JP6462762B2 - Method and apparatus for transmitting and receiving reference signals in a wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting / receiving a reference signal using a generated reference signal sequence.

  As an example of a mobile communication system to which the present invention can be applied, a 3GPP LTE (3rd Generation Partnership Project Long Term Evolution; hereinafter referred to as “LTE”), LTE-Advanced (hereinafter referred to as “LTE-A”) communication system. A brief description will be given.

  FIG. 1 is a diagram schematically showing an E-UMTS network structure as an example of a mobile communication system. E-UMTS (Evolved Universal Mobile Communications System) is a system developed from the existing UMTS (Universal Mobile Telecommunications System), and is currently undergoing basic standardization work in 3GPP. In general, E-UMTS can be referred to as an LTE (Long Term Evolution) system. The detailed contents of the UMTS and E-UMTS technical specifications are respectively referred to as “Release 8” in “3rd Generation Partnership Project: Technical Specification Group Radio Access Network”.

  Referring to FIG. 1, E-UMTS is a terminal (User Equipment, UE), a base station (eNode B; eNB), and an access gateway (Access) connected to an external network located at the end of a network (E-UTRAN). Gateway, AG). The base station can simultaneously transfer multiple data streams for broadcast service, multicast service and / or unicast service.

  One base station has one or more cells. The cell is set to one of bandwidths such as 1.25, 2.5, 5, 10, 15, 20 MHz, and provides a downlink or uplink transfer service to a plurality of terminals. Different cells can be configured to provide different bandwidths. The base station controls data transmission / reception with respect to a plurality of terminals. For downlink (DL) data, the BS transmits downlink scheduling information, and the time / frequency domain in which the data is transferred to the corresponding terminal, coding, data size, hybrid automatic repeat request (Hybrid Automatic Repeat). and request, HARQ) related information.

  Also, for uplink (Uplink, UL) data, the base station transfers uplink scheduling information to a corresponding terminal, and the time / frequency domain, coding, data size, and hybrid automatic repeat request related information that the terminal can use. Let us know. An interface for transferring user traffic or control traffic can be used between base stations. A core network (Core Network, CN) can be composed of AG, a network node for user registration of a terminal, and the like. AG manages the mobility of a terminal in TA (Tracking Area) units composed of a plurality of cells.

  Wireless communication technology has been developed up to LTE based on Wideband Code Division Multiple Access (WCDMA), but the demands and expectations of users and operators are increasing. In addition, new wireless connection technologies are being developed, and in order to be competitive in the future, new technologies must be developed. It is required to reduce cost per bit, increase service availability, use flexible frequency bands, simple structure and open interface, and appropriate power consumption of terminals.

  In recent years, 3GPP is proceeding with standardization work for LTE subsequent technologies. This technique is referred to herein as “LTE-Advanced” or “LTE-A”. One of the main differences between the LTE system and the LTE-A system is the difference in system bandwidth. The LTE-A system aims to support a wide band of up to 100 MHz, and for this purpose, it uses carrier aggregation or bandwidth aggregation technology that achieves a wide band using a plurality of frequency blocks. ing. Carrier aggregation is configured to use a plurality of frequency blocks as one large logical frequency band in order to obtain a wider frequency band. The bandwidth of each frequency block can be defined based on the bandwidth of the system block used in the LTE system. Each frequency block is transferred using a component carrier.

  However, in the LTE-A system, when a reference signal is transferred on eight layers, the reference signal sequence generation method for transferring the reference signal in each layer is not discussed at all.

  A technical problem to be achieved by the present invention is to provide a method for transmitting and receiving a reference signal in a wireless communication system.

  Another technical problem to be achieved by the present invention is to provide an apparatus for transmitting and receiving a reference signal in a wireless communication system.

  The technical problem to be achieved by the present invention is not limited to the above-mentioned technical problem, and other technical problems not mentioned can be obtained from the following description based on the general knowledge in the technical field to which the present invention belongs. It will be clearly understood by those who have it.

  In order to achieve the above technical problem, a method for transmitting a reference signal by a base station in a wireless communication system according to the present invention includes a first m-sequence and a second m-sequence for each layer. Is used to generate a pseudo-random sequence, to generate a reference signal sequence using the generated pseudo-random sequence and a Walsh code, and to apply a reference signal sequence generated for each layer The pseudo-random sequence is generated using a sequence initial value, and the sequence initial value includes a slot number, a physical layer cell in a radio frame, and the like. Indicates a layer index group distinguished by ID value and frequency It is generated using the values.

  In order to achieve the above technical problem, according to the present invention, a method of transmitting a reference signal in a wireless communication system according to the present invention includes a resource element (Resource Element, RE) allocated for reference signal transfer for each layer. ) To generate the reference signal sequence by spreading or covering the Walsh codes so as to be orthogonal to the time axis between the scrambling sequences generated by the resource elements. And transferring a reference signal to which the generated reference signal sequence is applied to a terminal through each layer, wherein the Walsh code spreading or covering is performed between resource blocks or resource block pairs. Different To have different sequences in each other with cans value is applied to the frequency axis a plurality of resource blocks (Resource Block, RB) or resource block pair units.

  In the above method, the Walsh code spreading or covering is performed in the first resource block among a plurality of resource block pairs, in a first code division multiplexing (CDM) group, each of the Walsh code elements is one by one. The resource element of the first subcarrier assigned to one resource block in the time axis direction, the resource element of the second subcarrier in the direction opposite to the time axis, and the resource element of the third subcarrier in the time axis direction Each of the plurality of resource block pairs is applied to be mapped, and in the second resource block, the first CDM group is assigned one Walsh code element to the second resource block. Time in the direction opposite to the time axis of the first subcarrier resource element and time in the second subcarrier resource element Direction, may be adapted to be respectively mapped in the time axis direction opposite to the resource elements of the third subcarrier.

  Here, the second CDM group in the first and second resource block pairs may be applied in a different order from the Walsh code elements applied to the first CDM group.

  In the above method, generating the reference signal sequence is performed by repeatedly applying different sequences having different sequence values on the frequency axis in units of two resource blocks (Resource Blocks, RBs). Good.

  The Walsh code element includes (1, 1, 1, 1) for the layer 1 and (1, -1, 1, -1) for the layer 2 among the four layers. ), (1, 1, -1, -1) may be applied to layer 3, and (1, -1, -1, 1) may be applied to layer 4.

  In order to achieve the above other technical problems, a base station apparatus for transferring a reference signal in a wireless communication system according to the present invention includes a first m-sequence and a second m-sequence for each layer. A processor that generates a pseudo-random sequence using an m-sequence and generates a reference signal sequence using the generated pseudo-random sequence and a Walsh code, and a reference signal sequence generated for each layer And a transfer module that transfers the reference signal to each terminal for each layer, and the processor generates the pseudo-random sequence using a sequence initial value, and the sequence initial value Rays distinguished by slot number, physical layer cell ID value, and frequency It is generated using a value indicating the over index group.

  In order to achieve the other technical problems described above, a base station apparatus for transferring a reference signal in a wireless communication system according to the present invention has a resource element (RE allocated for reference signal transfer for each layer). , Resource Element), the same scrambling sequence is generated, and the Walsh code is spread or covered so as to be orthogonal to the time axis between the scrambling sequences generated by the resource elements, and the reference signal sequence is generated. A processor for generating and a transfer module for transferring a reference signal to which the generated reference signal sequence is applied to a terminal through each layer, the Walsh code spreading or covering of the processor being a resource block or a resource block As different sequences in each other is mapped with different sequence value between A (pair), a plurality of resource blocks (Resource Block, RB) or resource block pair units can be applied to the frequency axis.

  According to the reference signal sequence generation and transfer method according to the present invention, it is possible to significantly improve the communication performance between a base station and a terminal in a 3GPP LTE-A system or the like.

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

  The accompanying drawings, which are included as part of the detailed description to assist in understanding the invention, provide examples of the invention and together with the detailed description explain the technical idea of the invention.

1 is a diagram schematically showing an E-UMTS network structure as an example of a mobile communication system. FIG. It is a figure which shows the control plane (Control Plane) and user plane (User Plane) structure of the radio | wireless interface protocol (Radio Interface Protocol) between the terminal and E-UTRAN based on 3GPP radio | wireless connection network specification. It is a figure for demonstrating the physical channel used for 3GPP system, and the general signal transfer method using these. It is a figure which illustrates the structure of the radio | wireless frame used with the 3GPP LTE system which is an example of a mobile communication system. It is a figure which shows the structure of the downlink and uplink sub-frame of 3GPP LTE system which is an example of a mobile communication system. 1 is a diagram illustrating a downlink time-frequency resource lattice structure used in a 3GPP LTE system which is an example of a mobile communication system. FIG. 1 is a configuration diagram of a general multiple antenna (MIMO) communication system. It is a figure which shows the channel from N _T transmitting antennas to the receiving antenna i. FIG. 2 shows a general system structure for OFDMA and SC-FDMA. It is a figure which shows the system structure for uplink SC-FDMA in 3GPP LTE system which is an example of a mobile communication system. It is a figure which shows an example of the uplink SC-FDMA transmission frame structure in the 3GPP LTE system which is an example of a mobile communication system. It is a figure which shows an example of the mapping relationship of the data signal for the MIMO system based on SC-FDMA transfer. It is a figure which shows the example of the reference signal pattern in 3GPP LTE system. 1 is a diagram illustrating an example of a pattern of REs that are code-multiplexed for DRS layers 1 and 2 in 1 RB. FIG. It is a figure which shows an example of the method of producing | generating a DRS sequence. It is a figure which shows the other example of the method of producing | generating a DRS sequence. It is a figure for demonstrating an example of the method of producing | generating a DRS sequence. It is a figure explaining the example of the method of producing | generating a sequence within 1 RB. It is a figure for demonstrating an example of the method of producing | generating a DRS sequence. It is a figure explaining the example of the method of producing | generating a sequence within 1 RB. It is a figure explaining the example of the method of producing | generating a DRS sequence within 1 RB. It is a figure which shows an example which two cells transfer DRS using the produced | generated DRS sequence. It is a figure explaining the example of the method of producing | generating a sequence within 1 RB. It is a figure which shows an example which two cells transfer DRS using the produced | generated DRS sequence. FIG. 4 is a diagram illustrating an example of a method of applying precoding to two DRS layers and mapping and transmitting to four transmission antennas, and a power difference between OFDM symbols in a case where DRS is transferred in such a manner. is there. It is a figure explaining the example of the method of producing | generating a DRS sequence. It is a figure which shows an example which transfers DRS using the DRS sequence produced | generated by the method of FIG. It is a figure which shows an example of the method of producing | generating a DRS sequence. It is a figure which shows an example of the method of producing | generating a DRS sequence. It is a figure which shows the example which transfers a DRS signal using the DRS sequence produced | generated by two cells. It is a figure explaining the other example of the DRS sequence generation method regarding FIG. It is a figure for demonstrating the example of the method of producing | generating a DRS sequence for every OFDM symbol. It is a figure which shows the sequence mapping method regarding FIG. 32 more concretely. (A) is a figure which shows the example of the pattern of the orthogonal code cover code used for a specific DRS layer, (b), (c) is a figure which shows the specific example of Walsh code use in RB. It is a figure which shows an example of the method of mapping a Walsh code with a frequency CDM RE set. It is a figure which shows the example of the code hopping with respect to two layers. It is a figure which shows the example of the code hopping with respect to two layers. It is a figure which shows the example of the Walsh code mapping with respect to four layers. It is a figure explaining the example of the production | generation method of 2 sequences. It is a figure which shows an example which two cells transfer DRS using the produced | generated DRS sequence. It is a figure which shows the other example which two cells transfer DRS using the produced | generated DRS sequence. It is a figure which shows the other example which two cells transfer DRS using the produced | generated DRS sequence. (A) is a figure which shows an example which transfers the produced | generated DRS sequence, (b) is a figure which shows the transfer power by the example of a transfer like (a). It is a figure which shows the other example which transfers DRS using the produced | generated DRS sequence. It is a figure which shows an example of the method of assigning a CDM code for every layer. (A) is a figure which shows the other example for transferring DM RS sequence, (b) is a figure which shows the transmission power by the example of (a). It is a figure which shows an example of the method of mapping a DRS sequence. It is a figure which shows the other example which transfers DRS using the produced | generated DRS sequence. It is a figure which shows the example of the method of applying a Walsh code to DM RS. It is a figure which shows the example of the method of applying a Walsh code to four DM RSs. It is a figure which shows the example of the method of applying a Walsh code to four DM RSs. It is a figure which shows an example of the method of mapping a DM RS sequence. 2 is a diagram showing the components of the device (50) according to the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description disclosed below in connection with the appended drawings is intended as a description of exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one skilled in the art will understand that the invention may be practiced without these specific details. For example, the following detailed description will be specifically described using an example in which the mobile communication system is a 3GPP LTE system, but is applicable to any other mobile communication system except for matters specific to the 3GPP LTE system. is there.

