JP5779595B2 - Method and apparatus for transmitting a downlink reference signal in a wireless communication system supporting multiple antennas - Google Patents

Description

  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.

  The multiple input multiple output (MIMO) system refers to a system that improves data transmission and reception efficiency using multiple transmission antennas and multiple reception antennas. The MIMO technology includes a spatial diversity method and a spatial multiplexing method. The spatial diversity method is suitable for data transmission to a terminal that moves at high speed because the transmission reliability (reliability) and the cell radius can be increased using diversity gain (gain). The spatial multiplexing method can increase the data transmission rate without increasing the system bandwidth by simultaneously transmitting different data.

  In a MIMO system, each transmit antenna has an independent data channel. A transmit antenna may refer to a virtual antenna or a physical antenna. The receiver estimates the channel for each of the transmission antennas and receives data transmitted from each transmission antenna. Channel estimation refers to a process of recovering a received signal by compensating for signal distortion caused by fading. Fading here refers to a phenomenon in which the signal strength suddenly varies due to multipath-time delay in a wireless communication system environment. For channel estimation, a reference signal known by both the transmitter and the receiver is required. Further, the reference signal may be abbreviated as RS (Reference Signal), and may be referred to as a pilot depending on an applied standard.

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

  Systems with an extended antenna configuration (eg, LTE-A standard supporting 8 transmit antennas) compared to existing communication systems that support 4 transmit antennas (eg, systems according to LTE release 8 or 9 standards) In order to support efficient reference signal operation and advanced transmission schemes, DMRS-based data demodulation is considered. That is, DMRS for two or more layers can be defined to support data transmission through an extended antenna. Since DMRS is precoded by the same precoder as the data, channel information for demodulating data can be easily estimated on the receiving side without using separate precoding information.

  On the other hand, on the downlink receiving side, pre-coded channel information for the extended antenna configuration can be obtained through DMRS, but a separate reference signal other than DMRS is used to obtain non-pre-coded channel information. Is required. Therefore, in a system according to the LTE-A standard, a reference signal for acquiring channel state information (CSI) on the receiving side, that is, a CSI-RS can be defined.

  The present invention provides a method and apparatus for transmitting a CSI-RS on a downlink resource element (RE) so that channel estimation can be performed efficiently on the downlink reception side in MIMO transmission. Is a technical issue.

  In order to solve the above technical problem, 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 is provided on a data region of a downlink subframe. 1 is selected from a plurality of CSI-RS resource element groups defined in the above, and CSI-RSs for the antenna ports of 8 or less are mapped, and CSI-RSs for the antenna ports of 8 or less are mapped. Transmitting the downlink subframe, wherein the plurality of CSI-RS resource element groups are defined such that a transmission diversity resource element pair for data transmitted on the downlink subframe is not damaged. It is good to be done.

  Also, the downlink subframe has a general CP (Cyclic Prefix) configuration, and a plurality of CSI-RS resource element groups to which CSI-RSs for eight antenna ports are mapped are included in one resource block. It is defined as five groups, and one CSI-RS resource element group is composed of two consecutive OFDM (Orthogonal Frequency Division) on a resource element in which a shared reference signal (CRS) and a demodulation reference signal (DMRS) are not arranged. It may be defined by two consecutive subcarrier positions of a Multiplexing symbol and two other consecutive subcarrier positions that are separated from the two consecutive subcarrier positions by four subcarriers.

  A plurality of CSI-RS resource element groups to which CSI-RSs for two antenna ports are mapped, or a plurality of CSI-RS resource element groups to which CSI-RSs for four antenna ports are mapped are: Each may be defined as a subset of a plurality of CSI-RS resource element groups to which CSI-RSs for the eight antenna ports are mapped.

  In addition, five CSI-RS resource element groups to which CSI-RSs for the eight antenna ports are mapped in the one resource block are the third, fourth, and ninth in the sixth and seventh OFDM symbols. 1st CSI-RS resource element group at the 10th and 10th subcarrier positions and the 2nd CSI-RS at the 1st, 2nd, 7th and 8th subcarrier positions in the 10th and 11th OFDM symbols Resource element group, third CSI-RS resource element group at the third, fourth, ninth and tenth subcarrier positions in the tenth and eleventh OFDM symbols, fifth in the tenth and eleventh OFDM symbols , Fourth CSI-RS resource at sixth, eleventh and twelfth subcarrier positions The third in-containing group, and 13 th and 14 th OFDM symbol, 4 th, can include ninth and tenth of the 5 CSI-RS resource element groups of the subcarriers positions.

The plurality of CSI-RS resource element groups are defined as resource element positions in which one CSI-RS resource element group is shifted in time and frequency domains with respect to another one CSI-RS resource element group. It is good to be done.
In addition, among CSI-RSs for the antenna ports of 8 or less, CSI-RSs for two antenna ports are code division multiplexed using orthogonal codes of length 2 over two consecutive OFDM symbols on the same subcarrier. It may be multiplexed by the (CDM) method.

  Further, in another downlink subframe different from the downlink subframe, another CSI-RS resource element group excluding one CSI-RS resource element group selected from the plurality of CSI-RS resource element groups, CSI-RS for the antenna ports of 8 or less may be mapped.

  In order to solve the above technical problem, a method 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 includes a downlink subframe. The downlink subframe in which CSI-RSs for the eight or less antenna ports are mapped to one CSI-RS resource element group selected from a plurality of CSI-RS resource element groups defined on the data area of Receiving and measuring channel information for each antenna port using CSI-RSs for the eight or less antenna ports, wherein the plurality of CSI-RS resource element groups may include the downscaling. Transmit divers for data transmitted on link subframes City resource element pair may be defined so as not to be damaged.

  Also, the downlink subframe has a general CP (Cyclic Prefix) configuration, and a plurality of CSI-RS resource element groups to which CSI-RSs for eight antenna ports are mapped are included in one resource block. It is defined as five groups, and one CSI-RS resource element group is composed of two consecutive OFDM (Orthogonal Frequency Division) on a resource element in which a shared reference signal (CRS) and a demodulation reference signal (DMRS) are not arranged. It may be defined by two consecutive subcarrier positions of a Multiplexing symbol and two other consecutive subcarrier positions that are separated from the two consecutive subcarrier positions by four subcarriers.

  A plurality of CSI-RS resource element groups to which CSI-RSs for two antenna ports are mapped, or a plurality of CSI-RS resource element groups to which CSI-RSs for four antenna ports are mapped are: Each may be defined as a subset of a plurality of CSI-RS resource element groups to which CSI-RSs for the eight antenna ports are mapped.

  In addition, five CSI-RS resource element groups to which CSI-RSs for the eight antenna ports are mapped in the one resource block are the third, fourth, and ninth in the sixth and seventh OFDM symbols. 1st CSI-RS resource element group at the 10th and 10th subcarrier positions and the 2nd CSI-RS at the 1st, 2nd, 7th and 8th subcarrier positions in the 10th and 11th OFDM symbols Resource element group, third CSI-RS resource element group at the third, fourth, ninth and tenth subcarrier positions in the tenth and eleventh OFDM symbols, fifth in the tenth and eleventh OFDM symbols , Fourth CSI-RS resource at sixth, eleventh and twelfth subcarrier positions The third in-containing group, and 13 th and 14 th OFDM symbol, 4 th, can include ninth and tenth of the 5 CSI-RS resource element groups of the subcarriers positions.

  Further, the plurality of CSI-RS resource element groups are defined as resource element positions where one CSI-RS resource element group is shifted in time and frequency domains with respect to other CSI-RS resource element groups. Good.

  In addition, among CSI-RSs for the antenna ports of 8 or less, CSI-RSs for two antenna ports are code division multiplexed using orthogonal codes of length 2 over two consecutive OFDM symbols on the same subcarrier. It may be multiplexed by the (CDM) method.

  Further, in another downlink subframe different from the downlink subframe, another CSI-RS resource element group excluding one CSI-RS resource element group selected from the plurality of CSI-RS resource element groups, CSI-RS for the antenna ports of 8 or less may be mapped.

  In order to solve the above technical problem, a base station transmitting channel state information-reference signals (CSI-RS) for 8 or less antenna ports according to still another embodiment of the present invention is provided by a terminal. A reception module for receiving a link signal; a transmission module for transmitting a downlink signal to the terminal; and a processor for controlling the base station including the reception module and the transmission module. One is selected from a plurality of CSI-RS resource element groups defined on the data area of the frame, CSI-RSs for the 8 or less antenna ports are mapped, and CSI-RSs for the 8 or less antenna ports are mapped. The downlink subframe to which is mapped via the transmission module Is configured to transmit the plurality of CSI-RS resource element group is transmit diversity resource element pairs for data transmitted on the downlink subframe may be defined so as not to be damaged.

  In order to solve the above technical problem, a terminal that measures channel information from channel state information-reference signal (CSI-RS) for 8 or less antenna ports according to still another embodiment of the present invention includes: A reception module for receiving a downlink signal from a station, a transmission module for transmitting an uplink signal to the base station, and a processor for controlling the terminal including the reception module and the transmission module, the processor comprising: The downlink in which CSI-RSs corresponding to the eight or less antenna ports are mapped to one CSI-RS resource element group selected from a plurality of CSI-RS resource element groups defined on a data region of a downlink subframe. A link subframe is received via the receiving module, and the previous The CSI-RS is configured to measure channel information for each antenna port using CSI-RS for 8 or less antenna ports, and the plurality of CSI-RS resource element groups are transmitted on the downlink subframe. The transmission diversity resource element pair for data may be defined so as not to be damaged.

  The foregoing general description of the invention and the detailed description to be described later are both exemplary and are intended to further illustrate the claimed invention.

  According to each embodiment of the present invention, it is possible to provide a method and apparatus for multiplexing and transmitting CSI-RS on a downlink physical resource so that channel estimation can be performed efficiently on the downlink reception side. In addition, a method capable of providing as many CSI-RS RE group patterns as possible without damaging transmission diversity RE pairs, and reducing inter-cell interference of CSI-RS transmission while maintaining the efficiency of data transmission, and An apparatus can be provided.

  The effects obtained from the present invention are not limited to the effects mentioned above, and other effects that are not mentioned are clearly apparent to those having ordinary knowledge in the technical field to which the present invention belongs from the following description. Will be understood.

