KR20190036497A - Superposition transmission method and apparatus for communication system - Google Patents

Abstract

Disclosed are a method for superposition transmission in a communication system and an apparatus thereof. According to the present invention, an operation method of a first terminal may comprise: a step of receiving a DCI from a base station; a step of receiving a superposition signal including a first data signal of the first terminal and a second data signal of a second terminal through time-frequency resources directed by resource allocation information; a step of receiving a first message which requests the transmission of an HARQ response to the second data signal; a step of decoding the second data signal included in the superposition signal based on an MCS for the second terminal directed by the MCS information and transmission power for the second terminal directed by allocation information of the transmission power; and a step of transmitting the HARQ response, which is a result of the decoding of the second data signal, to the base station as a response to the first message. As such, the performance of the communication system can be increased.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for superposition transmission in a communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superposition transmission technique in a communication system, and more particularly, to a method of transmitting and receiving channel state information and a hybrid automatic repeat request (HARQ) response in a superposition transmission procedure.

In a downlink based on orthogonal frequency division multiplexing (OFDM) of a 3 ^rd generation partnership project (LTE-A) system, a superposition transmission can be used for additional data rate enhancement. The downlink overlay transmission may be a technique of adding a signal of a terminal located near the base station and a terminal located far away from the base station. The DL link transmission may be a non-orthogonal transmission scheme that non-uniformly allocates the transmission power to the UEs in the same time and frequency resources.

In order to maximize the downlink data rate, a multi-user multiple-input multiple-output (MU-MIMO) transmission scheme and a superposition transmission scheme can be used together. In the MU-MIMO transmission scheme, a base station can form a plurality of beams using different precoding. The base station can transmit data to a plurality of terminals at the same time and frequency resources using a plurality of formed beams. Therefore, the base station can apply overlay transmission to each beam formed using MU-MIMO. However, if the orthogonality of the precoded channels of each terminal is small, the mutual interference is large and the data transmission rate may be seriously degraded.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of transmitting and receiving channel status information and a hybrid automatic repeat request (HARQ) response in a superposition transmission procedure.

According to an aspect of the present invention, there is provided a method of operating a first UE according to an embodiment of the present invention includes downlink control information (DCI) including resource allocation information, modulation and coding scheme (MCS) Receiving an overlap signal including a first data signal of the first terminal and a second data signal of the second terminal from the base station through time-frequency resources indicated by the resource allocation information; Receiving a first message requesting transmission of a hybrid automatic repeat request (HARQ) response for the second data signal from the base station, generating an MCS for the second terminal indicated by the MCS information, Based on the transmission power for the second terminal indicated by the transmission power allocation information, the second data included in the superposition signal And transmitting the HARQ response as a decoding result of the second data signal to the base station in response to the first message.

According to the present invention, when superposition transmission is applied to each beam formed using a multi-user multiple-input multiple-output (MU-MIMO) in a multi-antenna wireless communication system composed of a base station and a plurality of terminals, The problem of lowering the data transfer rate due to interference can be improved.

If the base station applies superposition transmission to each beam, it can transmit data to more terminals in the same time and frequency resources. However, if the orthogonality of the precoded channels in each terminal is small, mutual interference is large and the data transmission rate may be degraded.

According to the present invention, the base station can select an appropriate precoding method for each terminal and obtain additional channel state information for selecting an appropriate terminal pair. In addition, the UE can transmit acknowledgment / negative acknowledgment (ACK) / negative acknowledgment (ACK) information for data of another UE to the Node B during the overlap transmission. Therefore, the inter-beam interference can be reduced and the reliability of data transmission can be enhanced. Therefore, the performance of the communication system can be improved.

1 is a conceptual diagram showing a first embodiment of a communication system.
2 is a block diagram showing a first embodiment of a communication node constituting a communication system.
3 is a conceptual diagram showing a second embodiment of the communication system.
4 is a flowchart showing a first embodiment of a PMI transmission / reception method between a base station and terminals.
5 is a flowchart showing a second embodiment of a PMI transmission / reception method between a base station and terminals.
6 is a flowchart illustrating a method of transmitting / receiving ACK / NACK information between a Node B and UEs according to a first embodiment of the present invention.
7 is a flowchart illustrating a method of transmitting / receiving ACK / NACK information between a Node B and UEs according to a second embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

A communication system to which embodiments of the present invention are applied will be described. The communication system to which the embodiments according to the present invention are applied is not limited to the following description, and the embodiments according to the present invention can be applied to various communication systems. Here, the communication system can be used in the same sense as a communication network.

1 is a conceptual diagram showing a first embodiment of a communication system.

1, a communication system 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6. The communication system 100 also includes a core network (e.g., a serving gateway (S-GW), a packet data network (PDN) gateway, a mobility management entity .

The plurality of communication nodes may support 4G communication (e.g., long term evolution (LTE), advanced (LTE-A)), 5G communication, etc. defined in the 3rd generation partnership project (3GPP) standard. 4G communication can be performed in a frequency band of 6 GHz or less, and 5G communication can be performed not only in a frequency band of 6 GHz or less, but also in a frequency band of 6 GHz or more. For example, for 4G communication and 5G communication, a plurality of communication nodes may be classified into a code division multiple access (CDMA) based communication protocol, a wideband CDMA (WCDMA) based communication protocol, a time division multiple access (TDMA) A communication protocol based on FDMA (frequency division multiple access), a communication protocol based on orthogonal frequency division multiplexing (OFDM), a communication protocol based on Filtered OFDM, a communication protocol based on CP (cyclic prefix) (OFDMA) -based communication protocol, a single carrier (FD) -based communication protocol, NOMA (non-orthogonal multiple access), GFDM (generalized frequency division multiplexing based communication protocol, FBMC (filter bank multi-carrier) based communication protocol, UFMC (universal filtered multi-carrier) based communication protocol, SDMA division multiple access) -based communication protocols. Each of the plurality of communication nodes may have the following structure.