  In some instances, well-known structures and devices may be omitted or may be presented in the form of a block diagram with a central focus on each structure and device in order to avoid obscuring the concepts of the present invention. Further, throughout the present specification, the same constituent elements will be described with the same reference numerals.

  In the following description, a terminal is a generic term for a mobile or fixed user terminal device such as a UE (User Equipment), an MS (Mobile Station), an AMS (Advanced Mobile Station), or the like. The base station is a generic name for any node at the network end that communicates with a terminal such as Node B, eNode B, BS (Base Station), AP (Access Point), and the like.

  In a mobile communication system, a user equipment (UE) can receive information from a base station through a downlink and can transfer information through an uplink. Information transferred or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transferred or received by the terminal.

  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 in 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.

  In order to clarify the explanation, the 3GPP LTE and LTE-A systems will be mainly described. However, the technical idea of the present invention is not limited to this.

  In a mobile communication system, a user equipment (UE) can receive information from a base station through a downlink and can transfer information through an uplink. Information transferred or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transferred or received by the terminal.

  FIG. 2 is a diagram illustrating a structure of a control plane (Control Plane) and a user plane (User Plane) of a radio interface protocol (Radio Interface Protocol) between a terminal and the E-UTRAN based on the 3GPP radio access network standard.

  Referring to FIG. 2, the control plane refers to a path through which a control message used for managing a call by a user equipment (UE) and a network is transferred. The user plane means a path through which data generated in the application layer, for example, voice data or Internet packet data is transferred.

  The physical layer, which is the first layer, provides an information transfer service (Information Transfer Service) to an upper layer using a physical channel. The physical layer is connected to an upper medium connection control layer through a transfer channel. Data moves between the medium connection control layer and the physical layer through the transfer channel. Data moves between the physical layer on the transmission side and the physical layer on the reception side through a physical channel. The physical channel uses time and frequency as radio resources. In particular, the physical channel is modulated by an OFDMA (Orthogonal Frequency Division Multiple Access) scheme on the downlink, and is modulated by an SC-FDMA (Single Carrier Frequency Multiple Access) scheme on the uplink.

  The medium access control (MAC) layer in the second layer provides a service to a radio link control (RLC) layer, which is an upper layer, through a logical channel (Logical Channel). The second layer, the RLC layer, supports reliable data transfer. The function of the RLC layer may be implemented by a functional block inside the MAC. The PDCP (Packet Data Convergence Protocol) layer in the second layer is a header compression (Header) that reduces unnecessary control information in order to efficiently transfer IP packets such as IPv4 and IPv6 over a low-bandwidth wireless interface. (Compression) function is executed.

  The radio resource control (RRC) layer located at the bottom of the third layer is defined only in the control plane. The RRC layer is responsible for control of the logical channel, the transfer channel, and the physical channel in association with radio bearer (RB) configuration (configuration), re-configuration (re-configuration), and release (release). RB means a service provided by the second layer for data transmission between the terminal and the network. For this purpose, the RRC layer of the terminal and the network exchange RRC messages with each other. If there is an RRC connection (RRC Connected) between the terminal and the RRC layer of the network, the terminal will be in an RRC connected state (Connected Mode), otherwise it will be in an RRC dormant state (Idle Mode) . A NAS (Non-Access Stratum) layer above the RRC layer is responsible for functions such as session management and mobility management.

  One cell constituting a base station (eNB) is set to any one of bandwidths such as 1.25, 2.5, 5, 10, 15, 20 MHz, and downlink or uplink to a plurality of terminals Provide forwarding services. Different cells can be configured to provide different bandwidths.

  The downlink transfer channel for transferring data from the network to the terminal includes a BCH (Broadcast Channel) for transferring system information, a PCH (Paging Channel) for transferring paging messages, and a downlink SCH (Shared Channel) for transferring user traffic and control messages. )and so on. Downlink multicast or broadcast service traffic or control messages may be forwarded via the downlink SCH or may be forwarded via another downlink MCH (Multicast Channel). On the other hand, uplink transfer channels for transferring data from a terminal to a network include RACH (Random Access Channel) for transferring initial control messages and uplink SCH (Shared Channel) for transferring user traffic and control messages. Logical channels (Logical Channels) that are higher than the transport channel and are mapped to the transport channel include BCCH (Broadcast Control Channel), PCCH (Paging Control Channel), CCCH (Common Control Channel), MCCH (Multicast Channel, Multichannel). MTCH (Multicast Traffic Channel) is available.

  FIG. 3 is a diagram for explaining a physical channel used in the 3GPP system and a general signal transfer method using these channels.

  Referring to FIG. 3, when a terminal is turned on or newly enters a cell, the terminal performs an initial cell search operation such as synchronizing with a base station (S310). Therefore, a terminal receives a primary synchronization channel (Primary Synchronization Channel; P-SCH) and a secondary synchronization channel (Secondary Synchronization Channel; S-SCH) from a base station, and synchronizes with the base station to obtain information such as a cell ID. Can be earned. Thereafter, the terminal can acquire the broadcast information in the cell by receiving a physical broadcast channel from the base station. Meanwhile, the UE can check a downlink channel state by receiving a downlink reference signal (DLRS) in an initial cell search stage.

  The terminal that has completed the initial cell search receives a physical downlink control channel (Physical Downlink Control Channel; PDCCH) and a physical downlink shared channel (Physical Downlink Channel; PDSCH) based on information placed on the PDCCH. Thus, more specific system information can be acquired (S320).

  On the other hand, when the base station is first accessed or there is no radio resource for signal transfer, the terminal can perform a random access procedure (RACH) on the base station (steps S330 to S330). Step S360). For this purpose, the UE transmits a specific sequence as a preamble through a physical random access channel (PRACH) (S330 and S350), and receives a response message for the preamble through the PDCCH and the corresponding PDSCH (S340). And S360). In the case of a contention-based RACH, a contention resolution procedure can be further performed.

  The terminal that has performed the above-described procedure thereafter performs PDCCH / PDSCH reception (S370) and physical uplink shared channel (PUSCH) / physical uplink as a general uplink / downlink signal transfer procedure. A link control channel (PUCCH) transfer (S380) can be performed. Control information that the terminal transfers to the base station through the uplink or that the terminal receives from the base station includes downlink / uplink ACK / NACK signals, CQI (Channel Quality Indicator), PMI (Precoding Matrix Index), RI (Rank). Indicator) and the like. In the 3GPP LTE system, a terminal can transfer control information such as the above-mentioned CQI / PMI / RI through PUSCH and / or PUCCH.

  FIG. 4 is a diagram illustrating a structure of a radio frame used in a 3GPP LTE system that is an example of a mobile communication system.

Referring to FIG. 4, a radio frame has a length of 10 ms (327200 · T _s ), and is composed of 10 equally sized subframes. Each subframe has a length of 1 ms and is composed of two slots. Each slot has a length of 0.5 ms (15360 · T _s ). Here, T _s represents a sampling time and is displayed as T _s = 1 / (15 kHz × 2048) = 3.2552 × 10 ⁻⁸ (about 33 ns). The 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 LTE system, one resource block includes 12 subcarriers × 7 (6) OFDM symbols or SC-FDMA (Single Carrier Frequency Multiple Access). A transmission time interval (TTI), which is a unit time for transferring data, can be determined in units of one or more subframes. The structure of the radio frame described above 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 OFDM symbols or SC-FDMA included in the slots can be variously changed. .

  FIG. 5 is a diagram illustrating a structure of a downlink and an uplink subframe of a 3GPP LTE system which is an example of a mobile communication system.

  Referring to (a) of FIG. 5, one downlink subframe includes two slots in the time domain. Data at which the top three OFDM symbols in the first slot in the downlink subframe correspond to the control region to which the control channel is assigned, and the remaining OFDM symbols are assigned to the PDSCH (Physical Downlink Shared Channel). Corresponds to the area.

  Downlink control channels used in 3GPP LTE include PCFICH (Physical Control Format Channel), PDCCH (Physical Downlink Control Channel), and PHICH (Physical Hybrid-ARQ). The PCFICH transferred in the first OFDM symbol of the subframe carries information on the number of OFDM symbols (ie, the size of the control region) used for control channel transfer in the subframe. The control information transferred through the PDCCH is referred to as downlink control information (DCI). DCI indicates uplink resource allocation information, downlink resource allocation information, an uplink transfer power control command for an arbitrary terminal group, and the like. The PHICH carries an ACK (Acknowledgement) / NACK (Not-Acknowledgement) signal for an uplink HARQ (Hybrid Automatic Repeat Request). That is, the ACK / NACK signal for the uplink data transferred by the terminal is transferred by PHICH.

  Next, PDCCH which is a downlink physical channel will be described.

  PDCCH includes PDSCH resource allocation and transfer format (referred to as DL grant), PUSCH resource allocation information (referred to as UL grant), a set of transfer power control commands for individual terminals within an arbitrary terminal group, and VoIP. (Voice over Internet Protocol) activation and the like can be carried. Multiple PDCCHs can be transferred in the control region, and the terminal can monitor multiple PDCCHs. The PDCCH is configured by an aggregation of one or a plurality of continuous CCEs (Control Channel Elements). A PDCCH composed of a set of one or a plurality of continuous CCEs may be transferred through a control region after being subjected to subblock interleaving. CCE is a logical allocation unit used to provide a coding rate based on the state of a radio channel to PDCCH. A CCE corresponds to a plurality of resource element groups. The PDCCH format and the number of possible PDCCH bits are determined according to the relationship between the number of CCEs and the coding rate provided by the CCEs.

  Control information transferred through the PDCCH is referred to as downlink control information (DCI). Table 1 below represents DCI in the DCI format.

  DCI format 0 indicates uplink resource allocation information, DCI formats 1 and 2 indicate downlink resource allocation information, and DCI formats 3 and 3A indicate uplink TPC (transmission power control) commands for an arbitrary terminal group. Show.

  Referring to FIG. 5B, an uplink subframe can be distinguished into a control region and a data region in the frequency domain. The control region is assigned to a PUCCH (Physical Uplink Control Channel) that carries uplink control information. The data area is assigned to a PUSCH (Physical Uplink Shared Channel) for carrying user data. In order to maintain single carrier characteristics, one terminal does not transmit PUCCH and PUSCH at the same time. A PUCCH for one terminal is assigned to an RB pair in one subframe. Each RB belonging to an RB pair occupies different subcarriers in two slots. The RB pair assigned to the PUCCH is frequency hopped at a slot boundary.

  FIG. 6 is a diagram illustrating a downlink time-frequency resource lattice structure used in a 3GPP LTE system which is an example of a mobile communication system.

  A resource block (Resource Block, RB) shown in FIG. 6 is used to describe a mapping relationship between a certain physical channel and resource elements. The RB is classified into a physical resource block (Physical Resource Block, PRB) and a virtual resource block (Virtual Resource Block, VRB).

The VRB size is the same as the PRB size. VRB can be classified into local VRB (Localized VRB, LVRB) and distributed VRB (Distributed VRB, DVRB). For each type of VRB, a pair of VRBs in two slots within one subframe are assigned together with a single VRB number n _VRB .

  Next, an overview of a general multiple antenna (MIMO) technique will be described. MIMO is an abbreviation of “Multi-Input Multi-Output”. Since it has used one transmitting antenna and one receiving antenna so far, it adopts multiple transmitting antennas and multiple receiving antennas to transmit and receive data efficiency. Refers to a method of improving In other words, it refers to a technology that attempts to increase capacity or improve performance using multiple antennas at the transmitting end or receiving end of a wireless communication system. Hereinafter, “MIMO” is referred to as “multiple antenna”.