It is a figure which shows the structure of a downlink radio frame. It is a figure which shows an example of the resource grid (resource grid) with respect to 1 downlink slot. It is a figure which shows the structure of a downlink sub-frame. It is a figure which shows the structure of an uplink sub-frame. It is a block diagram of the radio | wireless communications system which has a multiple antenna. It is a figure which shows the general system structure of SC-FDMA and OFDMA. FIG. 2 is a diagram illustrating a system structure for uplink SC-FDMA in an LTE release-8 (release-8) system; It is a figure which shows the transmission frame structure with respect to uplink SC-FDMA in a LTE release-8 system. It is a figure which shows the data signal mapping relationship with respect to the MIMO system based on SC-FDMA transmission. It is a figure which shows the pattern by which CRS and DRS defined by the existing 3GPP LTE system (for example, release-8) are mapped on a downlink resource block. It is a figure which shows an example of the DMRS pattern for supporting maximum rank 8 transmission. It is a figure which shows various illustrations of a CSI-RS RE group. It is a figure which shows various illustrations of a CSI-RS RE group. It is a figure which shows various illustrations of a CSI-RS RE group. It is a figure which shows various illustrations of a CSI-RS RE group. It is a figure which shows various illustrations of a CSI-RS RE group. It is a figure for demonstrating the setting of the CSI-RS RE group which considered the transmission diversity RE pair. It is a figure for demonstrating the setting of the CSI-RS RE group which considered the transmission diversity RE pair. It is a figure for demonstrating the setting of the CSI-RS RE group which considered the transmission diversity RE pair. It is a figure for demonstrating the hopping of a CSI-RS RE group. It is a figure explaining the function which maps a virtual CSI-RS group index to a physical CSI-RS group index. It is a figure which shows an example of the CSI-RS RE group in the case of 8 transmission antennas. It is a figure which shows an example of the CSI-RS RE group in the case of 8 transmission antennas. It is a figure for demonstrating the mapping method of CSI-RS in the case of 8 transmission antennas. It is a figure which shows an example of the CSI-RS RE group in the case of 4 transmission antennas. It is a figure which shows an example of the CSI-RS RE group in the case of 4 transmission antennas. It is a figure for demonstrating the mapping method of CSI-RS in the case of 4 transmission antennas. It is a figure which shows the other example of the CSI-RS RE group in the case of 4 transmission antennas. It is a figure which shows the other example of the CSI-RS RE group in the case of 4 transmission antennas. It is a figure for demonstrating the mapping method of CSI-RS in the case of 4 transmission antennas. It is a figure which shows the other example of the CSI-RS RE group in the case of 4 transmission antennas. It is a figure which shows an example of the CSI-RS RE group in the case of 2 transmission antennas. It is a figure which shows an example of the CSI-RS RE group in the case of 2 transmission antennas. It is a figure which shows the other example of the CSI-RS RE group in the case of 2 transmission antennas. It is a flowchart explaining the CSI-RS transmission method and channel information acquisition method. It is a figure which shows the structure of the suitable Example of the radio | wireless communications system containing the base station apparatus and terminal device which concern on this invention.

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

  In the present specification, an embodiment of the present invention will be described focusing on the data transmission / reception relationship between the base station and the terminal. Here, the base station has a meaning as a terminal node of a network that directly communicates with a terminal. In this document, the specific operation that is performed by the base station may be performed by an upper node of the base station in some cases.

  That is, in a network composed of a large number of network nodes including a base station, various operations performed for communication with a terminal can be performed by the network node other than the base station or the base station. Is self-explanatory. The “base station (BS)” may be replaced with a fixed station (fixed station), a node B, an eNode B (eNB), an access point (AP), or the like. The repeater may be replaced with terms such as a relay node (Relay Node, RN), a relay station (Relay Station, RS), and the like. “Terminal” may be replaced with terms such as UE (User Equipment), MS (Mobile Station), MSS (Mobile Subscriber Station), SS (Subscriber Station), and the like.

  The specific terms used in the following description are provided to assist the understanding of the present invention, and the use of these specific terms can be changed to other forms without departing from the technical idea of the present invention. is there.

  In some instances, well-known structures and devices may be omitted or may be shown in block diagram form with the core functions of each structure and device being centered to avoid obscuring the concepts of the present invention. In addition, throughout the present specification, the same constituent elements will be described with the same reference numerals.

  Is the embodiment of the present invention supported by a standard document disclosed in at least one of the wireless connection systems IEEE 802 system, 3GPP system, 3GPP LTE and LTE-A (LTE-Advanced) system, and 3GPP2 system? it can. That is, in the embodiment of the present invention, stages or portions not described for clarifying the technical idea of the present invention can be supported by the standard document. It should be noted that all terms disclosed in this document can be explained by the above standard documents.

  The following technology, CDMA (Code Division Multiple Access), FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access), SC-FDMA (Single Carrier Frequency Division Multiple Access), etc. It can be used for various wireless connection systems. CDMA may be a radio technology such as UTRA (Universal Terrestrial Radio Access) or CDMA2000. The TDMA may be a radio technology such as Global System for Mobile Communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (Evolved UTRA), and the like. UTRA is a part of UMTS (Universal Mobile Telecommunication Systems). 3GPP (3rd Generation Partnership Project) LTE (long term evolution) is part of E-UMTS (Evolved UMTS) using E-UTRA, adopts OFDMA on the downlink, and SC-FDMA on the uplink . LTE-A (Advanced) is a development of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (Wireless MAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (Wireless MAN-OFDMA Advanced system). For clarity, the following description focuses on the 3GPP LTE and LTE-A standards, but the technical idea of the present invention is not limited thereto.

  The structure of the downlink radio frame will be described with reference to FIG.

  In the cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed in units of subframes, and one subframe is defined as a certain time interval including a number of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to FDD (Frequency Division Duplex) and a type 2 radio frame structure applicable to TDD (Time Division Duplex).

  FIG. 1 is a diagram illustrating a structure of a type 1 radio frame. The downlink radio frame is composed of 10 subframes, and one subframe is composed of 2 slots in a time domain. The time taken to transmit one subframe is called TTI (transmission time interval). For example, the length of one subframe is 1 ms and the length of one slot is 0.5 ms. One slot includes a plurality of OFDM symbols in the time domain, and includes 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. An OFDM symbol can 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 continuous subcarriers in one slot.

  The number of OFDM symbols included in one slot may vary depending on the configuration of CP (Cyclic Prefix). The CP includes an extended CP (extended CP) and a general CP (normal CP). For example, when the OFDM symbol is configured by a general CP, the number of OFDM symbols included in one slot may be seven. When an OFDM symbol is composed of an extended CP, the length of one OFDM symbol increases, so the number of OFDM symbols included in one slot is smaller than that of a general CP. In the case of the extended CP, for example, the number of OFDM symbols included in one slot may be six. An extended CP can be used to further reduce intersymbol interference when the channel state is not stable, such as when the terminal moves at high speed.

  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 in each subframe may be assigned to a PDCCH (physical downlink control channel), and the remaining OFDM symbols may be assigned to a PDSCH (physical downlink shared channel).

  The structure of the above radio frame is merely an example, and the number of subframes included in the radio frame, the number of slots included in the subframe, and the number of symbols included in the slots can be variously changed.

FIG. 2 is a diagram illustrating an example of a resource grid for one downlink slot. This corresponds to a case where the OFDM symbol is configured with a general 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, although one downlink slot includes 7 OFDM symbols and one resource block includes 12 subcarriers, the present invention is not limited thereto. Each element on the resource grid is called a resource element (RE). For example, resource element a (k, l) refers to a resource element located in the kth subcarrier and the lth OFDM symbol. In the case of a general CP, one resource block includes 12 × 7 resource elements (in the case of an extended CP, includes 12 × 6 resource elements). Since the interval between the subcarriers 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 can be determined according to the downlink transmission bandwidth set by the scheduling of the base station.

  FIG. 3 is a diagram illustrating a structure of a downlink subframe. The top three OFDM symbols in the first slot in one subframe correspond to a control region to which a control channel is assigned. The remaining OFDM symbols correspond to a data region 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. The downlink control channel used in the 3GPP LTE system includes, for example, a physical control format indicator channel (Physical Control Indicator Channel; PCFICH), a physical downlink control channel (Physical Downlink Control Channel; PDCCH indicator channel), and a physical HAR channel. (Physical Hybrid automatic repeat request Indicator Channel; PHICH). 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 to the uplink transmission. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information and includes an uplink transmission power control command for an arbitrary terminal group. PDCCH includes downlink shared channel (DL-SCH) resource allocation and transmission format, uplink shared channel (UL-SCH) resource allocation information, paging channel (PCH) paging information, system information on DL-SCH, Resource allocation of higher layer control messages such as a random access response (Random Access Response) transmitted on PDSCH, a set of transmission power control commands for individual terminals in an arbitrary terminal group, transmission power control information, VoIP (Voice over IP) ) Activation and the like. A plurality of PDCCHs are transmitted in the control region, and the terminal can monitor the plurality of PDCCHs. The PDCCH is transmitted in a combination of one or more consecutive control channel elements (CCE). CCE is a logical allocation unit used to provide 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 by the correlation between the number of CCEs and the coding rate provided by the CCE. The base station determines the PDCCH format based on the DCI transmitted to the terminal, and adds a cyclic redundancy check (CRC) to the control information. The CRC is masked by an identifier called a radio network temporary identifier (RNTI) depending on the owner or use of the PDCCH. If the PDCCH is for a specific terminal, the cell-RNTI (C-RNTI) of the terminal can be masked to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (P-RNTI) can be masked in the CRC. If the PDCCH is for system information (particularly, system information block (SIB)), the system information identifier and system information RNTI (SI-RNTI) can be masked in the CRC. Random access-RNTI (RA-RNTI) can be masked to the CRC to represent a random access response, which is a response to the terminal's random access preamble transmission.

FIG. 4 is a diagram illustrating a structure of an uplink subframe. The uplink subframe can be distinguished into a control region and a data region in the frequency domain. A physical uplink control channel (Physical Uplink Control Channel; PUCCH) including uplink control information is allocated to the control region. A physical uplink shared channel (PUSCH) including user data is allocated to the data area. In order to maintain the single carrier characteristic, one terminal does not transmit PUCCH and PUSCH at the same time. The PUCCH for one terminal is allocated to a resource block pair (RB pair) in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers for two slots. This can be said that the resource block pair allocated to the PUCCH is frequency-hopped at the slot boundary.

