation in the high signal-to-noise ratio (SNR) domain to the average symbol error probability, which is the average error in the high signal-to-noise ratio domain. It means the slope of the probability curve. The Alamouti technique is a representative technique for obtaining transmit diversity, and can be applied to a multi-antenna system environment having two transmit antennas. For example, assuming two receiving antennas, the channel H between the transmitting and receiving antennas is expressed by Equation 3 below.

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

When two reception signal vectors y ( t ) and y ( t +1) according to each transmission signal are accumulated, an effective channel ( H _eff ) as shown in Equation 4 below is formed.

Here, N _tx is the number of transmit antennas. Since the effective channel ( H _eff ) has orthogonal characteristics, it is possible to detect each stream through a reception filter of a simple form such as maximal-ratio combining (MRC), and the diversity order of the product of the number of transmit and receive antennas can get

In a full-duplex multi-user system, since all uplink/downlink signals use the same time and/or frequency band, an uplink transmission signal of a terminal acts as an interference with a downlink reception signal of an adjacent terminal. The null-space projection technique for removing such inter-terminal interference is a technique in which the interfering terminal transmits a signal to the null-space of the interference channel, thereby making the received interference signal of the interfering terminal to zero. When the null-space projection precoder is used, space resources are consumed as much as the number of reception antennas of the interfering terminal, so that the transmission rate of the uplink signal is greatly reduced. In addition, in order to design a null-space projection precoder, a prerequisite is that the number of transmit antennas of the interfering user terminal must be greater than the number of receive antennas of the interfered user terminal. It is impossible to acquire space. Therefore, the technique proposed in the present invention proposes a null-space-based precoder using an additional resource (frequency or time).

The technique proposed in the present invention requires downlink channel information in the base station and information on the inter-terminal interference channel in the interfering terminal in order to design a precoder. In addition, each terminal needs to know information about the existence of nearby interference and interfered terminals, and whether the precoder technique proposed in the present invention is applied or not based on information on the existence of interference and interfered terminals. need to decide Accordingly, the present invention proposes a control signal for exchanging downlink channel information between a base station and a terminal and an interference channel information between terminals, and a series of control signal transmission algorithms for exchanging information necessary to perform interference cancellation in the terminal.

The present invention proposes a technique for eliminating interference between terminals by using two resources in a multi-user multiple antenna (MU-MIMO) wireless communication system in which a base station and two terminals operate in a full-duplex manner. For convenience of description of the inter-terminal interference cancellation technique, it is said that two time resources (or time intervals) (eg, symbol units, time slots units, subframe units, etc. in LTE/LTE-A system) are used. Assume It is assumed that the base station completely knows the information on the downlink channel, and the channel does not change during two time intervals (eg, time slots). It is assumed that the number of transmit antennas of the base station is four, and the number of transmit and receive antennas of the terminal is two, respectively. Terminal 1 and Terminal 2 both perform communication in a full-duplex manner, so they act as interfering/interfered terminals at the same time. Only those cases will be analyzed and explained.

Feedback algorithm for CSIT (channel state information at transmitter) acquisition and operation of the proposal technique in the base station and the terminal

In the precoder design process of the terminal and the base station, downlink channel information in the base station and inter-terminal interference channel information in the interfering terminal are required. In addition, the terminal must determine the operation algorithm according to whether interference between terminals occurs. An algorithm for exchanging the control signal is shown in FIG. 3 below.

4 is a diagram illustrating a flow of transmission/reception of a control signal when a neighboring terminal requests a downlink while the base station supports uplink.

