WO2010058943A2 - Method and apparatus for transmitting reference signals in radio communication system - Google Patents

Abstract

The present invention provides a method and an apparatus for transmitting reference signals in a radio communication system. Said method comprises the steps of generating orthogonal frequency division multiplexing (OFDM) symbols for data and reference signal elements, and transmitting said OFDM symbols to a base station. The present invention provides an effective method for transmitting reference signals in a radio communication system.

Description

Method and apparatus for transmitting reference signal in wireless communication system

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

The next generation multimedia wireless communication system, which is being actively researched recently, requires a system capable of processing and transmitting various information such as video, wireless data, etc., out of an initial voice-oriented service. The purpose of a wireless communication system is to enable a large number of users to communicate reliably regardless of location and mobility. However, a wireless channel is a Doppler due to path loss, noise, fading due to multipath, intersymbol interference (ISI), or mobility of UE. There are non-ideal characteristics such as the Doppler effect. Various techniques have been developed to overcome the non-ideal characteristics of the wireless channel and to improve the reliability of the wireless communication.

In general, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available radio resources. Examples of radio resources include time, frequency, code, transmit power, and the like. Examples of multiple access systems include time division multiple access (TDMA) systems, code division multiple access (CDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single carrier frequency (SC-FDMA). division multiple access) system.

SC-FDMA may have almost the same complexity as OFDMA, but may have a low peak-to-average power ratio (PAPR) or cubic metric (CM). When the PAPR is low, the transmitter can efficiently transmit data avoiding the non-linear distortion interval of the power amplifier. Since low PAPR is beneficial to the UE in terms of transmission power efficiency, SC-FDMA is a 3rd Generation Partnership Project (3GPP) TS 36.211 V8.2.0 (2008-03) "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E- UTRA); physical channels and modulation (Release 8) ", is adopted for uplink transmission in 3GPP long term evolution (LTE).

In a wireless communication system, it is necessary to estimate an uplink channel or a downlink channel for data transmission / reception, system synchronization acquisition, channel information feedback, and the like. Channel estimation refers to a process of restoring a transmission signal by compensating for a distortion of a signal caused by a sudden environmental change due to fading. In general, for channel estimation, a reference signal (RS) known to both the transmitter and the receiver is required. The reference signal refers to a signal that is known to both the transmitter and the receiver used for channel estimation for demodulating data, and is also called a pilot.

Increasing the reference signal overhead can improve channel estimation performance. The reference signal overhead may be defined as the ratio of the number of subcarriers transmitting the reference signal to the total number of subcarriers. However, when the reference signal overhead is large, the channel estimation performance gain may be increased, but there is a problem in that the amount of data transmission is reduced. Reduced data throughput results in link throughput loss. Accordingly, there is a need to provide a method and apparatus for optimally transmitting a reference signal in consideration of a trade-off between channel estimation performance and link throughput loss.

An object of the present invention is to provide a method and apparatus for transmitting a reference signal in a wireless communication system.

In one aspect, there is provided a reference signal transmission method performed by a terminal in a wireless communication system. The method includes generating orthogonal frequency division multiplexing (OFDM) symbols for data and reference signal elements and transmitting the OFDM symbols to a base station.

In another aspect, there is provided a terminal including a radio frequency (RF) unit for transmitting a radio signal and a data processor connected to the RF unit to generate an OFDM symbol for data and reference signal elements, and transmit the OFDM symbol. do.

Provided are a method and apparatus for transmitting a reference signal for improving channel estimation performance in a wireless communication system. Thus, overall system performance can be improved.

1 illustrates a wireless communication system.

2 illustrates a structure of a radio frame in a 3rd generation partnership project (3GPP) long term evolution (LTE).

3 shows an example of a resource grid for one uplink slot in 3GPP LTE.

4 shows an example of a structure of an uplink subframe in 3GPP LTE.

5 is a flowchart illustrating an example of a data transmission method.

6 illustrates an example of a radio resource in which data is transmitted in the case of a normal cyclic prefix (CP).

7 illustrates an example of a radio resource for transmitting data in the case of an extended CP.

8 is a block diagram illustrating an example of a transmitter structure.

9 is a block diagram illustrating an example of a structure of a data processor.

10 illustrates an example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

11 shows another example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

12 is a block diagram illustrating another example of a data processing unit structure.

13 is a block diagram illustrating still another example of a data processing unit structure.

14 is a block diagram illustrating another example of a data processing unit structure.

15 is a block diagram illustrating an example of a reference signal processing unit.

16 illustrates a first example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP.

17 illustrates a second example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP.

18 illustrates a first example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP.

19 illustrates a third example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP.

20 illustrates a fourth example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP.

21 illustrates a fifth example of a radio resource with a beacon reference signal inserted in the case of a normal CP.

22 illustrates a second example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP.

23 illustrates a third example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP.

24 illustrates a fourth example of a radio resource with a beacon reference signal inserted in the case of an extended CP.

25 shows an example of symbols input to a DFT unit in which a beacon reference signal element is inserted.

26 shows an example of a beacon reference signal element inserted by a subcarrier mapper.

27 shows a first example of a radio resource with a beacon reference signal inserted.

28 shows a second example of a radio resource with a beacon reference signal inserted.

30 is a flowchart illustrating an example of a method for inserting a beacon reference signal.

31 is a flowchart illustrating an example of a method of performing HARQ using a beacon reference signal.

32 is a flowchart illustrating a method of transmitting a reference signal according to an embodiment of the present invention.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used for various multiple access schemes. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented by a wireless technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical spirit of the present invention is not limited thereto.

1 illustrates a wireless communication system.

Referring to FIG. 1, the wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides a communication service for a particular geographic area (generally called a cell) 15a, 15b, 15c. The cell can in turn be divided into a number of regions (called sectors). The user equipment (UE) 12 may be fixed or mobile, and may include a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), It may be called other terms such as a wireless modem and a handheld device. The base station 11 generally refers to a fixed station communicating with the terminal 12, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like. have.

Hereinafter, downlink (DL) means communication from the base station to the terminal, and uplink (UL) means communication from the terminal to the base station. In downlink, a transmitter may be part of a base station, and a receiver may be part of a terminal. In uplink, a transmitter may be part of a terminal, and a receiver may be part of a base station.

The wireless communication system may be any one of a multiple input multiple output (MIMO) system, a multiple input single output (MIS) system, a single input single output (SISO) system, and a single input multiple output (SIMO) system. The MIMO system uses a plurality of transmit antennas and a plurality of receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas.

Hereinafter, the transmit antenna means a physical or logical antenna used to transmit one signal or stream, and the receive antenna means a physical or logical antenna used to receive one signal or stream.

2 shows a structure of a radio frame in 3GPP LTE.