Modeling multiple antenna (MIMO) systems

  The MIMO system is a system that improves data transmission / reception efficiency using multiple transmission antennas and multiple reception antennas. In the MIMO technique, the entire data can be received by combining a plurality of data fragments received through a plurality of antennas without depending on a single antenna path for receiving the entire message.

FIG. 5 is a configuration diagram of a wireless communication system having multiple antennas. As shown in FIG. 5 (a), when the number of transmission antennas is increased to N _{T and the} number of reception antennas is increased to N _R , unlike the case of using a plurality of antennas only in either the transmitter or the receiver, The theoretical channel transmission capacity increases in proportion to the number of antennas. Therefore, the transmission rate can be improved and the frequency efficiency can be dramatically improved. By increasing the channel transmission capacity, the transmission rate can theoretically be increased by the rate increase rate (R _i ) multiplied by the maximum transmission rate (R _o ) when using a single antenna. Become.

  For example, in a MIMO communication system using four transmission antennas and four reception antennas, a transmission rate four times as high as that of a single antenna system can be obtained theoretically. Since the theoretical capacity increase of the multi-antenna system was proved in the mid-1990s, various techniques have been actively researched to date to lead to a substantial increase in data transmission rate. Some of these technologies are already reflected in various wireless communication standards such as 3rd generation mobile communication and next generation wireless RAN.

  Looking at research trends related to multiple antennas to date, research on information theory related to multi-antenna communication capacity calculation in various channel environments and multiple access environments, research on radio channel measurement and model derivation of multi-antenna systems, transmission Research is actively underway from various viewpoints, including research on spatio-temporal signal processing technology for improving reliability and transmission rate.

A communication method in a multi-antenna system will be described more specifically using mathematical modeling. Assume that there are N _T transmit antennas and N _R receive antennas in this system.

The transmission signal will be described. When there are N _T transmitting antennas, the maximum information that can be transmitted is N _T. Transmission information can be expressed as follows.

  On the other hand, the transmission signal x may be considered in different ways depending on two cases (for example, spatial diversity and spatial multiplexing). In the case of spatial multiplexing, different signals are multiplexed, and the multiplexed signals are transmitted to the receiving side, so that the information vector elements 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 have the same value. Of course, a combination of spatial multiplexing and spatial diversity techniques can also be considered. That is, the same signal can be transmitted by, for example, a spatial diversity method through three transmission antennas, and the remaining signals can be spatially multiplexed and transmitted to the reception side.

FIG. 5B shows a channel from N _T transmit antennas to receive antenna i. These channels can be displayed together in vector and matrix form. In FIG. 5B, a channel arriving at the receiving antenna i from a total of N _T transmitting antennas can be expressed as follows.

Accordingly, all channels arriving at N _R receive antennas from N _T transmit antennas can be expressed as follows:

  Through the above mathematical modeling, the received signal can be expressed as follows.

  In the above, the case where the multi-antenna communication system is used for a single user has been mainly described. However, the multi-antenna communication system can be applied to a plurality of users to obtain multi-user diversity. This will be briefly described as follows.

  Fading channels degrade the performance of wireless communication systems. The channel gain varies with time, frequency, and space, and the lower the channel gain value, the worse the performance degradation. Diversity, which is one of the methods that can overcome fading, focuses on the fact that the probability that multiple independent channels all have low gain is very low. Various diversity schemes are possible, and multi-user diversity is one of them.

  When there are multiple users in a cell, the probability that they all have low gain is very low because the channel gain of each user is stochastically independent of each other. According to information theory, if the transmission power of the base station is sufficient, when there are multiple users in the cell, the total channel capacity is maximized by allocating all channels to the user with the highest channel gain. Can be Multi-user diversity can be classified again in three ways.

  Temporal multiple user diversity is a scheme in which a channel is allocated to a user having the highest gain value each time the channel changes with time. Frequency multiple user diversity is a scheme in which a subcarrier is allocated to a user having the maximum gain in each frequency band in a frequency multicarrier system such as OFDM (Orthogonal Frequency Division Multiplexing).

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

  Next, spatial multiple user diversity is a method that uses the fact that the channel gain of a user generally varies with space. Specific examples include RBF (Random Beamforming). RBF is also called “opportunistic beamforming”, and is a technique for inducing channel change by beamforming with arbitrary weight values using multiple antennas at the transmitting end.

  A multi-user multi-antenna (Multiuser MIMO, MU-MIMO) system using the above multi-user diversity for a multi-antenna system will be described as follows.

  In the multi-user multiple antenna system, various combinations of the number of users and the number of antennas of each user are possible at the transmission and reception ends. The multi-user multi-antenna scheme will be described by distinguishing between downlink (downlink, forwardlink) and uplink (Uplink, reverselink). The downlink means a case where a signal is transmitted from a base station to a plurality of terminals. Uplink means a case where a plurality of terminals transmit signals to a base station.

In the downlink, and an extreme example, sometimes one person of the user receives signals through total N _R antennas, the user of the total N _R Name receives a signal using one antenna respectively Sometimes. An intermediate combination of these extreme examples is also possible. That is, while a certain user uses one receiving antenna, a certain user can use a combination of three receiving antennas. It should be noted that the sum of the number of reception antennas is kept constant as N _R in any combination. Such a case is generally called MIMO BC (Broadcast Channel) or SDMA (Space Division Multiple Access).

In the uplink, to give an extreme example, one user may transmit a signal through a total of N _T antennas, and a total of N _T users transmit a signal using one antenna each. Sometimes. An intermediate combination of these extreme examples is also possible. That is, while a certain user uses one transmission antenna, a certain user can use combinations such as three transmission antennas. It should be noted that in any combination, the sum of the number of transmission antennas is kept constant as N _T. Such a case is generally referred to as MIMO MAC (Multiple Access Channel). Since the uplink and the downlink are in a symmetric relationship with each other, the technique used in either one can be used in either one.

  Another definition of the rank can be defined as the number of eigenvalues other than 0 when the matrix is subjected to eigenvalue decomposition (Eigen value decomposition). Similarly, yet another definition of rank can be defined as the number of singular values other than 0 when subjected to singular value decomposition. Therefore, the physical meaning of rank in the channel matrix is the maximum number that can send different information on a given channel.

  In MIMO transmission, “Rank” refers to the number of paths through which a signal can be transmitted independently, and “Number of layers” refers to the number of signal streams transmitted through each path. Refers to that. In general, since the transmitting end transmits the 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.

  Next, characteristics of the precoding matrix will be described. First, a channel matrix that does not consider the precoding matrix can be expressed as follows.

In general, when a MMSE (Minimum Mean Square error) receiver is provided, ρ _k (kNR received Signal to Interference plus Noise Ratio (SINR)) can be defined as follows.

Thus, assuming that an MMSE receiver is used, ρ _k can be defined as:

Even when two column vectors are permutated in Equations 17 and 18, the received SINR value itself is not changed except for the order, and the channel capacity / sum. The rate of can be constant. Also for mathematical formulas 14 and 15, the permutated effective channel and ρ _k can be obtained as follows.

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

As the result of Equation 24, it can be ^confirmed that multiplying a specific column vector of the precoding matrix by e ^−jθ does not affect the received SINR and the ratio of channel capacity / sum.

  On the other hand, in the MIMO system, there are various MIMO transmission methods (transmission modes). The multi-antenna transmission / reception technique (scheme) used for the operation of the MIMO system includes FSTD (frequency switched transmission diversity), SFBC (Space Frequency Block Code), and STBC (Space CD C). Diversity) and TSTD (time switched transmission diversity). For rank 2 or higher, spatial multiplexing (SM), GCDD (Generalized Cyclic Delay Diversity), S-VAP (Selective Virtual Antenna Permutation), or the like can be used.

  The FSTD is a scheme for obtaining a diversity gain by assigning subcarriers having different frequencies for each signal transmitted to each multiple antenna. SFBC is a technique that can secure both diversity gain and multi-user scheduling gain in a corresponding dimension by efficiently applying selectivity in the spatial domain and frequency domain. STBC is a technique for applying selectivity in the space domain and the time domain. CDD is a technique for obtaining a diversity gain by using a path delay between transmitting antennas. TSTD is a method of dividing a signal transmitted to 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 for applying selectivity in the time domain and the frequency domain. S-VAP is a technique that uses a single precoding matrix, and in spatial diversity or spatial multiplexing, MCW (Multi Codeword) S-VAP that mixes multiple codewords between antennas and SCW (Single) that uses a single codeword. Codeword) S-VAP.

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

On the other hand, in a MIMO system, an open-loop method (or channel-independent method) that does not use feedback information from the receiving end and a closed loop that uses feedback information from the receiving end (closed-loop). There is a loop method (or channel-dependent method). In the closed loop system, the receiving end transmits feedback information about the channel state to the transmitting end, and the transmitting end can grasp the channel state from this information, thereby improving the performance of the radio communication system. The closed-loop MIMO system uses a precoding method in which a transmitting end performs predetermined processing on transmission data using feedback information about a channel environment transmitted from a receiving end, and minimizes the influence of the channel. The precoding method includes a codebook based precoding method and a precoding method in which channel information is quantized and fed back.

MIMO system based on OFDM and SC-FDMA

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

  FIG. 6 is a diagram illustrating a general system structure of SC-FDMA and OFDMA. In FIG. 6, N is smaller than M. S-to-P means that a serial signal is converted into a parallel signal, and P-to-S means that a parallel signal is converted into a serial signal. As shown in FIG. 6, at the transmitting end of the SC-FDMA system, the input information symbols are converted into serial-parallel conversion (611), N-point DFT (612), subcarrier mapping (613), M-point IDFT. (Inverse DFT) (614), parallel-serial conversion (615), CP addition (616) and digital-analog conversion (617) can be transmitted as a signal through a channel. At the receiving end of the SC-FDMA system, analog-digital conversion (621), CP removal (622), serial-parallel conversion (623), M-point DFT (624), subcarrier demapping is performed on the signal received through the channel. It can be recovered as an information symbol via / equalization (625), N-point IDFT (626), parallel-serial conversion (627) and detection (628). On the other hand, in the OFDMA system, the N-point DFT (612) and the parallel-serial conversion (615) are omitted and the parallel-serial conversion is performed together with the CP addition (616) as compared with the transmission end of the SC-FDMA system. Compared to the receiving end of the SC-FDMA system, the serial-parallel conversion (623) and the N-point IDFT (626) are omitted.