Referring to FIG. 4 , in a situation where terminal 2 is transmitting an uplink signal to a base station (S310), terminal 1 corresponding to a terminal adjacent to terminal 2 requests downlink support from the base station (S320). The base station notifies the terminal 2 that the downlink support terminal adjacent to the terminal 2 (UE 1 in FIG. 3) has been added (S330), and transmits a downlink grant signal to the terminal 1 and is required for precoder design. Downlink channel information may be requested (S340). The terminal 1 transmits a reference signal to the base station (S345), and the base station may obtain downlink channel information or a 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 may obtain channel information between the terminal 1 and the terminal 2 based on the reference signal received from the terminal 1, and the obtained channel information and Interference channel information between UEs (between UE 1 and UE 2) may be obtained using channel reciprocity (S355). On the other hand, the base station calculates a downlink channel gain value required for processing a received signal to remove inter-terminal interference to terminal 1 based on the acquired downlink channel state information with terminal 1, and transmits it to terminal 1 (S360) .

Thereafter, in the proposed method step described in FIG. 4 , the base station and two terminals proposed in the present invention perform the proposed method, and interference between terminals is removed through precoders of the base station and the terminal and reception signal processing in the downlink terminal. As the base station supports downlink to terminal 1 (S365) and terminal 2 transmits an uplink signal to which the NSP technique is applied (S370), the base station detects a y(t) signal (S375). Terminal 1 detects a signal of y(t) + y(t+1) from terminal 2, and applies a complex conjugate operation to the received signal in the time interval t+1 and multiplies the rotation matrix to remove the inter-terminal interference. The given operation can be performed. The details of the application of the NSP technique of the terminal 2 and the interference cancellation method of the terminal 1 will be described later.

5 is a diagram illustrating a flow of transmission/reception of a control signal when a neighboring terminal requests an uplink while the base station supports downlink.

Referring to FIG. 5 , the base station supports the downlink of terminal 1 (that is, transmitting a downlink signal to terminal 1) (S405), and at this time, terminal 2 requests uplink support from the base station ( S410). The base station notifies terminal 1 that inter-terminal interference has occurred, and requests downlink channel information required for precoder design from terminal 1 (S415). The base station transmits a signal notifying the approval of the uplink to the terminal 2 (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 by the adjacent uplink terminal 2, and the terminal 2 may acquire inter-terminal interference channel information using channel reciprocity (S435). The base station calculates a downlink channel gain value required for processing a received signal to remove inter-terminal interference to UE 1 based on the acquired downlink channel information with UE 1, and transmits the calculated downlink channel gain value to UE 1 do (S440).

Thereafter, the base station and the two terminals perform the inter-terminal interference cancellation technique according to the present invention, and the inter-terminal interference can be removed through the precoders of the base station and the terminal and the received signal processing in the downlink terminal.

Terminal precoder design to eliminate inter-terminal interference

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

Here, ^* means a complex conjugate.

In this case, the reception interference signal of UE 1 for two consecutive time intervals may be expressed as in Equation 6 below.

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 indicating an interference channel of UE 1 by UE 2 . As described above, the interference channel of the terminal 1 by the terminal 2 is channel information obtained by using the channel reciprocity for the channel information obtained when the reference signal of the terminal 1 is received by the terminal 2. Terminal 1 performs an operation of applying a complex conjugate operation and multiplying a reception signal of a time interval t +1 by a rotation matrix in order to remove inter-terminal interference caused by an uplink signal of UE 2 . A received signal calculation process for adding the received signal of the time interval t and the operation result is as shown in Equation 7 below.

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, the effective channel for inter-terminal interference is H _I,eff let's say Then, H _I,eff can be expressed as the following equation.

Interference effective channel H _{I,eff between terminals} The singular value decomposition for ? can be expressed as Equation 8 below. In the case of Equation 8, it is assumed that the number of transmit antennas of UE 2 is 4 and the number of receive antennas is 2.

Therefore, when an effective channel is configured using two consecutive time intervals, a null-space for the interference channel is formed. In this case, when F _I,eff =[ v ₃ v ₄ ] is used as the precoder of UE 2 As a result of the operation of the received signal in step 1, the effect of canceling the interference signal can be obtained. When the precoder F _I,eff =[ v ₃ v ₄ ] is used, the reception signal operation in the terminal 1 can be expressed as in Equation 9 below.