  The multi-antenna technique is an application of a technique that collects and completes data fragments received from a plurality of antennas without depending on a single antenna path to receive one whole message. With this technique, it is possible to improve the data transfer rate in a specific range or increase the system range with respect to a specific data transfer rate.

  Since next-generation mobile communications require a much higher data transfer rate than existing mobile communications, efficient multi-antenna technology is expected to be essential. Under these circumstances, the MIMO communication technology is a next-generation mobile communication technology that can be widely used for mobile communication terminals and repeaters, and the transfer amount limit of other mobile communication is limited according to the limit situation due to the expansion of data communication. Is attracting interest as a technology that can overcome

  On the other hand, among the various transfer efficiency improvement technologies currently under study, the multi-antenna (MIMO) technology that uses multiple antennas at both the transmitting and receiving ends breaks down communication capacity and transmission / reception performance without additional frequency allocation or power increase. Currently, it is attracting the most attention as a method that can be improved.

  FIG. 7 is a configuration diagram of a general multiple antenna (MIMO) communication system.

As shown in FIG. 7, when the number of transmitting antennas is increased to N _{T and the} number of receiving antennas is increased to N _R at the same time, it is different from the case where a plurality of antennas are used only in either the transmitter or the receiver. Since the theoretical channel transfer capacity increases in proportion to the number of antennas, the transfer rate can be improved and the frequency efficiency can be dramatically improved. The transfer rate obtained by increasing the channel transfer capacity is equal to the value obtained by multiplying the maximum transfer rate (Ro) when using one antenna by the rate increase rate (Ri) as shown below, and theoretically increases. Can do. The rate increase rate (Ri) can be expressed as in Equation 1 below.

  In order to describe the communication method in the multi-antenna system as described above in a more specific manner, mathematically modeling it is as follows.

First, as shown in FIG. 7, it is assumed that there are N _T transmit antennas and N _R receive antennas.

First, the transmission signal will be described. When N _T transmission antennas are present, the maximum transferable information is N _T , and can be expressed by a vector as shown in Equation 2 below.

On the other hand, each of the transfer information _{s 1,} s 2, ..., in _{s NT} can be separately transferred power, this time, each of the transmission power _{P 1,} P 2, ..., if _{P NT,} transfer The power-adjusted transfer information can be represented by a vector as shown in Equation 3 below.

On the other hand, adjustment information vector transfer power, since, N _T number of transfer signals x _1, x ₂ that is actually transferred hung weighting matrix _W, ..., constitute the x _NT. Here, the weight matrix plays a role of appropriately distributing the transfer information to each antenna according to a transfer channel condition or the like. Such transfer signals x ₁ , x ₂ ,..., X _NT can be expressed as the following Expression 5 using a vector x.

In Equation 5 above, w _ij represents a weight value between the i-th transmission antenna and the j-th transfer information, and W is a matrix. Such a matrix W is called a weighting matrix (Weight Matrix) or a precoding matrix (Precoding Matrix).

  On the other hand, the transfer signal (x) as described above can be considered separately when using spatial diversity and when using spatial multiplexing.

  When spatial multiplexing is used, different signals are multiplexed and transmitted. Therefore, the elements of the information vector s all have different values, whereas when spatial diversity is used, the same signal is transmitted through a plurality of channel paths. Therefore, all the elements of the information vector s have the same value.

Of course, a method of mixing spatial multiplexing and spatial diversity can also be considered. That is, for example, it is possible to consider a case where the same signal is transferred using spatial diversity through three transmission antennas, and the remaining signals are transmitted with different signals being spatially multiplexed. Next, when there are N _R reception antennas, the reception signal y ₁ , y ₂ ,..., Y _NR of each antenna is represented by a vector y as shown in Equation 6 below.

On the other hand, when modeling a channel in a multi-antenna communication system, the channel can be distinguished by a transmission / reception antenna index, and a channel passing from the transmission antenna j to the reception antenna i is denoted as h _ij . Note that the index order of h _ij is the receiving antenna index first and the transmitting antenna index behind. Such channels can be combined into a vector and matrix form. An example of vector display is as follows.

FIG. 8 is a diagram illustrating channels from N _T transmit antennas to receive antenna i.

As shown in FIG. 8, a channel arriving at the receiving antenna i from a total of N _T transmitting antennas can be expressed as Equation 7 below.

Further, when all the channels passing from N _T transmit antennas to N _R receive antennas are represented by a matrix expression like the above Expression 7, it can be expressed as Expression 8 below.

On the other hand, since white noise (AWGN: Additive White Gaussian Noise) is added to the actual channel after passing through such a channel matrix H, white noise n ₁ , n ₂ ,... Added to each of the N _R receiving antennas. , N _NR is expressed by a vector as shown in Equation 9 below.

  By modeling the transfer signal, the received signal, the channel, and the white noise as described above, each of them can be expressed by the following relationship in the multi-antenna communication system.

On the other hand, the number of rows and columns of the channel matrix H representing the channel state is determined by the number of transmission / reception antennas. As described above, in the channel matrix H, the number of rows corresponds to the number N _{R of} reception antennas, and the number of columns corresponds to the number N _{T of} transmission antennas. That is, the channel matrix H is an N _R × N _T matrix.

  In general, the rank of a matrix is defined as the minimum number of rows or columns that are independent of each other. Therefore, the rank of the matrix does not become larger than the number of rows or columns. To illustrate mathematically, the rank (rank (H)) of the channel matrix H is limited as in the following Expression 11.

  On the other hand, the characteristics of the precoding matrix can be observed. The channel matrix H that does not consider the precoding matrix can be expressed as in Equation 12 below.

In general, a k-th received SINR (Signal to Interference Noise Ratio) ρ _k can be defined as shown in Equation 13 below for a predetermined MMSE (Minimum Mean Square Error) receiver.

Therefore, the k-th effective reception SINRρ _k can be expressed as Equation 15 below under the assumption that an MMSE receiver is used.

Assuming that two column vectors are permutated from the above equation 17, the received SINR value itself does not change except for the order in order to keep the channel capacity / sum rate constant. Therefore, the permutated effective channel and the k-th received SINRρ _k can be _obtained as in the above-described Expression 14 and Expression 15.

  It should be noted from the above equation 19 that the interference and noise portions are as shown in equation 20 below.

  FIG. 9 is a diagram illustrating a general system structure for OFDMA and SC-FDMA.

  In a general MIMO antenna system based on OFDMA (Orthogonal Frequency Division Multiple Access) or SC-FDMA (Single Carrier-Frequency Multiple Access), a data signal is mapped in a single symbol a. It passes. The data to be transferred is separated into code words. In most applications, the codeword will be equivalent to the transport block given by the MAC (Medium Access Control) layer. Each codeword is individually encoded using a channel encoder such as a turbo code or a tail biting convolutional code. The codeword is rate matched to the appropriate size after encoding and mapped to the layer. As shown in FIG. 9, DFT (Discrete Fourier Transform) precoding is performed in each layer in SC-FDMA transfer, and DFT conversion is not performed in OFDMA transfer.

  A signal subjected to DFT conversion in each layer is multiplied by a precoding vector / matrix (multiple) and then mapped to a transfer antenna port. The transfer antenna port may be mapped back to an actual physical antenna by antenna virtualization.

  A common CM (Cubic Metric) for a single carrier signal (such as an SC-FDMA transfer signal) is much smaller than a multi-carrier signal. This general concept is the same as that of PAPR (Peak Power to Average power Ratio). CM and PAPR are related to the dynamic range of power to be supported by the power amplifier (PA) of the transmitter. Under the same PA, any transfer signal may have low CM and PAPR, and some other signal formats may be transferred with high transfer power. Conversely, if the maximum power of the PA is fixed and the transmitter desires to transfer high CM and PAPR signals, the transfer power can be reduced slightly compared to the low CM signals. The reason that a single carrier signal has a lower CM than a multi-carrier signal is that many of the signals in a multi-carrier signal overlap, sometimes leading to the addition of a co-phase of the signal. Such a possibility makes the signal size larger. This is why OFDM systems have large PAPR and CM values.

The output signal y is simply constituted by information symbols x _1, this signal can be regarded as a single carrier signal, such as y = x _1. However, the output signal y is a plurality of information symbols _{x 1, x 2, x 3} , ..., and consists of x _N, signal, as _{y = x 1 + x 2 +} x 3 + ... + x N, a multi-carrier It can be regarded as a signal. PAPR or CM is proportional to the number of information symbols added coherently in the output signal waveform, but the value tends to saturate when the number of information symbols reaches a specific number. Thus, the output signal waveform is generated with little added single carrier signal, and the CM and PAPR are smaller than the multi-carrier signal and slightly larger than the single carrier signal.

  FIG. 10 is a diagram illustrating a system structure for uplink SC-FDMA in a 3GPP LTE system which is an example of a mobile communication system, and FIG. 11 is an uplink SC- in the 3GPP LTE system which is an example of a mobile communication system. It is a figure which shows an example of a FDMA transfer frame structure.

  In the Rel-8 LTE system, the system structure and transport frame for uplink SC-FDMA have been adopted as shown in FIGS. The basic transfer unit is one subframe. One subframe is composed of two slots, and the number of SC-FDMA symbols in one slot is 7 or 6 depending on the configuration of CP (Cyclic Prefix). In each slot, there is at least one reference signal SC-FDMA symbol that is not used for data transfer. There are multiple subcarriers in one SC-FDMA symbol. RE (Resource Element) is a complex information symbol mapped to one subcarrier. When DFT transform precoding is used, since the DFT size and the number of subcarriers used in the transfer are the same as in SC-FDMA, RE is one information symbol mapped to the DFT transform index.

  In the LTE-A system, spatial multiplexing up to four layers is considered in uplink transfer. In the case of uplink single user spatial multiplexing, each uplink component carrier (CC) can be transmitted from a terminal scheduled for up to two transport blocks in one subframe. Depending on the number of transport layers, the modulation symbols associated with each transport block are mapped to one or two layers according to the same principle as Rel-8 LTE downlink spatial multiplexing. Furthermore, DFT-precoded OFDM is adopted as a multiple access scheme for uplink data transfer regardless of whether spatial multiplexing is applied. In the case of multiple component carriers, there is one DFT for each component carrier. In the LTE-A system, in particular, frequency-continuous and frequency-non-contiguous resource allocation is supported on each component carrier.

  FIG. 12 is a diagram illustrating an example of a data signal mapping relationship for a MIMO system based on SC-FDMA transfer.

The number of codewords in N _C, if the number of layers is N _L, N information symbols _C information symbols or N _C-number multiple (Multiple) is, or N _L pieces of multiples N _L symbols Assigned to the symbol. DFT transform precoding for SC-FDMA does not change the layer size. After precoding is performed at each layer, the number of information symbols changes from N _L to N _T , resulting in a N _T * N _L matrix multiplication. In general, the transfer rank of spatially multiplexed data is the same as the number of layers that carry the data at a given transfer instant (N _{L in} the example of FIG. 12).

  In order to support a very high data transfer rate such as 1 Gbps in the next generation communication system, it is necessary to support high-rank data transfer such as rank 8. It is necessary to accurately transfer the spatial layer multiplexed information and receive a well-designed reference signal sequence for data demodulation and channel estimation. Considering the control signal position (Placement) and other reference signals required for back IE measurement, the reference signal sequence for data information design with spatial layer multiplexing is complicated and difficult. Therefore, the present invention proposes a method of inserting a dedicated reference signal (dedicated reference signal) sequence into an RB (Resource Block) including data information.

  In a communication system such as LTE, a reference signal for data demodulation and channel estimation may be inserted into a resource element (Resource Element, RE) in a subframe as shown in FIG. it can.

  Below, the reference signal (Reference Signal, RS) transmitted / received between a transmission end and a reception end in a mobile communication system is demonstrated.

