JP2020022191A - Communication device, communication method, and integrated circuit - Google Patents

Abstract

To select appropriate DMRS pattern for the terminal from multiple DMRS patterns including Legacy DMRS and Reduced DMRS.SOLUTION: A receiving part 21 receives a piece of uplink control information. A control part 23 determines a specific arrangement pattern from a plurality of arrangement patterns of uplink DMRS (Demodulation Reference Signal) based on the control information. A DMRS generator 24 generates a DMRS according to the specific arrangement pattern.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a communication device, a communication method, and an integrated circuit.

  In LTE (Long Term Evolution) Rel. 8 (Release 8) formulated by 3GPP (3rd Generation Partnership Project Radio Access Network), SC-FDMA (single-carrier frequency-division multiple-access) is used as an uplink communication system. (Non-Patent Documents 1, 2, and 3). SC-FDMA has a small PAPR (Peak-to-Average Power Ratio) and a high power use efficiency of a terminal (UE: User Equipment).

  In the LTE uplink, both transmission of a data signal (Physical Uplink Shared Channel) and a control signal (Physical Uplink Control Channel) are performed in subframe units (Non-Patent Document 1). . FIG. 1 shows an example of a PUSCH subframe configuration in the case of a Normal cyclic prefix. As shown in FIG. 1, one subframe includes two time slots, and each slot is time-multiplexed with a plurality of SC-FDMA data symbols and pilot symbols (referred to as DMRS (Demodulation Reference Signal)). Upon receiving the PUSCH, the base station performs channel estimation using DMRS. Thereafter, the base station performs demodulation and decoding of SC-FDMA data symbols using the channel estimation result. In LTE-A (LTE-Advanced) Rel.10 (Release 10), DFT-S-OFDM (Discrete-Fourier-Transform Spread Orthogonal Frequency Division Multiplexing), which is an extended version of SC-FDMA, can also be used. . DFT-S-OFDM is a method of dividing the PUSCH obtained as shown in FIG. 1 into two spectrums and mapping each spectrum to different frequencies, thereby expanding the degree of freedom of scheduling.

  The DMRS multiplexed on the PUSCH is generated based on a CAZAC (Constant Amplitude Zero Auto-Correlation) sequence having excellent auto-correlation characteristics and cross-correlation characteristics. In LTE, 30 sequence groups in which CAZAC sequences with various sequence lengths (bandwidths) and large correlations are grouped into one group are defined (for example, see FIG. 2). One sequence group out of the 30 sequence groups is assigned to each cell based on a cell-specific ID (cell ID). As a result, sequence groups having low correlation with each other are assigned between cells.

  The terminal generates a DMRS using a CAZAC sequence corresponding to the allocated bandwidth among the sequence groups allocated to the cell to which the terminal belongs, and time-multiplexes the DNRS to the PUSCH. By this means, a DMRS with a high correlation is transmitted between terminals in the same cell, and a DMRS with a low correlation is transmitted between terminals in different cells. Here, since the correlation of DMRS between cells is small, even if interference of DMRS transmitted at the same timing occurs, the interference can be reduced by the window function method or averaging. On the other hand, in the same cell, orthogonalization is performed by assigning different frequencies or times between terminals, so that the terminals can be operated so as not to cause interference. It is also possible to allocate the same frequency or time between terminals (called MU-MIMO (Multi-user multi-input multi-output)). In this case, a different cyclic shift (CS) is assigned to the DMRS of each terminal. ) Or by multiplying two DMRSs in the PUSCH by different orthogonal codes (OCCs (Orthogonal Cover Codes)) between the terminals, so that the DMRSs between the terminals can be orthogonally multiplexed.

  In this way, spatial reuse of radio resources is realized between cells by using different sequence groups to reduce mutual interference. Also, in a cell, radio resources can be efficiently used by applying MU-MIMO. By doing so, highly efficient uplink transmission can be realized in LTE.

  Further, in LTE-A Rel. 11 (Release 11), a virtual cell ID has been added that allows an arbitrary sequence group to be assigned to an arbitrary terminal regardless of the cell ID of the cell to which the cell belongs.

  By the way, in recent years, mobile traffic has exploded with the spread of smartphones, and in order to provide mobile data communication services without stress to users, it is essential to dramatically improve the use efficiency of wireless resources. Therefore, in LTE-A Rel. 12 (Release 12), Small cell enhancement, in which countless small cell base stations forming small cells are arranged (Non-Patent Document 4). Small cell enhancement has the advantage of reducing the coverage and reducing the number of terminals per cell, thereby increasing the radio resources that each cell can allocate per terminal and improving the data rate of the terminals. On the other hand, it is impractical to cover all areas with small cells. Further, when a terminal having a high moving speed is connected to a small cell, there is a problem that the frequency of handover increases. Therefore, it is considered that a small cell is developed so as to overlap a macro cell having a large coverage (for example, see FIG. 3; sometimes referred to as a heterogeneous network (HetNet: Heterogeneous network)). This makes it possible to support all terminals while eliminating a coverage hole in a macro cell, and to provide a large capacity communication to a terminal requiring a low moving speed and a high-speed data communication service in a small cell.

3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation,” v.11.1.0 3GPP TS 36.212, “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding,” v.11.1.0 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures,” v.11.1.0 3GPP TR 36.932, “Scenarios and requirements of LTE small cell enhancements,” v.12.0.0

The network configuration (eg, FIG. 3) studied in Small cell enhancement has the following features.
(1) The state and quality of a propagation path for a terminal connected to a small cell are often good. This is because there is a high probability that the distance between the small cell base station and the terminal is short, and communication is easily performed at a high received power or a high signal-to-received power ratio (SNR). For the same reason, the transmission power required for the terminal is likely to be small.
(2) Since small cells have small coverage, the number of terminals operated simultaneously is smaller than that of macro cells. In some cases, a small cell may communicate with only one or two terminals.
(3) Unlike small cells, small cells are likely not to be arranged uniformly. Small cells may be locally densely arranged, or may be sparsely distributed over a large area.

  From the above characteristics, in the uplink of a terminal that communicates with a small cell in Small cell enhancement, the state and quality of the channel are good, so it is assumed that the base station can perform sufficiently accurate channel estimation. Further, since the number of terminals operated simultaneously in each small cell is small, the advantage of applying MU-MIMO is reduced. Therefore, it is not always necessary to use 14% or more (1/7 of the whole) of PUSCH subframes as DMRS as shown in FIG. That is, in the uplink of a terminal that communicates with a small cell, if the DMRS in the PUSCH subframe is reduced and the reduced radio resources can be diverted to data (PUSCH), higher terminal throughput can be achieved. .

  Against this background, Small cell enhancement uses a technique to improve the data rate per terminal and per subframe by replacing some of the PUSCH DMRS with data (in the following description, "Reduced DMRS (Reduced DMRS)"). ") Is being considered. For example, if the DMRS included in the PUSCH subframe shown in FIG. 1 can be reduced by half, a data rate improvement of about 7% can be realized, and if the DMRS can be reduced to 1/4, almost 11% of data can be reduced. The rate can be improved.

  FIG. 4 is an example of an arrangement pattern (Legacy DMRS pattern) indicating an arrangement in one subframe of DMRS (Legacy DMRS) up to Rel. 11, and an example of an arrangement pattern (Reduced DMRS) in a reduced DMRS indicating an arrangement in one subframe. DMRS pattern (1) to (4)). As shown in FIG. 4, the reduced DMRS pattern has a smaller ratio of DMRS than the Legacy DMRS pattern. That is, the reduced DMRS pattern has fewer resources to which the DMRS is mapped than the Legacy DMRS pattern.

  The Legacy DMRS pattern (FIG. 4A) is a pattern in which two DMRSs are arranged in one subframe, corresponding to the subframe configuration shown in FIG.

  Reduced DMRS patterns (1) and (2) (FIGS. 4B and 4C) are patterns obtained by replacing one of the two DMRSs included in the Legacy DMRS pattern (FIG. 4A) with data. This makes it difficult to apply the orthogonal code (OCC), but can increase the data allocation and improve the data rate. Also, if the PUSCH subframes of Reduced DMRS pattern (1) and (2) are temporally connected and transmitted continuously, two DMRSs can be used over two subframes, so that orthogonal codes are used. Multiplexing is also possible (for example, see FIG. 5A). Similarly, if PUSCH subframes of Reduced DMRS patterns (2) and (1) are temporally connected and transmitted continuously, multiplexing by orthogonal codes becomes possible (see FIG. 5B). Furthermore, in FIG. 5B, since the temporal distance between DMRSs multiplied by a code is smaller than that in FIG. 5A, MU-MIMO can be applied to a terminal having a high moving speed.

  Reduced DMRS pattern (3) (FIG. 4D) is a method of dispersively mapping DMRSs having a sequence length shorter than the allocated bandwidth in SC-FDMA symbols. By allocating data to a resource element (RE (Resource Element)) to which the DMRS is not mapped, the data rate can be improved as in the case of the reduced DMRS patterns (1) and (2). Also, in Reduced DMRS pattern (3), a configuration in which DMRSs are arranged in two different SC-FDMA symbols in one subframe is maintained. Therefore, similar to Rel.11 (FIG. 4A), different terminals between orthogonal terminals use orthogonal codes. Orthogonal multiplexing of the DMRS is possible. Therefore, the reduced DMRS pattern (3) has an advantage that MU-MIMO can be easily applied. On the other hand, in the Reduced DMRS pattern (3), there is a concern that the PAPR of the terminal may increase, considering that the DMRS and the data are frequency-multiplexed in the same SC-FDMA symbol. However, since the transmission power of a terminal connected to a small cell has a high probability of being small, an increase in PAPR of the terminal does not pose a significant problem. In Reduced DMRS pattern (3), resource elements to which DMRS is mapped may be shifted between two SC-FDMA symbols including DMRS (not shown). In this case, channel estimation accuracy can be improved by averaging or interpolating the channel estimation value using the DMRS included in the two SC-FDMA symbols.

  Reduced DMRS pattern (4) (FIG. 4E) is a method of locally mapping DMRSs having a sequence length shorter than the allocated bandwidth in SC-FDMA symbols. The reduced DMRS pattern (4) has the same effect as the reduced DMRS pattern (3), and also estimates the channel variation in the frequency direction within the band to which the DMRS is mapped, compared to the reduced DMRS pattern (3). There is a merit that it is easy to do. In the Reduced DMRS pattern (4), the position of the frequency to which the DMRS is mapped and the relative frequency position of the DMRS in the two SC-FDMA symbols are not limited to the example shown in FIG. 4E.

  The example of the reduced DMRS has been described above.

  However, Reduced DMRS is not always effective. For example, if the channel quality of the terminal is good, Reduced DMRS is effective, but if the channel quality is bad, it is desirable to increase the energy of the DMRS using Legacy DMRS to increase the channel estimation accuracy. Further, when large interference from a terminal to a neighboring cell is expected, it is necessary to keep the correlation of the interference with the DMRS of the terminal connected to the neighboring cell small by using Legacy DMRS. Furthermore, a terminal that supports only the functions up to Rel.8-11 (Legacy terminal) can only use the Legacy DMRS, so when applying MU-MIMO to a terminal that supports the Rel.12 function and a Legacy terminal Therefore, it is essential to use Legacy DMRS even for terminals supporting the Rel.12 function.

  It is desirable that such switching between the Legacy DMRS and the Reduced DMRS can be flexibly controlled according to the judgment of the base station in consideration of securing the flexibility of uplink scheduling. As described above (FIGS. 4B to 4E), it is conceivable to provide a plurality of arrangement patterns as Reduced DMRS. Therefore, according to the channel quality of the terminal, the surrounding conditions, or the data rate requested by the terminal, Legacy DMRS, and, from a plurality of DMRS patterns including a plurality of Reduced DMRS patterns, select a DMRS pattern suitable for the terminal You need to be able to do it.

  An object of the present invention is to provide a communication device, a communication method, and an integrated circuit that can select an appropriate DMRS pattern for a terminal from a plurality of DMRS patterns including a Legacy DMRS and a Reduced DMRS.

