KR20170106898A - Enhanced channel estimation method and user equipment performing the same - Google Patents

Abstract

A disclosure of the present specification provides a channel estimation method of user equipment (UE). The method includes the steps of: acquiring a first channel estimate based on a first reference signal allocated to a first resource element of a sub frame received from a base station; and removing a second reference signal from a second resource element of the sub frame when an additional reference signal is not required, and decoding a data channel multiplexed in the second resource element by using a channel estimation result of an entire channel performed based on the first channel estimate. In this case, the second reference signal and the data channel may be multiplexed together in the second resource element. Accordingly, the present invention can provide a method for performing enhanced channel estimation in a fast-moving environment or an environment with a poor channel state.

Description

[0001] The present invention relates to an improved channel estimation method and a user equipment

The present invention relates to mobile communications.

The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), an enhancement of Universal Mobile Telecommunications System (UMTS), is introduced as 3GPP release 8. 3GPP LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) in the uplink.

Such LTE is divided into a Frequency Division Duplex (FDD) scheme and a Time Division Duplex (TDD) scheme.

As disclosed in 3GPP TS 36.211 V10.4.0 (2011-12) "Physical Channels and Modulation (Release 10) ", the physical channel in the LTE is a Physical Downlink (PDSCH) A Physical Uplink Control Channel (PDCCH), a Physical Uplink Shared Channel (PUSCH), and a Physical Uplink Control Channel (PUCCH).

On the other hand, data is easily distorted and changed while being transmitted over a wireless channel. Therefore, a reference signal is needed to demodulate such transmission information without error. The reference signal is transmitted along with the transmission information to a known signal between the transmitter and the receiver. Since the transmission information transmitted from the transmitter undergoes a channel corresponding to each transmission antenna or layer, the reference signal can be allocated for each transmission antenna or for each layer. Each transmit antenna or layer-by-layer reference signal can be distinguished using resources such as time, frequency, and code.

However, in the case of a user equipment (UE) located in a high-speed environment or in an environment with poor channel conditions, when receiving data based only on a reference signal that has been previously defined, There is a limit that can not be exercised. Therefore, there is a need for a channel estimation solution for a high-speed moving environment or an environment with poor channel conditions.

It is an object of the present disclosure to provide a method for performing improved channel estimation in a high-speed moving environment or a poor channel condition.

Another object of the present invention is to provide a user apparatus capable of performing an improved channel estimation in a high-speed moving environment or a poor channel condition.

In order to achieve the above object, one aspect of the present disclosure provides a channel estimation method of a user equipment. The method includes obtaining a first channel estimate based on a first reference signal assigned to a first resource element of a subframe received from a base station; And removing the second reference signal from the second resource element of the subframe if an additional reference signal is not required, and using the channel estimation result of the entire channel based on the first channel estimate, And decoding the multiplexed data channel in the element. In this case, the second resource element may multiplex the second reference signal and the data channel together.

The step of decoding the data channel may determine whether to request the additional reference signal based on an indicator received through an RRC (Radio Resource Control) signal.

The method may further include receiving information on the second reference signal from the base station. In this case, the step of decoding the data channel may remove the second reference signal from the second resource element using information on the second reference signal.

The decoding of the data channel may include performing channel estimation of the entire channel based on the second channel estimate and the first channel estimate obtained based on the second reference signal when the additional reference signal is required have.

The channel estimation of the entire channel may be performed by applying a weight according to the degree of power boosting to the second channel estimate when the second reference signal is transmitted by power boosting the first reference signal. In addition, the channel estimation of the entire channel may be performed by applying the weight of the first channel estimate and the weight of the second channel estimate evenly.

The method may further comprise performing a Radio Resource Measurement (RRM) using only the first reference signal even when the additional reference signal is required.

In order to achieve the above object, another disclosure of the present specification provides a user equipment for performing channel estimation. The user equipment includes a radio frequency (RF) unit for transmitting and receiving a radio signal; And a processor for controlling the RF unit. The processor controls the RF unit to receive a subframe from the base station; Obtaining a first channel estimate based on a first reference signal assigned to a first Resource Element of the subframe; And removing the second reference signal from the second resource element of the subframe if an additional reference signal is not required, and using the channel estimation result of the entire channel based on the first channel estimate, It is possible to perform a procedure of decoding the multiplexed data channel to the element. In this case, the second resource element may multiplex the second reference signal and the data channel together.

According to the disclosure of the present specification, it is possible to perform an improved channel estimation in an environment moving at a high speed or in a poor channel condition. In addition, it is possible to minimize the transmission rate degradation due to the overhead of the reference signal transmission.

1 is a wireless communication system.
2 shows a structure of a radio frame according to FDD in 3GPP LTE.
3 shows a structure of a downlink radio frame according to TDD in 3GPP LTE.
4 is an exemplary diagram illustrating a resource grid for one uplink or downlink slot in 3GPP LTE.
5 shows a structure of a downlink sub-frame.
6 shows a structure of a UL subframe in 3GPP LTE.
7 is a comparative example of a single carrier system and a carrier aggregation system.
8 illustrates cross-carrier scheduling in a carrier aggregation system.
9-11 illustrate some examples of CRS structures along the antenna port.
12 shows an example of a CSI-RS structure.
13 shows an example of an antenna virtualization structure for an A-RS according to an embodiment of the present disclosure.
14 is a reference signal structure for an antenna port of an A-RS structure type 1 according to an embodiment of the present disclosure.
15 shows an example of a channel estimation method of a UE using an A-RS according to an embodiment of the present disclosure.
16 shows an example of a channel estimation method of a UE that does not use A-RS according to an embodiment of the present invention.
17 is a flowchart showing a channel estimation method according to an embodiment of the present invention.
18 is a block diagram illustrating a wireless communication system in which the present disclosure is implemented.

Hereinafter, it is described that the present invention is applied based on 3rd Generation Partnership Project (3GPP) 3GPP long term evolution (LTE) or 3GPP LTE-A (LTE-Advanced). This is merely an example, and the present invention can be applied to various wireless communication systems. Hereinafter, LTE includes LTE and / or LTE-A.

It is noted that the technical terms used herein are used only to describe specific embodiments and are not intended to limit the invention. It is also to be understood that the technical terms used herein are to be interpreted in a sense generally understood by a person skilled in the art to which the present invention belongs, Should not be construed to mean, or be interpreted in an excessively reduced sense. Further, when a technical term used herein is an erroneous technical term that does not accurately express the spirit of the present invention, it should be understood that technical terms that can be understood by a person skilled in the art are replaced. In addition, the general terms used in the present invention should be interpreted according to a predefined or prior context, and should not be construed as being excessively reduced.

Also, the singular forms "as used herein include plural referents unless the context clearly dictates otherwise. In the present application, the term "comprising" or "having ", etc. should not be construed as necessarily including the various elements or steps described in the specification, and some of the elements or portions thereof Or may further include additional components or steps.

Furthermore, terms including ordinals such as first, second, etc. used in this specification can be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

When an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may be present in between. On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the understanding of the present invention and should not be construed as limiting the scope of the present invention. The spirit of the present invention should be construed as extending to all modifications, equivalents, and alternatives in addition to the appended drawings.

The term base station, as used hereinafter, refers to a fixed station that typically communicates with a wireless device and includes an evolved-NodeB (eNodeB), an evolved-NodeB (eNB), a Base Transceiver System (BTS) Access Point).