2 is a block diagram showing a first embodiment of a communication node constituting a communication system.

Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to the network to perform communication. The communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, and the like. Each component included in the communication node 200 may be connected by a bus 270 and communicate with each other.

However, each component included in the communication node 200 may not be connected to the common bus 270 but may be connected to the processor 210 via an individual interface or a separate bus. For example, the processor 210 may be coupled to at least one of the memory 220, the transceiver 230, the input interface 240, the output interface 250 and the storage 260 via a dedicated interface .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods in accordance with embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be constituted of at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory 220 may comprise at least one of read-only memory (ROM) and random access memory (RAM).

Referring again to FIG. 1, the communication system 100 includes a plurality of base stations 110-1, 110-2, 110-3, 120-1, 120-2, a plurality of terminals 130- 1, 130-2, 130-3, 130-4, 130-5, and 130-6. The base stations 110-1, 110-2, 110-3, 120-1, and 120-2 and the terminals 130-1, 130-2, 130-3, 130-4, 130-5, The communication system 100 comprising may be referred to as an "access network ". Each of the first base station 110-1, the second base station 110-2 and the third base station 110-3 may form a macro cell. Each of the fourth base station 120-1 and the fifth base station 120-2 may form a small cell. The fourth base station 120-1, the third terminal 130-3 and the fourth terminal 130-4 may belong to the cell coverage of the first base station 110-1. The second terminal 130-2, the fourth terminal 130-4 and the fifth terminal 130-5 may belong to the cell coverage of the second base station 110-2. The fifth base station 120-2, the fourth terminal 130-4, the fifth terminal 130-5 and the sixth terminal 130-6 can belong to the cell coverage of the third base station 110-3 have. The first terminal 130-1 may belong to the cell coverage of the fourth base station 120-1. The sixth terminal 130-6 may belong to the cell coverage of the fifth base station 120-2.

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1 and 120-2 includes a Node B, an evolved Node B, a gNB, an ng-eNB, a BTS a base transceiver station, a radio base station, a radio transceiver, an access point, an access node, a road side unit (RSU), a radio remote head (RRH) transmission point, transmission and reception point (TRP), flexible (TRP), and the like. Each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5 and 130-6 includes a user equipment (UE), a terminal, an access terminal, A subscriber station, a mobile station, a portable subscriber station, a node, a device, an internet of things (IoT), a mobile station, a mobile station, a subscriber station, A device supporting the function, a mounted module / device / terminal, an on board unit (OBU), and the like.

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands, or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1 and 120-2 may be interconnected via an ideal backhaul link or a non-idle backhaul link , An idle backhaul link, or a non-idle backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to the core network via an idle backhaul link or a non-idle backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to the corresponding terminals 130-1, 130-2, 130-3, 130 130-2, 130-3, 130-4, 130-5, and 130-6, and transmits the signals received from the terminals 130-1, 130-2, 130-3, 130-4, Lt; / RTI >

In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 performs MIMO transmission (for example, SU (single user) -MIMO, MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, direct device to device communication (D2D) proximity services). Each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 includes base stations 110-1, 110-2, 110-3, and 120-1 , 120-2, and operations supported by the base stations 110-1, 110-2, 110-3, 120-1, and 120-2. For example, the second base station 110-2 can transmit a signal to the fourth terminal 130-4 based on the SU-MIMO scheme, and the fourth terminal 130-4 can transmit a signal based on the SU-MIMO scheme And may receive a signal from the second base station 110-2. Alternatively, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 and the fifth terminal 130-5 based on the MU-MIMO scheme, the fourth terminal 130-4, And the fifth terminal 130-5 may receive signals from the second base station 110-2 by the MU-MIMO scheme.

Each of the first base station 110-1, the second base station 110-2 and the third base station 110-3 can transmit a signal to the fourth terminal 130-4 based on the CoMP scheme, The terminal 130-4 can receive signals from the first base station 110-1, the second base station 110-2, and the third base station 110-3 by the CoMP method. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 includes terminals 130-1, 130-2, 130-3, 130-4 , 130-5, and 130-6) and the CA scheme. Each of the first base station 110-1, the second base station 110-2 and the third base station 110-3 controls the D2D between the fourth terminal 130-4 and the fifth terminal 130-5 And each of the fourth terminal 130-4 and the fifth terminal 130-5 can perform the D2D under the control of each of the second base station 110-2 and the third base station 110-3 .

Next, a method for solving the problem of combining superposition transmission in a multi-user multiple-input multiple-output (MU-MIMO) transmission is described.

3 is a conceptual diagram showing a second embodiment of the communication system.

Referring to FIG. 3, the communication system may include a base station 300, a terminal-1 310, a terminal-2 320, a terminal-3 330 and a terminal-4 340. The base station 300 may provide communication services to the terminals 310, 320, 330, 340 based on a communication protocol (e.g., 4G communication protocol, 5G communication protocol).

