KR101241916B1 - A method for transmitting downlink reference signal in multi-carrier supporting wireless communication system and an apparatus for the same - Google Patents

Abstract

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting a downlink reference signal in a wireless communication system supporting multiple antennas. In a method for transmitting channel state information-reference signal (CSI-RS) for 8 or less antenna ports according to an embodiment of the present invention, a plurality of CSI-RS resource element groups defined on a data region of a downlink subframe Selecting one from among the CSI-RSs for the 8 or less antenna ports, and transmitting the downlink subframe to which the CSI-RSs for the 8 or less antenna ports are mapped; The plurality of CSI-RS resource element groups may be defined such that transmission diversity resource element pairs for data transmitted on the downlink subframe are not compromised.

Description

Method and apparatus for transmitting a downlink reference signal in a wireless communication system supporting multiple antennas {A METHOD FOR TRANSMITTING DOWNLINK REFERENCE SIGNAL IN MULTI-CARRIER SUPPORTING WIRELESS COMMUNICATION SYSTEM AND AN APPARATUS FOR THE SAME}

The following description relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting a downlink reference signal in a wireless communication system supporting multiple antennas.

A multiple input multiple output (MIMO) system refers to a system that improves transmission and reception efficiency of data using multiple transmission antennas and multiple reception antennas. MIMO technology includes a spatial diversity technique and a spatial multiplexing technique. The spatial diversity scheme can increase transmission reliability or widen a cell radius through diversity gain, which is suitable for data transmission for a mobile terminal moving at high speed. Spatial multiplexing can increase the data rate without increasing the bandwidth of the system by simultaneously transmitting different data.

In a MIMO system, each transmit antenna has an independent data channel. The transmit antenna may refer to a virtual antenna or a physical antenna. The receiver estimates a channel for each of the transmit antennas and receives data transmitted from each transmit antenna. Channel estimation is a process of recovering a received signal by compensating for distortion of a signal caused by fading. Here, fading refers to a phenomenon in which the strength of a signal is rapidly changed due to multipath-time delay in a wireless communication system environment. For channel estimation, a reference signal known to both the transmitter and the receiver is required. The reference signal may also be referred to simply as a reference signal (RS) or as a pilot according to the applicable standard.

The downlink reference signal is a coherent signal such as a Physical Downlink Shared CHannel (PDSCH), a Physical Control Format Indicator CHannel (PCFICH), a Physical Hybrid Indicator CHannel (PHICH), and a Physical Downlink Control Channel (PDCCH) It is the pilot signal for demodulation. The DL reference signal includes a Common Reference Signal (CRS) shared by all UEs in a cell and a Dedicated Reference Signal (DRS) dedicated to a specific UE. The common reference signal may also be referred to as a cell-specific reference signal. The dedicated reference signal may also be called a UE-specific reference signal or a demodulation reference signal (DMRS).

LTE-based systems with extended antenna configurations (e.g., LTE-supporting 8 transmit antennas) compared to conventional communication systems supporting 4 transmit antennas (e.g., according to the LTE release 8 or 9 standard). In the system according to A standard, DMRS-based data demodulation is considered to support efficient reference signal operation and advanced transmission scheme. That is, DMRSs for two or more layers may be defined to support data transmission through an extended antenna. Since the DMRS is precoded by the same precoder as the data, channel information for demodulating data at the receiving side can be easily estimated without additional precoding information.

On the other hand, while the downlink receiving side can obtain precoded channel information for the extended antenna configuration through DMRS, a separate reference signal other than DMRS is required to acquire uncoded channel information. Accordingly, in the system according to the LTE-A standard, a reference signal for acquiring channel state information (CSI) may be defined at the receiving side, that is, the CSI-RS.

The present invention provides a method and apparatus for transmitting a CSI-RS on a downlink resource element (RE) to efficiently perform channel estimation in a downlink receiving side in MIMO transmission. .

In order to solve the above technical problem, a method of transmitting channel state information-reference signal (CSI-RS) for 8 or less antenna ports according to an embodiment of the present invention is defined on a data region of a downlink subframe. Selecting one of a plurality of CSI-RS resource element groups to map CSI-RSs for the 8 or less antenna ports, and performing the downlink subframe to which the CSI-RSs for the 8 or less antenna ports are mapped; And transmitting, wherein the plurality of CSI-RS resource element groups may be defined so that transmission diversity resource element pairs for data transmitted on the downlink subframe are not compromised.

In addition, the downlink subframe has a general Cyclic Prefix (CP) configuration, and a plurality of CSI-RS resource element groups to which CSI-RSs for eight antenna ports are mapped are defined as five groups in one resource block. One CSI-RS resource element group includes two contiguous sequences of two consecutive Orthogonal Frequency Division Multiplexing (OFDM) symbols on resource elements on which a common reference signal (CRS) and a demodulation reference signal (DMRS) are not arranged. The subcarrier position may be defined in two subcarrier positions spaced apart from the two consecutive subcarrier positions by four subcarriers.

In addition, the plurality of CSI-RS resource element groups to which the CSI-RSs are mapped to the two antenna ports or the plurality of CSI-RS resource element groups to which the CSI-RSs are mapped to the four antenna ports are respectively represented by the eight antennas. It may be defined as a subset of a plurality of CSI-RS resource element groups to which CSI-RSs for ports are mapped.

In addition, five CSI-RS resource element groups to which the CSI-RSs for the eight antenna ports are mapped in the one resource block are the third, fourth, ninth, and ten in the sixth and seventh OFDM symbols. First CSI-RS resource element group of the first subcarrier position, second CSI-RS resource element group of the 1st, 2nd, 7th and 8th subcarrier positions, 10th and 11th OFDM in the 10th and 11th OFDM symbols 3rd CSI-RS resource element group of 3rd, 4th, 9th and 10th subcarrier positions in the symbol, 4th CSI of 5th, 6th, 11th and 12th subcarrier positions in the 10th and 11th OFDM symbols -RS resource element group and the fifth CSI-RS resource element group of the third, fourth, ninth and tenth subcarrier positions in the 13th and 14th OFDM symbols.

In addition, the plurality of CSI-RS resource element groups may be defined as resource element positions in which one CSI-RS resource element group is shifted in the time and frequency domain with respect to another CSI-RS resource element group.

In addition, the CSI-RS for two antenna ports of the CSI-RS for the 8 or less antenna ports is code division multiplexed (CDM) using an orthogonal code of length 2 over two consecutive OFDM symbols on the same subcarrier. Can be multiplexed.

In addition, in a downlink subframe different from the downlink subframe, one or more CSI-RS resource element groups other than one CSI-RS resource element group selected from the plurality of CSI-RS resource element groups are equal to or less than 8; CSI-RS for the antenna port can be mapped.

In order to solve the above technical problem, a method of measuring channel information from a channel state information-reference signal (CSI-RS) for an antenna port of 8 or less according to another embodiment of the present invention includes a data region of a downlink subframe. Receiving the downlink subframe in which CSI-RSs for the 8 or less antenna ports are mapped to one CSI-RS resource element group selected from a plurality of CSI-RS resource element groups defined above; And measuring channel information for each antenna port using the CSI-RS for the antenna port of the plurality of CSI-RS resource element groups for data transmitted on the downlink subframe. The transmission diversity resource element pair may be defined so as not to be damaged.

In addition, the downlink subframe has a general Cyclic Prefix (CP) configuration, and a plurality of CSI-RS resource element groups to which CSI-RSs for eight antenna ports are mapped are defined as five groups in one resource block. One CSI-RS resource element group includes two contiguous sequences of two consecutive Orthogonal Frequency Division Multiplexing (OFDM) symbols on resource elements on which a common reference signal (CRS) and a demodulation reference signal (DMRS) are not arranged. The subcarrier position may be defined in two subcarrier positions spaced apart from the two consecutive subcarrier positions by four subcarriers.

In addition, the plurality of CSI-RS resource element groups to which the CSI-RSs are mapped to the two antenna ports or the plurality of CSI-RS resource element groups to which the CSI-RSs are mapped to the four antenna ports are respectively represented by the eight antennas. It may be defined as a subset of a plurality of CSI-RS resource element groups to which CSI-RSs for ports are mapped.

In addition, five CSI-RS resource element groups to which the CSI-RSs for the eight antenna ports are mapped in the one resource block are the third, fourth, ninth, and ten in the sixth and seventh OFDM symbols. First CSI-RS resource element group of the first subcarrier position, second CSI-RS resource element group of the 1st, 2nd, 7th and 8th subcarrier positions, 10th and 11th OFDM in the 10th and 11th OFDM symbols 3rd CSI-RS resource element group of 3rd, 4th, 9th and 10th subcarrier positions in the symbol, 4th CSI of 5th, 6th, 11th and 12th subcarrier positions in the 10th and 11th OFDM symbols -RS resource element group and the fifth CSI-RS resource element group of the third, fourth, ninth and tenth subcarrier positions in the 13th and 14th OFDM symbols.

In addition, the plurality of CSI-RS resource element groups may be defined as resource element positions in which one CSI-RS resource element group is shifted in the time and frequency domain with respect to another CSI-RS resource element group.

In addition, the CSI-RS for two antenna ports of the CSI-RS for the 8 or less antenna ports is code division multiplexed (CDM) using an orthogonal code of length 2 over two consecutive OFDM symbols on the same subcarrier. Can be multiplexed.

In addition, in a downlink subframe different from the downlink subframe, one or more CSI-RS resource element groups other than one CSI-RS resource element group selected from the plurality of CSI-RS resource element groups are equal to or less than 8; The CSI-RS for the antenna port can be mapped.

In order to solve the above technical problem, a base station transmitting channel state information-reference signal (CSI-RS) for an antenna port of 8 or less according to another embodiment of the present invention receives a UL signal from a terminal. Module, a transmitting module for transmitting a downlink signal to the terminal, and a processor controlling the base station including the receiving module and the transmitting module, wherein the processor includes a plurality of processors defined on a data region of a downlink subframe; Select one of the CSI-RS resource element groups to map CSI-RSs for the 8 or less antenna ports, and transmit the downlink subframes to which the CSI-RSs for the 8 or less antenna ports are mapped; A module, configured to transmit, wherein the plurality of CSI-RS resource element groups are data transmitted on the downlink subframe For transmit diversity resource element pairs can be defined to prevent damage.

In order to solve the above technical problem, a terminal for measuring channel information from channel state information-reference signal (CSI-RS) for 8 or less antenna ports according to another embodiment of the present invention, the downlink signal from the base station A receiving module for receiving, a transmitting module for transmitting an uplink signal to the base station, and a processor for controlling the terminal including the receiving module and the transmitting module, wherein the processor is configured on a data area of a downlink subframe. Receive, through the receiving module, the downlink subframe in which the CSI-RSs for the 8 or less antenna ports are mapped to one CSI-RS resource element group selected from a plurality of defined CSI-RS resource element groups. And measure channel information for each antenna port using the CSI-RS for the 8 or less antenna ports. It said plurality of CSI-RS resource element group may be defined to avoid damaging the pair transmit diversity resource element for the data sent on the DL subframe.

The foregoing general description and the following detailed description of the invention are exemplary and intended for further explanation of the invention as described in the claims.

According to each embodiment of the present invention as described above, a method and apparatus for multiplexing and transmitting the CSI-RS on the downlink physical resources so that the channel estimation can be efficiently performed at the downlink receiving side. In addition, as many CSI-RS RE group patterns as possible can be provided without compromising the transmission diversity RE pair, thereby providing a method and apparatus for reducing inter-cell interference of CSI-RS transmission while maintaining the efficiency of data transmission.