Hereinafter, the term UE (User Equipment), which is a used term, may be fixed or mobile and may be a device, a wireless device, a terminal, a mobile station (MS), a user terminal (UT) , Subscriber Station (SS), Mobile Terminal (MT), and the like.

1 is a wireless communication system.

1, the wireless communication system includes at least one base station (BS) 20. Each base station 20 provides a communication service to a specific geographical area (generally called a cell) 20a, 20b, 20c. A cell can again be divided into multiple regions (called sectors).

A UE typically belongs to one cell, and the cell to which the UE belongs is called a serving cell. A base station providing a communication service to a serving cell is called a serving BS. Since the wireless communication system is a cellular system, there are other cells adjacent to the serving cell. Another cell adjacent to the serving cell is called a neighbor cell. A base station that provides communication services to neighbor cells is called a neighbor BS. The serving cell and the neighboring cell are relatively determined based on the UE.

Hereinafter, the downlink refers to the communication from the base station 20 to the UE 10, and the uplink refers to the communication from the UE 10 to the base station 20. In the downlink, the transmitter may be part of the base station 20 and the receiver may be part of the UE 10. In the uplink, the transmitter may be part of the UE 10 and the receiver may be part of the base station 20.

Meanwhile, the wireless communication system can be used in a multiple-input multiple-output (MIMO) system, a multiple-input single-output (MISO) system, a single-input single-output (SISO) system, and a single- It can be either. A 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, a transmit antenna means a physical or logical antenna used to transmit one signal or stream, and a receive antenna means a physical or logical antenna used to receive one signal or stream.

Meanwhile, the wireless communication system can be broadly classified into a Frequency Division Duplex (FDD) system and a Time Division Duplex (TDD) system. According to the FDD scheme, uplink transmission and downlink transmission occupy different frequency bands. According to the TDD scheme, uplink transmission and downlink transmission occupy the same frequency band and are performed at different times. The channel response of the TDD scheme is substantially reciprocal. This is because the downlink channel response and the uplink channel response are almost the same in a given frequency domain. Therefore, in the TDD-based wireless communication system, the downlink channel response has an advantage that it can be obtained from the uplink channel response. The TDD scheme can not simultaneously perform downlink transmission by the base station and uplink transmission by the UE because the uplink transmission and the downlink transmission are time-divisional in the entire frequency band. In a TDD system in which uplink transmission and downlink transmission are divided into subframe units, uplink transmission and downlink transmission are performed in different subframes.

Hereinafter, the LTE system will be described in more detail.

2 is a cross- 3GPP In LTE  Shows the structure of a radio frame according to the FDD.

The radio frame shown in FIG. 2 can refer to section 5 of 3GPP TS 36.211 V10.4.0 (2011-12) "Evolved Universal Terrestrial Radio Access (E-UTRA), Physical Channels and Modulation (Release 10)".

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

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

On the other hand, one slot may include a plurality of OFDM symbols. How many OFDM symbols are included in one slot may vary according to a cyclic prefix (CP).

3, 3GPP In LTE TDD  And a downlink radio frame according to an embodiment of the present invention.

This can be referred to Section 4 of 3GPP TS 36.211 V10.4.0 (2011-12) "Evolved Universal Terrestrial Radio Access (E-UTRA), Physical Channels and Modulation (Release 10) will be..

A radio frame includes 10 subframes indexed from 0 to 9. One subframe includes two consecutive slots. For example, the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms.

One slot may include a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols in the time domain. OFDM symbols are used to represent one symbol period in the time domain since 3GPP LTE uses OFDMA (Orthogonal Frequency Division Multiple Access) in downlink (DL) It is not limited. For example, an OFDM symbol may be referred to as another name, such as a single carrier-frequency division multiple access (SC-FDMA) symbol, a symbol period, or the like.

One slot may illustratively include 7 OFDM symbols, but the number of OFDM symbols included in one slot may be changed according to the length of the CP. One slot in a normal CP includes 7 OFDM symbols, and one slot in an extended CP includes 6 OFDM symbols.

A resource block (RB) is a resource allocation unit and includes a plurality of subcarriers in one slot. For example, if one slot includes 7 OFDM symbols in the time domain and the resource block includes 12 subcarriers in the frequency domain, one resource block may include 7 × 12 resource elements (REs) .

A subframe having indexes # 1 and # 6 is called a special subframe and includes a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). DwPTS is used for initial cell search, synchronization, or channel estimation in the UE. UpPTS is used to match the channel estimation at the base station and the uplink transmission synchronization of the UE. The GP is a section for eliminating the interference caused in the uplink due to the multipath delay of the downlink signal between the uplink and the downlink.

In TDD, DL (downlink) subframe and UL (uplink) subframe coexist in one radio frame. Table 1 shows an example of the configuration of a radio frame.

UL-DL Setup Switch-point periodicity Subframe index 0 One 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U One 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D

'D' denotes a DL sub-frame, 'U' denotes a UL sub-frame, and 'S' denotes a special sub-frame. Upon receiving the UL-DL setting from the base station, the UE can know which subframe is the DL subframe or the UL subframe according to the setting of the radio frame.

A DL (downlink) subframe is divided into a control region and a data region in a time domain. The control region includes up to three OFDM symbols preceding the first slot in the subframe, but the number of OFDM symbols included in the control region may be changed. A PDCCH and another control channel are assigned to the control region, and a PDSCH is assigned to the data region.

Figure 4 3GPP In LTE  A resource grid for one uplink or downlink slot is shown. It is also an example .

Referring to FIG. 4, an uplink slot includes a plurality of OFDM symbols in a time domain, and includes N _RB resource blocks (RB) in a frequency domain. For example, the number of resource blocks (RBs) in the LTE system, i.e., N _RB , can be any of 6 to 110. The RB is also referred to as PRB (Physical Resource Block).

Herein, one resource block (RB) includes 7 OFDM symbols in the time domain and 7 × 12 resource elements (RE) including 12 subcarriers in the frequency domain. However, the number of sub-carriers in the resource block The number of OFDM symbols is not limited to this. The number of OFDM symbols or the number of subcarriers included in the resource block may be variously changed. That is, the number of OFDM symbols can be changed according to the length of the CP. Particularly, in the 3GPP LTE, seven OFDM symbols are included in one slot for a normal CP, and six OFDM symbols are included in one slot for an extended CP.

An OFDM symbol represents one symbol period and may be referred to as an SC-FDMA symbol, an OFDMA symbol, or a symbol interval depending on the system. The resource block includes a plurality of subcarriers in the frequency domain as a resource allocation unit. The number of resource blocks N _UL included in the uplink slot is dependent on the uplink transmission bandwidth set in the cell. Each element on the resource grid is called a resource element (RE).

On the other hand, the number of subcarriers in one OFDM symbol can be selected from among 128, 256, 512, 1024, 1536 and 2048.

In the 3GPP LTE of FIG. 4, a resource grid for one uplink slot can be applied to a resource grid for a downlink slot.

5 shows a structure of a downlink sub-frame.

In FIG. 5, seven OFDM symbols are included in one slot, assuming a normal CP. However, the number of OFDM symbols included in one slot may be changed according to the length of a cyclic prefix (CP). That is, as described above, according to 3GPP TS 36.211 V10.4.0, one slot in a normal CP includes 7 OFDM symbols, and one slot in an extended CP includes 6 OFDM symbols.