Referring to FIG. 2, a radio frame consists of 10 subframes, and one subframe consists of two slots. Slots in a radio frame are numbered from 0 to 19 slots. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

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

3 is an exemplary diagram illustrating a resource grid for one uplink slot in 3GPP LTE.

Referring to FIG. 3, an uplink slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and includes N ^UL resource blocks (RBs) in a frequency domain. do. The OFDM symbol is for representing one symbol period, and may be referred to as an SC-FDMA symbol, an OFDMA symbol, or a symbol period according to a system. The RB includes a plurality of subcarriers in the frequency domain in resource allocation units. The number N ^UL of resource blocks included in an uplink slot depends on an uplink transmission bandwidth set in a cell. Each element on the resource grid is called a resource element.

Here, an exemplary resource block includes 7 × 12 resource elements including 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, but the number of subcarriers and the OFDM symbols in the resource block is equal to this. It is not limited. The number of OFDM symbols or the number of subcarriers included in the resource block may be variously changed. The number of OFDM symbols may change depending on the length of a cyclic prefix (CP). For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP.

In 3GPP LTE of FIG. 3, a resource grid for one uplink slot may be applied to a resource grid for a downlink slot.

4 shows an example of a structure of an uplink subframe in 3GPP LTE.

Referring to FIG. 4, an uplink subframe may be divided into a control region to which a physical uplink control channel (PUCCH) carrying uplink control information is allocated and a data region to which a physical uplink shared channel (PUSCH) carrying uplink data is allocated. have. In 3GPP LTE (Release 8), in order to maintain a single carrier property, resource blocks allocated to one UE are contiguous in the frequency domain. One UE cannot transmit a PUCCH and a PUSCH at the same time. In LTE-A (Release 10), simultaneous transmission of PUCCH and PUSCH is under consideration.

PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers in each of a first slot and a second slot. The frequency occupied by RBs belonging to the RB pair allocated to the PUCCH is changed based on a slot boundary. By transmitting uplink control information through different subcarriers over time, the UE may obtain a frequency diversity gain. m is a location index indicating a logical frequency domain location of a resource block pair allocated to a PUCCH in a subframe.

The uplink control information transmitted on the PUCCH includes a hybrid automatic repeat request (HARQ) acknowledgment (ACK) / negative acknowledgment (NACK), a channel quality indicator (CQI) indicating a downlink channel state, and an SR radio resource allocation request (SR). scheduling request).

PUSCH is mapped to an uplink shared channel (UL-SCH) which is a transport channel. The uplink data transmitted on the PUSCH may be a transport block which is a data block for the UL-SCH transmitted during the TTI. The transport block may be user information. Alternatively, the uplink data may be multiplexed data. The multiplexed data may be a multiplexed transport block and control information for the UL-SCH. For example, control information multiplexed with data may include a CQI, a precoding matrix indicator (PMI), an HARQ ACK / NACK, a rank indicator (RI), and the like. Or, the uplink data may consist of control information only.

Hereinafter, a data transmission method is explained in full detail. The following description will be described based on uplink data transmitted by the terminal to the base station, but can also be applied to downlink data transmitted by the base station to the terminal.

5 is a flowchart illustrating an example of a data transmission method.

Referring to FIG. 5, the base station BS transmits an uplink grant to the terminal UE (S110). The terminal transmits uplink data using the uplink grant to the base station (S120). The uplink grant may be transmitted on a physical downlink control channel (PDCCH), and the uplink data may be transmitted on a PUSCH. The relationship between the subframe in which the PDCCH is transmitted and the subframe in which the PUSCH is transmitted may be previously defined between the base station and the terminal. For example, in a frequency division duplex (FDD) system, if a PDCCH is transmitted through subframe n, a PUSCH may be transmitted through subframe n + 4.

The uplink grant is downlink control information for uplink data scheduling. The uplink grant includes a resource allocation field. The uplink grant includes a hopping flag indicating whether frequency hopping is performed, a flag distinguishing an uplink grant from other downlink control information, and a transmission format field indicating a transmission format for uplink data. A new data indicator (NDI) indicating whether the uplink grant is for new uplink data transmission or retransmission of uplink data, and a transmit power control (TPC) command for uplink power control The field may further include a CS field indicating a cyclic shift (CS) of a demodulation reference signal (DM RS), a CQI request indicator indicating a CQI request, and the like.

The resource allocation field indicates a radio resource for uplink data transmission. The radio resource may be a time-frequency resource. The radio resource allocated by the resource allocation field in 3GPP LTE is a resource block. The UE may know the location of the resource block, the number of resource blocks, etc. in the subframe allocated to uplink data transmission using the resource allocation field.

If the hopping flag does not indicate frequency hopping, the resource blocks allocated by the UE in each of the first slot and the second slot in the subframe are the same in the frequency domain. When the hopping flag indicates frequency hopping, the resource blocks allocated by the UE in each of the first slot and the second slot in the subframe may be different in the frequency domain.

Radio resource scheduling methods include dynamic scheduling, persistent scheduling, and semi-persistent scheduling (SPS). If the radio resource scheduling scheme is a continuous scheduling scheme or a semi-persistent scheduling scheme, the terminal may transmit uplink data without receiving an uplink grant.

6 illustrates an example of a radio resource for transmitting data in the case of a normal CP.

Referring to FIG. 6, a subframe includes a first slot and a second slot. Each of the first slot and the second slot includes 7 OFDM symbols. 14 OFDM symbols in a subframe are symbol indexed from 0 to 13. Reference signals are transmitted over OFDM symbols having symbol indices of 3 and 10. Data is transmitted through the remaining OFDM symbols except for the OFDM symbol on which the reference signal is transmitted. The reference signal is a signal known to both the transmitter and the receiver used for channel estimation for demodulating data.

7 illustrates an example of a radio resource for transmitting data in the case of an extended CP.

Referring to FIG. 7, a subframe includes a first slot and a second slot. Each of the first slot and the second slot includes 6 OFDM symbols. 12 OFDM symbols in a subframe are indexed from 0 to 11 symbols. The reference signal is transmitted through an OFDM symbol having symbol indexes 2 and 8. Data is transmitted through the remaining OFDM symbols except for the OFDM symbol on which the reference signal is transmitted.

Hereinafter, an OFDM symbol for data transmission is referred to as a data symbol, and an OFDM symbol for reference signal transmission is referred to as a reference signal symbol. In FIG. 6, there are 12 data symbols and 2 reference signal symbols in one subframe. In FIG. 7, there are 10 data symbols and 2 reference signal symbols in one subframe.

Although not shown in FIGS. 6 and 7, a sounding reference signal (SRS) may be transmitted through an OFDM symbol in a subframe. For example, a sounding reference signal may be transmitted through the last OFDM symbol in the subframe. The sounding reference signal is a reference signal transmitted by the terminal to the base station for uplink scheduling. The base station estimates an uplink channel based on the received sounding reference signal and uses the estimated uplink channel for uplink scheduling. Hereinafter, the reference signal may mean not only a demodulation reference signal for data demodulation but also a sounding reference signal.