  In a mobile communication system, when a transmitting end transfers a packet (or signal) to a receiving end, a packet transferred by the transmitting end is transferred through a wireless channel, and thus signal distortion may occur in the transfer process. In order to correctly receive such a distorted signal at the receiving end, the receiving end finds channel information and can correct the distortion of the transfer signal in the received signal by an amount corresponding to the channel information. In order to find the channel information in this way, it is necessary to transfer a signal known to both the transmitting end and the receiving end. In other words, when a signal known at the receiving end is received through a channel, a method of finding channel information according to the degree of distortion of the signal is mainly used, but both the transmitting side and the receiving side transferred at this time know it. The signal is referred to as a reference signal or a pilot signal.

  Up to now, one transmitting antenna and one receiving antenna have been used when the transmitting end transfers a packet to the receiving end. In contrast, recently, most mobile communication systems employ a method of improving transmission / reception data efficiency by adopting multiple transmission antennas and multiple reception antennas. When transmitting and receiving data using multiple antennas in order to increase capacity and improve communication performance at the transmitting end or receiving end of a mobile communication system, there is a separate reference signal for each transmitting antenna. The receiving end can correctly receive the signal transferred from each transmitting antenna using the known reference signal for each transmitting antenna.

  In a mobile communication system, reference signals can be roughly divided into two types according to their purposes. There are reference signals for channel information acquisition and data demodulation. The former is for the terminal to acquire downlink channel information and needs to be transferred over a wide band. That is, even a terminal that does not receive downlink data in a specific subframe must be able to receive and measure this reference signal. Further, such a channel measurement reference signal may be used for handover measurement or the like. The latter is a reference signal that is transmitted together with a corresponding resource when the base station transfers a downlink signal. By receiving this reference signal, the terminal can perform channel estimation and demodulate data. . This demodulation reference signal must be transferred in an area where data is transferred.

  In the Release 8 LTE system, which is an example of a mobile communication system, two types of downlink reference signals are defined for a unicast service. Common reference signal (Common Reference Signal; hereinafter referred to as “CRS”) used for acquisition of information on channel state and measurement of handover, etc., and dedicated reference signal (DRS: Dedicated RS) used for data demodulation Hereinafter referred to as “DRS”) (which corresponds to a UE-specific reference signal). In the Release 8 LTE system, the UE-specific reference signal is used only for data demodulation, and the CRS is used for two purposes: channel information acquisition and data demodulation. The CRS is a cell-specific reference signal, and the base station transmits the CRS every subframe over a wide band. The cell-specific CRS is transferred to a maximum of four antenna ports according to the number of transfer antennas of the base station. For example, if the number of transmission antennas of the base station is 2, CRSs for the antenna ports 0 and 1 are transferred, and if it is 4, the CRSs for the antenna ports 0 to 3 are transferred. .

  FIG. 13 is a diagram illustrating an example of a reference signal pattern in the 3GPP LTE system.

  (A), (b), and (c) in FIG. 13 each represent an RS position in one RB. Multiple reference signals (RS) can be transferred in different applications within 1 RB. A CRS (Common Reference Signal) shown in FIG. 13 is a cell-common reference signal and is transferred over the entire system band. The CRS may be used for applications such as data transfer demodulation, channel estimation, channel tracking, cell detection, and the like. DRS (Dedicated Reference Signal) is a reference signal used for data demodulation, and is transferred with a specific RB only when the terminal receives data from the base station. Since DRS is transferred as a terminal specific signal, generally, a specific terminal does not know DRS transfer to other terminals. N DRSs are needed to support up to N spatial layer data transfers.

  In the following example, it is assumed that the system supports up to eight spatial layer data transfers. In order to correctly support MU-MIMO (Multi User-MIMO) transmission, the eight DRSs transmitted from the base station to each terminal need to be orthogonal or have good correlation characteristics. In addition, a system supporting up to eight layers can transfer DRS for each layer, and one or more layers can be used for data transfer to combinations of different terminals. DRS is also called DM RS (Data Demodulation RS) in the LTE-A system and the like.

  Each layer DRS can be multiplexed by various methods. For example, code division multiplexing (CDM), frequency division multiplexing (FDM), time division multiplexing (Time Division Multiplexing, TDM), or a combination thereof is multiplexed. Can be (A), (b), and (c) of FIG. 13 show CDM and FDM systems based on DRS multiplexing, respectively. Examining 12 REs for layers 1 and 2 (DRS layers 3 and 4 or even layers 5, 6, 7, and 8 follow a method similar to mapping DRS sequences), within 1 RB These 12 REs are as shown in FIG.

  FIG. 14 is a diagram illustrating an example of a pattern of REs that are code-multiplexed for DRS layers 1 and 2 within 1 RB.

  In FIG. 14, codes such as Walsh-Hadamard codes have been applied to RE (1410) and RE (1420) (ie, RE (1410) plus +1, RE (1420) also Multiply +1, or +1 for RE (1410) and -1 for RE (1420), so that two consecutive REs on the time axis are multiplied by the Walsh code). The method in which the actual DRS sequence is applied to each DRS RE is described below. In general, an RB allocated for a specific terminal corresponds to a subset of all available RBs used in the system.

  FIG. 15 is a diagram illustrating an example of a method for generating a DRS sequence.

  As shown in FIG. 15, some RBs may be allocated to specific terminals for reasons such as scheduling in the entire system bandwidth. As shown in FIG. 15, the base station can generate a DRS sequence with an RB size corresponding to the entire system bandwidth. When the base station performs scheduling for a specific terminal, the base station can use a DRS sequence corresponding to the RB assigned to the corresponding terminal among the overall generated DRS sequences.

  FIG. 16 is a diagram illustrating another example of a method for generating a DRS sequence.

  Referring to FIG. 16, unlike the method of generating the DRS sequence in FIG. 15, the base station can generate the DRS sequence with the same size as the data RB allocated for the specific terminal. As described above, when the DRS sequence is generated and used with the same size as the RB size assigned to the specific terminal by the base station, the base station is assigned different RBs through spatial domain multiplexing like MU-MIMO. Multiple terminals can be scheduled. When spatially multiplexed terminals are assigned different RBs, the DRS sequence used for each terminal can be generated such that the sequences used for the spatially multiplexed RBs are different.

  As shown in FIG. 16A, the hatched area is an RB assigned to transfer the DRS to the specific terminal. The base station can generate the DRS sequence by applying the RS sequence corresponding to the data RB size to the RB assigned to the specific terminal.

  FIG. 16B shows a case where the base station generates a DRS sequence by applying different sequences to each terminal (UE1, UE2). If different sequences are applied to each terminal, the DRS for each terminal is not orthogonal, resulting in degradation of channel estimation performance and loss of communication performance. In order for the base station to use orthogonal DRS for each transport layer for transfer to multiple terminals, it is necessary to use the same sequence for DRS for the code multiplexed layer. However, it is not necessary to use the same sequence for DRS for frequency multiplexed layers. In order to generate the same DRS sequence for different terminals, two sequence generation methods can be considered.

  FIG. 17 is a diagram for explaining an example of a method for generating a DRS sequence.

  As a first method, there is a method of generating a DRS sequence for each assigned RB. A sequence used for DRS may be generated for each assigned RB. Further, in order to randomize the sequence pattern used in each RB, different DRS sequences can be generated for each RB. One method for generating different sequences for different RBs is to add an RB index to the initial value portion of the sequence generation function.

  Next, with reference to FIG. 18, three methods for adding (or inserting) a sequence for the RE set used in the code division multiplexing scheme within 1 RB will be described.

  FIG. 18 is a diagram illustrating an example of a method for generating a sequence within 1 RB.

  Each of the sequence generation methods shown in (a), (b), and (c) of FIG. 18 corresponds to a method of generating a sequence for the RE set used in the code division multiplexing method within 1 RB.

  As shown in FIG. 18A, as a first sequence generation method, one DRS sequence for a code-multiplexed DRS RE layer can be generated. In this first sequence generation method, a long sequence generated and mapped at the DRS RE position is common to all CDM DRS layers. For each DRS layer, different Walsh codes are applied to ensure orthogonality between different DRS layers (Walsh covering). The advantage of having a long sequence and the possibility of different sequence elements across Walsh codes applied to the RE is that the DRS RE can be efficiently randomized and consequently more randomized to other cells. It is.

  As shown in FIG. 18B, as the second sequence generation method, one or more DRS sequences can be generated for the code-multiplexed DRS RE layer. In a second sequence generation method, a long sequence is generated and mapped at a DRS RE location where the same sequence is repeated on the resource to which a Walsh code is to be applied (eg, Walsh spread). Is done. The sequence for each layer may be different from each other. In each DRS layer, different Walsh codes can be applied to ensure orthogonality between different DRS layers. In such a method, the same sequence is repeated along the RE to which the Walsh code is applied, and different layers can have different DRS sequences, and in this case as well, there is orthogonality between different DRS layers. Guaranteed. This enables orthogonal DRS transfer between different cells having different DRS sequences. In the second sequence generation method, the layer index may be input to the DRS sequence generation initial value.

  As shown in FIG. 18C, as the third sequence generation method, the first and second sequence generation methods in FIGS. 18A and 18B can be mixed. Possible different DRS sequences are mapped to the DRS RE, and a Walsh code is applied to the DRS RE. As illustrated in FIG. 18 (c), two different DRS sequences are mapped to DRS RE positions so that Walsh codes are applied across different DRS sequences. In such a method, it is also possible to configure the DRS sequence by making the second DRS sequence actually the same as the first DRS sequence. In this case, if different DRS sequences are configured in the same manner as the third sequence generation method, it can be seen as the second sequence generation method. When the DRS sequences are different from each other, the third sequence generation method can be similar to the first sequence generation method. According to such a method, DRS interference between different cells can be randomized, and a configuration that maintains orthogonality of DRS transfer between cells can be realized.

  In the third sequence generation method, the same or different DRS sequence (as much as possible the same DRS sequence) and the layer index are input for the DRS sequence generation initial value during the Walsh code applied RE set indicator. May be.

  FIG. 19 is a diagram for explaining an example of a method for generating a DRS sequence.

  As a second method, a DRS sequence is generated for the entire system bandwidth, and a part (sub-portion) of the long generated DRS sequence can be used at each RB position. The base station can generate a DRS sequence for the entire system bandwidth, and can use a partial DRS sequence of the long DRS sequence for each of the allocated RBs. In such a DRS sequence generation method, three methods for inserting a sequence for an RE set used for code division multiplexing will be described.

  FIG. 20 is a diagram illustrating an example of a method for generating a sequence within 1 RB.

  (A), (b), and (c) of FIG. 20 show a method of inserting a sequence for an RE set used in the code division multiplexing scheme within 1 RB.

  In the first sequence generation method shown in FIG. 20A, a part of the generated long DRS sequence can be mapped as a DRS sequence for a specific RB. Long DRS sequences are mapped from the lowest frequency subcarrier to the highest frequency subcarrier. Depending on which RB is used for data transfer, a part of the long DRS sequence already mapped over the entire system bandwidth is used as the DRS sequence for the specific RB. In this first sequence generation method, the same DRS sequence is used for different OFDM symbols to which one Walsh code set is applied. This is equivalent to allowing different DRS sequences between layers, and ensures orthogonality between DRS layers. Also, DRS orthogonality with other cells can be ensured.

  In the second sequence generation method illustrated in FIG. 20B, a part of the generated long DRS sequence can be mapped for DRS for a specific RB. Long DRS sequences are mapped from the lowest frequency subcarrier to the highest frequency subcarrier. Depending on which RB is used for data transfer, a part of the long DRS sequence that has already been mapped over the entire system bandwidth is used as the DRS sequence for the specific RB. In this second sequence generation method, different possible DRS sequences are used for different OFDM symbols that are multiplied by one Walsh code set. In this case, the base DRS sequence for each layer subjected to code division multiplexing is the same, and different DRS layers can use different Walsh codes in addition to the given basic DRS sequence.

  DRS for different layers that are frequency division multiplexed (FDM) may have different basic DRS sequences. The second sequence generation method described above may be applied to have different DRS sequences for each OFDM symbol. A layer index, an OFDM symbol index, and a slot number (or subframe number) can be input to a long DRS sequence generation initial value.