  A communication device according to an aspect of the present invention determines control information used for PUSCH (Physical Uplink Shared Channel) allocation, and arranges an uplink DMRS (Demodulation Reference Signal) in a resource element. A transmitting unit that transmits the control information to the terminal, and receives the DMRS (Demodulation Reference Signal) from the terminal, which is arranged in the resource element based on the control information and transmitted by multiplexing with the PUSCH. A configuration including a receiving unit and a circuit unit for performing channel estimation based on the received DMRS is adopted.

  A communication method according to an aspect of the present invention determines control information used for PUSCH (Physical Uplink Shared Channel) allocation, and arrangement of uplink DMRS (Demodulation Reference Signal) in a resource element. Transmitting the control information to the terminal, receiving the DMRS (Demodulation Reference Signal) transmitted from the terminal, the DMRS being arranged in the resource element based on the control information and multiplexed with the PUSCH and transmitted. Channel estimation is performed based on the DMRS.

  The integrated circuit according to one aspect of the present invention determines control information used for PUSCH (Physical Uplink Shared Channel) allocation and allocation of uplink DMRS (Demodulation Reference Signal) to resource elements. Transmitting the control information to the terminal, and receiving from the terminal the DMRS (Demodulation Reference Signal) arranged in the resource element based on the control information and multiplexed with the PUSCH and transmitted. And a process of performing channel estimation based on the received DMRS.

  According to the present invention, an appropriate DMRS pattern for a terminal can be selected from a plurality of DMRS patterns including a Legacy DMRS and a Reduced DMRS.

Diagram showing uplink subframe configuration Diagram showing DMRS sequence group assignment Diagram showing network configuration in small cell enhancement Diagram showing an example of Legacy DMRS pattern and Reduced DMRS pattern Diagram showing orthogonal multiplexing by OCC using Reduced DMRS pattern FIG. 2 shows a communication system according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing a main configuration of a base station according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing a configuration of a base station according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a main configuration of a terminal according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a terminal according to Embodiment 1 of the present invention. FIG. 4 is a diagram showing correspondence between DPI and DMRS patterns according to Embodiment 1 of the present invention. FIG. 6 is a diagram showing correspondence between DPI, DMRS patterns, and virtual cell IDs according to Embodiment 1 of the present invention. FIG. 6 is a diagram showing correspondence between DPI and DMRS patterns and ON / OFF of base sequence group hopping according to Embodiment 1 of the present invention. FIG. 9 is a diagram showing a notification example of a DMRS pattern according to Embodiment 1 of the present invention. FIG. 9 is a diagram showing a notification example of a DMRS pattern according to Embodiment 1 of the present invention. FIG. 10 is a diagram showing a relationship between a PUSCH allocation band and each RIV parameter according to Embodiment 2 of the present invention. FIG. 14 is a diagram showing DMRS patterns corresponding to each allocated bandwidth according to Embodiment 2 of the present invention. FIG. 14 is a diagram showing DMRS patterns corresponding to each allocated bandwidth according to Embodiment 2 of the present invention. FIG. 10 is a diagram showing a correspondence between an allocated bandwidth and a DMRS pattern according to Embodiment 2 of the present invention. FIG. 14 is a diagram showing DMRS patterns corresponding to each allocated bandwidth according to Embodiment 2 of the present invention. FIG. 10 is a diagram showing a correspondence between a start position of an allocated bandwidth and a DMRS pattern according to Embodiment 2 of the present invention. FIG. 10 is a diagram showing DMRS patterns corresponding to respective start positions of an allocated bandwidth according to Embodiment 2 of the present invention. FIG. 13 is a diagram showing correspondence between A-SRS trigger bits and DMRS patterns according to Embodiment 3 of the present invention. FIG. 17 is a diagram showing correspondence between control channels and DMRS patterns according to Embodiment 4 of the present invention. FIG. 14 is a diagram showing a correspondence between a CS field and a DMRS pattern according to the fifth embodiment of the present invention. FIG. 14 is a diagram showing a correspondence between a CS field and a DMRS pattern according to the fifth embodiment of the present invention. The figure which shows the data mapping order concerning Embodiment 6 of this invention. FIG. 14 is a diagram showing a DMRS pattern at the time of ACK / NACK multiplexing according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each of the embodiments, the same components are denoted by the same reference numerals, and the description thereof will not be repeated.

(Embodiment 1)
[Overview of Communication System]
FIG. 6 shows a communication system according to the present embodiment. The communication system illustrated in FIG. 6 includes a base station 100 in a cell and one or a plurality of terminals 200. In FIG. 6, the base station 100 may be a macro cell base station or a small cell base station. Further, the communication system may be a HetNet system in which macro cell base stations and small cell base stations are mixed, or may be a CoMP (Coordinated multipoint) system in which a plurality of base stations cooperate and communicate with terminals. . The macro cell and the small cell may be operated at different frequencies or may be operated at the same frequency.

[Configuration of Base Station 100]
FIG. 7 is a block diagram showing a main part of base station 100.

  The base station 100 shown in FIG. 7 includes a control signal generation unit 11, a transmission unit 12, a reception unit 13, a channel estimation unit 14, and a reception signal processing unit 15.

  The control signal generation unit 11 generates a control signal for the terminal 200, and the transmission unit 12 transmits the generated control signal via an antenna. The control signal includes a UL grant for instructing PUSCH allocation. The UL grant is composed of a plurality of bits and includes information indicating a frequency allocation resource (RB: Resource Block), a modulation / coding method, an SRS (Sounding Reference Signal) trigger, and the like. Further, the UL grant includes a DMRS pattern indicator (DPI) for specifying a DMRS arrangement pattern (DMRS pattern) when transmitting the allocated PUSCH. DPI consists of one or more bits. It is assumed that DMRS pattern candidates that can be selected by DPI are notified to terminal 200 in advance by an upper layer or are defined. Also, the control signal is transmitted using a downlink control channel (PDCCH (Physical downlink control channel) or EPDCCH (Enhanced physical downlink control channel)). Note that the EPDCCH is sometimes called an EPDCCH set, and is arranged in the PDSCH as a new control channel different from the PDCCH.

  That is, control signal generating section 11 generates uplink control information based on an allocation pattern instructed to terminal 200 among a plurality of uplink DMRS allocation patterns, and transmitting section 12 generates the generated control information. Submit information.

  The receiving unit 13 receives, via an antenna, the PUSCH transmitted by the terminal 200 according to the UL grant, and extracts data and DMRS. Channel estimating section 14 performs channel estimation using DMRS. The reception signal processing unit 15 demodulates and decodes data based on the estimated channel estimation value.

  FIG. 8 is a block diagram illustrating details of the base station 100.

  Base station 100 shown in FIG. 8 includes control section 101, control information generation section 102, coding section 103, modulation section 104, mapping section 105, IFFT (Inverse Fast Fourier Transform) section 106, CP (Cyclic Prefix) addition section 107. , Radio transmitting section 108, radio receiving section 109, CP removing section 110, FFT (Fast Fourier Transform) section 111, demapping section 112, CSI (Channel State Information) measuring section 113, channel estimating section 114, equalizing section 115, It includes an IDFT (Inverse Discrete Fourier Transform) unit 116, a demodulation unit 117, a decoding unit 118, and a determination unit 119.

  Among them, the control unit 101, the control information generation unit 102, the encoding unit 103, and the modulation unit 104 mainly function as the control signal generation unit 11 (FIG. 7), and include the mapping unit 105, the IFFT unit 106, and the CP addition unit 107. , The wireless transmission unit 108 mainly functions as the transmission unit 12 (FIG. 7). In addition, the radio receiving unit 109, the CP removing unit 110, the FFT unit 111, and the demapping unit 112 mainly function as the receiving unit 13 (FIG. 7), the channel estimating unit 114 functions as the channel estimating unit 14, and the equalizing unit. 115, the IDFT unit 116, the demodulation unit 117, the decoding unit 118, and the determination unit 119 mainly function as the reception signal processing unit 15 (FIG. 7).

  In base station 100 shown in FIG. 8, control section 101 determines PUSCH subframe allocation to terminal 200 according to the state or reception state of terminal 200. For example, the control unit 101 determines whether the received data of the terminal 200 received from the determination unit 119 is determined (error or not; ACK or NACK), the channel information (CSI) of the terminal 200 input from the CSI measurement unit 113, or the like. Based on this, PUSCH subframe allocation for terminal 200 is determined. At this time, control section 101 allocates frequency resource block (RB) allocation information to terminal 200, coding method, modulation scheme, information indicating first transmission or retransmission, process number of hybrid automatic retransmission request (HARQ), and , DMRS pattern information (DPI) and the like, and outputs the determined information to the control information generator 102.

  Further, control section 101 determines an encoding level for a control signal for terminal 200, and outputs the determined encoding level to encoding section 103. The coding level is determined according to the amount of control information included in the control signal to be transmitted or the state of terminal 200.

  Further, control section 101 determines a radio resource element (RE) to which a control signal for terminal 200 is mapped, and instructs mapping section 105 on the determined RE.

  Control information generating section 102 generates a control information bit sequence using control information for terminal 200 input from control section 101, and outputs the generated control information bit sequence to encoding section 103. Since the control information may be transmitted to a plurality of terminals 200, the control information generation unit 102 generates a bit string including the terminal ID of each terminal 200 in the control information for each terminal 200. For example, a CRC bit masked with the terminal ID of the destination terminal 200 is added to the control information.

  Encoding section 103 encodes the control information bit string input from control information generation section 102 using the encoding level specified by control section 101. Coding section 103 outputs the obtained coded bit sequence to modulation section 104.

  Modulating section 104 modulates the coded bit sequence input from coding section 103 and outputs the obtained symbol sequence to mapping section 105.

  Mapping section 105 maps the control signal input as a symbol sequence from modulation section 104 to a radio resource specified by control section 101. The control channel to which the control signal is mapped may be a PDCCH or an EPDCCH. Mapping section 105 inputs, to IFFT section 106, a downlink subframe signal including a PDCCH or EPDCCH to which a control signal has been mapped.

  IFFT section 106 applies IFFT to the downlink subframe input from mapping section 105, and converts a frequency-domain signal sequence into a time waveform. IFFT section 106 outputs the converted time waveform to CP adding section 107.

  CP adding section 107 adds a CP to the time waveform input from IFFT section 106 and outputs a signal with the CP added to wireless transmitting section 108.

  Radio transmitting section 108 performs transmission processing such as D / A conversion and up-conversion on the signal input from CP adding section 107, and transmits the signal after the transmission processing to terminal 200 via the antenna.

  Radio receiving section 109 receives an uplink signal (PUSCH) transmitted from terminal 200 via an antenna, performs reception processing such as down-conversion and A / D conversion on the received signal, and performs reception processing. The signal is output to CP removing section 110.

  CP removing section 110 removes the waveform corresponding to CP from the signal (time waveform) input from radio receiving section 109 and outputs the signal after CP removal to FFT section 111.

  The FFT unit 111 applies an FFT to the signal (time waveform) input from the CP removing unit 110, decomposes the signal into frequency-domain signal sequences (frequency elements in subcarrier units), and supports PUSCH subframes. And take out the signal. FFT section 111 outputs the obtained signal to demapping section 112.

  Demapping section 112 extracts a PUSCH subframe portion allocated to terminal 200 from the input signal. Also, demapping section 112 decomposes the extracted PUSCH subframe of terminal 200 into DMRS and data symbols (SC-FDMA data symbols), outputs the DMRS to channel estimation section 114, and outputs the data symbols to the equalization section. Output to 115. Further, when terminal 200 transmits a sounding reference signal (SRS) in the subframe of the PUSCH, demapping section 112 extracts the SRS and outputs the extracted SRS to CSI measurement section 113. When the SRS is transmitted, since the last data symbol of the PUSCH subframe has been replaced with the SRS, demapping section 112 may separate the SRS from the data symbols.

  When the SRS is input from the demapping unit 112, the CSI measurement unit 113 performs the CSI measurement using the SRS. CSI measurement section 113 outputs the obtained CSI measurement result to control section 101.

  Channel estimating section 114 performs channel estimation using DMRS input from demapping section 112. Channel estimation section 114 outputs the obtained channel estimation value to equalization section 115.

