Patent Description:
3rd Generation Partnership Project Long Term Evolution (3GPP LTE) adopts Orthogonal Frequency Division Multiple Access (OFDMA) as a downlink communication scheme from a base station (may be referred to as "eNB") to a terminal (may be referred to as "UE" (User Equipment)) and also adopts a Single Carrier-Frequency Division Multiple Access (SC-FDMA) as an uplink communication scheme from a terminal to a base station (e.g., see Non-Patent Literature (hereinafter, referred to as "NPL") <NUM> to NPL <NUM>).

In LTE, base stations allocate resource blocks (RBs) in a system band to terminals for every time-unit called "subframe" to perform communication. <FIG> illustrates a subframe configuration example in an uplink shared channel (Physical Uplink Shared Channel: PUSCH). As illustrated in <FIG>, one subframe consists of two time slots. In each slot, multiple SC-FDMA data symbols and a demodulation reference signal (DMRS) are time-multiplexed. Upon receiving PUSCH, the base station performs channel estimation using DMRS. The base station then demodulates and decodes the SC-FDMA data symbols using the channel estimate.

Meanwhile, Machine-to-Machine (M2M) communication has been considered a promising technique for an infrastructure to support the future information society in recent years. The M2M communication enables service using inter-device autonomous communication without involving user's judgment. "Smart grid" may be a specific application example of the M2M communication system. The smart grid is an infrastructure system that efficiently supplies a lifeline such as electricity or gas, and performs M2M communication between a smart meter provided in each home or building and a central server, and autonomously and effectively brings supply and demand for resources into balance. Other application examples of the M2M communication system include a monitoring system for goods management or remote medical care, or remote inventory or charge management of vending machines.

In M2M communication systems, use of a cellular system having a broad range of a communication area in particular is attracting attention. In 3GPP, studies on M2M to be used in such a cellular network have been carried out in LTE and LTE-Advanced standardization under the title of "Machine Type Communication (MTC). " In particular, studies on "Coverage Enhancement," which further expands the communication area, have been carried out in order to support situations where an MTC communication device such as a smart meter is installed at a location where the device cannot be used in the existing communication area, such as the basement of a building (e.g., see NPL <NUM>).

In the MTC coverage enhancement, in particular, a technique called "repetition," which repeatedly transmits the same signal multiple times, is considered an important technique for expanding the communication area. More specifically, performing repetition transmission on PUSCH has been discussed. The base stations, which are the receiver side of PUSCH, can attempt to improve the received signal power by combining the signals transmitted by repetition transmission and thus can expand the communication area.

The repetition transmission requires a large number of time resources for transmission of the same signal and thus causes degradation of spectral efficiency. For this reason, it is desirable to reduce the number of repetitions required for achieving a required coverage enhancement, as much as possible. In this respect, studies have been carried out on techniques for reducing the number of repetitions required for achieving a required coverage enhancement on PUSCH. Examples of the techniques for reducing the number of repetitions required for achieving a required coverage enhancement include "multiple subframe channel estimation and symbol level combining" (e.g., see NPL <NUM>).

In multiple subframe channel estimation and symbol level combining, the base station performs coherent combining on a per-symbol basis over the number of subframes (NSF subframes) equal to or smaller than the number of repetitions for the signals transmitted by repetition transmission over multiple subframes (NRep subframes) as illustrated in <FIG>. The base station then performs channel estimation using the DMRS after the coherent combining and demodulates and decodes SC-FDMA data symbols using the obtained channel estimate.

When the number of subframes (NSF), which is the unit for multiple subframe channel estimation and symbol level combining, is smaller than the number of repetitions (NRep), the base station combines the modulated and decoded symbols (NRep/NSF).

It has already become obvious that the use of multiple subframe channel estimation and symbol level combining can improve the transmission quality of PUSCH compared with plain repetition that performs channel estimation and demodulation and decoding of SC-FDMA data symbols on a per-subframe basis (e.g., see NPL <NUM>). For example, in multiple subframe channel estimation and symbol level combining with four subframes (NSF=<NUM>), Signal to Noise power Ratio (SNR) required for achieving a required Block Error Ratio (BLER) can be improved by <NUM> to <NUM>. 6dB compared with plain repetition. In addition, in multiple subframe channel estimation and symbol level combining with eight subframes (NSF=<NUM>), SNR required for achieving a required BLER can be improved by <NUM> to <NUM>. 5dB compared with plain repetition.