8 is a block diagram illustrating an example of a transmitter structure. Here, the transmitter may be part of the terminal or the base station.

Referring to FIG. 8, the transmitter 100 includes a data processor 110, a reference signal processor 120, and a radio frequency (RF) unit 130. The RF unit 130 is connected to the data processor 110 and the reference signal processor 120. The data processor 110 processes the data to generate a baseband signal for the data. The reference signal processor 120 generates and processes a reference signal to generate a baseband signal for the reference signal. The RF unit 130 converts a baseband signal (a baseband signal for data and / or a baseband signal for a reference signal) into a radio signal and transmits the radio signal. In this case, the baseband signal may be upconverted to a carrier frequency, which is a center frequency of the cell, and then converted to a wireless signal.

9 is a block diagram illustrating an example of a structure of a data processor. Here, the data processor may be included in the transmitter.

Referring to FIG. 9, the data processor 110 includes a discrete fourier transform (DFT) unit 111, a subcarrier mapper 112, an inverse fast fourier transform (IFFT) unit 113, and a CP insertion unit 114. . The data processor 110 may further include a channel coding unit (not shown) and a modulator (not shown). The channel coding unit performs channel coding on information bits to generate coded bits. The information bits may be referred to as data transmitted from a transmitter. The modulator maps the encoded bit into a symbol representing a location on a signal constellation to produce modulated symbols. The modulation scheme is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM). The modulated symbols are input to the DFT unit 111.

The DFT unit 111 outputs complex-valued symbols by performing a DFT on the input symbols. For example, when Ntx symbols are input, the DFT size is Ntx (Ntx is a natural number).

The subcarrier mapper 112 maps the complex symbols to each subcarrier in the frequency domain. Complex symbols may be mapped to resource elements corresponding to resource blocks allocated for data transmission. The IFFT unit 113 performs an IFFT on the input symbol and outputs a baseband signal for data which is a time domain signal. When an IFFT size N _FFT d, N _FFT may be determined by the channel bandwidth (channel bandwidth) (N _FFT is a natural number). The CP inserter 114 copies a part of the rear part of the baseband signal for data and inserts it in front of the baseband signal for data. By interpolating CP, Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) are prevented, so that orthogonality can be maintained even in a multipath channel.

As such, a transmission scheme in which IFFT is performed after DFT spreading is called SC-FDMA. SC-FDMA may also be referred to as FTTS-OFDM (DFT spread-OFDM). In SC-FDMA, a peak-to-average power ratio (PAPR) or a cubic metric (CM) may be lowered. In the case of using the SC-FDMA transmission scheme, transmission power efficiency may be increased in a terminal with limited power consumption. Accordingly, user throughpupt may be high.

10 illustrates an example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

Referring to FIG. 10, the subcarrier mapper maps complex symbols output from the DFT unit to consecutive subcarriers in the frequency domain. '0' is inserted into a subcarrier to which complex symbols are not mapped. This is called localized mapping. In 3GPP LTE, a centralized mapping scheme is used.

11 shows another example of a method in which the subcarrier mapper maps complex symbols to each subcarrier in the frequency domain.

Referring to FIG. 11, the subcarrier mapper inserts L-1 '0's between two consecutive complex symbols output from the DFT unit (L is a natural number). That is, the complex symbols output from the DFT unit are mapped to subcarriers distributed at equal intervals in the frequency domain. This is called distributed mapping.

When the subcarrier mapper uses a centralized mapping scheme as shown in FIG. 10 or a distributed mapping scheme as shown in FIG. 11, a single carrier characteristic is maintained.

12 is a block diagram illustrating another example of a data processing unit structure. Here, the data processor may be included in the transmitter.

Referring to FIG. 12, the data processor 210 includes a DFT unit 211, a subcarrier mapper 212, an IFFT unit 213, and a CP inserter 214.

The complex symbols output from the DFT unit 211 are divided into N subblocks (N is a natural number). Herein, N subblocks may be represented by subblock # 1, subblock # 2, ..., subblock #N. The subcarrier mapper 212 distributes N subblocks in the frequency domain and maps the subcarriers to subcarriers. NULL may be inserted between every two consecutive subblocks. Complex symbols in one subblock may be mapped to consecutive subcarriers in the frequency domain. That is, the centralized mapping scheme may be used in one subblock.

The data processor of FIG. 12 may be used for both a single carrier transmitter or a multi-carrier transmitter. A single carrier transmitter is a transmitter with one carrier, and a multicarrier transmitter is a transmitter with multiple carriers. When used in a single carrier transmitter, all N subblocks correspond to one carrier. When used in a multi-carrier transmitter, one subcarrier may correspond to each subblock among N subblocks. Alternatively, even when used in a multi-carrier transmitter, a plurality of subblocks among N subblocks may correspond to one carrier.

In the data processor of FIG. 12, a time domain signal is generated through one IFFT unit. Accordingly, in order for the data processor of FIG. 12 to be used in a multicarrier transmitter, subcarrier spacing between adjacent carriers must be aligned in a continuous carrier allocation situation.

13 is a block diagram illustrating still another example of a data processing unit structure. Here, the data processor may be included in the multi-carrier transmitter.

Referring to FIG. 13, the data processor 310 may include a DFT unit 311, a subcarrier mapper 312, a plurality of IFFT units 313-1, 313-2,..., 313 -N and a CP insertion unit ( 214), where N is a natural number. IFFT is performed separately for each subblock among the N subblocks. The nth IFFT unit 313-n performs an IFFT on subblock #n and outputs an nth baseband signal (n = 1, 2,..., N). The nth baseband signal is multiplied by an nth carrier f _n signal to generate an nth radio signal. After the N radio signals generated from the N subblocks are added, a CP is inserted by the CP inserting unit 214.

The data processor of FIG. 13 may be used in a non-contiguous carrier allocation situation in which carriers allocated by the transmitter are not adjacent to each other.

12 and 13, a method in which symbols output from the DFT unit are divided into a plurality of subblocks and processed is referred to as a clustered SC-FDMA.

14 is a block diagram illustrating another example of a data processing unit structure. Here, the data processor may be included in the multi-carrier transmitter.

Referring to FIG. 14, the data processor 410 includes a code block divider 411, a chunk divider 412, a plurality of channel coding units 413-1,. Modulators 414-1, ..., 414-N, a plurality of DFT units 415-1, ..., 415-N, a plurality of subcarrier mappers 416-1, ..., 416-N ), A plurality of IFFT units 417-1,..., 417 -N and a CP insertion unit 418 (N is a natural number). Here, N may be the number of multicarriers used by the multicarrier transmitter.