A DL (downlink) subframe is divided into a control region and a data region in a time domain. The control region includes up to three OFDM symbols preceding the first slot in the subframe, but the number of OFDM symbols included in the control region may be changed. A Physical Downlink Control Channel (PDCCH) and another control channel are allocated to the control region, and a PDSCH is allocated to the data region.

In the 3GPP LTE, a physical channel includes a Physical Downlink Shared Channel (PDSCH), a Physical Uplink Shared Channel (PUSCH), a Physical Downlink Control Channel (PDCCH), a Physical Control Format Indicator Channel (PCFICH) ARQ Indicator Channel) and PUCCH (Physical Uplink Control Channel).

The PCFICH transmitted in the first OFDM symbol of the subframe carries CFI (Control Format Indicator) with respect to the number of OFDM symbols (i.e., the size of the control region) used for transmission of the control channels in the subframe. The wireless device first receives the CFI on the PCFICH and then monitors the PDCCH.

Unlike PDCCH, PCFICH does not use blind decoding, but is transmitted through a fixed PCFICH resource of a subframe.

The PHICH carries an ACK (positive-acknowledgment) / NACK (Negative-acknowledgment) signal for UL HARQ (Hybrid Automatic Repeat reQuest). The ACK / NACK signal for the UL data on the PUSCH transmitted by the wireless device is transmitted on the PHICH.

A PBCH (Physical Broadcast Channel) is transmitted in four OFDM symbols preceding the second slot of the first subframe of the radio frame. The PBCH carries the system information necessary for the radio equipment to communicate with the base station, and the system information transmitted through the PBCH is called the master information block (MIB). In comparison, the system information transmitted on the PDSCH indicated by the PDCCH is called a system information block (SIB).

The PDCCH includes a resource allocation and transmission format of a downlink-shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a PCH, system information on a DL- Resource allocation of an upper layer control message such as a response, a set of transmission power control commands for individual UEs in an arbitrary UE group, and activation of VoIP (Voice over Internet Protocol). A plurality of PDCCHs may be transmitted in the control domain, and the UE may monitor a plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive CCEs (Control Channel Elements). The CCE is a logical allocation unit used to provide the PDCCH with the coding rate according to the state of the radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the number of bits of the possible PDCCH are determined according to the relationship between the number of CCEs and the coding rate provided by the CCEs.

The control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes a set of transmission power control commands for individual UEs in any UE group, resource allocation (also referred to as DL grant) of the PDSCH, resource allocation of PUSCH (also referred to as UL grant) And / or Voice over Internet Protocol (VoIP).

The base station determines the PDCCH format according to the DCI to be sent to the UE, and attaches a CRC (Cyclic Redundancy Check) to the control information. The CRC is masked with a Radio Network Temporary Identifier (RNTI) unique to the owner or use of the PDCCH. If it is a PDCCH for a particular UE, the unique identifier of the UE, e.g. C-RNTI (Cell-RNTI), may be masked in the CRC. Alternatively, if the PDCCH is a PDCCH for a paging message, a paging indication identifier, e.g., P-RNTI (P-RNTI), may be masked on the CRC. If the PDCCH is for a system information block (SIB), the system information identifier, SI-RNTI (System Information-RNTI), may be masked in the CRC. Random Access-RNTI (R-RNTI) may be masked in the CRC to indicate a random access response that is a response to the transmission of the UE's random access preamble.

In 3GPP LTE, blind decoding is used for PDCCH detection. Blind decoding is a method for checking whether a corresponding PDCCH is a control channel by checking a CRC error by demodulating a desired identifier in a cyclic redundancy check (CRC) of a received PDCCH (referred to as a candidate PDCCH) . The base station determines the PDCCH format according to the DCI to be transmitted to the wireless device, attaches a CRC to the DCI, and masks a unique identifier (RNTI) to the CRC according to the owner or use of the PDCCH.

A control region in a subframe includes a plurality of CCEs (Control Channel Elements). The CCE is a logical allocation unit used to provide the PDCCH with the coding rate according to the state of the radio channel, and corresponds to a plurality of REGs (Resource Element Groups). The REG includes a plurality of resource elements (REs). The format of the PDCCH and the number of bits of the possible PDCCH are determined according to the relationship between the number of CCEs and the coding rate provided by the CCEs.

One REG includes four REs, and one CCE includes nine REGs. {1, 2, 4, 8} CCEs can be used to construct one PDCCH, and each element of {1, 2, 4, 8} is called a CCE aggregation level.

The number of CCEs used for transmission of the PDCCH is determined by the base station according to the channel state. For example, a UE having a good downlink channel state can use one CCE for PDCCH transmission. For a UE having a poor downlink channel state, eight CCEs can be used for PDCCH transmission.

A control channel composed of one or more CCEs performs REG interleaving and is mapped to a physical resource after a cyclic shift based on a cell ID is performed.

On the other hand, the UE can not know at which position in the control area its PDCCH is transmitted using any CCE aggregation level or DCI format. Since a plurality of PDCCHs can be transmitted in one subframe, the UE monitors a plurality of PDCCHs in each subframe. Here, monitoring refers to the UE attempting to decode the PDCCH according to the PDCCH format.

In 3GPP LTE, a search space is used to reduce the burden due to blind decoding. The search space is a monitoring set of the CCE for the PDCCH. The terminal monitors the PDCCH within the search space.

When the UE monitors the PDCCH based on the C-RNTI, the DCI format and the search space to be monitored are determined according to the Transmission Mode (TM) of the PDSCH. The following table shows an example of PDCCH monitoring in which C-RNTI is set.

Transfer mode DCI format Search space The transmission mode of the PDSCH according to the PDCCH Transfer mode 1 DCI Format 1A Public and terminal specific Single antenna port, port 0 DCI format 1 Terminal specific Single antenna port, port 0 Transfer mode 2 DCI Format 1A Public and terminal specific Transmit diversity < RTI ID = 0.0 > DCI format 1 Terminal specific Transmit diversity Transfer Mode 3 DCI Format 1A Public and terminal specific Transmit diversity DCI Format 2A Terminal specific CDD (Cyclic Delay Diversity) or transmission diversity Transfer Mode 4 DCI Format 1A Public and terminal specific Transmit diversity DCI format 2 Terminal specific Closed-loop spatial multiplexing Transfer mode 5 DCI Format 1A Public and terminal specific Transmit diversity DCI format 1D Terminal specific Multi-user Multiple Input Multiple Output (MU-MIMO) Transfer Mode 6 DCI Format 1A Public and terminal specific Transmit diversity DCI Format 1B Terminal specific Closed-loop spatial multiplexing Transfer Mode 7 DCI Format 1A Public and terminal specific If the number of PBCH transmission ports is 1, then a single antenna port, port 0, otherwise, DCI format 1 Terminal specific Single antenna port, port 5 Transfer Mode 8 DCI Format 1A Public and terminal specific If the number of PBCH transmission ports is 1, then a single antenna port, port 0, otherwise, DCI format 2B Terminal specific Dual layer transmission (port 7 or 8), or single antenna port, port 7 or 8 Transfer Mode 9 DCI Format 1A Public and terminal specific Non-MBSFN subframe: if the number of PBCH antenna ports is one, port 0 is used as a single antenna port; otherwise, the transmit diversity is used.
MBSFN subframe: as a single antenna port, port 7 DCI format 2C Terminal specific Up to 8 transport layers, ports 7-14 are used, or port 7 or port 8 is used as the sole antenna port Transfer mode 10 DCI Format 1A Public and terminal specific Non-MBSFN subframe: if the number of PBCH antenna ports is one, port 0 is used as a single antenna port; otherwise, the transmit diversity is used.
MBSFN subframe: as a single antenna port, port 7 DCI format 2D Terminal specific Up to 8 transport layers, ports 7-14 are used, or port 7 or port 8 is used as the sole antenna port

The use of the DCI format is divided into the following table.