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

1 is a diagram illustrating a structure of a downlink radio frame.
2 is an exemplary diagram illustrating an example of a resource grid for one downlink slot.
3 is a diagram illustrating a structure of a downlink subframe.
4 is a diagram illustrating the structure of an uplink subframe.
5 is a configuration diagram of a wireless communication system having multiple antennas.
6 is a diagram illustrating a general system structure of SC-FDMA and OFDMA.
7 shows a system structure for an uplink SC-FDMA of an LTE release-8 system.
8 shows a transport frame structure for uplink SC-FDMA in an LTE release-8 system.
9 is a diagram illustrating a data signal mapping relationship for a MIMO system based on SC-FDMA transmission.
FIG. 10 is a diagram illustrating a pattern in which CRSs and DRSs defined in an existing 3GPP LTE system (eg, Release-8) are mapped onto a downlink resource block.
11 shows an example of a DMRS pattern for supporting maximum rank 8 transmission.
12 to 16 illustrate various examples of a CSI-RS RE group.
17 to 19 are diagrams for explaining setting of a CSI-RS RE group in consideration of a transmit diversity RE pair.
20 is a diagram for explaining hopping of a CSI-RS RE group.
21 is a diagram illustrating a function of mapping a virtual CSI-RS group index to a physical CSI-RS group index.
22 and 23 show an example of a CSI-RS RE group in the case of an 8 transmit antenna.
FIG. 24 is a diagram for describing a CSI-RS mapping method in case of an 8 transmit antenna. FIG.
25 and 26 show an example of a CSI-RS RE group in the case of four transmit antennas.
FIG. 27 is a diagram for describing a mapping method of CSI-RS in case of 4 transmission antennas. FIG.
28 and 29 show another example of a CSI-RS RE group in case of a 4 transmit antenna.
30 is a diagram for explaining a mapping method of CSI-RS in the case of 4 transmission antennas.
31 shows another example of a CSI-RS RE group in case of a 4 transmit antenna.
32 and 33 show an example of a CSI-RS RE group in the case of two transmit antennas.
34 shows another example of a CSI-RS RE group in the case of a two transmit antenna.
35 is a flowchart illustrating a CSI-RS transmission method and a channel information acquisition method.
36 is a diagram showing the configuration of a preferred embodiment of a wireless communication system including a base station apparatus and a terminal apparatus according to the present invention.

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

Embodiments of the present invention will be described herein with reference to the relationship between data transmission and reception between a base station and a terminal. Here, the BS has a meaning as a terminal node of a network that directly communicates with the MS. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases.

That is, it is obvious that various operations performed for communication with a terminal in a network composed of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A 'base station (BS)' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point (AP), and the like. The repeater may be replaced by terms such as relay node (RN) and relay station (RS). In addition, the term “terminal” may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), a subscriber station (SS), and the like.

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

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

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

The following techniques 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), and the like. It can be used in various radio access systems. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, the following description focuses on the 3GPP LTE and LTE-A standards, but the technical spirit of the present invention is not limited thereto.

A structure of a downlink radio frame will be described with reference to FIG. 1.

In a cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed on a subframe basis, and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

1 is a diagram illustrating a structure of a type 1 radio frame. A downlink radio frame is composed of 10 subframes, and one subframe is composed of two slots in a time domain. The time it takes for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms. One slot includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. In the 3GPP LTE system, since OFDMA is used in the downlink, an OFDM symbol represents one symbol period. The OFDM symbol may also be referred to as an SC-FDMA symbol or a symbol interval. A resource block (RB) is a resource allocation unit and may include a plurality of consecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may vary depending on the configuration of a cyclic prefix (CP). CP has an extended CP (normal CP) and a normal CP (normal CP). For example, when an OFDM symbol is configured by a general CP, the number of OFDM symbols included in one slot may be seven. When the OFDM symbol is configured by an extended CP, since the length of one OFDM symbol is increased, the number of OFDM symbols included in one slot is smaller than that of the normal CP. In the case of the extended CP, for example, the number of OFDM symbols included in one slot may be six. If the channel condition is unstable, such as when the UE moves at a high speed, an extended CP may be used to further reduce inter-symbol interference.

When a general CP is used, since one slot includes 7 OFDM symbols, one subframe includes 14 OFDM symbols. In this case, the first two or three OFDM symbols of each subframe may be allocated to a physical downlink control channel (PDCCH), and the remaining OFDM symbols may be allocated to a physical downlink shared channel (PDSCH).

The structure of the radio frame is only an example, and the number of subframes included in the radio frame or the number of slots included in the subframe and the number of symbols included in the slot may be variously changed.

2 is an exemplary diagram illustrating an example of a resource grid for one downlink slot. This is the case in which an OFDM symbol consists of a normal CP. Referring to FIG. 2, the downlink slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks in the frequency domain. Here, one downlink slot includes 7 OFDM symbols, and one resource block includes 12 subcarriers as an example, but is not limited thereto. Each element on the resource grid is called a resource element (RE). For example, the resource element a (k, l) becomes a resource element located in the k-th subcarrier and the l-th OFDM symbol. In the case of a normal CP, one resource block includes 12x7 resource elements (in the case of an extended CP, it includes 12x6 resource elements). Since the interval of each subcarrier is 15 kHz, one resource block includes about 180 kHz in the frequency domain. N ^DL is the number of resource blocks included in the downlink slot. The value of N ^DL may be determined according to a downlink transmission bandwidth set by scheduling of the base station.

3 is a diagram illustrating a structure of a downlink subframe. Up to three OFDM symbols at the front of the first slot in one subframe correspond to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to data regions to which a physical downlink shared channel (PDSCH) is allocated. The basic unit of transmission is one subframe. That is, PDCCH and PDSCH are allocated over two slots. Downlink control channels used in the 3GPP LTE system include, for example, a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), and a Physical HARQ Indicator Channel. Physical Hybrid automatic repeat request Indicator Channel (PHICH). The PCFICH is transmitted in the first OFDM symbol of a subframe and includes information on the number of OFDM symbols used for control channel transmission in the subframe. The PHICH includes a HARQ ACK / NACK signal as a response of uplink transmission. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). DCI includes uplink or downlink scheduling information or an uplink transmit power control command for a certain terminal group. The PDCCH is a resource allocation and transmission format of the downlink shared channel (DL-SCH), resource allocation information of the uplink shared channel (UL-SCH), paging information of the paging channel (PCH), system information on the DL-SCH, on the PDSCH Resource allocation of upper layer control messages such as random access responses transmitted to the network, a set of transmit power control commands for individual terminals in an arbitrary terminal group, transmission power control information, and activation of voice over IP (VoIP) And the like. A plurality of PDCCHs may be transmitted in the control region. The terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted in a combination of one or more consecutive Control Channel Elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH at a coding rate based on the state of a radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the number of available bits are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs. The base station determines the PDCCH format according to the DCI transmitted to the terminal, and adds a cyclic redundancy check (CRC) to the control information. The CRC is masked with an identifier called a Radio Network Temporary Identifier (RNTI) according to the owner or purpose of the PDCCH. If the PDCCH is for a specific terminal, the cell-RNTI (C-RNTI) identifier of the terminal may be masked to the CRC. Or, if the PDCCH is for a paging message, a paging indicator identifier (P-RNTI) may be masked to the CRC. If the PDCCH is for system information (more specifically, system information block (SIB)), the system information identifier and system information RNTI (SI-RNTI) may be masked to the CRC. Random Access-RNTI (RA-RNTI) may be masked to the CRC to indicate a random access response that is a response to the transmission of the random access preamble of the terminal.

4 is a diagram illustrating the structure of an uplink subframe. The uplink subframe may be divided into a control region and a data region in the frequency domain. A physical uplink control channel (PUCCH) including uplink control information is allocated to the control region. In the data area, a physical uplink shared channel (PUSCH) including user data is allocated. In order to maintain a single carrier characteristic, one UE does not simultaneously transmit a PUCCH and a PUSCH. PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers for two slots. This is called a resource block pair allocated to the PUCCH is frequency-hopped at the slot boundary.

Multiple antennas ( MIMO ) Of the system modelling

MIMO system is a system that improves the transmission and reception efficiency of data using multiple transmit antennas and multiple receive antennas. MIMO technology can receive full data by combining a plurality of data pieces received through a plurality of antennas, without relying on a single antenna path to receive the entire message.

5 is a configuration diagram of a wireless communication system having multiple antennas. As shown in Fig. 5 (a), the number of transmit antennas is N _T. The number of receiving antennas is N _R The theoretical channel transmission capacity increases in proportion to the number of antennas, unlike the case where a plurality of antennas are used only in a transmitter or a receiver. Therefore, the transmission rate can be improved and the frequency efficiency can be remarkably improved. As the channel transmission capacity increases, the transmission rate can theoretically increase by the rate of increase R _i multiplied by the maximum transmission rate R _{o at the} time of single antenna use.

For example, in a MIMO communication system using four transmit antennas and four receive antennas, it is possible to obtain a transmission rate four times higher than the single antenna system. After the theoretical capacity increase of the multi-antenna system has been proved in the mid-90s, various techniques have been actively researched to bring it up to practical data rate improvement. In addition, several technologies have already been reflected in various wireless communication standards such as 3G mobile communication and next generation wireless LAN.

The research trends related to multi-antenna up to now include information theory study related to calculation of multi-antenna communication capacity in various channel environment and multiple access environment, study of wireless channel measurement and modeling of multi-antenna system, improvement of transmission reliability and improvement of transmission rate And research on space-time signal processing technology.

A communication method in a multi-antenna system will be described in more detail using mathematical modeling. It is assumed that there are N _T transmit antennas and N _R receive antennas in the system.

Looking at the transmitted signal, if there are N _T transmit antennas, the maximum transmittable information is N _T. The transmission information can be expressed as follows.

는 전송 전력이 다를 수 있다. 각각의 전송 전력을

라고 하면, 전송 전력이 조정된 전송 정보는 다음과 같이 표현될 수 있다.Each transmission information

The transmission power may be different. Each transmission power

, The transmission information whose transmission power is adjusted can be expressed as follows.

는 전송 전력의 대각행렬

를 이용해 다음과 같이 표현될 수 있다.Also,

Is a diagonal matrix of transmit power

Can be expressed as follows.

에 가중치 행렬

가 적용되어 실제 전송되는 N _T 개의 송신신호

가 구성되는 경우를 고려해 보자. 가중치 행렬

는 전송 정보를 전송 채널 상황 등에 따라 각 안테나에 적절히 분배해 주는 역할을 한다.

는 벡터

를 이용하여 다음과 같이 표현될 수 있다.Information vector with adjusted transmission power

Weighting matrix

_Lt ; RTI ID = 0.0 _& gt; N _& lt; / RTI >

Consider the case where is configured. Weighting matrix

Which distributes the transmission information to each antenna according to the transmission channel condition and the like.

Vector

Can be expressed as follows.

는 i번째 송신 안테나와 j번째 정보간의 가중치를 의미한다.

는 프리코딩 행렬이라고도 불린다.From here,

Denotes a weight between the i- th transmit antenna and the j- th information.

Is also referred to as a precoding matrix.

On the other hand, the transmission signal x may be considered in different ways according to two cases (for example, spatial diversity and spatial multiplexing). In the case of spatial multiplexing, different signals are multiplexed and the multiplexed signal is sent to the receiving side so that the elements of the information vector (s) have different values. On the other hand, in the case of spatial diversity, the same signal is repeatedly transmitted through a plurality of channel paths so that the elements of the information vector (s) have the same value. Of course, a combination of spatial multiplexing and spatial diversity techniques can also be considered. That is, the same signal may be transmitted through, for example, three transmit antennas according to a spatial diversity scheme, and the remaining signals may be spatially multiplexed and transmitted to the receiver.

은 벡터로 다음과 같이 표현될 수 있다. N _R When there are two or more reception antennas,

Can be expressed as a vector as follows.