In addition to the second sequence generation method described above, the system can be configured to apply the same DRS sequence to different OFDM symbols, and the same DRS sequence is shown in FIG. Similar to the first sequence generation method shown, it can be used for REs multiplied with Walsh code sets. In FIG. 20B, the DRS sequences b _i and d _i may be the same as the DRS sequences a _i and c _i , respectively. This is so that the first sequence generation method in FIG. 20A is configured like the second sequence generation method in FIG. The same or different DRS sequences for indications of different OFDM symbol configurations may be input to the DRS sequence generation initial value.

  The third sequence generation method shown in (c) of FIG. 20 includes the DRS sequence element (element) generated by each of the first and second sequence generation methods in (a) and (b) of FIG. On the other hand, a new DRS sequence can be generated by an element by element. The DRS sequence generated by the method shown on the left side of FIG. 20C is a sequence corresponding to 1 RB. Similarly, the DRS sequence generated by the method shown on the right side of FIG. This is a sequence corresponding to 1 RB. A new DRS sequence can be generated by multiplying the elements generated in each RB. In such a case, generating the DRS sequence in units of 2 RBs can be repeated. If the system bandwidth of the 3GPP LTE system is 12 RB, this process can be repeated 6 times.

  In this way, the Walsh spread RS sequence can be further scrambled by different RS sequences having different sequence values in all REs. By this method, interference randomization effective loss due to Walsh spread RS sequence (same sequence on DRS OFDM symbol) can be reduced by secondary RS sequence scrambling. This third sequence generation method can be implemented by having two input fields in sequence generation values that control different sequence characteristics and one RS sequence. The third sequence generation method is useful when a group of cells cooperate, when cells in the group share different Walsh codes and at the same time other groups of cells need to be randomized. .

  Next, a sequence initialization value necessary for generating the DRS sequence will be described.

  In order to support effective MU-MIMO, the DRS sequence cannot be initialized with the terminal ID, but rather the cell ID, subframe number (or slot number), OFDM symbol index (within the subframe or slot). ), Layer index, normal cyclic prefix (CP) or extended CP (extended CP) indication, etc. (ie, the same or different DRS sequences for different OFDM symbol configuration indications). Additional sequence initialization parameters include layer index (calculated in the code division multiplexed DRS layer) and frequency offset index (generally DRS mapped to different RE time / frequency position sets). To be distinguished between the FDM DRS layers).

  Further, the DRS sequence may be mapped to the DRS layer RE in such a manner that the Walsh code spreads the DRS sequence on the time axis or the Walsh code is covered (or multiplexed) to the DRS sequence. Walsh code spreading sequences ensure better orthogonality, while Walsh covered sequences make cross-correlation properties more favorable. This allows for a configuration that allows Walsh codes to be used in the DRS mapping process in the system.

Here, it is assumed that all DRS sequences are generated by a PRBS (Pseudo Random Binary Sequence) generator. The PR (Pseudo Random) sequence is defined by a gold sequence of length 31. The output sequence c (n) of length _MPN can be defined as in Equation 24 below (where n = 0, 1,..., _MPN− 1).

Here, N _C = 1600, and the first m-sequence is initialized as x ₁ (0) = 1, x ₁ (n) = 0, n = 1, 2,... .

  In all DRS sequence generation methods, it is proposed that the layer index value indicates that a specific CDM RE set of all CDM / FDM DRS RE sets is used as part of the sequence generation initial value. In this case, all layer index indicator values need not necessarily be different for all DRS layers. Some DRS layers may have the same layer index indicator. The layer index indicator can also be expressed as a frequency offset indicator.

  The DRS sequence generation function applicable to the first and second sequence generation methods described in FIGS. 18A and 18B and the initial value thereof can be expressed as the following Expression 25 and Expression 26, respectively. it can.

The DRS sequence generation function applicable to the third sequence generation method described with reference to (c) of FIG. 18 and its initial value can be expressed as the following Expression 27 and Expression 28, respectively. Here, _NFO is a function of the DRS layer index and is used as a value indicating a layer group distinguished by frequency.

Here, N _rb represents a resource block (RB) index of the corresponding PDSCH transfer, and w (m) represents a Walsh code applied to the DRS sequence. N _layer represents a layer index for the basic DRS sequence, and l ′ is a DRS sequence index that is a function of the OFDM symbol index. The same two DRS sequence indexes can be used within 1 RB. Different DRS layers may have the same base sequence in order to ensure orthogonality between the DRS layers and apply Walsh codes. As an example of the sequence initialization value, it can have a value as shown in Equation 28 below.

  Further, the DRS sequence generation function applicable to the first sequence generation method described with reference to FIG. 20A and its initial value can be expressed as the following Expression 29 and Expression 30, respectively. Expression 29 represents an example of an expression for generating a DRS sequence, and Expression 30 represents an initial value for generating the DRS sequence.

Here, l ′ represents a DRS sequence index that is a function of the OFDM symbol index, and N _layer represents a layer index for the basic DRS sequence. Different DRS layers may have the same base sequence in order to apply Walsh codes and ensure orthogonality. The DRS sequence index may be an index obtained by calculating an OFDM symbol including a DRS RE within a subframe. Specific DRS sequences having the same DRS sequence in different OFDM symbols are selected to have the same value so that the same sequence is generated. Two different DRS sequences as a whole are used for 1 DRS layer within 1 RB, and N _dmrs may be a value like 2. As represented by Equation 31 and Equation 32 below, the specific layer additionally has different basic sequence layer information inserted into the initial value.

  Since DRS is a dedicated reference signal, it is not necessary to distinguish the sequence between normal CP and extended CP. Therefore, no CP information is inserted to obtain the initial value. An example of the initial value can be expressed as the following Expression 32.

  The DRS sequence generation function applicable to the second sequence generation method described with reference to (b) of FIG. 20 and its initial value can be expressed as the following Expression 33 and Expression 34, respectively.

  Here, l ′ is a DRS sequence index that is a function of the OFDM symbol index, and the DRS sequence index may be an index obtained by calculating an OFDM symbol including a DRS RE within a subframe. Specific DRS sequences having the same DRS sequence in different OFDM symbols are selected to have the same l 'value so that the same sequence is generated. The specific layer additionally has different basic sequence layer information inserted into the initial value. This can be expressed as Equation 35 below.

  DRS sequence generation applicable in the second sequence generation method described in FIG. 20C can be implemented in three ways.

  As a first implementation, a DRS sequence can be generated using two Gold code sequences that are initialized with different initial values. The following Expression 36 represents an example of such DRS sequence generation.

  The initialization value of the first sequence can be expressed by any one of the following Expressions 37 to 39.

Possible Gold code initialization properties for the second sequence are as follows:
1. 1. Same sequence for each code division multiplexed layer 2. The same sequence for each frequency division multiplexed layer 3. Different sequences between Walsh-coded REs Different sequences between cells

In the sequence generation method related to (c) of FIG. 20 described above, one of the RS sequences is initialized by combining a cell ID, an OFDM symbol index (or DRS symbol counter / index), a layer index, and a frequency offset index. Can do. Other RS sequence, N _I, and can be initialized by combining an OFDM symbol index (or DRS symbol counter / index). The first RS sequence will have the same sequence in the Walsh code multiplexed RE. However, the second RS sequence will not have the same sequence in the Walsh code multiplexed RE.

N _I may be a CoMP (Coordinated Multi Point) cell ID number or a value shared by many cells. N _I needs to be signaled to the terminal in order for the terminal to receive the RS sequence correctly. The first initialization value does not change on all DRSs included in the OFDM symbol, but the second initialization value may change on all DRSs included in the OFDM symbol.

  FIG. 21 is a diagram illustrating an example of a method for generating a DRS sequence within 1 RB.

  FIG. 21 shows a case where different sequences are generated for each layer and Walsh spreading is used. In FIG. 21, different sequences are used across all code division multiplexing (CDM) DRS layers and different Walsh codes are used to maintain orthogonality across the DRS layers. Each sequence used for each CDM DRS layer is spread with a Walsh code. In this case, one RE set is spread with a Walsh code, and the same sequence value is used except for a Walsh code element multiplication value.

  FIG. 22 is a diagram illustrating an example in which two cells transfer DRS using the generated DRS sequence.

  The equation of the signal received at the receiving end on the right side of FIG. 22 and the channel estimated for the signal received at the receiving antenna port can be expressed as Equation 44 and Equation 45 below, respectively.

Here, h ₀ , h ₁ , h ₂ , and h ₃ represent effective channel coefficients, a _i and b _i represent scrambling code sequences, and n ₀ and n ₁ represent noise, respectively.

From Equation 44 and Equation 45 above, the estimated effective channel coefficient has one interference coefficient Z ₁ . Therefore, the effective channel coefficient estimated at the receiving end is affected by the interference coefficient.

  FIG. 23 is a diagram illustrating an example of a method for generating a sequence within 1 RB.

  FIG. 23 shows a case where the base station generates the same sequence for each layer and uses Walsh spreading. In FIG. 23, different sequences are used across all CDM DRS layers, and different Walsh codes are used to maintain orthogonality across the DRS layers. The example shown in FIG. 23 allows maximizing interference randomization between cells.

  FIG. 24 is a diagram illustrating an example in which two cells transfer DRS using the generated DRS sequence.

  The equation of the signal received at the receiving end on the right side of FIG. 24 and the channel estimated for the signal received at the receiving antenna port can be expressed as the following equations 46 and 47, respectively.

Here, h ₀ , h ₁ , h ₂ , and h ₃ represent effective channel coefficients, s _i and x _i represent scrambling code sequences, and n ₀ and n ₁ represent noise.

Referring to Equation 45 above, the estimated effective channel coefficients have four different coefficients Z ₁ , Z ₂ , Z ₃ , Z ₄ , and the randomized coefficients cancel each other, so h Channel estimation for ₀ can be more accurate. From these equations, it can be seen that the sequence generation method described in FIG. 23 has an interference randomization effect four times that of the sequence generation method described in FIG.

  In order to maximize DRS sequence interference randomization from different cells, the DRS sequence should preferably have a random value in all REs. However, in order to maintain orthogonality between DRS layers at the same time, the same DRS sequence needs to be used in all DRS layers. Having the same DRS sequence in all DRS layers leads to a problem that a Walsh code causes a serious power difference between OFDM symbols under a specific precoding environment.

  FIG. 25 shows an example of a method for mapping and transferring to four transmit antennas by applying precoding to two DRS layers, and a power difference generated between OFDM symbols when DRS is transferred by this method. FIG.

  Referring to (a) of FIG. 25, it is possible to transfer signals from four transmission antennas using two DRS layers at the transmission end and applying precoding. When the precoding shown in FIG. 25 is applied, a signal transferred for each symbol through each transmission antenna is shown on the right side of FIG. When the signal is transferred at the transmitting end in this way, the power difference between adjacent OFDM symbols becomes as large as about 2.25 dB as shown in (b) of FIG.

  FIG. 26 is a diagram illustrating an example of a method for generating a DRS sequence.

  In FIG. 26, different sequences are Walsh spread for each layer, and then the Walsh spread sequences can be scrambled.

  In FIG. 26, the first sequence indicated by “a” is used to change the sequence between the CDM layers. The second sequence indicated by “s” is used to change the sequence between IDs (IDentities) designated by higher layers. The ID specified by the higher layer may be a cell ID, a CoMP cell group ID, or another ID given to make the DRS sequence different from each ID. It is preferable that the value of the first sequence indicated by “a” does not change between REs multiplied by the Walsh code set (for example, between two adjacent OFDM symbols RE). The Walsh code can be applied over the first sequence. This can be implemented by spreading the first sequence in the time domain where the RE for DRS with Walsh-Hadamard code is located (by multiplying the sequence that generates the long sequence by the Walsh code). it can. The value of the second sequence indicated by “s” changes randomly in all REs. The second sequence is invariant with layers, so that the same common sequence is used for all layers.

  FIG. 27 is a diagram illustrating an example of transferring the DRS using the DRS sequence generated by the method of FIG.

  The equation of the signal received at the receiving end on the right side of FIG. 27 and the channel estimated for the signal received at the receiving antenna port can be expressed as Equation 48 and Equation 49 below, respectively.