  Equalization section 115 equalizes the SC-FDMA data symbols input from demapping section 112 using the channel estimation values input from channel estimation section 114. Equalization section 115 outputs the equalized SC-FDMA data symbols to IDFT section 116.

  IDFT section 116 applies IDFT of a bandwidth corresponding to the allocated bandwidth to SC-FDMA data symbols in the frequency domain, input from equalization section 115, and converts the data symbols into time-domain signals. IDFT section 116 outputs the obtained time-domain signal to demodulation section 117.

  Demodulation section 117 performs data demodulation on the time-domain signal input from IDFT section 116. Specifically, demodulation section 117 converts the symbol sequence into a bit sequence based on the modulation scheme instructed to terminal 200, and outputs the obtained bit sequence to decoding section 118.

  Decoding section 118 performs error correction decoding on the bit sequence input from demodulation section 117, and outputs the decoded bit sequence to determination section 119.

  Determination section 119 performs error detection on the bit sequence input from decoding section 118. Error detection is performed using CRC bits added to the bit sequence. If the CRC bit determination result shows no error, determination section 119 extracts the received data and notifies control section 101 of an ACK. On the other hand, if the CRC bit determination result indicates an error, the determination unit 119 notifies the control unit 101 of a NACK.

[Configuration of Terminal 200]
FIG. 9 is a block diagram showing a main part of the terminal.

  The terminal 200 shown in FIG. 9 includes a reception unit 21, a control signal extraction unit 22, a control unit 23, a DMRS generation unit 24, and a transmission unit 25.

  The receiving unit 21 receives a control signal (UL grant) transmitted to the terminal 200 on the PDCCH or the EPDCCH, and the control signal extracting unit 22 extracts information on PUSCH subframe allocation from the control signal. Specifically, the control signal extraction unit 22 can blindly decode a control signal allocation candidate on a preset control channel and decode a control signal to which a CRC bit masked by the terminal ID of the terminal 200 is added. Then, the control signal is extracted as control information addressed to the terminal 200. The control information includes frequency resource block (RB) allocation information, modulation scheme, information indicating whether the transmission is first transmission or retransmission, HARQ process number, A-SRS trigger (Aperiodic SRS transmission request), and DMRS pattern information (DPI) And so on.

  The control unit 23 determines a PUSCH subframe configuration based on the extracted control information (UL grant). For example, the control unit 23 determines a DMRS pattern to be used according to the value of the DPI included in the UL grant. The DMRS generation unit 24 generates a DMRS according to an instruction from the control unit 23, and the transmission unit 25 transmits a PUSCH subframe signal including the DMRS according to an instruction from the control unit 23.

  That is, receiving section 21 receives uplink control information, and control section 23 determines a specific arrangement pattern from a plurality of arrangement patterns of uplink DMRS based on the control information, 24 generates a DMRS according to a specific arrangement pattern.

  FIG. 10 is a block diagram showing details of terminal 200.

  Terminal 200 shown in FIG. 10 includes radio reception section 201, CP removal section 202, FFT section 203, control signal extraction section 204, control section 205, encoding section 206, modulation section 207, DMRS generation section 208, and SRS generation section 209. , A multiplexing unit 210, a DFT (Discrete Fourier Transform) unit 211, a mapping unit 212, an IFFT unit 213, a CP adding unit 214, and a wireless transmission unit 215.

  Among them, the wireless receiving unit 201, the CP removing unit 202, and the FFT unit 203 mainly function as the receiving unit 21 (FIG. 9). Further, encoding section 206, modulation section 207, SRS generating section 209, multiplexing section 210, DFT section 211, mapping section 212, IFFT section 213, CP adding section 213, and radio transmitting section 215 are mainly composed of transmitting section 25 (FIG. 9). ). Further, the control signal extraction unit 204 functions as the control signal extraction unit 22, the control unit 205 functions as the control unit 23, and the DMRS generation unit 208 functions as the DMRS generation unit 24.

  In terminal 200 shown in FIG. 10, radio reception section 201 receives a control signal (PDCCH or EPDCCH) transmitted from base station 100 (FIG. 8) via an antenna, down-converts and A / It performs reception processing such as D conversion, and outputs the control signal after the reception processing to CP removing section 202.

  CP removing section 202 removes a CP from a downlink subframe signal including a PDCCH or an EPDCCH in a control signal input from radio receiving section 201, and outputs a signal after the CP removal to FFT section 203.

  FFT section 203 applies an FFT to the signal (downlink subframe) input from CP removing section 202 and converts the signal into a frequency domain signal. FFT section 203 outputs the frequency domain signal to control signal extraction section 204.

  Control signal extraction section 204 performs blind decoding on the frequency domain signal (PDCCH or EPDCCH) input from FFT section 203 and attempts to decode the control signal. A CRC masked by the terminal ID of the terminal 200 is added to the control signal addressed to the terminal 200. Therefore, if the result of the blind decoding indicates that the CRC determination is OK, the control signal extracting unit 204 extracts the control signal and outputs the control signal to the control unit 205.

  Control section 205 controls PUSCH transmission based on the control signal input from control signal extraction section 204.

  Specifically, control section 205 instructs mapping section 212 to perform RB allocation at the time of PUSCH transmission based on PUSCH RB allocation information included in the control signal. Further, control section 205 instructs coding section 206 and modulation section 207, respectively, on the coding method and modulation scheme at the time of PUSCH transmission, based on the information on the coding method and modulation scheme included in the control signal. Further, based on the SRS trigger included in the control signal, control section 205 instructs SRS generating section 209 whether or not to transmit an SRS after a predetermined time has elapsed. The SRS indicated by the SRS trigger may be multiplexed and transmitted on the PUSCH subframe indicated by the UL grant, or may be transmitted at a time later than the subframe. Further, control section 205 determines the DMRS pattern at the time of PUSCH transmission based on the DPI included in the control signal, and instructs DMRS generation section 208 on the determined DMRS pattern.

  Encoding section 206 adds CRC bits masked with the terminal ID to the input transmission data, and performs error correction encoding. Note that the coding rate and codeword length used by the coding unit 206 are instructed by the control unit 205. Encoding section 206 outputs the encoded bit sequence to modulation section 207.

  Modulating section 207 modulates a bit sequence input from encoding section 206. Note that the control unit 205 instructs the modulation level (ie, the number of modulation levels) used by the modulation unit 207. Modulating section 207 outputs the modulated data symbol sequence to multiplexing section 210.

  DMRS generating section 208 generates a DMRS according to the DMRS pattern instructed by control section 205 and outputs the DMRS to multiplexing section 210.

  SRS generating section 209 generates an SRS in accordance with an instruction from control section 205 and outputs the SRS to multiplexing section 210. Note that the transmission timing of the SRS is not always the same as the PUSCH subframe indicated by the UL grant.

  Multiplexing section 210 multiplexes the data symbol sequences, DMRS and SRS input from modulation section 207, DMRS generating section 208 and SRS generating section 209, respectively, and outputs the multiplexed signal to DFT section 211.

  DFT section 211 applies DFT to the signal input from multiplexing section 210, decomposes the signal into frequency component signals in subcarrier units, and outputs the resulting frequency component signals to mapping section 212. .

  Mapping section 212 maps a signal (ie, a data symbol sequence, a DMRS and an SRS) input from DFT section 211 to a time / frequency resource in an allocated PUSCH subframe according to an instruction from control section 205. Mapping section 212 outputs a PUSCH subframe signal to IFFT section 213.

  IFFT section 213 applies IFFT to the signal of the PUSCH subframe in the frequency domain input from mapping section 212 and converts the signal into a time domain signal. IFFT section 213 outputs the obtained time domain signal to CP adding section 214.

  CP adding section 214 adds a CP to the time domain signal (for each output unit of IFFT section 213) input from IFFT section 213, and outputs the signal after the CP addition to wireless transmission section 215.

  Radio transmitting section 215 performs transmission processing such as D / A conversion and up-conversion on the signal input from CP adding section 214, and transmits the signal after the transmission processing to base station 100 via the antenna.

[motion]
The processing flow of base station 100 and terminal 200 according to the present embodiment will be described in steps (1) to (4).

  Step (1): Before transmitting / receiving PUSCH, the base station 100 notifies the terminal 200 that a plurality of DMRS patterns can be designated. The DMRS pattern that can be specified may be defined in advance, and the base station 100 may notify the terminal 200 from a plurality of candidates to the terminal 200 via an upper layer. The DMRS pattern that can be specified includes, for example, a reduced DMRS pattern as shown in FIGS. 4B to 4E and 5 in addition to the Legacy DMRS pattern (for example, see FIG. 4A) used in Rel. 8-10.

  The notification to terminal 200 in step (1) may be performed by base station 100 that transmits and receives PUSCH, or may be performed by base station 100 other than the base station that transmits and receives PUSCH. For example, the base station 100 that transmits and receives PUSCH may be a small cell base station, and the base station that notifies step (1) may be a macro cell base station.

  Step (2): The base station 100 transmits a control signal (UL grant) to the terminal 200 via the PDCCH or the EPDCCH, and instructs PUSCH allocation. The UL grant includes a DMRS pattern indicator (DPI) indicating a DMRS pattern. The DPI indicates to terminal 200 any one specific DMRS pattern from a plurality of DMRS pattern candidates. That is, base station 100 (control section 101) generates a DPI based on a specific DMRS pattern instructed to terminal 200.

  FIG. 11 shows an example in which the DPI is 2 bits. In FIG. 11, a Legacy DMRS pattern and a Reduced DMRS pattern (1) to (3) are associated with each value of the DPI.

  The transmission of the UL grant including the DPI to the terminal 200 may be performed by the base station 100 that transmits and receives the PUSCH, or may be performed by the base station 100 other than the base station that transmits and receives the PUSCH. For example, the base station 100 that transmits and receives PUSCH may be a small cell base station, and the base station that transmits UL grant may be a macro cell base station.

  Step (3): The terminal 200 performs blind decoding on the PDCCH or EPDCCH received in step (2), and obtains a control signal (UL grant) addressed to the terminal itself. When the DPI is included in the UL grant, terminal 200 (control section 205) determines a specific DMRS pattern used by terminal 200 from a plurality of DMRS pattern candidates based on the DPI. Then, terminal 200 (DMRS generating section 208) generates a DMRS used for PUSCH transmission according to the specific DMRS pattern.

  Step (4): The base station 100 receives the PUSCH transmitted by the terminal 200 in step (3), and performs channel estimation based on the DMRS extracted from the PUSCH subframe. The base station 100 performs equalization, demodulation, and decoding of data symbols using the obtained channel estimation values.

  If it is determined that the data has been correctly decoded, the base station 100 transmits an ACK to the terminal 200 and prompts transmission of the next data. If it is determined that an error is included in the data decoding result, the base station 100 transmits a NACK to the terminal 200 to urge retransmission of HARQ.

[effect]
As described above, base station 100 instructs terminal 200 to any one of a plurality of DMRS patterns defined in advance using the DPI included in the UL grant on the downlink control channel (PDCCH or EPDCCH). . Terminal 200 specifies the DMRS pattern in the PUSCH subframe according to the DPI included in the UL grant transmitted from base station 100.

  By doing so, the DMRS pattern of terminal 200 can be dynamically switched. Therefore, according to the present embodiment, a DMRS pattern appropriate for terminal 200 can be selected from a plurality of DMRS patterns including Legacy DMRS and Reduced DMRS.

  For example, the base station 100 dynamically switches between a DMRS pattern (Legacy DMRS pattern) that can be received with high channel estimation accuracy and a DMRS pattern (Reduced DMRS pattern) with small overhead according to the situation or environment of the terminal 200. be able to. Therefore, according to the present embodiment, high reliability and increase in communication capacity can be flexibly realized.

  Also, for example, when a Legacy terminal (for example, a terminal supporting the function of Rel.10) exists in a cell, the base station 100 instructs the terminal 200 to use the Legacy DMRS, and the Legacy terminal and the terminal 200 May be spatially multiplexed by CS and OCC. Further, base station 100 may instruct terminal 200 to use Reduced DMRS, and cause terminal 200 to transmit data using a PUSCH subframe with low overhead. In this way, base station 100 can flexibly instruct uplink scheduling for terminal 200. Therefore, according to the present embodiment, it is possible to avoid characteristic degradation due to scheduling restrictions.