In order to prevent degradation of channel estimation accuracy in PUSCH repetition, as illustrated in <FIG>, increasing the number of symbols within which DMRS is inserted with respect to the existing DMRS symbols (see upper part of <FIG>) in PUSCH has been proposed (see lower part of <FIG>, and also see NPL <NUM>, for example). Increasing the number of DMRS symbols results in an increase in the number of DMRSs (i.e., DMRS density) available for channel estimation and symbol level combining and thus is effective in improving the channel estimation accuracy.

Further , <NPL>) models improving channel estimation due to additional PUSCH symbols carrying DMRS by applying power boost to DMRS while reducing data symbol power without changing the actual number of symbols reserved for DMRS/data.

<CIT> discloses a method for receiving control information in a wireless communication system and a device therefor, the method comprising the steps of: receiving a PDCCH signal including uplink scheduling information; transmitting a PUSCH signal by using the uplink scheduling information; and receiving a PHICH signal including acknowledgement information on the PUSCH signal, wherein an RS for the PUSCH signal exists only in one slot per RB pair within an RB set in which the PUSCH signal is transmitted, and a resource for receiving the PHICH signal is determined by using an index of the slot in which the RS exists.

Enabling disclosure can be found, for instance, in aspect <NUM> of the description. Examples, aspects and embodiments presented in the following and not necessarily falling under the scope of the claims are provided in the application to better understand the invention. All embodiments other than aspect <NUM> do not fall under the scope of the claims (but are considered to be useful for highlighting specific aspects of the claims).

Increasing the number of DMRSs (or DMRS density) (hereinafter, may be referred to as "DMRS increase") reduces the number of data bits transmittable in each subframe via PUSCH. For this reason, when Modulation and Coding Scheme (MCS) is fixed, a higher coding rate has to be used for data, which causes degradation of the data transmission quality. In other words, 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 non-limiting and exemplary aspect provides a base station capable of improving the channel estimation accuracy without degradation of transmission quality.

It should be noted that, a comprehensive or specific aspect mentioned above may be implemented by a system, an apparatus, a method, an integrated circuit, a computer program or a recoding medium, or any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recoding medium.

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

Hereinafter, a detailed description will be given of aspects of this disclosure with reference to the drawings.

Aspects not covered by the claims are to be understood as examples useful for understanding the invention.

In MTC coverage enhancement, defining multiple coverage enhancement levels has been discussed. For example, defining about three coverage enhancement levels including 5dB, 10dB, and 15dB compared with the normal coverage (i.e., when no coverage enhancement is applied) has been discussed. Moreover, in MTC coverage enhancement, studies have been carried out on a configuration in which, when a terminal having low maximum transmission power compared with the normal terminal is defined, the coverage enhancement level for the terminal is set to 6dB, 12dB, and 18dB compared with the normal coverage.

Hereinafter, the coverage enhancement level that requires a coverage enhancement of 5dB or 6dB may be referred to as "small coverage enhancement level," the coverage enhancement level that requires a coverage enhancement of 10dB or 12dB may be referred to as "middle coverage enhancement level," and the coverage enhancement level that requires a coverage enhancement of 15dB or 18dB may be referred to as "large coverage enhancement level. " Note that, the levels required for the enhancement levels mentioned above are by no means limited to 5dB, 6dB, 10dB, 12dB, 15dB, or 18dB.

In general, in order to achieve a larger coverage enhancement level, a larger number of repetitions is required. For example, the number of repetitions required for achieving coverage enhancements of 15dB and 18dB are approximately <NUM> and <NUM> subframes.

In the case of repetitions over <NUM> or <NUM> subframes, however, the phases of received signals do not match due to the influence of frequency offset, causing performance degradation when multiple subframe channel estimation and symbol level combining are performed using the number of subframes identical to the number of repetitions in the base stations. For this reason, it can be said that the number of subframes (NSF) useable with multiple subframe channel estimation and symbol level combining is limited to around four or eight subframes.

Accordingly, even when an extremely large number of repetitions over <NUM> or <NUM> subframes, for example, is required, the base station performs multiple subframe channel estimation and symbol level combining for approximately four or eight subframes. However, performing multiple subframe channel estimation and symbol level combining with a small number of subframes such as four or eight subframes when an extremely large number of repetitions (<NUM> or <NUM> repetitions) is required results in degradation of the channel estimation accuracy because the signal to interference power ratio (SIR) or SNR of DMRS after coherent combining becomes extremely small.

<FIG> each illustrate the BLER performance of PUSCH repetition using multiple subframe channel estimation and symbol level combining. <FIG> indicates the BLER performance of eight repetitions while <FIG> indicates the BLER performance of <NUM> repetitions. In addition, <FIG> each indicate the BLER performance with ideal channel estimation for the purpose of comparison.