From Equation 48 and Equation 49 above, the estimated effective channel coefficients have four different coefficients Z ₁ , Z ₂ , Z ₃ , Z ₄ , and the randomized coefficients cancel each other, Channel estimation for h ₀ can be more accurate. From these equations, the sequence generation method described with reference to FIG. 27 has the same level of interference randomization effect as the sequence generation method described with reference to FIG. 23, and has four times the interference as compared with the sequence generation method described with reference to FIG. It can be seen that it has a randomizing effect.

  FIGS. 28A and 28B are diagrams illustrating an example of a method for generating a DRS sequence.

  Also, the first sequence for each layer can be generated by combining a random complex value sequence generated from a sequence such as a gold code and a fixed phase offset complex value sequence in a unit circle. Such an example is shown in FIGS. 29A and 29B. FIGS. 29A and 29B are diagrams illustrating an example of a method for generating a DRS sequence.

  The sequence generation method described above with reference to FIGS. 21, 23, and 26 can be defined again by another method. The sequence generation method related to FIG. 21 uses different sequences for different layers, but the sequence does not change over the time axis (excluding the Walsh code multiplication factor). The sequence generation method related to FIG. 24 can use the same sequence for different layers, but the sequence changes according to the time axis. The sequence generation method related to FIG. 21 has an effect of randomizing interference from other cells, and the sequence generation method related to FIG. 23 has a problem of power amplifier (PA) design in the base station. ing. The sequence generation method related to FIG. 26 includes the sequence generation method related to FIGS. 21 and 23 by using different sequences on the time axis as different sequences for different layers. In order to maintain the orthogonality of the two types of sequences, the sequence can be generated with the sequence generation method associated with FIG. Among sequences, specific sequences generate different sequences between layers, and other sequences generate different sequences on the time axis. Furthermore, both types of sequences may change on the frequency axis.

  The sequence generation method related to FIG. 26 can be implemented in various ways. The first implementation scheme can generate different sequences for each layer, spread the sequences using Walsh codes, and apply a second sequence that is common to all layers. The second implementation method can generate a common sequence for the layers, cover the sequence using a Walsh code, and then apply a second sequence different for each layer. The third implementation scheme can reconstruct the sequence mapping of the first and second sequences and apply a Walsh code.

  As another example of generating the DRS sequence, different sequences may be generated for each layer, and alamouti coding may be applied to the layer.

  FIG. 30 is a diagram illustrating an example in which a DRS signal is transferred using a generated DRS sequence in two cells.

  In FIG. 30, each cell may generate a different sequence for each layer and transfer a DRS sequence generated using alamouti coding to the layer. By generating different sequences for each layer and applying alamouti coding to each sequence pair, orthogonality between layers can be maintained. This method can obtain a good interference randomization effect from other cells, and is effective for obtaining different sequences for each layer at the same time.

  FIG. 31 is a diagram for explaining another example of the DRS sequence generation method related to FIG.

  The DRS sequence generation method related to FIG. 26 can generate a final DRS sequence by applying a part of the sequence. That is, an entire DRS (also referred to as DM RS in the LTE-A system) sequence is generated by spreading the layer specific sequence, and a common layer scrambling sequence is applied to a specific portion of the Walsh spread layer specific sequence. In particular, the second sequence is applied to a part of the first sequence and is effectively extended with a Walsh code. This can be implemented so that a part of the second sequence that scrambles a part of the Walsh spreading sequence as illustrated in FIG. 31 is “1”.

  FIGS. 32A and 32B are diagrams for explaining an example of a method for generating a DRS sequence for each OFDM symbol.

  Referring to (a) of FIG. 32, in this DRS mapping method, the first or / and second sequence used in DRS for each layer is generated with the maximum bandwidth in each subframe.

  In the sequence mapping method related to (b) of FIG. 32, since the first sequence is spread with the Walsh-Hadamard code, the sequence lengths for the first sequence and the second sequence are different from each other. The spread first sequence has the same sequence length as the penultimate sequence.

  FIG. 33 is a diagram more specifically showing the sequence mapping method related to FIG.

  In general, the sequence is first mapped to the frequency axis in the RB and then mapped to the OFDM symbol including the DRS RE. Alternatively, scrambling sequence mapping may be such that all CDM DRS layers are first mapped to the frequency axis with a set of CDM REs, and then mapped to an OFDM symbol RE set that includes the DRS REs. By using such a method, when the terminal receives only some downlink subframes, the channel can be estimated so that the terminal generates a DRS sequence.

  In the following, Walsh code randomization will be described.

In order to solve the problem of high transmission power of a specific transmission antenna port for a specific precoding matrix, it can be considered to use a Walsh code that is cyclically shifted in the frequency axis. From the viewpoint of one DRS layer, the RE to which the Walsh code is applied varies along the frequency axis. In particular, the Walsh code applied to the RE set is a cyclically shifted Walsh code. Assume that a length 2 Walsh code is used and the two orthogonal codes for a given Walsh code are W _0,1 and W _1,1 . Further, the cyclically shifted orthogonal code can be represented by W _0,2 and W _1,2 .
W _0,1 = {+1, +1}
W _1,1 = {+1, -1}

W _0,2 = {+1, +1}
W _1,2 = {-1, +1}

Suppose a length 4 Walsh code is used and four orthogonal codes for a given Walsh code are given W _0,1 and W _1,1 . Further, the cyclically shifted orthogonal codes are W _{0, k} , W _{1, k} , W _{2, k} , and W _{3, k} , where k is a cyclically shifted value.
W _0,1 = {+1, +1, +1, +1}
W _1,1 = {+1, -1, +1, -1}
W _2,1 = {+1, +1, -1, -1}
W _3,1 = {+1, -1, -1, +1}

W _0,2 = {+1, +1, +1, +1}
W _1,2 = {-1, +1, -1, +1}
W _2,2 = {+1, -1, -1, +1}
W _3,2 = {-1, -1, +1, +1}

W _0,3 = {+1, +1, +1, +1}
W _1,3 = {+1, -1, +1, -1}
W _2,3 = {-1, -1, +1, +1}
W _3,3 = {-1, +1, +1, -1}

W _0,4 = {+1, +1, +1, +1}
W _1,4 = {-1, +1, -1, +1}
W _2,4 = {-1, +1, +1, -1}
W _3,4 = {+1, +1, -1, -1}

Each DRS layer uses a Walsh code W _{n, m} to apply the DRS sequence, where n is a function of the DRS layer index and m is a function of the subcarrier index. As an example, m = k mod 2 or m = k mod 4 and k is a subcarrier index counting only subcarriers carrying DRS. The exact pattern of orthogonal code cover codes used for a particular DRS layer within 1 RB may vary between RBs.

  (A) of FIG. 34 is a diagram illustrating an example of an orthogonal code cover code pattern used for a specific DRS layer. (B) and (c) of FIG. 34 are diagrams showing specific examples of using Walsh codes in RB.

  Applying a different cyclically shifted Walsh code for each subcarrier (to ensure that the cyclic Walsh code pattern itself is repeated after 2 RBs or 4 RBs) is an OFDM symbol from the transmit (Tx) antenna perspective. Helps reduce the power difference between.

As illustrated in FIG. 25 (b), a power pooled symbol (2 * S _i after precoding) induces a power difference between OFDM symbols. OFDM symbols are interleaved. By randomizing symbols in which power is accumulated on the time axis, power concentration in one OFDM symbol can be reduced.

  FIG. 35 is a diagram illustrating an example of a method for mapping Walsh codes in a frequency CDM RE set.

  A randomizing method will be described using a form as shown in FIG. Walsh codes can be mapped differently in each frequency CDM RE set or time-frequency CDM RE set. As an example, for a specific first RB pair (or 1 RB), Walsh code elements are mapped in the time axis direction (or forward direction) in the CDM RE set and adjacent to the first RB pair. For the second RB pair that is the other RB pair to be mapped, the mapping can be started in the opposite direction of the time axis (or the reverse direction) with another CDM RE set.

  Walsh code elements applied to the first RB pair and the second RB pair adjacent to the first RB pair correspond to elements of the Walsh code set. There may be multiple CDM groups for one or more such RB pairs. For example, CDM group 1 and CDM group 2 can exist in each RB pair. Here, it is assumed that the Walsh code set applied to each RB pair includes {a, b, c, d}. Here, when a Walsh code is applied to a specific CDM group (eg, CDM group 1) in the first RB pair, Walsh code elements a, b, c in the Walsh code set {a, b, c, d} are used. , D are mapped (applied) to each RE one by one in the time axis direction, a, b, c, d are again mapped to each RE one by one in the opposite direction to the time axis, and again a, b in the time axis direction , C, d can be mapped to each RE one by one.

  When applying a Walsh code to a specific CDM group (eg, CDM group 1) in another second RB pair adjacent to the first RB pair, the Walsh code set {a, b, c, d} , The Walsh code elements a, b, c, and d can start mapping to each RE in the opposite direction of the time axis, unlike the first RB pair. Thereafter, Walsh code elements a, b, c, and d are mapped to each RE one by one in the time axis direction, and Walsh code elements a, b, c, and d are again mapped to each RE in the opposite direction to the time axis. Can be done.

  The Walsh code is applied to the CDM group 1 and the CDM group 2 in the first and second RB pairs in a hopped form, respectively. For example, for the first RB pair, when Walsh code elements a, b, c, and d are mapped to each RE one by one in the time axis direction in CDM group 1, CDM group 2 is Walsh code elements c, d, a, and b are mapped to each RE one by one in the time axis direction as if CDM group 1 was hopped (Walsh code elements applied to CDM group 1 and CDM group 2) Are different from each other). Such a hopping configuration can be similarly applied to the second RB pair. In this way, each RB can apply a Walsh code element hopped for each CDM group. To randomize code-interference between layers, code hopping can be applied to each layer with a time-frequency CDM RE set. In such a method, each layer uses a Walsh code in a specific time-frequency CDM RE set (referring to a set of REs to which CDM is applied).

  FIGS. 36A and 36B are diagrams showing an example of code hopping for two layers.

36 (a) and (b), the length of Walsh code 2 is used, W _0,0 is Walsh code {+ 1, + 1}, and W _1,0 is Walsh code {+ 1, −1. }. If the Walsh code used in a specific time-frequency CDM RE set is W _k (where k represents a code index), the k value can be defined as a frequency or a time-frequency function. As an example, k = (I _RB + I _freq + n _s ) mod 2, where I _RB is the RB index and n _s is the slot index. I _freq can have frequency index 0, 1, 2 values of CDM RE set within 1 RB. As another example, k = (I _RB mod 3 + I _freq ).

  FIG. 37 is a diagram illustrating an example of code hopping for two layers.

FIG. 37 shows a case where a length 4 Walsh code is used. If the Walsh code and W _{k, k} represents the code index. An example of the Walsh code W _k can be expressed as follows:
W ₀ = {+1, +1, +1, +1}
W ₁ = {+1, -1, +1, -1}
W ₂ = {+1, +1, -1, -1}
W ₃ = {+1, -1, -1, +1}
Or
W ₀ = {+1, +1, +1, +1}
W ₁ = {+1, -1, +1, -1}
W ₂ = {+1, -1, -1, +1}
W ₃ = {+1, +1, -1, -1}

  Furthermore, a method of using code hopping in combination with frequency or time-frequency CDM RE sets is also possible.

  When the Walsh code mapping randomization scheme shown in FIG. 35 is applied and a length 4 Walsh code is used, the sequence is not randomized between layers.

  FIGS. 38A and 38B are diagrams illustrating an example of Walsh code mapping for four layers.

As can be seen from FIG. 38 (a), the values between layers 1 and 4 are not randomized. For such special cases, it can be considered to use DFT-based codes for symbol randomization between all layers. As shown in FIG. 38B, when a DFT-based orthogonal code is used, values can be effectively randomized for all combinations of layers. Here, instead of the DFT sequence value (the DFT column vector shown below), it is also possible to use a DFT-converted code sequence.

In order to ensure orthogonality between layers, instead of using a column vector of a DFT matrix as a code, a column vector of M ′ can be used (where M ′ = U · M _DFT , and U is A unitary matrix). In addition to the code hopping method proposed in the present invention, the DFT-based code can be applied to other features.

Referring to (a) of FIG. 38, as described above, when the Walsh code mapping randomization method shown in FIG. 35 is applied to (a) of FIG. In the meantime, the sequence is not randomized. The Walsh code elements described in FIG. 35 can be represented by a 4 * 4 matrix as shown below, which can also be applied to FIG.