The code block dividing unit 411 divides the transport block into a plurality of code blocks. The chunk divider 412 divides the code block into a plurality of chunks. Here, the code block may be referred to as data transmitted from the multicarrier transmitter, and the chunk may be referred to as a piece of data transmitted through one carrier of the multicarrier. The data processor 410 performs a DFT in chunk units. The data processor 410 may be used both in a discontinuous carrier allocation situation or in a continuous carrier allocation situation. A transmission scheme in which DFT is performed in chunks as shown in FIG. 14 is referred to as chunk specific DFTS-OFDM or N × SC-FDMA.

Hereinafter, the OFDM symbol refers to a symbol to which OFDMA, SC-FDMA, clustered DFTS-OFDM, or chunk-specific DFTS-OFDM transmission scheme is applied.

15 is a block diagram illustrating an example of a reference signal processing unit. Here, the reference signal processor may be included in the transmitter.

Referring to FIG. 15, the reference signal processor 120 includes a reference signal sequence generator 121, a subcarrier mapper 122, an IFFT unit 123, and a CP insertion unit 124.

The reference signal sequence generator 121 generates a reference signal sequence composed of complex elements. The subcarrier mapper 122 maps the complex elements constituting the reference signal sequence to each subcarrier. Complex elements are mapped to subcarriers of a demodulation reference signal symbol in a subframe (see FIGS. 6 and 7). In 3GPP LTE, a centralized mapping scheme is used, but the subcarrier mapping scheme is not limited to the centralized mapping scheme. The subcarrier mapping scheme may be a distributed mapping scheme, an interleaved mapping scheme, a block level interleaved mapping scheme, a random allocation mapping scheme, or the like.

The IFFT 123 performs an IFFT on an input symbol and outputs a baseband signal for a reference signal which is a time domain signal. The CP inserting unit 124 copies a part of the rear part of the baseband signal for the reference signal and inserts it before the baseband signal for the reference signal.

The subcarrier mapper, the IFFT unit, and the CP inserter included in the reference signal processor may be the same as the subcarrier mapper, the IFFT unit, and the CP inserter included in the data processor. The reference signal processor and the data processor may share the subcarrier mapper, the IFFT unit, and the CP inserter through a switching operation over time.

Hereinafter, the reference signal sequence will be described in detail.

As the reference signal sequence, any sequence may be used without particular limitation. The reference signal sequence may use a PSK-based computer generated sequence. Examples of PSKs include binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Alternatively, the reference signal sequence may use a constant amplitude zero auto-correlation (CAZAC) sequence. Examples of CAZAC sequences are ZC-based sequences, ZC sequences with cyclic extensions, ZC sequences with truncation, etc. There is this. Alternatively, the reference signal sequence may use a pseudo-random (PN) sequence. Examples of PN sequences include m-sequences, computer generated sequences, Gold sequences, and Kasami sequences. In addition, the reference signal sequence may use a cyclically shifted sequence.

Hereinafter, the case where the cyclic shift sequence is used as the reference signal sequence will be described in detail. The cyclically shifted sequence may be generated by cyclically shifting a base sequence by a specific cyclic shift amount. Various kinds of sequences can be used as the base sequence. For example, a well-known sequence such as a PN sequence or a ZC sequence can be used as the base sequence. Alternatively, a computer generated CAZAC sequence may be used. Alternatively, the base sequence may be generated in different ways depending on the length of the base sequence.

The basic sequence may be represented by r _{u, v} (n). Where u ∈ {0,1, ..., 29} is a sequence group number, v is a base sequence number in the group, and n is an element index, 0≤n≤M -1, M is the length of the base sequence. The length M of the basic sequence may be equal to the number of subcarriers included in one demodulation reference signal symbol in a subframe. For example, if one resource block includes 12 subcarriers and three resource blocks are allocated for data transmission, the length M of the base sequence is 36.

The following equation shows an example of the basic sequence r _{u, v} (n).

Equation 1

Where x _q is a ZC sequence whose root index is q and N is the length of x _q . That is, the basic sequence r _{u, v} (n) has a form in which x _q is cyclically expanded. When one resource block includes 12 subcarriers, the length M of the base sequence may be 36 or more.

The ZC sequence x _q (m) having the raw index q may be defined as in the following equation.

Equation 2

Where N is the length of x _q (m) and m is 0 ≦ m ≦ N−1. N may be the largest prime number among natural numbers smaller than the length M of the base sequence. q is a natural number less than or equal to N, and q and N are relatively prime. If N is a prime number, the number of raw indexes q is N-1.

The raw index q can be expressed as the following equation.

Equation 3

When one resource block includes 12 subcarriers, when the length M of the base sequence is 12 or 24, a CAZAC sequence generated through a computer may be used as the base sequence. If the length M of the base sequence is 12 or 24, each group contains only one base sequence, so the base sequence number v in the group is zero.

When the length M of the base sequence is 12 or 24, an example of the base sequence r _{u, v} (n) may be expressed by the following equation.

Equation 4

Different base sequences are defined according to the group number u.

When M = 12, b (n) may be defined as shown in the following table.

Table 1

When M = 24, b (n) can be defined as shown in the following table.

TABLE 2

The base sequence r _{u, v} (n) may vary depending on the sequence group number u and the base sequence number v. The sequence group number u and the base sequence number v in the group may each change semi-statically or slot by slot. When the sequence group number u changes from slot to slot is called group hopping, and the basic sequence number v in the group changes from slot to slot is called sequence hopping. Each of group hopping and sequence hopping may be set by a higher layer of a physical layer. For example, the upper layer may be RRC (Radio Resource Control) which plays a role of controlling radio resources between the terminal and the network.

The sequence group number u may be determined as in the following equation.

Equation 5

Here, f _gh (n _s) is a group of hopping patterns and, n _s is a slot number within a radio frame, f _ss is a sequence shift pattern. At this time, there are 17 different hopping patterns and 30 different sequence shift patterns.

If group hopping is not set, the group hopping pattern f _gh (n _s ) is zero. When group hopping is set, the group hopping pattern f _gh (n _s ) can be expressed by the following equation.

Equation 6

Where c (n) is a PN sequence. c (n) may be defined by a gold sequence of length-31. The following equation shows an example of the sequence c (n).

Equation 7

Wherein N _C = 1600, x ₁ (i) is the first m-sequence and x ₂ (i) is the second m-sequence. For example, the first m-sequence may be initialized to x ₁ (0) = 1, x ₁ (n) = 0 (n = 1, 2, ..., 30) every radio frame. . In addition, the second m-sequence may be initialized according to a cell identity for every radio frame. The following equation is an example of initialization of the second m-sequence.

Equation 8

Here, N _{cell_ID} is a cell ID.

The sequence shift pattern f _ss may be expressed as in the following equation.

Equation 9

Here, d ∈ {0, 1, ..., 29} is a group assignment parameter. The group assignment parameter d may be set by a higher layer such as RRC. The group assignment parameter may be a common parameter common to all terminals in the cell.