As indicated in <FIG>, when the number of repetitions is eight, which is a relatively small number of repetitions, the amount of degradation from the ideal channel estimation can be kept around 2dB by multiple subframe channel estimation and symbol level combining. Meanwhile, it can be observed that, when the number of repetitions is <NUM>, which is a relatively large number of repetitions, channel estimation and symbol level combining with four or eight subframes results in a degradation of 5dB from the ideal channel estimation, which is larger than the amount of degradation in eight repetitions.

As described above, performing multiple subframe channel estimation and symbol level combining when the number of repetitions is relatively large results in performance degradation compared with the ideal channel estimation.

Next, a case where the number of symbols within which DMRSs are inserted is increased with respect to the existing number of DMRS symbols (upper part of <FIG>) in PUSCH will be discussed.

<FIG> illustrates the BLER performance of the case where one DMRS is mapped in one slot as illustrated in the upper part of <FIG> (i.e., case where the number of DMRSs is not increased; 1x DMRS) and of the case where two DMRSs are mapped in one slot as illustrated in the lower part of <FIG> (i.e., case where the number of DMRSs is doubled; 2x DMRS) for the numbers of repetitions NRep=<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In addition, <FIG> indicates the BLER performance of a case where the number of repetitions NRep=<NUM> (no repetitions) and one DMRS is mapped in one slot as in the upper part of <FIG> (i.e., case corresponding to the normal coverage) for the purpose of comparison. Moreover, <FIG> indicates the BLER performance of a case where channel estimation and symbol level combining over four subframes (NSF=<NUM>) are used.

As indicated in <FIG>, the small coverage enhancement level, which requires a coverage enhancement of 5dB or 6dB, requires approximately <NUM> repetitions (NRep=<NUM>).

Moreover, the middle coverage enhancement level, which requires a coverage enhancement of 10dB or 12dB, requires approximately <NUM> repetitions (NRep=<NUM>). Furthermore, the large coverage enhancement level, which requires a coverage enhancement of 15dB or 18dB, requires approximately <NUM> repetitions (NRep=<NUM>).

Meanwhile, as indicated in <FIG>, it can be observed that, when the number of DMRSs is doubled, the BLER performance are the same or degrade with <NUM>, <NUM>, or <NUM> repetitions (NRep=<NUM>, <NUM>, <NUM>) required for the small or middle coverage enhancement level, as compared with the case where the number of DMRSs is not increased. Meanwhile, it can be observed that, when the number of DMRSs is doubled, the BLER performance are improved with <NUM> or <NUM> repetitions (NRep=<NUM>, <NUM>) required for the large coverage enhancement level as compared with the case where the number of DMRSs is not increased.

As described above, it can be observed that increasing the number of DMRSs is effective when the number of repetitions is relatively large (NRep=<NUM> or larger in <FIG>).

As described above, with the small or middle coverage enhancement level, which involves a relatively small number of repetitions, performance improvement of PUSCH by multiple subframe channel estimation and symbol level combining can be obtained as indicated in <FIG>, but no performance improvement of PUSCH by the DMRS increase is obtained as indicated in <FIG>.

Meanwhile, in the large coverage enhancement level, which involves a relatively large number of repetitions, although the performance improvement of PUSCH by multiple subframe channel estimation and symbol level combining is not sufficient as indicated in <FIG>, the performance improvement of PUSCH by the DMRS increase is obtained as indicated in <FIG>.

In this respect, in one mode of this disclosure, a larger number of DMRSs is configured for a terminal with the large coverage enhancement level than the number of DMRSs for the normal terminal (i.e., predefined number of DMRSs) among terminals configured with the MTC coverage enhancement mode. Meanwhile, the same number of DMRSs as the number of DMRSs for the normal terminal is configured for a terminal with the middle or small coverage enhancement level (i.e., the number of DMRSs is not increased).

Thus, when multiple subframe channel estimation and symbol level combining are performed, the PUSCH transmission performance can be improved in the small or middle coverage enhancement level without any increase in the number of DMRSs. In addition, the DMRS increase can improve the PUSCH transmission performance in the large coverage enhancement level.

Moreover, the DMRS increase is applied only to the large coverage enhancement level where a performance improvement can be expected, and the DMRS increase is not applied to the small or middle coverage enhancement level. Thus, there is no reduction in the number of data bits transmittable via PUSCH in the small or middle coverage enhancement level.

A communication system according to each aspect of this disclosure is an LTE-Advanced compliant system, for example, and includes base station <NUM> and terminal <NUM>.