로 표시하기로 한다.

에서, 인덱스의 순서가 수신 안테나 인덱스가 먼저, 송신 안테나의 인덱스가 나중임에 유의한다. When a channel is modeled in a multi-antenna wireless communication system, the channel may be classified according to the transmission / reception antenna index. The channel passing through the receiving antenna i from the transmitting antenna j

.

, It is noted that the order of the index is the reception antenna index, and the index of the transmission antenna is the order of the index.

N _T in FIG. 5 (b) Channels from two transmit antennas to receive antenna i are shown . The channels can be grouped and displayed in vector and matrix form. In FIG. 5 (b), the channel arriving from the total N _T transmit antennas to receive antenna i may be expressed as:

Thus, N _T Lt; RTI ID = 0.0 & _gt; N _R All channels arriving at the two receiving antennas may be expressed as follows.

를 거친 후에 백색잡음(AWGN; Additive White Gaussian Noise)이 더해진다. N _R 개의 수신 안테나 각각에 더해지는 백색잡음

은 다음과 같이 표현될 수 있다.The actual channel includes a channel matrix

And additive white Gaussian noise (AWGN) is added. N _R White Noise Added to Each of Receive Antennas

Can be expressed as follows.

Through the above-described equation modeling, the received signal can be expressed as follows.

The above description has focused on the case where a multi-antenna communication system is used for a single user. However, it is possible to obtain multiuser diversity by applying a multi-antenna communication system to a plurality of users. Briefly described as follows.

Fading channels are a major cause well known to cause poor performance of wireless communication systems. The channel gain changes with time, frequency, and space, and the lower the channel gain, the more severe the degradation. Diversity, one way to overcome fading, takes advantage of the fact that multiple independent channels are all very unlikely to have low gain. Various diversity schemes are possible, and multi-user diversity is one of them.

When there are several users in a cell, the channel gains of each user are stochastically independent of each other, so the probability that they all have low gains is very small. According to the information theory, if the base station has sufficient transmission power, allocating all channels to a user having the highest channel gain when there are several users in a cell can maximize the total capacity of the channel. Multi-user diversity can be divided into three categories.

Temporal multiuser diversity is a method of allocating a channel to a user who has the highest gain at the time when the channel changes over time. Frequency multiuser diversity is a method of allocating subcarriers to a user having maximum gain in each frequency band in a frequency multicarrier system such as orthogonal frequency division multiplexing (OFDM).

If the channel changes very slowly in a system that does not use multicarrier, the user with the highest channel gain will monopolize the channel for a long time. Thus, other users will not be able to communicate. In this case, it is necessary to induce a channel change in order to use multi-user diversity.

Next, spatial multiuser diversity is a method that generally uses that the channel gain of users varies from space to space. An example of the implementation may include random beamforming (RBF). RBF, also known as "opportunistic beamforming," is a technique of inducing a channel change by performing beamforming with arbitrary weights using multiple antennas at a transmitting end.

The multiuser multi-antenna (Multiuser MIMO, MU-MIMO) scheme using the above-described multi-user diversity for a multi-antenna scheme will be described below.

In the multi-user multi-antenna scheme, the number of users and the number of antennas of each user may be variously combined at the transmitting and receiving end. Multi-user multi-antenna scheme will be divided into downlink (downlink, forward link) and uplink (uplink, reverse link). The downlink refers to a case where a base station transmits a signal to various terminals. The uplink refers to a case in which several terminals transmit a signal to a base station.

In the downlink case, for example, one user may receive a signal through a total of N _R antennas, and a total of N _R users may receive a signal using one antenna each. In addition, an intermediate combination of the preceding two extreme examples is also possible. That is, some users use one receive antenna, while some users use three receive antennas. Note that in any combination, the sum of the number of receive antennas remains constant at N _R. This case is commonly referred to as MIMO Broadcast Channel (BC) or Space Division Multiple Access (SDMA).

In the uplink case, for example, one user may transmit a signal through a total of N _T antennas, and a total of N _T users may transmit a signal using one antenna each. In addition, an intermediate combination of the preceding two extreme examples is also possible. That is, some users use one transmit antenna, while some users use three transmit antennas. Note that in any combination, the sum of the number of transmit antennas remains constant at N _T. This case is commonly referred to as MIMO Multiple Access Channel (MAC). Since uplink and downlink are symmetrical with each other, the technique used on either side can be used on the other side.

의 행과 열의 수는 송수신 안테나의 수에 의해 결정된다. 채널 행렬

에서 행의 수는 수신 안테나의 수 N _R 과 같고, 열의 수는 송신 안테나의 수 N _T 와 같다. 즉, 채널 행렬

는 행렬이 N _R ×N _T 된다. On the other hand, a channel matrix

The number of rows and columns of the antenna is determined by the number of transmitting and receiving antennas. Channel matrix

The number of rows is equal to the number N _R of receive antennas and the number of columns is equal to the number N _T of transmit antennas. That is,

The matrix is N _R x N _T.

의 랭크(

)는 다음과 같이 제한된다.The rank of a matrix is defined as the minimum number of independent rows or columns. Thus, the rank of the matrix can not be greater than the number of rows or columns. Channel matrix

Rank of

) Is limited as follows.

Another definition of the rank is defined as the number of eigenvalues that are not zero when the matrix is eigenvalue decomposition. Similarly, another definition of a rank is defined as the number of non-zero singular values when singular value decomposition is performed. Therefore, the physical meaning of a rank in a channel matrix is the maximum number that can transmit different information in a given channel.

In MIMO transmission, 'rank' indicates the number of paths that can independently transmit a signal, and 'number of layers' indicates the number of signal streams transmitted through each path. In general, since the transmitting end transmits a number of layers corresponding to the number of ranks used for signal transmission, the rank has the same meaning as the number of layers unless otherwise specified.

은 다음과 같이 표현될 수 있다.Hereinafter, the characteristics of the precoding matrix will be described. First, the channel matrix without considering the precoding matrix

Can be expressed as follows.

In general, when a minimum mean square error (MMSE) receiver is given, ρ _k (k-th received SINR (Signal to Interference plus Noise Ratio)) may be defined as follows.

은 프리코딩 행렬

를 사용하여 다음과 같이 표현될 수 있다.Meanwhile, the effective channel reflected on the precoding matrix

Is a precoding matrix

Can be expressed as

Therefore, assuming that the MMSE receiver is used, ρ _k can be defined as follows.

와 j 번째 열 벡터

간의 퍼뮤테이션의 경우에, 퍼뮤테이션된 프리코딩 행렬

은 다음과 같이 표현될 수 있다.Here, some validity on the received SINR can be confirmed based on the variation of the precoding matrix based on the theoretical background. First, the validity of column permutation in one precoding matrix can be confirmed. That is, the ith column vector

J th column vector

In the case of permutation of the liver, the permutated precoding matrix

Can be expressed as follows.

에 따른 유효 채널

및 프리코딩 행렬

에 따른 유효 채널

은 각각 다음과 같이 표현될 수 있다. Thus, the precoding matrix

Effective channel according to

And precoding matrices

Effective channel according to

Each can be expressed as follows.

In Equations 17 and 18, even when two column vectors are permutated, the received SINR value itself does not change except for order, and the channel capacity / sum ratio may be constant. have. Also for Equations 14 and 15, the permuted effective channel and ρ _k can be obtained as follows.

In Equation 20, the interference and noise portions may be expressed as follows.

은 다음과 같이 표현될 수 있다.Newly received SINR

Can be expressed as follows.

는 다음과 같이 표현될 수 있다. Next, it is possible to verify the validity of what multiplying e ^-jθ (0≤θ≤2π) to a specific column vector in a precoding matrix. For example, e ^-jθ may be ± 1, ± j . e- ^jθ multiplied by the k th column

Can be expressed as follows.

) 은 다음과 같이 표현될 수 있다.Where received SINR (

) Can be expressed as

As shown in Equation 24, multiplying e − ^jθ to a specific column vector of the precoding matrix may have no effect on the received SINR and the channel capacity / sum ratio.

In the MIMO system, various MIMO transmission schemes (transmission modes) exist. Multiple antenna transmit / receive schemes used for the operation of MIMO systems include frequency switched transmit diversity (FST), Space Frequency Block Code (SFBC), Space Time Block Code (STBC), Cyclic Delay Diversity (CDD), TSTD (time switched transmit diversity) may be used. In Rank 2 or higher, spatial multiplexing (SM), Generalized Cyclic Delay Diversity (GCDD), Selective Virtual Antenna Permutation (S-VAP), and the like may be used.

FSTD is a method of obtaining diversity gain by allocating subcarriers having different frequencies for each signal transmitted to each of the multiple antennas. SFBC is a technique that can efficiently obtain diversity gain and multi-user scheduling gain at the corresponding dimension by efficiently applying selectivity in the spatial domain and frequency domain. STBC is a technique for applying selectivity in space and time domain. CDD is a technique of obtaining diversity gain by using path delay between transmission antennas. TSTD is a technique that divides the signals transmitted by multiple antennas by time. Spatial multiplexing is a technique for increasing the transmission rate by transmitting different data for each antenna. GCDD is a technique that applies selectivity in time domain and frequency domain. The S-VAP is a technique using a single precoding matrix. The S-VAP uses MCC (Multi Codeword) S-VAP, which mixes multiple codewords between antennas in spatial diversity or spatial multiplexing, and Single Codeword -VAP.

Various types of scheduling signaling (PDCCH DCI format) may be used according to various MIMO transmission schemes (MIMO transmission mode) as described above. That is, the scheduling signaling may have a different form for various MIMO transmission modes, and the terminal may determine the MIMO transmission mode according to the scheduling signaling.

On the other hand, in the MIMO system, an open-loop method (or a channel-independent method) that does not use the feedback information from the receiver and a closed-loop method that uses the feedback information from the receiver are used. (Or channel-dependent). In the closed loop scheme, the receiving end transmits feedback information about the channel state to the transmitting end, thereby allowing the transmitting end to grasp the channel state, thereby improving the performance of the wireless communication system. The closed loop MIMO system uses a precoding scheme in which a transmitter minimizes the influence of a channel by performing a predetermined process on transmission data using feedback information about a channel environment transmitted from a receiver. Precoding schemes include a codebook based precoding scheme and a precoding scheme for quantizing and feeding back channel information.

OFDM  And SC - FDMA  By way MIMO  system

In general, in a MIMO system based on the OFDM scheme or the SC-FDMA scheme, the data signal undergoes a complicated mapping relationship in a transmission symbol. First, data is divided into codewords. In most cases, the codewords correspond to transport blocks given by the MAC layer. Each codeword is separately encoded using a channel coder, such as a turbo code or tail-biting convolutional code. The encoded codeword is rate matched to the appropriate size and mapped to the layers. Discrete Fourier Transform (DFT) precoding is performed for each layer in SC-FDMA transmission, and DFT transform is not applied in OFDM transmission. The precoding vector / matrix is multiplied by the DFT transformed signal in each layer and mapped to the transmit antenna port. The transmit antenna port may be mapped back to the physical antenna by a method such as antenna virtualization.

6 is a diagram illustrating a general system structure of SC-FDMA and OFDMA. In FIG. 6, N is smaller than M. FIG. S-to-P means converting a serial signal into a parallel signal, and P-to-S means converting a parallel signal into a serial signal. As shown in FIG. 6, at the transmitting end of an SC-FDMA system, input information symbols are serial-to-parallel conversion 611, N-point DFT 612, subcarrier mapping 613, and M-point IDFT (Inverse DFT). The signal may be transmitted over the channel via 614, parallel-to-serial conversion 615, CP addition 616, and digital-to-analog conversion 617. At the receiving end of the SC-FDMA system, the signal received through the channel is analog-to-digital conversion (621), CP cancellation (622), serial-to-parallel conversion (623), M-point DFT (624), subcarrier de-mapping / equalization Information symbol may be recovered via 625, N-point IDFT 626, parallel-to-serial conversion 627, and detection 628. Meanwhile, in the OFDMA system, the N-point DFT 612 and the parallel-serial conversion 615 of the transmitting end of the SC-FDMA system are not performed, and the parallel-serial conversion may be performed together with the CP addition 616. Serial-to-parallel conversion 623 and N-point IDFT 626 of the receiving end of the FDMA system are not performed.