Next, the basic sequence number v in the group will be described. When one resource block includes 12 subcarriers, when the length M of the base sequence is less than 72, each group includes only one base sequence (v = 0). In this case, sequence hopping is not applied.

When one resource block includes 12 subcarriers, when the length M of the base sequence is 72 or more, each group includes 2 base sequences (v = 0, 1). In this case, when group hopping is not set and sequence hopping is set, sequence hopping may be performed in which the basic sequence number v in the group changes from slot to slot. If sequence hopping is not performed, the base sequence number v in the group may be fixed to zero.

When sequence hopping is performed, the basic sequence number v in the group can be expressed as the following equation.

Equation 10

Here, c (n) may be the same as Equation 7 as the PN sequence. For example, the first m-sequence may be initialized to x ₁ (0) = 1, x ₁ (n) = 0 (n = 1, 2, ..., 30) every radio frame. . In addition, the second m-sequence may be initialized according to a cell ID and a sequence shift pattern f _ss for every radio frame. The following equation is an example of initialization of the second m-sequence.

Equation 11

The cyclically shifted sequence r _{u, v} (n, Ics) may be generated by circularly shifting the basic sequence r _{u, v} (n) as shown in the following equation.

Equation 12

Here, 2πIcs / 12 is a CS amount, and Ics is a CS index indicating a CS amount (0 ≦ Ics <12, and Ics is an integer).

The CS index Ics may be determined according to a cell-specific CS parameter, a UE-specific CS parameter, and a hopping CS parameter. The cell specific CS parameter has a different value for each cell but is common to all terminals in the cell. The UE-specific CS parameter may have a different value for each UE in a cell. The hopping CS parameter may have a different value for each slot. Thus, the CS index may change from slot to slot. The change in the CS amount by changing the CS index for each slot is called CS level slot level hopping.

The CS index Ics may be expressed as the following equation.

Equation 13

Here, Ia is determined by a cell specific CS parameter, Ib is a terminal specific CS parameter, and I (n _s ) is a hopping CS parameter.

The cell specific CS parameter may be set by a higher layer such as RRC. The following table shows examples of Ia determined by cell specific CS parameters.

TABLE 3

The UE-specific CS parameter Ib may be indicated by the CS field of the uplink grant. If the radio resource scheduling method for the data transmission is the continuous scheduling method or the ringless scheduling method, when there is no uplink grant corresponding to the data transmission, the terminal specific CS parameter Ib may be zero.

The following table shows an example of the UE-specific CS parameter Ib determined by the CS field.

Table 4

The hopping CS parameter I (n _s ) can be expressed by the following equation.

Equation 14

Here, c (n) is a PN sequence and N _symb is the number of OFDM symbols included in a slot. The PN sequence c (n) may be as shown in Equation 7. For example, the first m-sequence may be initialized to x ₁ (0) = 1, x ₁ (n) = 0 (n = 1, 2, ..., 30) every radio frame. . In addition, the second m-sequence may be initialized according to a cell ID and a sequence shift pattern f _ss for every radio frame. The initialization of the second m-sequence may be as in Equation (11).

As such, the reference signal sequence consisting of the generated complex elements is mapped to subcarriers of the reference signal symbol in the subframe.

Good channel estimation performance can increase the reliability of wireless communication. The reference signal should be allocated in consideration of coherent time in the time domain and in consideration of coherent bandwidth in the frequency domain. Coherent time is inversely proportional to Doppler spread. The coherent time may be used to determine whether the channel is a time selective channel or a time flat channel. In general, when the terminal moves at a high speed, the wireless communication environment becomes a time selective channel. For example, when the terminal moves at a speed of 100 km / h (kilometers per hour) or more, it may be referred to as high speed. In the case of a time-selective channel, more reference signals are used in the time domain to improve channel estimation performance. Coherent bandwidth is inversely proportional to delay spread. The coherent bandwidth may be used to determine whether the channel is a frequency selective channel or a frequency flat channel. For example, in the case of a frequency selective channel, channel estimation performance can be improved when a reference signal is used a lot in the frequency domain.

However, the reference signal structure (see FIGS. 6 and 7) for uplink in 3GPP LTE has a low reference signal overhead in the time domain. Thus, channel estimation performance may be degraded in a time selective channel. In addition, degradation of channel estimation performance is a more sensitive problem in MIMO systems. In particular, when data is transmitted through a spatial multiplexing scheme, degradation of channel estimation performance can be a serious problem. However, if the reference signal overhead is simply increased in the time domain, the channel estimation performance gain may be increased, but there is a problem in that the amount of data transmission is reduced. Reduced data throughput results in link throughput loss. Therefore, there is a need for a method of optimally allocating a reference signal in consideration of a trade-off between channel estimation performance and link throughput loss.

Hereinafter, it is assumed that a radio resource to which data is transmitted includes a plurality of OFDM symbols in a time domain and a plurality of subcarriers in a frequency domain. A reference signal is transmitted through an OFDM symbol of a fixed position among radio resources. Hereinafter, in order to increase channel estimation performance, a reference signal additionally inserted into a time domain or a frequency domain in a radio resource is referred to as a beacon reference signal. The content related to the reference signal described so far may be applied to the beacon reference signal. Hereinafter, a value corresponding to a beacon reference signal transmitted through one resource element is referred to as a beacon RS element. The beacon reference signal element may be a value before input to the DFT unit or a complex value output from the DFT unit.

Hereinafter, a method of inserting a beacon reference signal will be described based on the radio resource structure of FIGS. 6 and 7. For convenience of description, a case in which a sounding reference signal is transmitted through an OFDM symbol in a subframe may be omitted. However, even when a sounding reference signal is transmitted, the beacon reference signal insertion method described below may be applied as it is. Alternatively, the case in which a sounding reference signal is transmitted through an OFDM symbol in a subframe may be illustrated. Even when a sounding reference signal is not transmitted through the OFDM symbol, data is inserted. The method can be applied as it is.

In addition, for convenience of description, it is assumed that frequency hopping is not performed in the first slot and the second slot in the subframe. However, even when frequency hopping is performed in the first slot and the second slot in the subframe, the beacon reference signal insertion method described below may be applied as it is. However, when frequency hopping is performed, channel estimation through interpolation between reference signals inserted into respective slots is impossible.

The beacon reference signal may be inserted into at least one or more OFDM symbols in the subframe. Hereinafter, a case in which a beacon reference signal is inserted into one OFDM symbol and two OFDM symbols in a subframe will be described as an example.

First, the beacon reference signal may be inserted into one OFDM symbol in a subframe.

16 illustrates a first example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 6 in a subframe.

17 illustrates a second example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 7 in a subframe.

18 illustrates a first example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 5 in a subframe.

