JP6785285B2 - Base station, terminal, receiving method and transmitting method - Google Patents

Description

The present disclosure relates to base stations, terminals, receiving methods and transmitting methods.

In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), OFDMA (Orthogonal Frequency Division) is used as a downlink communication method from a base station (sometimes called eNB) to a terminal (sometimes called UE (User Equipment)). Multiple Access) is adopted, and SC-FDMA (Single Carrier-Frequency Division Multiple Access) is adopted as an uplink communication method from a terminal to a base station (see, for example, Non-Patent Documents 1-3).

In LTE, a base station communicates by allocating a resource block (RB: Resource Block) in the system band to a terminal for each time unit called a subframe. FIG. 1 shows an example of a subframe configuration in a physical uplink shared channel (PUSCH). As shown in FIG. 1, one subframe is composed of two time slots. A plurality of SC-FDMA data symbols and a demodulation reference signal (DMRS) are time-multiplexed in each slot. When the base station receives PUSCH, it uses DMRS to estimate the channel. After that, the base station demodulates / decodes the SC-FDMA data symbol using the channel estimation result.

By the way, as a mechanism to support the information society in the future, M2M (Machine-to-Machine) communication, which realizes a service by autonomous communication between devices without the judgment of a user, is expected in recent years. There is a smart grid as a concrete application example of the M2M system. A smart grid is an infrastructure system that efficiently supplies lifelines such as electricity or gas, and autonomously and effectively implements M2M communication between smart meters installed in each home or building and a central server. Adjust the demand balance of resources. Other application examples of M2M communication systems include monitoring systems for goods management or telemedicine, remote management of vending machine inventory or billing, and the like.

In the M2M communication system, attention is paid to the use of a cellular system having a particularly wide communication area. In 3GPP, the study of M2M based on the cellular network in the standardization of LTE and LTE-Advanced is underway under the name of Machine Type Communication (MTC). In particular, "Coverage Enhancement" is available to further expand the communication area in order to handle cases where MTC communication devices such as smart meters are placed in places that cannot be used in existing communication areas such as the basement of buildings. It is being studied (see, for example, Non-Patent Document 4).

In particular, in MTC coverage enhancement, repetition in which the same signal is repeatedly transmitted multiple times is considered to be an important technology for expanding the communication area. Specifically, it is being considered to perform repetition transmission in PUSCH. At the base station on the receiving side of PUSCH, the received signal power can be improved and the communication area can be expanded by synthesizing the signals transmitted by repetition.

Repetition transmission requires a lot of time resources to transmit the same signal, which causes deterioration of frequency utilization efficiency. Therefore, it is desirable to minimize the number of repetitions required to achieve the required coverage enhancement. Therefore, a technique for reducing the number of repetitions required to achieve the required coverage enhancement in PUSCH is being studied. For example, as one of the techniques for reducing the number of repetitions required to achieve the required coverage enhancement, there is "multiple subframe channel estimation and symbol level synthesis" (see, for example, Non-Patent Document 5). ..

In multiple subframe channel estimation and symbol level synthesis, as shown in FIG. 2, the base station has the same number of repetitions or the same as the number of repetitions for a signal transmitted over multiple subframes (N _Rep subframes). In-phase synthesis is performed on a symbol-by-symbol basis over a small number of subframes ( _NSF subframes). After that, the base station performs channel estimation using DMRS after in-phase synthesis, and demodulates / decodes the SC-FDMA data symbol using the obtained channel estimation result.

If the number of subframes (N _SF ), which is the unit in which multiple subframe channel estimation and symbol level synthesis are performed, is less than the number of repetitions (N _Rep ), the base station will perform demodulation / decoding (N _Rep / N _SF). ) Synthesize symbols.

It is clear that the transmission quality of PUSCH can be improved by using multiple subframe channel estimation and symbol level synthesis compared to a simple repetition of channel estimation and demodulation / decoding of SC-FDMA data symbols on a subframe basis. (See, for example, Non-Patent Document 5). For example, multi-subframe channel estimation and symbol-level synthesis of 4 subframes (N _SF = 4) are required to achieve the required Block Error Ratio (BLER) compared to simple repetition. SNR (Signal to Noise Power Ratio) can be improved by 1.4 to 2.6 dB. In addition, multi-subframe channel estimation and symbol-level synthesis of 8 subframes (N _SF = 8) can improve the SNR required to achieve the required BLER by 1.9 to 3.5 dB compared to simple repetition.

Further, in order not to deteriorate the channel estimation accuracy in the PUSCH repetition, as shown in FIG. 3, in PUSCH, the number of DMRS symbols to be inserted is increased with respect to the existing DMRS symbols (Fig. 3, upper figure). (See the figure below in FIG. 3, see, for example, Non-Patent Document 6). Increasing the number of DMRS symbols is effective in improving the channel estimation accuracy because the number of DMRSs that can be used for channel estimation and symbol level synthesis increases.

3GPP TS 36.211 V12.0.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation,” December 2014. 3GPP TS 36.212 V12.0.0, ““ Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding, ”December 2014. 3GPP TS 36.213 V12.0.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures,” December 2014. RP-141660, Ericsson, Nokia Networks, “New WI proposal: Further LTE Physical Layer Enhancements for MTC” R1-150312, Panasonic, “Discussion and performance evaluation on PUSCH coverage enhancement” R1-150289, NEC, “Uplink Reference Signal Enhancement for MTC”

If DMRS is increased, the number of data bits that can be sent in each subframe in PUSCH decreases. Therefore, if MCS (Modulation and Coding Scheme) is fixed, a high coding rate must be used for the data. However, the data transmission quality deteriorates. That is, there is a trade-off relationship between the channel estimation accuracy based on the number of DMRSs and the transmission quality based on the data coding rate.

One aspect of the present disclosure is to provide a base station, a terminal, a receiving method and a transmitting method capable of improving the channel estimation accuracy without deteriorating the transmission quality.

The base station according to one aspect of the present disclosure is for a terminal that repeats an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe over a plurality of subframes. When the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value, a first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, it is larger than the first number. A channel using a control unit for setting a second number of DMRSs, a receiving unit for receiving the uplink signal including the DMRS transmitted from the terminal, and the DMRS included in the received uplink signal. A configuration is adopted that includes a channel estimation unit that performs estimation.

The terminal according to one aspect of the present disclosure applies a repetition over a plurality of subframes to an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe. When the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value for the local terminal, the first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, the first A configuration is adopted in which a control unit for setting a second number of DMRSs larger than the number of 1 and a transmission unit for transmitting the uplink signal including the DMRS are provided.

The receiving method according to one aspect of the present disclosure is for a terminal that repeats an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe over a plurality of subframes. When the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value, a first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, it is larger than the first number. A second number of DMRSs are set, the uplink signal including the DMRS transmitted from the terminal is received, and channel estimation is performed using the DMRS included in the received uplink signal.

The transmission method according to one aspect of the present disclosure is a case where a repetition over a plurality of subframes is applied to an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe. When the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value for the own terminal, the first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, the above A second number of DMRSs larger than the first number is set, and the uplink signal including the DMRS is transmitted.

It should be noted that these comprehensive or specific embodiments may be realized in a system, device, method, integrated circuit, computer program, or recording medium, and the system, device, method, integrated circuit, computer program, and recording medium. It may be realized by any combination of.

According to one aspect of the present disclosure, the channel estimation accuracy can be improved without degrading the transmission quality.

Further advantages and effects in one aspect of the present disclosure will be apparent from the specification and drawings. Such advantages and / or effects are provided by some embodiments and features described in the specification and drawings, respectively, but not all need to be provided in order to obtain one or more identical features. There is no.

