KR101241917B1 - A method and a base station for transmitting reference signals, and a method and a user equipment for receiving reference signals - Google Patents

Abstract

The present invention relates to a method and apparatus for multiplexing a reference signal into a predetermined number of CDM groups to provide power balancing between OFDM symbols. In the wireless communication system according to the present invention, the orthogonal sequence used for the multiplexing of the reference signal is a sequence of orthogonal sequences assigned to subcarriers of another CDM group adjacent to the subcarriers in the order of the orthogonal sequences assigned to the subcarriers of one CDM group. And so as to have a predetermined offset.

Description

Method for transmitting downlink reference signal and base station, method for receiving downlink reference signal, and user equipment {A METHOD AND A BASE STATION FOR TRANSMITTING REFERENCE SIGNALS

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting a reference signal for data demodulation, and a method and apparatus for receiving a reference signal for data demodulation.

Recently, multiple input multiple output (MIMO) systems have attracted attention in order to maximize performance and communication capacity of wireless communication systems. The MIMO technique is a method of improving transmission / reception data transmission efficiency by employing multiple transmit antennas and multiple receive antennas by avoiding the use of one transmit antenna and one receive antenna. A MIMO system is also referred to as a multiple antenna system. MIMO technology is an application of a technique of gathering and completing fragmented pieces of data received from multiple antennas without relying on a single antenna path to receive one entire message. As a result, it is possible to improve the data transmission speed in a specific range or increase the system range for a specific data transmission speed.

MIMO techniques include transmit diversity, spatial multiplexing, and beamforming. Transmit diversity is a technique for increasing transmission reliability by transmitting the same data in multiple transmit antennas. Spatial multiplexing is a technology that allows high-speed data transmission without increasing the bandwidth of the system by simultaneously transmitting different data from multiple transmit antennas. Beamforming is used to increase the signal to interference plus noise ratio (SINR) of a signal by applying weights according to channel conditions in multiple antennas. In this case, the weight may be expressed by a weight vector or a weight matrix, which is referred to as a precoding vector or a precoding matrix.

Spatial multiplexing is spatial multiplexing for a single user and spatial multiplexing for multiple users. Spatial multiplexing is also referred to as single user MIMO, and spatial multiplexing for multiple users is called spatial division multiple access (SDMA) or multi-user MIMO.

Meanwhile, the base station may transmit a plurality of layers together for one or more users. The base station multiplexes the multiple layers in a predetermined frequency / time domain to transmit the multiple layers together, and transmits the multiple layers together to one or more user equipments in the predetermined frequency / time domain. In general, the maximum transmit power available to the base station for downlink transmission is determined by the frequency bandwidth supported by the base station, the data throughput of the base station, the power efficiency of the base station, and the like. Since the total transmit power available to the base station is limited to a predetermined value, the base station is required to efficiently allocate the transmit power per subcarrier in one OFDM symbol period.

In order for the user equipment to demodulate data allocated to a predetermined time / frequency region, the user equipment uses a reference signal (RS) transmitted from the base station to transmit the data. A channel estimate for estimating the configuration and channel quality of the physical antenna is performed. The channel estimation method and the reference signal will be briefly described as follows. In order to detect the synchronization signal, the receiver needs to know the information of the radio channel (such as attenuation, phase shift or time delay). In this case, channel estimation refers to estimating the size and reference phase of the carrier. The wireless channel environment has a fading characteristic in which the channel state changes irregularly in time and frequency domain. Estimating amplitude and phase for these channels is called channel estimation. That is, channel estimation estimates the frequency response of the radio section or the radio channel. As a channel estimation method, there is a method of estimating reference values based on reference signals of several base stations using a two-dimensional channel estimator. In this case, the reference signal refers to a symbol having a high output although it does not have actual data to help carrier phase synchronization and base station information acquisition. The transmitter and the receiver can perform channel estimation using the above reference signals. The receiver may restore data received from the transmitter based on the channel estimation result based on the reference signal.

In order for the receiving device to correctly demodulate the signal transmitted by the transmitting device, a reference signal for demodulating the signal is required to be appropriately configured.

In addition, in order for the receiving apparatus to receive the reference signal with high accuracy, the reference signal is required to be configured so that the base station can appropriately distribute the transmission power of the demodulation reference signal within the total available transmission power.

In addition, in order for the base station to efficiently use the available power, power is required to be evenly distributed among the OFDM symbols.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

Aspects of the present invention for solving the technical problem as described above are as follows.

In an embodiment of the present invention, an orthogonal sequence used for multiplexing a reference signal may include a sequence of orthogonal sequences assigned to subcarriers of one CDM group and an orthogonal sequence assigned to subcarriers of another CDM group adjacent to the subcarriers. Assign to have an offset.

In another embodiment of the present invention, the reference signal for each layer is multiplexed on a predetermined radio resource after the phase offset is applied for each layer.

In one aspect of the present invention, a method for transmitting a plurality of RSs to a user equipment by a base station in a wireless communication system, the method comprising: spreading the plurality of RSs using spreading orthogonal sequences; And transmitting the plurality of RSs through at least one of a first CDM group and a second CDM group, which are two Code Division Multiplexing (CDM) groups, wherein the first CDM is among the plurality of RSs. The RS transmitted in the group is spread according to one of the spreading orthogonal sequences defined as in the first table and transmitted through a subcarrier belonging to the first CDM group, and is transmitted in the second CDM group among the plurality of RSs. RS is spread according to any one of spreading orthogonal sequences defined as shown in the second table, and transmitted through a partial carrier belonging to the second CDM group.

In another aspect of the present invention, in a method for receiving a plurality of reference signals (RS) from a base station by a user equipment in a wireless communication system, the plurality of RS from the base station (Code Division Multiplexing, CDM) group Receiving via at least one of the first CDM group and the second CDM group; And detecting a first RS for the user equipment from the plurality of RSs using a first spreading orthogonal sequence used for spreading the RS of the user equipment, wherein the first confident orthogonal sequence comprises: the first RS; When 1 RS is received through the first CDM group, it is one of spreading orthogonal sequences defined as in the first table, and when the first RS is received through the second CDM group, as shown in the second table. A reference signal receiving method, which is one of the defined spreading orthogonal sequences, is provided.

In another aspect of the present invention, a base station transmits a plurality of reference signals (RS) to the user equipment in a wireless communication system, the transmitter; And a processor configured to control the transmitter, the processor comprising: a first spreading the plurality of RSs using spreading orthogonal sequences and the plurality of RSs as two Code Division Multiplexing (CDM) groups The transmitter is controlled to be transmitted through at least one of a CDM group and a second CDM group, and wherein the processor is further configured to transmit a spreading orthogonal number of RSs transmitted from the first CDM group among the plurality of RSs as defined in the second table. The transmitter is controlled to spread according to any one of sequences and transmit on a subcarrier belonging to the first CDM group, and RSs transmitted from the second CDM group among the plurality of RSs are spread as defined in Table 2 A base station is provided that controls the transmitter to spread according to any one of orthogonal sequences and transmit on some carriers belonging to the second CDM group.

In still another aspect of the present invention, in a wireless communication system, a user equipment receives a plurality of RSs from a base station, the receiver comprising: a receiver; And a processor configured to control the receiver, wherein the receiver receives the plurality of RSs from the base station through at least one of a first CDM group and a second CDM group, which are Code Division Multiplexing (CDM) groups; Configured to; The processor controls the receiver to detect a first RS for the user equipment from the plurality of RSs using a first spreading orthogonal sequence used for spreading the RS of the user equipment, wherein the first confident orthogonal sequence Is any one of the spreading orthogonal sequences defined as in the first table when the first RS is received through the first CDM group, and when the first RS is received through the second CDM group, A user equipment, which is one of the spreading orthogonal sequences defined as shown in Table 2, is provided.

In each aspect of the invention, the first table is

And the second table

.

.

In each aspect of the present invention, the plurality of RSs may be spread by the base station according to the third table and transmitted to the user equipment through at least one of the first CDM group and the second CDM group. The third table,

Here, RS 0 to RS 7 may correspond to layers 0 to layer 7 in a one-to-one manner.

In each aspect of the present invention, the plurality of RSs are represented by multiplexed orthogonal sequences a and b, c, d defined as follows.

,

,

At least one of the first CDM group and the second CDM group may be multiplexed and transmitted. RS 0 and RS 1, RS 4, RS 6 are

,

,

Multiplexed to the first CDM group by using RS 2 and RS 3, RS 5, RS 7

Can be multiplexed into the second CDM group using.

In each aspect of the present invention, each of the plurality of RSs includes two adjacent groups belonging to the first CDM group and the second CDM group, respectively, by one of (a, c) or (b, d) multiplexed orthogonal sequence pairs. It can be multiplexed on subcarriers.

In each aspect of the present invention, r (m), which is a demodulation reference signal RS p for layer p, may be allocated to the first CDM group or the second CDM group according to the following equation.

. 여기서, n_PRB는 물리자원블록 인덱스이며, N^RB _sc는 일 RB를 구성하는 부반송파의 개수이고, N^max,DL _RB는 하향링크 슬롯에 포함된 RB의 최대개수를 나타내며, p는 레이어 인덱스이며, k 및 l은 일 서브프레임 내 부반송파 인덱스 및 OFDM 심볼 인덱스이며, m'는 일 자원블락(RB)에서 RS를 포함하는 RS 부반송파의 인덱스이고, l'는 상기 일 서브프레임에서 RS를 포함하는 RS OFDM 심볼들의 인덱스이다.

. Here, n _PRB is a physical resource block index, N ^RB _sc is the number of subcarriers constituting one RB, N ^{max, DL} _RB represents the maximum number of RBs included in the downlink slot, p is a layer index, k and l are the subcarrier index and the OFDM symbol index in one subframe, m 'is the index of the RS subcarrier including RS in one resource block (RB), l' is RS OFDM including RS in the one subframe Index of symbols.

In each aspect of the present invention, the plurality of RSs may be multiplexed in one subframe by the base station and transmitted to the user equipment in the following pattern.

.

.

The above technical solutions are only a part of embodiments of the present invention, and various embodiments reflecting the technical features of the present invention are based on the detailed description of the present invention described below by those skilled in the art. Can be derived and understood.

According to the present invention, there is an advantage that the transmission power can be evenly distributed over all OFDM symbols in one subframe.