16 to 18 are only examples of beacon reference signal structures, and do not limit the position of an OFDM symbol into which a beacon reference signal is inserted in a subframe. For each subframe, the position of the OFDM symbol into which the beacon reference signal is inserted in the subframe may be changed. Alternatively, the positions of the OFDM symbols in which the beacon reference signals are inserted in the subframes may be the same for the plurality of subframes. Alternatively, the position of the OFDM symbol in which the beacon reference signal is inserted in the subframe may be the same during the radio frame. If the positions of the OFDM symbols into which the beacon reference signals are inserted in the subframes during the plurality of subframes or radio frames are the same, equal intervals between the beacon reference signals may be maintained.

Second, the beacon reference signal may be inserted into 2 OFDM symbols in a subframe.

19 illustrates a third example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 0 and 13 in a subframe.

20 illustrates a fourth example of a radio resource in which a beacon reference signal is inserted in the case of a normal CP. The beacon reference signal is inserted into an OFDM symbol having 0 and 6 symbol indices in a subframe. The sounding reference signal is transmitted through an OFDM symbol having a symbol index of 13.

21 illustrates a fifth example of a radio resource with a beacon reference signal inserted in the case of a normal CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 0 and 7 in a subframe. The sounding reference signal is transmitted through an OFDM symbol having a symbol index of 13.

22 illustrates a second example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP. The beacon reference signal is inserted into an OFDM symbol with symbol indexes 5 and 11 in the subframe.

23 illustrates a third example of a radio resource in which a beacon reference signal is inserted in the case of an extended CP. The beacon reference signal is inserted into an OFDM symbol having 4 and 6 symbol indices in a subframe. The sounding reference signal is transmitted through an OFDM symbol having a symbol index of 11.

24 illustrates a fourth example of a radio resource with a beacon reference signal inserted in the case of an extended CP. The beacon reference signal is inserted into an OFDM symbol having a symbol index of 5 and 10 in a subframe. The sounding reference signal is transmitted through an OFDM symbol having a symbol index of 11.

Now, a method of inserting a beacon reference signal into a radio resource will be described in detail. The beacon reference signal may be inserted in the time domain or in the frequency domain.

First, a method of inserting a beacon reference signal in the time domain will be described. The symbols input to the DFT are symbols in the time domain. Accordingly, the beacon reference signal may be inserted into the symbols input to the DFT unit.

25 shows an example of symbols input to a DFT unit in which a beacon reference signal element is inserted. Here, the DFT unit may be included in the data processing unit of the transmitter.

Referring to FIG. 25, M symbols z (0), z (1), ..., z (M-1) are input to the DFT unit. Here, M may be the number of subcarriers included in the frequency domain by a radio resource allocated for data transmission. For example, when one resource block includes 12 subcarriers and N resource blocks are allocated for data transmission, M may be 12 × N. A beacon reference signal element is inserted into one symbol z (m) of the M symbols. The beacon reference signal element may be located in the middle of the M symbols.

The following equation shows an example of the position of a symbol into which the beacon reference signal element is inserted.

Equation 15

Punching or rate matching may be used to insert the beacon reference signal element among the M symbols input to the DFT unit.

The following table shows an example of insertion of a reference signal element for each case of puncturing and rate matching.

Table 5

Here, d (n) is a data element corresponding to a symbol input to the DFT unit, and b (k) is a beacon reference signal element inserted in z (m). In the case of puncturing, the data element d (m) corresponding to the position where the beacon reference signal element is inserted is punctured, and the beacon reference signal element is inserted. In the case of rate matching, data elements are mapped to symbols except for the positions where the beacon reference signal elements are inserted.

The DFT unit outputs complex symbols by performing a DFT on the input M symbols, and the subcarrier mapper maps the complex symbols to each subcarrier in the frequency domain. The IFFT unit performs an IFFT on the input symbol and outputs a time domain signal. The time domain signal carries a data and a beacon reference signal.

FIG. 25 illustrates an example of inserting one beacon reference signal element among symbols input to the DFT unit, but this does not limit the number of inserted beacon reference signal elements.

Hereinafter, various examples of beacon reference signal elements inserted among symbols input to the DFT unit will be described. For convenience of description, the number of symbols input to the DFT unit is 12. This is a case where one resource block includes 12 subcarriers and one resource block is allocated for data transmission. Hereinafter, the reference signal density (RS density, RSD) means the degree to which the beacon reference signal element is inserted. The reference signal density may be defined as the ratio of the inserted beacon reference signal elements to the number of symbols input to the DFT unit.

The following table shows an example in which beacon reference signal elements are inserted at equal intervals according to the reference signal density RSD. This takes into account the random process of the channel.

Table 6

Here, 'b' is a beacon reference signal element, and a data element is inserted into the blank. For example, when the reference signal density is 2/12, the beacon reference signal element may be inserted in z (3) and z (7).

The following table shows an example in which beacon reference signal elements are randomly inserted according to a reference signal density (RSD).

TABLE 7

However, this is only an example of inserting a beacon reference signal element, and does not limit the position at which the beacon reference signal element is inserted.

The beacon reference signal may be inserted at any position as well as the cases shown in Tables 6 and 7. In addition, the beacon reference signal may be inserted into all of the symbols input to the DFT unit (RSD = 1).

When there are two or more beacon reference signal elements inserted into symbols input to the DFT unit, the following cases may be used between the beacon reference signal elements. (1) beacon reference signal elements are apart, (2) beacon reference signal elements are adjacent, (3) beacon reference signal elements are located in the middle, and (4) beacon reference signal elements are located at both ends. As in the case of (1) and (3), each case can be variously combined.

The following table shows an example in which (1) beacon reference signal elements are separated and (3) beacon reference signal elements are located in the middle.

Table 8

The following table shows an example in which (1) beacon reference signal elements are separated and (4) beacon reference signal elements are positioned at both ends.

Table 9

The following table shows an example where (2) beacon reference signal elements are adjacent and (3) beacon reference signal elements are located in the middle.

Table 10

The following table shows an example in which (2) beacon reference signal elements are adjacent and (4) beacon reference signal elements are positioned at both ends.

Table 11

Now, a method of inserting a beacon reference signal in the frequency domain will be described. The complex symbols output from the DFT unit are symbols in the frequency domain. Accordingly, the subcarrier mapper may insert a beacon reference signal when the symbols of the frequency domain are mapped to the subcarriers.

26 shows an example of a beacon reference signal element inserted by a subcarrier mapper. Here, the subcarrier mapper may be included in the data processor of the transmitter.