In a communication system using multiple antennas, a closed-loop precoding transmission method or an AMC (adaptive modulation and coding) method may be used to improve a data transmission rate. The closed loop precoding transmission method can adjust the size and phase of multiple antenna channels. By adjusting the size and phase of the multiple antenna channels, the received signal gain of the terminal can be improved. The AMC method can adjust the modulation and coding scheme (MCS) level of data to be transmitted according to the channel quality. By adjusting the MCS level of the data, the reception error rate of the data can be kept low and the data transmission rate can be maximized.

Each of the UEs 310, 320, 330, and 340 may feed back downlink channel state information to the Node B 300 through an uplink control channel. The base station 300 may receive channel status information from each of the terminals 310, 320, 330, and 340. The base station 300 may determine the closed loop precoding transmission method and the AMC method based on the feedback channel state information.

In the 3 ^rd generation partnership project (3GPP) LTE system, a single carrier-frequency division multiple access (SC-FDMA) based uplink defines a subframe as a basic transmission unit. The subframe may be composed of 14 SC-FDMA symbols and a plurality of RBs (resource blocks). One RB may be composed of 12 subcarriers. RB may be a basic unit of scheduling.

The uplink control channel includes an acknowledgment / negative acknowledgment ACK / NACK for hybrid automatic repeat request (HARQ) operation, a rank indicator (RI) for channel downlink precoding and AMC, a precoding matrix indicator (PMI) Channel quality indication (CQI) information, and the like. For example, an LTE system using four transmit antennas may use a codebook as shown in Table 1 for feedback of PMI information.

The UEs 310, 320, 330, and 340 may transmit channel state information to the base station 300 through the uplink control channel at predetermined predetermined periods. Alternatively, the UEs 310, 320, 330, and 340 may periodically transmit channel state information to the Node B 300 using the uplink data channel allocated according to the request of the Node B.

In a downlink based on an orthogonal frequency division multiplexing (OFDM) of a 3GPP LTE system, downlink overlay transmission can be used to improve an additional data rate. The DL-DL transmission scheme is used to transmit a DL-DL transmission scheme to a terminal (for example, terminal-2 320 or terminal-4 320) (340), and transmits the signal. The DL link transmission may be a non-orthogonal transmission scheme that non-uniformly allocates the transmission power to the two terminals (e.g., the UE-1 310 and the UE-2 320) in the same time and frequency resources. When a signal to be transmitted to a nearby terminal (for example, the terminal-1 310) is s1 and a signal to be transmitted to a remote terminal (for example, the terminal-2 320) is s2, The signal may be equal to Equation (1).

In Equation (1), x may be a superposition coding signal, and a1 and a2 may be transmission power allocation coefficients for the s1 signal and the s2 signal. The superposition coding signals received at the terminal-1 310 and the terminal-2 320 may be as shown in Equations (2) and (3), respectively.

In Equation (2), y1 may be a received signal of the UE-1 310 and h1 may indicate a channel condition between the BS 300 and the UE-1. n1 may be a noise signal of the UE-1 (310). In Equation (3), y2 may be a received signal of the terminal-2 320, and h2 may indicate a channel state between the base station 300 and the terminal-2. n2 may be a noise signal of the terminal-2 (320).

The channel quality of the terminal-1 310 close to the base station 300 may be better than the channel quality of the terminal-2 320 far from the base station 300. Accordingly, each terminal can decode the superposed data assuming that the channel state of the terminal (for example, the terminal-1 310) close to the base station 300 is excellent.

(i.e., the channel state between the base station 300 and the terminal-1 310 is better than the channel state between the base station 300 and the terminal-2 320), the transmission power allocation coefficient May be a1 <a2. That is, the base station 300 may allocate a relatively large power to a terminal having a relatively poor channel state (for example, the terminal-2 320) in order to maintain the reliability of a transmission signal.

를 제거할 수 있다. 이 후 단말-1(310)은 s1을 디코딩할 수 있다. 반면, 단말-2(320)는 신호 s1을 제거하지 않고, 신호 s2를 바로 디코딩할 수 있다. 여기서 단말-1(310)의 데이터 신호 성분인

은 잡음으로 처리될 수 있다.When the received signal y1 is received from the base station 300, the terminal-1 310 can obtain the s2 signal by decoding the received signal y1 using the information of h1 and a2. After acquiring the s2 signal from y1, the terminal-1 310 uses the successive interference cancellation (SIC)

Can be removed. After this, the terminal-1 310 can decode s1. On the other hand, the terminal-2 320 can directly decode the signal s2 without removing the signal s1. Here, the data signal component of the terminal-1 (310)

Can be treated as noise.

In order to improve the downlink data rate, the MU-MIMO transmission scheme and the superposition transmission scheme can be used together. The base station 300 can form a plurality of beams to a plurality of terminals 310, 320, 330, and 340 through the MU-MIMO transmission scheme. A plurality of beams can be formed by using different precoding for each of a plurality of terminals. The base station 300 can transmit data to a plurality of terminals 310, 320, 330, and 340 at the same time and frequency resources using a plurality of beams.

The base station 300 may apply overlay transmission to each beam formed using MU-MIMO. For example, the base station 300 may transmit data to the terminal-1 310 and the terminal-2 320 simultaneously by applying superposition transmission to the first beam and may apply the superposition transmission to the second beam, (330) and the terminal-4 (340). The base station 300 can transmit data to more terminals at the same time and frequency resources by applying overlap transmission to multiple beams, respectively.