  Generally, CM (Cubic Metric) or PAPR (peak power to average power ratio) of a single carrier signal such as an SC-FDMA transmission signal is much lower than that of a multi-carrier signal. CM and PAPR are related to the dynamic range that the power amplifier (PA) of the transmitter should support. When the same PA is used, a transmission signal having a lower CM or PAPR than other types of signals may be transmitted with high transmission power. In other words, when the maximum power of the PA is fixed, in order for the transmitter to transmit a high CM or PAPR signal, the transmission power must be slightly lower than that of the low CM or PAPR signal. The reason why a single carrier signal has a lower CM or PAPR than a multi-carrier signal is that, in a multi-carrier signal, a plurality of signals may overlap to add a common-phase (co-phase) to the signal. It is. As a result, the amplitude of the signal increases and the OFDM system may have a large PAPR or CM value.

If the transmission signal (y) consists only of one information symbol (x ₁ ), this signal can be regarded as a single carrier signal such as y = x ₁ . However, the transmission signal (y) a plurality of information symbols _{(x 1, x 2, x} 3, ..., x N) when consisting of this _{signal, y = x 1 + x 2} + x 3 + ... + x N Such a multi-carrier signal. PAPR or CM is proportional to the number of information symbols that are coherently added together in the transmission signal waveform, but when a certain number of information symbols are reached, the value tends to saturate. Therefore, if the signal waveform is generated by summing a small number of single carrier signals, the CM or PAPR has a much smaller value than a multi-carrier signal, but compared to a pure single carrier signal. It has a slightly high value.

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

  FIG. 8 is a diagram illustrating a transmission frame structure for uplink SC-FDMA in the LTE Release-8 system. The basic transmission unit is one subframe. One subframe is composed of two slots, and the number of SC-FDMA symbols included in one slot is 7 or 6 depending on the CP configuration (for example, general CP or extended CP). FIG. 8 illustrates the case of a general CP in which seven SC-FDMA symbols exist in one slot. There is at least one Reference Signal (RS) SC-FDMA symbol in each slot, and this symbol is not used for data transmission. There are multiple 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, in SC-FDMA, the size of DFT transform and the number of subcarriers used for transmission are the same, so RE is one information symbol mapped to one DFT transform index. Applicable.

  In the LTE-A system, a maximum of four layers of spatial multiplexing is considered for uplink transmission. In the case of uplink single user spatial multiplexing, a maximum of two transmission blocks can be transmitted from a scheduled terminal in one subframe for each uplink component carrier. Here, the constituent carrier wave means a carrier wave of a unit to be merged in a carrier aggregation technique for obtaining an effect of using a logically large band by physically combining a plurality of carrier waves. . Depending on the number of transmission layers, modulation symbols associated with each transmission block can be mapped onto one or two layers. The mapping relationship between the transmission block and the layer can use the same principle as the mapping principle of the transmission block and the layer in LTE Release-8 downlink spatial multiplexing. For both cases where spatial multiplexing is used and not used, DFT precoded OFDM can be used for multiple access techniques for uplink data transmission. In the case of multiple constituent carriers, one DFT can be applied to each constituent carrier. In particular, in an LTE-A system, frequency-continuous and frequency-non-continuous resource allocation can be supported for each constituent carrier.

FIG. 9 is a diagram showing a data signal mapping relationship for a MIMO system based on SC-FDMA transmission. The SC-FDMA system stores a layer mapper that maps a signal to be transmitted to a number of layers corresponding to a specific rank, a predetermined number of DFT modules that perform DFT spreading on each of a predetermined number of layer signals, and a memory. A precoder for selecting a precoding matrix from the codebook and precoding the transmission signal may be provided. 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 N _C integer multiples of information symbols are N _L or N _L integer multiples. Can be mapped to as many layers as possible. DFT transform precoding for SC-FDMA does not change the layer size. When precoding is performed on a layer, the number of information symbols is changed from N _L to N _T by applying a matrix of size N _T × N _L. In general, the transmission rank of spatially multiplexed data is the same as the number of layers (eg, N _L ) that carry data at a given transmission time. As shown in FIG. 9, the DFT module for transmitting the uplink signal by the SC-FDMA method is arranged in the front stage of the precoder and the rear stage of the layer mapper. Therefore, the DFT-spreaded signal for each layer is transmitted after IFFT despreading after precoding. Therefore, the effect of canceling the effects of DFT spreading and IFFT despreading excluding precoding is used to improve the PAPR or CM characteristics. It can be maintained well.

Reference signal (RS)

  When transmitting a packet in a wireless communication system, since the packet is transmitted through a wireless channel, signal distortion may occur in the transmission process. In order to correctly receive the distorted signal on the receiving side, it is necessary to correct the distortion of the received signal using the channel information. In order to find the channel information, a method is mainly used in which a signal known by both the transmitting side and the receiving side is transmitted, and the channel information is found by using the degree of distortion when the signal is received through the channel. This signal is called a pilot signal (Pilot Signal) or a reference signal (Reference Signal).

  When transmitting and receiving data using multiple antennas, in order to receive a correct signal, it is necessary to know the channel conditions between each transmitting antenna and receiving antenna. For this purpose, a reference signal needs to exist for each transmission antenna.

  The downlink reference signals include a common reference signal (Common Reference Signal; CRS) shared by all terminals in the cell and a dedicated reference signal (Dedicated Reference Signal; DRS) for a specific terminal. These reference signals can provide information for channel estimation and demodulation.

  The receiving side (terminal) estimates a channel state from the CRS, and transmits an indicator related to channel quality such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Index) and / or RI (Rank Indicator). It is possible to feed back to the side (base station). CRS may also be referred to as a cell-specific reference signal.

  On the other hand, the DRS can be transmitted through the corresponding RE when demodulation of data on the PDSCH is necessary. The terminal is instructed from the upper layer whether or not DRS exists, and can receive an instruction that the DRS is valid only when the corresponding PDSCH is mapped. The DRS can also be referred to as a UE-specific reference signal or a demodulation reference signal (DMRS).

  FIG. 10 is a diagram illustrating a pattern in which CRS and DRS defined in an existing 3GPP LTE system (for example, Release-8) are mapped on a downlink resource block. A downlink resource block as a unit to which a reference signal is mapped can be expressed as a unit of 12 subcarriers in 1 subframe × frequency in time. In the case of a general CP, one resource block has 14 OFDM symbol lengths in time.

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

  Next, CRS will be specifically described.

  The CRS is used to estimate the channel at the physical antenna end, and is a reference signal that can be commonly received by all terminals (UEs) within a cell, and is distributed over the entire band. CRS can be used for channel state information (CSI) acquisition and data demodulation.

  CRS is defined as various forms depending on the antenna configuration on the transmission side (base station). The 3GPP LTE (eg, Release-8) system supports various antenna configurations (Antenna configuration), and the downlink signal transmission side (base station) has three types such as a single antenna, two transmission antennas, and four transmission antennas. Antenna configuration. When the base station performs single antenna transmission, a reference signal for a single antenna port is arranged. When the base station performs 2-antenna transmission, the reference signals for the two antenna ports are arranged in a time division multiplexing (Time Division Multiplexing) and / or frequency division multiplexing (Frequency Division Multiplexing) scheme. That is, the reference signals for the two antenna ports are arranged in different time resources and / or different frequency resources, and can be distinguished from each other. When the base station performs 4-antenna transmission, reference signals for the 4 antenna ports are arranged in the TDM / FDM scheme. Channel information estimated on the downlink signal receiving side (terminal) using CRS includes single antenna transmission (Transmission diversity), closed-loop spatial multiplexing, and open-loop spatial multiplexing. It can be used for demodulating data transmitted by a transmission technique such as Open-loop Spatial Multiplexing or Multi-User MIMO (MU-MIMO).

  When supporting a multiple antenna, when transmitting a reference signal at a certain antenna port, the reference signal is transmitted to a resource element (RE) position specified according to the reference signal pattern, and a resource specified for another antenna port. No signal is transmitted to the element (RE) position.

  The rules for mapping CRS onto resource blocks follow the following mathematical formula.

  Specifically, in order to improve channel estimation performance using CRS, the position of the CRS in the frequency domain can be shifted for each cell to be different. For example, if the reference signal is located every 3 subcarriers, one cell may be placed on 3k subcarriers and the other cell on 3k + 1 subcarriers. From the point of view of one antenna port, the reference signals are arranged in the frequency domain at 6 RE intervals (ie, 6 subcarrier intervals), and the REs in which the reference signals for the other antenna ports are arranged are 3 RE intervals in the frequency domain. To maintain.

  Also, power boosting can be applied to the CRS. The power boosting means that the reference signal is transmitted with higher power by borrowing the power of the REs other than the RE allocated for the reference signal among the resource elements (RE) of one OFDM symbol. To do.

  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 to be different depending on the CP length. In the case of a general CP, it is located at symbol indexes 0 and 4 of the slot, and in the case of an extended CP, it is located at symbol indexes 0 and 3 of the slot. Only one reference signal for a maximum of two antenna ports is defined in one OFDM symbol. Therefore, when transmitting four transmission antennas, the reference signals for antenna ports 0 and 1 are located at slot symbol indexes 0 and 4 (symbol indexes 0 and 3 in the case of an extended CP), and antenna ports 2 and 3 The reference signal for is located at symbol index 1 of the slot. However, the frequency positions of the reference signals for antenna ports 2 and 3 are interchanged in the second slot.

  A system with an extended antenna configuration (eg, LTE-A system) can be designed to support higher spectral efficiency than existing 3GPP LTE (eg, Release-8) systems. . The extended antenna configuration may be, for example, eight transmission antenna configurations. In a system having such an extended antenna configuration, it is necessary to support a terminal that operates with the existing antenna configuration, that is, support backward compatibility. Therefore, it is necessary to support a reference signal pattern with an existing antenna configuration and design a new reference signal pattern for an additional antenna configuration. Here, if a CRS for a new antenna port is added to a system having an existing antenna configuration, the reference signal overhead increases rapidly and the data transmission rate decreases. In consideration of such matters, it is necessary to design a new reference signal (CSI-RS) for channel state information (CSI) measurement for a new antenna port. It will be described after the explanation.

  Below, DRS is demonstrated concretely.

  The DRS (or terminal-specific reference signal) is a reference signal used for data demodulation, and the terminal uses the precoding weight value used for the specific terminal when performing multi-antenna transmission as it is for the reference signal. When a reference signal is received, a precoding weight value transmitted from each transmission antenna and an equal channel combined with a transmission channel can be estimated.