DCI format Contents DCI format 0 Used for PUSCH scheduling DCI format 1 Used for scheduling of one PDSCH codeword DCI Format 1A Used for compact scheduling and random access procedure of one PDSCH codeword DCI Format 1B Used for simple scheduling of one PDSCH codeword with precoding information DCI format 1C Used for very compact scheduling of one PDSCH codeword DCI format 1D Used for simple scheduling of one PDSCH codeword with precoding and power offset information DCI format 2 Used for PDSCH scheduling of UEs set in closed loop space multiplexing mode DCI Format 2A Used for PDSCH scheduling of UEs set to open-loop spatial multiplexing mode DCI format 2B DCI format 2B is used for resource allocation for dual-layer beamforming of the PDSCH. DCI format 2C DCI format 2C is used for resource allocation for per-loop SU-MIMO or MU-MIMO operations up to eight layers. DCI format 2D DCI format 2C is used for resource allocation up to 8 layers. DCI format 3 Used to transmit TPC commands of PUCCH and PUSCH with 2-bit power adjustments DCI format 3A Used for transmission of TPC commands of PUCCH and PUSCH with 1 bit power adjustment DCI format 4 Used for PUSCH scheduling of uplink (UL) cells operating in multi-antenna port transmission mode

The uplink channel includes a PUSCH, a PUCCH, a sounding reference signal (SRS), and a physical random access channel (PRACH).

On the other hand, the PDCCH is monitored in a limited area called a control region in a subframe, and a CRS transmitted in the entire band is used for demodulating the PDCCH. As the types of control information are diversified and the amount of control information is increased, the flexibility of scheduling is degraded only by the existing PDCCH. Also, in order to reduce the burden due to CRS transmission, enhanced PDCCH (EPDCCH) is being introduced.

6, 3GPP In LTE  And shows the structure of the uplink subframe.

Referring to FIG. 6, an uplink subframe may be divided into a control region and a data region in a frequency domain. A PUCCH (Physical Uplink Control Channel) for transmitting uplink control information is allocated to the control region. A data area is allocated a physical uplink shared channel (PUSCH) for transmitting data (in some cases, control information may be transmitted together).

The PUCCH for one UE is allocated as a resource block pair (RB pair) in a subframe. The resource blocks belonging to the resource block pair occupy different subcarriers in the first slot and the second slot. The frequency occupied by the resource blocks belonging to the resource block pair allocated to the PUCCH is changed based on the slot boundary. It is assumed that the RB pair allocated to the PUCCH is frequency-hopped at the slot boundary.

A frequency diversity gain can be obtained by transmitting uplink control information through different subcarriers according to time. and m is a position index indicating the logical frequency domain position of the resource block pair allocated to the PUCCH in the subframe.

The uplink control information transmitted on the PUCCH includes a Hybrid Automatic Repeat reQuest (ACKnowledgment) / NACK (Non-acknowledgment), a CQI (Channel Quality Indicator) indicating a downlink channel state, (Scheduling Request).

The PUSCH is mapped to a UL-SCH, which is a transport channel. The uplink data transmitted on the PUSCH may be a transport block that is a data block for UL-SCH transmitted during a transmission time interval (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.

≪ Carrier Aggregation (CA) >

Now, the carrier aggregation system will be described.

7 is a comparative example of a single carrier system and a carrier aggregation system.

Referring to FIG. 7A, in a single carrier system, only one carrier is supported for uplink and downlink in a UE. The bandwidth of the carrier wave may vary, but one carrier is allocated to the UE. On the other hand, referring to FIG. 8B, a plurality of element carriers (DL CC A to C, UL CC A to C) may be allocated to a UE in a carrier aggregation (CA) system. Component carrier (CC) means a carrier wave used in a carrier wave integration system and can be abbreviated as a carrier wave. For example, three 20 MHz element carriers may be allocated to allocate a bandwidth of 60 MHz to the UE.

A carrier aggregation system can be classified into a contiguous carrier aggregation system in which aggregated carriers are continuous and a non-contiguous carrier aggregation system in which aggregated carriers are separated from each other. Hereinafter, when it is simply referred to as a carrier aggregation system, it should be understood that this includes both continuous and discontinuous element carriers. The number of element carriers to be aggregated between the downlink and the uplink may be set differently. The case where the number of downlink CCs and the number of uplink CCs are the same is referred to as a symmetric aggregation, and the case where the number of downlink CCs is different is referred to as asymmetric aggregation.

When composing more than one element carrier, the element carrier can use the bandwidth used in the existing system for backward compatibility with the existing system. For example, the 3GPP LTE system can support a bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz, and in the 3GPP LTE-A system, a broadband of 20 MHz or more can be constructed using only the bandwidth of the 3GPP LTE system. Alternatively, a broadband may be configured by defining a new bandwidth without using the bandwidth of the existing system.

The system frequency band of a wireless communication system is divided into a plurality of carrier frequencies. Here, the carrier frequency means a center frequency of a cell. In the following, a cell may mean a downlink frequency resource and an uplink frequency resource. Or a cell may mean a combination of a downlink frequency resource and an optional uplink frequency resource. In general, in a case where a carrier aggregation (CA) is not considered, uplink and downlink frequency resources may always exist in one cell.

In order to transmit and receive packet data through a specific cell, the UE must first complete a configuration for a specific cell. Here, the 'configuration' means a state in which the reception of the system information necessary for data transmission / reception for the corresponding cell is completed. For example, the configuration may include common physical layer parameters required for data transmission and reception, media access control (MAC) layer parameters, or a general procedure for receiving parameters required for a specific operation in a radio resource control (RRC) layer . ≪ / RTI > The set-up cell is in a state in which it can transmit and receive packets immediately when it receives only information that packet data can be transmitted.

The cell in the set completion state may be in an activated state or a deactivation state. Here, activation means that data transmission or reception is performed or is in a ready state. The UE may monitor or receive the active cell's control channel (PDCCH) and data channel (PDSCH) to ascertain the resource (which may be frequency, time, etc.) allocated to it.

Deactivation means that transmission or reception of traffic data is impossible and measurement or transmission / reception of minimum information is possible. The UE may receive System Information (SI) necessary for receiving a packet from the deactivation cell. On the other hand, the UE does not monitor or receive the control channel (PDCCH) and the data channel (PDSCH) of the deactivated cell in order to confirm the resource (which may be frequency, time, etc.) allocated to the UE.

A cell may be divided into a primary cell, a secondary cell, and a serving cell.

The primary cell refers to a cell operating at a primary frequency. The primary cell is a cell in which a UE performs an initial connection establishment procedure or connection re-establishment process with a base station, Cell.

A secondary cell is a cell operating at a secondary frequency, and once established, an RRC connection is established and used to provide additional radio resources.

The serving cell is configured as a primary cell if the carrier aggregation is not established or the UE is not capable of providing carrier aggregation. When carrier aggregation is set, the term serving cell indicates a cell set for the UE and may be composed of a plurality. One serving cell may be composed of one downlink component carrier or {pair of downlink component carrier, uplink component carrier}. The plurality of serving cells may consist of a primary cell and a set of one or more of all secondary cells.