However, if the orthogonality between the precoded channels of each of the terminals is small, mutual interference between the beams becomes large, which may lead to a decrease in data transmission rate. Therefore, it is important to select an appropriate precoding method and an appropriate terminal pair for each terminal. The base station 300 may need additional channel state information for the precoding method and terminal pair selection.

In addition, a terminal (for example, terminal-1 310) closer to the base station 300 in the overlap transmission transmits the data signal (i.e., s2 The decoding of the data signal (i.e., s2) for the terminal-2 320 is successively performed in the terminal-2 320. The decoding of the data signal (i.e., s2) 1 &lt; / RTI &gt; 310 (i.e., s1). Therefore, if the terminal-1 310 nearest the base station 300 transmits only ACK / NACK for transmission of its data (i.e., s1), data transmission can be performed inefficiently. That is, when the terminal-1 310 has not successfully received the data signal (i.e., s2) for the terminal-2 320, the terminal-1 310 has not received the data signal The UE-1 310 transmits only NACK to the BS 300, so that the BS 300 fails to receive the signal s2 from the UE-1 310 and the signal s1 It can not be known that the reception of the packet has failed. Therefore, desirable feedback may be difficult to perform. Therefore, the base station 300 may need ACK / NACK information for the reception of the data signal (i.e., s2) for the UE-2 320 from the UE-1.

Next, a method in which the base station 300 transmits and receives additional PMI information to the UEs 310, 320, 330, and 340 to resolve inter-beam interference is described.

In a communication system using multiple antennas, a closed loop precoding scheme can be used to support downlink MU-MIMO. Closed-loop precoding can be performed based on control information (RI, PMI, CQI) transmitted from the UEs 310, 320, 330, and 340 in the base station 300. Each of the terminals 310, 320, 330, and 340 can select the RI and the PMI to be transmitted from among the predefined codebooks as shown in Table 1. Each of the terminals 310, 320, 330, and 340 can select RI and PMI that maximize the beamforming gain. The base station 300 transmits a terminal-specific precoding vector (or a matrix) for MU-MIMO transmission based on control information (i.e., RI, PMI, CQI) received from a plurality of terminals 310, 320, Can be determined. The base station 300 may obtain a total data rate for each terminal pair based on the precoding vector (or matrix) of each terminal. The base station 300 can select a pair of terminals that maximizes the total data rate.

The transmission signal when superposition transmission is applied to the MU-MIMO transmission is expressed by Equation (4).

과

는 각각 MU-MIMO에서 형성된 제1 빔 및 제2 빔에 대한 N-by-1 프리코딩 벡터를 의미할 수 있다. 즉, 수학식 4의 송신 신호 X는 도 3에서 기지국(300)이 제1 빔을 통해 단말-1(310) 및 단말-2(320)에게 데이터를 전송함과 동시에 제2 빔을 통해 단말-3(330) 및 단말-4(340)에게 데이터를 전송하는 신호일 수 있다.It is assumed that the number of transmission antennas of the base station 300 is N and the number of layers is one for each terminal. In Equation (4), X may be an N-by-1 MU-MIMO and a superposition coding signal matrix. a1, a2, a3 and a4 are the transmission powers of the data signals s1, s2, s3 and s4 of the terminal-1 (310), terminal-2 (320), terminal- Lt; / RTI &gt;

and

May be an N-by-1 precoding vector for the first beam and the second beam formed in the MU-MIMO, respectively. 3, the base station 300 transmits data to the terminal-1 310 and the terminal-2 320 through the first beam and simultaneously transmits the terminal- 3 (330) and the terminal-4 (340).

When a combination of MU-MIMO transmission and superposition transmission is used, the data transmission rate can be increased. However, MU-MIMO transmission and superposition transmission can be performed when the inter-beam interference is small. (For example, when transmitting a superposition signal of the terminal-1 310 and the terminal-2 320 through the first beam), the superposition signal of the two terminals having different channels in one beam is transmitted The UE may experience more severe beam-to-interference than a normal MU-MIMO transmission.

The base station 300 can select one RI and one PMI for each terminal. Since the PMI that can be selected by the base station 300 is limited, the interference at the terminals 310, 320, 330, and 340 may become worse. Therefore, the base station 300 may require additional PMI feedback from each terminal to reduce inter-beam interference.

In this embodiment, each of the terminals 310, 320, 330, and 340 may provide additional PMI feedback without providing only one PMI that provides the maximum beamforming gain. Each of the UEs 310, 320, 330, and 340 may provide a PMI that provides a maximum beamforming gain as well as a PMI that provides a second or third largest beamforming gain. The BS 300 can increase the degree of freedom when selecting the precoding vector for each UE through a plurality of PMI feedbacks. Therefore, the base station 300 can select a precoding vector that can reduce inter-beam interference between the terminals. In addition, since the candidate group of the terminal pair receiving the overlap signal in each beam can be extended, the number of cases in which the base station 300 selects a terminal pair capable of increasing the data rate can be increased.

There are two methods for transmitting and receiving additional PMI information between the base station 300 and each of the terminals 310, 320, 330, and 340. There may be a method in which each of the UEs 310, 320, 330, and 340 periodically feedback PMI information to the base station 300 and periodically feedbacks the PMI information. Next, a method of transmitting and receiving a PMI through an aperiodic feedback method of a UE will be described.

4 is a flowchart showing a first embodiment of a PMI transmission / reception method between a base station and terminals.