Diagram showing an example of PUSCH subframe configuration Diagram showing operation examples of multiple subframe channel estimation and symbol level synthesis Diagram showing an example of DMRS arrangement Diagram showing BLER characteristics when the number of repetitions N _Rep = 8 Diagram showing BLER characteristics when the number of repetitions N _Rep = 128 The figure which shows the BLER characteristic when DMRS is increased Block diagram showing the main part configuration of the base station according to the first embodiment Block diagram showing the main part configuration of the terminal according to the first embodiment Block diagram showing the configuration of the base station according to the first embodiment Block diagram showing the configuration of the terminal according to the first embodiment Diagram showing an example of an existing DMRS layout The figure which shows an example of the DMRS arrangement when the DMRS which concerns on Embodiment 1 is increased. The figure which shows an example of the DMRS arrangement when the DMRS which concerns on Embodiment 1 is increased. The figure which shows an example of the signal arrangement in the subframe of PUSCH Diagram showing an example of DMRS placement in extended CP mode The figure which shows an example of the DMRS arrangement when the DMRS which concerns on variation 1 of Embodiment 1 is increased. The figure which shows an example of the DMRS arrangement when the DMRS which concerns on variation 1 of Embodiment 1 is increased. The figure which shows an example of the DMRS arrangement when the DMRS which concerns on the variation 2 of Embodiment 1 is increased. The figure which shows an example of the DMRS arrangement when the DMRS which concerns on Embodiment 2 is increased. The figure which shows the arrangement example of DMRS and SRS The figure which shows an example of the DMRS arrangement when the DMRS which concerns on the variation of Embodiment 3 is increased. The figure which shows an example of the signal arrangement in the subframe which SRS is transmitted which concerns on the variation of Embodiment 3.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[Points of view of one aspect of the present disclosure]
MTC coverage enhancement is considering defining multiple coverage enhancement levels. For example, it is being considered to define about three coverage enhancement levels of 5 dB, 10 dB, and 15 dB as compared with normal coverage (when coverage enhancement is not applied). In addition, when a terminal with a smaller maximum transmission power than a normal terminal is defined in MTC coverage enhancement, the coverage enhancement level for that terminal is 6 dB, 12 dB, and 18 dB compared to the normal coverage. Is being considered.

In the following, the coverage enhancement level that requires 5 dB or 6 dB coverage enhancement is called the "Small coverage enhancement level", and the coverage enhancement level that requires 10 dB or 12 dB coverage enhancement is called the "Middle coverage enhancement level", which is 15 dB or 18 dB. The coverage enhancement level that requires coverage enhancement is sometimes called the "Large coverage enhancement level". The level required for each enhancement level is not limited to 5 dB, 6 dB, 10 dB, 12 dB, 15 dB, and 18 dB.

In general, more repetition is needed to achieve a large coverage enhancement level. For example, the number of repetitions required to achieve coverage enhancement of 15 dB and 18 dB is around 64 and 128 subframes.

However, when performing 64 or 128 subframe repetition, due to the influence of frequency offset, even if multiple subframe channel estimation and symbol level synthesis are performed using the same number of subframes as the number of repetitions at the base station, the received signal The phases are not aligned and the characteristics deteriorate. Therefore, it can be said that the number of subframes ( _NSF ) that can be used for multiple subframe channel estimation and symbol level synthesis is limited to about 4 or 8 subframes.

Therefore, even when a very large number of repetitions such as 64 or 128 subframes are required, the base station will perform multiple subframe channel estimation and symbol level synthesis of about 4 or 8 subframes. However, when a very large number of repetitions (64 or 128 times) is required, even if multiple subframe channel estimation and symbol level synthesis with as few subframes as 4 or 8 subframes are performed, DMRS after in-phase synthesis is performed. Since the received signal power to interference power ratio (SNR) of is very small, the channel estimation accuracy is deteriorated.

4A and 4B show the BLER characteristics of PUSCH repetition using multiple subframe channel estimation and symbol level synthesis. FIG. 4A shows the BLER characteristic in the case of 8 times repetition, and FIG. 4B shows the BLER characteristic in the case of 128 times repetition. In addition, FIGS. 4A and 4B also show BLER characteristics in the case of ideal channel estimation for comparison.

From FIGS. 4A and 4B, in the case of 8 repetitions in which the number of repetitions is relatively small, the amount of deterioration from the ideal channel estimation can be suppressed to about 2 dB by performing multiple subframe channel estimation and symbol level synthesis. .. On the other hand, in the case of 128 repetitions in which the number of repetitions is relatively large, it can be seen that the deterioration from the ideal channel estimation becomes as large as 5 dB in the channel estimation and symbol level synthesis of 4 or 8 subframes.

As described above, when multiple subframe channel estimation and symbol level synthesis are performed when the number of repetitions is relatively large, the characteristics are deteriorated as compared with the case of ideal channel estimation.

Next, in PUSCH, a case where the number of DMRS symbols to be inserted is increased with respect to the existing DMRS symbols (Fig. 3, upper figure) will be examined.

FIG. 5 shows the case where one DMRS is arranged in one slot for each of the repetition times N _Rep = 4,8,16,32,64,128 as shown in the upper figure of FIG. 3 (1 x DMRS. DMRS is increased). The BLER characteristics when not allowed) and the BLER characteristics when two DMRSs are arranged in one slot as shown in the lower figure of FIG. 3 (2x DMRS. When DMRS is doubled) are shown. Further, in FIG. 5, as a comparison, when the number of repetitions is N _Rep = 1 (no repetition) and one DMRS is arranged in one slot as shown in the upper figure of FIG. 3 (corresponding to normal coverage). ) BLER characteristics. In addition, FIG. 5 shows the BLER characteristics when channel estimation and symbol level synthesis of 4 subframes (N _SF = 4) are used.

As shown in FIG. 5, at the Small coverage enhancement level that requires 5 dB or 6 dB coverage enhancement, about 4 repetitions (N _Rep = 4) are required. Also, at the Middle coverage enhancement level, which requires 10 dB or 12 dB coverage enhancement, about 16 repetitions (N _Rep = 16) are required. It can also be seen that at the Large coverage enhancement level, which requires 15 dB or 18 dB coverage enhancement, about 128 repetitions (N _Rep = 128) are required.

On the other hand, as shown in FIG. 5, when DMRS is doubled, the repetition of 4, 8 or 16 times (N _Rep = 4,8,16) required for the Small or Middle coverage enhancement level , It can be seen that the BLER characteristics are equivalent or deteriorated as compared with the case where DMRS is not increased. In contrast, in the 64 or 128 repetitions required for the Large coverage enhancement level (N _Rep = 64,128), when DMRS was doubled, compared to when DMRS was not increased, It can be seen that the BLER characteristics are improved.

As described above, it can be seen that the increase in DMRS is effective only when the number of repetitions is relatively large (N _Rep = 64 or more in FIG. 5).

As described above, at the Small or Middle coverage enhancement level where the number of repetitions is relatively small, the characteristics of PUSCH can be improved by multiple subframe channel estimation and symbol level synthesis as shown in FIG. 4A, whereas in FIG. As shown, the characteristics of PUSCH cannot be improved by increasing DMRS.

On the other hand, at the Large coverage enhancement level where the number of repetitions is relatively large, the improvement of PUSCH characteristics by multiple subframe channel estimation and symbol level synthesis is not sufficient as shown in FIG. 4B, whereas the characteristics of PUSCH are not sufficiently improved as shown in FIG. Improvement of PUSCH characteristics can be obtained by increasing DMRS.

Therefore, in one aspect of the present disclosure, among the terminals for which the MTC coverage enhancement mode is set, DMRS (predetermined number of DMRS) for a normal terminal is set for a terminal having a large coverage enhancement level. To do. On the other hand, for terminals with Middle coverage enhancement level and Small coverage enhancement level, set DMRS similar to DMRS for normal terminals (that is, DMRS is not increased).

As a result, when performing multiple subframe channel estimation and symbol level synthesis, the transmission characteristics of PUSCH can be improved at the Small or Middle coverage enhancement level without increasing DMRS. Also, at the Large coverage enhancement level, the transmission characteristics of PUSCH can be improved by increasing DMRS.