  Existing 3GPP LTE systems (eg, Release-8) support up to 4 transmit antenna transmissions and DRS for rank 1 beamforming is defined. The DRS for rank 1 beamforming can also be expressed as a reference signal for antenna port index 5. The rules for mapping the DRS onto the resource block follow the following mathematical formulas 26 and 27. Equation 26 is for the general CP and Equation 27 is for the extended CP.

  On the other hand, in the LTE-A (Advanced) system, which is an advance of 3GPP LTE, high-order MIMO, multiplex-cell transmission, advanced MU-MIMO, and the like are considered, but efficient use of reference signals In order to support advanced transmission schemes, DMRS-based data demodulation is considered. That is, in order to support data transmission through the added antenna, separately from DMRS (antenna port index 5) for rank 1 beamforming defined in existing 3GPP LTE (eg, release-8), 2 DMRS for the above layers can be defined. Since DMRS is precoded by the same precoder as data, the receiving side can easily estimate channel information for demodulating data without additional precoding information.

  When the DMRS for supporting the maximum rank 8 transmission is arranged on the radio resource, the DMRS for each layer can be multiplexed and arranged. Time division multiplexing (TDM) means that DMRSs for two or more layers are arranged on different time resources (for example, OFDM symbols). Frequency division multiplexing (FDM) means that DMRSs for two or more layers are arranged on different frequency resources (for example, subcarriers). Code division multiplexing (CDM) means that DMRSs for two or more layers arranged on the same radio resource are multiplexed using an orthogonal sequence (or orthogonal covering).

FIG. 11 is a diagram illustrating an example of a DMRS pattern for supporting maximum rank 8 transmission. In FIG. 11, a control region (first 1 to 3 symbols of one subframe) represents an RE that can transmit a PDCCH. The CRS for the four transmission antennas represents an RE in which the CRSs for the antenna ports “0”, “1”, “2”, and “3” described in FIG. 10 are arranged, and the V _shift value is 0 as an example did.

  In general, in the case of single user-MIMO (SU-MIMO) transmission, the number of DMRS antenna ports (or virtual antenna ports) used for data transmission is the same as the transmission rank of data transmission. In this case, DMRS antenna ports (or virtual antenna ports) can be numbered from 1 to 8, with the lowest “N” DMRS antenna port being used for rank “N” SU-MIMO transmission. Can do.

When the DMRS antenna port number is determined as shown in FIG. 11, the total number of REs in which data is not transmitted due to the DMRS arrangement within a single transmission layer is determined by the transmission rank. In the case of a low rank (for example, 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 (for example, ranks 3 to 8), the number of REs used for DMRS transmission may be 24 in one resource block. That is, as shown in FIG. 11, in the case of rank 2, DMRS for layers 1 and 2 are transmitted on 12 REs (REs indicated as DMRS positions for layers 1, 2, 5, and 7 in FIG. 11). In the case of rank 3, the DMRS for layers 1 and 2 is transmitted by the above 12 REs, and the DMRS for layer 3 is an additional 12 REs (layers 3, 4, 6, 8 in FIG. 11). Can be transmitted on the DMRS location labeled RE). The position of the RE where the DMRS for each layer is arranged is an example, and the present invention is not limited to this.

CSI-RS pattern

  The present invention proposes a new method for arranging (multiplexing) CSI-RS on radio resources in consideration of the above-mentioned CRS and DMRS positions. As described above, CSI-RS is transmitted by a base station and can be used for estimating channel state information at a terminal. Channel state information measured by CSI-RS includes precoding information (eg, precoding matrix index (PMI)), number of preferred transmission layers (eg, rank indicator (RI)), preferred modulation and A coding and coding scheme (MCS) (eg, channel quality indicator (CQI)) may be included.

  CRS is required for correct operation of terminals operating on the existing LTE system (legacy terminals), and DMRS is required to facilitate data demodulation for extended antenna configurations. . Therefore, in order to support efficient channel information acquisition on the downlink receiving side through CSI-RS, considering the arrangement of CRS and DMRS on radio resources, as many CSI-RSs as possible are transmitted. It is necessary to determine the CSI-RS pattern (location on the resource block). This is because the terminal cannot correctly estimate the channel between the serving cell and the terminal unless the CSI-RS from the neighboring cell and the CSI-RS from the serving cell collide with each other (that is, the CSI-RS is transmitted at different positions). Because. Therefore, the larger the number of CSI-RS patterns that can be distinguished and used by a large number of cells, the better the channel estimation performance through CSI-RS can be guaranteed.

  The present invention proposes that REs used by a group of CSI-RS antenna ports are grouped, and that the CSI-RS RE group is composed of consecutive REs usable in the frequency domain. In this way, the CSI-RS group is configured with REs that are continuous in the frequency domain in order to perform transmission diversity transmission techniques such as SFBC (Space-Frequency Block Coding) and SFBC-FSTD (Frequency Selective Transmit Diversity). This is to prevent the block (base transmission block) from collapsing due to the arrangement of the CSI-RS. Specifically, in the RE in which CSI-RS is transmitted, data cannot be transmitted. Therefore, when data is transmitted on a basic transmission block for transmission diversity, only a part of the basic transmission block is used. This is because when the CSI-RS is arranged, there is a problem that the transmission diversity RE pair of data transmission is broken.

  Here, the usable RE is a downlink resource block (one subframe (12 or 14 OFDM symbol) in the time domain × one resource block (12 subcarriers) in the frequency domain) to a control region (downlink subframe). It means an RE that does not include CRS and DMRS in the data area excluding the first 1 to 3 OFDM symbols). That is, usable REs in which CSI-RSs can be arranged correspond to REs to which nothing is assigned in FIG.

  An example of the CSI-RS RE group is as shown in FIGS.

  FIG. 12 shows an example in which a CSI-RS RE group is set on two consecutive subcarriers. In the example of FIG. 12, it can be seen that the CSI-RS RE group is defined other than the RE in which the CRS and DMRS are arranged.

  FIG. 13 shows an example in which a CSI-RS RE group is set on four consecutive subcarriers. In the example of FIG. 13, a CSI-RS RE group may appear as if it is configured over 5 subcarriers, but a CSI-RS is transmitted in an RE in which CRS is arranged in the CSI-RS RE group. In the end, it can be seen that a 4RE-sized CSI-RS RE group is set.

  FIG. 14 shows an example in which a CSI-RS RE group is set 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 arranged.

  FIG. 15 shows an example in which a CSI-RS RE group is set 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 DMRS are arranged.

  FIG. 16 shows an example in which a CSI-RS RE group is set on four consecutive subcarriers. Note that in the illustration of FIG. 16, CSI-RS is not transmitted at the CRS RE location. 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 arranged.

  The CSI-RS RE group as illustrated in FIGS. 12 to 16 is used by a single cell to transmit a group of CSI-RS antenna ports. For example, when one cell performs transmission of two CSI-RS antenna ports, if the CSI-RS RE group size is 2, CSI-RS REs for two CSI-RS antenna ports are assigned to one cell. It can be mapped in the CSI-RS RE group. Alternatively, when one cell performs transmission of four CSI-RS antenna ports in total, if the CSI-RS RE group size is 4RE, the CSI-RS RE for the four CSI-RS antenna ports is set to one. It can be mapped in the CSI-RS RE group. Or, when one cell supports transmission of 8 CSI-RS antenna ports, if the CSI-RS RE group size is 4RE, 2 CSI-RS REs for 8 CSI-RS antenna ports are provided. To CSI-RS RE groups. At this time, it is not necessary to arrange the two CSI-RS RE groups so as to be adjacent to each other, and they may be arranged in any CSI-RS RE group in the corresponding resource block.

  In a simple channel estimation implementation, a CSI-RS RE pattern (including at least a primary broadcast channel, a primary synchronization channel, and a secondary synchronization channel) is not included. ) Can be configured identically over the entire bandwidth. Mapping within the smallest possible number of CSI-RS groups of CSI-RS antenna ports is particularly important when a cell seeks to support a transmit diversity transmission scheme for a base station. This is because when a CSI-RS RE is distributed among a plurality of CSI-RS groups, a plurality of SFBC time-space coded RE pairs for a transmission diversity transmission technique may be corrupted. This is because SFBC and SFBC-FSTD transmit diversity transmission schemes have a basic RE block to which space-frequency coding and / or antenna selective / frequency selective diversity is applied. If the CSI-RS is transmitted with a specific RE, the diversity basic block may be damaged, leading to a decrease in performance of the transmission diversity transmission technique.

  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 may be any CSI mapped in one CSI-RS RE group. -RS RE is also preferred over other embodiments in that it does not break one or more SFBC RE pairs. However, the present invention does not exclude the CSI-RS RE group defined in FIGS. 13 and 15.

  As shown in FIG. 17, in an OFDM symbol not including CRS or DMRS, a CSI-RS RE group (including 4 REs in each group) is defined as 4 consecutive REs in one resource block. You can also. Note that these CSI-RS RE groups do not overlap. The CSI-RS RE group is the same as the basic RE group to which transmission diversity is applied. If each CSI-RS RE group has only two REs, the CSI-RS RE group can be defined as two consecutive REs.

  As shown in FIG. 18, when a CSI-RS RE group is composed of four REs, the CSI-RS RE group located on the same OFDM symbol as the DMRS RE is not necessarily one transmission diversity basic RE group. It is not composed of four consecutive usable REs to which it belongs. In such a case, the CSI-RS RE group located in the same OFDM symbol as the DMRS RE can be defined by two sets of two REs, and each set is different from the transmission diversity RE group. Can be composed of two consecutive REs belonging to. In FIG. 18, one thick solid line quadrilateral group represents a set composed of two REs, and two thick solid line quadrilateral groups constitute one CSI-RS RE group. The CSI-RS RE group defined in this manner is defined by a CSI-RS RE group composed of four REs, which defines two RE sets, and Alamouti − Coding (SFBC) and antenna / frequency selective diversity are used. This is because four consecutive REs (four consecutive REs consisting of one thick dotted quadrilateral group and one thick solid quadrilateral group, in FIG. 18, a transmission composed of four consecutive REs. 2 diversity basic blocks are shown), the previous 2 REs (eg, thick dotted square groups) are mapped to common antenna ports 0 and 2 coded using SFBC, and later This is because the two REs (for example, thick solid rectangular groups) are mapped to the common antenna ports 1 and 3 coded using SFBC. That is, when the CSI-RS RE is mapped by the previous two REs in the transmission diversity basic block composed of four consecutive REs, the two previous REs are used for the common antenna ports 0 and 2. Similarly, when the CSI-RS RE is mapped by the latter two REs, the latter two REs cannot be used for the common antenna ports 1 and 3. Therefore, one transmission diversity basic block (first four consecutive REs) takes the next two REs, and the other transmission diversity basic block (the next four consecutive REs) takes the previous two When a RE is taken, a virtual transmission diversity basic block can be configured by four REs. The definition of the CSI-RS RE group in the OFDM symbol including the DMRS is such that when the CSI-RS RE is mapped to such a specific type of CSI-RS RE group, all common antenna ports (0, 1, 2, 3 ) Is important in that it can balance puncturing efficiently. Here, puncturing means that when CSI-RS is transmitted on a specific RE, the RE cannot be used for a common antenna port.