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

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.
1 is a block diagram illustrating components of a user equipment (UE) and a base station for carrying out the present invention.
2 illustrates an example of a structure of a transmitter in a user equipment and a base station.
3 illustrates an example of a radio frame structure used in a wireless communication system.
4 shows an example of a DL / UL slot structure in a wireless communication system.
5 shows an example of a downlink subframe structure in a wireless communication system.
6 is a conceptual diagram of DRS transmission.
7 illustrates an example of a DRS pattern used in an LTE system.
8 illustrates an example of a DRS pattern used in an LTE-A system.
FIG. 9 illustrates a pattern multiplexed into subframes having normal CPs using an OCC having a length of two DRSs of two layers.
10 shows an example in which DRSs for four layers are transmitted through two CDM groups.
11 shows a method of multiplexing four DRSs into two CDM groups.
12 shows an example in which two DRSs are multiplexed in one CDM group.
FIG. 13 illustrates an embodiment of the present invention that distributes transmit power evenly over OFDM symbols in rank-2 transmission.
14 and 15 show power allocation examples for the DRS RE and the data RE in rank-2 transmission.
16 illustrates an example in which DRSs for layers corresponding to antenna ports 11 to 14 are allocated to two CDM groups.
17 shows a method of multiplexing eight DRSs into two CDM groups.
18 to 22 illustrate embodiments of the present invention for multiplexing DRS with an OCC of length 4 in one CDM group.
23 to 30 illustrate embodiments of the present invention for multiplexing DRS with an OCC of length 4 in two CDM groups.
31 shows other examples according to an embodiment of the present invention for allocating an OCC to have a predetermined OCC offset between two CDM groups.
32 to 38 are diagrams illustrating the advantages of OCC being allocated such that two CDM groups have a predetermined OCC offset, in accordance with embodiments of the present invention.
39 illustrates a phase offset according to DRS subcarriers for each DRS port.
40 to 42 illustrate the advantages of applying a phase offset for each layer according to a DRS subcarrier according to embodiments of the present invention.
FIG. 43 is a diagram for illustrating an advantage when an OCC is allocated such that two CDM groups have a predetermined OCC offset, and a phase offset is applied for each layer according to a DRS subcarrier according to embodiments of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate 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, those skilled in the art will appreciate that the present invention may be practiced without these specific details.

In addition, the techniques, devices, and systems described below may be applied to various wireless multiple access systems. Examples of multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (MC-FDMA) system, and a multi-carrier frequency division multiple access (MC-FDMA) system. CDMA may be implemented in a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented in wireless technologies such as Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Enhanced Data Rates for GSM Evolution (EDGE), and the like. OFDMA may be implemented in wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, evolved-UTRA (E-UTRA), and the like. UTRA is part of Universal Mobile Telecommunication System (UMTS), and 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is part of E-UMTS using E-UTRA. 3GPP LTE adopts OFDMA in downlink and SC-FDMA in uplink. LTE-advanced (LTE-A) is an evolution of 3GPP LTE. For convenience of explanation, hereinafter, it will be described on the assumption that the present invention is applied to 3GPP LTE / LTE-A. However, the technical features of the present invention are not limited thereto. For example, even if the following detailed description is described based on the mobile communication system corresponding to the 3GPP LTE / LTE-A system, any other mobile communication except for those specific to 3GPP LTE / LTE-A is described. Applicable to the system as well.

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

In the present invention, a user equipment (UE) may be fixed or mobile, and various devices which communicate with a base station to transmit and receive user data and / or various control information belong to the same. The user equipment may be a terminal equipment, a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem ( It may be called a wireless modem, a handheld device, or the like. In addition, in the present invention, a base station (BS) generally refers to a fixed station that communicates with a user equipment and / or another base station, and communicates with the user equipment and other base stations for various data and control information. Replace it. The base station may be called in other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point.

In the following description, PDCCH / PCFICH / PHICH / PDSCH / DRS / CRS / DMRS / CSI-RS Resource Element (RE) is allocated to PDCCH / PCFICH / PHICH / PDSCH / DRS / CRS / DMRS / CSI-RS, respectively. Means available RE. Hereinafter, in particular, the resource element to which the reference signal is transmitted is referred to as RS RE, and the resource element to which control information or data is transmitted is called data RE.

In addition, hereinafter, a symbol / carrier / subcarrier to which DRS / CRS / DMRS / CSI-RS is assigned is referred to as a DRS / CRS / DMRS / CSI-RS symbol / carrier / subcarrier. For example, a symbol to which a DRS is assigned is called a DRS symbol, and a subcarrier to which a DRS is assigned is called a DRS subcarrier. In addition, a symbol to which user data (for example, PDSCH data, PDCCH data, etc.) are allocated is called a data symbol, and a subcarrier to which user data is assigned is called a data subcarrier.

Meanwhile, in the present invention, that a specific signal is allocated to a frame / subframe / slot / carrier / subcarrier means that the specific signal is transmitted through a corresponding carrier / subcarrier during a period / timing of the frame / subframe / slot / symbol. Means that.

In the present invention, the rank or transmission rank refers to the number of layers multiplexed / assigned on one OFDM symbol or one data RE.

Hereinafter, when a specific signal in a frame / subframe / slot / symbol / carrier / subcarrier is not transmitted, it is expressed that the transmission of the specific signal is a drop, mute, null or blank. For example, when the transmitter transmits a specific signal with zero transmission power on a predetermined resource element, the transmitter drops the transmission of the specific signal, or mutes or blanks the predetermined resource element, or the predetermined signal. It can be expressed as transmitting a null signal in a radio resource.

1 is a block diagram illustrating components of a user equipment (UE) and a base station (BS) for carrying out the present invention.

The UE operates as a transmitter in an uplink and as a receiver in a downlink. Conversely, the base station can operate as a receiving apparatus in the uplink and as a transmitting apparatus in the downlink.

The UE and the base station are antennas 500a and 500b capable of receiving information and / or data, signals, messages, and the like, transmitters 100a and 100b that control the antennas to transmit messages, and control the antennas to transmit messages. Receiving receiver (Receiver) (300a, 300b), and memory (200a, 200b) for storing a variety of information related to communication in a wireless communication system. In addition, the UE and the base station each include processors 400a and 400b configured to control components such as transmitters, receivers, and memory included in the UE or the base station to perform the present invention. The transmitter 100a, the receiver 300a, the memory 200a, and the processor 400a in the UE may be implemented as independent components by separate chips, respectively, and two or more are one chip. It may be implemented by. Similarly, the transmitter 100b, the receiver 300b, the memory 200b, and the processor 400b in the base station may be implemented as independent components by separate chips, respectively, and two or more chips may be included in one chip ( chip). The transmitter and the receiver may be integrated to be implemented as one transceiver in a user equipment or a base station.

The antennas 500a and 500b transmit a signal generated by the transmitters 100a and 100b to the outside, or receive a radio signal from the outside and transmit the signal to the receivers 300a and 300b. Antennas 500a and 500b are also called antenna ports. Each antenna port may correspond to one physical antenna or may be configured by a combination of more than one physical antenna. A transceiver supporting a multi-input multi-output (MIMO) function for transmitting and receiving data using a plurality of antennas may be connected to two or more antennas.

Processors 400a and 400b typically control the overall operation of various modules in a UE or base station. In particular, the processor 400a or 400b includes various control functions for performing the present invention, a medium access control (MAC) frame variable control function according to service characteristics and a propagation environment, a power saving mode function for controlling idle mode operation, and a hand. Handover, authentication and encryption functions can be performed. The processors 400a and 400b may also be referred to as a controller, a microcontroller, a microprocessor, a microcomputer, or the like. Meanwhile, the processors 400a and 400b may be implemented by hardware or firmware, software, or a combination thereof. When implementing the present invention using hardware, application specific integrated circuits (ASICs) or digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays) may be provided in the processors 400a and 400b. Meanwhile, when implementing the present invention using firmware or software, the firmware or software may be configured to include a module, a procedure, or a function for performing the functions or operations of the present invention, and configured to perform the present invention. The firmware or software may be provided in the processors 400a and 400b or may be stored in the memory 200a and 200b to be driven by the processors 400a and 400b.

The transmitters 100a and 100b perform a predetermined encoding and modulation on a signal and / or data to be transmitted from the processor 400a or 400b or a scheduler connected to the processor to be transmitted to the outside, and then an antenna ( 500a, 500b). For example, the transmitters 100a and 100b convert a data stream to be transmitted into K layers through demultiplexing, channel encoding, and modulation processes. The K layers are transmitted through the transmit antennas 500a and 500b through a transmitter in the transmitter. The transmitters 100a and 100b and the receivers 300a and 300b of the UE and the base station may be configured differently according to a process of processing a transmission signal and a reception signal.

The memories 200a and 200b may store a program for processing and controlling the processors 400a and 400b and may temporarily store information input and output. The memory 200a, 200b may be utilized as a buffer. The memory may be a flash memory type, a hard disk type, a multimedia card micro type or a card type memory (e.g. SD or XD memory, etc.), RAM Access Memory (RAM), Static Random Access Memory (SRAM), Read-Only Memory (ROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Programmable Read-Only Memory (PROM), Magnetic Memory, Magnetic Disk, It can be implemented using an optical disk or the like.

2 illustrates an example of a structure of a transmitter in a user equipment and a base station. The operation of the transmitters 100a and 100b will be described in more detail with reference to FIG. 2 as follows.

Referring to FIG. 2, the transmitters 100a and 100b in the UE or the base station may include a scrambler 301, a modulation mapper 302, a layer mapper 303, a precoder 304, a resource element mapper 305, and an OFDM / SC. -May comprise an FDM signal generator 306.

The transmitters 100a and 100b may transmit one or more codewords. Coded bits in each codeword are scrambled by the scrambler 301 and transmitted on a physical channel. Codewords are also referred to as data streams and are equivalent to data blocks provided by the MAC layer. The data block provided by the MAC layer may also be referred to as a transport block.

The scrambled bits are modulated into complex-valued modulation symbols by the modulation mapper 302. The modulation mapper may be arranged as a complex modulation symbol representing a position on a signal constellation by modulating the scrambled bit according to a predetermined modulation scheme. There is no restriction on a modulation scheme, and m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM) may be used to modulate the encoded data.

The complex modulation symbol is mapped to one or more transport layers by the layer mapper 303.

The complex modulation symbol on each layer is precoded by the precoder 304 for transmission on the antenna port. Specifically, the precoder 304 processes the complex modulation symbol in a MIMO scheme according to the multiple transmit antennas 500-1, ..., 500-N _t to output antenna specific symbols, and applies the antenna specific symbols. The resource element mapper 305 is distributed. That is, mapping of the transport layer to the antenna port is performed by the precoder 304. The precoder 304 may be output to the matrix z of the layer mapper 303, an output x N _t × M _t precoding matrix W is multiplied with N _t × M _F of the.

The resource element mapper 305 maps / assigns the complex modulation symbols for each antenna port to appropriate resource elements. The resource element mapper 305 may assign a complex modulation symbol for each antenna port to an appropriate subcarrier and multiplex it according to a user.

The OFDM / SC-FDM signal generator 306 modulates a complex modulation symbol for each antenna port, that is, an antenna specific symbol by an OFDM or SC-FDM scheme, thereby complex-valued time domain OFDM (Orthogonal) Generates a Frequency Division Multiplexing (SCC) symbol signal or a Single Carrier Frequency Division Multiplexing (SC-FDM) symbol signal. The OFDM / SC-FDM signal generator 306 may perform an Inverse Fast Fourier Transform (IFFT) on an antenna specific symbol, and a cyclic prefix (CP) may be inserted into a time domain symbol on which the IFFT is performed. The OFDM symbol is transmitted to the receiving apparatus through each of the transmission antennas 500-1, ..., 500-N _t through digital-to-analog conversion, frequency up-conversion, and the like. The OFDM / SC-FDM signal generator 306 may include an IFFT module and a CP inserter, a digital-to-analog converter (DAC), a frequency uplink converter, and the like.