Also, the increase in DMRS is applied only at the Large coverage enhancement level, which is expected to improve transmission quality, not at the Small or Middle coverage enhancement level, so the number of data bits that can be sent by PUSCH at the Small or Middle coverage enhancement level. Does not have to be reduced.

[Outline of communication system]
The communication system according to each embodiment of the present disclosure is, for example, a system corresponding to LTE-Advanced, and includes a base station 100 and a terminal 200.

It is assumed that the terminal 200 in the MTC coverage enhancement mode exists in the cell of the base station 100. For example, when the MTC coverage enhancement mode is applied, the terminal 200 applies repetition transmission over a plurality of subframes when transmitting PUSCH. That is, the terminal 200 repeatedly transmits the same signal in consecutive subframes for a predetermined number of repetitions (sometimes referred to as repetition level or repetition factor).

For example, when N _Rep repetitions are performed (that is, the number of repetitions: N _Reps ), the terminal 200 continuously transmits a signal of one subframe over the N _Rep subframes.

On the other hand, the base station 100 performs "multiple subframe channel estimation and symbol level synthesis" on the signal transmitted from the terminal 200 for repetition (see, for example, FIG. 2). Specifically, the base station 100 performs in-phase synthesis on a symbol-by-symbol basis over subframes ( _NSF subframes) that are the same as or less than the repetition count N _Rep . After that, the base station 100 performs channel estimation using DMRS after in-phase synthesis, and demodulates / decodes the SC-FDMA data symbol using the obtained channel estimation result.

FIG. 6 is a block diagram showing a configuration of a main part of the base station 100 according to the embodiment of the present disclosure. In the base station 100 shown in FIG. 6, the control unit 101 is a terminal that repeats an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe over a plurality of subframes. For 200, if the coverage enhancement level corresponding to the number of multiple subframes is less than the predetermined value, the first number of DMRS is set, and if the coverage enhancement level is greater than or equal to the predetermined value, it is larger than the first number. Set a second number of DMRS. The receiving unit 110 receives the uplink signal including the DMRS transmitted from the terminal 200. The channel estimation unit 115 performs channel estimation using the DMRS included in the received uplink signal.

Further, FIG. 7 is a block diagram showing a main configuration of the terminal 200 according to each embodiment of the present disclosure. In the terminal 200 shown in FIG. 7, the control unit 206 applies repetition over a plurality of subframes to an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe. In this case, if the coverage enhancement level corresponding to the number of multiple subframes is less than the predetermined value for the local terminal, the first number of DMRS is set, and if the coverage enhancement level is equal to or more than the predetermined value, the first Set a second number of DMRSs greater than the number of. The transmission unit 216 transmits an uplink signal including DMRS.

(Embodiment 1)
[Base station configuration]
FIG. 8 is a block diagram showing the configuration of the base station 100 according to the first embodiment of the present disclosure. In FIG. 8, the base station 100 includes a control unit 101, a control signal generation unit 102, an encoding unit 103, a modulation unit 104, a mapping unit 105, an IFFT (Inverse Fast Fourier Transform) unit 106, and a CP ( Cyclic Prefix) Addition section 107, transmitter section 108, antenna 109, receiver section 110, CP removal section 111, FFT (Fast Fourier Transform) section 112, synthesis section 113, demapping section 114, and channel. It has an estimation unit 115, an equalization unit 116, a demodulation unit 117, a decoding unit 118, and a determination unit 119.

The control unit 101 determines the allocation of PUSCH to the resource allocation target terminal 200. For example, the control unit 101 determines the frequency allocation resource and the modulation / coding method for the terminal 200, and outputs information regarding the determined parameters to the control signal generation unit 102.

Further, the control unit 101 determines the coding level for the control signal, and outputs the determined coding level to the coding unit 103. Further, the control unit 101 determines a radio resource (downlink resource) for mapping the control signal, and outputs information regarding the determined radio resource to the mapping unit 105.

Further, the control unit 101 determines the coverage enhancement level of the terminal 200, and outputs information on the determined coverage enhancement level or the number of repetitions required for PUSCH transmission at the determined coverage enhancement level to the control signal generation unit 102. To do. Further, the control unit 101 generates information on the number of DMRSs or DMRS arrangement used by the terminal 200 for PUSCH repetition based on the information on the coverage enhancement level or the number of repetitions required for PUSCH transmission, and demaps the generated information. Output to unit 114.

The control signal generation unit 102 generates a control signal for the terminal 200. The control signal includes an uplink DCI (Downlink Control Indicator) for instructing information regarding PUSCH allocation received from the control unit 101. The uplink DCI is composed of a plurality of bits and includes information indicating a frequency allocation resource, a modulation / coding method, and the like.

In addition, when the information on the coverage enhancement level or the number of repetitions required for PUSCH transmission is transmitted on the downlink control channel for MTC, this information is also included in the DCI for uplink. Information on the coverage enhancement level or the number of repetitions required for PUSCH transmission may be notified to the control unit 206 of the terminal 200 by signaling in the upper layer.

The control signal generation unit 102 generates a control information bit string (control signal) using the information input from the control unit 101, and outputs the generated control signal to the coding unit 103. Since the control signal may be transmitted to a plurality of terminals 200, the control signal generation unit 102 generates a bit string including the terminal ID of each terminal 200 in the control signal for each terminal 200. For example, a CRC (Cyclic Redundancy Check) bit masked by the terminal ID of the destination terminal is added to the control signal.

The coding unit 103 encodes the control signal (encoded bit string) received from the control signal generation unit 102 according to the coding level instructed by the control unit 101, and outputs the coded control signal to the modulation unit 104.

The modulation unit 104 modulates the control signal received from the coding unit 103, and outputs the modulated control signal (symbol string) to the mapping unit 105.

The mapping unit 105 maps the control signal received from the modulation unit 104 to the radio resource instructed by the control unit 101. The control channel to which the control signal is mapped may be a PDCCH for MTC or an EPDCCH (Enhanced PDCCH). The mapping unit 105 outputs a downlink subframe signal including the PDCCH or EPDCCH for MTC to which the control signal is mapped to the IFFT unit 106.

The IFFT unit 106 converts the frequency domain signal into a time domain signal by performing IFFT processing on the signal received from the mapping unit 105. The IFFT unit 106 outputs a time domain signal to the CP addition unit 107.

The CP addition unit 107 adds a CP to the signal received from the IFFT unit 106, and outputs the CP-added signal (OFDM signal) to the transmission unit 108.

The transmission unit 108 performs RF (Radio Frequency) processing such as D / A (Digital-to-Analog) conversion and up-conversion on the OFDM signal received from the CP addition unit 107, and wirelessly transmits to the terminal 200 via the antenna 109. Send a signal.

The receiving unit 110 obtains the uplink signal (PUSCH) received from the terminal 200 via the antenna 109 by performing RF processing such as down-conversion or A / D (Analog-to-Digital) conversion. The received signal is output to the CP removal unit 111. The uplink signal (PUSCH) transmitted from the terminal 200 includes a repetition-processed signal over a plurality of subframes.

The CP removing unit 111 removes the CP added to the received signal received from the receiving unit 110, and outputs the signal after removing the CP to the FFT unit 112.

The FFT unit 112 performs FFT processing on the signal received from the CP removal unit 111, decomposes it into a signal sequence in the frequency domain, extracts a signal corresponding to the PUSCH subframe, and combines the extracted signal. Output to 113.

The synthesis unit 113 uses symbol-level synthesis to synthesize a data signal and a signal corresponding to DMRS in phase with the PUSCH over a plurality of subframes transmitted by repetition. The synthesis unit 113 outputs the combined signal to the demapping unit 114.

The demapping unit 114 is a sub of the PUSCH assigned to the terminal 200 from the signal received from the synthesis unit 113 by using the information regarding the number of DMRSs and the DMRS arrangement used by the terminal 200 for the PUSCH repetition input from the control unit 101. Extract the frame part. Further, the demapping unit 114 decomposes the extracted PUSCH subframe portion of the terminal 200 into DMRS and data symbols (SC-FDMA data symbols), outputs the DMRS to the channel estimation unit 115, and outputs the data symbols, etc. Output to the conversion unit 116.