As described above, unlike a single carrier system, the carrier aggregation system can support a plurality of element carriers (CC), i.e., a plurality of serving cells.

Such a carrier aggregation system may support cross-carrier scheduling. Cross-carrier scheduling may be performed by assigning a resource allocation of a PDSCH that is transmitted over a different element carrier over a PDCCH that is transmitted over a specific element carrier and / or a resource allocation of elements other than an element carrier that is basically linked with the particular element carrier A scheduling method that can allocate resources of a PUSCH transmitted through a carrier wave. That is, the PDCCH and the PDSCH can be transmitted through different downlink CCs, and the PUSCH can be transmitted through the uplink CC other than the uplink CC linked with the downlink CC to which the PDCCH including the UL grant is transmitted . Thus, in a system supporting cross-carrier scheduling, a carrier indicator is required to indicate to which DL CC / UL CC the PDSCH / PUSCH for providing control information is transmitted through the PDCCH. A field including such a carrier indicator is hereinafter referred to as a Carrier Indication Field (CIF).

A carrier aggregation system that supports cross-carrier scheduling may include a carrier indication field (CIF) in a conventional DCI (Downlink Control Information) format. For example, in the LTE-A system, the CIF is added to the existing DCI format (i.e., the DCI format used in LTE), so that 3 bits can be extended. The PDCCH structure can be divided into an existing coding method, Resource allocation method (i.e., CCE-based resource mapping), and the like can be reused.

8 illustrates cross-carrier scheduling in a carrier aggregation system.

Referring to FIG. 8, a base station can set up a PDCCH monitoring DL CC (monitoring CC) set. PDCCH Monitoring The DL CC aggregation is composed of some DL CCs among aggregated DL CCs. When cross-carrier scheduling is set, the UE performs PDCCH monitoring / decoding only on the DL CCs included in the PDCCH monitoring DL CC aggregation. In other words, the BS transmits the PDCCH for the PDSCH / PUSCH to be scheduled only through the DL CC included in the PDCCH monitoring DL CC set. PDCCH Monitoring The DL CC aggregation can be UE-specific, UE group-specific, or cell-specific.

FIG. 8 shows an example in which three DL CCs (DL CC A, DL CC B, and DL CC C) are aggregated and a DL CC A is set as a PDCCH monitoring DL CC. The UE can receive the DL grant for the PDSCH of DL CC A, DL CC B, and DL CC C through the PDCCH of DL CC A. The DCI transmitted through the PDCCH of the DL CC A may include the CIF to indicate which DC CC is for the DL CC.

<Reference Signal: RS )>

The reference signal will now be described.

Generally, transmission information, e.g., data, is easily distorted or changed while being transmitted over a wireless channel. Therefore, a reference signal is needed to demodulate such transmission information without error. The reference signal is transmitted along with the transmission information to a known signal between the transmitter and the receiver. Since the transmission information transmitted from the transmitter undergoes a channel corresponding to each transmission antenna or layer, the reference signal can be allocated for each transmission antenna or for each layer. Each transmit antenna or layer-by-layer reference signal can be distinguished using resources such as time, frequency, and code. The reference signal can be used for two purposes: demodulation of the transmission information and channel estimation.

In general, the reference signal is transmitted in a sequence. The reference signal sequence may be any sequence without any particular limitation. The reference signal sequence may use a PSK-based computer generated sequence (PSK) -based computer. 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 the CAZAC sequence include a ZC-based sequence, a ZC sequence with a cyclic extension, a truncation ZC sequence (ZC sequence with truncation), and the like . Alternatively, the reference signal sequence may use a PN (pseudo-random) sequence. Examples of PN sequences include m-sequences, computer generated sequences, Gold sequences, and Kasami sequences. Also, the reference signal sequence may use a cyclically shifted sequence.

The reference signal may be divided into a cell-specific RS (CRS), an MBSFN reference signal, and a UE-specific RS. The CRS is used for channel estimation as a reference signal transmitted to all UEs in a cell. The MBSFN reference signal may be transmitted in a subframe allocated for MBSFN transmission. The UE-specific reference signal may be referred to as a dedicated reference signal (DRS: Dedicated RS) as a reference signal received by a specific UE or a specific UE group in a cell. DRS is mainly used for data demodulation by a specific terminal or a specific terminal group.

Also, the reference signal may be classified according to the use. For example, a reference signal used for demodulating data is referred to as a demodulation reference signal (DM-RS). A reference signal used for feedback information indicating a channel state such as CQI / PMI / RI is referred to as CSI-RS (channel state information-RS). The above-described dedicated reference signal DRS can be used as the demodulation reference signal DM-RS.

First, we explain CRS.

9 To  11 shows some examples of the CRS structure according to the antenna port.

FIG. 9 shows a case where a base station uses one antenna, FIG. 10 shows an example of a CRS structure when a base station uses two antennas, and FIG. 11 shows an example of a CRS structure when a base station uses four antennas. This can be referred to in 3GPP TS 36.211 V8.2.0 (2008-03), clause 6.10.1. The CRS structure may also be used to support features of the LTE-A system. For example, cooperative multi-point (CoMP) transmission reception techniques or spatial multiplexing. The CRS can also be used for channel quality measurement, CP detection, time / frequency synchronization, and the like.

Referring to FIGS. 9 to 11, in the case of a multi-antenna transmission in which a base station uses a plurality of antennas, there is one resource grid for each antenna. 'R0' denotes a reference signal for the first antenna, 'R1' denotes a reference signal to the second antenna, 'R2' denotes a reference signal to the third antenna, and 'R3' denotes a reference signal to the fourth antenna. The positions in the sub-frames of R0 to R3 do not overlap each other. ℓ is the position of the OFDM symbol in the slot, and ℓ in the normal CP has a value between 0 and 6. In one OFDM symbol, the reference signal for each antenna is located at six subcarrier spacing. The number of R0 and the number of R1 in the subframe are the same, and the number of R2 and the number of R3 are the same. The number of R2, R3 in the subframe is less than the number of R0, R1. The resource element used for the reference signal of one antenna is not used for the reference signal of the other antenna. To avoid interference between antennas.

CRS is always transmitted by the number of antennas regardless of the number of streams. The CRS has an independent reference signal for each antenna. The position of the frequency domain and the position of the time domain within the subframe of the CRS are determined regardless of the UE. The CRS sequence multiplied by the CRS is also generated regardless of the UE. Therefore, all terminals in the cell can receive the CRS. However, the position in the sub-frame of the CRS and the CRS sequence can be determined according to the cell ID. The position of the CRS in the time domain within the subframe can be determined according to the number of the antenna and the number of OFDM symbols in the resource block. The position of the frequency domain in the subframe of the CRS can be determined according to the antenna number, the cell ID, the OFDM symbol index (l), the slot number in the radio frame, and the like.

The CRS sequence can be applied in OFDM symbols in one subframe. The CRS sequence may vary depending on the cell ID, the slot number in one radio frame, the OFDM symbol index in the slot, the CP type, and the like. The number of reference signal subcarriers for each antenna on one OFDM symbol is two. Assuming that the subframe includes N _RB resource blocks in the frequency domain, the number of reference signal subcarriers for each antenna on one OFDM symbol is 2 x N _RB . Therefore, the length of the CRS sequence is 2 x N _RB .

Equation (1) shows an example of the CRS sequence r (m).