Meanwhile, when the transmitters 100a and 100b adopt a SC-FDM connection (SC-FDMA) scheme for transmitting codewords, the transmitters 100a and 100b may include a fast Fourier transformer. have. The fast Fourier transform performs a fast fourier transform (FFT) on the antenna specific symbol and outputs the fast Fourier transformed symbol to the resource element mapper 305.

The signal processing of the receivers 300a and 300b consists of the inverse of the signal processing of the transmitter. In detail, the receivers 300a and 300b decode and demodulate the radio signals received through the antennas 500a and 500b from the outside and transmit them to the corresponding processors 400a and 400b. The antennas 500a and 500b connected to the receivers 300a and 300b may include N _r multiple receive antennas, and each of the signals received through the receive antennas is restored to a baseband signal and then multiplexed and MIMO demodulated. The transmitters 100a and 100b restore the data sequence originally intended to be transmitted. The receivers 300a and 300b may include a signal restorer for restoring a received signal to a baseband signal, a multiplexer for combining and multiplexing the received processed signals, and a channel demodulator for demodulating the multiplexed signal sequence with a corresponding codeword. have. The signal restorer, the multiplexer, and the channel demodulator may be composed of one integrated module or each independent module for performing their functions. More specifically, the signal restorer is an analog-to-digital converter (ADC) for converting an analog signal into a digital signal, a CP remover for removing a CP from the digital signal, and a fast fourier transform (FFT) to the signal from which the CP is removed. FFT module for outputting a frequency domain symbol by applying a, and may include a resource element demapper (equalizer) to restore the frequency domain symbol to an antenna-specific symbol (equalizer). The antenna specific symbol is restored to a transmission layer by a multiplexer, and the transmission layer is restored to a codeword intended to be transmitted by a transmitting device by a channel demodulator.

On the other hand, when the receiver (300a, 300b) receives a signal transmitted by the SC-FDMA scheme, the receiver (300a, 300b) further includes an IFFT module. The IFFT module performs an IFFT on the antenna specific symbol reconstructed by the resource element demapper and outputs the inverse fast Fourier transformed symbol to the multiplexer.

For reference, in FIG. 1 and FIG. 2, the scrambler 301, the modulation mapper 302, the layer mapper 303, the precoder 304, the resource element mapper 305, and the OFDM / SC-FDMA signal generator 306 are provided. Although described as being included in the transmitter (100a, 100b), the processor (400a, 400b) of the transmitting device is a scrambler 301, modulation mapper 302, layer mapper 303, precoder 304, resource element mapper ( 305), it may be configured to include an OFDM / SC-FDMA signal generator 306. Similarly, in FIGS. 1 and 2, the signal restorer, the multiplexer, and the channel demodulator are included in the receivers 300a and 300b. It is also possible to be configured to include a demodulator. Hereinafter, for convenience of description, the scrambler 301, the modulation mapper 302, the layer mapper 303, the precoder 304, the resource element mapper 305, and the OFDM / SC-FDMA signal generator 306 may include these. Receivers included in the transmitters 100a and 100b separated from the processors 400a and 400b for controlling the operation of the processor, and signal receivers, multiplexers, and channel demodulators are separated from the processors 400a and 400b for controlling their operations. It will be described as being included in (300a, 300b). However, the scrambler 301 and the modulation mapper 302, the layer mapper 303, the precoder 304, the resource element mapper 305, and the OFDM / SC-FDMA signal generator 306 are provided to the processors 400a and 400b. In the case where the signal restorer, the multiplexer, and the channel demodulator are included in the processors 400a and 400b, the embodiments of the present invention may be equally applied.

3 illustrates an example of a radio frame structure used in a wireless communication system. In particular, FIG. 3 illustrates the structure of a radio frame of a 3GPP LTE / LTE-A system. The radio frame structure of FIG. 3 may be applied to an FDD mode, a half FDD (H-FDD) mode, and a TDD mode.

Referring to FIG. 3, a radio frame used in 3GPP LTE / LTE-A has a length of 10 ms (327200 Ts) and consists of 10 equally sized subframes. Here, T _s denotes a sampling time, T _s = 1 / (2048x15kHz). Each subframe is 1 ms long and consists of two slots. 20 slots in one radio frame are sequentially numbered from 0 to 19. Each slot has a length of 0.5 ms. The time for transmitting one subframe is defined as a transmission time interval (TTI).

4 shows an example of a DL / UL slot structure in a wireless communication system. In particular, FIG. 4 shows a structure of a resource grid of a 3GPP LTE / LTE-A system.

Referring to FIG. 4, a slot includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. The OFDM symbol also means one symbol period. The resource block includes a plurality of subcarriers in the frequency domain. The OFDM symbol may be referred to as an OFDM symbol, an SC-FDM symbol, or the like according to a multiple access scheme. The number of OFDM symbols included in one slot may be variously changed according to the channel bandwidth and the length of the CP. For example, one slot includes seven OFDM symbols in the case of a normal CP, whereas one slot includes six OFDM symbols in an extended CP. In FIG. 4, for convenience of description, a subframe in which one slot includes 7 OFDM symbols is illustrated. However, embodiments of the present invention may be applied to subframes having other numbers of OFDM symbols in the same manner. For reference, a resource composed of one OFDM symbol and one subcarrier is referred to as a resource element (RE) or a tone.

Referring to FIG. 4, a signal transmitted in each slot is represented by a resource grid composed of N ^{DL / UL} _RB N ^RB _sc subcarriers and N ^{DL / UL} _symb OFDM or SC-FDM symbols. Can be. Here, N ^DL _RB represents the number of resource blocks (RBs) in the downlink slot, and N ^UL _RB represents the number of _RBs in the uplink slot. N ^DL _symb denotes the number of OFDM or SC-FDM symbols in the downlink slot, and N ^UL _symb denotes the number of OFDM or SC-FDM symbols in the uplink slot. N ^RB _sc represents the number of sub-carriers constituting one RB.

In other words, a physical resource block (PRB) is defined as N ^{DL / UL} _symb consecutive OFDM symbols or SC-FDM symbols in the time domain and is defined by N ^RB _sc consecutive subcarriers in the frequency domain. . Therefore, one PRB consists of N ^{DL / UL} _symb × N ^RB _sc resource elements.

Each resource element in the resource grid can be uniquely defined by an index pair (k, 1) in one slot. k is an index assigned from 0 to N ^{DL / UL} _RB N ^RB _sc -1 in the frequency domain, and 1 is an index assigned from 0 to N ^{DL / UL} _symb -1 in the time domain.

5 shows an example of a downlink subframe structure in a wireless communication system.

Referring to FIG. 5, each subframe may be divided into a control region and a data region. The control region includes one or more OFDM symbols starting from the first OFDM symbol. The number of OFDM symbols used as a control region in a subframe may be independently set for each subframe, and the number of OFDM symbols is transmitted through a physical control format indicator channel (PCFICH). The base station may transmit various control information to the user device (s) through the control area. In order to transmit control information, a PDCCH (physical downlink control channel), a PCFICH, a physical hybrid automatic repeat request indicator channel (PHICH), or the like may be allocated to the control region.

The base station may transmit data for the user equipment or the user equipment group through the data area. Data transmitted through the data area is also referred to as user data. For transmission of user data, a PDSCH (Physical Downlink Shared CHannel) may be allocated to the data area. The user equipment may read the data transmitted through the PDSCH by decoding the control information transmitted through the PDCCH. For example, information indicating to which user equipment or group of user equipments the PDSCH data is transmitted and how the user equipment or user equipment group should receive and decode PDSCH data is included in the PDCCH and transmitted.

The PDCCH includes transport format and resource allocation information of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information about a paging channel (PCH), and the DL-SCH. System information about the system, allocation information of upper layer control messages such as random access response transmitted on PDSCH, collection of Tx power control commands for each UE in a certain UE group, voice over IP (VoIP) Carry activation information and the like. A plurality of PDCCHs may be transmitted in the control domain. The UE can monitor the plurality of PDCCHs and detect its PDCCH. The PDCCH has different sizes and uses of control information according to a downlink control indicator (DCI) format, and may vary in size according to a coding rate.

The DCI format is independently applied to each UE, and PDCCHs of multiple UEs may be multiplexed in one subframe. The PDCCH of each UE is independently channel coded to add a cyclic redundancy check (CRC). The CRC is masked with a unique identifier of each UE so that each UE can receive its own PDCCH. However, since the UE basically does not know where its PDCCH is transmitted, blind detection (also called blind decoding) is performed every subframe until all PDCCHs of the corresponding DCI format have received the PDCCH having their identifiers. .

Meanwhile, various reference signals are transmitted between the BS and the UE for mitigation of interference signals, estimation of channel conditions between the BS and the UE, and demodulation of signals transmitted between the BS and the UE. The reference signal refers to a signal of a predefined, special waveform that the BS and the UE know from each other, transmitted from the BS to the UE or from the UE to the BS.

The reference signals can be classified into a dedicated reference signal (DRS) and a common reference signal (CRS). The CRS is transmitted in all downlink subframes in the cell supporting PDSCH transmission. The CRS is a reference signal that can be used for both demodulation and measurement purposes and is shared by all user equipment in the cell. The CRS sequence is transmitted on all antenna ports regardless of layer. In contrast, DRS is generally used for demodulation purposes, and can be used only by a specific UE. CRS and DRS are also referred to as cell-specific RSs and demodulation RSs (DMRSs), respectively. The DMRS is also referred to as a UE-specific RS.

6 is a conceptual diagram of DRS transmission. In particular, FIG. 6 illustrates a transmitter for transmitting a precoded RS.

The DRS may be used only in a specific UE, and other UEs may not use the DRS transmitted for the specific UE. The DRS used for data demodulation of a given UE may be classified into a precoded RS and a non-precoded RS. If a precoded RS is adopted as the DRS, the DRS is precoded into a precoding matrix used for precoding a data symbol, so that the same number of RS sequences as K layers (stream 0 to stream K-1) Is sent. Here, K is equal to or smaller than the number N _t of physical antenna ports. The K layers may be assigned to one or multiple UEs. When a plurality of UEs share the K layers, 1 to K UEs may receive the K layers using the same time / frequency resources.

The UE may demodulate the received data signal by, for example, arranging the received data signal at a predetermined position on a signal property according to a predetermined modulation scheme based on the DRS transmitted together with the data signal.

7 illustrates an example of a DRS pattern used in an LTE system. In particular, FIG. 7A illustrates a DRS pattern in a normal CP subframe, and FIG. 7B illustrates a DRS pattern in an extended CP subframe. In FIG. 7, 'l' indicates the position of an OFDM symbol in one slot.

Among the resource elements constituting one resource block or one resource block pair, resource elements to which a DRS can be transmitted are generally determined. In this case, the UE may detect the DRS in the resource element (s) at a predetermined position among the resource elements of each resource block or each resource block pair. For example, referring to FIG. 7, the BS transmits an allocated DRS as shown in FIG. 7 (a) or FIG. 7 (b) in one or more resource block pairs through the antenna port 5. Hereinafter, embodiments of the present invention will be described with reference to a position of resource elements for transmitting DRS in one resource block or one resource block pair as a DRS pattern.