Referring to FIG. 26, M beacon reference signal elements and data elements are mapped to resource elements Z (0), Z (1), ..., Z (M-1) by the subcarrier mapper. Z (0), Z (1), ..., Z (M-1) are included in the radio resource allocated for data transmission. Here, M may be the number of subcarriers included in the frequency domain by a radio resource allocated for data transmission. For example, when one resource block includes 12 subcarriers and N resource blocks are allocated for data transmission, M may be 12 × N. A beacon reference signal element is inserted into one resource element Z (m) of the M resource elements. The beacon reference signal element may be located in the middle of the M resource elements. The position of the resource element into which the beacon reference signal element is inserted may be as shown in Equation 15.

Perforation or rate matching may be used to insert the beacon reference signal element among the M resource elements.

The following table shows an example of insertion of a reference signal element for each case of puncturing and rate matching.

Table 12

Here, D (n) is a complex symbol output from the DFT unit, and B (k) is a beacon reference signal element inserted in Z (m). In the case of puncturing, M complex symbols are output from D (0) to D (M-1) from the DFT unit. In this case, the DFT size is M. D (m) of the M complex symbols is punctured, and a beacon reference signal element B (k) is inserted. In the case of rate matching, M-1 complex symbols are output from D (0) to D (M-2) from the DFT unit. In this case, the DFT size is M-1. M-1 complex symbols are sequentially mapped to resource elements except for Z (m). 0 is inserted into the resource element except for the radio resource allocated for data transmission.

FIG. 26 illustrates an example of inserting one beacon reference signal element in the frequency domain of one OFDM symbol, but this does not limit the number of inserted beacon reference signal elements.

Hereinafter, various examples of beacon reference signal elements inserted among resource elements will be described. For convenience of description, the number of resource elements is 12. This is a case where one resource block includes 12 subcarriers and one resource block is allocated for data transmission. The reference signal density may be a ratio of inserted beacon reference signal elements to the number of subcarriers included in the frequency domain by radio resources allocated for data transmission.

The following table shows an example in which a beacon reference signal element is inserted according to a reference signal density (RSD).

Table 13

In addition, the beacon reference signal element may be inserted in all of the resource elements (RSD = 1).

So far, a method of inserting a beacon reference signal into a time domain or a frequency domain in 1 OFDM symbol has been described. A beacon reference signal may be inserted into two or more OFDM symbols. In this case, the method of inserting a beacon reference signal into the time domain or the frequency domain described so far may be combined like the time axis at the OFDM symbol level.

Hereinafter, a case in which a beacon reference signal is inserted into a frequency domain in all OFDM symbols in a subframe will be described. For convenience of description, it is assumed that one resource block includes 12 subcarriers and one resource block is allocated for data transmission.

The location of the time domain and the location of the frequency domain where the beacon reference signal is inserted may be fixed. 27 and 28 show examples of a case where a position where a beacon reference signal is inserted is fixed.

27 shows a first example of a radio resource with a beacon reference signal inserted.

Referring to FIG. 27, one beacon reference signal element is inserted in every OFDM symbol except for an OFDM symbol in which a reference signal is transmitted in a subframe. The positions in the frequency domain of the beacon reference signal elements are the same. The reference signal density is 1/12.

28 shows a second example of a radio resource with a beacon reference signal inserted. The reference signal density is 1/2.

The position of the time domain where the beacon reference signal is inserted and the position of the frequency domain may be varied. In this case, the position where the beacon reference signal is inserted into the radio resource may be a predetermined position or a random position. An example of an insertion position of a predetermined beacon reference signal is a staggered position.

29 shows a third example of a radio resource with a beacon reference signal inserted. This is an example of the case where the insertion position of the beacon reference signal is staggered. The reference signal density is 1/12.

In addition, the beacon reference signal may be inserted into the radio resource in various patterns according to the reference signal density.

Although the method of inserting the beacon reference signal into one resource block has been described so far, the beacon reference signal may be inserted into the plurality of resource blocks according to the reference signal density. The radio resource to which data is transmitted may be a contiguous resource block or a non-contiguous resource block in the frequency domain. In the case of a discontinuous resource block, a beacon reference signal may be inserted according to the reference signal density for each separated resource block. Alternatively, the radio resource for transmitting data may be one or more resource block clusters. In this case, clustered SC-FDMA, N × SC-FDMA, OFDMA, or the like may be used for the multiple access scheme. The resource block cluster may be one or more resource blocks to which one subblock is mapped. The number of resource blocks included in the resource block cluster may be the same or different for each resource block cluster. A beacon reference signal may be inserted for each resource block cluster or the entire resource block cluster according to the reference signal density.

The beacon reference signal may be a common RS or a dedicated RS.

The common reference signal may be the same cell-common reference signal to all terminals in a cell or may be different cell-specific reference signals for each cell or cell ID. If the beacon reference signal is a common reference signal, the beacon reference signal may be inserted according to the reference signal density for the entire transmission bandwidth. In the case of the common reference signal, the common reference signal is always transmitted by the number of transmit antennas regardless of the number of streams. The common reference signal has an independent reference signal for each transmit antenna. That is, common reference signals having orthogonality or low correlation with each other are transmitted for each transmit antenna.

The dedicated RS is a UE-specific RS that may be different for each UE or UE group in a cell. When the beacon reference signal is a dedicated reference signal, the beacon reference signal may be inserted according to the reference signal density in a radio resource allocated by the terminal for data transmission. In the case of a dedicated reference signal, as many dedicated reference signals as the number of streams are transmitted. The beacon reference signal may or may not be precoded.

30 is a flowchart illustrating an example of a method for inserting a beacon reference signal.

Referring to FIG. 30, the transmitter determines whether to insert a beacon reference signal (S210). If the beacon reference signal insertion is determined, the transmitter determines the reference signal density (S220). The transmitter inserts a beacon reference signal into a radio resource through which data is transmitted according to the reference signal density (S230).

Whether the beacon reference signal is inserted and / or the reference signal density may be explicitly set. For example, when the transmitter is part of the terminal, the base station may indicate whether the beacon reference signal is inserted and / or the reference signal density to the terminal. In this case, whether the beacon reference signal is inserted and / or the reference signal density may be set by an upper layer such as RRC. Whether the beacon reference signal is inserted and / or the reference signal density may be common to all terminals in a cell or may be set differently for each terminal. Alternatively, whether the beacon reference signal is inserted and / or the reference signal density may be predetermined in advance through a protocol between the base station and the terminal. Alternatively, whether to insert a beacon reference signal implicitly and / or a reference signal density may be set in association with a communication environment.

Whether the beacon reference signal is inserted and / or the reference signal density may be set according to a channel environment, a transmission antenna technique, and the like. For example, a beacon reference signal is inserted in a high speed Doppler environment and a beacon reference signal is not inserted in a low speed environment. Alternatively, the reference signal density of the beacon reference signal may be increased in a high speed environment, and the reference signal density of the beacon reference signal may be decreased in a low speed environment. As another example, in the case of a transmission antenna technique in which channel estimation performance is sensitive, a beacon reference signal is inserted or a reference signal density is increased. An example of a transmission antenna technique in which channel estimation performance is sensitive is a spatial multiplexing technique among multiple input multiple output (MIMO) techniques. In the case of a transmission antenna technique in which channel estimation performance is not sensitive, a beacon reference signal is not inserted or a reference signal density is reduced. Examples of a transmission antenna technique in which channel estimation performance is not sensitive include a single antenna transmission technique and a transparent transmission diversity technique.