Here, v _{3, i} , v _{4 , j} ( i =1,…,4, j =1,…,4) means the components of v ₃ , 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 in Equation 10 below, it is possible to remove the received interference signal through signal processing at the interfering terminal. it can be seen that

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

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

The precoders F _I ( t ) and F _I ( t +1) in UE 2 may be finally expressed as Equations 12 and 13 below.

Base station precoder design to achieve transmit diversity

In the present invention, an additional gain in downlink can be obtained through a precoder design of a general codebook method in a base station. For example, the base station may acquire spatial diversity in downlink by using a maximum rate transmission precoder. Under the above assumption, the base station can orthogonalize a downlink channel by transmitting a transmission signal vector as shown in Equation 14 below in two consecutive time intervals t , t+1.

At this time, the downlink signal received by UE 1 for two consecutive time intervals can be expressed as in Equation 15 below.

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 indicating a downlink channel between the base station and the terminal 1. In order to orthogonalize the effective channel of the downlink, UE 1 uses a rotation matrix

, the received signal operation is performed as shown in Equation 16 below.

In Equation 16, the downlink effective channel can be expressed as in Equation 17 below.

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

( k ₁ is a constant) is satisfied. In addition, the following Equation 18 holds by the definition of the Penrose inverse matrix.

를 적용하면 수학식 16을 다음 수학식 19와 같이 나타낼 수 있다.Accordingly, it can be seen that the maximum ratio transmission precoder has the same shape as the zero-forcing precoder considering the transmission power condition. Maximum ratio transmit precoder to H _eff

By applying Equation 16, Equation 16 can be expressed as Equation 19 below.

Let H ( t ) and H _eff ( t +1) be the parts corresponding to time intervals t and t +1 among the components of the downlink effective channel, respectively. As shown in Equation 19, when it is assumed that the transmission signal of the base station is s =[ s ₁ s ₂ ] ^T , in the time interval t , t +1 ( H ( t )) ^H and ( H _eff ( t +1), respectively ) ^H It can be confirmed that transmit diversity can be obtained by using as a precoder.

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

and the interference target terminal (terminal 1 in FIG. 4 ) performs a reception signal operation as shown in Equation 20 below.

The base station precoders F ( t ) and F ( t +1) for the time interval t , t +1 may be finally expressed as Equations 21 and 22 below, respectively.

Here, N _{tx and BS} are the number of transmit antennas of the base station for each supported terminal.

When the base station and the precoder of the terminal 2 are used, the reception signal of the terminal 1 can be expressed as in Equation 23 below.

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 standpoint of the terminal 1 and transmit diversity is improved.

6 is a view summarizing the content to be proposed in the present invention.

Due to the ease of receiving a downlink signal in the interfering terminal, the transmitting terminal may use the null-space projection precoder obtained in Equations (12) and (13) to cancel the received interference signal of the interfering terminal. That is, since the interfering terminal receives only the downlink signal, a separate technique such as a post-processor design for inter-terminal interference cancellation at the receiving end is not required.

In addition, the terminal repeatedly transmits the same symbol using additional resources other than the spatial resource. As a result, interference between terminals can be removed by generating a null-space of an effective interference channel. However, since the base station also needs to transmit the same symbol using additional resources, there is a problem that the spatial multiplexing gain cannot be obtained in the downlink signal. Therefore, in the present invention, diversity in downlink can be increased by using the maximum rate transmission-based base station precoder designed according to Equations 21 and 22 to compensate for this loss.

As can be seen from Equation 23, from the standpoint of UE 1, inter- UE interference cancellation and downlink signal diversity are improved through the sum of received signals of two time intervals (eg, two time slots). will become

The embodiments described above are those in which elements and features of the present invention are combined in a predetermined form. Each component or feature should be considered optional unless explicitly stated otherwise. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to configure embodiments of the present invention by combining some elements and/or features. The order of operations described in the embodiments of the present invention may be changed. Some features or features of one embodiment may be included in another embodiment, or may be replaced with corresponding features or features of another embodiment. It is obvious that claims that are not explicitly cited in the claims can be combined to form an embodiment or included as a new claim by amendment after filing.