  In particular, it is assumed that the downlink control channel is not congested especially in a small cell because the number of terminals performing simultaneous communication is small. Furthermore, in a small cell, since the distance between the terminal and the small cell base station is relatively short, even if a bit for DPI is newly added to the control signal, reduction of the coverage does not pose a problem. That is, according to the present embodiment, by notifying the DMRS pattern using the DPI, the switching of the DMRS pattern can be flexibly realized without any major disadvantage.

[Variation 1]
In variation 1, the DPI indicates a DMRS pattern and a virtual cell ID (VCID) or a cell ID (PCID).

  Specifically, base station 100 notifies terminal 200 of not only the DMRS pattern that can be instructed, but also the virtual cell ID corresponding to each DPI value in advance. Then, the base station 100 uses the DPI to instruct the use of the DMRS pattern and the virtual cell ID (or cell ID) corresponding to the DMRS pattern. The terminal 200 specifies a DMRS pattern and a virtual cell ID (or cell ID) based on the DPI, and generates a DMRS.

  FIG. 12 shows the correspondence between the DPI, the DMRS pattern, and the virtual cell ID. For example, in FIG. 12, when the DPI is 00, the terminal 200 generates a DMRS using a Legacy DMRS pattern and a base sequence corresponding to a cell ID. When the DPI is 10, the terminal 200 generates a DMRS using the reduced DMRS (Pattern 2) and the base sequence corresponding to the virtual cell ID 1 (VCID 1). The same applies to the cases where the DPI is 01 and 11.

  As described above, Reduced DMRS is often used when the channel state of terminal 200 is good (for example, when the distance between terminal 200 and base station 100 is relatively short). Such a case is likely to occur when the terminal 200 is connected to the small cell base station. In addition, it is conceivable that the small cell base stations are arranged unevenly, such as a large number of small cell base stations are arranged at a high density or a small cell base station is sparsely arranged.

  Therefore, by notifying the same virtual cell ID to a plurality of small cell base stations to orthogonalize the interference or notifying different virtual cell IDs to randomize the interference, the virtual cell ID is used. Thus, interference control between small cells may be performed more flexibly. That is, there is a high possibility that the reduced DMRS and the virtual cell ID are operated simultaneously.

  Therefore, as shown in FIG. 12, the DMRS pattern and the virtual cell ID are simultaneously notified from the base station 100 to the terminal 200 using the DPI, thereby instructing the use of both the reduced DMRS and the virtual cell ID only by the DPI. Therefore, interference control between small cells can be more flexibly and appropriately realized while suppressing an increase in overhead.

[Variation 2]
In Variation 2, DPI indicates a DMRS pattern and ON / OFF of base sequence group hopping.

  Here, the base sequence group hopping is introduced from Rel.8, and hops the group number of the base sequence group so as to generate a DMRS using a different base sequence group for each DMRS transmission. This is a method for further reducing the interference between them. On the other hand, when base sequence group hopping is performed, there is a problem that inter-terminal multiplexing by OCC cannot be performed because base sequences used for two DMRSs in a PUSCH subframe are different. Therefore, in Rel.10, a function of semi-statically turning on / off base sequence group hopping was added by notification from an upper layer, thereby realizing OCC multiplexing.

  Thus, base station 100 notifies terminal 200 in advance not only the DMRS pattern that can be instructed, but also the ON / OFF of base sequence group hopping corresponding to each DPI value. Then, the base station 100 uses the DPI to instruct a DMRS pattern and ON / OFF of base sequence group hopping corresponding to the DMRS pattern. Terminal 200 specifies a DMRS pattern and ON / OFF of base sequence group hopping based on the DPI, and generates a DMRS.

  FIG. 13 shows the correspondence between DPI, DMRS pattern, and ON / OFF of base sequence group hopping. For example, in FIG. 13, when the DPI is 00, the terminal 200 generates the DMRS by using the Legacy DMRS and turning on the base sequence group hopping. When the DPI is 11, terminal 200 generates DMRS using Reduced DMRS (Pattern 2) and turning off base sequence group hopping. The same applies to cases where the DPI is 01 and 10.

  FIG. 14 shows an example in which a DMRS pattern and base sequence group hopping ON / OFF are notified using the DPI shown in FIG. 13 in each subframe. FIG. 14 shows four subframes, and each subframe is composed of two slots.

  As illustrated in FIG. 14, since DPI = “00” is indicated in the first and fourth subframes, terminal 200 uses the Legacy DMRS and transmits the base sequence of two DMRSs in the subframe. The group is hopped (sequence group number: # 3, # 15). This enables randomization of other-cell interference.

  Also, as shown in FIG. 14, terminal 200 specifies DPI = “01” in the second subframe, and thus does not perform hopping of the base sequence group using Legacy DMRS, and Alternatively, a DMRS is generated using a sequence (sequence group number: # 3) determined by the virtual cell ID. This enables orthogonalization of interference by OCC.

  Further, as shown in FIG. 14, terminal 200 generates DMRS using Reduced DMRS without performing hopping of the base sequence group since DPI = “11” is indicated in the third subframe. I do. As a result, overhead due to Reduced DMRS can be reduced.

  Turning on base sequence group hopping enables randomization of interference, but makes orthogonalization of interference by OCC impossible. On the other hand, turning off base sequence group hopping enables orthogonalization by OCC, but does not randomize interference. In contrast, as shown in FIG. 14, base station 100 simultaneously instructs the DMRS pattern and ON / OFF of base sequence group hopping using DPI. Thereby, terminal 200 can dynamically switch ON / OFF of DMRS pattern and base sequence group hopping according to the state of terminal 200, interference to neighboring cells, or the presence or absence of a spatially multiplexed terminal. it can. Therefore, according to Variation 2, interference suppression and increase in throughput can be realized more flexibly.

[Variation 3]
In variation 2 (FIG. 14), when base sequence group hopping is OFF, a sequence determined by a cell ID or virtual cell ID is used in all slots (sequence group number: # 3 in FIG. 14). On the other hand, in variation 3, when base sequence group hopping is OFF in a certain subframe, terminal 200 transmits the DMRS used in the first slot in the subframe when sequence group hopping is ON. Are used in two slots in the subframe.

  FIG. 15 illustrates an example of a case where a DMRS pattern and a base sequence group hopping ON / OFF are notified using the DPI illustrated in FIG. 13 in each subframe. Note that FIG. 15 shows four subframes as in FIG. 14, and each subframe is composed of two slots.

  As shown in FIG. 15, since DPI = “01” is indicated in the second subframe, hopping of the base sequence group is not performed. On the other hand, when hopping of the base sequence group is performed in the second subframe, the sequence group number of the DMRS used in the first slot is # 6. Therefore, terminal 200 generates DMRS using sequence group number # 6 without performing hopping of the base sequence group using Legacy DMRS in the second subframe.

  Similarly, as shown in FIG. 15, since DPI = “11” is indicated in the third subframe, hopping of the base sequence group is not performed. On the other hand, when hopping of the base sequence group is performed in the third subframe, the sequence group number of the DMRS used in the first slot is # 7. Therefore, terminal 200 generates a DMRS using Reduced DMRS and sequence group number # 7 without performing hopping of the base sequence group in the third subframe.

  That is, in variation 2 (FIG. 14), when sequence group hopping is OFF, DMRS of sequence group number # 3 is always used, whereas in variation 3 (FIG. 15), sequence group hopping is OFF. In this case (second and third subframes), the sequence group number is changed.

  By doing so, any terminal 200 switches the DMRS sequence group to be used at least every 1 ms (one subframe), so that in addition to the effect of variation 2, randomization of interference given to other neighboring cells The effect is obtained.

(Embodiment 2)
[Overview of Communication System]
The communication system according to the present embodiment includes base station 100 and one or more terminals 200, as in Embodiment 1 (FIG. 6).

  However, in the present embodiment, unlike Embodiment 1, DPI indicating a DMRS pattern is not used, and the RB allocation information and the DMRS pattern are simultaneously determined by the value of Resource Indication Value (RIV) included in the UL grant. Be instructed. That is, the plurality of DMRS patterns are associated with each value of RIV, which is existing uplink RB allocation information, included in control information transmitted from base station 100 to terminal 200. That is, the DMRS pattern is notified using the existing RIV.

  Specifically, terminal 200 is notified in advance of a plurality of DMRS patterns that can be instructed, and is notified in advance of the DMRS patterns corresponding to each value of RIV. Then, terminal 200 specifies an RB used for PUSCH subframe transmission based on the value of the RIV notified from base station 100, and determines a DMRS pattern corresponding to the RIV as a DMRS pattern used in the PUSCH subframe. I do. The plurality of DMRS patterns that can be instructed, and the DMRS pattern corresponding to each value of the RIV, may be notified in advance by the base station 100 to the terminal 200 in the upper layer or the like, and only the specified combination is used. You may.

[Configuration of Base Station 100]
Control section 101 of base station 100 determines PUSCH subframe allocation for terminal 200. At this time, control section 101 determines the value of RB allocation information (RIV) in consideration of both the RB to be allocated to terminal 200 and the DMRS pattern to be notified to terminal 200.

[Configuration of Terminal 200]
Control section 205 of terminal 200 instructs mapping section 212 to perform RB allocation at the time of PUSCH transmission based on the value of the RIV included in the UL grant. Further, control section 205 determines a DMRS pattern at the time of PUSCH transmission based on the value of the RIV.

[motion]
The operation of base station 100 and terminal 200 according to the present embodiment will be described. The processing flow of base station 100 and terminal 200 according to the present embodiment is substantially the same as steps (1) to (4).

  However, unlike Embodiment 1, in this embodiment, the UL grant does not include DPI. Instead, the base station 100 sets the value of the RIV based on the DMRS pattern instructed to the terminal 200, and the terminal 200 sets the DMRS pattern used in the PUSCH subframe based on the value of the RIV included in the UL grant. To determine.

The RIV is information notified by the number of bits according to the system bandwidth (for example, when PUSCH is not frequency-hopped, Log ₂ (N _RB ^UL (N _RB ^UL +1) / 2) bits). The value is determined based on the following equation (1) (when there is no frequency hopping of PUSCH).

Here, N _RB ^UL indicates the uplink system bandwidth, L _CRBs indicates the number of allocated RBs of terminal 200, and RB _START indicates the lowest frequency RB among the allocated RBs of terminal 200. Equation (1) is used for continuous band allocation. The number of RBs assigned to terminal 200 and the position of the RB are uniquely determined from the value of RIV shown in equation (1) (see FIG. 16). There is a restriction that L _CRBs can be selected only in multiples of 2, 3, and 5. For this reason, in the mechanism up to Rel. 11, the value of the RIV corresponding to L _CRBs other than a multiple of 2, 3, or 5 is not specified.

[effect]
As described above, the base station 100 notifies the terminal 200 of any of the plurality of DMRS patterns using the frequency resource allocation information (RIV) indicating the frequency resource allocation information bit included in the UL grant. Terminal 200 specifies a DMRS pattern to be used from among a plurality of DMRS patterns based on the value of the RIV included in the received UL grant.

  As described above, it is highly likely that the reduced DMRS is instructed to the terminal 200 when communicating with the small cell base station. In a small cell, the number of terminals simultaneously communicating is small, and the channel quality of a terminal communicating with the small cell is likely to be good. Therefore, in a small cell, even if the granularity of frequency scheduling is made fine, the frequency scheduling gain cannot be increased. In other words, even if the granularity of frequency scheduling is reduced and the DMRS pattern is specified accordingly, the effect of the demerit hardly occurs. Therefore, by specifying the DMRS pattern used in terminal 200 according to the value of the RIV as in the present embodiment, the DMRS pattern can be flexibly switched.

  Further, in the present embodiment, the notification of the DMRS pattern is performed using the existing RIV, so that an additional bit indicating the DMRS pattern is not required, and an increase in overhead does not occur.