4, the communication system may include a base station 300, a terminal-1 310, a terminal-2 (not shown), a terminal-3 (not shown), and a terminal-4 (not shown). (Not shown), a terminal-3 (not shown), a terminal-2 (not shown), and a terminal-2 (not shown) based on a communication protocol (e.g., 4G communication protocol, -4 (not shown)). The base station 300 of FIG. 4 may be the base station 300 of FIG. 3, and the terminal-1 310 of FIG. 4 may be the terminal-1 310 of FIG.

The base station 300 may request the UE-1 310 to feedback one or a plurality of PMI information through a downlink control channel (S400). That is, the base station 300 may transmit a PMI feedback request message to the UE- The PMI feedback request message transmitted from the base station 300 to the UE-1 310 through the downlink control channel may include information on the number of additional PMIs requested. For example, the PMI feedback request message may include a field indicating the number of PMIs requesting, and the field may indicate 2 if the number of additional PMIs requesting is two. The manner in which the PMI feedback request message includes the additional information of the number of PMIs is not limited to the above embodiment but can be done by other methods.

The UE-1 310 may receive a PMI feedback request message from the BS 300. [ The UE-1 310 can confirm the number of additional PMIs requested by the BS 300 included in the received PMI feedback request message. The UE-1 310 may select PMI as much as the number of PMIs requested by the base station 300 in order of increasing beamforming gain (S401). For example, when the number of additional PMIs requested by the base station 300 is two, the UE-1 310 not only has a first-order PMI that provides the maximum beam-forming gain but also a second- PMI, and third-order PMI with a large beam-forming gain.

The UE-1 310 may transmit a PMI feedback message including the selected PMI information to the base station 300 (S402). The base station 300 can receive the PMI feedback message from the UE-1 310 and confirm the PMI information included in the PMI feedback message.

The base station 300 can request a desired number of PMI information and receive a desired number of PMI information at a desired time. That is, PMI transmission / reception can be performed non-periodically in this embodiment. Since the base station 300 can receive feedback of a plurality of PMIs, it may be advantageous in selecting a per-terminal precoding vector. Also, since the candidate group of the terminal pair receiving the superposed signal is extended, it can be advantageous in selecting the terminal pair.

Only the PMI transmission and reception method performed between the base station 300 and the UE-1 310 is described, but the PMI transmission and reception is performed between the base station 300 and other UEs (i.e., UE-2 (not shown) ) And terminal-4 (not shown)). Next, a method of transmitting and receiving a PMI through a periodic feedback method of a UE will be described.

5 is a flowchart showing a second embodiment of a PMI transmission / reception method between a base station and terminals.

5, the communication system may include a base station 300, a terminal-1 310, a terminal-2 (not shown), a terminal-3 (not shown), and a terminal-4 (not shown). (Not shown), a terminal-3 (not shown), a terminal-2 (not shown), and a terminal-2 (not shown) based on a communication protocol (e.g., 4G communication protocol, -4 (not shown)). The base station 300 of FIG. 5 may be the base station 300 of FIG. 3 and the terminal-1 310 of FIG. 5 may be the terminal-1 310 of FIG. The communication system of Fig. 5 may be the same or similar to the communication system of Fig.

The UE-1 310 may periodically transmit one PMI information to the BS 300 through the uplink control channel without a request from the BS 300 (S500). At this time, the period of time in which the UE-1 310 transmits the PMI information to the base station 300 can be determined by the base station 300. The base station 300 may request the UE-1 310 with a desired PMI through a downlink control channel or higher signaling. The order of the PMI can be determined by how large the beamforming gain a particular PMI provides. If the base station 300 does not request a particular order of PMI, the UE-1 310 may send PMI information providing the largest beamforming gain to the base station 300. That is, in step S500, the UE-1 310 may transmit to the base station 300 a primary PMI that provides the largest beamforming gain. The base station 300 may receive the first order PMI information from the UE-

When the base station 300 desires second rank PMI information, the base station 300 may transmit a message requesting the second rank PMI to the UE-1 310 (S501). The UE-1 310 may receive a message requesting a secondary PMI. The UE-1 310 may periodically transmit a PMI message including one PMI information to the base station 300. If the UE-1 310 receives a second PMI request message from the BS 300 before one period (i.e., one period) elapses after the UE-1 310 transmits the previous PMI message, the UE- The second PMI can be transmitted to the base station 300 in the next transmission period (S502). The base station 300 may receive second order PMI information from the UE-

When the base station 300 desires the third rank PMI information, the base station 300 may transmit a message requesting the third rank PMI to the terminal-1 310 (S503). The UE-1 310 may receive a message requesting a third rank PMI. When the UE-1 310 receives a message requesting the third highest PMI from the BS 300 before one period (i.e., two periods) elapses after the UE-1 310 transmits the previous PMI message, the UE- It may transmit the third order PMI to the base station 300 in the next transmission period (S504). The base station 300 may receive the third order PMI information from the UE-1 310. [

Since the channel status is continuously changing, the base station 300 may need the first order PMI information again. When the base station 300 desires the first rank PMI information, the base station 300 may transmit a message requesting the first rank PMI to the terminal-1 310 (S505). The UE-1 310 may receive a message requesting a primary PMI. If the UE-1 310 receives a first PMI request message from the BS 300 before one period (i.e., three periods) elapses after the UE-1 310 transmits the previous PMI message, the UE- It may transmit the first-order PMI to the base station 300 in the next transmission period (S506). The base station 300 may receive the first order PMI information from the UE-

Since the base station 300 can receive feedback of a plurality of PMIs by receiving PMI messages several times, it can be advantageous in selecting a per-terminal precoding vector. Also, since the candidate group of the terminal pair receiving the superposed signal is extended, it can be advantageous in selecting the terminal pair.