Here, m is 0, 1, ..., 2N _RB ^max- 1. 2N _RB ^max is the number of resource blocks corresponding to the maximum bandwidth. For example, 2N _RB ^max in a 3GPP LTE system is 110. c (i) can be defined by a Gold sequence of length-31, as a PN sequence and a mock random sequence. Equation (2) shows an example of the gold sequence c (n).

Here, _{Nc = 1600, x 1 (i} ) is the m- sequence of claim 1, x ₂ (i) it is the m- sequence of claim 2. For example, the first m-sequence or the second m-sequence may be initialized according to a cell ID, a slot number in one radio frame, an OFDM symbol index in a slot, a CP type, and the like for every OFDM symbol.

In the case of a system having a bandwidth smaller than 2N _RB ^max , only a certain portion of 2 × N _RB lengths can be selected and used in the reference signal sequence generated with a length of 2 × 2N _RB ^max .

CRS can be used for estimation of channel state information (CSI) in an LTE-A system. A Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), and a Rank Indicator (RI) may be reported from the UE, if necessary, through the estimation of the CSI.

Next, the CSI-RS will be described.

Figure 12 shows the CSI- RS  &Lt; / RTI &gt; structure.

The CSI-RS is used for channel estimation for the PDSCH of the LTE-A terminal and channel measurement for channel information generation. The CSI-RS is relatively sparse in the frequency domain or time domain and can be punctured in the data domain of the normal subframe or MBSFN subframe. CQI, PMI and RI can be reported from the terminal if necessary through the estimation of CSI.

The CSI-RS is transmitted over one, two, four or eight antenna ports. The antenna ports used here are p = 15, p = 15, 16, p = 15, ..., 18 and p = 15, ..., That is, the CSI-RS can be transmitted through 1, 2, 4, or 8 antenna ports. The CSI-RS can only be defined for subcarrier spacing [Delta] f = 15 kHz. The CSI-RS is a member of the 3rd Generation Partnership Project (3GPP) TS 36.211 V10.1.0 (2011-03) "Technical Specification Group Radio Access Network (E-UTRA) See Section 6.10.5.

Up to 32 different configurations may be proposed to reduce inter-cell interference (ICI) in a multi-cell environment including a heterogeneous network environment in the transmission of CSI-RS. have. The CSI-RS configuration differs according to the number of antenna ports and the CP in the cell, and neighboring cells may have different configurations as much as possible. In addition, the CSI-RS configuration can be divided into the case of applying to both the FDD frame and the TDD frame and the case of applying to only the TDD frame according to the frame structure. A plurality of CSI-RS configurations may be used in one cell. Zero or one CSI-RS configuration for a terminal assuming a non-zero power CSI-RS, zero or more CSI-RSs for a terminal assuming a zero power CSI- RS configuration can be used.

The CSI-RS configuration may be indicated by an upper layer. For example, a CSI-RS-Config IE (Information Element) transmitted through an upper layer may indicate a CSI-RS configuration. The following table shows an example of the CSI-RS-Config IE.

Referring to Table 4, the 'antennaPortsCount' field indicates the number of antenna ports used for CSI-RS transmission. The 'resourceConfig' field indicates the CSI-RS configuration. The 'SubframeConfig' field and the 'zeroTxPowerSubframeConfig' field indicate the subframe configuration in which the CSI-RS is transmitted.

The 'zeroTxPowerResourceConfigList' field indicates the configuration of the zero power CSI-RS. a CSI-RS configuration corresponding to a bit set to 1 in a 16-bit bitmap constituting the 'zeroTxPowerResourceConfigList' field may be set to zero power CSI-RS.

The sequence r _{l, ns} (m) for the CSI-RS can be generated as:

here,

Where n _s is the slot number in the radio frame and l is the OFDM symbol number in the slot. c (i) is a pseudo random sequence and starts in each OFDM symbol with c _init shown in Equation (3). N _ID ^cell means physical cell ID.

In the subframes set to transmit CSI-RS, the reference signal sequence rl _{, ns} (m) is mapped to a complex-valued modulation symbol a _{k, l} ^(p) used as a reference symbol for antenna port p.

The relation between r _{l, n s} (m) and a _{k, l} ^(p) is as follows.

here,

(K ', l') and n _s in the above equation are given in Tables 5 and 6 below. The CSI-RS can be transmitted in a downlink slot satisfying the conditions of Table 5 and Table 6 below (n _s mod 2), where mod denotes a modular operation: (n _s mod 2) Means the remainder of 2 divided by n _s ).

Table 5 below shows the configuration of the CSI-RS in the normal CP, and Table 6 shows the configuration of the CSI-RS in the extended CP.

Number of CSI-RSs to be configured 1 or 2 4 8 CSI-RS configuration index (k`, l`) n _s mod 2 (k`, l`) n _s mod 2 (k`, l`) n _s mod 2 TDD and
FDD
frame 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 One (11,2) One (11,2) One (11,2) One 2 (9,2) One (9,2) One (9,2) One 3 (7,2) One (7,2) One (7,2) One 4 (9, 5) One (9, 5) One (9, 5) One 5 (8, 5) 0 (8, 5) 0 6 (10, 2) One (10, 2) One 7 (8,2) One (8,2) One 8 (6,2) One (6,2) One 9 (8, 5) One (8, 5) One 10 (3,5) 0 11 (2,5) 0 12 (5,2) One 13 (4,2) One 14 (3,2) One 15 (2,2) One 16 (1, 2) One 17 (0,2) One 18 (3,5) One 19 (2,5) One TDD
frame 20 (11, 1) One (11, 1) One (11, 1) One 21 (9, 1) One (9, 1) One (9, 1) One 22 (7,1) One (7,1) One (7,1) One 23 (10, 1) One (10, 1) One 24 (8, 1) One (8, 1) One 25 (6,1) One (6,1) One 26 (5, 1) One 27 (4,1) One 28 (3, 1) One 29 (2,1) One 30 (1,1) One 31 (0, 1) One

Number of CSI-RSs to be configured 1 or 2 4 8 CSI-RS configuration index (k`, l`) n _s mod 2 (k`, l`) n _s mod 2 (k`, l`) n _s mod 2 TDD and
FDD
frame 0 (11,4) 0 (11,4) 0 (11,4) 0 One (9, 4) 0 (9, 4) 0 (9, 4) 0 2 (10,4) One (10,4) One (10,4) One 3 (9, 4) One (9, 4) One (9, 4) One 4 (5, 4) 0 (5, 4) 0 5 (3,4) 0 (3,4) 0 6 (4,4) One (4,4) One 7 (3,4) One (3,4) One 8 (8,4) 0 9 (6, 4) 0 10 (2,4) 0 11 (0,4) 0 12 (7, 4) One 13 (6, 4) One 14 (1,4) One 15 (0,4) One TDD
frame 16 (11, 1) One (11, 1) One (11, 1) One 17 (10, 1) One (10, 1) One (10, 1) One 18 (9, 1) One (9, 1) One (9, 1) One 19 (5, 1) One (5, 1) One 20 (4,1) One (4,1) One 21 (3, 1) One (3, 1) One 22 (8, 1) One 23 (7,1) One 24 (6,1) One 25 (2,1) One 26 (1,1) One 27 (0, 1) One

The UE can transmit the CSI-RS only in the downlink slot satisfying the condition of n _s mod 2 in Tables 5 and 6. In addition, the UE may use a special subframe of a TDD frame, a subframe in which transmission of the CSI-RS conflicts with a synchronization signal, a PBCH (Physical Broadcast CHannel), a system information block type 1 (SystemInformationBlockType1) The CSI-RS is not transmitted in the subframe in which the message is transmitted. In the set S with S = {15}, S = {15, 16}, S = {17, 18}, S = {19, 20} or S = {21, 22} The resource element to which the -RS is transmitted is not used for transmission of PDSCH or CSI-RS of another antenna port.