In general, the cubic metric (CM) or peak power to average power ratio (PAPR) of a single carrier signal, such as an SC-FDMA transmission signal, is much lower than a multicarrier signal. CM and PAPR relate to the dynamic range that the transmitter's power amplifier (PA) must support. In the case of using the same PA, a transmission signal having a low CM or PAPR compared to other types of signals may be transmitted at a high transmission power. In other words, when the maximum power of the PA is fixed, for the transmitter to transmit a signal of high CM or PAPR, the transmit power must be slightly lowered compared to the signal of low CM or PAPR. The reason why a single carrier signal has a lower CM or PAPR than a multicarrier signal is that in the case of a multicarrier signal, a plurality of signals can be superimposed so that a co-phase can be added to the signal. Accordingly, the amplitude of the signal may be increased, and the OFDM system may have a large PAPR or CM value.

If the transmission signal y consists of only one information symbol x ₁ , this signal may be referred to as a single carrier signal such that y = x ₁ . However, if the transmission signal y consists of a plurality of information symbols (x ₁ , x ₂ , x ₃ , ..., x _N ), then this signal is y = x ₁ + x ₂ + x ₃ +. It can be referred to as a multi-carrier signal such as .. + x _N. The PAPR or CM is proportional to the number of information symbols that are coherently summed together in the transmission signal waveform, but when a certain number of information symbols are reached, their values tend to saturate. Thus, when the signal waveform is generated by the sum of a small number of single carrier signals of single carrier signals, the CM or PAPR has a much smaller value than the multicarrier signal, but slightly higher than a pure single carrier signal. Has

7 shows a system structure for an uplink SC-FDMA of an LTE release-8 system. The system structure of the uplink SC-FDMA in the LTE release-8 system is scrambling 710, modulation mapper 720, transform precoder 730, resource element mapper 740 and SC-FDMA signal generation as shown in FIG. It may be configured in the order of (750). As shown in FIG. 7, the transform precoder 730 corresponds to the N-point DFT 612 of FIG. 6, the resource element mapper 740 corresponds to the subcarrier mapping 613 of FIG. 6, and the SC- FDMA signal generation 750 corresponds to M-point IDFT 614, parallel-to-serial conversion 615, and CP addition 616 in FIG. 6.

8 shows a transport frame structure for uplink SC-FDMA in an LTE release-8 system. The basic transmission unit consists of one subframe. One subframe consists of two slots, and the number of SC-FDMA symbols included in one slot is 7 or 6 according to a CP configuration (eg, a general CP or an extended CP). 8 illustrates a case of a general CP in which seven SC-FDMA symbols exist in one slot. In each slot there is at least one Reference Signal (RS) SC-FDMA symbol, which is not used for data transmission. There are a plurality of subcarriers within one SC-FDMA symbol. The resource element (RE) is a complex information symbol mapped to one subcarrier. When DFT transform precoding is used, since the size of the DFT transform and the number of subcarriers used for transmission are the same in SC-FDMA, RE corresponds to one information symbol mapped to one DFT transform index.

In the LTE-A system, spatial multiplexing of up to four layers is considered for uplink transmission. In the case of uplink single user space multiplexing, up to two transport blocks may be transmitted from a scheduled UE in one subframe for each uplink component carrier. Here, the component carrier refers to a carrier of a unit to be merged in a carrier aggregation technique for physically binding a plurality of carriers to produce an effect such as using a logically large band. According to the number of transport layers, modulation symbols associated with each transport block may be mapped on one or two layers. The mapping relationship between a transport block and a layer may be the same as that of the transport block and layer mapping in LTE release-8 downlink spatial multiplexing. For both cases with or without spatial multiplexing, the DFT precoded OFDM scheme can be used as a multiple access scheme for uplink data transmission. In the case of multiple component carriers, one DFT may be applied to each component carrier. In particular, in the LTE-A system, frequency-contiguous and frequency-non-contiguous resource allocation may be supported for each component carrier.

9 is a diagram illustrating a data signal mapping relationship for a MIMO system based on SC-FDMA transmission. In the SC-FDMA system, a layer mapper for mapping a signal to be transmitted to a number of layers corresponding to a specific rank, a predetermined number of DFT modules for performing DFT spreading on a predetermined number of layer signals, and a precoding matrix from a codebook stored in a memory It may include a precoder to select to perform precoding on the transmission signal. In the example of FIG. 9, when the number of codewords is N _C and the number of layers is N _L , N _C or an integer multiple of N _C are assigned to N _L or an integer multiple of N _L. Can be mapped. DFT transform precoding for SC-FDMA does not change the size of the layer. When precoding is performed on a layer, the number of information symbols is changed from N _L to N _T by multiplying a matrix of size N _T × N _L. In general, the transmission rank of data to be spatially multiplexed is equal to the number of layers carrying the data at a given transmission time point (eg, N _L ). As shown in FIG. 9, the DFT module for transmitting an uplink signal in the SC-FDMA scheme is disposed in front of the precoder and after the layer mapper. Accordingly, the DFT-spreaded signal for each layer is precoded and then IFFT despread and transmitted, so that the effects of DFT spreading and IFFT despreading are canceled except for precoding, thereby maintaining good PAPR or CM characteristics. have.

Reference signal ( Reference Signal ; RS )

When transmitting a packet in a wireless communication system, since the transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to correctly receive the distorted signal at the receiving end, the distortion must be corrected in the received signal using the channel information. In order to determine the channel information, a method is used in which a signal known to both the transmitting side and the receiving side is transmitted, and channel information is detected with a degree of distortion when the signal is received through the channel. The signal is called a pilot signal or a reference signal.

When transmitting and receiving data using multiple antennas, it is necessary to know the channel condition between each transmitting antenna and the receiving antenna so that a correct signal can be received. Therefore, a separate reference signal must exist for each transmit antenna.

The DL reference signal includes a Common Reference Signal (CRS) shared by all UEs in a cell and a Dedicated Reference Signal (DRS) dedicated to a specific UE. Such reference signals may provide information for channel estimation and demodulation.

The receiver (terminal) estimates the state of the channel from the CRS and feeds back indicators related to channel quality such as channel quality indicator (CQI), precoding matrix index (PMI), and / or rank indicator (RI) to the transmitter (base station). can do. The CRS may be called a cell-specific reference signal.

Meanwhile, when demodulation of data on the PDSCH is required, the DRS may be transmitted through the corresponding RE. The UE may be instructed as to whether DRS is present from a higher layer and may be instructed that the DRS is valid only when the corresponding PDSCH is mapped. The DRS may also be called a UE-specific reference signal or a demodulation reference signal (DMRS).

FIG. 10 is a diagram illustrating a pattern in which CRSs and DRSs defined in an existing 3GPP LTE system (eg, Release-8) are mapped onto a downlink resource block. A DL resource block as a unit to which a reference signal is mapped can be expressed in units of 12 subcarriers in time on one subframe x frequency. In case of a normal CP, one resource block has a length of 14 OFDM symbols in time.

10 shows a location on a resource block of a reference signal in a system in which a base station supports four transmission antennas. In FIG. 10, resource elements RE denoted by '0', '1', '2' and '3' indicate positions of CRSs for antenna port indexes 0, 1, 2, and 3, respectively. Meanwhile, the resource element denoted as 'D' in FIG. 10 indicates the position of the DRS defined in LTE Release-8 (or Release-9).

Hereinafter, the CRS will be described in detail.

The CRS is used to estimate a channel of a physical antenna terminal, and is a reference signal that can be commonly received by all UEs in a cell, and is distributed over all bands. CRS may be used for channel state information (CSI) acquisition and data demodulation purposes.

CRS is defined in various forms according to the antenna configuration of the transmitting side (base station). The 3GPP LTE (eg, Release-8) system supports various antenna configurations, and the downlink signal transmitter (base station) uses three types of antenna configurations such as a single antenna, two transmit antennas, and four transmit antennas. Have When the base station transmits a single antenna, a reference signal for a single antenna port is arranged. When the base station transmits two antennas, reference signals for two antenna ports are arranged in a time division multiplexing and / or frequency division multiplexing scheme. That is, the reference signals for the two antenna ports can be placed at different time resources and / or different frequency resources and can be distinguished from each other. In addition, when the base station transmits four antennas, reference signals for four antenna ports are arranged in a TDM / FDM scheme. The channel information estimated by the receiving side (terminal) of the downlink signal through the CRS is divided into a single antenna transmission, a transmission diversity, a closed-loop spatial multiplexing, Can be used for demodulation of data transmitted by transmission techniques such as open-loop spatial multiplexing and multi-user MIMO (MU-MIMO).

When supporting multiple antennas, when transmitting a reference signal from one antenna port, the reference signal is transmitted to a resource element (RE) position designated according to the reference signal pattern, and a signal is transmitted to a resource element (RE) position designated for another antenna port. Do not send.

The rule in which the CRS is mapped on the resource block is according to the following equation.

는 하나의 하향링크 슬롯의 OFDM 심볼의 개수이고,

는 하향링크에 할당된 자원블록의 개수이고,

는 슬롯 인덱스이고,

는 셀 ID를 의미한다. mod 는 모듈러 연산을 의미한다. 주파수 영역에서 참조신호의 위치는 V_shift 값에 의존한다. V_shift 값은 또한 셀 ID에 의존하므로, 참조신호의 위치는 셀 별로 상이한 주파수 시프트 값을 가지게 된다. In Equation 25, k is a subcarrier index, l is a symbol index, and p is an antenna port index.

Is the number of OFDM symbols in one downlink slot,

Is the number of resource blocks allocated to the downlink,

Is the slot index,

Means a cell ID. mod stands for modular operation. The position of the reference signal in the frequency domain depends on the V _shift value. Since the V _shift value also depends on the cell ID, the position of the reference signal has a different frequency shift value for each cell.

Specifically, in order to improve channel estimation performance through the CRS, the position on the frequency domain of the CRS may be shifted for each cell to be different. For example, when a reference signal is located every 3 subcarriers, one cell may be arranged on a 3k subcarrier and another cell on a 3k + 1 subcarrier. In terms of one antenna port, the reference signal is arranged at 6 RE intervals (ie, 6 subcarrier intervals) in the frequency domain, and maintains 3 RE intervals in the frequency domain from the RE where reference signals for other antenna ports are arranged.

In addition, power boosting may be applied to the CRS. Power boosting refers to the transmission of a reference signal with higher power by taking power from another RE other than the RE allocated for the reference signal among the resource elements RE of one OFDM symbol.

In the time domain, reference signal positions are arranged at regular intervals starting from the symbol index ( l ) 0 of each slot. The time interval is defined differently depending on the CP length. The general CP case is located at symbol indexes 0 and 4 of the slot, and the extended CP case is located at symbol indexes 0 and 3 of the slot. Only one reference signal is defined for up to two antenna ports in one OFDM symbol. Therefore, when transmitting 4 Tx antennas, reference signals for antenna ports 0 and 1 are located at symbol indexes 0 and 4 (symbol indexes 0 and 3 in case of extended CP) of the slot, and reference signals for antenna ports 2 and 3 Lt; RTI ID = 0.0 > 1 < / RTI > However, the frequency positions of the reference signals for the antenna ports 2 and 3 are switched with each other in the second slot.