Meanwhile, the LTE system supports up to two layers, and the layer is simultaneously transmitted with the DRS for demodulation of the layer and the CRS for channel estimation between the UE and the BS transmitting the layer. CRS-based downlink transmission requires RS to be transmitted on all physical antenna ports. Therefore, CRS-based downlink transmission has a problem that the overall RS overhead also increases as the number of physical antenna ports increases, resulting in a decrease in data transmission efficiency. In order to solve this problem, the LTE-A system capable of transmitting a larger number of layers than the LTE system utilizes DRS as a demodulation reference signal instead of CRS in which transmission overhead increases according to the number of physical antenna ports. In the case of DRS-based downlink transmission, only a virtual antenna port needs a reference signal for coherent demodulation. That is, in the case of DRS-based downlink transmission, only the virtual antenna port, not all physical antenna ports of the BS, needs to transmit the DRS of the corresponding virtual antenna. Since the number of virtual antenna ports is generally less than or equal to the number N _t of physical antenna ports, the RS transmission overhead of DRS-based downlink transmission is reduced compared to the RS overhead of CRS-based downlink transmission.

For reference, since the DRS using the same precoder as the data is an RS used only for demodulation purposes, in LTE-A, an additional measurement RS for allowing a UE to measure channel state information is Channel State Information RS. ) Is transmitted to the UE. The CSI-RS is transmitted every predetermined transmission period consisting of a plurality of subframes, unlike the CRS transmitted for each subframe, based on the fact that the channel state is not relatively varied with time. Because of the transmission characteristics of the CSI-RS, there is an advantage that the CSI-RS transmission overhead is lower than the transmission overhead of the CRS.

For reference, the DRS of the present invention is used for PDSCH transmission and is transmitted for demodulation of each layer by the number of layers used for transmission of the PDSCH. The DRS of the present invention is transmitted only on a resource block (RB) to which the corresponding PDSCH is mapped. In addition, the DRS of the present invention is not transmitted on the RE used for transmission of other RS regardless of the antenna port.

8 illustrates an example of a DRS pattern used in an LTE-A system. In particular, FIG. 8 illustrates a DRS pattern in one resource block pair of a regular subframe having a normal CP.

In the LTE-A system, a plurality of layers may be multiplexed and transmitted to a UE in one subframe. In the case of multi-layer transmission, since the DRS should also be transmitted for each layer, the number of DRS is also increased in proportion to the number of transmitted layers. When a plurality of DRSs are transmitted through different REs, as the number of layers increases, the number of DRS REs also increases, resulting in a low data transmission efficiency. Therefore, in order to reduce the DRS transmission overhead, when a plurality of DRSs should be transmitted, it is preferable that one or more DRSs are multiplexed and transmitted to a predetermined RE.

Accordingly, in the LTE-A system, a plurality of DRSs are largely transmitted in two groups of REs. For example, in FIG. 8, one or more DRSs may be multiplexed to the REs labeled 'C' and transmitted to the UE, and one or more other DRSs may be multiplexed and transmitted to the UE. When a plurality of DRSs are multiplexed on a predetermined radio resource, in order to distinguish the plurality of DRSs from each other, for example, when the DRS is extended using an orthogonal cover code (OCC) having a length of 2, Up to two different DRSs may be transmitted through one RE. As another example, if a DRS is extended using an Orthogonal Cover Code (OCC) having a length of 4, up to four different DRSs may be multiplexed and transmitted through one RE. An example of an orthogonal cover code is Walsh-Hadmard code. Orthogonal cover codes are also called orthogonal sequences.

Hereinafter, a collection of REs in which DRSs, which can be distinguished from each other by being extended by an orthogonal cover code and transmitted from among REs of one resource block or one resource block pair, is transmitted, is referred to as a Code Division Multiplexing (CDM) group. Referring to FIG. 8, for example, REs designated as 'C' belong to one CDM group (hereinafter, CDM group 1), and REs designated as 'D' are the other CDM group (hereinafter, CDM group 2). Belongs to. Within a pair of contiguous resource blocks (hereinafter, referred to as resource block pairs), each CDM group of FIG. 8 includes 12 REs.

FIG. 9 illustrates a pattern multiplexed into subframes having normal CPs using an OCC having a length of two DRSs of two layers.

9 (a) to 9 (c), mapping of two DRSs to radio resources for two layers may be expressed as follows. For example, assume that the virtual antenna ports corresponding to the two layers one-to-one are antenna port 7 and antenna port 7. In case of a subframe having a normal CP, a part of each DRS sequence r (m) for the antenna port 7 and the antenna port 8 is a physical resource block having a frequency domain index n _PRB allocated for the corresponding PDSCH transmission. Block, PRB) may be mapped to complex-valued modulation symbols a ^(p) _{k, l} according to the following equations.

Here, p is an antenna port index, which is p ∈ {7,8}. k and l are the subcarrier index and the OFDM symbol index described with reference to FIG. r (s) is a random sequence. m 'represents a counter of DRS REs in each OFDM symbol of the corresponding PDSCH transmission. Since each DRS OFDM symbol includes three DRS subcarriers for each RB, m 'has one of 0, 1, and 2. N ^{max , DL} _RB represents the maximum number of resource blocks in the downlink slot allocated to the PDSCH. n _s represents a slot number in a radio frame. l 'corresponds to a counter of DRS OFDM symbols in a subframe. In the case of a normal subframe that is not a special subframe, since there are a total of four DRS OFDM symbols in a normal CP, l 'has one of 0, 1, 2, and 3 values.

9, it can be seen that the DRS of the layer corresponding to antenna port 7 and the DRS of the layer corresponding to antenna port 8 are allocated to the same REs and transmitted. In other words, the DRS of the antenna port 7 and the DRS of the antenna port 8 may be multiplexed and transmitted to a predetermined CDM group, for example, CDM group 1.

Hereinafter, embodiments of the present invention will be described with reference to a general subframe in which a CDM group is configured as shown in FIG. 9 (a). However, the present invention can be applied to the special subframe as well as the general subframe in the same manner.

FIG. 10 illustrates an example in which DRSs for four layers are transmitted through two CDM groups. When two CDM groups are used, two DRSs may be multiplexed and transmitted for each CDM group.

As such, when the OCC having a length of 2 (OCC = 2) is used, two DRSs can be multiplexed in one RE, and the number of layers that can be multiplexed and transmitted in proportion to the number of CDM groups increases. For example, using OCC having a length of 2 (OCC = 2), up to four DRS sequences can be transmitted through two CDM groups.

11 shows a method of multiplexing four DRSs into two CDM groups. In a system supporting MIMO up to 4, up to 4 DRS sequences may be transmitted through 2 CDM groups. That is, two DRSs for each CDM group may be multiplexed by two OCC sequences having a length of 2 (OCC = 2).

Referring to FIG. 11, the virtual antenna ports corresponding to DRSx, DRSy, DRSz, and DRSw are referred to as DRS port X and DRS port Y, DRS port Z, and DRS port W, respectively. In addition, it is assumed that the two OCC sequences of length 2 are [1 1] and [1 -1]. The two OCC sequences correspond to a row direction sequence in the 2 × 2 matrix of FIG. 11.

Referring to FIG. 11, DRSx may be extended by a sequence [1 1], and DRSy may be extended by a sequence [1-1] and allocated to CDM group 1. DRSz can be extended by any one of sequences [1 1] and [1 -1], and DRSw can be extended by the remaining sequences and assigned to CDM group 2.

The RB pair of FIG. 11 includes four DRS symbols 1 to 4 in total. The DRS symbol 1 is assigned a portion of the DRSx extended by the sequence [1 1] and a portion of the DRSy extended by the sequence [1 -1]. For example, DRSx is extended to [1 1] by [1 1] x DRSx = [DRSx DRSx], and DRSy is [1 -1] by [1 -1] × DRSy = [DRSy -DRSy]. Expanded, the first elements DRSx and DRSy may be assigned to DRS symbol 1 and the second elements DRSx and -DRSy may be assigned to DRS symbol 2. That is, (1 × DRSx) + (1 × DRSy) is assigned to DRS symbol 1, and (1 × DRSx) + (− 1 × DRSy) is assigned to DRS symbol 2.

In summary, four DRSs may be allocated to two CDM groups to DRS REs using an orthogonal cover code as follows.

In Table 1, the DRS ports correspond one-to-one to the layer. Therefore, the DRS port index may be utilized as a layer index. Conversely, it is also possible for the layer index to be used as the DRS port index. Antenna ports 7 to 10 may correspond to DRS ports 0 to 3. The DRS for each DRS port is extended by [w _p (0) w _p (1)] and mapped to every pair of REs on that CDM group.

Based on each CDM group, the DRS port assigned to the CDM group and the orthogonal cover code used for the spread of the DRS are summarized as follows.

Referring to Table 1 or Table 2, (+ 1 × DRS0) + (+ 1 × DRS1) and (+ 1 × DRS0) + (-1 × DRS1) are mapped to REs belonging to CDM group 1 in order. (+ 1 × DRS2) + (+ 1 × DRS3) and (+ 1 × DRS2) + (− 1 × DRS3) may be mapped to REs belonging to CDM group 2 in order.

As described above, the OCC used for spreading the DRS by the OCC having a length of 2 and the OCC used for multiplexing to one RE can be simply expressed by the following equation.

Here, the column vector a and the column vector b are OCCs which multiplex a plurality of DRSs, respectively, and each column vector is composed of coefficients multiplied by each DRS when multiplexed to one RE. Each of the row vector x and the row vector y represents an OCC that diffuses one DRS and may be regarded as a spreading factor. Hereinafter, the present invention will be described by referring to an OCC viewed from the viewpoint of diffusion as an OCC viewed from the viewpoint of diffusion OCC and multiplexing.

Hereinafter, for convenience of description, the present invention will be described by expressing a form in which a plurality of DRSs are multiplexed in one RE by a column vector a and a column vector b representing a weight multiplied by each DRS. For example, in FIG. 12 illustrating an example in which two DRSs are multiplexed in one CDM group, an RE denoted by 'a' denotes an RE allocated by multiplying each of the two DRSs by an element of the column vector a. RE denoted RE denotes an RE allocated by two DRSs each multiplied by an element of the column vector b.

Referring to FIG. 12, when multiplexed OCCs are allocated, multiple OCCs used in one OFDM symbol layer are determined, and multiple OCCs are allocated to each RB in the same form even if multiple RBs are allocated for the UE. In this case, since the layers transmitted to one UE are scrambled with the same scrambling sequence, when DRSs are allocated as shown in FIG. 12, a shape in which transmission power is biased may occur in a specific OFDM symbol. Since this results in a biased result, there is a problem that the transmission power cannot be used efficiently. The transmission power of the BS is consistently maximized within the maximum transmission power range regardless of the time point to increase the data transmission rate by the BS. Thus, multiple OCC codes need to be appropriately allocated so that the transmit power is not biased to a particular OFDM symbol, i.e., an even transmit power distribution can appear across the OFDM symbols.

FIG. 13 illustrates an embodiment of the present invention that distributes transmit power evenly over OFDM symbols in rank-2 transmission.