Only the PMI transmission and reception method performed between the base station 300 and the UE-1 310 is described, but the PMI transmission and reception is performed between the base station 300 and other UEs (i.e., UE-2 (not shown) ) And terminal-4 (not shown)). Next, a method of transmitting ACK / NACK information for data of the other terminal to the base station in the overlapping transmission is described.

6 is a flowchart illustrating a method of transmitting / receiving ACK / NACK information between a Node B and UEs according to a first embodiment of the present invention.

6, the communication system may include a base station 300, a terminal-1 310, a terminal-2 320, a terminal-3 (not shown), and a terminal-4 (not shown). The base station 300 is connected to the terminals (terminal-1 310, terminal-2 320, terminal-3 (not shown) and terminal- 4 (not shown)). 3 may be the base station 300 of FIG. 3, the terminal-1 310 of FIG. 6 may be the terminal-1 310 of FIG. 3, May be the terminal-2 320 of FIG.

When the UE-1 310 and the UE-2 320 are connected to the BS 300 in the communication system, the BS 300 transmits the CSI-RS (channel state information) through the downlink sub- reference signal. Each of the UE-1 310 and the UE-2 320 can receive the CSI-RS from the base station 300 and perform a channel measurement operation based on the received CSI-RS. Here, the channel between the base station 300 and the terminal-1 310 may be referred to as a "first channel" and the channel between the base station 300 and the terminal-2 320 may be referred to as a " have. The terminal-1 310 may transmit the measurement information (e.g., CSI) of the first channel to the base station 300 and the terminal-2 320 may transmit the measurement information (e.g., CSI) To the base station (300).

The base station 300 may receive the measurement information of the first channel from the terminal-1 310 and the measurement information of the second channel from the terminal- Alternatively, the base station 300 may acquire the measurement information of the first channel by performing channel measurement operation based on the SRS (sounding reference signal) received from the terminal-1 310, And the measurement information of the second channel can be obtained by performing the channel measurement operation based on the received SRS.

AMC technology and scheduling technology can be used to improve the data rate of the data unit in the communication system. When the AMC technique is used, the base station 300 may adjust the MCS level according to channel conditions between the base station 300 and the terminals 310 and 320 to maintain a target reception error rate. For example, if the channel condition is bad, the base station 300 may lower the MCS level so that the actual reception error rate is reduced to the target reception error rate at the terminals 310 and 320. [ If the channel condition is good, the base station 300 may increase the MCS level so that the actual reception error rate is increased to the target reception error rate at the terminals 310 and 320. [ Thus, when the AMC technique is used, the actual reception error rate at the terminal can be maintained at the target reception error rate through adjustment of the MCS level, and the maximum transmission rate of the data signal can be provided while the actual reception error rate is maintained at the target reception error rate .

When a scheduling technique is used, the BS 300 may selectively allocate resources (e.g., time and frequency resources) to the MS in consideration of channel conditions, service quality, and the like of the MSs 310 and 320. Here, the scheduling technique may be a greedy algorithm-based scheduling technique, a PF (proportional fairness) scheduling technique, or the like.

When AMC technology, scheduling technology, or the like is used in the communication system, the base station 300 transmits AMC information of the UEs 310 and 320 (for example, MCS information for the UE-1 310 and UE- ) And scheduling information (e.g., time and frequency resource information allocated to the UE) to the UE through the control channel of the DL subframe. The AMC information, the scheduling information, and the like may be transmitted through the downlink control information (DCI), and the DCI format may include the information elements described in Table 2 below.

The base station 300 may set a DCI including parameters necessary for the overlay transmission (S600). The superposition transmission parameters may include at least one of the resource allocation information, the MCS information for the UE-1 310, the MCS information for the UE-2 320, and the information indicating the transmission power allocation factor.

The DCI may include information indicating transmission power allocation coefficients (a1, a2). a1 and a2 May be "a1 + a2 = 1 &quot;, so that the DCI may include information indicating one of a1 or a2. In this case, a separate DCI including information indicating the transmission power allocation coefficients a1 and a2 is not generated, and transmission power allocation coefficients a1 and a2 (for example, DC1 shown in Table 2) ) May be further included. Alternatively, the DCI size may vary depending on the number of bits of information indicating the transmit power allocation coefficient.

The base station 300 may transmit control information (e.g., DCI) including overlap transmission parameters to the terminal-1 310 and the terminal-2 320 (S601). The UE-1 310 and the UE-2 320 can receive control information (e.g., DCI) from the base station 300 and receive resource allocation information from the received signal, MCS information, MCS information for the terminal-2 320, and transmission power allocation coefficients a1 and a2. a1 and a2 may be transmission power allocation coefficients for the s1 signal and the s2 signal, respectively. When the channel state between the BS 300 and the UE-1 310 is different from the channel state between the BS 300 and the UE-2 320, the transmission power allocation coefficients a1 and a2 included in the DCI may be different from each other have.

When the data signal s1 to be transmitted to the UE-1 310 and the data signal s2 to be transmitted to the UE-2 320 are present in the BS 300, the BS 300 transmits the same resources (for example, Resources) can be used to transmit the data signal s1 and the data signal s2 (S602).