A system (e.g., an LTE-A system) with an extended antenna configuration can be designed to support higher spectral efficiency than existing 3GPP LTE (e.g., Release-8) systems. The extended antenna configuration may be, for example, eight transmit antenna configurations. In a system having such an extended antenna configuration, it is necessary to support terminals operating in an existing antenna configuration, that is, to support backward compatibility. Therefore, it is necessary to support the reference signal pattern according to the existing antenna configuration, and to design a new reference signal pattern for the additional antenna configuration. Here, if a CRS for a new antenna port is added to a system having an existing antenna configuration, there is a disadvantage that the reference signal overhead rapidly increases and the data transmission rate is lowered. Considering the above, it is necessary to design a new reference signal (CSI-RS) for measuring channel state information (CSI) for a new antenna port, and a detailed method thereof will be described after the DRS.

Hereinafter, the DRS will be described in detail.

The DRS (or terminal-specific reference signal) is a reference signal used for data demodulation. When the terminal receives the reference signal by using the precoding weight used for the specific terminal as the reference signal when transmitting multiple antennas, Equivalent channel combined with the precoding weight transmitted in the transmission antenna and the transmission channel can be estimated.

Existing 3GPP LTE systems (eg, Release-8) support up to 4 transmit antenna transmissions, and DRS is defined for rank 1 beamforming. The DRS for rank 1 beamforming may also be indicated as a reference signal for antenna port index 5. The rule in which the DRS is mapped on the resource block is according to Equations 26 and 27 below. Equation 26 is for the case of a general CP, and Equation 27 is for the case of an extended CP.

는 주파수 영역에서 자원 블록 크기를 나타내며 부반송파의 개수로 표현된다.

는 물리자원블록 넘버를 나타낸다.

는 대응하는 PDSCH 전송의 자원 블록의 대역폭을 나타낸다.

는 슬롯 인덱스이고,

는 셀 ID를 의미한다. mod 는 모듈러 연산을 의미한다. 주파수 영역에서 참조신호의 위치는 V_shift 값에 의존한다. V_shift 값은 또한 셀 ID에 의존하므로, 참조신호의 위치는 셀 별로 상이한 주파수 시프트 값을 가지게 된다. In Equations 26 and 27, k is a subcarrier index, l is a symbol index, and p is an antenna port index.

Denotes the resource block size in the frequency domain and is represented by the number of subcarriers.

Indicates a physical resource block number.

Denotes the bandwidth of the resource block of the corresponding PDSCH transmission.

Is the slot index,

Means a cell ID. mod stands for modular operation. The position of the reference signal in the frequency domain depends on the V _shift value. Since the V _shift value also depends on the cell ID, the position of the reference signal has a different frequency shift value for each cell.

Meanwhile, in the LTE-A (Advanced) system, which is an evolution of 3GPP LTE, high order MIMO, multi-cell transmission, and advanced MU-MIMO are considered, which supports efficient reference signal operation and advanced transmission scheme. DMRS-based data demodulation is considered. That is, apart from DMRS (antenna port index 5) for rank 1 beamforming defined in the existing 3GPP LTE (eg, Release-8), two or more layers may be used to support data transmission through an added antenna. DMRS can be defined. Since the DMRS is precoded by the same precoder as the data, channel information for demodulating data at the receiving side can be easily estimated without additional precoding information.

In arranging DMRSs for supporting maximum rank 8 transmission on radio resources, DMRSs for each layer may be multiplexed and arranged. Time Division Multiplexing (TDM) means placing the DMRS for two or more layers on different time resources (e.g., OFDM symbols). Frequency Division Multiplexing (FDM) means placing the DMRS for two or more layers on different frequency resources (e.g., subcarriers). Code Division Multiplexing (CDM) means multiplexing DMRSs for two or more layers disposed on the same radio resource using an orthogonal sequence (or orthogonal covering).

11 shows an example of a DMRS pattern for supporting maximum rank 8 transmission. In FIG. 11, the control region (first 1 to 3 symbols of one subframe) indicates an RE to which a PDCCH can be transmitted. CRS for a four transmit antenna represents a RE that CRS is disposed on the antenna port '0', '1', '2' and '3' as described in Figure 10, shows the case of V _shift value is 0, illustratively .

In general, in the case of single user-MIMO (SU-MIMO) transmission, the number of antenna ports (or virtual antenna ports) of DMRS used for data transmission is the same as the transmission rank of data transmission. In this case, the DMRS antenna ports (or virtual antenna ports) may be numbered from 1 to 8, and the lowest 'N' DMRS antenna ports may be used for rank 'N' SU-MIMO transmission.

When the DMRS antenna port number is assigned as shown in FIG. 11, the total number of REs for which data is not transmitted due to the arrangement of DMRSs within a single transport layer is determined according to the transmission rank. In the case of low rank (eg, rank 1 or 2), the number of REs used for DMRS transmission may be 12 in one resource block. In the case of a high rank (eg, ranks 3 to 8), the number of REs used for DMRS transmission may be 24 in one resource block. That is, in the case of rank 2 as shown in FIG. 11, DMRSs for layers 1 and 2 may be transmitted on 12 REs (REs indicated as DMRS positions for layers 1, 2, 5, and 7 of FIG. 11). In case of rank 3, DMRSs for layers 1 and 2 are transmitted in the 12 REs, and DMRSs for layer 3 are represented by DMRS positions for additional 12 REs (layers 3, 4, 6, and 8 of FIG. 11). RE). The location of the RE where the DMRS is disposed for each layer is exemplary and is not limited thereto.

CSI - RS  pattern

The present invention proposes a new method for deploying (multiplexing) CSI-RS on a radio resource in consideration of the aforementioned CRS and DMRS locations. As described above, the CSI-RS may be transmitted by the base station and used to estimate channel state information at the terminal. The channel state information measured by the CSI-RS includes precoding information (eg, precoding matrix index (PMI)), the number of preferred transport layers (eg, rank indicator (RI)), preferred modulation, and Modulation and Coding Schemes (MCS) (eg, Channel Quality Indicators (CQI)) and the like.

The CRS is necessary for correct operation of a terminal (legacy terminal) operating according to an existing LTE system, and the DMRS is necessary for easily performing data demodulation for an extended antenna configuration. Accordingly, in order to support efficient channel information acquisition by the downlink receiver through the CSI-RS, a CSI-RS pattern (resource) may be transmitted to allow as many CSI-RSs as possible in consideration of the arrangement of the CRS and the DMRS on a radio resource. Position on the block). This is because the UE can correctly estimate the channel between the serving cell and the UE only when the CSI-RS from the neighboring cell and the CSI-RS from the serving cell are prevented from colliding (that is, the CSI-RS is transmitted at a different location). . Therefore, the greater the number of CSI-RS patterns that can be used by different cells, the more guaranteed the channel estimation performance through the CSI-RS.

The present invention groups the REs used by a group of CSI-RS antenna ports, and proposes that the CSI-RS RE groups consist of consecutive REs usable in the frequency domain. As described above, configuring the CSI-RS group with a continuous RE in the frequency domain includes a base transport block for transmission diversity transmission schemes such as space-frequency block coding (SFBC) and frequency selective transmit diversity (SFBC-FSTD). This is to prevent the transmission block from being broken due to the arrangement of the CSI-RS. Specifically, since data cannot be transmitted in the RE to which the CSI-RS is transmitted, if data is transmitted on the basic transport block for transmit diversity, if only the CSI-RS is arranged in some of the basic transport blocks, This is because the problem of breaking the transmit diversity RE pair occurs.

Here, the available RE is the control region (the first 1 of the downlink subframe) in the downlink resource block (one subframe (12 or 14 OFDM symbols) in the time domain × one resource block (12 subcarriers) in the frequency domain)). RE, which does not include CRS and DMRS in a data region excluding 3 to 3 OFDM symbols). That is, the available REs to which the CSI-RS can be placed correspond to the REs to which nothing is allocated in FIG. 11.

An example of the CSI-RS RE group is shown in FIGS. 12 to 16.

12 shows an example in which a CSI-RS RE group is configured on two consecutive subcarriers. In the example of FIG. 12, it can be seen that the CSI-RS RE group is defined except for the RE where the CRS and the DMRS are disposed.

13 shows an example in which a CSI-RS RE group is configured on four consecutive subcarriers. In the example of FIG. 13, some CSI-RS RE groups may appear to be set up over five subcarriers, but CSI-RSs are not transmitted in REs in which CRSs are arranged in the corresponding CSI-RS RE groups, so that a size of 4 REs is eventually obtained. It can be seen that the CSI-RS RE group is set.

14 shows an example in which a CSI-RS RE group is configured on two consecutive subcarriers. In the example of FIG. 14, it can be seen that the CSI-RS RE group is not defined on the OFDM symbol in which the CRS is disposed.

15 shows an example in which a CSI-RS RE group is configured on four consecutive subcarriers. In the example of FIG. 15, it can be seen that the CSI-RS RE group is not defined on the OFDM symbol in which the CRS and the DMRS are arranged.

16 shows an example in which a CSI-RS RE group is configured on four consecutive subcarriers. In the example of FIG. 16, it should be noted that the CSI-RS is not transmitted in the CRS RE position. In addition, in the example of FIG. 16, it can be seen that the CSI-RS RE group is not defined on the OFDM symbol in which the DMRS is disposed.

The CSI-RS RE group as illustrated in FIGS. 12 to 16 is used for a single cell to transmit a group of CSI-RS antenna ports. For example, if one cell transmits all two CSI-RS antenna ports, if the CSI-RS RE group size is 2, the CSI-RS RE for two CSI-RS antenna ports is one CSI-RS antenna port. It can be mapped within an RS RE group. Or, if one cell transmits all four CSI-RS antenna ports, if the CSI-RS RE group size is 4 RE, the CSI-RS REs for the four CSI-RS antenna ports are one CSI-RS. It can be mapped within an RE group. Or, if one cell supports 8 CSI-RS antenna port transmissions, if the CSI-RS RE group size is 4 RE, the CSI-RS RE for the 8 CSI-RS antenna ports is 2 CSI-RS It can be mapped to an RE group. In this case, the two CSI-RS RE groups need not be arranged adjacent to each other, but may be arranged in any CSI-RS RE group in the corresponding resource block.

In a simple channel estimation implementation, the CSI-RS RE pattern has the full bandwidth (at least in subframes that do not include the Primary Broadcast Channel, the Primary Synchronization Channel, and the Secondary Synchronization Channel). The same can be configured over. Mapping within the smallest possible number of CSI-RS groups of CSI-RS antenna ports is particularly important if the cell wishes to support a transmit diversity transmission scheme for a base station. This is because a plurality of SFBC time-space coded RE pairs for the transmission diversity transmission scheme may be broken when the CSI-RS RE is distributed to a plurality of CSI-RS groups. This is because the SFBC and SFBC-FSTD transmit diversity transmission schemes have a base RE block to which space-frequency coding and / or antenna selective / frequency selective diversity are applied. Transmitting a CSI-RS in a particular RE may corrupt the diversity basic block and impair the performance of the transmit diversity transmission scheme.

Among the embodiments of the CSI-RS RE group proposed in the present invention, the embodiments of the CSI-RS RE group shown in FIGS. 12, 14, and 16 are any CSI-RS RE mapped in one CSI-RS RE group. It is more preferred than other embodiments in that it does not compromise one or more SFBC RE pairs. However, the present invention does not exclude the CSI-RS RE group defined in FIGS. 13 and 15.

Referring to FIG. 17, in an OFDM symbol not including CRS or DMRS, a CSI-RS RE group (including four REs in each group) in one resource block may be defined as four consecutive REs. have. Note that the CSI-RS RE groups do not overlap with each other. The CSI-RS RE group is identical to the basic RE group (s) to which transmit diversity is applied. When each CSI-RS RE group has only two REs, the CSI-RS RE group may be defined as two consecutive REs.