The following table shows an example of a subframe configuration in which the CSI-RS is transmitted.

CSI-RS-SubframeConfig
_{ICSI - RS} CSI-RS cycle
T _{CSI - RS} (subframe) CSI-RS sub-frame offset
Δ _{CSI - RS} (subframes) 0 - 4 5 _{ICSI - RS} 5 - 14 10 _{ICSI - RS -5} 15 - 34 20 _{ICSI - RS -15} 35 - 74 40 _{ICSI - RS -35} 75 - 154 80 _{ICSI - RS -75}

Referring to the above table, a period (T _{CSI - RS} ) and an offset ( _CSI-RS ) of a subframe through which a CSI-RS is transmitted may be determined according to a CSI-RS subframe configuration (I _{CSI - RS} ). The CSI-RS subframe structure in the above table may be any one of the 'SubframeConfig' field or the 'ZeroTxPowerSubframeConfig' field of the CSI-RS-Config IE in Table 5. The CSI-RS subframe configuration can be configured separately for non-power CSI-RS and zero power CSI-RS.

Generally, when the number of reference signals RS increases, the performance of channel estimation improves. However, when the number of reference signals increases, the weight of the resource elements allocated to the reference signals in the subframe increases as the number of reference signals increases, resulting in a lower data transmission rate. Thus, allocating additional resource elements for additional reference signals is not a matter of decision.

On the other hand, in the case of a UE located in a high-speed environment or in an environment with poor channel conditions, if data is received based only on a reference signal that has been previously defined, a limit that can not exhibit normal data reception performance due to deteriorated channel estimation have.

&Lt; Disclosure of the present invention &

Therefore, the present invention proposes a scheme capable of performing more advanced channel estimation in an environment where a high-speed mobile station or a poor channel state is present, and minimizing a transmission rate drop due to overhead of reference signal transmission.

More specifically, the present invention plays a role of a reference signal for a UE requiring an additional reference signal (i.e., a UE located in a high-speed moving environment or an environment with poor channel conditions) An additional reference signal that may not serve as a reference signal is presented. In the following description, an additional reference signal provided herein will be referred to as an A-RS (Assisted Reference Signal).

A UE located in a high-speed moving environment or a poor channel condition uses the A-RS as an additional reference signal. That is, the UE can improve channel estimation and data reception performance by using both the existing reference signal (e.g., the common reference signal (CRS)) and the A-RS.

A UE located in a general environment receives multiplexed data (e.g., PDSCH) in the RE to which the A-RS is assigned. A UE located within a particular cell may be aware of the A-RS in the cell in advance. Therefore, the UE located in the general environment can receive the data by removing the A-RS from the RE allocated with the A-RS. In this case, since the UE does not separately estimate the A-RS, the complexity of data reception does not greatly increase. That is, even if the A-RS is additionally used, it is possible to minimize an increase in the overhead of the reference signal of the UE located in a general environment.

A UE located in a high-speed moving environment or a channel-poor environment performs channel estimation additionally using an A-RS, and a UE located in a general environment removes an A-RS from an RE allocated with an A- The base station can send an indication to the UE about whether to use the A-RS. The base station can transmit an indication of whether or not to use the A-RS through a radio resource control (RRC) broadcast signal (RRC broadcast signal) or an RRC dedicated signal (RRC dedicated signal). In this case, the indicator of whether to use the A-RS can be a 1-bit indicator. Also, the base station may transmit the level (e.g., P _D ) of the A-RS transmit power via the SIB2 message.

The following table shows an example of A-RS-Config for A-RS.

The A-RS may have a structure added to the cell-specific RS. In addition, the A-RS may be in the form of a new structure not defined in LTE, or may be a form in which the structure of a reference signal defined in LTE is changed. Although the present specification describes the structure of an A-RS based on the structure of a CSI-RS defined in LTE, the present invention is not limited thereto and the A-RS may have a new structure.

The A-RS according to the present specification can be defined as follows.

1. A- RS  Structure type 1

Antenna port A-RS Settings CSI-RS setting (k`, l`) n _s mode 2 Antenna port
31, 32 0 0 (9, 5) 0 One 2 (9,2) One 2 10 (3,5) 0 3 14 (3,2) One Antenna port
33, 34 4 5 (8, 5) 0 5 7 (8,2) One 6 11 (2,5) 0 7 15 (2,2) One

2. A- RS  Structure Type 2

Antenna port A-RS Settings CSI-RS setting (k`, l`) n _s mode 2 Antenna port
31, 32 0 0 (9, 5) 0 One 2 (9,2) One Antenna port
33, 34 4 5 (8, 5) 0 5 7 (8,2) One

3. A- RS  Rescue Type 3

Antenna port A-RS Settings CSI-RS setting (k`, l`) n _s mode 2 Antenna port
31, 32 0 0 (9, 5) 0 Antenna port
33, 34 4 5 (8, 5) 0

The A-RS structure types of Tables 9 to 11 can be selected by the base station according to the network environment. Then, the base station can inform the UE about the selected A-RS structure type through the RRC message.

Further, the sequence rl _{, ns} (m) of the A-RS may be mapped to a complex-valued modulation symbol a _{k, l} ^(p) used as a reference symbol for the antenna port p.

The relation between r _{l, ns} (m) and a _{k, l} ^(p) for A-RS is as follows.

here,

13 is a cross-sectional view taken along line A- RS  Antenna Virtualization  &Lt; / RTI &gt; structure.

As shown in FIG. 13, antenna virtualization for A-RS can use an antenna virtualization scheme such as CRS.

14 is a cross-sectional view of an A- RS  Antenna of structure type 1 The reference signal structure for the port .

In Fig. 14, one resource grid is shown for each antenna port. R31 is the reference signal for the 32nd antenna port, R33 is the reference signal for the 33rd antenna port, and R34 is the reference signal for the 31st antenna port. Gt; reference signal. The positions in the sub-frames of R31 to R34 do not overlap each other. ℓ is the position of the OFDM symbol in the slot, and ℓ in the normal CP has a value between 0 and 6.

The 31st to 34th antenna ports can be defined as the 0th to 3rd antenna ports and the Quasi-Co-Located (QCL) type A, respectively.

Hereinafter, the operation of the UE according to the A-RS will be described.

1. Operation of UE using A-RS

A UE located in a high-speed moving environment or a poor channel condition can use the A-RS. Even if the UE uses the A-RS, it performs RRM (Radio Resource Measurement) based on the existing reference signal except for the A-RS or the CSI-RS. The UE using the A-RS performs channel estimation and demodulation using the existing reference signal and the A-RS.

15 is a cross-sectional view of an A- RS  using UE  An example of a channel estimation method is shown.