It is apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit and essential characteristics of the present invention. Accordingly, the above detailed description should not be construed as restrictive in all respects but as exemplary. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are included in the scope of the present invention.

Claims (10)

A method for a first terminal to cancel an interference signal between adjacent terminals, the method comprising:
obtaining, by the first terminal, interference channel information between the first terminal and an adjacent second terminal;
singular value decomposition of the interference channel information;
When the number of receive antennas of the first terminal is r and the number of transmit antennas is y (y>r), the first matrix from the r+1 column to the y column in the singular value decomposed right singular vector matrix or y in the r+1 row applying precoding in the precoder using the second matrix up to the row; and
Comprising the step of transmitting the signals to which the precoding is applied in two consecutive time intervals,
The interference channel information is calculated on the assumption that the first terminal transmits the same symbol in the two consecutive time intervals. The method of claim 1,
The step of applying precoding in the precoder comprises:
The first matrix is [V _r+1 ^H ... … In the case of V _y ^H ] (where H represents a Hermitian matrix), in the precoder, [V _r+1 … … V _y ], characterized in that applying a matrix, inter-terminal interference cancellation method. 3. The method of claim 1 or 2,
The same symbol transmitted in the two consecutive time intervals is represented by a matrix such as the following Equation A,
[Equation A]

Here, ^* means a complex conjugate, T is a symbol representing a transpose matrix, t is a first time interval, and t+1 is a second time interval continuous with the first time interval A method for removing interference between a user and a terminal. 4. The method of claim 3,
The matrix of y * r [V _r+1 ... … V _y ], the first precoding matrix corresponding to the partial matrix from the first row to the r row is applied to the symbol transmitted in the first time interval t, and the part from the r+1 row to the y row An inter-terminal interference cancellation method for applying 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 method of claim 1,
Further comprising the step of receiving a reference signal from the second terminal,
The interference channel information is obtained based on the channel information and channel reciprocity estimated by the reference signal received from the second terminal, the inter-terminal interference cancellation method. In the first terminal capable of canceling the interference signal between adjacent terminals,
The first terminal acquires interference channel information between the first terminal and a second adjacent terminal,
singular value decomposition of the interference channel information,
When the number of receive antennas of the first terminal is r and the number of transmit antennas is y (y>r), the first matrix from the r+1 column to the y column in the singular value decomposed right singular vector matrix or y in the r+1 row a processor configured to apply precoding at the precoder using the second matrix up to the row; and
A transmitter configured to transmit the precoding-applied signals in two consecutive time intervals,
The processor calculates the interference channel information on the assumption that the first terminal transmits the same symbol in the two consecutive time intervals. 7. The method of claim 6,
The processor is
The first matrix is [V _r+1 ^H ... … In the case of V _y ^H ] (where H represents a Hermitian matrix), in the precoder, [V _r+1 … … V _y ] matrix, the first terminal. 8. The method of claim 6 or 7,
The same symbol transmitted in the two consecutive time intervals is represented by a matrix such as the following Equation A,
[Equation A]

Here, ^* means a complex conjugate, T is a symbol representing a transpose matrix, t is a first time interval, and t+1 is a second time interval continuous with the first time interval In, the first terminal. 9. The method of claim 8,
The processor, the matrix of y * r [V _r+1 ... … V _y ], the first precoding matrix corresponding to the partial matrix from the first row to the r row is applied to the symbol transmitted in the first time interval t, and the part from the r+1 row to the y row A first terminal that 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). 7. The method of claim 6,
Further comprising a receiver for receiving a reference signal from the second terminal,
The processor is configured to obtain the interference channel information based on channel information and channel reciprocity estimated as a reference signal received from the second terminal.

Images