  Next, specific examples 1 to 4 of notification / specification of the DMRS pattern of base station 100 and terminal 200 in the present embodiment will be described in detail.

[Specific example 1]
The base station 100 _sets the value of the number of allocated RBs (that is, the allocated bandwidth) L _{CRBs in} the _RIV to either an even number or an odd number in consideration of the DMRS pattern. Terminal 200 specifies a DMRS pattern to be used according to whether the value of the number of allocated RBs (allocated bandwidth) L _{CRBs in} the RIV included in the UL grant is an even number or an odd number.

For example, a Legacy DMRS pattern is associated with an RIV indicating allocation of an odd number of RBs, and a Reduced DMRS pattern is associated with an RIV indicating allocation of an even number of RBs. That is, the terminal 200, the base station 100, using the Legacy DMRS if RIV where L _CRBS corresponds to an odd number of RB is informed, if the RIV where L _CRBS corresponds to an even number of RB is informed For this, Reduced DMRS is used.

Note that the _{association between the} number of allocated RBs (even number and odd number) indicated in the L _CRBs and whether to use the reduced DMRS is predetermined, or the base station 100 and the terminal 200 and shared. Further, the reduced DMRS pattern specified by the RIV may be defined in advance, or may be notified from the base station 100 to the terminal 200 in an upper layer or the like.

  FIG. 17 illustrates a notification example of the DMRS pattern in the first specific example. In FIG. 17, for example, the reduced DMRS pattern (3) shown in FIG. 4D is used as the reduced DMRS.

As shown in FIG. 17, when the number of L _CRBs in the RIV notified by the UL grant is an odd number (1 RB or 3 _RBs ), the Legacy DMRS pattern is used as the DMRS pattern. On the other hand, when the number of L _CRBs in the RIV notified by the UL grant is an even number (2 RBs or 4 RBs), Reduced DMRS pattern (3) is used as the DMRS pattern.

In FIG. 17, one type of Reduced DMRS pattern associated with an even number of L _CRBs is used. However, for different values of L _CRBs (for example, 2 RBs and 4 RBs), a plurality of Reduced DMRS patterns are used. May be respectively associated with different patterns.

Here, in the existing DMRS, a sequence length corresponding to integer L _CRBs is defined. Therefore, when L _CRBs is an even number, there is a DMRS having a sequence length half that of L _CRBs . On the other hand, when L _CRBs is an odd number, a sequence length obtained by dividing L _CRBs by a power of 2 (for example, 2) cannot be defined.

Therefore, when L _CRBS is even, the terminal 200, even with Reduced DMRS pattern such that DMRS half sequence length L _CRBS, using existing DMRS half sequence length L _CRBS be able to. That is, as shown in FIG. 17, by _defining that Reduced DMRS is used only when L _CRBs are even and to use Legacy DMRS when L _CRBs are odd, terminal 200 Using only the long DMRS, a DMRS having half the bandwidth of the PUSCH can be generated. In other words, when using Reduced DMRS, it is not necessary to newly define a DMRS having a sequence length other than the existing sequence length.

  Also, it is assumed that Reduced DMRS is likely to be used in small cells, has poor frequency selectivity of channel quality, and has a small number of terminals performing simultaneous communication. In other words, Reduced DMRS is likely to be used in an environment where there is no disadvantage even if the granularity of frequency scheduling is coarse. Therefore, by associating the number of allocated RBs (allocated bandwidth) in the RIV with the DMRS pattern, the flexibility of the RIV is restricted, but there is almost no adverse effect of this restriction, and dynamic notification of Reduced DMRS is realized. be able to.

[Variation of Specific Example 1]
Here, the RIV indicating the allocation of the odd number of RBs is associated with the allocation of the odd number + 1 and the reduced DMRS pattern, and the RIV indicating the allocation of the even number of RBs is associated with the even number of RBs. And the Legacy DMRS pattern are associated with each other.

That is, when the base station 100 notifies the RIV of L _CRBs corresponding to an odd number of RBs, the terminal 200 uses Reduced DMRS with the number of RBs as (L _CRBs +1), and uses an even number of L _CRBs . When the RIV corresponding to the RB is notified, the legacy DMRS is used with the number of RBs as L _CRBs .

Note that the _{association between the} number of allocated RBs (even number and odd number) indicated in the L _CRBs and whether to use the reduced DMRS is predetermined, or the base station 100 and the terminal 200 and shared. Further, the reduced DMRS pattern specified by the RIV may be defined in advance, or may be notified from the base station 100 to the terminal 200 in an upper layer or the like.

  FIG. 18 illustrates a notification example of the DMRS pattern in the variation of the first specific example. In FIG. 18, as in FIG. 17, for example, the reduced DMRS pattern (3) shown in FIG. 4D is used as the reduced DMRS.

As shown in FIG. 18, when the number of L _CRBs in the RIV notified by the UL grant is an even number (2 RBs or 4 RBs), the allocated bandwidth is set according to the L _CRBs , and a Legacy DMRS pattern is used as the DMRS pattern. On the other hand, as shown in FIG. 18, when the number of L _CRBs in the RIV notified by the UL grant is an odd number (1 RB or 3 _RBs ), the allocated bandwidth is set according to (L _CRBs +1; that is, 2 RBs or 4 RBs). Reduced DMRS pattern (3) is used as the DMRS pattern.

  By doing so, unlike the specific example 1 (FIG. 17), although an allocated bandwidth (odd number of allocated RBs) that cannot be specified for the terminal 200 that can notify the reduced DMRS occurs, the same allocated bandwidth (even number) is used. (The number of allocated RBs), Legacy DMRS and Reduced DMRS can be selected. That is, terminal 200 can select one DMRS pattern from a plurality of DMRS patterns including Legacy DMRS and Reduced DMRS in the same allocated bandwidth, so that it is necessary to change the bandwidth for DMRS pattern selection. Absent. Therefore, the circuit configuration and algorithm of the scheduler can be simplified.

Note that the terminal 200 uses the Legacy DMRS with the number of RBs being (L _CRBs +1) when the _{RIV in} which L _CRBs is equivalent to an odd number of RBs is notified, and the _{RIV in} which L _CRBs corresponds to an even number of RBs. Is notified, Reduced DMRS may be used as the number of RBs as L _CRBs .

  Further, the RIV indicating the assignment of the odd number of RBs may be associated with the assignment of the odd number of −1 RBs and the reduced DMRS pattern.

[Example 2]
The base station 100 _sets the value of the number of allocated RBs (allocated bandwidth) L _{CRBs in} the RIV in consideration of the DMRS pattern. The terminal 200 specifies the DMRS pattern to be used by comparing the value of the number of allocated RBs (allocated bandwidth) L _{CRBs in} the RIV included in the UL grant with a predetermined value.

For example, a Legacy DMRS pattern is associated with an RIV indicating an allocated bandwidth equal to or less than a predetermined value x, and a Reduced DMRS pattern is associated with an RIV indicating an allocated bandwidth wider than the predetermined value x. That is, the terminal 200, the RIV notified from the base station 100, if L _CRBS satisfies 0 <L _CRBs ≦ x by using the Legacy DMRS, if L _CRBS satisfies x <L _CRBs ≦ N _RB ^UL For this, Reduced DMRS is used.

  That is, the DMRS pattern used by terminal 200 is switched for each bandwidth range allocated to terminal 200.

Whether or not to use Reduced DMRS when x <L _CRBs ≦ N _RB ^UL is satisfied is defined in advance or shared between the base station 100 and the terminal 200 by notification of an upper layer or the like. Shall be Further, the _reduced DMRS pattern specified by the L _CRBs may be defined in advance, or may be notified from the base station 100 to the terminal 200 in an upper layer or the like.

Further, it is assumed that the predetermined value x (0 <x <N _RB ^UL ) is defined in advance or is shared between base station 100 and terminal 200 by notification of an upper layer or the like.

Further, a plurality of values (x ₁ , x ₂ ,...) _May be notified as x, and the DMRS pattern used by terminal 200 may be switched from the plurality of DMRS patterns according to the value of L _CRBs .

FIGS. 19 and 20 show examples of the notification of the DMRS pattern when a plurality of predetermined values x ₁ , x ₂ , and x ₃ are used.

In FIG. 19, x ₁ = 2, x ₂ = 8, and x ₃ = 15 are set. N _RB ^UL = 25. In this case, Legacy DMRS is used when 0 <L _{CRBs ≤x 1} is satisfied (L _CRBs = 1 to 2), and when x ₁ <L _{CRBs ≤x 2} is satisfied (L _CRBs = 3 to 8) If Reduced DMRS pattern (1) is used and x ₂ <L _CRBs ≤ x ₃ (L _CRBs = 9 to 15), Reduced DMRS pattern (2) is used and x ₃ <L _CRBs ≤ N _RB ^UL If _LCRBs = 16 to 25, Reduced DMRS pattern (3) is used. Here, as shown in FIG. 20, Reduced DMRS pattern (1) shown in FIG. 19 corresponds to Reduced DMRS pattern (1) shown in FIG. 4B, and Reduced DMRS pattern (2), (3) One of the two DMRSs included in the Legacy DMRS pattern (FIG. 4A) is replaced with data, and in the remaining DMRS frequency resources, a DMRS having a sequence length shorter than the allocated bandwidth is converted to an SC-FDMA symbol. This is a method of performing distributed mapping inside.

As described above, in the specific example 2, when the RIV specifies the bandwidth of the RB that is equal to or smaller than the predetermined value (x _{1 in} FIGS. 19 and 20), the Legacy DMRS is selected, and the RIV for which the RIV is larger than the predetermined value is selected. When one bandwidth is designated, one DMRS pattern is selected from one or a plurality of Reduced DMRS patterns.

  The terminal 200 that can use Reduced DMRS is often connected to a small cell or has good channel quality. In such a case, there is a high possibility that the bandwidth allocated to the terminal 200 is wide. That is, as the channel state of terminal 200 is better, a wider band is more likely to be allocated. In addition, the better the channel state of the terminal 200 is, the more accurate the channel estimation can be made using the DMRS with less energy or less resources.

  Therefore, as in the specific example 2, the DMRS pattern is changed for each allocated bandwidth of the terminal 200. At this time, the energy or resources of the DMRS are reduced as the wider bandwidth is allocated, and the corresponding amount is allocated to data. Becomes possible. That is, as shown in FIGS. 19 and 20, the wider the allocated bandwidth, the lower the density of DMRS in the subframe.

  In this way, for the terminal 200 having a good channel quality and a high data rate, a wider allocated bandwidth is instructed, and the reduced DMRS is instructed to provide more data resources and achieve a higher throughput. can do. On the other hand, the terminal 200 where high channel estimation accuracy is required, or the terminal 200 where MU-MIMO with the Legacy terminal is required, indicates a narrow allocated bandwidth, and indicates a Legacy DMRS, so that the channel Improvement of estimation accuracy or application of MU-MIMO can be realized.

[Specific example 3]
The base station 100 sets the value of the lowest RB position RB _START of the allocated band in the RIV in consideration of the DMRS pattern. The terminal 200 specifies the DMRS pattern to be used by comparing the value of the RB position RB _START in the RIV included in the UL grant with a predetermined value.

For example, a Legacy DMRS pattern is associated with an RIV having the lowest allocated frequency higher than the predetermined value y, and a Reduced DMRS pattern is associated with an RIV having the lowest frequency not higher than the predetermined value y. That is, the terminal 200, the RIV notified from the base station 100, if the RB _START satisfies 0 ≦ RB _START ≦ y by using the Reduced DMRS, if RB _START satisfies y _{<RB START} <N RB ^UL Use Legacy DMRS.

  That is, the DMRS pattern used by terminal 200 is switched for each start position of the band allocated to terminal 200.

Note that whether to use Reduced DMRS when 0 ≦ RB _START ≦ y is defined in advance or shared between the base station 100 and the terminal 200 by notification of an upper layer or the like And Also, the reduced DMRS pattern specified by RB _START may be defined in advance, or may be notified from the base station 100 to the terminal 200 in an upper layer or the like.

Further, it is assumed that the predetermined value y (0 ≦ y <N _RB ^UL ) is defined in advance or is shared between the base station 100 and the terminal 200 by notification of an upper layer or the like.