As shown in FIG. 18, when the CSI-RS RE group is composed of four REs, the CSI-RS RE group located on the same OFDM symbol as the DMRS RE necessarily belongs to one transmission diversity basic RE group. It may not consist of four usable REs. In this case, a CSI-RS RE group located in the same OFDM symbol as the DMRS RE may be defined as two sets of two REs, each set being two consecutive REs belonging to different transmit diversity RE groups. Can be configured. In FIG. 18, one thick solid line square group represents a set composed of two REs, and two thick solid line square groups constitute one CSI-RS RE group. The definition of a CSI-RS RE group in this manner is that a CSI-RS RE group consisting of four REs defines two RE sets, and Alamouti-coding (SFBC) over these two RE sets. And antenna / frequency selective diversity can be used. This means that a transmission diversity basic block consisting of four consecutive REs (four consecutive REs consisting of one thick dotted square group and one thick solid square group, and four consecutive REs in FIG. Are shown, the first two REs (e.g., a group of bold dotted rectangles) are mapped to common antenna ports 0 and 2 coded using SFBC and the next two REs (e.g., bold, solid) Square groups) are mapped to common antenna ports 1 and 3 that are coded using SFBC. That is, if a CSI-RS RE is mapped to the first two REs in a transmit diversity basic block consisting of four consecutive REs, the first two REs cannot be used for common antenna ports 0 and 2, and the last two If CSI-RS REs are mapped in two REs, the last two REs cannot be used for common antenna ports 1 and 3. Thus, we take the latter two REs in one transmit diversity base block (the first four consecutive REs) and the first two REs in the other transmit diversity base block (the next four consecutive REs). Taken, four REs can be used to construct a virtual transport diversity basic block. The definition of a CSI-RS RE group in an OFDM symbol containing DMRS is that the mapping of all common antenna ports (0, 1, 2, 3) when mapping the CSI-RS RE to this particular type of CSI-RS RE group. This is important because it can effectively balance the treatment. Here, puncturing means that when a CSI-RS is transmitted on a specific RE, the corresponding RE cannot be used for a common antenna port.

As shown in FIG. 19, when the CSI-RS RE group is composed of four REs, the CSI-RS RE group located on the same OFDM symbol as the CRS RE necessarily belongs to one transmission diversity basic RE group. It may not consist of four usable REs. The CSI-RS RE groups on the OFDM symbol including the CRS can be conceptually configured as shown in FIG. 19, and according to the configuration of the CSI-RS RE group, puncturing for the common antenna port can be effectively balanced.

As shown in FIG. 20, the CSI-RS antenna port RE mapped to the CSI-RS RE group may be hopped (modified or randomized) within each CSI-RS transmission subframe. In FIG. 20, '1', '2', '3' and '4' indicate REs used for CSI-RS antenna ports 0, 1, 2 and 3, respectively.

This hopping can be performed in a variety of ways.

One method is to define the time and frequency shift of the CSI-RS RE group in each transmission subframe. The CSI-RS RE group hopping pattern may be repeated once in one radio frame (10 subframes) or N radio frames (10 × N subframes, N ≧ 2). N may be 4, for example, and four radio frames correspond to a period during which the main broadcast channel is transmitted.

Another method is to define a virtual CSI-RS group index and define a hopping (randomized or permutation) mapping function that maps the virtual CSI-RS group index to the physical CSI-RS group index (see FIG. 21). In this mapping function, cyclic virtual index shifting, a subblock interleaver, a quadratic permutation polynomial (QPP) interleaver, or the like can be used.

The circular virtual index shifting method is a method of mapping a CSI-RS group to a virtual index. In relation to cyclic virtual index shifting, a case in which the UE operates according to a cooperative multi-point (CoMP) transmission scheme may be considered. CoMP transmission method is an improved MIMO transmission method that can be applied in a multi-cell environment. It can reduce inter-cell interference and improve throughput of a user at a cell boundary, thereby improving system-wide performance. In this way, techniques such as Joint Processing and Cooperative Beamforming may be applied. In the CoMP transmission scheme, a terminal receiving data through cooperation of a multi-cell may transmit channel information on a channel from a multi-cell to a terminal to each cell belonging to the corresponding multi-cell (CoMP transmission cluster). have. The virtual index may be set not to overlap between cells belonging to one CoMP transport cluster. Cells belonging to different CoMP clusters may use the same virtual indexes, but each CoMP cluster may cyclically shift the indexes when mapping virtual indexes to physical indexes. In this way, orthogonal CSI-RS RE group mapping is possible in one CoMP cluster. In addition, non-orthogonal CSI-RS RE group mapping is basically possible between different CoMP clusters, and different CSI-RS RE groups can be mapped between different CoMP clusters by cyclic shifting of virtual indexes. .

Next, a block interleaver may be used to randomize CSI-RS RE group mapping between cells. The CSI-RS RE group index can be defined as v _k (k = 1, 2, ..., L), where L is the interleaver input size. The block interleaver may be composed of a matrix, input information may be recorded in a row by row interleaver, and output information may be read from a column by column interleaver. In other words, when recording information to the interleaver, record by increasing the column number in one row, and recording by moving to the next row when one row is filled, and when reading information from the interleaver, the row number in one column. It reads in increments and reads one row, moving to the next one. The columns of the matrix constituting the block interleaver may be permuted. Alternatively, the block interleaver may be configured by writing in columns and reading in rows.

Using the block interleaver as described above, the CSI-RS group index can be effectively randomized. The following equation shows an example of a block interleaver matrix in which the CSI-RS group index is input in units of rows.

In Equation 28, M is the largest integer satisfying L ≦ MN. When MN> L, N _D = MN-L and v _{L + j} = [NULL] (j = 1, 2, ..., N _D ). That is, if the number of CSI-RS group indexes (L) does not exactly fit the size of the block interleaver matrix, the number of elements (N _D ) minus the number (L) of CSI-RS group indexes (MN) of the interleaver. You can pad null values. Null values are ignored when output from the block interleaver. That is, the CSI-RS group index is read from the interleaver except for the null value. The column permutation of the block interleaver may be defined as follows.

The matrix permutated according to Equation 29 may be expressed as follows.

The block interleaver output can be read column by column. In Equation 30, the output starts from v _{π (1)} of the first column, and the output index sequence is {v _{π (1) + N} , ..., v _{π (1) + (M-1) N} , v _{π (2)} , ..., v _{π (N) + MN} }. If a null value is present, the null value can be ignored and read, as described above.

Different CoMP clusters may use different column permutation or apply different cyclic shift values before mapping CSI-RS group indices to the interleaver matrix. Accordingly, different CSI-RS group index randomization can be applied for different CoMP clusters.

22 shows an example of a CSI-RS RE group in the case of an 8 transmit antenna. In the case of an 8 transmit antenna, 8 CSI-RS need to be transmitted to the terminal. Accordingly, this embodiment proposes a CSI-RS RE group having four SFBC encoded RE pairs when configuring a general CP subframe in a cell. One CSI-RS RE group may be defined as being composed of two RE sets, and one RE set is composed of two RE pairs (ie, four REs). That is, within one RE set, four REs are continuous in the time and frequency domain (the thick solid line square in FIG. 22 corresponds to one RE set), and the two RE sets are spaced at four subcarrier intervals in the frequency domain. It may have a form. Accordingly, from the viewpoint of the transmitting end, the same CSI-RS RE group pattern may be used in an OFDM symbol including a DMRS and an OFDM symbol not including a CRS or a DMRS. The RE positions indicated by the thick dashed line in FIG. 22 are similarly considered in FIG. 18 to effectively balance the puncturing of the common antenna port in the transmit diversity basic block.

In addition, this embodiment proposes that such a CSI-RS RE group is time shifted, frequency shifted, or time and frequency shifted from cell to cell. That is, the CSI-RS RE group pattern used in one cell may be used as a time and / or frequency shifted pattern in another cell.

In addition, each cell may hop the CSI-RS transmission among candidates of the CSI-RS RE group position at every transmission time point. Examples of candidates for the CSI-RS RE group position are as shown in FIG. 23. That is, two thick solid line squares denoted by 1 in FIG. 23 represent one candidate position of the CSI-RS RE group position, and similarly, two thick solid line squares denoted by 2, 3, 4, and 5 are similar. These represent one candidate positions of the CSI-RS RE group position. For example, in one resource block (14 OFDM symbols in the time domain × 12 subcarriers in the frequency domain), the CSI-RS RE group position indicated by 1 is the 3rd, 4th, 9th in the 6th and 7th OFDM symbols. The CSI-RS RE group position, labeled 2, corresponds to the 1st and 10th subcarrier positions, and corresponds to the 1st, 2nd, 7th, and 8th subcarrier positions in the 10th and 11th OFDM symbols, and denoted 3 The CSI-RS RE group position corresponds to the 3rd, 4th, 9th, and 10th subcarrier positions in the 10th and 11th OFDM symbols, and the CSI-RS RE group position indicated by 4 is the 10th and 11th OFDM symbols. The CSI-RS RE group position, denoted 5, corresponds to the fifth, sixth, eleventh, and twelfth subcarrier positions in the third, fourth, ninth, and tenth subcarrier positions in the thirteenth and fourteenth OFDM symbols. It may correspond to. Thus, 5 cells can use different CSI-RS RE group pattern at the same time.

In terms of transmit antennas, it is possible to re-allocate transmit power in the frequency domain but not in the time domain. In other words, when the total transmit power is limited, certain REs in one OFDM symbol can be power boosted by borrowing power from other REs in that OFDM symbol. When CSI-RSs for different antenna ports are multiplexed and orthogonalized, each CSI-RS borrows the same power from different REs to prevent orthogonality when different power boosting is applied per CSI-RS. All CSI-RSs need to be transmitted on the same OFDM symbol to be equally power boosted. When the CSI-RS RE group is defined as shown in FIG. 23, two methods of mapping the CSI-RS antenna ports may be considered. Examples of these two methods are as shown in Figs. 24 (a) and 24 (b).

In FIG. 24 (a), two thick solid line squares in one resource block represent one CSI-RS RE group, and other REs are not shown for clarity. According to the first mapping method shown in FIG. 24A, CSI-RS mapping may be switched between RBs, and all CSI-RS antenna ports may be efficiently mapped on the same OFDM symbol. Specifically, within the CSI-RS RE group on the odd-numbered resource block index, the CSI-RSs for four antenna ports are mapped to the first OFDM symbol (eg, 1,2 / 3,4) and the second OFDM The CSI-RSs for the remaining four antenna ports may be mapped to the symbol (eg, 5, 6/7, 8). The CSI-RS mapping on the even-numbered resource block index is applied in the opposite direction to the odd-numbered resource block index so that the CSI-RS insertion pattern is swapped between OFDM symbols. That is, within the CSI-RS group on the even-numbered resource block index, the CSI-RSs for four antenna ports are mapped to the first OFDM symbol (for example, 5,6 / 7,8) and the second OFDM symbol. CSI-RSs for the remaining four antenna ports may be mapped (eg, 1,2 / 3,4). Accordingly, CSI-RSs for all eight transmit antenna ports may be mapped in one OFDM symbol (over two resource blocks).