  In the 4 * 4 matrix, the Walsh code elements (a, b, c, d) may change for each layer. For example, in layer 1, (a, b, c, d) is (1, 1, 1, 1) which is the first row of the 4 * 4 matrix, and in layer 2, (a, b, c, d) is the second row (1, -1,1, -1), and in layer 3, (a, b, c, d) is the third row (1, (1, -1, -1), and in layer 4, (a, b, c, d) may be (1, -1, -1, 1) in the fourth row.

  For each layer, Walsh code elements (a, b, c, d) are mapped to a plurality of RB pairs (for example, first and second RB pairs) in the same manner as described in FIG. be able to.

  Referring to (a) of FIG. 38, in layer 1, (a, b, c, d) = (1, 1, 1, 1) is mapped to resource elements in the time axis direction, and ( 1, 1, 1, 1) are mapped to resource elements, and (1, 1, 1, 1) are again mapped to resource elements in the time axis direction. In layer 1 of FIG. 38 (a), only resource elements for two subcarriers are shown, but Walsh code elements are applied to three subcarriers for one CDM group in one RB pair. This is as already explained. In layer 3, (a, b, c, d) = (1, 1, −1, −1) is first mapped to resource elements in the time axis direction, and then (1, 1, − in the opposite direction of the time axis). 1, -1) is mapped, and (1,1, -1, -1) is again mapped in the time axis direction.

  In this manner, the Walsh sequence applied in FIG. 35 can be mapped in a form that is repeated in a plurality of frequency units (for example, 2 RBs) as shown in FIG.

  Next, the sequence initial value will be described.

Assume that all DRS sequences are generated by a PRBS (Pseudo Random Binary Sequence) generator. PRS (Pseudo Random Sequence) is defined by a gold sequence of length 31. The output sequence c (n) of length _MPN can be defined as in Equation 52 below (where n = 0, 1,..., _MPN− 1).

Here, N _C = 1600, the first m-sequence must be initialized as x ₁ (0) = 1, x ₁ (n) = 0, n = 1, 2,.

  FIG. 39 is a diagram illustrating an example of a method for generating two sequences.

  The initialization parameters loaded in the cyclic registers of initialization values for the first and second sequences use a cyclic register field that is exclusive to each parameter. Also, the initialization parameter loaded in the first sequence should not be co-inside with the initialization parameter loaded in the second sequence from the viewpoint of the cyclic register position. This is to ensure that both sequences do not generate the same sequence.

  Equation 53 below represents an example of an equation for generating a sequence.

The first sequence involved in scrambling values between different DRS layers requires the following parameter combinations in initialization values. N _layer is a layer index, N _cellid is a cell ID, n _s is a slot index in a radio frame, l is an OFDM symbol index in a subframe, and k is a DRS OFDM symbol index in a subframe.

The second sequence involved in the scrambling value between IDs specified by different upper layers requires the following parameter combinations in the initialization value. N _LH-ID is an ID specified by an upper layer (for example, Cell-ID, CoMP group ID, etc.), N _cellid is a cell ID, n _s is a slot index in a radio frame, and l is an OFDM in a subframe. Symbol index, k is the DRS OFDM symbol index within the subframe.

  Examples of the initialization value can be expressed as in the following Expression 54 and Expression 55.

In the example of the initialization values of Equation 54 and Equation 55 above, the values i ₁ , i ₂ , i ₃ , and i ₄ are the shift register positions having different information loaded on the initialization value shift registers (for example, Assuming N _layer is 3 bits and N _HL-ID is 9 bits, i ₁ = 7, i ₂ = 16, i ₃ = 0, i ₄ = 3) are loaded and take values from 0 to 13 be able to. k can take from 0 to 3, and n _s can take from 0 to 20.

  Another example of the sequence generation method will be described. Equation 56 below represents an example of an equation for generating a sequence.

The first sequence involved in scrambling values between different DRS layers requires the following parameter combinations in initialization values. N _layer is a layer index, and N _cellid is a cell ID.

The second sequence involved in the scrambling value between IDs specified by different upper layers requires the following parameter combinations in the initialization value. N _LH-ID is an ID specified by an upper layer (for example, Cell-ID, CoMP group ID, etc.), N _cellid is a cell ID, and n _s is a slot index in a radio frame.

  An example of the initialization value can be expressed as the following Expression 57.

In the example of the initialization value of Expression 57 above, the i ₁ , i ₂ , and i ₃ values are shift register positions having different information loaded on the shift register of the initialization value (for example, N _layer is 3 bits If N _HL-ID is 9 bits, i ₁ = 3, i ₂ = 12, i ₃ = 0) can be loaded.

Other sequence generation method and mapping method

  The first sequence (ie, the layer specific Walsh spreading sequence) can be generated and mapped with the same sequence length generated for the assigned RBs. At the same time, the same sequence length as the system bandwidth (or as much as possible with the maximum RB size supported by each communication specification) is generated, and the second sequence (ie, layer common sequence) is generated and mapped. Can do. The sequence initial value in such a case can be expressed as in the following Expression 58.

In order to maintain the orthogonality between the DRS layers, the first sequence (ie, the layer specific Walsh spreading sequence) is involved in scrambling values between different DRS layers, and the following combinations of parameters in the initialization values: Need. The parameter, N _cellid representing the N _layer, the cell ID representing the layer index, N _RNTI indicating a terminal ID, there is a n _s representing the slot index within a radio frame.

The second sequence involved in the scrambling value between IDs specified by different upper layers requires the following parameter combinations in the initialization value. The parameters, the upper layer indicated ID (e.g., Cell-ID, CoMP and group _ID) N _LH-ID representing a, N _cellid representing the cell ID, there is a n _s representing the slot index within a radio frame.

  An example of the initialization value can be expressed as in Equation 59 below.

In the example of the above initialization value, i ₁ = 0, i ₂ = 9, i ₃ = 30, i ₄ = 16, i ₅ = 0, and N _HL-ID is 9-bit information.

  Layer index to any one of the m-sequences for the first sequence (ie, layer specific Walsh spreading sequence) and other m-sequence loadings composed of cell ID, terminal ID and subframe index Can be loaded into value.

In the example of the initialization value, i ₁ = 0, i ₂ = 9, i ₃ = 1, i ₄ = 16, i ₅ = 0, and N _HL-ID is 9-bit information.

  Next, a reason and a method for randomizing interference between different cells will be described.

  FIG. 40 is a diagram illustrating an example in which DRS is transferred using a DRS sequence in which two cells are generated.

  As shown on the right side of FIG. 40, from the viewpoint of the receiving antenna port at the receiving end, the equation of the received signal and the equation for the estimated channel can be expressed as the following equations 60 and 61, respectively.

Here, h ₀ , h ₁ , h ₂ , and h ₃ represent effective channel coefficients, a _i and c _i represent scrambling code sequences, and n ₀ and n ₁ represent noise, respectively.

  FIG. 41 is a diagram illustrating another example in which two cells transfer DRS using the generated DRS sequence.

  From the viewpoint of the receiving antenna port as shown in FIG. 41, the equation of the received signal and the equation for the estimated channel can be expressed as the following equations 62 and 63, respectively.

Here, h ₀ , h ₁ , h ₂ , and h ₃ represent effective channel coefficients, s _i and x _i represent scrambling code sequences, and n ₀ and n ₁ represent noise.

  In the above equations 62 and 63, which are the received signal and estimated channel equations associated with FIG. 41, the interference between layers from other cells is spread to all layers, which is related to FIG. This is because there are more interference random factors (factors) than the above-described equations 60 and 61, which are equations for the received signal and the estimated channel. This method makes it possible to obtain total interference randomization.

  FIG. 42 is a diagram illustrating another example in which two cells transfer DRS using the generated DRS sequence.

  In FIG. 42, the same interference randomization effect such as Walsh covering for the hybrid method can be obtained.

  From the reception antenna port viewpoint as shown in FIG. 42, the equation of the received signal and the equation for the estimated channel can be expressed as the following equations 64 and 65, respectively.

Here, h ₀ , h ₁ , h ₂ , and h ₃ represent effective channel coefficients, s _i and x _i represent scrambling code sequences, and n ₀ and n ₁ represent noise.

  FIG. 43A shows an example in which DRS is transferred using the generated DRS sequence. FIG. 43B is a diagram showing the transfer power in the transfer example as shown in FIG.

  When the same DRS sequence is applied to two code division multiplexed layers (4 layers as much as possible), adjacent OFDM symbols can be connected with each other in a specific precoding environment as shown in FIG. To transfer power difference.

  In FIG. 43A, it is assumed that a layer common sequence is simply used. The same sequence is used for each layer. Also, the precoding matrix [+1, -1, +1, -1; +1, + j, -1, +1] is used as wideband precoding for one terminal occupying most of the bandwidth. The maximum transmission power difference due to the precoded Walsh code combination has a power difference of +1 dB to -1.25 dB as shown in FIG. In the LTE-A system, four layers can be code-multiplexed. Therefore, in the LTE-A system, the potential maximum transmission power difference may increase to about +2.4 dB to −1.24 dB.

  FIG. 44 is a diagram illustrating another example of transferring the DRS using the generated DRS sequence.

As shown in FIG. 44, when each layer has a different sequence value, the power concentration and the power nulling effect can be randomized. Such power concentration occurs when a specific symbol has 2 * S _i (full constructive sum) after precoding, as shown in FIG. 43, and power nulling occurs in the precoding matrix. When a specific symbol is 0 (full destructive sum), it occurs at a specific frequency subcarrier and OFDM symbol position.

  The worst case scenario (developed or destructive addition that occurs along the entire bandwidth) is because all evolutionary and all destructive additions are effectively randomized because the sequence values change on the frequency and time axis. Can be avoided. In order to avoid such power concentration or power nulling at a specific antenna port, the sequence for each layer needs to be different from each other. Therefore, power concentration is distributed to other REs, and power concentration can be effectively prevented.

  Hereinafter, a method for solving the Walsh code variation and the average peak power problem will be described.

  FIG. 45 is a diagram illustrating an example of a method of assigning a CDM code for each layer.

  When the same sequence is applied to all layers, DM RSs for each layer maintain orthogonality between DM RSs using different CDM codes. As shown in FIG. 45, the simplest method for assigning CDM codes to each DM RS layer is to add {+1, +1} codes to the first layer for all CDM RE sets in the assigned RB. Assign {+1, -1} to the second layer.

  46A shows another example for transferring the DM RS sequence, and FIG. 46B shows the transfer power in the example of FIG. 46A.

  The DM RS sequence for each layer is multiplexed with a precoding element. The precoding element refers to a row vector of a specific precoding matrix such as [+1, +1] or [+1, −1] as shown in FIG. The DM RS sequence values are combined and transferred on the physical antenna port. From a combination of CDM codes at the physical antenna port, a specific precoded RE can have a power of 0 and other precoded REs can have twice the power.

  FIG. 46 (a) shows a DM RS sequence before precoding and a DM RS sequence at each transmission antenna after precoding. Referring to (b) of FIG. 45, if wideband precoding is applied and two layers are transferred, all DM RS REs in one physical antenna port in a specific OFDM symbol are doubled. Can have power or power 0. Also, if four layers are multiplexed and transferred by the CDM method, the specific DM RS RE can have four times the transfer power and the other DM RSREs can have the power 0 in the specific OFDM symbol. FIG. 46 (b) shows a worst case scenario for a specific physical antenna port where the average transfer power for each OFDM symbol varies.

  FIG. 47 is a diagram illustrating an example of a method for mapping a DRS sequence.

  For a base station, peak average (PA) with high power at a specific RE is an important issue. Part of the peak average needs to be designed so that a higher transfer power can be transferred in a particular OFDM symbol. From this point of view, it is preferable to randomize the CDM code so that the precoded DM RS value changes along the frequency axis. One method for randomizing the CDM code is to map the Walsh code differently in each frequency carrier that carries the DM RS, as shown in FIG.

  FIG. 48 is a diagram illustrating another example in which the DRS is transferred using the generated DRS sequence.