The channel estimation unit 115 performs channel estimation using the DMRS input from the demapping unit 114. The channel estimation unit 115 outputs the obtained channel estimation value to the equalization unit 116.

The equalization unit 116 equalizes the data symbol input from the demapping unit 114 by using the channel estimation value input from the channel estimation unit 115. The equalization unit 116 outputs the equalized data symbol to the demodulation unit 117.

The demodulation unit 117 applies IDFT (Inverse Descrete Fourier Transform) processing to the SC-FDMA data symbol in the frequency domain input from the equalization unit 116, converts it into a time domain signal, and then demodulates the data. Specifically, the demodulation unit 117 converts the symbol sequence into a bit sequence based on the modulation method instructed to the terminal 200, and outputs the obtained bit sequence to the decoding unit 118.

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

The determination unit 119 detects an error in the bit sequence input from the decoding unit 118. Error detection is performed using CRC bits added to the bit sequence. If the determination result of the CRC bit is correct, the determination unit 119 extracts the received data and outputs ACK. On the other hand, the determination unit 119 outputs NACK when the determination result of the CRC bit has an error. The ACK and NACK output by the determination unit 119 are used for the retransmission control process in a processing unit (not shown).

[Terminal configuration]
FIG. 9 is a block diagram showing the configuration of the terminal 200 according to the first embodiment of the present disclosure. In FIG. 9, the terminal 200 includes an antenna 201, a receiving unit 202, a CP removing unit 203, an FFT unit 204, an extraction unit 205, a control unit 206, a DMRS generation unit 207, and a coding unit 208. It has a modulation unit 209, a multiplexing unit 210, a DFT unit 211, a diffusion unit 212, a mapping unit 213, an IFFT unit 214, a CP addition unit 215, and a transmission unit 216.

The receiving unit 202 performs RF processing such as down-conversion or AD conversion on the radio signal (PDCCH or EPDCCH for MTC) received from the base station 100 via the antenna 201, and outputs the baseband OFDM signal. obtain. The receiving unit 202 outputs the OFDM signal to the CP removing unit 203.

The CP removing unit 203 removes the CP added to the OFDM signal received from the receiving unit 202, and outputs the signal after removing the CP to the FFT unit 204.

The FFT unit 204 converts the time domain signal into a frequency domain signal by performing FFT processing on the signal received from the CP removal unit 203. The FFT unit 204 outputs a frequency domain signal to the extraction unit 205.

The extraction unit 205 blindly decodes the frequency domain signal (PDCCH or EPDCCH for MTC) received from the FFT unit 204, and attempts to decode the control signal addressed to its own unit. A CRC masked by the terminal ID of the terminal is added to the control signal addressed to the terminal 200. Therefore, if the CRC determination is OK as a result of blind decoding, the extraction unit 205 extracts the control information and outputs the control information to the control unit 206.

The control unit 206 controls the PUSCH transmission based on the control signal input from the extraction unit 205. Specifically, the control unit 206 instructs the mapping unit 213 to allocate resources at the time of PUSCH transmission based on the resource allocation information of PUSCH included in the control signal. Further, the control unit 206 instructs the coding unit 208 and the modulation unit 209, respectively, of the coding method and the modulation method at the time of PUSCH transmission based on the information of the coding / modulation method included in the control signal.

Further, when the control signal includes information on the coverage enhancement level or information on the number of repetitions required for PUSCH transmission, the control unit 206 sets the number of repetitions during PUSCH repetition transmission and DMRS based on the information. Whether or not the number is increased is determined, and the determined number of repetitions and information indicating whether or not the number of DMRSs are increased are instructed to the repetition unit 212 and the DMRS generation unit 207, respectively.

Further, when the base station 100 notifies the information about the coverage enhancement level or the information about the number of repetitions required for PUSCH transmission from the base station 100 in the upper layer, the control unit 206 sets the repetition at the time of PUSCH repetition transmission based on the notified information. It is determined whether or not the number of rotations and the number of DMRSs are increased, and the determined information is instructed to the repetition unit 212 and the DMRS generation unit 207, respectively. Further, the control unit 206 may instruct the DMRS generation unit 207 of information regarding the increase number of DMRS or the position of the DMRS notified from the base station 100 in the upper layer.

The DMRS generation unit 207 generates DMRS according to the presence / absence of increase in the number of DMRSs instructed by the control unit 206, the number of DMRSs to be increased, the position of DMRS, and the DMRS pattern, and outputs the generated DMRS to the multiplexing unit 210.

The coding unit 208 adds a CRC bit masked by the terminal ID of the terminal 200 to the input transmission data (uplink data), performs error correction coding, and modulates the coded bit string. Output to 209.

The modulation unit 209 modulates the bit string received from the coding unit 208 and outputs the modulated signal (data symbol sequence) to the multiplexing unit 210.

The multiplexing unit 210 time-multiplexes the data symbol sequence input from the modulation unit 209 and the DMRS input from the DMRS generation unit 207, and outputs the signal after multiplexing to the DFT unit 211.

The DFT unit 211 applies DFT to the signal input from the multiplexing unit 210 to generate a frequency domain signal, and outputs the generated frequency domain signal to the repetition unit 212.

When the own terminal is in the MTC coverage enhancement mode, the repetition unit 212 repeats the signal input from the DFT unit 211 over a plurality of subframes based on the number of repetitions instructed by the control unit 206. Generate a repetition signal. The repetition unit 212 outputs the repetition signal to the mapping unit 213.

The mapping unit 213 maps the signal received from the repetition unit 212 to the time / frequency resource of the PUSCH instructed by the control unit 206. The mapping unit 213 outputs the PUSCH signal to which the signal is mapped to the IFFT unit 214.

The IFFT unit 214 generates a time domain signal by performing IFFT processing on the PUSCH signal in the frequency domain input from the mapping unit 213. The IFFT unit 214 outputs the generated signal to the CP addition unit 215.

The CP addition unit 215 adds a CP to the time domain signal received from the IFFT unit 214, and outputs the signal after the CP addition to the transmission unit 216.

The transmission unit 216 performs RF processing such as D / A conversion and up-conversion on the signal received from the CP addition unit 215, and transmits a radio signal to the base station 100 via the antenna 201.

[Operation of base station 100 and terminal 200]
The operations of the base station 100 and the terminal 200 having the above configuration will be described in detail.

The base station 100 notifies the terminal 200 of the coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) prior to the transmission and reception of PUSCH.

For example, the Large coverage enhancement level (15dB, 18dB) is associated with the repetition count N _Rep = 128, the Middle coverage enhancement level (10dB, 12dB) is associated with the repetition count N _Rep = 16, and Small coverage is associated. The enhancement level (5 dB, 6 dB) may be associated with the number of repetitions N _Rep = 4.

The coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) may be notified from the base station 100 to the terminal 200 via the upper layer (RRC signaling), and is downlinked for MTC. It may be notified using a link control channel. Further, since the number of repetitions can be obtained from the coding rate set in the terminal 200, the number of repetitions is explicitly notified when the base station 100 notifies the terminal 200 of the MCS. It may be notified to Implicit instead.

[How to decide to add DMRS]
The base station 100 (control unit 101) is the number of DMRSs used by the terminal 200 for PUSCH repetition with respect to the terminal 200 in which the coverage enhancement mode is set and the middle coverage enhancement level or the small coverage enhancement level is set. Does not increase. Further, in the terminal 200 (control unit 206), the coverage enhancement level or the number of repetitions (N _Rep ) notified from the base station 100 is Middle, the Small coverage enhancement level or the number of repetitions corresponding thereto (for example, 16 times, 8 times), do not increase the number of DMRSs placed in PUSCH.