)와 A-RS가 할당된 RE에서의 채널 추정치(

)를 구하고, 구해진 채널 추정치를 기초로 전체 채널에 대한 시간/주파수 채널 값을 계산할 수 있다. 한편, 기지국은 A-RS의 채널 추정 향상을 위하여, 파워 부스팅(power boosting)하여 A-RS를 전송할 수 있다. 이 경우, UE는 A-RS의 파워 부스팅에 따라, A-RS가 할당된 RE에서의 채널 추정치(

)에 가중치(weight(α))를 부여하여 전체 채널에 대한 시간/주파수 채널 값을 계산할 수도 있다.Referring to FIG. 15, the UE determines a channel estimate

) And the channel estimate at the RE to which the A-RS is assigned (

), And calculate a time / frequency channel value for the entire channel based on the obtained channel estimation value. Meanwhile, the base station can transmit the A-RS by power boosting to improve the channel estimation of the A-RS. In this case, according to the power boosting of the A-RS, the UE calculates the channel estimate

(Weight (?)) To a time / frequency channel value for the entire channel.

2. Operation of UE without A-RS

A UE located in a typical environment may not use the A-RS. A UE that does not use A-RS naturally performs RRM based on existing CRS or CSI-RS except for A-RS. A UE not using the A-RS receives the multiplexed data in the RE allocated with the A-RS.

16 is a cross-sectional view taken along line A- RS  unused UE  An example of a channel estimation method is shown.

)를 수행한다. 그리고, UE는 기지국으로부터 수신한 A-RS에 대한 정보를 기반으로 A-RS가 할당된 RE에서 A-RS를 제거한 후, A-RS가 제거된 RE로부터 데이터(예컨대, PDSCH)를 수신한다.Referring to FIG. 16, the UE performs channel estimation based on an existing reference signal

). Then, the UE removes the A-RS from the RE allocated A-RS based on the information about the A-RS received from the base station, and then receives data (e.g., PDSCH) from the RE from which the A-RS is removed.

The embodiments described herein can be applied to both the FDD scheme and the TDD scheme and can be applied to a cell-specific reference signal in a new radio access technology frame structure that can be introduced in the next generation mobile communication. RS).

17 is a flowchart showing a channel estimation method according to an embodiment of the present invention.

Referring to FIG. 17, the UE receives an indication of whether to use the A-RS through the RRC signal (S100). In this case, the UE may receive an indication of whether to use the A-RS through either the RRC broadcast signal or the RRC dedicated signal.

The UE determines whether the A-RS is required based on an indicator of whether to use the A-RS (S200).

If A-RS is required, the UE obtains the first channel estimate based on the first RS allocated to the first RE of the subframe received from the base station and adds the multiplexed A-RS with the PDSCH to the second RE And obtains the second channel estimation value based on S300. Here, the first RS may be any one of CRS and CSI-RS, but is not limited thereto.

The UE performs channel estimation of the entire channel based on the first channel estimate and the second channel estimate (S400). In this case, when the A-RS is transmitted by power boosting the first reference signal, the UE may perform channel estimation of the entire channel by applying a weight according to the degree of power boosting to the A-RS to the second channel estimate . Alternatively, the UE may perform channel estimation of the entire channel by uniformly applying weights of the first channel estimate and the second channel estimate.

Then, the UE decodes the PDSCH received from the base station using the channel estimation result of the entire channel (S500).

Alternatively, if A-RS is not required, the UE performs channel estimation of the entire channel based on the first channel estimate obtained based on the first RS allocated to the first RE of the subframe received from the base station (S600).

The UE removes the A-RS from the multiplexed second RE with the PDSCH (S700). In this case, the UE may remove the A-RS from the second RE using information about the A-RS previously received from the base station.

In step S800, the UE decodes the multiplexed PDSCH in the second RE from which the A-RS is removed, using the channel estimation result of the entire channel.

The embodiments of the present invention described above can be implemented by various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof. More specifically, it will be described with reference to the drawings.

Figure 18 illustrates a wireless communication system in which the present disclosure is implemented; It is a block diagram. .

The base station 200 includes a processor 201, a memory 202 and an RF unit (radio frequency (RF) unit 203). The memory 202 is connected to the processor 201 and stores various information for driving the processor 201. [ The RF unit 203 is connected to the processor 201 and transmits and / or receives a radio signal. The processor 201 implements the proposed functions, procedures and / or methods. In the above-described embodiment, the operation of the base station can be implemented by the processor 201. [

The UE 100 includes a processor 101, a memory 102, and an RF unit 103. [ The memory 102 is connected to the processor 101 and stores various information for driving the processor 101. [ The RF unit 103 is connected to the processor 101 to transmit and / or receive a radio signal. The processor 101 implements the proposed functions, procedures and / or methods.

The processor may comprise an application-specific integrated circuit (ASIC), other chipset, logic circuitry and / or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit may include a baseband circuit for processing the radio signal. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module is stored in memory and can be executed by the processor. The memory may be internal or external to the processor and may be coupled to the processor by any of a variety of well known means.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

Claims (14)

A channel estimation method of a user equipment,
Obtaining a first channel estimate based on a first reference signal assigned to a first Resource Element of a subframe received from a base station; And
The second reference signal is removed from the second resource element of the subframe, and if the second reference signal is not required, the second resource element is removed using the channel estimation result of the entire channel based on the first channel estimate, And decoding the multiplexed data channel,
Wherein the second resource element is multiplexed together with the second reference signal and the data channel. 2. The method of claim 1, wherein decoding the data channel comprises:
Determining whether to request the additional reference signal based on an indicator received via an RRC (Radio Resource Control) signal. The method according to claim 1,
Further comprising receiving information on the second reference signal from the base station,
The step of decoding the data channel
And removing the second reference signal from the second resource element using information on the second reference signal. 2. The method of claim 1, wherein decoding the data channel comprises:
And performs channel estimation of the entire channel based on the second channel estimate and the first channel estimate obtained based on the second reference signal when the additional reference signal is required. 5. The method of claim 4,
Wherein the second channel estimation value is weighted according to the degree of power boosting when the second reference signal is transmitted by power boosting than the first reference signal. 5. The method of claim 4,
Wherein the weighting is performed by applying the first channel estimate and the second channel estimate equally. 5. The method of claim 4,
Further comprising the step of performing Radio Resource Measurement (RRM) using only the first reference signal even when the additional reference signal is required. A user equipment for performing channel estimation,
An RF (Radio Frequency) unit for transmitting and receiving a radio signal; And
And a processor for controlling the RF unit, wherein the processor
Controlling the RF unit to obtain a first channel estimate based on a first reference signal assigned to a first resource element of a subframe received from the base station; And
The second reference signal is removed from the second resource element of the subframe, and if the second reference signal is not required, the second resource element is removed using the channel estimation result of the entire channel based on the first channel estimate, The method comprising the steps of:
Wherein the second resource element is multiplexed together with the second reference signal and the data channel. 9. The apparatus of claim 8, wherein the processor
And determines whether to request the additional reference signal based on an indicator received via an RRC (Radio Resource Control) signal. 9. The apparatus of claim 8, wherein the processor
And receives information on the second reference signal from the base station and uses the information on the second reference signal to remove the second reference signal from the second resource element. 9. The apparatus of claim 8, wherein the processor
And performs channel estimation of the entire channel based on the second channel estimate and the first channel estimate obtained based on the second reference signal when the additional reference signal is required. 12. The method of claim 11,
Wherein the weighting is performed by applying a weight according to the degree of power boosting to the second channel estimate value when the second reference signal is transmitted by power boosting than the first reference signal. 12. The method of claim 11,
Wherein the first channel estimation value and the second channel estimation value are weighted and applied uniformly. 12. The system of claim 11, wherein the processor
And performs a radio resource measurement (RRM) using only the first reference signal even when the additional reference signal is required.

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