  As shown in FIG. 19, when a CSI-RS RE group is composed of four REs, the CSI-RS RE group located on the same OFDM symbol as the CRS RE is not necessarily one transmission diversity basic RE group. It is not composed of four consecutive usable REs to which it belongs. A CSI-RS RE group may be conceptually configured as shown in FIG. 19 on an OFDM symbol including CRS. According to the configuration of such a CSI-RS RE group, puncturing for a common antenna port is efficient. Can be well balanced.

  As shown in FIG. 20, the CSI-RS antenna port RE mapped to the CSI-RS RE group may be hopped (changed 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.

  Such hopping can be performed in various ways.

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

  Alternatively, a virtual CSI-RS group index can be defined and a hopping (randomized or permutation) mapping function can be defined that maps the virtual CSI-RS group index to a physical CSI-RS group index ( (See FIG. 21). In such a mapping function, a circular virtual index shifting, a subblock interleaver, a QPP (Quadratic Permutation Polynomial) interleaver, or the like can be used.

  The cyclic virtual index shifting method is a method of mapping a CSI-RS group to a virtual index. In connection with the cyclic virtual index shifting, it may be considered that the terminal operates according to a cooperative multi-point (CoMP) transmission scheme. The CoMP transmission scheme is an improved MIMO transmission scheme applicable in a multi-cell environment, which can reduce inter-cell interference and improve the throughput of users at the cell boundary. In this method, the overall performance of the system can be improved, and techniques such as joint processing and cooperative beamforming can be applied. In a CoMP transmission scheme, a terminal that receives data through multi-cell cooperation transmits channel information regarding a channel from the multi-cell to the terminal to each cell belonging to the multi-cell (CoMP transmission cluster (cluster)). be able to. The virtual index may be set so as not to overlap between cells belonging to one CoMP transmission cluster. Cells belonging to different CoMP clusters can use the same virtual index, but each CoMP cluster can cyclically shift the index when mapping the virtual index to the physical index. This enables CSI-RS RE group mapping that is orthogonal within one CoMP cluster. In addition, non-orthogonal CSI-RS RE group mapping is possible between different CoMP clusters, and different CSI-RS RE groups between different CoMP clusters by cyclic shifting of virtual indexes. Can be mapped.

A block interleaver can then be used to randomize the 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 includes a matrix, and input information can be recorded in the interleaver in units of rows (row by row), and output information can be read from the interleaver in units of columns (column by column). That is, when recording information in the interleaver, recording is performed while increasing the column number in one row, recording is performed in such a way that the next row is moved when one row is filled, and when information is read from the interleaver, Reading while increasing the row number in one column, and reading one column, it reads in the method that moves to the next column. The columns of the matrix constituting the block interleaver may be permutated. Alternatively, the block interleaver may be recorded in units of columns and read in units of rows.

  The block interleaver as described above can be used to effectively randomize the CSI-RS group index. The following mathematical formula 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 that satisfies L ≦ MN. When MN> L, it can be defined that 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 match the size of the block interleaver matrix, the number of CSI-RS group indexes (L) is subtracted from the size of the interleaver (MN). The number (N _D ) of elements can be padded with null ([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. Block interleaver column permutation can be defined as follows:

  The matrix permutated by the mathematical formula 29 can be expressed as follows.

The block interleaver output can be read in units of columns. In Equation 30, the output starts with v _{π (1) in 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 exists, the null value can be ignored and read as described above.

  Different CoMP clusters can use different column permutations or apply different cyclic shift values before mapping the CSI-RS group index to the interleaver matrix. This makes it possible to apply different CSI-RS group index randomization to different CoMP clusters.

  FIG. 22 is a diagram illustrating an example of a CSI-RS RE group in the case of 8 transmission antennas. In the case of 8 transmission antennas, 8 CSI-RSs need to be transmitted to the terminal. Therefore, 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 can be defined as two RE sets, and one RE set can be defined as two RE pairs (that is, four REs). That is, four REs are continuous in the time and frequency domain within one RE set (the thick solid square in FIG. 22 corresponds to one RE set), and two RE sets are four in the frequency domain. It can have a form separated by subcarrier spacing. Thereby, from the viewpoint of the transmission end, the same CSI-RS RE group pattern can be used in an OFDM symbol including DMRS and an OFDM symbol not including CRS or DMRS. The RE position displayed by the thick dotted line in FIG. 22 takes into consideration that the puncturing of the common antenna port is effectively balanced in the transmission diversity basic block, as in the description of FIG.

  Also, in this embodiment, it is proposed to shift such a CSI-RS RE group for each cell by time shift, frequency shift, or time and frequency shift. That is, a CSI-RS RE group pattern used in one cell can be used as a pattern shifted in time and / or frequency in another cell.

  In addition, each cell can hop CSI-RS transmission in CSI-RS RE group position candidates at every transmission time point. Examples of CSI-RS RE group position candidates are as shown in FIG. That is, in FIG. 23, two thick solid squares labeled as number 1 represent one candidate position of the CSI-RS RE group position, and similarly, numbers 2, 3, 4, 5, and so on. The two thick solid squares displayed represent one candidate position 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 as No. 1 is the third and fourth in the sixth and seventh OFDM symbols. , Corresponding to the 9th and 10th subcarrier positions, the CSI-RS RE group positions indicated as 2nd are the 1st, 2nd, 7th and 8th positions in the 10th and 11th OFDM symbols. The CSI-RS RE group position indicated as No. 3 corresponding to the subcarrier position corresponds to the third, fourth, ninth and tenth subcarrier positions in the 10th and 11th OFDM symbols, The CSI-RS RE group position labeled 4 is the 5th, 6th, 1st in the 10th and 11th OFDM symbols. The CSI-RS RE group positions corresponding to the first and twelfth subcarrier positions and denoted as number 5 are the third, fourth, ninth and tenth subcarriers in the thirteenth and fourteenth OFDM symbols. Can correspond to the position. Therefore, a CSI-RS RE group pattern in which five cells are different from each other at the same time can be used.

  From the transmission antenna perspective, it is possible to re-allocate transmission power in the frequency domain, but not in the time domain. In other words, when the total transmission power is limited, a specific RE of one OFDM symbol can be power boosted by borrowing power from other REs in the OFDM symbol. When CSI-RSs for different antenna ports are multiplexed and orthogonalized, in order to prevent the orthogonality from being lost when different power boosting is applied to each CSI-RS, All CSI-RSs need to be transmitted on the same OFDM symbol so that the same power boost is borrowed from other REs. When the CSI-RS RE group is defined as shown in FIG. 23, two methods for mapping the CSI-RS antenna port can be considered. Examples of these two methods are as shown in FIGS. 24 (a) and 24 (b).

In FIG. 24A, two thick solid squares in one resource block represent one CSI-RS RE group, and other REs are not shown for the sake of clarity. According to the first mapping method shown in FIG. 24 (a), CSI-RS mapping is switched between resource blocks, and all CSI-RS antenna ports are effectively mapped on the same OFDM symbol. Is possible. Specifically, in the CSI-RS RE group on the odd-numbered resource block index, CSI-RSs for four antenna ports are mapped to the first OFDM symbol (for example, 1, 2/3, 4), CSI-RSs for the remaining four antenna ports are mapped to the second OFDM symbol (for example, 5, 6/7, 8). The CSI-RS mapping on the even-numbered resource block index is oppositely applied in the time domain to the odd-numbered resource block index, and the CSI-RS insertion pattern is swapped between OFDM symbols. That is, in the CSI-RS group on the even-numbered resource block index, CSI-RSs for four antenna ports are mapped to the first OFDM symbol (for example, 5, 6/7, 8), and the second CSI-RSs for the remaining four antenna ports are mapped to the OFDM symbol (for example, 1, 2/3, 4). Thereby, CSI-RS with respect to eight transmission antenna ports is mapped by one OFDM symbol (over two resource blocks).
In FIG. 24B, the horizontal axis indicates the frequency domain, and the vertical axis indicates the code resource area. FIG. 24 (b) shows two CSI-RS RE groups (one CSI-RS RE group is composed of two thick solid squares). Note that the CSI-RS RE group is used to explain the use of different code resources, and in fact, the CSI-RS RE group exists at the same time / frequency location. According to the second mapping method shown in FIG. 24 (b), the first CSI-RS (1, 2/3, 4) is frequency-division multiplexed (FDM) on one OFDM symbol. An orthogonal code ({+1, +1}) is arranged and the remaining four CSI-RSs (5, 6/7, 8) are placed on the same OFDM symbol and subcarrier on the second orthogonal code ({+1 , -1}). Thereby, CSI-RS with respect to eight antenna ports can be transmitted on the same OFDM symbol within one resource block. Since there are only four REs that can be used for CSI-RS transmission on one OFDM symbol, code division multiplexing (CDM) is performed by using orthogonal codes in which two sets of CSI-RSs are time spread. ) Is possible. In this way, the case where orthogonal codes are applied over the time domain can be referred to as CDM-T multiplexing. As the orthogonal code, for example, a Walsh-Hadamard code can be used. Thereby, four groups of REs multiplexed by the CDM method can be generated, and the CSI-RS for each antenna port can be multiplexed by the FDM method in each of these four RE groups.