That is, when the coverage enhancement mode (repetition transmission) is applied to the terminal 200, the base station 100 and the terminal 200 become normal terminals when the coverage enhancement level is less than a predetermined value (for example, 15 dB or 18 dB). Set the DMRS to be set (predetermined number of DMRS).

In this case, for example, as shown in FIG. 10A, DMRS is arranged in one symbol (third and tenth SC-FDMA symbols) of each slot in one subframe.

On the other hand, the base station 100 (control unit 101) increases the number of DMRSs used by the terminal 200 for PUSCH repetition with respect to the terminal 200 in which the coverage enhancement mode is set and the large coverage enhancement level is set. .. Further, when the coverage enhancement level or the number of repetitions (N _Rep ) notified from the base station 100 is the Large coverage enhancement level or the corresponding number of repetitions (for example, 128 times), the terminal 200 (control unit 206) Increase the number of DMRSs placed in PUSCH.

That is, when the coverage enhancement mode (repetition transmission) is applied to the terminal 200, the base station 100 and the terminal 200 become normal terminals when the coverage enhancement level is equal to or higher than a predetermined value (for example, 15 dB or 18 dB). Set a predetermined number of DMRSs added to the set DMRSs (predetermined number of DMRSs).

In the present embodiment, the DMRS to be added is arranged in symbol units within one subframe.

For example, in FIG. 10B or FIG. 10C, in addition to the existing DMRS arranged in one symbol (third and tenth SC-FDMA symbols) of each slot in one subframe, the first and eighth SCs -DMRS is added to the FDMA symbol or the 5th and 12th SC-FDMA symbols. That is, in FIGS. 10B and 10C, twice as many DMRSs are arranged as in FIG. 10A.

When increasing the number of DMRSs, DMRS may be increased by only one symbol (that is, only DMRS in one of the slots) in one subframe (that is, increased by 1.5 times). For example, in addition to the 3rd and 10th SC-FDMA symbols, the DMRS symbol is placed in any one of the 1st, 5th, 8th, and 12th SC-FDMA symbols shown in FIG. 10B or FIG. 10C. May be done.

The particle size of the DMRS increase due to the addition of DMRS on a symbol-by-symbol basis is 7% (≈1/14). That is, if DMRS is increased by one symbol in one subframe, the overhead due to DMRS increases by 7%. Therefore, if DMRS is doubled (ie, 2 symbols) as in FIGS. 10B and 10C, the DMRS overhead is increased by 14%.

By adding DMRS in symbol units as in the present embodiment, there is an advantage that PAPR (Peak to Average Power Ratio) can be kept low.

Further, as the DMRS series to be added, a series similar to the existing DMRS series may be used. By doing so, in the base station 100, in addition to the channel estimation and the in-phase synthesis over a plurality of subframes, the added DMRS can also be in-phase synthesized, so that the channel estimation accuracy can be improved.

Further, in the present embodiment, DMRS is added only to the terminal 200 in which the Large coverage enhancement level is set, and DMRS is added to the terminal 200 in which the other Middle and Small coverage enhancement levels are set. Not added.

By doing so, in the terminal 200 in which the Large coverage enhancement level is set, the channel estimation accuracy can be improved and the transmission quality of PUSCH can be improved by increasing the DMRS.

Further, in the terminal 200 in which the Middle and Small coverage enhancement levels are set, DMRS is not added, so that the number of data bits of PUSCH data does not decrease. In other words, there is no deterioration in data transmission quality due to the increase in DMRS. Further, as described above, in the terminal 200 in which the Middle and Small coverage enhancement levels are set, the transmission quality of PUSCH can be improved by the estimation of multiple subframe channels and the symbol level synthesis without increasing the number of DMRSs. Yes (see Figure 4A).

As described above, according to the present embodiment, it is possible to improve the channel estimation accuracy in the base station 100 without deteriorating the transmission quality in PUSCH.

[How to place the added DMRS]
Here, the reason why DMRS is additionally arranged in the 1st, 5th, 8th, or 12th SC-FDMA symbols when the number of DMRSs is increased as shown in FIG. 10B or FIG. 10C will be described.

When uplink control information is multiplexed in PUSCH, as shown in FIG. 11, the response signal (ACK / NACK) for the downlink data signal is the SC-FDMA symbol (3rd and 10th SC-) in which DMRS is placed. It is multiplexed on the SC-FDMA symbol (that is, the 2nd, 4th, 9th, and 11th SC-FDMA symbols) adjacent to the FDMA symbol). In addition, the number of rank indicators (RI) of MIMO (Multiple-Input Multiple Output) of downlink data is the SC-FDMA symbol (that is, the first and first) adjacent to the SC-FDMA symbol in which ACK / NACK is placed. It is multiplexed on the 5th, 8th and 12th SC-FDMA symbols).

In MTC coverage enhancement, it is assumed that the operation is performed in an environment where the received power of the desired signal transmitted from the terminal 200 to the base station 100 and / or the base station 100 to the terminal 200 is very small. Therefore, the MTC coverage enhancement mode is not intended to increase the communication capacity by MIMO, and it is assumed that MIMO multiplexing is not used. That is, since the number of ranks RI of MIMO multiplex is always 1, the terminal 200 does not need to feed back the case of RI> 1 to the base station 100.

Therefore, in the present embodiment, the added DMRS (additional DMRS. Additional DMRS) may be arranged in the symbol in which the RI is arranged. For example, as shown in FIG. 10B or FIG. 10C, 12 pieces constituting each SC-FDMA symbol by arranging DMRS added in the 1st, 5th, 8th, or 12th SC-FDMA symbols. Of the resource elements (REs) of, 6 REs replace RIs that are not used in MTC coverage enhancement mode with DMRS. Therefore, the remaining 6 REs are the only resources for replacing PUSCH data with DMRS.

In this way, the added DMRS is placed on the 1st, 5th, 8th, and 12th SC-FDMA symbols used for RI transmission, so that the DMRS is added to the PUSCH. It is possible to suppress a decrease in the number of data bits of data. In other words, the impact on PUSCH data can be minimized.

Further, as shown in FIG. 10B or FIG. 10C, ACK / NACK is arranged by arranging DMRS added to the first, fifth, eighth and twelfth SC-FDMA symbols. Since DMRS is placed on the symbols on both sides of the FDMA symbol, it is possible to maintain high quality of ACK / NACK transmission quality.

[How to set DMRS Increase and DMRS Mapping]
Next, a method of setting DMRS increase and DMRS arrangement will be described. The following three options can be considered for setting the DMRS increase and DMRS placement.

(Option 1: RRC signaling)
In option 1, the base station 100 notifies the terminal 200 of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) in advance by RRC signaling.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

Further, when the candidate for the number of symbols to be added as DMRS can be set, the terminal 200 may determine the number of symbols to be used for DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. .. In addition, the base station 100 may also notify the terminal 200 of the position of the SC-FDMA symbol when DMRS is added (increase) by using RRC signaling.

(Option 2: L1 signaling)
In option 2, the base station 100 notifies the terminal 200 in advance of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) using the downlink control channel for MTC. To do.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

Further, when the candidate for the number of symbols to be added as DMRS can be set, the terminal 200 may determine the number of symbols to be used for DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. .. Further, the base station 100 may also notify the terminal 200 of the position of the SC-FDMA symbol to which DMRS is added by using the downlink control channel for MTC, or may notify the terminal 200 in advance by RRC signaling. Good.

(Option 3: Implicit signaling)
In option 3, the base station 100 does not explicitly notify the terminal 200 of the number of repetitions (N _Rep ). The base station 100 notifies the terminal 200 of only the MCS by using the downlink control channel for MTC.

When the number of repetitions can be expressed using the coding rate in the repetition transmission, the terminal 200 can obtain the coding rate and the number of repetitions in the repetition transmission from the MCS notified from the base station 100. In this case, the terminal 200 determines whether or not to increase the DMRS based on the obtained number of repetitions. Specifically, the terminal 200 increases the DMRS when the number of repetitions (for example, 128 times) corresponds to the Large coverage enhancement level.