Referring to FIG. 13, in order to prevent DRS sequences from being canceled or sum of DRS sequences in a specific OFDM symbol from being too large, allocation positions of multiplexed OCCs in a frequency domain or a time domain may be swapped.

Meanwhile, FIGS. 14 and 15 show power allocation examples for the DRS RE and the data RE in rank-2 transmission.

Referring to FIG. 14, when the transmission rank is 2, the BS may transmit two layers and two DRSs through two DRS ports. Since the precoder used for the precoding of the two layers is used for the precoding of the two DRSs, the power ratio between the data RE and the DRS RE in each layer is the same.

Accordingly, the UE can know the power ratio between the data RE and the DRS RE in each layer without receiving the separate information from the BS. This is because the power ratio between the data RE and the DRS RE is implicitly signaled to the UE by each DRS port transmitting the signal assigned to the data RE and the signal assigned to the DRS RE at the same power. Accordingly, in the case of rank-2 transmission, the power ratio between layers may be different. Referring to FIG. 15, layer 0 and layer 1 may be transmitted at different powers.

14 and 15, it can be seen that the transmission power per RE as well as the transmission power per layer per RE are constant. That is, power may be uniformly distributed over OFDM symbols in one subframe up to rank-2 transmission. However, in case of rank-3 or higher transmission, the number of layers per data RE and the number of layers per DRS RE may vary within one OFDM symbol according to the length of the OCC and the number of CDM groups. For example, referring to FIG. 10, assuming that a total of four layers correspond one-to-one to antenna ports 7 to 10, four layers are multiplexed in each data RE, but two DRSs are multiplexed in each DRS RE. As a result, the transmission power per layer may vary in the data RE and the DRS RE in the transmission of rank-3 or higher. Accordingly, it may be more difficult to evenly distribute power in OFDM symbols in a subframe in rank-3 or higher transmissions than in rank-2 or lower transmissions. Accordingly, in an LTE-A system capable of transmitting a rank-3 or higher, a power balancing method should be provided to prevent a large fluctuation in transmit power for each OFDM symbol.

Hereinafter, a method of allocating / configuring a DRS so that power can be evenly distributed over OFDM symbols in one subframe. For convenience of description, the present invention will be described with an example of using two CDM groups to support a maximum of eight layers.

In order to transmit DRSs for eight layers through two CDM groups, an OCC having a length of 4 (OCC = 4) may be used as shown in FIG. 15. 16 illustrates an example in which DRSs for layers corresponding to antenna ports 11 to 14 are allocated to two CDM groups. Referring to FIGS. 10 and 16, it can be seen that DRSs for layers corresponding to antenna ports 7 to 14 may be multiplexed and transmitted four by two CDM groups.

17 shows a method of multiplexing eight DRSs into two CDM groups.

In a system supporting MIMO up to 8, up to 8 DRS sequences may be transmitted through two Code Division Multiplexing (CDM) groups. Four DRSs for each CDM group may be multiplexed by four OCC sequences having a length of four. Let DRSx, DRSy, DRSz, and DRSw transmit the virtual antenna ports DRS port X and DRS port Y, DRS port Z, and DRS port W, respectively. In addition, it is assumed that the four OCC sequences of length 4 are [1 1 1 1] and [1 -1 1 -1], [1 1 -1 -1], and [1 -1 -1 1]. The four OCC sequences correspond to a row direction sequence in the 4x4 matrix of FIG. 17.

Referring to Fig. 17, DRSx is extended by a sequence [1 1 1 1], DRSy is extended by a sequence [1 -1 1 -1], and DRSz is extended by a sequence [1 1 -1 -1]. DRSw can be extended by the sequence [1 -1 -1 1] and assigned to CDM group 1. Four DRSs different from DRSx and DRSy, DRSz, and DRSw are extended by [1 1 1 1] and [1 -1 1 -1], [1 1 -1 -1], [1 -1 -1 1] Can be assigned to CDM group 2.

The RB pair of FIG. 17 includes four DRS symbols 1 to 4 in total. DRS symbol 1 contains DRSx and DRSy, DRSz, and DRSw extended by the sequence [1 1 1 1] and [1 -1 1 -1], [1 1 -1 -1], [1 -1 -1 1], respectively. Portions of are assigned. For example, DRSx is extended to [1 1 1 1] by [1 1 1 1] x DRSx = [DRSx DRSx DRSx DRSx], and DRSy is [1 -1 1 -1] by [1 -1 1] -1] × DRSy = [DRSy -DRSy DRSy -DRSy], where DRSz is [1 1 -1 -1] by [1 1 -1 -1] × DRSz = [DRSz DRSz -DRSz -DRSz] DRSw can be extended to [1 -1 -1 1] x DRSw = [DRSw -DRSw -DRSw DRSw] by [1 -1 -1 1]. Among the extended DRS sequences, for example, the first elements DRSx and DRSy, DRSz, and DRSw are assigned to DRS symbol 1, the second elements DRSx and -DRSy, DRSz, and -DRSw are assigned to DRS symbol 2, and the third The elements DRSx and DRSy, -DRSz, and -DRSw may be allocated to DRS symbol 3, and the fourth elements, DRSx and -DRSy, -DRSz, and DRSw. That is, a component of (1 × DRSx) + (1 × DRSy) + (1 × DRSz) + (1 × DRSw) is allocated to DRS symbol 1, and (1 × DRSx) + (− 1 × DRSy) to DRS symbol 2 ) + (1 × DRSz) + (− 1 × DRSw), and the component of DRS symbol 3 is (1 × DRSx) + (1 × DRSy) + (− 1 × DRSz) + (− 1 × DRSw). A component is allocated, and a component of (1 × DRSx) + (− 1 × DRSy) + (− 1 × DRSz) + (1 × DRSw) may be allocated to the DRS symbol 4.

In summary, four DRSs may be allocated to two CDM groups to DRS REs using an orthogonal cover code as follows.

Here, the column vectors a, b, c, and d represent multiplexed OCCs composed of coefficients multiplied by each DRS when a plurality of DRSs are multiplexed into one RE. The row vectors x and y, z, w represent spreading OCCs that spread one DRS. Hereinafter, for convenience of description, the present invention will be described by expressing DRSs multiplexed in one RE with a multiplexed OCC representing a weight multiplied by each DRS in a form in which a plurality of DRSs are multiplexed in one RE.

For reference, in the wireless communication system, the DRS multiplexing of FIG. 11 and the DRS multiplexing of FIG. 17 may be used simultaneously or only one of them may be used. For example, the DRS multiplexing scheme of FIG. 11 is used when the BS multiplexes 1 to 4 layers and is transmitted, and the DRS multiplexing scheme according to FIG. 17 is used when the BS multiplexes and transmits 5 to 8 layers. Can be. As another example, the BS may multiplex 1 to 8 layers using the DRS multiplexing scheme of FIG. 17 and transmit the same. However, in the former case, since the length of the OCC varies according to the total number of layers transmitted by the BS, in order for the UE to detect its own layer using the OCC, the total number of layers transmitted by the BS or multiplexing of layers is determined. Information indicating the length of the used OCC should be signaled to the UE, either implicitly or explicitly.

In the following, embodiments of the present invention are described, in which a DRS is allocated such that transmission power is distributed evenly over OFDM symbols according to a scenario.

<1 CDM group and OCC = 4 assignment>

18 to 22 illustrate embodiments of the present invention for multiplexing DRS with an OCC of length 4 in one CDM group.

Example 1

Referring to FIG. 18, four OCCs may be allocated to four DRS OFDM symbols in the same order in the DRS subcarriers in all RBs. However, in this case, since only one OCC is used among four OCCs in view of one DRS OFDM symbol, power is biased in one DRS OFDM symbol. In case of assigning four multiplexed OCCs having a length of 4 to one CDM group, the following Embodiment 2 to Allocation can be considered for even distribution of OFDM symbol power.

Example 2

Referring to FIG. 19, OCC groups (a, b) may be allocated according to a DRS subcarrier in a slot and OCC groups (c, d) may be swapped and allocated according to a DRS subcarrier in another slot. That is, in Example 2-1, when the OCC is allocated in the order of [a b] in the DRS subcarriers in one slot, the OCC is allocated in the order of [b a], which is the reverse of [a b] in the next DRS subcarrier. According to the second embodiment, two OCCs are allocated in the order of forward-> reverse-> forward-> reverse-> forward-> reverse as DRS subcarriers change in one slot. Accordingly, the allocation pattern of the OCCs is the same for each pair of consecutive RBs. Therefore, even if multiple RBs are allocated for a given UE, the OCC is allocated in the same pattern every two PRBs. However, in the case of allocating the OCC according to the second embodiment, from the viewpoint of one DRS OFDM symbol, only two OCCs are used among the four OCCs. Also from the standpoint of one RB, only two OCCs are used in one RB. That is, the OCC is not evenly distributed within one subframe. For this reason, when the OCC is allocated according to the second embodiment, it is difficult to obtain a result of evenly distributing power over all OFDM symbols in one subframe.

Example 3-1

In order that all OCCs exist on one OFDM symbol, Embodiment 3-1 swaps and allocates an OCC pattern allocated to two slots in one RB in the next RB. Referring to FIG. 20 (a), although all OCCs are not allocated in one RB, all OCCs exist in one OFDM symbol. Therefore, Embodiment 3-1 can obtain even power distribution over OFDM symbols in one subframe compared with Embodiment 2.

However, in Example 3-1, only some OCCs are allocated from one RB's point of view, so that the power rises and falls in accordance with the change of the RB index from the viewpoint of the frequency domain.

Example 3-2

 In order to distribute the OCCs evenly at the RB level, the embodiment 3-2 allocates the four OCCs by changing the directions of the four OCCs according to the DRS subcarriers within one subframe. Referring to FIG. 20 (b), when the OCC is allocated to the first DRS subcarrier in the order of [abcd] in one subframe, the next DRS subcarrier is in the order of [dcba], which is the reverse order of [abcd]. The next DRS subcarrier is allocated to the next DRS subcarrier in the reverse order of the OCC pattern allocated to the previous DRS subcarrier.

According to the embodiment 3-2, all OCCs are allocated in one slot. However, according to the embodiment 3-2, only two OCCs are repeated on one DRS OFDM symbol.

Example 4

In order to distribute the OCC evenly in one RB and one DRS OFDM symbol, Embodiment 4 of the present invention can allocate OCC (a, b, c, d) to one CDM group while swapping according to the DRS subcarriers. Referring to FIG. 21, an OCC is allocated to the first DRS subcarrier of RB #n in one subframe in the order of [a b c d]. In the next DRS subcarrier, the OCC is swapped and allocated in the order of [b c d a], and in the next subcarrier, it is allocated in the order of [c d a b].

According to the fourth embodiment of the present invention, all OCCs are allocated not only to one DRS OFDM symbol but also to one RB. However, according to the fourth embodiment, four OCCs cannot be allocated to the resource region formed by one DRS OFDM symbol and one RB. This is because only three DRS REs are available in a resource region constituted by one DRS OFDM symbol and one RB.