Each of the terminal-1 310 and the terminal-2 320 can acquire the data signal s1 and the data signal s2 from the base station 300 based on parameters necessary for superposition transmission. The superposition coding signals received at the terminal-1 310 and the terminal-2 320 may be as shown in Equations (2) and (3), respectively. In Equation (2), y1 may be a received signal of the UE-1 310 and h1 may indicate a channel condition between the BS 300 and the UE-1. n1 may be a noise signal of the UE-1 (310). In Equation (3), y2 may be a received signal of the terminal-2 320, and h2 may indicate a channel state between the base station 300 and the terminal-2. n2 may be a noise signal of the terminal-2 (320).

The channel quality of the terminal-1 310 close to the base station 300 may be better than the channel quality of the terminal-2 320 far from the base station 300. (i.e., the channel state between the base station 300 and the terminal-1 310 is better than the channel state between the base station 300 and the terminal-2 320), the transmission power allocation coefficient May be a1 <a2. That is, the base station 300 may allocate a relatively large power to a terminal having a relatively poor channel state (for example, the terminal-2 320) in order to maintain the reliability of a transmission signal.

를 제거할 수 있다.When the received signal y1 is received from the base station 300, the terminal-1 310 acquires the s2 signal by decoding the received signal y1 using the information of h1 and a2 and the MCS information of the terminal- . After acquiring the s2 signal from y1, the terminal-1 310 uses the successive interference cancellation (SIC)

Can be removed.

The base station 300 may request the transmission of the HARQ response (S603) whether the UE-1 310 receives the superposition coding signal and has successfully decoded the data signal s2 included in the superposition coding signal. That is, the base station 300 may transmit a request message to the terminal-1 310 to feedback ACK / NACK information on the data signal (i.e., s2) for the terminal-2 320. [ The HARQ response request message for the data signal of the other terminal (i.e., the terminal-2 320) may include an HARQ response request indicator (e.g., 1 bit) for the data signal of the other terminal. The UE-1 310 may receive an HARQ response request message for the other UE data signal (i.e., s2). When there is an ACK / NACK information feedback request (i.e., an HARQ response request) for the other terminal data signal, the terminal-1 310 transmits ACK / NACK information for its own data signal s1 and the ACK / (ACK / NACK information) for the data signal s2 to the base station 300 through the uplink data channel allocated by the base station 300 (S604). Alternatively, if there is an HARQ response request for another terminal data signal, the UE-1 310 may transmit ACK / NACK information for s1 and ACK / NACK information for s2 to the base station 300 separately. The UE-1 310 transmits only the ACK / NACK information for its own data signal (i.e., s1) to the Node B 300 when the UE-310 does not receive the HARQ response request message for the UE data signal from the Node B 300 .

The base station 300 may request and receive an HARQ response to the data signal of the other terminal (i.e., the terminal-2 320) to the terminal-1 310 when desired. That is, ACK / NACK transmission / reception of data signals of other terminals in the present disclosure can be performed non-periodically.

Only the ACK / NACK transmission / reception method performed between the base station 300 and the first terminal pair (i.e., the terminal-1 310 and the terminal-2 320) (I.e., the terminal-3 330 and the terminal-4 340). Next, a method of transmitting and receiving ACK / NACK information for a data signal of the other terminal periodically between the Node B and the UE will be described.

7 is a flowchart illustrating a method of transmitting / receiving ACK / NACK information between a Node B and UEs according to a second embodiment of the present invention.

Referring to FIG. 7, the communication system may include a base station 300, a terminal-1 310, a terminal-2 320, a terminal-3 (not shown) and a terminal-4 (not shown). The base station 300 is connected to the terminals (terminal-1 310, terminal-2 320, terminal-3 (not shown) and terminal- 4 (not shown)). 3 may be the base station 300 of FIG. 3, the terminal-1 310 of FIG. 7 may be the terminal-1 310 of FIG. 3, May be the terminal-2 320 of FIG. The communication system of Fig. 7 may be the same as or similar to the communication system of Fig.

When the terminal-1 310 and the terminal-2 320 are connected to the base station 300 in the communication system, the base station 300 can transmit the CSI-RS through the downlink subframe according to a predetermined period. Each of the UE-1 310 and the UE-2 320 can receive the CSI-RS from the base station 300 and perform a channel measurement operation based on the received CSI-RS. Here, the channel between the base station 300 and the terminal-1 310 may be referred to as a "first channel" and the channel between the base station 300 and the terminal-2 320 may be referred to as a " have. The terminal-1 310 may transmit the measurement information (e.g., CSI) of the first channel to the base station 300 and the terminal-2 320 may transmit the measurement information (e.g., CSI) To the base station (300).

The base station 300 may receive the measurement information of the first channel from the terminal-1 310 and the measurement information of the second channel from the terminal- Alternatively, the base station 300 may acquire the measurement information of the first channel by performing channel measurement operation based on the SRS (sounding reference signal) received from the terminal-1 310, And the measurement information of the second channel can be obtained by performing the channel measurement operation based on the received SRS.

The base station 300 may set a DCI including parameters necessary for superposition transmission (S700). The superposition transmission parameters may include at least one of the resource allocation information, the MCS information for the UE-1 310, the MCS information for the UE-2 320, and the information indicating the transmission power allocation factor.