Further, when the candidate for the number of symbols to be added as DMRS can be set, the terminal 200 may determine the number of symbols to be used for DMRS based on the obtained number of repetitions. Further, the base station 100 may also notify the terminal 200 in advance of the position of the SC-FDMA symbol to which DMRS is added by using RRC signaling.

[Variation 1 of Embodiment 1]
In MTC coverage enhancement, since it is assumed that the terminal 200 is very far from the base station 100, it is conceivable that the terminal 200 is operated in the extended CP mode. FIG. 12A shows an example of arrangement of an existing DMRS when operated in the extended CP mode. On the other hand, FIGS. 12B and 12C show an example of arrangement of DMRS when the number of DMRS shown in FIG. 12A is doubled in the same manner as in the above embodiment. As a result, even when the terminal 200 is operated in the extended CP mode, the transmission quality of PUSCH can be improved by increasing the DMRS in the terminal 200 in which the Large coverage enhancement level is set.

[Variation 2 of Embodiment 1]
As a variation when increasing DMRS in symbol units, as shown in FIG. 13, DMRS is arranged according to the subframe configuration (DMRS arrangement pattern) defined by the existing PUCCH (Physical Uplink Control Channel) format 2. May be good. This has the advantage that even when the number of DMRSs is increased, the existing standard can be used without specifying a new subframe format.

(Embodiment 2)
In the first embodiment, a case where the added DMRS is arranged in symbol units has been described. On the other hand, in the present embodiment, the case where the added DMRS is arranged in the resource element (RE) unit will be described.

Since the base station and the terminal according to the present embodiment have the same basic configuration as the base station 100 and the terminal 200 according to the first embodiment, FIGS. 8 and 9 will be referred to for description.

The base station 100 notifies the terminal 200 of the coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) prior to the transmission and reception of PUSCH.

For example, the Large coverage enhancement level (15dB, 18dB) is associated with the repetition count N _Rep = 128, the Middle coverage enhancement level (10dB, 12dB) is associated with the repetition count N _Rep = 16, and Small coverage is associated. The enhancement level (5 dB, 6 dB) may be associated with the number of repetitions N _Rep = 4.

In the base station 100 and the terminal 200, as in the first embodiment, when the coverage enhancement mode (repetition transmission) is applied to the terminal 200, the coverage enhancement level is less than a predetermined value (for example, 15 dB or 18 dB). , Set the DMRS (predetermined number of DMRS) set in the normal terminal. That is, in the base station 100 (control unit 101) and the terminal 200 (control unit 206), the coverage enhancement level or the number of repetitions (N _Rep ) set in the terminal 200 is Middle, the Small coverage enhancement level, or a repeat corresponding thereto. If the number of ticks (for example, 16 or 8), do not increase the number of DMRSs placed in PUSCH.

In this case, as in the first embodiment, for example, as shown in FIG. 10A, DMRS is arranged in one symbol (third and tenth SC-FDMA symbols) of each slot in one subframe.

Further, in the base station 100 and the terminal 200, when the coverage enhancement mode (repetition transmission) is applied to the terminal 200, the coverage enhancement level is equal to or higher than a predetermined value (for example, 15 dB or 18 dB) as in the first embodiment. In the case of, a predetermined number of DMRSs are added to the DMRSs (predetermined number of DMRSs) set in a normal terminal. That is, in the base station 100 (control unit 101) and the terminal 200 (control unit 206), the coverage enhancement level or the number of repetitions (N _Rep ) set in the terminal 200 is the Large coverage enhancement level or the number of repetitions corresponding to it ( For example, 128 times), increase the number of DMRSs placed in PUSCH.

In the present embodiment, the DMRS to be added is arranged in RE units within one subframe.

For example, in FIG. 14, in addition to the existing DMRS arranged in one symbol (third, tenth SC-FDMA symbol) of each slot in one subframe, the first, fifth, eighth and first DMRS is added to 6 REs in the 12th SC-FDMA symbol. That is, in FIG. 14, the DMRSs to be added are arranged in 24 REs (the same number as the number of REs for 2 symbols).

When increasing the number of DMRS, the number of DMRS is not limited to the arrangement example shown in FIG. 14, and DMRS may be increased in 1RE units in one subframe.

The particle size of the increase in DMRS due to the addition of DMRS in RE units is 0.6% (≈1 / (14 * 12)). That is, if DMRS is increased by 1RE in one subframe, the overhead due to DMRS increases by 0.6%.

By adding DMRS in RE units as in the present embodiment, the ratio of the data in the subframe to DMRS can be compared with the case where DMRS is added in symbol units as in Embodiment 1. It is possible to make more detailed settings.

Further, as a series of DMRS to be added, a QPSK symbol pattern known between the base station 100 and the terminal 200 may be used. By doing so, the base station 100 can perform in-phase synthesis of the added DMRS in addition to the channel estimation and in-phase synthesis over a plurality of subframes, so that the channel estimation accuracy can be improved.

Further, as in the first embodiment, in the present embodiment, DMRS is added only to the terminal 200 for which the Large coverage enhancement level is set, and the terminal 200 for which the other Middle and Small coverage enhancement levels are set. DMRS is not added for. By doing so, in the terminal 200 in which the Large coverage enhancement level is set, the channel estimation accuracy can be improved and the transmission quality of PUSCH can be improved by increasing the DMRS. Further, in the terminal 200 in which the Middle and Small coverage enhancement levels are set, DMRS is not added, so that the number of data bits of PUSCH data does not decrease. Further, as described above, in the terminal 200 in which the Middle and Small coverage enhancement levels are set, the transmission quality of PUSCH can be improved by the estimation of multiple subframe channels and the symbol level synthesis without increasing the number of DMRSs. Yes (see Figure 4A).

As described above, according to the first embodiment, it is possible to improve the channel estimation accuracy in the base station 100 without deteriorating the transmission quality in the PUSCH, as in the first embodiment.

Further, as described in the first embodiment, it is assumed that MIMO multiplexing is not used in MTC coverage enhancement, and the rank number RI of MIMO multiplexing is always 1, so that the terminal 200 has a case of RI> 1. There is no need to feed back to the base station 100.

Therefore, in the present embodiment, the added DMRS may be placed in the RE where the RI is placed. For example, as shown in FIG. 14, the added DMRS is 6RE each of the 1st, 5th, 8th and 12th SC-FDMA symbols used for RI transmission (see, for example, FIG. 11). By arranging it in, the influence on PUSCH data due to the addition of DMRS is smaller than that in the first embodiment. Specifically, in FIG. 14, the number of REs (24RE) in which the added DMRS is arranged is the same as in the first embodiment (FIGS. 10B and C), but the PUSCH data is replaced by the added DMRS. There are no resources available. That is, in FIG. 14, DMRS can be added without reducing the number of data bits of PUSCH data.

Further, as in the first embodiment, as shown in FIG. 14, ACK / NACK is arranged by arranging DMRS added to the first, fifth, eighth, and twelfth SC-FDMA symbols. Since DMRS is placed on the symbols on both sides of the SC-FDMA symbol, it is possible to maintain high quality of ACK / NACK transmission.

[How to add DMRS and set DMRS layout]
Next, a method of setting DMRS increase and DMRS arrangement will be described. As in the first embodiment, the following three options can be considered for the method of setting the DMRS increase and the DMRS arrangement.

(Option 1: RRC signaling)
In option 1, the base station 100 notifies the terminal 200 of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) in advance by RRC signaling.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

If the candidate for the number of REs to be added as DMRS can be set, the terminal 200 may determine the number of REs to be used for DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. .. In addition, the base station 100 may also notify the terminal 200 of the position of the RE or the DMRS sequence pattern when adding DMRS (increase) using RRC signaling.