  FIGS. 25 to 27 are diagrams for explaining an example of CSI-RS multiplexing in a case where four CSI-RSs are transmitted from a single cell. The four CSI-RS multiplexing may be a subset of the eight CSI-RS multiplexing. That is, for the eight CSI-RS multiplexing, as described in FIG. 23, eight REs (two thick solid squares) can be used, and four CSI-RS multiplexings can be used. For that, the subset (4 REs) can be used. For example, four CSI-RSs can be mapped to four RE units (one thick solid square in FIGS. 25 to 27) that are continuous in the time and frequency domains. A CSI-RS RE group in which four CSI-RSs are multiplexed is defined as a form in which two REs (SFBC RE pairs) continuous in the frequency domain that can be used as SFBC pairs are continuous in the time domain. can do. That is, a group of four REs (one thick solid square) continuous in the time / frequency domain can be defined as one CSI-RS RE group. Accordingly, as shown in FIG. 26, 10 CSI-RS RE group patterns can be defined, and one CSI-RS RE group among 10 CSI-RS RE group patterns can be defined for 4CSI-RS transmission. Can be used. Further, as shown in FIG. 27 (a), the CSI-RS mapping can be performed by swapping in the time domain in the odd-numbered resource blocks and the even-numbered resource blocks, and thus, over two resource blocks. CSI-RSs for four antenna ports can be transmitted on the same OFDM symbol, and power reassignment can be fully utilized. Also, as shown in FIG. 27 (b), CSI-RS mapping is performed by multiplexing two CSI-RSs in one CSI-RS RE group (thick solid line square) using the FDM method and extending the length over the time domain. By multiplying 2 orthogonal code resources ({+ 1, + 1} and {+ 1, -1}), 2 CSI-RSs are multiplexed by the CDM-T system, and 4 CSI-RSs in one CSI-RS RE group. Can be multiplexed and transmitted. The specific contents for the setting of the CSI-RS RE group and the multiplexing of a plurality of CSI-RSs in the CSI-RS RE group can be described in the same principle as the contents described in the other embodiments described above. Description of overlapping contents is omitted for clarity.

  Also, in this embodiment, it is proposed that such a CSI-RS RE group is time-shifted, frequency-shifted, or time-frequency-shifted for each cell. That is, the CSI-RS RE group pattern used in one cell can be used as a pattern shifted in time and / or frequency in another cell. In addition, each cell can hop CSI-RS transmission in CSI-RS RE group position candidates at every transmission time point. As an example of CSI-RS RE group position candidates, as shown in FIG. 26, there can be ten CSI-RS RE group position candidates. Therefore, 10 cells at the same time can use different CSI-RS RE group patterns.

  FIGS. 28 to 30 are diagrams for explaining another example of CSI-RS multiplexing when four CSI-RSs are transmitted from a single cell. The four CSI-RS multiplexing may be a subset of the eight CSI-RS multiplexing. That is, for the eight CSI-RS multiplexing, as described in FIG. 23, eight REs (two thick solid squares) can be used, and four CSI-RS multiplexings can be used. For that, the subset (4 REs) can be used. For example, as shown in FIG. 28, four CSI-RSs can be mapped to four CSI-RS REs existing on the same OFDM symbol. In the four CSI-RS REs, two consecutive REs (SFBC RE pairs) in the frequency domain that can be used as SFBC pairs are arranged apart from each other by four subcarriers on the same OFDM symbol. Can be defined as Four CSI-RS REs defined in this way can constitute one CSI-RS RE group. Accordingly, as shown in FIG. 29, 13 CSI-RS RE group patterns can be defined, and one CSI-RS RE group among 13 CSI-RS RE group patterns for 4 CSI-RS transmission. Can be used. Further, as shown in FIG. 30, CSI-RSs for four antenna ports can be multiplexed and transmitted by the FDM method within one CSI-RS RE group. The specific contents for the setting of the CSI-RS RE group and the multiplexing of a plurality of CSI-RSs in the CSI-RS RE group can be described in the same principle as the contents described in the other embodiments described above. Description of overlapping contents is omitted for clarity.

  Also, in this embodiment, it is proposed to shift such a CSI-RS RE group for each cell by time shift, frequency shift, or time and frequency shift. That is, the CSI-RS RE group pattern used in one cell can be used as a pattern shifted in time and / or frequency in another cell. In addition, each cell can hop CSI-RS transmission in CSI-RS RE group position candidates at every transmission time point. As an example of CSI-RS RE group position candidates, as shown in FIG. 29, there can be 13 CSI-RS RE group position candidates. Therefore, 13 cells at the same time can use different CSI-RS RE group patterns.

  Alternatively, as described above, the CSI-RS RE group for the four CSI-RS antenna ports is the pattern of the CSI-RS RE group for the eight transmission CSI-RS antenna ports (for example, the CSI-RS RE pattern of FIG. 23). The predetermined subset can 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 is a CSI-RS RE group pattern for eight CSI-RS antenna ports (for example, the CSI-RS RE group in FIG. 23). 2) on two consecutive OFDM symbols at a predetermined subcarrier position in the pattern) and the above 2 at other subcarrier positions (subcarrier positions separated from the predetermined subcarrier position by 5 subcarriers). It can also be defined as two REs on consecutive OFDM symbols. One CSI-RS RE group is composed of four REs, and each RE can transmit CSI-RS for four CSI-RS antenna ports one by one. In this case, in TDM / FDM scheme It can be expressed that four CSI-RSs are multiplexed. Alternatively, in one CSI-RS RE group, the CSI-RS for two CSI-RS antenna ports can be obtained by a CDM-T scheme using orthogonal codes of length 2 over two REs existing on the same subcarrier. The CSI-RS for the remaining two CSI-RS antenna ports can be multiplexed by the CDM-T method using an orthogonal code of length 2 over two REs existing on other subcarriers. . In the CSI-RS RE group for four CSI-RS antenna ports as shown in FIG. 31, there can be 10 CSI-RS RE group position candidates in one resource block. One cell selects one of these ten CSI-RS RE group position candidates, and the other cell selects another candidate position, so that each cell has four CSI- The CSI-RS for the RS antenna port can be transmitted.

  FIGS. 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, as described with reference to FIG. 23, 8 REs (2 thick solid squares) can be used for 8 CSI-RS multiplexing. The subset (two REs) can be used. For example, as shown in FIG. 32, two CSI-RSs can be defined as two REs (SFBCRE pairs) that are continuous in the frequency domain that can be used as SFBC pairs. Two CSI-RS REs defined in this way can constitute one CSI-RS RE group. Therefore, as shown in FIG. 33, 26 CSI-RS RE group patterns can be defined, and one CSI-RS RE group among 26 CSI-RS RE group patterns can be defined for 2 CSI-RS transmission. Can be used. Also, CSI-RSs for two antenna ports in one CSI-RS RE group can be multiplexed and transmitted by the FDM method. The specific contents for setting up a CSI-RS RE group and multiplexing a plurality of CSI-RSs in the CSI-RS RE group can be described based on the same principle as described in the other embodiments. Description of overlapping contents is omitted for clarity.

  Also, in this embodiment, it is proposed to shift such a CSI-RS RE group for each cell by time shift, frequency shift, or time and frequency shift. That is, the CSI-RS RE group pattern used in one cell can be used as a pattern shifted in time and / or frequency in another cell. In addition, each cell can hop CSI-RS transmission in CSI-RS RE group position candidates at every transmission time point. Examples of CSI-RS RE group position candidates include 26 CSI-RS RE group position candidates as shown in FIG. Therefore, 26 cells at the same time can use different CSI-RS RE group patterns.

  Alternatively, as described above, the CSI-RS RE group for two CSI-RS antenna ports is a CSI-RS RE group pattern for 8 transmission CSI-RS antenna ports (for example, the CSI-RS RE pattern of FIG. 23). The predetermined subset can be set as a set of various RE positions. For example, as shown in FIG. 34, the CSI-RS RE group for two CSI-RS antenna ports is a CSI-RS RE group pattern for eight CSI-RS antenna ports (for example, the CSI-RS RE group of FIG. 23). Pattern) may be defined as two REs on two consecutive OFDM symbols at a given subcarrier position. One CSI-RS RE group is composed of two REs, and each RE can transmit CSI-RS for two CSI-RS antenna ports one by one. In such a case, the TDM scheme is used. It can be expressed that two CSI-RSs are multiplexed. Alternatively, in one CSI-RS RE group, the CSI-RS for two CSI-RS antenna ports can be obtained by a CDM-T scheme using orthogonal codes of length 2 over two REs existing on the same subcarrier. Can be multiplexed. In the CSI-RS RE group for two CSI-RS antenna ports as shown in FIG. 34, there can be 20 CSI-RS RE group position candidates in one resource block. One cell selects one of these 20 CSI-RS RE group position candidates, and the other cell selects another candidate position, so that each cell has two CSI- The CSI-RS for the RS antenna port can be transmitted.

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

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

  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 the downlink subframe are not damaged. For example, when the downlink subframe has a general CP configuration, the plurality of CSI-RS RE groups are the five CSI-RS RE groups in FIG. 23 for 8 transmission antennas in one resource block. Good. That is, each of the plurality of CSI-RS RE groups includes two consecutive subcarrier positions of two consecutive OFDM symbols and the two consecutive subcarriers on a resource element in which CRS and DMRS are not arranged. It can be defined by two other consecutive subcarrier positions that are four subcarriers away from the carrier position. Such a plurality of CSI-RS resource element groups can be defined as resource element positions in which one CSI-RS resource element group is shifted in time and frequency domains with respect to other CSI-RS resource element groups.

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

  In addition, a plurality of CSI-RS RE groups to which CSI-RSs for two antenna ports are mapped are parts of a plurality of CSI-RS RE groups to which CSI-RSs for eight antenna ports are mapped. It can be defined as a set. For example, in the case of two transmission antennas, the plurality of CSI-RS RE groups may be the 20 CSI-RS RE groups in FIG. Alternatively, the 26 CSI-RS RE groups in FIG. 33 may be used for two transmission antennas.

  In step S3520, the base station may map CSI-RSs corresponding to 8 or less antenna ports to one CSI-RS RE group selected from the plurality of CSI-RS RE groups. At this time, among CSI-RSs for 8 or less antenna ports, CSI-RSs for 2 antenna ports are CDM-T schemes using orthogonal codes having a length of 2 over two OFDM symbols on the same subcarrier. Can be multiplexed.

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

  When a CSI-RS for 8 or less antenna ports is mapped and transmitted to one CSI-RS RE group selected as described above in one subframe, this selected in the other subframe. A CSI-RS RE group different from one CSI-RS RE group can be transmitted by mapping a CSI-RS for 8 or less antenna ports.