Example 5

In order to distribute the OCCs evenly over a plurality of RBs in each DRS OFDM symbol, Embodiment 5 of the present invention recursively allocates DRS REs in each DRS OFDM symbol of the OCCs. Referring to FIG. 22, four DRS OFDM symbols in one subframe include a DRS and three DRS REs may be used for each RB in each OFDM symbol. The starting OCC, which is the first allocated OCC in one OFDM symbol, is changed according to the OFDM symbol index so that all OCCs are located on one DRS subcarrier in one subframe.

<2 CDM groups and OCC = 4 assignments>

23 to 30 illustrate embodiments of the present invention for multiplexing DRS with an OCC of length 4 in two CDM groups. When assigning four multiplexed OCCs of length 4 to each of two CDM groups, the following embodiments may be considered for even distribution of OFDM symbol power. Embodiments 6 to 8 to be described later may be used in combination with any one of the embodiments 1 to 5 described above.

Example 6

The simplest way to assign four OCCs to each of the two CDM groups is to repeat the OCC allocation pattern in one CDM group to the second CDM group. For example, referring to FIGS. 21 and 23, assuming that Embodiment 4 is adopted in CDM group 1, OCCs may be allocated to CDM group 2 in the same pattern as that in which OCCs are assigned to CDM group 1.

On the other hand, if the OCC is allocated to two adjacent DRS subcarriers according to Embodiment 5, the spreading OCC and the DRS port for the CDM group 1 and the CDM group 2 have the following correspondence, for example.

In Table 3, the DRS port represents a virtual antenna port for transmitting the DRS among the antenna ports. DRS ports correspond one-to-one to a layer. For example, antenna ports 7-14 may correspond to DRS ports 0-7. In Table 5, DRS port 0 to DRS port 7 may correspond one-to-one to layer 0 to layer 7. In this case, the spreading OCC for each DRS port becomes a spreading OCC for each layer. The DRS for each DRS port (or each layer) is extended by [w _p (0) w _p (1) w _p (2) w _p (3)], for every four consecutive DRS REs on that CDM group. Is mapped to.

Based on each CDM group, the DRS port allocated to the CDM group and the spreading orthogonal cover code of the layer corresponding to the DRS port in two DRS subcarriers are summarized as follows.

In Table 4, w _p (l ') means a weight multiplied by one layer in the DRS OFDM symbol l'. A vector consisting of weights of DRS ports allocated to one CDM group may be viewed as a multiplexed OCC. For example, referring to Table 4, w _p (0) for DRS ports 0, 1, 4, and 6 assigned to CDM group 1, and for DRS ports 2, 3, 5, and 7 assigned to CDM group 2. Since w _p (0) is +1, +1, +1, +1, the multiplexed OCC assigned to the starting DRS OFDM in the starting DRS subcarrier of CDM group 1 corresponds to a of [+1 +1 +1 +1]. do. Referring to FIG. 24, multiplexed OCCs are allocated to four DRS OFDM symbols in a start DRS subcarrier of each CDM group in the order of [abcd].

Example 7

Embodiment 7 swaps the OCC allocation pattern for the first CDM group in a slot-wise manner and allocates the same to the second CDM group. Referring to FIG. 24 (a), OCCs (a, b, c, d) are allocated to CDM group 1 while being swapped by one OCC according to the DRS subcarriers according to the fourth embodiment. Each DRS subcarrier of the CDM group 2 is assigned an OCC pattern allocated to an adjacent DRS subcarrier of the CDM group 1 by two OCCs in the slot direction. According to Embodiment 7, if the starting OCC pattern for one CDM group assigned to DRS OFDM symbols is [a b c d], the starting OCC pattern for another CDM group is [c d a b].

Example 8

In the eighth embodiment, the OCC allocation pattern for the first CDM group is swapped in the slot-wise manner and allocated to the second CDM group, but is allocated by swapping by one OCC. Referring to FIG. 25 (a), OCCs (a, b, c, d) are allocated to CDM group 1 while being swapped by one OCC according to the DRS subcarriers according to the fourth embodiment. Each subcarrier of CDM group 2 is allocated with an OCC pattern allocated to adjacent DRS subcarriers of CDM group 1 by one OCC in the slot direction. According to Embodiment 8, if the starting OCC pattern for one CDM group allocated to DRS OFDM symbols is [a b c d], the starting OCC pattern for another CDM group is [d a b c].

24 (a) and 25 (a), OCC patterns allocated to two CDM groups may be swapped with each other in the two CDM groups. 24 (b) and 25 (b) show embodiments in which the OCC allocation pattern of CDM group 1 and the OCC allocation pattern of CDM group 2 are swapped with each other, respectively, in FIGS. 24 (a) and 25 (a).

In Embodiments 1-8 described above, the scrambling sequence may be the same for all DRS ports or may be different for each DRS port group and / or for each DRS port.

23 to 25 of Embodiments 6 to 8 are examples of the case where OCC is assigned to the first CDM group according to Embodiment 4 (corresponding to FIG. 21). A method of allocating OCC to two CDM groups is illustrated. Assuming that an OCC is allocated to the first CDM group according to the fifth embodiment, the OCC patterns allocated to the two CDM groups according to the sixth to eighth embodiments may be represented, for example, as shown in FIGS. 26 to 28. . 26 to 28, the OCC allocation pattern of CDM group 1 and the OCC allocation pattern of CDM group 2 may be swapped with each other.

Meanwhile, in the seventh embodiment, in assigning OCCs to two CDM groups, when OCCs are assigned to one DRS subcarrier in one CDM group in [abcd] order, two embodiments are provided for DRS subcarriers in another CDM group adjacent to the DRS subcarrier. As many OCCs are allocated in order of shifted [cdab]. In the eighth embodiment, in assigning OCCs to two CDM groups, when assigning OCCs to one DRS subcarrier of one CDM group in [abcd] order, two DRS subcarriers of another CDM group adjacent to the DRS subcarrier are allocated. Assign OCC in the order of shifted [bcda]. That is, in the seventh embodiment and the eighth embodiment, OCCs allocated to two adjacent DRS subcarriers have an offset of a predetermined number. If this is called an OCC offset, the sixth embodiment may have an OCC offset of 0, the seventh embodiment may have an OCC offset of two, and the eighth embodiment may have an OCC offset of one. Assuming that OCCs are allocated to the starting DRS subcarriers in CDM group 1 in the order of [a b c d], the method of allocating OCCs according to the sixth to eighth embodiments will be described with reference to FIG. 29. In FIG. 29, offset-N means that the number of OCCs in the CDM group is left by N different from each other. In particular, FIG. 29 shows the case where N is 2. 28 shows a case where the OCC pattern of CDM group 1 is allocated to CDM group 2 such that there is one difference to the left. However, as shown in FIG. 30, the OCC patterns of CDM group 1 may be assigned to CDM group 2 such that there is one difference to the right, that is, three to the left. If the OCC offset is 2, the same result will be obtained no matter which direction is shifted.

Meanwhile, the OCC offset of the second CDM group with respect to the first CDM group may be a fixed value or a value configured by the BS. In addition, the OCC offset may be defined according to the frequency position so that the OCC can be more evenly distributed. It is also possible that the OCC offset is defined to vary with rank and / or transmission mode.

An embodiment in which an OCC pattern allocated to one DRS subcarrier of the first CDM group and an OCC pattern allocated to the DRS subcarrier of the second CDM group adjacent to the DRS subcarrier have an offset of a predetermined size are described. It can be applied regardless. That is, in the sixth embodiment to the eighth embodiment, it is assumed that an OCC is allocated to the first CDM group according to the fourth embodiment, and an embodiment in which the OCC is allocated to have a predetermined OCC between two CDM groups has been described. The same applies to the fifth embodiment.

According to an embodiment of the present invention in which an OCC is allocated to have a predetermined OCC offset between two CDM groups, the correspondence of the spreading OCC and the DRS port for CDM group 1 and CDM group 2 allocated to two adjacent DRS subcarriers may be, for example. For example, it can be expressed as follows. Table 5 illustrates the case where the offset is 2.

Based on each CDM group, the DRS port allocated to the CDM group and spreading orthogonal cover code of the layer corresponding to the DRS port in two DRS subcarriers are rearranged as follows.

In Table 5, DRS port 0 to DRS port 7 may correspond one-to-one to layer 0 to layer 7. In this case, the spreading OCC for each DRS port becomes a spreading OCC for each layer.

In Tables 5 and 6, w _p (l ') means a weight multiplied by one layer in the DRS OFDM symbol l'. The DRS of one DRS port is extended to a spreading OCC [w _p (0) w _p (1) w _p (2) w _p (3)], corresponding to four DRS OFDM symbols in one subframe. Meanwhile, a vector composed of weights of DRS ports allocated to one CDM group may be regarded as a multiplexed OCC. For example, referring to Table 6, w _p (0) for DRS ports 0, 1, 4, 6 assigned to CDM group 1 is +1, +1, +1, +1, The multiplexed OCC allocated to the starting DRS OFDM in the starting DRS subcarrier corresponds to a, which is [+1 +1 +1 +1]. Since w _p (0) for DRS ports 2, 3, 5, and 7 assigned to CDM group 2 is +1, +1, -1, -1, it is assigned to the starting DRS OFDM within the starting DRS subcarrier of CDM group 2. The multiplexed OCC corresponds to c, which is [+1 +1 +1 +1].

31 shows other examples according to an embodiment of the present invention for allocating an OCC to have a predetermined OCC offset between two CDM groups. In particular, FIG. 31 (a) illustrates a case in which an OCC is allocated such that an OCC offset becomes 2 in another CDM group when the OCC is allocated to one CDM group according to Embodiment 1 (see FIG. 18), and FIG. 31. (b) illustrates the case where the OCC is allocated such that the OCC offset is 2 in the other CDM group when the OCC is allocated to the CMD group according to Embodiment 4 (see FIG. 20 (b)).

Referring to FIG. 31 (a), [a b c d] is sequentially assigned to each DRS subcarrier belonging to CDM group 1 with a as a starting OCC. Each subcarrier belonging to the CDM group 2 is assigned an OCC pattern [a b c d] allocated to the DRS of the CDM group 1 and a [c d a b] having an offset of 2 in that order. This may be expressed as an equation as follows.

Here, w _p (i) is given as in Table 5. k '= 0 indicates a DRS port assigned to CDM group 1 and k' = 1 indicates a DRS port assigned to CDM group 2. The DRS ports 0 to 7 may correspond to the antenna ports 7 to 14 of FIGS. 10 and 16.

When OCCs are allocated to one CDM group according to Embodiment 1, since only one OCC is allocated per CDM group on one DRS OFDM symbol, only two OCCs are used on one DRS OFDM symbol for two CDM groups. OCC may be allocated as shown in FIG. 31 (b) so that all OCCs exist on one DRS OFDM symbol for two CDM groups.