(Option 2: L1 signaling)
In option 2, the base station 100 notifies the terminal 200 in advance of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) using the downlink control channel for MTC. To do.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

If the candidate for the number of REs to be added as DMRS can be set, the terminal 200 may determine the number of REs to be used for DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. .. Further, the base station 100 may also notify the terminal 200 of the position of the RE to which DMRS is added or the DMRS series pattern by using the downlink control channel for MTC, and notifies the terminal 200 in advance by RRC signaling. May be good.

(Option 3: Implicit signaling)
In option 3, the base station 100 does not explicitly notify the terminal 200 of the number of repetitions (N _Rep ). The base station 100 notifies the terminal 200 of only the MCS by using the downlink control channel for MTC.

When the number of repetitions can be expressed using the coding rate in the repetition transmission, the terminal 200 can obtain the coding rate and the number of repetitions in the repetition transmission from the MCS notified from the base station 100. In this case, the terminal 200 determines whether or not to increase the DMRS based on the obtained number of repetitions. Specifically, the terminal 200 increases the DMRS when the number of repetitions (for example, 128 times) corresponds to the Large coverage enhancement level.

Further, when the candidate for the number of REs to be added as DMRS can be set, the terminal 200 may determine the number of REs to be used for DMRS based on the obtained number of repetitions. Further, the base station 100 may also notify the terminal 200 in advance of the position of the RE to which the DMRS is added or the DMRS series pattern by using RRC signaling.

(Embodiment 3)
In the present embodiment, a case where a sounding reference signal (SRS) transmitted from a terminal to a base station is used as an additional DMRS (additional DMRS) for measuring uplink channel quality will be described. To do.

As shown in FIG. 15, the SRS is multiplexed with the final symbol of the subframe, and is specified to be periodically transmitted from the terminal 200 to the base station 100. FIG. 15 shows an example in which SRS is transmitted in one subframe cycle. Normally, the base station 100 schedules the terminal 200 to transmit the PUSCH signal based on the measurement result of the channel quality using SRS.

Since the base station and the terminal according to the present embodiment have the same basic configuration as the base station 100 and the terminal 200 according to the first embodiment, FIGS. 8 and 9 will be referred to for description.

In the present embodiment, as in the first embodiment, the base station 100 (control unit 101) and the terminal 200 (control unit 206) have a large coverage enhancement level or repetition count (N _Rep ) set in the terminal 200. If the coverage enhancement level or the equivalent number of repetitions (eg 128), increase the number of DMRSs placed in the PUSCH.

At that time, the base station 100 performs channel estimation using SRS in addition to DMRS transmitted by the terminal 200. More specifically, in the base station 100 according to the present embodiment, with respect to the terminal 200 in which the MTC coverage enhancement mode is set, the demapping unit 114 extracts the terminal 200 in the subframe in which the SRS is transmitted. PUSCH subframes are decomposed into SRS, DMRS, and data symbols, DMRS and SRS are output to the channel estimation unit 115, and the data symbols are output to the equalization unit 116. Then, the channel estimation unit 115 performs channel estimation using DMRS and SRS input from the demapping unit 114.

As described above, in the base station 100, the channel estimation accuracy can be improved by performing the channel estimation using SRS in addition to DMRS as the reference signal for demodulation of the data symbol.

By doing so, in the present embodiment, as in the first and second embodiments, the number of reference signals for demodulating the data symbol can be increased without newly adding the DMRS. Therefore, it is possible to improve the channel estimation accuracy without changing the code rate of PUSCH data.

As shown in FIG. 15, since only one symbol is transmitted in one subframe, the channel estimation improvement is achieved in the first embodiment or the second embodiment when the SRS is transmitted in one subframe cycle. It is equivalent to increasing DMRS by 1.5 times.

[Variation of Embodiment 3]
The channel estimation accuracy in the base station 100 depends on the transmission cycle of the SRS. For example, when the transmission cycle of SRS is every 2 subframes, in the subframe where SRS is not transmitted, since there are only DMRS for 2 symbols in 1 subframe as in the conventional case, SRS is transmitted every 1 subframe. The channel estimation accuracy deteriorates compared to the case where there is.

Therefore, in order to solve the problem that the channel estimation accuracy depends on the transmission cycle of SRS, in the variation of the present embodiment, DMRS is added to the final symbol as shown in FIG. 16A in the subframe in which SRS is not transmitted. In the subframe where the SRS is transmitted, DMRS is not added as shown in FIG. 16B.

At this time, in the terminal 200, the control unit 206 instructs the DMRS generation unit 207 to additionally transmit the DMRS in the subframe in which the SRS is not transmitted.

The DMRS generation unit 207 generates DMRS according to the presence / absence of increase in the number of DMRSs instructed by the control unit 206, the number of DMRSs to be increased, the position of DMRS (the position of the subframe and the symbol in the subframe), and the DMRS pattern. Generate and output the generated DMRS to the multiplexing unit 210.

On the other hand, in the base station 100, when DMRS is added to the terminal 200, the channel estimation unit 115 includes the existing DMRS (predetermined number of DMRS) and the SRS in the subframe in which the SRS is transmitted. Channel estimation is performed using. On the other hand, the channel estimation unit 115 estimates the channel by using the existing DMRS and the DMRS added to the position (final symbol) where the SRS is arranged in the subframe where the SRS is arranged in the subframe where the SRS is not transmitted. I do.

In this way, when adding DMRS, by using SRS for channel estimation, the influence of the addition of DMRS on the data symbol is minimized, and the channel estimation accuracy is independent of the transmission cycle of SRS. Can be improved.

[How to add DMRS and set DMRS layout]
Next, a method of setting the increase of DMRS and the arrangement of DMRS in the variation of the present embodiment will be described. As in the first embodiment, the following three options can be considered for the method of setting the DMRS increase and the DMRS arrangement.

(Option 1: RRC signaling)
In option 1, the base station 100 notifies the terminal 200 of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) in advance by RRC signaling.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS at the final symbol of the subframe that does not transmit the SRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

(Option 2: L1 signaling)
In option 2, the base station 100 notifies the terminal 200 in advance of the PUSCH coverage enhancement level (Large, Middle, Small, No coverage enhancement) or the number of repetitions (N _Rep ) using the downlink control channel for MTC. To do.

The terminal 200 determines whether to increase the DMRS based on the coverage enhancement level or the number of repetitions notified from the base station 100. Specifically, the terminal 200 increases the DMRS at the final symbol of the subframe that does not transmit the SRS when the base station 100 notifies the large coverage enhancement level or the corresponding number of repetitions (for example, 128 times).

(Option 3: Implicit signaling)
In option 3, the base station 100 does not explicitly notify the terminal 200 of the number of repetitions (N _Rep ). The base station 100 notifies the terminal 200 of only the MCS by using the downlink control channel for MTC.

When the number of repetitions can be expressed using the coding rate in the repetition transmission, the terminal 200 can obtain the coding rate and the number of repetitions in the repetition transmission from the MCS notified from the base station 100. In this case, the terminal 200 determines whether or not to increase the DMRS based on the obtained number of repetitions. Specifically, the terminal 200 increases the DMRS at the final symbol of the subframe that does not transmit the SRS when the number of repetitions (for example, 128 times) corresponds to the Large coverage enhancement level.

The embodiments of the present disclosure have been described above.

The values of the number of repetitions, the MTC coverage enhancement level, and the number of DMRSs arranged in the subframe used in the above embodiment are examples, and are not limited thereto. Further, the position where the added DMRS is placed in the above embodiment is an example, and the position is not limited to these.

Further, in the above-described embodiment, the case where one aspect of the present disclosure is configured by hardware has been described as an example, but the present disclosure can also be realized by software in cooperation with hardware.

Further, each functional block used in the description of the above embodiment is typically realized as an LSI which is an integrated circuit. The integrated circuit may control each functional block used in the description of the above embodiment and include an input and an output. These may be individually integrated into one chip, or may be integrated into one chip so as to include a part or all of them. Although it is referred to as LSI here, it may be referred to as IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

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

Furthermore, if an integrated circuit technology that replaces an LSI appears due to advances in semiconductor technology or another technology derived from it, it is naturally possible to integrate functional blocks using that technology. There is a possibility of applying biotechnology.