31 is a flowchart illustrating an example of a method of performing HARQ using a beacon reference signal.

Referring to FIG. 31, the base station BS transmits an uplink grant to the terminal UE (S310). The terminal transmits data to the base station through a radio resource indicated by the uplink grant (S320). At this time, the reference signal density is 0 (RSD = 0), and the beacon reference signal is not inserted into the radio resource. It is assumed that the base station has failed to receive data. The base station transmits a NACK for the data to the terminal (S330). The terminal retransmits data to the base station (S340). For data retransmission, the base station may transmit an uplink grant for data retransmission to the terminal. At this time, the reference signal density is 1/12 (RSD = 1/12), and a beacon reference signal is inserted into a radio resource. The base station transmits a NACK to the terminal (S350). The terminal retransmits data to the base station (S360). At this time, the reference signal density is 2/12 (RSD = 2/12), and a beacon reference signal is inserted into a radio resource. The base station transmits a NACK to the terminal (S370). The terminal retransmits data to the base station (S380). At this time, the reference signal density is 3/12 (RSD = 3/12), and a beacon reference signal is inserted into a radio resource. That is, the initial transmission of data does not insert a beacon reference signal, but increases the reference signal density as the number of retransmissions of data increases.

As such, the terminal may insert the beacon reference signal in case of data retransmission. In addition, each time the number of data retransmissions increases, the reference signal density may increase with the number of retransmissions.

In an environment in which reception of data from the receiver fails, the traffic itself may be low, resulting in high error rate or poor channel estimation performance. When retransmitting data, the receiver may combine the previously received data with the retransmitted data to obtain a signal-to-noise ratio (SNR) gain and to obtain reliability of data communication. On the other hand, when the RS structure is fixed, the SRN for channel estimation performance at the receiver may be fixed at every retransmission. Therefore, by inserting a beacon reference signal during retransmission, it is possible to improve the channel estimation performance in the receiver. Through this, it is possible to improve traffic performance and obtain reliability of data communication.

32 is a flowchart illustrating a method of transmitting a reference signal according to an embodiment of the present invention.

Referring to FIG. 32, the terminal generates OFDM symbols for data and beacon reference signal elements (S410). The terminal transmits the generated OFDM symbol to the base station (S420).

OFDM symbols for the data and beacon reference signal elements may be generated in two ways. First, the UE outputs complex symbols by performing a DFT on symbols consisting of modulation symbols and beacon reference signal elements for data, maps the complex symbols to subcarriers allocated for data transmission, and performs IFFT to perform OFDM You can create a symbol. Second, the terminal outputs a plurality of complex symbols by performing a DFT on the modulation symbol for the data, maps the plurality of complex symbols and beacon reference signal elements to subcarriers allocated for data transmission, and performs an IFFT to perform an OFDM symbol Can be generated.

As such, at least one beacon reference signal may be inserted in the time domain or the frequency domain. In this case, the insertion of the beacon reference signal may be a method of puncturing data corresponding to the position where the beacon reference signal is to be inserted. Alternatively, a method of not mapping data to a position to insert a beacon reference signal may be used. In detail, a complex symbol corresponding to a subcarrier to which a beacon reference signal element is mapped may be punctured, or a plurality of complex symbols may be mapped to subcarriers other than the subcarrier to which the beacon reference signal element is mapped.

The ratio of data and the beacon reference signal element may be determined according to a reference signal density. The reference signal density may be determined according to a channel environment, a transmission antenna technique, or the number of times of retransmission of data.

As such, a method of transmitting a reference signal capable of improving channel estimation performance in a wireless communication system is provided. A beacon reference signal may be inserted by detecting a channel change caused by the Doppler effect. In addition, the reference signal density of the beacon reference signal may be adaptively changed according to the channel environment or the error rate. Through this, channel estimation performance can be improved and reliability of wireless communication can be improved. Thus, overall system performance can be improved.

So far, the description has been made based on uplink data transmission, but the above description may be applied to downlink data transmission as it is.

All of the above functions may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), or the like according to software or program code coded to perform the function. The design, development and implementation of the code will be apparent to those skilled in the art based on the description of the present invention.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

Claims (12)

1. A reference signal transmission method performed by a terminal in a wireless communication system,

   Generating orthogonal frequency division multiplexing (OFDM) symbols for data and reference signal elements; And

   Transmitting the OFDM symbol to a base station.
2. The method of claim 1,

   Generating the OFDM symbol

   Outputting complex symbols by performing a Discrete Fourier Transform (DFT) on symbols consisting of the modulation symbol for the data and the reference signal element; And

   Mapping the complex symbols to subcarriers allocated for data transmission, and performing an Inverse Fast Fourier Transform (IFFT) to generate the OFDM symbol.
3. The method of claim 1,

   Generating the OFDM symbol

   Outputting a plurality of complex symbols by performing a DFT on the modulation symbols for the data; And

   Mapping the plurality of complex symbols and the reference signal element to subcarriers allocated for data transmission, and performing an IFFT to generate the OFDM symbol.
4. The method of claim 3, wherein

   The complex symbol corresponding to the subcarrier to which the reference signal element is mapped is punctured.
5. The method of claim 3, wherein

   And the plurality of complex symbols are mapped to subcarriers other than the subcarrier to which the reference signal element is mapped among the subcarriers.
6. The method of claim 1,

   The ratio of the data and the reference signal element is determined according to a reference signal density.
7. The method of claim 6,

   The reference signal density is determined according to the channel environment.
8. The method of claim 6,

   The reference signal density is determined according to the transmit antenna technique.
9. The method of claim 6,

   The reference signal density is determined according to the number of retransmission of the data.
10. RF (radio frequency) unit for transmitting a radio signal; And

    Connected to the RF unit,

    Generate OFDM symbols for data and reference signal elements,

    And a data processor for transmitting the OFDM symbol.
11. The method of claim 10,

    The data processing unit

    A DFT unit outputting complex symbols by performing a DFT on the symbols consisting of the modulation symbol for the data and the reference signal element; And

    And an IFFT unit for mapping the complex symbols to subcarriers allocated for data transmission, and performing the IFFT to generate the OFDM symbol.
12. The method of claim 10,

    The data processing unit

    A DFT unit performing a DFT on the modulation symbol for the data and outputting a complex symbol; And

    And an IFFT unit for mapping the complex symbol and the reference signal element to subcarriers allocated for data transmission, and performing the IFFT to generate the OFDM symbol.

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