The DCI may include information indicating transmission power allocation coefficients (a1, a2). a1 and a2 May be "a1 + a2 = 1 &quot;, so that the DCI may include information indicating one of a1 or a2. In this case, a separate DCI including information indicating the transmission power allocation coefficients a1 and a2 is not generated, and transmission power allocation coefficients a1 and a2 (for example, DCI shown in Table 2) ) May be further included. Alternatively, the DCI size may vary depending on the number of bits of information indicating the transmit power allocation coefficient.

The base station 300 may transmit control information (e.g., DCI) including overlap transmission parameters to the terminal-1 310 and the terminal-2 320 (S701). The UE-1 310 and the UE-2 320 can receive control information (e.g., DCI) from the base station 300 and receive resource allocation information from the received signal, MCS information, MCS information for the terminal-2 320, and transmission power allocation coefficients a1 and a2. a1 and a2 may be transmission power allocation coefficients for the s1 signal and the s2 signal, respectively. When the channel state between the BS 300 and the UE-1 310 is different from the channel state between the BS 300 and the UE-2 320, the transmission power allocation coefficients a1 and a2 included in the DCI may be different from each other have.

When the data signal s1 to be transmitted to the UE-1 310 and the data signal s2 to be transmitted to the UE-2 320 are present in the BS 300, the BS 300 transmits the same resources (for example, Resources) to transmit the data signal s1 and the data signal s2 (S702).

Each of the terminal-1 310 and the terminal-2 320 can acquire the data signal s1 and the data signal s2 from the base station 300 based on parameters necessary for superposition transmission. The superposition coding signals received at the terminal-1 310 and the terminal-2 320 may be as shown in Equations (2) and (3), respectively. In Equation (2), y1 may be a received signal of the UE-1 310 and h1 may indicate a channel condition between the BS 300 and the UE-1. n1 may be a noise signal of the UE-1 (310). In Equation (3), y2 may be a received signal of the terminal-2 320, and h2 may indicate a channel state between the base station 300 and the terminal-2. n2 may be a noise signal of the terminal-2 (320).

The channel quality of the terminal-1 310 close to the base station 300 may be better than the channel quality of the terminal-2 320 far from the base station 300. (i.e., the channel state between the base station 300 and the terminal-1 310 is better than the channel state between the base station 300 and the terminal-2 320), the transmission power allocation coefficient May be a1 <a2. That is, the base station 300 may allocate a relatively large power to a terminal having a relatively poor channel state (for example, the terminal-2 320) in order to maintain the reliability of a transmission signal.

를 제거할 수 있다.When the received signal y1 is received from the base station 300, the terminal-1 310 acquires the s2 signal by decoding the received signal y1 using the information of h1 and a2 and the MCS information of the terminal- . After acquiring the s2 signal from y1, the terminal-1 310 uses the successive interference cancellation (SIC)

Can be removed.

The UE-1 310 may transmit ACK / NACK information for its own data signal (i.e., s1) to the base station 300 through the uplink control channel (S703). The UE-1 310 may periodically transmit ACK / NACK information to the Node B 300 and the period of transmission may be determined by the Node B 300.

The base station 300 may receive ACK / NACK information for the data signal (i.e., s1) of the UE-1 310 from the UE-1 310. [ The base station 300 may request the transmission of the HARQ response (S704) whether the UE-1 310 receives the superposition coding signal and has successfully decoded the data signal s2 included in the superposition coding signal. That is, the base station 300 can transmit a message requesting the ACK / NACK information for the data signal (i.e., s2) of the other terminal (i.e., the terminal-2 320) A message for requesting an HARQ response to a data signal of another terminal may include an indicator for requesting an HARQ response to the data signal of the other terminal (for example, 1 bit). The UE-1 310 may receive an HARQ response request message for a data signal of the other UE.

When the UE-1 310 receives a HARQ response request message for other UE data from the Node B 300 before one UE cycle (i.e., one period) elapses after transmitting the previous ACK / NACK feedback message, The UE-1 310 transmits ACK / NACK information for its own data signal s1 and ACK / NACK information for the data signal s2 to the other terminal (i.e., the UE-2 320) 300 to the base station 300 through the uplink data channel (S705). The base station 300 may receive ACK / NACK information for s1 and ACK / NACK information for s2 from the UE-1 310. [

The UE-1 310 receives a message requesting ACK / NACK information for other UE data from the Node B 300 before one period (i.e., two periods) elapses after transmitting the previous ACK / NACK feedback message , It can transmit only ACK / NACK information for its own data signal s1 to the base station 300 (S706).

The methods according to the present invention can be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the computer readable medium may be those specially designed and constructed for the present invention or may be available to those skilled in the computer software.

Examples of computer readable media include hardware devices that are specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (1)

A method of operating a first terminal in a communication system including a base station, a first terminal and a second terminal,
Receiving DCI (downlink control information) including resource allocation information, modulation and coding scheme (MCS) information, and transmission power allocation information from the base station;
Receiving a superposition signal including a first data signal of the first terminal and a second data signal of the second terminal from the base station through time-frequency resources indicated by the resource allocation information;
Receiving a first message requesting transmission of a hybrid automatic repeat request (HARQ) response for the second data signal from the base station;
The second data signal included in the superposition signal is decoded based on the MCS for the second terminal indicated by the MCS information and the transmission power for the second terminal indicated by the transmission power allocation information ; And
And transmitting the HARQ response as a decoding result of the second data signal to the base station in response to the first message.

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