The base station of the present disclosure refers to a terminal that repeats an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe over a plurality of subframes. If the coverage enhancement level corresponding to the number of subframes is less than a predetermined value, a first DMRS is set, and if the coverage enhancement level is equal to or greater than the predetermined value, a second number of DMRSs larger than the first number is set. Channel estimation that performs channel estimation using the control unit that sets the above, the receiving unit that receives the uplink signal including the DMRS transmitted from the terminal, and the DMRS included in the received uplink signal. Adopt a configuration that includes a part and.

Further, in the base station of the present disclosure, the second number of DMRSs can be obtained by adding an additional DMRS (additional DMRS) to the first number of DMRSs.

Further, in the base station of the present disclosure, the second number of DMRSs is obtained by adding an additional DMRS (additional DMRS) to the first number of DMRSs, and the additional DMRSs are within one subframe. It is placed in symbol units.

Further, in the base station of the present disclosure, the additional DMRS is arranged at the symbol on which the rank indicator (RI) is arranged.

Further, in the base station of the present disclosure, when the second number of DMRSs are set for the terminal, the DMRSs are arranged according to the arrangement pattern of DMRS defined by PUCCH format 2.

Further, in the base station of the present disclosure, the second number of DMRSs is obtained by adding an additional DMRS (additional DMRS) to the first number of DMRSs, and the additional DMRSs are within one subframe. It is placed in each resource element.

Further, in the base station of the present disclosure, the second number DMRS is obtained by adding an additional DMRS (additional DMRS) to the first number DMRS, and the additional DMRS is a rank indicator (RI). ) Is placed in the resource element.

Further, in the base station of the present disclosure, the second number of DMRSs can be obtained by adding an additional DMRS (additional DMRS) to the first number of DMRSs, and the second number of DMRSs can be obtained with respect to the terminal. When a number of DMRSs is set, the channel estimation unit performs channel estimation using the first number of DMRSs and the SRS in the first subframe in which the sounding reference signal (SRS) is transmitted. In the second subframe in which the SRS is not transmitted, channel estimation is performed using the first number of DMRS and the additional DMRS arranged at the position where the SRS is arranged in the first subframe.

The terminal of the present disclosure applies a repetition over a plurality of subframes to an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe. When the coverage enhancement level corresponding to the number of the plurality of subframes is less than the predetermined value, the first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, the first number is used. A configuration including a control unit for setting a large second number of DMRSs and a transmission unit for transmitting the uplink signal including the DMRS is adopted.

The receiving method of the present disclosure is for a terminal that repeats an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe over a plurality of subframes. If the coverage enhancement level corresponding to the number of subframes is less than a predetermined value, the DMRS of the first number is set, and if the coverage enhancement level is equal to or more than the predetermined value, a second number larger than the first number is set. DMRS is set, the uplink signal including the DMRS transmitted from the terminal is received, and channel estimation is performed using the DMRS included in the received uplink signal.

The transmission method of the present disclosure applies to a local terminal when applying repetition over a plurality of subframes to an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe. On the other hand, when the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value, the first number of DMRS is set, and when the coverage enhancement level is equal to or more than the predetermined value, the first number. A larger second number of DMRSs is set and the uplink signal containing the DMRS is transmitted.

One aspect of the present disclosure is useful for mobile communication systems.

100 Base station 200 Terminal 101, 206 Control unit 102 Control signal generation unit 103, 208 Coding unit 104, 209 Modulation unit 105, 213 Mapping unit 106, 214 IFFT unit 107, 215 CP addition unit 108, 216 Transmission unit 109, 201 Antenna 110, 202 Reception part 111, 203 CP removal part 112, 204 FFT part 113 Synthesis part 114 Demapping part 115 Channel estimation part 116 Equalization part 117 Demodulation part 118 Decoding part 119 Judgment part 205 Extraction part 207 DMRS generation part 210 Multiplexing Part 211 DFT part 212 Repetition part

Claims (15)

For a terminal that transmits an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe, a first or higher number that is a predetermined value common to each subframe . A control unit that sets a number of DMRSs or a second number of DMRSs larger than the first number, and
A receiving unit that receives the uplink signal including the DMRS transmitted from the terminal, and
A channel estimation unit that performs channel estimation using the DMRS included in the received uplink signal, and a channel estimation unit.
Equipped with
The control unit adds the additional DMRS to the first number, which is the specified value, for the subframe to which the terminal does not transmit the sounding reference signal (SRS), so that the second number of DMRSs can be obtained. To set,
base station. The control unit sets the first number of DMRSs for the subframe in which the terminal transmits the SRS.
The base station according to claim 1. The terminal repeats and transmits the uplink signal over a plurality of subframes.
The control unit sets the first number of DMRS when the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value, and when the coverage enhancement level is equal to or more than the predetermined value, the first Set 2's DMRS,
The base station according to claim 1 or 2 . The additional DMRS is arranged in symbol units within one subframe.
The base station according to claim 3 . The additional DMRS is placed on the symbol on which the rank indicator (RI) is placed.
The base station according to claim 1 or 4 . The additional DMRS is placed at the final symbol of the subframe where the terminal does not transmit the SRS.
The base station according to claim 1 or 4 . The additional DMRS is arranged in one subframe in units of resource elements.
The base station according to claim 1 . The additional DMRS is placed in the resource element where the rank indicator (RI) is placed.
The base station according to claim 1 or 7 . When the second number of DMRS is set for the terminal,
The DMRS is arranged according to the DMRS arrangement pattern specified in PUCCH format 2.
The base station according to any one of claims 1 to 8 . When the second number of DMRS is set for the terminal,
The channel estimation unit performs channel estimation using the first number of DMRSs and the SRS in the first subframe in which the SRS is transmitted, and in the second subframe in which the SRS is not transmitted, the channel estimation unit performs the channel estimation. Channel estimation is performed using the first number of DMRSs and the additional DMRSs arranged at positions where SRSs are arranged in the first subframe.
The base station according to any one of claims 1 to 9 . For an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe, a first number of one or more, which is a predetermined value common to each subframe . A control unit that sets DMRS or a second number of DMRS larger than the first number, and
A transmission unit that transmits the uplink signal including the DMRS, and
Equipped with
The control unit sets the second number of DMRSs obtained by adding the additional DMRSs to the first number, which is the specified value, for the subframes that do not transmit the sounding reference signal (SRS). ,
Terminal. The control unit sets the first number of DMRSs for the subframe that transmits the SRS.
The terminal according to claim 11 . The transmitter transmits the uplink signal by repeating it over a plurality of subframes.
The control unit sets the first number of DMRS when the coverage enhancement level corresponding to the number of the plurality of subframes is less than a predetermined value, and when the coverage enhancement level is equal to or more than the predetermined value, the first Set 2's DMRS,
The terminal according to claim 11 or 12 . For a terminal that transmits an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe, a first or higher number that is a predetermined value common to each subframe . Set a number of DMRSs of 1 or a second number of DMRSs greater than the first number,
Upon receiving the uplink signal including the DMRS transmitted from the terminal,
Channel estimation is performed using the DMRS included in the received uplink signal.
It is a receiving method
For a subframe in which the terminal does not transmit a sounding reference signal (SRS), the second number of DMRSs obtained by adding an additional DMRS to the first number, which is the specified value, is set.
Reception method. For an uplink signal in which a data symbol and a demodulation reference signal (DMRS) are time-multiplexed in one subframe, a first number of one or more, which is a predetermined value common to each subframe . Set DMRS or a second number of DMRS greater than the first number,
Transmit the uplink signal including the DMRS,
It is a transmission method
For subframes that do not transmit a sounding reference signal (SRS), the second number of DMRSs obtained by adding an additional DMRS to the first number, which is the specified value, is set.
Sending method.

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