Also, a plurality of values (y ₁ , y ₂ ,...) May be notified as y, and the DMRS pattern used by terminal 200 may be switched from the plurality of DMRS patterns according to the value of RB _START .

FIGS. 21 and 22 show examples of notification of the DMRS pattern when a plurality of predetermined values y ₁ , y ₂ and y ₃ are used.

In FIG. 21, y ₁ = 10, y ₂ = 15, and y ₃ = 20 are set. N _RB ^UL = 25. In this case, Reduced DMRS pattern (3) is used when 0 ≦ RB _START ≦ y ₁ is satisfied (RB _START = 0 to 10), and y ₁ <RB _START ≦ y ₂ is satisfied (RB _START = 11 to Reduced DMRS pattern (2) is used for 15), and if y ₂ <RB _START ≦ y ₃ (RB _START = 16 to 20), Reduced DMRS pattern (1) is used and y ₃ <RB _START If ≦ N _RB ^UL is satisfied (RB _START = 21 to 25), Legacy DMRS is used. Here, as in the specific example 2, as shown in FIG. 22, the reduced DMRS pattern (1) shown in FIG. 21 corresponds to the reduced DMRS pattern (1) shown in FIG. 4B, and the reduced DMRS pattern (2) , (3) replace one of the two DMRSs included in the Legacy DMRS pattern (FIG. 4A) with data and, in the remaining DMRS frequency resources, DMRSs having a sequence length shorter than the allocated bandwidth. Is distributedly mapped into SC-FDMA symbols.

Thus, in the specific example 3, when the RIV specifies an RB start position larger than a predetermined value (y _{3 in} FIGS. 21 and 22), the Legacy DMRS is selected, and the RB start position whose RIV is equal to or smaller than the predetermined value is determined. If specified, one DMRS pattern is selected from one or more Reduced DMRS patterns.

As described above, PUSCH resource allocation is indicated by the start position of the allocated RB (the RB number of the lowest frequency; the starting point) and the bandwidth from the start position (the number of consecutive RBs in the high frequency direction). 16). Therefore, in order to allocate a wide band to terminal 200, base station 100 must notify the RIV so that start position RB _START has a low frequency RB number (for example, see FIG. 22). Also, the reduced DMRS is highly likely to be instructed to the terminal 200 having good channel quality, and is assumed to be effective in an environment where RB allocation in a wider band is performed.

On the other hand, in Example 3, Reduced DMRS is instructed when RB _START is a low frequency RB number, and Legacy DMRS is instructed when RB _START is a high frequency RB number. That is, according to Specific Example 3, the base station 100 allows the wideband RB allocation to the terminal 200 when instructing the reduced DMRS, and the narrowband RB allocation when instructing the legacy DMRS. It becomes possible.

  As a result, terminal 200 can use Reduced DMRS at the time of RB allocation in a wider band. Therefore, it is possible to reduce the overhead of the terminal 200 in a good state in which a wideband is allocated and achieve higher throughput.

  Further, in the third specific example, the base station 100 can concentrate the allocation of the terminal 200 instructed for the Legacy DMRS to the RB of the high frequency. By this means, it is possible to prevent interference between the Legacy terminal and the terminal 200 capable of using Reduced DMRS (terminal allocated to a low frequency RB).

[Example 4]
As described above, in PUSCH before _Rel.11 , the bandwidth L _CRBs that can be specified by the UL grant is limited to a multiple of 2, 3, or 5 RBs. Therefore, for example, when the bandwidth (L _CRBs ) indicates 7 RBs, there are some RIV values that are not notified.

  Therefore, in specific example 4, the base station 100 notifies the terminal 200 of the use of Reduced DMRS by using an RIV value that is not used in the PUSCH before Rel.11. That is, the plurality of DMRS patterns are respectively associated with RIV values corresponding to bandwidths other than the bandwidth that can be allocated by the RIV (that is, bandwidths that cannot be allocated).

  That is, when the RIV notified from the base station 100 is a value other than the number of RBs (bandwidth) which is a multiple of 2, 3, or 5, the terminal 200 selects one of a plurality of reduced DMRS patterns from one or a plurality of reduced DMRS patterns. One Reduced DMRS is determined.

  Note that whether to use Reduced DMRS when an RIV that is not used in the PUSCH before Rel. 11 is notified is defined in advance, or between the base station 100 and the terminal 200 by notification of an upper layer or the like. Shall be shared. Further, the reduced DMRS pattern specified by the RIV may be defined in advance, or may be notified from the base station 100 to the terminal 200 in an upper layer or the like.

Also, it is assumed that the values of L _CRBs and RB _{START in} the _RIV indicating the reduced DMRS pattern are notified from an upper layer in advance. Alternatively, the values of L _CRBs and RB _{START in} the _RIV indicating the reduced DMRS pattern may be used as L _CRBs and RB _START corresponding to the values of the RIV that can be actually indicated, which can be identified from the value of the _RIV. . In this case, using one RIV, it is possible to simultaneously achieve the instruction of the reduced DMRS and the flexible frequency scheduling.

  In this way, by diverting the value of the RIV not used as the allocation RB information for the notification of the DMRS pattern, the terminal from the base station 100 while maintaining the same degree of freedom of PUSCH frequency scheduling as before Rel. 11 The instruction of Reduced DMRS to 200 becomes possible.

(Embodiment 3)
[Overview of Communication System]
The communication system according to the present embodiment includes base station 100 and one or more terminals 200, as in Embodiment 1 (FIG. 6).

  However, in the present embodiment, unlike Embodiment 1, DPI indicating the DMRS pattern is not used, and the DMRS pattern is indicated by the value of the A-SRS trigger bit (SRS request field) included in the UL grant. . That is, the plurality of DMRS patterns are respectively associated with the respective values of the existing Aperiodic SRS trigger bits included in the control information transmitted from base station 100 to terminal 200.

  The A-SRS trigger bit is a bit for instructing the transmission of the A-SRS at the specified transmittable timing. That is, in the present embodiment, the A-SRS trigger bit simultaneously indicates the presence or absence of the A-SRS transmission request and the DMRS pattern. That is, the DMRS pattern is notified using the existing A-SRS trigger.

  Specifically, terminal 200 is notified in advance of a plurality of DMRS patterns that can be instructed, and is notified in advance of the DMRS pattern corresponding to the A-SRS trigger bit. Then, terminal 200 specifies the transmission timing of the A-SRS based on the value of the A-SRS trigger bit notified from base station 100, and transmits the DMRS pattern corresponding to the A-SRS trigger bit to the PUSCH sub- It is determined as the DMRS pattern used in the frame. Note that a plurality of DMRS patterns that can be instructed, and a DMRS pattern corresponding to each value of the A-SRS trigger bit, the base station 100 may notify the terminal 200 in advance to the terminal 200 in an upper layer or the like. Only a combination may be used.

  Further, the transmission timing of the A-SRS indicated by the A-SRS trigger bit and the transmission timing of the PUSCH indicated by the UL grant do not necessarily have to be the same. For example, the transmission timing of the A-SRS may be a common timing in the entire cell, and the transmission timing of the PUSCH may be a timing after a specified time from the reception of the UL grant. By doing so, it is possible to easily perform SRS interference control between terminals while suppressing delay of uplink data.

[Configuration of Base Station 100]
Control section 101 of base station 100 determines PUSCH subframe allocation for terminal 200. At this time, the control unit 101 determines the value of the A-SRS trigger bit in consideration of both the presence / absence of an A-SRS transmission request to the terminal 200 and the DMRS pattern notified to the terminal 200.

[Configuration of Terminal 200]
The control unit 205 of the terminal 200 determines the presence or absence of A-SRS transmission at the next A-SRS transmission timing based on the value of the A-SRS trigger bit included in the UL grant, and instructs the SRS generation unit 209. . Further, control section 205 determines a DMRS pattern at the time of PUSCH transmission based on the value of the A-SRS trigger bit.

[motion]
The operation of base station 100 and terminal 200 according to the present embodiment will be described. The processing flow of base station 100 and terminal 200 according to the present embodiment is substantially the same as steps (1) to (4).

  However, unlike Embodiment 1, in this embodiment, the UL grant does not include DPI. Instead, the base station 100 sets the value of the A-SRS trigger bit based on the DMRS pattern instructed to the terminal 200, and the terminal 200 sets the PUSCH based on the value of the A-SRS trigger bit included in the UL grant. Determine the DMRS pattern used in the subframe.

  Note that the number of DMRS patterns selectable by terminal 200 differs according to the number of bits of the A-SRS trigger. FIG. 23A shows a notification example of the DMRS pattern when the A-SRS trigger bit is 1 bit, and FIG. 23B shows a notification example of the DMRS pattern when the A-SRS trigger bit is 2 bits.

  For example, as shown in FIG. 23A (in the case of 1 bit), when the value of the A-SRS trigger bit is 0, it is indicated that there is no A-SRS transmission request (No trigger) and that it is Legacy DMRS. You. Also, when the value of the A-SRS trigger bit is 1, it indicates that there is an A-SRS transmission request and that it is a reduced DMRS pattern (1).

  Also, as shown in FIG. 23B (in the case of 2 bits), when the value of the A-SRS trigger bit is 00, it is indicated that there is no A-SRS transmission request and that it is Legacy DMRS, and A-SRS If the value of the trigger bit is 01, it indicates that there is an A-SRS transmission request and that the received bit is a Reduced DMRS pattern (1). Similarly, when the value of the A-SRS trigger bit is 10, there is an A-SRS transmission request, and it is indicated that it is Legacy DMRS, and when the value of the A-SRS trigger bit is 11, the A-SRS It is indicated that there is no transmission request and that the reduced DMRS pattern (2) is used.

  As described above, terminal 200 is instructed simultaneously with the A-SRS transmission request and the DMRS pattern according to the value of the A-SRS trigger bit included in the UL grant. Also, when the number of A-SRS trigger bits is plural (for example, FIG. 23B), A-SRS and DMRS patterns of different Configurations (1st SRS parameter set and 2nd SRS parameter set in FIG. 23) can be set for each value of the trigger bit. Becomes Also, it is assumed that the A-SRS Configuration and DMRS pattern corresponding to each value of the A-SRS trigger bit can be set independently.

[effect]
As described above, the base station 100 and the terminal 200 notify and select the DMRS pattern by associating the value of the A-SRS trigger bit with the DMRS pattern.

  In LTE, in addition to A-SRS, Periodic SRS (P-SRS) that is transmitted periodically without a trigger bit is defined. When the transmission cycle of the P-SRS is short, the necessity of the A-SRS transmission request may be low. When the necessity of the A-SRS transmission request is low, the base station 100 and the terminal 200 can use the A-SRS trigger bit as the DMRS pattern indication bit as in the present embodiment. By doing so, it is possible to select an appropriate DMRS pattern for terminal 200 from a plurality of DMRS patterns including Legacy DMRS and Reduced DMRS, as in Embodiment 1, without increasing overhead.

(Embodiment 4)
[Overview of Communication System]
The communication system according to the present embodiment includes base station 100 and one or more terminals 200, as in Embodiment 1 (FIG. 6).

  However, in the present embodiment, unlike Embodiment 1, DPI indicating the DMRS pattern is not used, and the DMRS pattern is switched according to the downlink control channel (PDCCH or each EPDCCH set) through which the UL grant is transmitted. Can be That is, a plurality of DMRS patterns are respectively associated with a plurality of control channels used for transmitting control information transmitted from base station 100 to terminal 200.

  Specifically, terminal 200 is notified in advance of a plurality of DMRS patterns that can be instructed, and is notified in advance of the DMRS patterns corresponding to each control channel (PDCCH and each EPDCCH set). Then, terminal 200 determines the DMRS pattern corresponding to the control channel used for transmitting the UL grant notified from base station 100 as the DMRS pattern used in the PUSCH subframe. Note that the plurality of DMRS patterns that can be instructed, and the DMRS patterns corresponding to each control channel, may be notified in advance by the base station 100 to the terminal 200 in the upper layer or the like. Is also good.