  In step S3540, the UE transmits a CSI for eight or less 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 from the base station. -It is possible to receive downlink subframes mapped with RS.

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

  For the sake of clarity, FIG. 35 illustrates a method according to an embodiment of the present invention that is executed in a base station and a terminal. The contents described in the above may be applied.

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

  The base station apparatus (eNB) 3610 can include a reception module 3611, a transmission module 3612, a processor 3613, a memory 3614, and an antenna 3615. The reception module 3611 can receive various signals, data, information, and the like from a terminal or the like. The transmission module 3612 can transmit various signals, data, information, and the like to a terminal or the like. The processor 3613 can be configured to control the general operation of the base station device 3610 including the reception module 3611, the transmission module 3612, the memory 3614, and the antenna 3615. The antenna 3615 can be formed using a plurality of antennas.

  The base station apparatus 3610 which concerns on one Example of this invention can transmit CSI-RS with respect to 8 or less antenna ports. The processor 3613 of the base station apparatus is configured to select one from a plurality of CSI-RS RE groups defined on the data region of the downlink subframe and map CSI-RSs for 8 or less antenna ports. can do. Further, the processor 3613 may be configured to transmit the downlink subframe on which CSI-RS is mapped to 8 or less antenna ports via the transmission module 3612. A plurality of CSI-RS RE groups may be defined such that a transmission diversity resource element pair for data transmitted on a downlink subframe is not damaged.

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

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

  The terminal device 3620 according to an embodiment of the present invention can measure channel information from CSI-RS for 8 or less antenna ports. The processor 3623 of the terminal apparatus receives eight or less antennas in one CSI-RS RE group selected from a plurality of CSI-RS RE groups defined on the data area of the downlink subframe via the reception module 3621. A downlink subframe in which CSI-RS for a port is mapped may be received. Further, the processor 3623 can be configured to measure channel information for each antenna port using CSI-RS for eight or fewer antenna ports. A 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 damaged.

  In addition, the processor 3623 performs a function of performing arithmetic processing on information received by the terminal device, information transmitted to the outside, and the like, and the memory 3634 can store the processed information and the like for a predetermined time. It may be replaced by a component such as (not shown).

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

  In the case of implementation by hardware, a method according to an embodiment of the present invention includes one or more application specific integrated circuits (ASICs), DSPs (Digital Signal Processors), DSPSs (Digital Signal Processors). Devices), FPGAs (Field Programmable Gate Arrays), processors, controllers, microcontrollers, microprocessors, and the like.

  In the case of implementation by firmware or software, the method according to the embodiment of the present invention may be in the form of a module, procedure, function, or the like that performs the function or operation described above. The software code can be stored in a memory unit and driven by a processor. The memory unit is provided inside or outside the processor, and can exchange data with the processor by various known means.

  The detailed description of the preferred embodiments of the present invention disclosed above is provided to enable any person skilled in the art to implement and practice the present invention. Although the foregoing has been described with reference to the preferred embodiments of the present invention, it will be understood by those skilled in the art that the present invention can be variously modified and changed without departing from the scope of the present invention. Will be understood. For example, those skilled in the art can use the configurations described in the above embodiments in a combination manner. Accordingly, the present invention is not intended to be limited to the embodiments disclosed herein, but is to provide 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 and essential characteristics of the invention. As such, the above detailed description should not be construed as limiting in any respect, but should be considered as exemplary. The scope of the invention should be determined by reasonable interpretation of the appended claims and any changes that come within the equivalent scope of the invention are included in the scope of the invention. The present invention is not limited to the embodiments disclosed herein, but has the widest scope consistent with the principles and novel features disclosed herein. In addition, claims which do not have an explicit citation relationship in the claims can be combined to constitute an embodiment, or can be included as a new claim by amendment after application.

3611, 3621 Receiver module 3612, 3622 Transmission module 3613, 3623 Processor 3614, 3624 Memory 3615, 3625 Antenna

Claims (12)

A method for transmitting channel state information-reference signal (CSI-RS) for eight or fewer antenna ports,
Transmitting the CSI-RS in a downlink subframe,
The CSI-RS is mapped to one resource element set among a plurality of resource element set candidates, and the resource element set has a plurality of resource elements;
The number of candidate resource element sets for 8 antenna ports is 5,
Five resource element set candidates for the eight antenna ports in a resource region defined by 14 OFDM symbols and 12 subcarriers in the downlink subframe are:
First resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the sixth and seventh OFDM symbols;
Second resource element set candidates defined on the first, second, seventh and eighth subcarriers in the tenth and eleventh OFDM symbols;
Third resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the 10th and 11th OFDM symbols;
A fourth resource element set candidate defined on the fifth, sixth, eleventh and twelfth subcarriers in the tenth and eleventh OFDM symbols; and
A fifth resource element set candidate defined on the third, fourth, ninth and tenth subcarriers in the 13th and 14th OFDM symbols;
A CSI-RS transmission method. The downlink subframe is composed of a general CP,
On resource elements that are not used for the shared reference signal and the demodulation reference signal , each of the plurality of resource element set candidates is defined by two consecutive subcarrier positions in two consecutive OFDM symbols, and others. The CSI-RS transmission method according to claim 1, wherein the two consecutive subcarriers are separated from the two consecutive subcarrier positions by four subcarriers. Multiple resource element sets candidates for two antenna ports, and four more sets of resource elements for the antenna port candidates are defined as a subset of a plurality of resource element sets candidates for the eight antenna ports, wherein Item 3. The CSI-RS transmission method according to Item 2. One resource element set candidates in at least one time and frequency domains, it is shifted with respect to other sets of resource elements candidate, CSI-RS transmission method according to claim 1.   CSI-RSs for two antenna ports among CSI-RSs for the eight or fewer antenna ports are code division multiplexed using orthogonal codes of length 2 on two OFDM symbols on the same subcarrier. The CSI-RS transmission method according to claim 1, multiplexed by a method. A method of measuring channel information from channel state information-reference signal (CSI-RS) for eight or fewer antenna ports,
Receiving the CSI-RS in a downlink subframe ;
Measuring the channel information based on CSI-RS for the eight or fewer antenna ports;
The CSI-RS is mapped to one resource element set among a plurality of resource element set candidates, and the resource element set has a plurality of resource elements;
The number of candidate resource element sets for 8 antenna ports is 5,
Five resource element set candidates for the eight antenna ports in a resource region defined by 14 OFDM symbols and 12 subcarriers in the downlink subframe are:
First resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the sixth and seventh OFDM symbols;
Second resource element set candidates defined on the first, second, seventh and eighth subcarriers in the tenth and eleventh OFDM symbols;
Third resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the 10th and 11th OFDM symbols;
A fourth resource element set candidate defined on the fifth, sixth, eleventh and twelfth subcarriers in the tenth and eleventh OFDM symbols; and
A fifth resource element set candidate defined on the third, fourth, ninth and tenth subcarriers in the 13th and 14th OFDM symbols;
A channel information measuring method including: The downlink subframe is composed of a general CP,
On resource elements that are not used for the shared reference signal and the demodulation reference signal , each of the plurality of resource element set candidates is defined by two consecutive subcarrier positions in two consecutive OFDM symbols, and others. 7. The channel information measurement method according to claim 6 , wherein the two consecutive subcarriers are separated from the two consecutive subcarrier positions by four subcarriers. Multiple resource element sets candidates for two antenna ports, and four more sets of resource elements for the antenna port candidates are defined as a subset of a plurality of resource element sets candidates for the eight antenna ports, wherein Item 8. The channel information measurement method according to Item 7 . One resource element set candidates in at least one time and frequency domains, is shifted with respect to other sets of resource elements candidate channel information measuring method according to claim 6. CSI-RSs for two antenna ports among CSI-RSs for the eight or fewer antenna ports are code division multiplexed using orthogonal codes of length 2 on two OFDM symbols on the same subcarrier. The channel information measuring method according to claim 6 , wherein the channel information is multiplexed in a manner. A base station that transmits channel state information-reference signals (CSI-RS) for eight or fewer antenna ports,
A receiving module configured to receive an uplink signal from the terminal;
A transmission module configured to transmit a downlink signal to the terminal;
A processor configured to control a base station including the receiving module and the transmission module;
With
The processor is configured to transmit the CSI-RS in a downlink subframe using the transmission module;
The CSI-RS is mapped to one resource element set among a plurality of resource element set candidates, and the resource element set has a plurality of resource elements;
The number of candidate resource element sets for 8 antenna ports is 5,
Five resource element set candidates for the eight antenna ports in a resource region defined by 14 OFDM symbols and 12 subcarriers in the downlink subframe are:
First resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the sixth and seventh OFDM symbols;
Second resource element set candidates defined on the first, second, seventh and eighth subcarriers in the tenth and eleventh OFDM symbols;
Third resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the 10th and 11th OFDM symbols;
A fourth resource element set candidate defined on the fifth, sixth, eleventh and twelfth subcarriers in the tenth and eleventh OFDM symbols; and
A fifth resource element set candidate defined on the third, fourth, ninth and tenth subcarriers in the 13th and 14th OFDM symbols;
A CSI-RS transmission base station. A terminal that measures channel information from channel state information-reference signal (CSI-RS) for eight or fewer antenna ports,
A receiving module configured to receive a downlink signal from a base station;
A transmission module configured to transmit an uplink signal to the base station;
A processor configured to control a terminal including the receiving module and the transmission module;
With
The processor is configured to receive the CSI-RS in a downlink subframe via the receiving module and measure the channel information based on CSI-RS for the eight or fewer antenna ports;
The CSI-RS is mapped to one resource element set among a plurality of resource element set candidates, and the resource element set has a plurality of resource elements;
The number of candidate resource element sets for 8 antenna ports is 5,
Five resource element set candidates for the eight antenna ports in a resource region defined by 14 OFDM symbols and 12 subcarriers in the downlink subframe are:
First resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the sixth and seventh OFDM symbols;
Second resource element set candidates defined on the first, second, seventh and eighth subcarriers in the tenth and eleventh OFDM symbols;
Third resource element set candidates defined on the third, fourth, ninth and tenth subcarriers in the 10th and 11th OFDM symbols;
A fourth resource element set candidate defined on the fifth, sixth, eleventh and twelfth subcarriers in the tenth and eleventh OFDM symbols; and
A fifth resource element set candidate defined on the third, fourth, ninth and tenth subcarriers in the 13th and 14th OFDM symbols;
Including channel information measuring terminal.

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