In FIG. 24B, the horizontal axis represents a frequency domain and the vertical axis represents a code resource region. In FIG. 24 (b), two CSI-RS RE groups (one CSI-RS RE group is composed of two thick solid line squares) are shown, which means that each CSI-RS RE group uses different code resources. In order to illustrate, it should be noted that the CSI-RS RE group is actually present at the same time / frequency position. According to the second mapping method shown in FIG. 24 (b), four CSI-RSs (1, 2/3, 4) have a first orthogonal code ({+) on one OFDM symbol in frequency division multiplexing (FDM). 1, + 1}), and the remaining four CSI-RSs (5,6 / 7,8) are arranged by multiplying a second orthogonal code ({+ 1, -1}) on the same OFDM symbol and subcarrier Can be. Accordingly, all of the CSI-RSs for the eight antenna ports may be transmitted on the same OFDM symbol in one resource block. Since there are only four REs that can be used for CSI-RS transmission on one OFDM symbol, two sets of CSI-RSs can be code division multiplexed (CDM) by using a time spread orthogonal code. . As described above, the case where the orthogonal codes are multiplied over the time domain may be referred to as multiplexing of the CDM-T scheme. As the orthogonal code, for example, Walsh-Hadamard code may be used. Accordingly, four groups of REs multiplexed by the CDM scheme are generated, and the CSI-RS for each antenna port may be multiplexed by the FDM scheme in each of the four RE groups.

25 to 27 are diagrams for explaining an example of CSI-RS multiplexing when four CSI-RSs are transmitted from a single cell. Four CSI-RS multiplexing may be a subset of eight CSI-RS multiplexing. That is, eight REs (two thick solid squares) can be used for eight CSI-RS multiplexing, and a subset (four REs) can be used for four CSI-RS multiplexing. have. For example, four CSI-RSs may be mapped to four RE units (one thick solid line square in FIGS. 25 to 27) that are continuous in the time and frequency domain. A CSI-RS RE group in which four CSI-RSs are multiplexed may be defined in a form in which two of two REs (SFBC RE pairs) that are contiguous in the frequency domain that can be used as SFBC pairs are contiguous in the time domain. That is, a group of four REs (one thick solid line square) continuous in the time / frequency domain may be defined as one CSI-RS RE group. Accordingly, as illustrated in FIG. 26, 10 CSI-RS RE group patterns may be defined, and one CSI-RS RE group among 10 CSI-RS RE group patterns may be used for 4 CSI-RS transmission. have. In addition, as shown in FIG. 27A, the CSI-RS mapping may be mapped in a manner of swapping in the time domain in odd-numbered resource blocks and even-numbered resource blocks, and thus the same OFDM symbol over two resource blocks. All of the CSI-RS for the four antenna ports can be transmitted in the above, and power reallocation can be fully utilized. In addition, as shown in FIG. 27B, the CSI-RS mapping multiplexes two CSI-RSs in one CSI-RS RE group (bold solid square) by the FDM scheme, and is orthogonal to length 2 over a time domain. Multiplex four CSI-RSs in one CSI-RS RE group by multiplexing two CSI-RSs in a CDM-T scheme by multiplying code resources ({+ 1, + 1} and {+1, -1}) Can be sent. The details of the configuration of the CSI-RS RE group and the multiplexing of a plurality of CSI-RSs in the CSI-RS RE group may be described by the same principle as described in the above-described other embodiments, and overlapping information may be used for clarity. The description is omitted for the sake of brevity.

In addition, this embodiment proposes that such a CSI-RS RE group is time shifted, frequency shifted, or time and frequency shifted from cell to cell. That is, the CSI-RS RE group pattern used in one cell may be used as a time and / or frequency shifted pattern in another cell. In addition, each cell may hop the CSI-RS transmission among candidates of the CSI-RS RE group position at every transmission time point. Examples of candidates of CSI-RS RE group positions may include candidates of 10 CSI-RS RE group positions, as shown in FIG. 26. Thus, 10 cells can use different CSI-RS RE group patterns at the same time.

28 to 30 are diagrams for explaining another example of CSI-RS multiplexing when four CSI-RSs are transmitted from a single cell. Four CSI-RS multiplexing may be a subset of eight CSI-RS multiplexing. That is, eight REs (two thick solid squares) can be used for eight CSI-RS multiplexing, and a subset (four REs) can be used for four CSI-RS multiplexing. have. For example, as illustrated in FIG. 28, four CSI-RSs may be mapped to four CSI-RS REs existing on the same OFDM symbol. The four CSI-RS REs may be defined in such a manner that two of two consecutive REs (SFBC RE pairs) are spaced apart by four subcarriers on the same OFDM symbol in a frequency domain that can be used as an SFBC pair. Four CSI-RS REs defined as described above may form one CSI-RS RE group. Accordingly, as illustrated in FIG. 29, 13 CSI-RS RE group patterns may be defined, and one CSI-RS RE group among 13 CSI-RS RE group patterns may be used for 4 CSI-RS transmission. have. In addition, as shown in FIG. 30, CSI-RSs for four antenna ports in one CSI-RS RE group may be multiplexed and transmitted by the FDM scheme. The details of the configuration of the CSI-RS RE group and the multiplexing of a plurality of CSI-RSs in the CSI-RS RE group may be described by the same principle as described in the above-described other embodiments, and overlapping information may be used for clarity. The description is omitted for the sake of brevity.

In addition, this embodiment proposes that such a CSI-RS RE group is time shifted, frequency shifted, or time and frequency shifted from cell to cell. That is, the CSI-RS RE group pattern used in one cell may be used as a time and / or frequency shifted pattern in another cell. In addition, each cell may hop the CSI-RS transmission among candidates of the CSI-RS RE group position at every transmission time point. Examples of candidates of CSI-RS RE group positions may include candidates of 13 CSI-RS RE group positions, as shown in FIG. 29. Thus, 13 cells can use different CSI-RS RE group pattern at the same time.

Or, as described above, the CSI-RS RE group for the four CSI-RS antenna ports may be a pattern of the CSI-RS RE group for the eight transmitting CSI-RS antenna ports (eg, the CSI-RS RE of FIG. 23). Pattern), and the subset may be set as a set of various RE positions. For example, as shown in FIG. 31, the CSI-RS RE group for four CSI-RS antenna ports may include a CSI-RS RE group pattern for eight CSI-RS antenna ports (eg, FIG. 23). The two consecutive OFDM symbols at two RE and two other subcarrier positions (subcarrier positions spaced apart from the predetermined subcarrier position by 5 subcarriers) from two REs on two consecutive OFDM symbols at a predetermined subcarrier position in the CSI-RS RE pattern of It may be defined as two REs on a phase. One CSI-RS RE group is composed of four REs, and each CSI-RS for four CSI-RS antenna ports can be transmitted, one in each RE, and in this case, four CSI-RSs in a TDM / FDM manner. Can be expressed as multiplexed. Alternatively, in one CSI-RS RE group, CSI-RSs for two CSI-RS antenna ports may be multiplexed in a CDM-T scheme using a length 2 orthogonal code over two REs existing on the same subcarrier. The CSI-RS for the remaining two CSI-RS antenna ports may be multiplexed in a CDM-T scheme using an orthogonal code of length 2 across two REs present on different subcarriers. In the CSI-RS RE group for four CSI-RS antenna ports as shown in FIG. 31, candidates of 10 CSI-RS RE group positions may exist in one resource block. One cell selects one of the 10 CSI-RS RE group candidates and the other cell selects another candidate position so that each cell transmits CSI-RS for four CSI-RS antenna ports without overlapping. Can be.

32 and 33 are diagrams for explaining an example of CSI-RS multiplexing when two CSI-RSs are transmitted from a single cell. Two CSI-RS multiplexing may be a subset of eight CSI-RS multiplexing. That is, eight REs (two thick solid squares) can be used for eight CSI-RS multiplexing, and a subset (two REs) can be used for two CSI-RS multiplexing. have. For example, as illustrated in FIG. 32, two CSI-RSs may be defined as two REs (SFBC RE pairs) contiguous in the frequency domain that may be used as SFBC pairs. Two CSI-RS REs defined as described above may constitute one CSI-RS RE group. Accordingly, as illustrated in FIG. 33, 26 CSI-RS RE group patterns may be defined, and one CSI-RS RE group may be used among 26 CSI-RS RE group patterns for 2 CSI-RS transmission. have. In addition, the CSI-RS for two antenna ports in one CSI-RS RE group may be multiplexed and transmitted by the FDM scheme. The details of the configuration of the CSI-RS RE group and the multiplexing of a plurality of CSI-RSs in the CSI-RS RE group may be described by the same principle as described in the above-described other embodiments, and overlapping information may be used for clarity. The description is omitted for the sake of brevity.

In addition, this embodiment proposes that such a CSI-RS RE group is time shifted, frequency shifted, or time and frequency shifted from cell to cell. That is, the CSI-RS RE group pattern used in one cell may be used as a time and / or frequency shifted pattern in another cell. In addition, each cell may hop the CSI-RS transmission among candidates of the CSI-RS RE group position at every transmission time point. Examples of candidates of CSI-RS RE group positions may include 26 candidate CSI-RS RE group positions as shown in FIG. 33. Thus, 26 cells can use different CSI-RS RE group pattern at the same time.

Or, as described above, the CSI-RS RE group for the two CSI-RS antenna ports may be a pattern of the CSI-RS RE group for the 8 transmitting CSI-RS antenna ports (eg, the CSI-RS RE of FIG. 23). Pattern), and the subset may be set as a set of various RE positions. For example, as shown in FIG. 34, a CSI-RS RE group for two CSI-RS antenna ports may include a CSI-RS RE group pattern (eg, FIG. 23 for eight CSI-RS antenna ports). In the CSI-RS RE pattern), two REs on two consecutive OFDM symbols at a predetermined subcarrier location may be defined. One CSI-RS RE group is composed of two REs. In each RE, CSI-RSs for two CSI-RS antenna ports can be transmitted. In this case, two CSI-RSs are multiplexed by TDM. It can be expressed as being. Alternatively, in one CSI-RS RE group, CSI-RSs for two CSI-RS antenna ports may be multiplexed in a CDM-T scheme using a length 2 orthogonal code over two REs existing on the same subcarrier. Can be. In the CSI-RS RE group for two CSI-RS antenna ports as shown in FIG. 34, candidates of 20 CSI-RS RE group positions may exist in one resource block. One cell selects one of the candidates of the 20 CSI-RS RE group positions, and the other cell selects another candidate position so that each cell transmits CSI-RS for two CSI-RS antenna ports without overlapping. Can be.

35 is a view for explaining a CSI-RS transmission method and a channel information acquisition method.

In step S3510, the base station may select one of a plurality of CSI-RS RE groups defined on the data region of the downlink subframe for CSI-RS transmission for 8 or less antenna ports.

The plurality of CSI-RS resource element groups may be defined such that transmission diversity resource element pairs (eg, SFBC pairs) for data transmitted on a downlink subframe are not compromised. For example, when the downlink subframe has a general CP configuration, the plurality of CSI-RS RE groups may be five CSI-RS RE groups shown in FIG. 23 for 8 transmit antennas in one resource block. . That is, each of the plurality of CSI-RS RE groups has two consecutive subcarrier positions of two consecutive OFDM symbols and other two spaced apart from the two consecutive subcarrier positions on resource elements where CRS and DMRS are not disposed. It can be defined at two consecutive subcarrier positions. Such a plurality of CSI-RS resource element groups may be defined as resource element positions in which one CSI-RS resource element group is shifted in the time and frequency domain with respect to another CSI-RS resource element group.

In addition, the plurality of CSI-RS RE groups to which the CSI-RSs are mapped to the four antenna ports may be defined as a subset of the plurality of CSI-RS RE groups to which the CSI-RSs to the eight antenna ports are mapped. have. For example, in the case of 4 transmit antennas, the plurality of CSI-RS RE groups may be 10 CSI-RS RE groups of FIG. 26 or 10 CSI-RS RE groups of FIG. 31. Alternatively, 13 CSI-RS RE groups of FIG. 29 may be used for four transmit antennas.