Referring to FIG. 31 (b), [abcd] is sequentially assigned to one DRS subcarrier belonging to CDM group 1 with a as the starting OCC, and the next DRS subcarrier is assigned to [dcba] in the reverse order of [abcd]. Is assigned. That is, the order of the OCC assigned to one DRS subcarrier and the order of the OCC assigned to the next DRS subcarrier are in the reverse order. On the other hand, each DRS subcarrier belonging to CDM group 2 is allocated an OCC to have an offset equal to 2 and an OCC pattern allocated to an adjacent DRS subcarrier among subcarriers belonging to CDM group 1. For example, if the OCC is allocated to the DRS subcarriers of CDM group 1 in the order of [a b c d], the OCC is allocated to the adjacent DRS subcarriers of the CDM group 2 in order of [c d a b]. If the OCC is allocated to the DRS subcarriers of CDM group 1 in the order of [d c b a], the OCC is allocated to the DRS subcarriers of the CDM group 2 adjacent thereto in the order of [b a d c]. According to this embodiment, in CDM group 1, [a b c d] and [d c b a] are alternated each time the DRS subcarriers are changed, and in CDM group 2, [c d a b] and [b a d c] are alternated every time the DRS subcarriers are changed.

This may be expressed as an equation as follows.

Here, w _p (i) is given as in Table 5. k '= 0 indicates a DRS port assigned to CDM group 1 and k' = 1 indicates a DRS port assigned to CDM group 2. The DRS ports 0 to 7 may correspond to the antenna ports 7 to 14 of FIGS. 10 and 16.

If the OCC is allocated to one CDM group and the OCC is allocated to have one offset and two CDM groups according to the embodiment 3-2, all four OCCs are used on one DRS OFDM symbol for two CDM groups. There is an advantage that it can.

On the other hand, when OCC is allocated to have a predetermined OCC offset between CDM groups, the number of OCC pairs that can be allocated to two adjacent DRS subcarriers belonging to different CDM groups is limited to two. For example, referring to FIG. 31, if the OCC offset is 2, only OCC pairs that can be allocated to two adjacent DRS subcarriers belonging to different CDM groups are (a, c) and (b, d).

32 to 38 are diagrams illustrating the advantages of OCC being allocated such that two CDM groups have a predetermined OCC offset, in accordance with embodiments of the present invention.

Assume that eight DRS ports transmit corresponding layers and DRS in one-to-one correspondence to eight layers. Assume that an OCC is allocated to two CDM groups as shown in FIG. 32. When OCC is mapped as shown in FIG. 32, when a common scrambling sequence is applied to all layers, power is increased in a specific OFDM symbol, or a DRS signal is canceled in a DRS subcarrier of a predetermined OFDM symbol so that the power of the predetermined OFDM symbol is low. Losing problems occur.

If the DRS port corresponding to layer m is a DRS port m, when multiple OCCs are allocated as shown in FIG. 32, each layer may be spread as shown in FIG. 33 (a). In FIG. 33, s _i represents the position of a DRS OFDM symbol in one subframe. In view of one layer, s _i and s _{i +1} , s _{i +2} , and s _{i +3} all have the same value. In FIG. 33, CDM # 1 represents CDM group 1 and CDM # 2 represents CDM group 2. In FIG.

Referring to FIG. 33, the DRS of each layer spread by the corresponding spreading OCC is multiplied by the precoding matrix W by the precoder 304 to the resource element mapper 305 corresponding to transmit antennas # 0 to # 7. Is distributed. This can be expressed as follows.

Referring to FIG. 33 (b), it can be seen that the transmit antenna # 0 needs very high power in the DRS OFDM symbol 0, and the transmit antenna # 4 needs very high power in the DRS OFDM symbol 2. For two PRBs in one subframe, a power ratio between OFDM symbols allocated to antenna # 0 is calculated as shown in FIG. 34. FIG. 34 shows that power allocated to data RE is 1, and power per RE is calculated according to OFDM symbols over two PRBs. Referring to FIG. 34, it can be seen that the peak power is generated in the first DRS OFDM symbol in antenna # 0, and the power is lower than the OFDM symbols in which the DRS is not allocated because power is not allocated in the remaining DRS OFDM symbols.

Meanwhile, when the OCC is allocated to have a predetermined offset between two CDM groups according to the present invention, for example, when the OCC is allocated as shown in FIG. 31 (a), the DRS distributed from antenna # 0 to antenna # 7 is It can be expressed as:

If the powers of the symbols distributed to antenna # 0 among the antenna specific symbols distributed according to Equation 7 are represented in two RB intervals in one subframe, they may be expressed as shown in FIG. 35. Compared to FIG. 34 in which the OFDM symbol power varies from -3.01 dB to 3.98 dB, the power change according to OFDM symbols is reduced from -3.01 dB to 2.2 dB according to FIG. The power for the symbols distributed to antenna # 0 among the antenna-specific symbols distributed according to Equation 7 may be represented as shown in FIG. 36 when represented in one RB period in one subframe.

On the other hand, if the OCC is allocated as shown in FIG. 31 (b), power can be more evenly distributed over OFDM symbols as shown in FIG. 36.

Example 9

On the other hand, phase offset may be used for power unbalance cancellation. Embodiment 9 of the present invention, which applies a phase offset to at least one of the CDM groups to balance power among OFDM symbols, may be used in combination with any one of the above-described embodiments of applying an OCC offset to eliminate power imbalance. Can be. Alternatively, only the phase offset may be used without applying the OCC offset.

37 and 38 illustrate embodiments of the present invention using phase offset.

FIG. 37 shows an example in which the OCC offset is not used, that is, the OCC offset is 0, and two phase offsets are alternately applied only to the CDM group 2. Referring to FIG. 37A, according to the DRS subcarriers, two phase offsets θ _a and θ _b are alternately multiplied by the DRS multiplexed on the CDM group 2.

38 shows an example in which the OCC offset is set to 2 and two phase offsets are alternately applied to the CDM group 2. In particular, FIG. 38 illustrates a case in which an OCC is allocated as shown in FIG. 31 (b), and two right-sided offsets θ _a and θ _b are alternately multiplied by a DRS multiplexed onto CDM group 2 according to a DRS subcarrier.

For example, when θ _a and θ _b are 0 and π, respectively, as shown in FIGS. 37B and 38B, DRSs multiplexed onto CDM group 2 have 1 and −1 depending on the DRS subcarriers. Multiply alternately.

Example 10

It is possible to apply a phase offset, but different phase offsets depending on the DRS port. In the ninth embodiment, the same phase offset is applied to each DRS subcarrier to all the DRS ports assigned to one CDM group, whereas in the tenth embodiment, the phase offset is applied according to the DRS port. That is, according to the tenth embodiment of the present invention, different phase offsets are multiplied for each layer on the same DRS subcarrier. In addition, Embodiment 10 of the present invention applies the same phase offset to layers and corresponding DRSs that are spread by the same diffusion OCC. For reference, in Embodiment 10 of the present invention, the phase offset may be defined such that the product of the predetermined number and the DRS subcarriers per RB is an integer multiple of 2 so that the same OCC pattern may be repeated for each predetermined number of RBs.

39 illustrates a phase offset according to DRS subcarriers for each DRS port. In particular, FIG. 39 illustrates a case in which a layer and a DRS of each DRS port are spread by a spreading OCC according to Table 3. In FIG. 39, subcarriers 0, 5, and 10 are logical indexes of subcarriers belonging to one RB and correspond to DRS subcarriers 0, 1, and 2. FIG.

Referring to FIG. 39, a phase offset is applied to a layer corresponding to DRS ports 0 and 2 and a DRS in the same pattern regardless of a CDM group, and a layer corresponding to DRS ports 1 and 3 and a DRS is identical to a layer regardless of a CDM group. The phase offset is applied to the pattern, the layer corresponding to DRS ports 4 and 5, and the DRS is applied to the phase with the same pattern regardless of the CDM group, and the layer corresponding to the DRS ports 6 and 7 and the CDM group to the DRS. The phase offset is applied in the same pattern without. Referring to FIG. 39 (a), for each DRS port, the phase offset between the DRS subcarriers is 0. Referring to FIG. 39 (b), for each DRS port, the phase offset between the DRS subcarriers is π. to be. 39 (c) and 39 (d), ω is e ^{j (π / 3)} , and in the case of FIG. 39 (c), the phase offset between the DRS subcarriers is π / 3 for each DRS port. In the case of 39 (d), the phase offset between the DRS subcarriers is −π / 3 for each DRS port.

40 to 42 illustrate the advantages of applying a phase offset for each layer according to a DRS subcarrier according to embodiments of the present invention.

FIG. 40 illustrates a DRS signal distributed to antenna # 0 in two RB sections in one subframe when the layer-based phase offset is applied without applying the OCC offset between CDM groups. In FIG. 40, the phase offset according to the DRS subcarrier illustrated in FIG. 39 is used for each layer, and the same matrix as the precoding matrix illustrated in FIG. 34 is used for the precoding matrix.

Referring to FIG. 41, if a phase offset is applied according to a DRS subcarrier for each layer, an even power distribution may be obtained over OFDM symbols over two RB intervals. However, according to the present embodiment, the phase offset must be varied according to the DRS subcarrier, and different offsets must be applied for each layer, and thus, a process of multiplexing a plurality of layers is complicated. In other words, the present embodiment requires processors 400a and 400b having higher performance in both the transmitter and the receiver, as compared to embodiments regarding power balancing using OCC offsets between CDM groups.

On the other hand, as shown in Figure 41, even power distribution can be obtained over the OFDM symbols over an even number of RB intervals. However, power odds still exist over odd RB intervals as shown in FIG. For an odd number of RBs, phase offset alone does not provide perfect power balance.

FIG. 43 is a diagram for illustrating an advantage when an OCC is allocated such that two CDM groups have a predetermined OCC offset, and a phase offset is applied for each layer according to a DRS subcarrier according to embodiments of the present invention.

As can be seen in FIG. 43, when the OCC offset and the phase offset are applied together, even power distribution can be obtained even for the odd RB.

The BS of the present invention may spread the DRS of each layer to the corresponding spreading OCC based on the allocated OCC according to any one of the above embodiments. The BS outputs the spread DRS as an antenna specific symbol by precoding the spread DRS using a predetermined precoding matrix. For example, referring to FIG. 33, the BS spreads some or all of layers 0 through 8 to a corresponding Walsh code, and precodes the precoding matrix W to some or all of transmit antennas # 0 to # 7. Can be distributed. The distributed signal is converted into an OFDM signal and transmitted to the UE (s) in coverage of the BS.

BS processor 400b according to the present invention may allocate one or more layers to a given subframe. In this case, the BS processor 400b may allocate a DRS for demodulation of each layer to the predetermined subframe. The BS transmitter 100b transmits the allocated layer together with the corresponding DRS under the control of the BS processor 400b.

The BS processor 400b according to the present invention may control the BS transmitter 100b to transmit the DRS through one or more CDM groups according to any one of the above-described embodiments. To this end, the BS processor 400b according to the present invention may be configured to allocate a spreading OCC to each layer according to any one of the above-described embodiments. The BS processor 400b controls the BS transmitter 100b to spread the corresponding DRS (s) of the layer (s) to be transmitted together to the corresponding spreading OCC, and assign the spread DRS to the corresponding CDM group. The BS transmitter 100b may transmit the spread DRS through the corresponding CDM group under the control of the BS processor 400b. The resource element mapper 305 maps each part of the spread DRS sequence to a DRS RE in the corresponding CDM group under the control of the BS processor 400b.