[Configuration of Base Station 100]
Control section 101 of base station 100 determines PUSCH subframe allocation for terminal 200. At this time, control section 101 considers both a control channel (PDCCH and EPDCCH set) for mapping a control signal (including a UL grant) for terminal 200 and a DMRS pattern to be notified to terminal 200, and considers the control signal Determine the mapping.

[Configuration of Terminal 200]
Control section 205 of terminal 200 determines a DMRS pattern at the time of PUSCH transmission according to whether the control channel to which the UL grant has been transmitted is a PDCCH or an EPDCCH set.

[motion]
The operation of base station 100 and terminal 200 according to the present embodiment will be described. The processing flow of base station 100 and terminal 200 according to the present embodiment is substantially the same as steps (1) to (4).

  However, unlike Embodiment 1, in this embodiment, the UL grant does not include DPI. Instead, base station 100 sets a control channel used for UL grant transmission based on the DMRS pattern instructed to terminal 200, and terminal 200 sets a control channel (PDCCH or EPDCCH set) used for UL grant transmission. Based on this, a DMRS pattern used in the PUSCH subframe is determined.

  Note that only one EPDCCH set may be set, or a plurality of EPDCCH sets may be set. FIG. 24 shows a notification example of a DMRS pattern when a PDCCH and three EPDCCH sets are set.

  In FIG. 24, terminal 200 blind-decodes three types of EPDCCH sets in addition to the PDCCH. Then, terminal 200 determines a DMRS pattern in PUSCH transmission indicated by the UL grant according to which control channel the UL grant can be decoded.

  For example, as shown in FIG. 24, when a UL grant is transmitted using PDCCH or EPDCCH set 1, terminal 200 determines that Legacy DMRS has been instructed. Further, when the UL grant is transmitted using EPDCCH set 2, terminal 200 determines that Reduced DMRS pattern (1) has been instructed, and when the UL grant is transmitted using EPDCCH set 3, terminal 200 transmits , Reduced DMRS pattern (2) is instructed.

[effect]
As described above, the base station 100 and the terminal 200 perform notification / selection of the DMRS pattern by associating the control channel on which the UL grant is transmitted with the DMRS pattern.

  Since the PDCCH has wide coverage and is also supported by conventional (Rel.8) terminals, there is a high possibility that the macrocell base station will use it for UL grant transmission. On the other hand, for the EPDCCH, a plurality of sets (two EPDCCH sets in Rel. 11) can be set as blind decoding targets. From this, it is conceivable to associate different EPDCCH sets with the macro cell base station and the small cell base station, and transmit UL grants from different base stations according to the situation of terminal 200. As described above, an operation in which a different control channel (or a different EPDCCH set) is set for each of a plurality of base stations (or transmission / reception points) capable of communicating with the terminal 200 can be considered.

  For example, in FIG. 24, PDCCH and EPDCCH set 1 are used for transmission of a UL grant from a macro cell base station having high coverage and high reliability, and EPDCCH set 2 and EPDCCH set 3 are used for UL grant from a nearby small cell base station. An operation used for transmission of a message is considered. In such a case, the control channel (PDCCH and EPDCCH set 1) used by the macro cell base station for transmitting the UL grant is associated with the Legacy DMRS pattern, and the control channel (EPDCCH) used by the small cell base station for transmitting the UL grant A Reduced DMRS pattern is associated with set 2,3).

  In this way, by associating the DMRS pattern with the control channel on which the UL grant is transmitted, the terminal 200 can be operated to use Reduced DMRS when communicating with a specific base station (transmission / reception point). it can. By doing so, it is possible to appropriately switch the DMRS pattern without increasing the overhead and without restricting the control bits included in the UL grant.

(Embodiment 5)
[Overview of Communication System]
The communication system according to the present embodiment includes base station 100 and one or more terminals 200, as in Embodiment 1 (FIG. 6).

  However, in the present embodiment, unlike Embodiment 1, DPI indicating the DMRS pattern is not used, and the DMRS is determined by the value of the cyclic shift notification bit (CS field or cyclic shift index) included in the UL grant. A pattern is indicated. That is, the plurality of DMRS patterns are respectively associated with the respective values of the existing CS field included in the control information transmitted from base station 100 to terminal 200.

  The CS field is a bit for indicating a cyclic shift amount and an OCC code number (OCC index) to be applied to the DMRS when transmitting the PUSCH indicated by the UL grant. That is, in the present embodiment, the CS field simultaneously indicates the amount of cyclic shift applied to the DMRS, the code number of the OCC, and the DMRS pattern. That is, the DMRS pattern is notified using the existing CS field.

  Specifically, terminal 200 is notified in advance of a plurality of DMRS patterns that can be instructed, and the DMRS pattern corresponding to each CS field is notified in advance. Then, terminal 200 specifies the cyclic shift amount and the code number of the OCC based on the value of the CS field notified from base station 100, and uses the DMRS pattern corresponding to the CS field in the PUSCH subframe. Is determined as the DMRS pattern to be used. In addition, a plurality of DMRS patterns that can be instructed, and the DMRS pattern corresponding to each value of the CS field, the base station 100 may notify the terminal 200 in advance in the upper layer or the like, and only a specified combination is used May be.

[Configuration of Base Station 100]
Control section 101 of base station 100 determines PUSCH subframe allocation for terminal 200. At this time, the control unit 101 determines the value of the CS field in consideration of both the cyclic shift amount of the DMRS for the terminal 200, the code number of the OCC, and the DMRS pattern to be notified to the terminal 200.

[Configuration of Terminal 200]
The control unit 205 of the terminal 200 specifies the cyclic shift amount applied to the DMRS and the code number of the OCC based on the value of the CS field included in the UL grant, and instructs the DMRS generation unit 208. Further, control section 205 determines a DMRS pattern at the time of PUSCH transmission based on the value of the CS field, and instructs DMRS generation section 208.

[motion]
The operation of base station 100 and terminal 200 according to the present embodiment will be described. The processing flow of base station 100 and terminal 200 according to the present embodiment is substantially the same as steps (1) to (4).

  However, unlike Embodiment 1, in this embodiment, the UL grant does not include DPI. Instead, the base station 100 sets the value of the CS field based on the DMRS pattern instructed to the terminal 200, and the terminal 200 is used in the PUSCH subframe based on the value of the CS field included in the UL grant Determine the DMRS pattern.

  FIG. 25 shows a notification example of a DMRS pattern using a CS field (3 bits). In FIG. 25, λ represents a layer number. The cyclic shift amount that can be notified by the CS field is 0 to 11, and the OCC code numbers are 0 and 1. The code number 0 of the OCC corresponds to [+1 +1], and the code number 1 of the OCC corresponds to [+1 -1].

  As shown in FIG. 25, the case where the value of the CS field is 000, 001, 010, 111 is associated with the Legacy DMRS, and the case where the value of the CS field is 011, 100, the case is associated with the Reduced DMRS pattern (1). , CS field values of 101 and 110 are associated with Reduced DMRS pattern (2).

[effect]
As described above, the base station 100 and the terminal 200 notify and select the DMRS pattern by associating the value of the A-SRS trigger bit with the DMRS pattern.

  Reduced DMRS is likely to be used when terminal 200 is connected to a small cell base station and when the channel quality is sufficiently good. It is assumed that the number of such terminals is small and other cell interference is small. In other words, Reduced DMRS is more likely to be used in situations where the need to perform orthogonalization and interference control using CS and OCC is low. Therefore, by instructing the DMRS pattern at the same time as the CS / OCC using the CS field, there is a certain restriction on the notification of the CS / OCC, but there is almost no adverse effect of this restriction, and the DMRS pattern is appropriately switched. be able to. Also, since the notification of the DMRS pattern is performed using the existing CS field, there is no addition of new bits, and no increase in overhead occurs.

  In the present embodiment, the use of a DMRS pattern other than Legacy DMRS (that is, any of Reduced DMRS patterns) is limited to only when the number of layers (transmission rank) is 1 (that is, when λ = 0). May be. Specifically, when the number of layers (transmission rank) is 1, terminal 200 (control section 205) determines a specific DMRS pattern used by terminal 200 based on the CS field, and determines the number of layers (transmission rank). Is 2 or more, the legacy DMRS pattern is determined as a specific DMRS pattern used by the terminal 200 irrespective of the value of the CS field.

  FIG. 26 shows a case where the use of the reduced DMRS pattern is limited to only λ = 0 (the number of layers is 1) in the CS field shown in FIG. In FIG. 26, when the number of layers is 1 (λ = 0) in the CS field associated with Reduced DMRS, the associated Reduced DMRS is used, but the number of layers is 2 or more (λ = 1 to λ). In the case of 3), the legacy DMRS is used instead of the associated reduced DMRS.

  When the number of layers is large, high throughput can be realized by simultaneously transmitting (multiplexing) a plurality of data from different layers with the same time / frequency resource. At this time, since the DMRS is also multiplexed, it is easily affected by the channel estimation error. Therefore, when the number of layers is large, the throughput can be expected to be further improved by using Reduced DMRS in the same manner as in the case of the number of layers, but the channel estimation is more accurate than the slight improvement in resource efficiency. It is desirable to perform well and give priority to correctly receiving data without retransmission. When the number of layers is large, a high data rate can be achieved without relying on Reduced DMRS. Therefore, as shown in FIG. 26, by switching the DMRS pattern according to the number of layers, it is possible to use an appropriate DMRS corresponding to the number of layers.

  Note that, even if the DMRS is changed according to the format of the UL grant or the search space in which the UL grant has been transmitted, the same as in the above-described embodiment can be realized. For example, UL grants include DCI format 0 for instructing one-layer transmission and DCI format 4 for instructing two or more layers. Therefore, in the UL grant (e.g., DCI format 0) that instructs one-layer transmission, using Legacy DMRS regardless of the value of the CS field, a part of the UL grant that can instruct two or more layer transmission (e.g., DCI format 4) The reduced DMRS may be used in the case of the value of the CS field. Alternatively, a control channel for transmitting a UL grant includes a common search space (CSS (Common Search Space)) for instructing one-layer transmission and a terminal-specific search space (USS (UE specific Search Space)) for instructing two or more layers. There is. Therefore, in the search space (CSS) that instructs one-layer transmission, the legacy DMRS is used regardless of the value of the CS field, and in the search space (USS) that can instruct two or more layer transmissions, some of the values of the CS field are used. In such a case, Reduced DMRS may be used.

(Embodiment 6)
The communication system according to the present embodiment includes base station 100 and one or more terminals 200, as in Embodiment 1 (FIG. 6).

  However, in the present embodiment, unlike Embodiment 1, the DPI indicating the DMRS pattern is not included in the UL grant, and is transmitted as a control signal different from the UL grant in the control channel.

  In the following description, a control signal when the DPI is 2 bits is called DCI format 3d, and a control signal when the DPI is 1 bit is called DCI format 3dA.

  Specifically, the base station 100 transmits DCI format 3d or DCI format 3dA as DPI. On the other hand, the terminal 200 blind-decodes each of the DCI format 3d / 3dA, can correctly decode the DCI format 3d / 3dA, and uses the DMRS pattern indicated by the DPI when the DPI addressed to the terminal 200 is included. .

  The base station 100 notifies the terminal 200 of the use of DCI format 3d / 3dA and the DMRS pattern indicated by the DPI of DCI format 3d / 3dA in advance. In addition, the base station 100 notifies the terminal 200 of the pseudo terminal ID necessary for decoding the DCI format 3d / 3dA in advance. The pseudo terminal ID may be a common value among the plurality of terminals 200. Then, base station 100 transmits DCI format 3d / 3dA together with the UL grant. The DCI format 3d / 3dA includes a DPI addressed to one or more terminals 200, and has a CRC bit masked with a pseudo terminal ID added. That is, the control signal transmitted from base station 100 to terminal 200 includes the DPI and the UL grant, and the DPI is subjected to masking different from masking (scrambling) for the UL grant.