  The average power from the transmitting antenna 1 can be expressed as the sum of REs from subcarriers k to k + 4. Walsh codes can reduce peak power somewhat, but are difficult to remove completely. Therefore, the general approach of the peak power problem needs to be further considered.

  FIG. 49 is a diagram illustrating an example of a method of applying a Walsh code to a DM RS.

  An approach to solve the peak power problem is to randomize the Walsh code for the second layer. As shown in FIG. 48, different values of Walsh codes can be applied to the subcarriers carrying the DM RS. If sufficient randomization is allowed for each DM RS layer, the peak power problem for the four CDM layers can be solved. For this purpose, a specific value of Walsh code can be applied in a specific frequency or time domain. It is also possible to randomize the precoded DM RS RE for each physical antenna port.

  50 and 51 are diagrams illustrating examples of a method of applying a Walsh code to four DM RSs.

  As illustrated in FIGS. 50 and 51, another fixed sequence is applied to the Walsh code of each DM RS layer in the frequency domain (or time domain under the assumption that a length 2 Walsh code is used). Through such a process, the orthogonality of each DM RS can be ensured in addition to the randomization of peak power.

  FIG. 52 is a diagram illustrating an example of a method for mapping a DM RS sequence.

  A scrambling code used for DM RS to efficiently implement channel estimation in the terminal needs to be mapped in a direction in which the terminal generates scrambling code and proceeds with channel estimation. Since the DM RS CDM code is applied on the time axis, it is preferable to implement the specific terminal such that the DM RS sequence is mapped to all CDM pairs and moved to the next subcarrier. An example of such an implementation method is shown in FIG.

  The use of the same Walsh code on different CDM RE sets will cause a peak problem, which is an important issue in base station PA design. In order to solve such a problem, the Walsh code used for each layer can be randomized with respect to the precoded DM RS RE by applying a specific value (which may be an arbitrary value). For LTE Rel-10, this can be solved by determining four CDM DM RS layers. FIG. 48 shows an example for the 2CDM layer. By mapping the DM RS scrambling code as shown in FIG. 50, it is possible to efficiently implement channel estimation of the terminal.

  The term 1 RB described in the present invention includes the concept of 1 RB pair. That is, 1 RB is composed of 12 subcarriers on the frequency axis and 7 OFDM symbols on the time axis, and 1 RB pair further includes 7 OFDM symbols than 1 RB on the time axis. It consists of 14 OFDM symbols. In the present invention, the term 1RB is expressed in a format including resources corresponding to one RB pair.

  FIG. 53 is a diagram showing the components of the apparatus 50 according to the present invention.

  Referring to FIG. 53, the device 50 may be a terminal or a base station. The device 50 includes a processor 51, a memory 52, a radio frequency (RF) unit 53, a display unit 54, and a user interface unit 55.

  The layers of the radio interface protocol are implemented in the processor 51. The processor 51 provides a control plane and a user plane. The functions of each layer can be implemented in the processor 51. The memory 52 is connected to the processor 51 and stores an operating system, applications, and general files.

  The display unit 54 displays various kinds of information and can use well-known elements such as an LCD (liquid crystal display) and an OLED (organic light emitting diode).

  The user interface unit 55 can be configured by a combination of known user interfaces such as a keypad, a touch screen, and the like.

  The RF unit 53 can be connected to the processor 51 to transmit and receive wireless signals. The RF unit 53 can be distinguished into a transfer module (not shown) and a receiving module (not shown).

  The layer of the radio interface protocol between the terminal and the network is based on the first three layers (L1), the second layer (L2), and the second layer (L2) based on the lower three layers of the OSI (open system interconnection) model that is well known in the communication system. It can be classified into 3 layers (L3).

  The physical layer belongs to the first layer and provides an information transfer service through a physical channel. The RRC (radio resource control) layer belongs to the third layer and provides control radio resources between the terminal and the network. The terminal and the network exchange RRC messages through the RRC layer.

  In the embodiment described above, the constituent elements and features of the present invention are combined in a predetermined form. Each component or feature should be considered optional unless 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 form an embodiment of the present invention. The order of operations described in the embodiments of the present invention can be changed. Some configurations or features of one embodiment may be included in another embodiment, and may be replaced with corresponding configurations or features of another embodiment. It is obvious that 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.

  Embodiments according to the present invention may be implemented by various means such as hardware, firmware, software, or a combination thereof. In the case of implementation by hardware, one embodiment of the present invention includes one or more ASICs (application specific integrated circuits), DSPs (digital signal processing), DSPDs (digital signal processing), DSPs (digital signal processing), DSPs (digital signal processing). , FPGAs (Field Programmable Gate Arrays), processors, controllers, microcontrollers, microprocessors, and the like.

  In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, or the like that performs the functions or operations described above. The software code may 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.

  It will be apparent to those skilled in the art that the present invention can 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 exemplary. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes that come within the equivalent scope of the invention are included in the scope of the invention.

  The apparatus and method for transmitting / receiving a reference signal in a wireless communication system according to the present invention can be applied to a wireless communication system such as 3GPP LTE, LTE-A, IEEE 802.16 system and the like.

Claims (12)

A method in which a base station transmits downlink data to a terminal,
Generating a UE-specific reference signal (UE-RS) for demodulation of the downlink data;
Transmitting the UE-RS for the downlink data and a plurality of layers of the downlink data to the terminal on a plurality of resource block (RB) pairs allocated to the terminal;
Have
Each of the plurality of RB pairs includes subcarriers 0 to 11 in the frequency domain and OFDM symbols 0 to 13 in the time domain,
Each of the plurality of RB pairs corresponds to the UE among the three subcarriers k1, k2, k3 used for the UE-RS among the subcarriers 0-11 and the OFDM symbols 0-13. -Contains 4 OFDM symbols l1, l2, l3, l4 used for RS,
The UE-RS has a reference signal sequence in a UE-RS resource element (RE) for UE-RS transmission according to a first mapping pattern and a second mapping pattern, respectively, for each of the multiple layers of the downlink data. Generated by multiplying the Walsh code,
The first mapping pattern is as follows:

Mapping each of the Walsh codes (a, b, c, d) in one of two consecutive RB pairs out of the plurality of RB pairs;
The second mapping pattern is as follows:

Mapping the respective Walsh codes (a, b, c, d) in the other one of the two consecutive RB pairs out of the plurality of RB pairs;
The downlink data transmission method, wherein the first mapping pattern and the second mapping pattern are alternately generated along the frequency domain of the plurality of RB pairs. The four OFDM symbols l1, l2, l3 and l4 used for the UE-RS in each of the plurality of RB pairs are OFDM symbols 5, 6, 12 and 13 according to claim 1 . Downlink data transmission method. The three sub-carrier k1, k2 and k3 which are used for the UE-RS in each of the plurality of RB pairs are subcarriers 0, 5 and 10 or 1, 6 and 11, according to claim 2 The downlink data transmission method described in 1. A method for a terminal to receive downlink data,
The terminal receives a UE-specific reference signal (UE-RS) for demodulation of the downlink data on a plurality of resource block (RB) pairs assigned to the terminal;
The terminal receiving the downlink data using the UE-RS for a plurality of layers of the downlink data on the plurality of RB pairs;
Have
Each of the plurality of RB pairs includes subcarriers 0 to 11 in the frequency domain and OFDM symbols 0 to 13 in the time domain,
Each of the plurality of RB pairs corresponds to the UE among the three subcarriers k1, k2, k3 used for the UE-RS among the subcarriers 0-11 and the OFDM symbols 0-13. -Contains 4 OFDM symbols l1, l2, l3, l4 used for RS,
The UE-RS has a reference signal sequence in a UE-RS resource element (RE) for UE-RS transmission according to a first mapping pattern and a second mapping pattern, respectively, for each of the multiple layers of the downlink data. Generated by multiplying the Walsh code,
The first mapping pattern is as follows:

Mapping each of the Walsh codes (a, b, c, d) in one of two consecutive RB pairs out of the plurality of RB pairs;
The second mapping pattern is as follows:

Mapping the respective Walsh codes (a, b, c, d) in the other one of the two consecutive RB pairs out of the plurality of RB pairs;
The downlink data reception method, wherein the first mapping pattern and the second mapping pattern are alternately generated along the frequency domain of the plurality of RB pairs. The four OFDM symbols l1, l2, l3, and l4 used for the UE-RS in each of the plurality of RB pairs are OFDM symbols 5, 6, 12, and 13 according to claim 4 . Downlink data reception method. Wherein the plurality of RB the three sub-carriers k1, k2 and k3 which are used for the UE-RS in each pair is a subcarrier 0, 5 and 10 or 1, 6 and 11, according to claim 5 The downlink data receiving method according to 1. A base station device for transmitting downlink data to a terminal,
An RF unit;
A processor configured to control the RF unit;
The processor is
Generating a UE-specific reference signal (UE-RS) for demodulation of the downlink data;
Controlling the RF unit to transmit to the terminal the UE-RS for the downlink data and a plurality of layers of the downlink data on a plurality of resource block (RB) pairs allocated to the terminal;
Each of the plurality of RB pairs includes subcarriers 0 to 11 in the frequency domain and OFDM symbols 0 to 13 in the time domain,
Each of the plurality of RB pairs corresponds to the UE among the three subcarriers k1, k2, k3 used for the UE-RS among the subcarriers 0-11 and the OFDM symbols 0-13. -Contains 4 OFDM symbols l1, l2, l3, l4 used for RS,
The UE-RS has a reference signal sequence in a UE-RS resource element (RE) for UE-RS transmission according to a first mapping pattern and a second mapping pattern, respectively, for each of the multiple layers of the downlink data. Generated by multiplying the Walsh code,
The first mapping pattern is as follows:

Mapping each of the Walsh codes (a, b, c, d) in one of two consecutive RB pairs out of the plurality of RB pairs;
The second mapping pattern is as follows:

Mapping the respective Walsh codes (a, b, c, d) in the other one of the two consecutive RB pairs out of the plurality of RB pairs;
The base station apparatus, wherein the first mapping pattern and the second mapping pattern are alternately generated along the frequency domain of the plurality of RB pairs. The four OFDM symbols l1, l2, l3 and l4 to be used for the UE-RS in each of the plurality of RB pairs is an OFDM symbol 5, 6, 12 and 13, according to claim 7 Base station device. The three sub-carrier k1, k2 and k3 which are used for the UE-RS in each of the plurality of RB pairs are subcarriers 0, 5 and 10 or 1, 6 and 11, according to claim 8 The base station apparatus as described in. A terminal for receiving downlink data,
An RF unit;
A processor configured to control the RF unit;
The processor is
Receiving a UE-specific reference signal (UE-RS) for demodulation of the downlink data on a plurality of resource block (RB) pairs assigned to the terminal;
Receiving the downlink data using the UE-RS for a plurality of layers of the downlink data on the plurality of RB pairs;
Each of the plurality of RB pairs includes subcarriers 0 to 11 in the frequency domain and OFDM symbols 0 to 13 in the time domain,
Each of the plurality of RB pairs corresponds to the UE among the three subcarriers k1, k2, k3 used for the UE-RS among the subcarriers 0-11 and the OFDM symbols 0-13. -Contains 4 OFDM symbols l1, l2, l3, l4 used for RS,
The UE-RS has a reference signal sequence in a UE-RS resource element (RE) for UE-RS transmission according to a first mapping pattern and a second mapping pattern, respectively, for each of the multiple layers of the downlink data. Generated by multiplying the Walsh code,
The first mapping pattern is as follows:

Mapping each of the Walsh codes (a, b, c, d) in one of two consecutive RB pairs out of the plurality of RB pairs;
The second mapping pattern is as follows:

Mapping the respective Walsh codes (a, b, c, d) in the other one of the two consecutive RB pairs out of the plurality of RB pairs;
The terminal, wherein the first mapping pattern and the second mapping pattern are alternately generated along the frequency domain of the plurality of RB pairs. The four OFDM symbols l1, l2, l3 and l4 to be used for the UE-RS in each of the plurality of RB pairs is an OFDM symbol 5, 6, 12 and 13, according to claim 10 Terminal. 12. The three subcarriers k1, k2 and k3 used for the UE-RS in each of the plurality of RB pairs are subcarriers 0, 5 and 10, or 1, 6 and 11. The terminal described in.

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