In addition, the plurality of CSI-RS RE groups to which the CSI-RSs are mapped to the two antenna ports may be defined as a subset of the plurality of CSI-RS RE groups to which the CSI-RSs to the eight antenna ports described above are mapped. have. For example, in the case of two transmit antennas, the plurality of CSI-RS RE groups may be 20 CSI-RS RE groups of FIG. 34. Alternatively, 26 CSI-RS RE groups of FIG. 33 may be used for two transmit antennas.

In operation S3520, the base station may map CSI-RSs for 8 or less antenna ports to one CSI-RS RE group selected from the plurality of CSI-RS RE groups described above. In this case, the CSI-RSs for two antenna ports among the CSI-RSs for the 8 or less antenna ports may be multiplexed by the CDM-T scheme using an orthogonal code of length 2 over two consecutive OFDM symbols on the same subcarrier. have.

In step S3530, the base station may transmit a downlink subframe mapped to the CSI-RS for the 8 or less antenna ports.

In the case where CSI-RSs for 8 or less antenna ports are mapped and transmitted to one CSI-RS RE group selected as described above in one subframe, another CSI-RS RE group different from the CSI-RS RE group selected above is transmitted in another subframe. CSI-RSs for 8 or less antenna ports may be mapped and transmitted to the RS RE group.

In step S3540, the UE is a downlink in which the CSI-RS for 8 or less antenna ports are mapped to one CSI-RS RE group selected from a plurality of CSI-RS RE groups defined on a data region of a downlink subframe from a base station. Subframes may be received.

In step S3550, the UE can measure the channel information for each antenna port using the CSI-RS for the 8 or less antenna ports. Additionally, the terminal may feed back the measured channel information (channel state information (CSI)) to the base station.

35 illustrates a method according to an embodiment of the present invention performed by a base station and a terminal for clarity, the details of the above-described embodiments of the present invention may be applied.

36 is a diagram showing the configuration of a preferred embodiment of a wireless communication system including a base station apparatus and a terminal apparatus according to the present invention.

The base station apparatus (eNB) 3610 may include a receiving module 3611, a transmitting module 3612, a processor 3613, a memory 3614, and an antenna 3615. The receiving module 3611 may receive various signals, data, information, and the like from the terminal. The transmission module 3612 may transmit various signals, data, information, and the like to the terminal. The processor 3613 may be configured to control the overall operation of the base station apparatus 3610 including the receiving module 3611, the transmitting module 3612, the memory 3614, and the antenna 3615. The antenna 3615 may be configured of a plurality of antennas.

The base station apparatus 3610 according to an embodiment of the present invention may transmit CSI-RSs for 8 or less antenna ports. The processor 3613 of the base station apparatus may be configured to select one of a plurality of CSI-RS RE groups defined on the data region of the downlink subframe to map CSI-RSs for 8 or less antenna ports. In addition, the processor 3613 may be configured to transmit the downlink subframe to which the CSI-RSs for 8 or less antenna ports are mapped through the transmission module 3612. A plurality of CSI-RS RE groups may be defined so that a pair of transmit diversity resource elements for data transmitted on a downlink subframe is not compromised.

In addition, the processor 3613 performs a function of processing information received by the terminal device, information to be transmitted to the outside, and the like, and the memory 3614 may store the processed information for a predetermined time and may include a buffer (not shown). May be replaced by a component such as).

Meanwhile, the UE 3620 may include a receiving module 3621, a transmitting module 3622, a processor 3623, a memory 3624, and an antenna 3625. The receiving module 3621 may receive various signals, data, information, and the like from the terminal. The transmission module 3622 may transmit various signals, data, information, and the like to the terminal. The processor 3623 may be configured to control overall operation of the base station apparatus 3620 including the receiving module 3621, the transmitting module 3622, the memory 3624, and the antenna 3625. The antenna 3625 may be configured of a plurality of antennas.

The terminal device 3620 according to an embodiment of the present invention can measure channel information from the CSI-RS for 8 or less antenna ports. The processor 3623 of the terminal device transmits 8 or fewer antenna ports to one CSI-RS RE group selected from a plurality of CSI-RS RE groups defined on the data region of the downlink subframe through the receiving module 3621. The CSI-RS may be configured to receive the mapped downlink subframe. In addition, the processor 3623 may be configured to measure channel information for each antenna port using CSI-RS for 8 or less antenna ports. The plurality of CSI-RS resource element groups may be defined such that a transmission diversity resource element pair for data transmitted on a downlink subframe is not compromised.

In addition, the processor 3623 performs a function of processing information received by the terminal device, information to be transmitted to the outside, and the like, and the memory 3624 may store the processed information for a predetermined time and may include a buffer (not shown). May be replaced by a component such as).

The above-described embodiments of the present invention can be implemented by various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

For implementation in hardware, a method according to embodiments of the present invention may include one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), and Programmable Logic Devices (PLDs). It may be implemented by field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, the method according to embodiments of the present invention may be implemented in the form of a module, a procedure or a function for performing the functions or operations described above. The software code can be stored in a memory unit and driven by the processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various well-known means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the present invention. While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, those skilled in the art can utilize each of the configurations described in the above-described embodiments in a manner of mutually combining them. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above detailed description should not be interpreted as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, claims that do not have an explicit citation in the claims can be combined to form an embodiment or included as a new claim by amendment after the application.

3611, 3621 Receive Module 3612, 3622 Transmission Module
3613, 3623 Processor 3614, 3624 Memory
3615, 3625 Antenna

Claims (16)

A method of transmitting channel state information-reference signal (CSI-RS) for up to eight antenna ports,
Transmitting the CSI-RS in a downlink subframe,
The CSI-RS is mapped to one RE set among a plurality of RE element candidates, and the one RE set includes a plurality of REs.
The number of the plurality of candidates in the set of resource elements (RE) for eight antenna ports is five,
Within the resource region defined by 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols and 12 subcarriers in the downlink subframe, the 5 RE set candidates for the 8 antenna ports are:
A first RE set defined on third, fourth, ninth, and tenth subcarriers on the sixth and seventh OFDM symbols;
A second RE set defined on first, second, seventh and eighth subcarriers on the tenth and eleventh OFDM symbols;
A third RE set defined on third, fourth, ninth, and tenth subcarriers on the tenth and eleventh OFDM symbols;
A fourth RE set defined on the fifth, sixth, eleventh, and twelfth subcarriers on the tenth and eleventh OFDM symbols; And
A fifth RE set defined on the third, fourth, ninth, and tenth subcarriers on the thirteenth and fourteenth OFDM symbols,
The plurality of RE set candidates for two antenna ports and the plurality of RE set candidates for four antenna ports are defined as a subset of the plurality of RE set candidates for the eight antenna ports. Transmission method. delete delete delete The method of claim 1,
One RE set candidate is shifted with respect to another RE set candidate in one or more of a time domain or a frequency domain. The method of claim 1,
The CSI-RSs of two antenna ports of the CSI-RSs for the eight or less antenna ports are multiplexed using a code division multiplexing (CDM) scheme using an orthogonal code of length 2 over two OFDM symbols on the same subcarrier. CSI-RS transmission method. delete A method of measuring channel information from channel state information-reference signals (CSI-RS) for up to eight antenna ports,
Receiving the CSI-RS in a downlink subframe; And
Measuring the channel information based on the CSI-RSs for the eight antenna ports or less;
The CSI-RS is mapped to one RE set among a plurality of RE element candidates, and the one RE set includes a plurality of REs.
The number of the plurality of candidates in the set of resource elements (RE) for eight antenna ports is five,
Within the resource region defined by 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols and 12 subcarriers in the downlink subframe, the 5 RE set candidates for the 8 antenna ports are:
A first RE set defined on third, fourth, ninth, and tenth subcarriers on the sixth and seventh OFDM symbols;
A second RE set defined on first, second, seventh and eighth subcarriers on the tenth and eleventh OFDM symbols;
A third RE set defined on third, fourth, ninth, and tenth subcarriers on the tenth and eleventh OFDM symbols;
A fourth RE set defined on the fifth, sixth, eleventh, and twelfth subcarriers on the tenth and eleventh OFDM symbols; And
A fifth RE set defined on the third, fourth, ninth and tenth subcarriers on the thirteenth and fourteenth OFDM symbols,
The plurality of RE set candidates for two antenna ports and the plurality of RE set candidates for four antenna ports are defined as a subset of the plurality of RE set candidates for the eight antenna ports Way. delete delete delete The method of claim 8,
One RE set candidate is shifted with respect to another RE set candidate in at least one of a time domain or a frequency domain. The method of claim 8,
The CSI-RS of two antenna ports among the CSI-RSs for the eight or less antenna ports are multiplexed using a code division multiplexing (CDM) scheme using an orthogonal code having a length of 2 over two OFDM symbols on the same subcarrier. Method of measuring channel information. delete A base station transmitting channel state information-reference signal (CSI-RS) for up to eight antenna ports,
A receiving module for receiving an uplink signal from a terminal;
A transmission module for transmitting a downlink signal to the terminal; And
A processor for controlling the base station including the receiving module and the transmitting module,
The processor is configured to transmit the CSI-RS in a downlink subframe using the transmission module,
The CSI-RS is mapped to one RE set among a plurality of RE element candidates, and the one RE set includes a plurality of REs.
The number of the plurality of candidates in the set of resource elements (RE) for eight antenna ports is five,
Within the resource region defined by 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols and 12 subcarriers in the downlink subframe, the 5 RE set candidates for the 8 antenna ports are:
A first RE set defined on third, fourth, ninth, and tenth subcarriers on the sixth and seventh OFDM symbols;
A second RE set defined on first, second, seventh and eighth subcarriers on the tenth and eleventh OFDM symbols;
A third RE set defined on third, fourth, ninth, and tenth subcarriers on the tenth and eleventh OFDM symbols;
A fourth RE set defined on the fifth, sixth, eleventh, and twelfth subcarriers on the tenth and eleventh OFDM symbols; And
A fifth RE set defined on the third, fourth, ninth and tenth subcarriers on the thirteenth and fourteenth OFDM symbols,
The plurality of RE set candidates for two antenna ports and the plurality of RE set candidates for four antenna ports are defined as a subset of the plurality of RE set candidates for the eight antenna ports. Transmission base station. A terminal for measuring channel information from channel state information-reference signal (CSI-RS) for up to eight antenna ports,
A receiving module for receiving a downlink signal from a base station;
A transmission module for transmitting an uplink signal to the base station; And
And a processor for controlling the terminal including the receiving module and the transmitting module,
The processor is configured to receive the CSI-RS in a downlink subframe using the receiving module and to measure the channel information based on CSI-RSs for the eight or less antenna ports.
The CSI-RS is mapped to one RE set among a plurality of RE element candidates, and the one RE set includes a plurality of REs.
The number of the plurality of candidates in the set of resource elements (RE) for eight antenna ports is five,
Within the resource region defined by 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols and 12 subcarriers in the downlink subframe, the 5 RE set candidates for the 8 antenna ports are:
A first RE set defined on third, fourth, ninth, and tenth subcarriers on the sixth and seventh OFDM symbols;
A second RE set defined on first, second, seventh and eighth subcarriers on the tenth and eleventh OFDM symbols;
A third RE set defined on third, fourth, ninth, and tenth subcarriers on the tenth and eleventh OFDM symbols;
A fourth RE set defined on the fifth, sixth, eleventh, and twelfth subcarriers on the tenth and eleventh OFDM symbols; And
A fifth RE set defined on the third, fourth, ninth and tenth subcarriers on the thirteenth and fourteenth OFDM symbols,
The plurality of RE set candidates for two antenna ports and the plurality of RE set candidates for four antenna ports are defined as a subset of the plurality of RE set candidates for the eight antenna ports Terminal.

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