  The terminal 200 performs blind decoding of the DCI format 3d / 3dA in addition to the UL grant. At this time, the terminal 200 determines the success or failure of the decoding using the CRC masked with the terminal ID of the terminal 200 for the UL grant, and, for the DCI format 3d / 3dA, the CRC masked with the pseudo terminal ID. Is used to determine the success or failure of decoding. When decoding of DCI format 3d / 3dA succeeds at the same time as decoding of UL grant, terminal 200 selects a DMRS pattern according to the DPI value addressed to terminal 200 included in DCI format 3d / 3dA, and UL grant Transmit the PUSCH allocated by

  Base station 100 receives the PUSCH transmitted by terminal 200 and decodes the PUSCH. Since base station 100 cannot determine whether terminal 200 has correctly decoded DCI format 3d / 3dA, it is assumed that PUSCH has been transmitted using either the Legacy DMRS or the DMRS pattern indicated by DPI, and PUSCH Are sequentially decoded.

  As described above, in the present embodiment, the DPI is transmitted and received using the control signal (DCI format 3 / 3A) subjected to scrambling different from the UL grant, and the DMRS pattern is switched according to the value of the DPI. .

  By doing so, the reduced DMRS can be notified separately while using the UL grant of Rel.11 or earlier as it is, so that the base station 100 operates the terminal using Legacy DMRS with the scheduler of Rel.11 or earlier, Only terminals using Reduced DMRS can be notified of the DMRS pattern by independent control signals. That is, only by adding the function of DCI format 3d / 3dA to the conventional scheduler of the base station 100, the notification of the reduced DMRS can be realized, so that the mounting of the base station 100 is facilitated.

  Note that when the terminal 200 uses Reduced DMRS, more transmission data is transmitted than when the terminal 200 uses Legacy DMRS. At this time, terminal 200 maps transmission data in the same manner as when using Legacy DMRS (that is, avoids resources left blank by Reduced DMRS), and removes transmission data that could not be completely mapped by Reduced DMRS. May be mapped to the resource. FIG. 27 shows an example of the data mapping order. When Reduced DMRS is used, the amount of transmission data is determined according to the DMRS pattern. At this time, as shown in FIG. 27, first, data is mapped from the head of the subframe as in the case of Legacy DMRS. Since data that cannot be mapped occurs due to the reduced DMRS, finally, the data that cannot be mapped is mapped to a blank resource by Reduced DMRS.

  As a result, the resources other than resources to which data is newly mapped by Reduced DMRS (but resources left blank by Reduced DMRS) have the same data mapping order as in Legacy DMRS. Therefore, even when the base station 100 cannot determine whether the terminal 200 has correctly decoded the DCI format 3d / 3dA (that is, whether it is Legacy DMRS or not DMRS), the base station 100 considers a plurality of different data mapping patterns, and There is no need to decode the data in accordance with the data mapping order. Further, even if terminal 200 transmits PUSCH in a Legacy DMRS pattern, base station 100 may be able to correctly decode data in a data mapping order assuming Reduced DMRS. By doing so, the configuration of the receiver in the base station 100 can be simplified, and the processing delay associated with decoding can be reduced.

  The embodiment of the invention has been described.

(Other embodiments)
[1] If the transmission of the ACK / NACK response signal for the downlink data and the transmission of the PUSCH indicated by the UL grant are at the same timing, the ACK / NACK response signal is inserted in place of the data in the PUSCH subframe. Since high determination accuracy (low error rate) is required for the ACK / NACK response signal, it is defined that the ACK / NACK response signal is mapped to an SC-FDMA symbol adjacent to the DMRS before Rel.11. Was. On the other hand, when Reduced DMRS is used, since some DMRSs are replaced with data, the ACK / NACK response signal cannot be mapped to SC-FDMA symbols adjacent to the DMRS, and the channel estimation accuracy for ACK / NACK response signal determination is reduced. There is a possibility that it cannot be secured. FIG. 28 shows an example in which an ACK / NACK response signal is mapped in the PUSCH in the Legacy DMRS (FIG. 28A) and a certain Reduced DMRS pattern (FIG. 28B). For example, in FIG. 28B, it can be seen that the Reduced DMRS pattern (1) shown in FIG. 4B is used, and the ACK / NACK response signal is mapped to a location away from the DMRS.

  Therefore, when ACK / NACK response signals are multiplexed on PUSCH, terminal 200 may always use Legacy DMRS even when Reduced DMRS is instructed. By doing so, the channel estimation accuracy for the determination of the ACK / NACK response signal can be made equal to Rel.11 or earlier.

  Alternatively, the reduced DMRS that can be used when the ACK / NACK response signal is multiplexed on the PUSCH may be limited to only the pattern in which the DMRS is arranged in SC-FDMA adjacent to the ACK / NACK response signal. The pattern in which the DMRS is arranged in SC-FDMA adjacent to the ACK / NACK response signal is, for example, Reduced DMRS pattern (3) shown in FIG. 4D. By doing so, it is possible to suppress deterioration in channel estimation accuracy for the determination of the ACK / NACK response signal.

  Alternatively, when Reduced DMRS is used, the location of the ACK / NACK response signal may be changed. For example, in the case of FIG. 28B, the ACK / NACK response signal may be mapped around the remaining DMRS in the reduced DMRS. By doing so, it is possible to flexibly use the reduced DMRS while securing the channel estimation accuracy for the determination of the ACK / NACK response signal.

  [2] In the above embodiment, the case where the present invention is configured by hardware has been described as an example. However, the present invention can be realized by software in cooperation with hardware.

  Each functional block used in the description of the above embodiment is typically realized as an LSI which is an integrated circuit. These may be individually integrated into one chip, or may be integrated into one chip so as to include some or all of them. Although an LSI is used here, it may be called an IC, a system LSI, a super LSI, or an ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. After manufacturing the LSI, an FPGA (Field Programmable Gate Array) that can be programmed or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Furthermore, if an integrated circuit technology that replaces the LSI appears due to the progress of the semiconductor technology or another derivative technology, the functional blocks may be naturally integrated using the technology. Application of biotechnology, etc. is possible.

  The communication device according to the present disclosure is control information used for allocating a Physical Uplink Shared Channel (PUSCH), the control information being used to determine an arrangement of an uplink DMRS (Demodulation Reference Signal) in a resource element. A transmitting unit that transmits the DMRS (Demodulation Reference Signal), which is arranged in the resource element based on the control information and is multiplexed with the PUSCH and transmitted, from the terminal, And a circuit unit for performing channel estimation based on the received DMRS.

  In the communication device of the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and the plurality of arrangement patterns include at least two arrangements in which the number of resource elements for arranging the DMRS is different. Including patterns.

  In the communication device of the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and the plurality of arrangement patterns include at least two arrangement patterns having different numbers of symbols for arranging the DMRS. Including.

  In the communication device of the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and the plurality of arrangement patterns is the number of symbols for arranging the DMRS per slot or one subframe. Include at least two different arrangement patterns.

  In the communication device of the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and in the plurality of arrangement patterns, a resource for arranging the DMRS is transmitted in LTE-A Release 11. Includes an allocation pattern that is less than the resources where the DMRS of the line is allocated.

  In the communication device according to the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and the plurality of arrangement patterns are notified to the terminal in an upper layer.

  In the communication device of the present disclosure, based on the control information, one of the plurality of allocation patterns is determined, the allocation pattern for allocating the DMRS having a sequence length shorter than the frequency bandwidth to which the PUSCH is allocated. including.

  In the communication device according to the present disclosure, one arrangement of a plurality of arrangement patterns is determined based on the control information, and the plurality of arrangement patterns include hopping or non-hopping.

  In the communication device of the present disclosure, the control information includes information for determining a cyclic shift and an orthogonal code, and the receiving unit is configured to generate the cyclic shift and the orthogonal code based on the determined orthogonal code. Receive DMRS.

  In the communication device of the present disclosure, when ACK / NACK is multiplexed with the PUSCH and transmitted, the receiving unit is configured to receive the ACK / NACK arranged adjacent to the DMRS arranged based on the determined arrangement. Receive NACK.

  The communication method according to the present disclosure is control information used for allocating a Physical Uplink Shared Channel (PUSCH), the control information being used to determine an arrangement of an uplink DMRS (Demodulation Reference Signal) in a resource element. To the terminal, the DMRS (Demodulation Reference Signal) arranged in the resource element based on the control information, multiplexed with the PUSCH and transmitted from the terminal, and received by the DMRS Channel estimation is performed based on the channel estimation.

  The integrated circuit according to an embodiment of the present disclosure is control information used for PUSCH (Physical Uplink Shared Channel) allocation, the control information determining allocation of uplink DMRS (Demodulation Reference Signal) to resource elements. A process of transmitting the DMRS (Demodulation Reference Signal), which is arranged in the resource element based on the control information and multiplexed with the PUSCH and transmitted from the terminal, to the terminal. And a process of performing channel estimation based on the DMRS.

  The present invention can be applied to a mobile communication system.

Reference Signs List 100 base station 200 terminal 11 control signal generation unit 12, 25 transmission unit 13, 21 reception unit 14, 114 channel estimation unit 15 reception signal processing unit 101, 23, 205 control unit 102 control information generation unit 103, 206 coding unit 104 , 207 Modulation unit 105, 212 Mapping unit 106, 213 IFFT unit 107, 214 CP addition unit 108, 215 Wireless transmission unit 109, 201 Wireless reception unit 110, 202 CP removal unit 111, 203 FFT unit 112 Demapping unit 113 CSI measurement Unit 115 Equalization unit 116 IDFT unit 117 Demodulation unit 118 Decoding unit 119 Judgment unit 22, 204 Control signal extraction unit 24, 208 DMRS generation unit 209 SRS generation unit 210 Multiplexing unit 211 DFT unit

Claims (12)

Transmission of control information used for allocating a Physical Uplink Shared Channel (PUSCH), which determines allocation of an uplink DMRS (Demodulation Reference Signal) to a resource element, is transmitted to a terminal. Department and
A receiving unit that is arranged in the resource element based on the control information and receives the DMRS (Demodulation Reference Signal) multiplexed with the PUSCH and transmitted from the terminal;
A circuit unit for performing channel estimation based on the received DMRS,
A communication device comprising: Based on the control information, one arrangement of a plurality of arrangement patterns is determined, the plurality of arrangement patterns include at least two arrangement patterns different in the number of resource elements to arrange the DMRS,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, the plurality of arrangement patterns include at least two arrangement patterns different in the number of symbols to arrange the DMRS,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, and the plurality of arrangement patterns are at least two arrangement patterns in which the number of symbols for arranging the DMRS per slot or one subframe is different. including,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, and in the plurality of arrangement patterns, a resource for arranging the DMRS is arranged with an uplink DMRS in LTE-A Release 11. Including less placement patterns than resources,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, and the plurality of arrangement patterns are notified to the terminal in an upper layer,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, including an arrangement pattern to arrange the DMRS of a sequence length shorter than the frequency bandwidth to which the PUSCH is allocated,
The communication device according to claim 1. Based on the control information, one arrangement of a plurality of arrangement patterns is determined, the plurality of arrangement patterns, hopping or not, including,
The communication device according to claim 1. The control information includes information for determining a cyclic shift and an orthogonal code, the receiving unit receives the DMRS generated based on the determined cyclic shift and the orthogonal code,
The communication device according to claim 1. When ACK / NACK is multiplexed and transmitted with the PUSCH, the receiving unit receives the ACK / NACK arranged adjacent to the DMRS arranged based on the determined arrangement,
The communication device according to claim 1. Transmitting to the terminal control information used for PUSCH (Physical Uplink Shared Channel) allocation, the control information determining the allocation of uplink DMRS (Demodulation Reference Signal) to resource elements;
The DMRS (Demodulation Reference Signal), which is arranged in the resource element based on the control information and multiplexed with the PUSCH and transmitted, is received from the terminal,
Perform channel estimation based on the received DMRS,
Communication method. A process of transmitting control information, which is control information used for PUSCH (Physical Uplink Shared Channel) allocation and determines allocation of an uplink DMRS (Demodulation Reference Signal) to a resource element, to a terminal. When,
A process of receiving, from the terminal, the DMRS (Demodulation Reference Signal) that is arranged in the resource element based on the control information and multiplexed with the PUSCH and transmitted;
A process of performing channel estimation based on the received DMRS,
Control the integrated circuit.

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