That is, the BS processor 400b according to the present invention may allocate the multiplexed OCC to one or more CDM groups according to any one of the above-described embodiments. The BS transmitter 400b may multiplex a plurality of DRSs into the one or more CDM groups under the control of the BS processor 400b. In multiplexing a plurality of DRSs in one DRS RE, the BS processor 400b multiplexes the plurality of DRSs using a multiplexed OCC allocated to the DRS RE. The BS transmitter 400b transmits the multiplexed DRS through the DRS RE.

Under the control of the BS processor 400b, the BS transmitter 100b spreads the DRS of each layer, maps each element of the spread DRS to one DRS RE, and maps the spread DRS to corresponding DRS RE (s). ) Can be sent. The layer element (s) and corresponding DRS (s) mapped to one subframe by the resource element mapper 305 are converted into an OFDM signal by the OFDM / SC-FDM signal generator 306 to be a UE in coverage of the BS. Is sent to (s).

The UE receives an OFDM signal from the BS and restores the OFDM signal to an antenna specific symbol. The UE reconstructs the recovered antenna specific symbol into one or more layer signals using the precoding matrix W used in the BS. The precoding matrix W may be predetermined between the UE and the BS, or may be determined by the UE or BS selecting an appropriate W and signaling to the BS or the UE.

The UE may detect a layer and / or DRS for the UE among the reconstructed layer signals. For example, referring to FIG. 33, the UE may restore the received OFDM signal to a specific DRS RE signal as shown in FIG. 33B by restoring the received OFDM signal to an antenna specific symbol. The UE reconstructs the recovered signal into one or more layer signals using a precoding matrix W. When the BS transmits a plurality of layers, a plurality of DRSs exist in a multiplexed form in the DRS RE. The UE may obtain a value corresponding to an integer multiple of the corresponding layer signal by multiplying the multiplexed signal by a spreading OCC used for spreading of layers for the UE.

For example, referring to FIG. 33 (a), in one DRS subcarrier of CDM group 1 (CDM # 1), spread DRSs of layer 0 and layer 1, layer 4, and layer 6 are received over four DRS OFDM symbols. Suppose you did. Assuming that DRS i is a reference signal for layer i, the UE receives signals through CDM group 1 such that (DRS 0) × [+1 +1 +1 +1] + (DRS 1) × [+1 −1 +1 -1] + (DRS 4) x [+1 +1 -1 -1] + (DRS 6) x [+1 -1 -1 +1]. If the layer transmitted to the UE is layer 1, the UE may extract DRS 1 by multiplying the signal by [+1 -1 +1 -1] ^T which is a spreading OCC used for multiplexing of layer 1. The UE may demodulate a corresponding layer by using layer-specific DRS for the UE.

The UE receiver 300a according to the present invention may receive one or more layers from the BS. In addition, the UE receiver 300a may receive one or more DRS from the BS, multiplexed in one or more CDM groups and transmitted to the UE according to any one of the above-described embodiments of the present invention. The UE processor 400a controls the UE receiver 300a to restore the OFDM signal received by the UE to a baseband signal. Under the control of the UE processor 400a, the UE receiver 300a demaps the baseband signal from resource elements to generate antenna specific symbols. Under the control of the UE processor 400a, the UE receiver 300a reconstructs the antenna specific symbols into the one or more layers transmitted by the BS using the precoding matrix used by the BS for precoding. In order to demodulate one of the one or more layers transmitted for the UE, under the control of the UE processor 400a, the UE receiver 300a detects the DRS of the layer using a spreading OCC corresponding to the layer. do. In this case, the diffusion OCC used to detect the layer is determined according to the embodiment of the present invention described above. The UE processor 400a may control the UE receiver 300a to demodulate the layer using the detected DRS.

In the above-described embodiments, the present invention has been described by taking a method of multiplexing an OCC having a length of 4 into two CDM groups as an example. However, embodiments of the present invention may be used even when multiplexing OCCs having different lengths into multiple CDM groups It can be applied as well. For example, even when multiplexing OCCs longer than 4 into one or two CDM groups, or multiplexing OCCs longer than 4 into three or more CDM groups, by applying embodiments of the present invention, OFDM symbols Power balance can be achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the present invention. Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Embodiments of the present invention may be used in a base station or user equipment or other equipment in a wireless communication system.

100a, 100b: transmitter 200a, 200b: memory
300a, 300b: receiver 400a, 400b: processor
500a, 500b: antenna
301: scrambler 302: modulation mapper
303: layer mapper 304: precoder
305: resource element mapper 306: OFDM / SC-FDM signal generator

Claims (16)

In the method of transmitting a plurality of reference signals (RS) to the user equipment in the base station in a wireless communication system,
Spreading the plurality of RSs using spreading orthogonal sequences; And
Transmitting the plurality of RSs through at least one of a first CDM group and a second CDM group, which are two Code Division Multiplexing (CDM) groups,
RS transmitted in the first CDM group among the plurality of RSs is spread according to one of spreading orthogonal sequences defined as shown in the following table and transmitted through subcarriers belonging to the first CDM group.

,
The RS transmitted in the second CDM group among the plurality of RSs is spread according to any one of spreading orthogonal sequences defined as shown in the following table and transmitted through subcarriers belonging to the second CDM group.

,
Reference signal transmission method. The method of claim 1,
The plurality of RSs are spread according to the following table and transmitted through at least one of the first CDM group and the second CDM group,

,
Here, RS 0 to RS 7 correspond one-to-one to eight antenna ports for transmission of user equipment-specific RS,
Reference signal transmission method. The method according to claim 1 or 2,
The plurality of RSs are represented by multiplexed orthogonal sequences a and b, c, and d defined as follows.

,
Are multiplexed and transmitted in at least one of the first CDM group and the second CDM group,
RS 0 and RS 1, RS 4, RS 6 are

,
Multiplexed to the first CDM group by using RS 2 and RS 3, RS 5, RS 7

Multiplexed into the second CDM group by using. The method of claim 3,
Wherein the plurality of RSs are multiplexed onto two adjacent subcarriers belonging to the first CDM group and the second CDM group, respectively, by one of the multiplexed orthogonal sequence pairs of (a, c) or (b, d),
Reference signal transmission method. In the wireless communication system, a user equipment receives a plurality of reference signals (RS) from a base station,
Receiving the plurality of RSs from the base station through at least one of a first CDM group and a second CDM group, which are Code Division Multiplexing (CDM) groups; And
Detecting a first RS for the user equipment from the plurality of RSs using a first spreading orthogonal sequence used for spreading the RS of the user equipment;
The first spreading orthogonal sequence is any one of spreading orthogonal sequences defined as shown in the following table when the first RS is received through the first CDM group.

,
When the first RS is received through the second CDM group, it is any one of spreading orthogonal sequences defined as shown in the following table.

,
Receiving reference signal. The method of claim 5,
The user equipment detects the plurality of RSs received through at least one of the first CDM group and the second CDM group according to the following table.

,
Here, RS 0 to RS 7 correspond one-to-one to eight antenna ports for transmitting user equipment-specific reference signals.
Receiving reference signal. The method according to claim 5 or 6,
The plurality of RSs are represented by multiplexed orthogonal sequences a and b, c, and d defined as follows.

,
Received by the user equipment multiplexed in at least one of the first CDM group and the second CDM group,
RS 0 and RS 1, RS 4, RS 6 are

,
Multiplexed to the first CDM group by using, RS 2 and RS 3, RS 5, RS 7 is

Multiplexed to the second CDM group using
Receiving reference signal. The method of claim 7, wherein
Wherein the plurality of RSs are multiplexed with one of multiplexed orthogonal sequence pairs of (a, c) or (b, d) to two adjacent subcarriers belonging to the first CDM group and the second CDM group, respectively;
Receiving reference signal. In the base station transmits a plurality of reference signals (RS) to the user equipment in a wireless communication system,
transmitter; And
A processor configured to control the transmitter;
The processor is configured to spread the plurality of RSs using spreading orthogonal sequences and to distribute the plurality of RSs through at least one of a first CDM group and a second CDM group, which are two Code Division Multiplexing (CDM) groups. Control the transmitter to transmit,
The processor spreads the RS transmitted from the first CDM group among the plurality of RSs according to any one of a spreading orthogonal sequence defined as shown in the following table, and controls the transmitter to spread the spread RS to the first CDM group. Configured to transmit on subcarriers belonging to

,
The RS transmitted from the second CDM group among the plurality of RSs is spread according to one of spreading orthogonal sequences defined as shown in the following table, and the transmitter is controlled and transmitted through a subcarrier belonging to the second CDM group. Configured to

,
Base station. 10. The method of claim 9,
The processor is configured to spread the plurality of RSs according to the following table, and to control the transmitter to transmit through at least one of the first CDM group and the second CDM group.

,
Here, RS 0 to RS 7 correspond one-to-one to eight antenna ports for transmitting user equipment-specific reference signals.
Base station. 11. The method according to claim 9 or 10,
The processor uses multiplexed orthogonal sequences a and b, c, d defined as

,
Multiplexing the plurality of RSs into at least one of the first CDM group and the second CDM group;
RS 0 and RS 1, RS 4, RS 6 are

,
By multiplexing to the first CDM group, and RS 2 and RS 3, RS 5, RS 7

Configured to multiplex to the second CDM group by
Base station The method of claim 11,
The processor is further configured to multiplex the plurality of RSs to two adjacent subcarriers belonging to the first CDM group and the second CDM group, respectively, by one of the multiplexed orthogonal sequence pairs of (a, c) or (b, d). Configured,
Base station. In the user equipment receiving a plurality of reference signals (RS) from the base station in a wireless communication system,
receiving set; And
A processor configured to control the receiver,
The receiver is configured to receive from the base station via at least one of a first CDM group and a second CDM group, which are Code Division Multiplexing (CDM) groups;
The processor is configured to detect a first RS for the user equipment from the plurality of RSs using a first spreading orthogonal sequence used for spreading the RS of the user equipment,
The first spreading orthogonal sequence is any one of spreading orthogonal sequences defined as shown in the following table when the first RS is received through the first CDM group.

,
When the first RS is received through the second CDM group, it is any one of spreading orthogonal sequences defined as shown in the following table.

,
User device. The method of claim 13,
The processor is configured to detect the plurality of RSs received through at least one of the first CDM group and the second CDM group based on the following table:

,
Here, RS 0 to RS 7 correspond one-to-one to eight antenna ports for user equipment-specific RS transmission.
User device. The method according to claim 13 or 14,
The plurality of RSs are represented by multiplexed orthogonal sequences a and b, c, and d defined as follows.

,
Received by the receiver multiplexed in at least one of the first CDM group and the second CDM group,
RS 0 and RS 1, RS 4, RS 6 are

,
Multiplexed to the first CDM group by using, RS 2 and RS 3, RS 5, RS 7 is

Multiplexed to the second CDM group using
User device. 16. The method of claim 15,
The plurality of RSs are received by the receiver while being multiplexed with one of multiplexed orthogonal sequence pairs of (a, c) or (b, d) to two adjacent subcarriers belonging to the first CDM group and the second CDM group, respectively. felled,
User device.

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