Let us suppose a situation where MTC coverage enhancement mode terminal <NUM> exists in a cell provided by base station <NUM>. When the MTC coverage enhancement mode is applied, for example, terminal <NUM> applies repetition transmission over multiple subframes during PUSCH transmission. In other words, terminal <NUM> repeatedly transmits the same signal over consecutive subframes for a predetermined number of repetitions (may be referred to as "repetition level" or "repetition factor").

When NRep repetitions (i.e., the number of repetitions: NRep) are performed, terminal <NUM> consecutively transmits one subframe signal over NRep subframes.

Meanwhile, base station <NUM> performs "multiple subframe channel estimation and symbol level combining" for the signal transmitted by repetition transmission from terminal <NUM> (e.g., see <FIG>). More specifically, base station <NUM> performs coherent combining, on a per-symbol basis, over the number of subframes (NSF subframes) equal to or smaller than the number of repetitions NRep. Base station <NUM> then performs channel estimation using the coherently combined DMRS and demodulates and decodes the SC-FDMA data symbols using the obtained channel estimate.

<FIG> is a block diagram illustrating a primary configuration of base station <NUM> according to an aspect of this disclosure. In base station <NUM> illustrated in <FIG>, control section <NUM> configures a first number of DMRSs for terminal <NUM> configured to perform repetition of an uplink signal over multiple subframes, when the coverage enhancement level corresponding to the number of multiple subframes is smaller than a determined value. The uplink signal transmitted by repetition is obtained by time-multiplexing a data symbol with a demodulation reference signal (DMRS) in one subframe. Meanwhile, control section <NUM> configures a second number of DMRSs to the predefined number of DMRSs for terminal <NUM> configured in the same manner, when the coverage enhancement level is equal to or larger than the determined value, the second number being larger than the first number. Receiving section <NUM> receives an uplink signal including the DMRSs that is transmitted from terminal <NUM>. Channel estimation section <NUM> performs channel estimation using the DMRSs included in the received uplink signal.

Meanwhile, <FIG> is a block diagram illustrating a primary configuration of terminal <NUM> according to each aspect of this disclosure. In terminal <NUM> illustrated in <FIG>, when applying repetition for an uplink signal obtained by time-multiplexing a data symbol with a demodulation reference signal (DMRS) in one subframe, over multiple subframes, control section <NUM> configures a first number of DMRSs for terminal <NUM> of control section <NUM> when the coverage enhancement level corresponding to the number of multiple subframes is smaller than a determined value. Meanwhile, control section <NUM> configures a second number of DMRSs for terminal <NUM> of control section <NUM>, when the coverage enhancement level is equal to or larger than the determined value, the second number being larger than the first number. Transmission section <NUM> transmits an uplink signal including the DMRSs.

<FIG> is a block diagram illustrating a configuration of base station <NUM> according to Aspect <NUM> of this disclosure. In <FIG>, base station <NUM> includes control section <NUM>, control signal generating section <NUM>, coding section <NUM>, modulation section <NUM>, a mapping section <NUM>, inverse fast Fourier transform (IFFT) section <NUM>, cyclic prefix (CP) adding section <NUM>, transmission section <NUM>, antenna <NUM>, receiving section <NUM>, CP removal section <NUM>, fast Fourier transform (FFT) section <NUM>, combining section <NUM>, demapping section <NUM>, channel estimation section <NUM>, equalizing section <NUM>, demodulation section <NUM>, decoding section <NUM>, and determining section <NUM>.

Control section <NUM> determines PUSCH assignment for resource allocation target terminal <NUM>. Control section <NUM>, for example, determines a frequency allocation resource and a modulation and coding scheme for terminal <NUM> and outputs information on the determined parameters to control signal generating section <NUM>.

Moreover, control section <NUM> determines a coding level for the control signal and outputs the determined coding level to coding section <NUM>. Moreover, control section <NUM> determines a radio resource to which the control signal is mapped (downlink resource) and outputs information on the determined radio resource to mapping section <NUM>.

Control section <NUM> determines a coverage enhancement level of terminal <NUM> and outputs information on the determined coverage enhancement level or the number of repetitions required for PUSCH transmission in the determined coverage enhancement level to control signal generating section <NUM>. In addition, control section <NUM> generates information on the number of DMRSs or DMRS mapping used in PUSCH repetition performed by terminal <NUM>, based on information on the coverage enhancement level or the number of repetitions required for PUSCH transmission, and outputs the generated information to demapping section <NUM>.

Control signal generating section <NUM> generates a control signal for terminal <NUM>. The control signal includes a downlink control indicator (DCI) for uplink grant for indicating information on PUSCH assignment received from control section <NUM>. The DCI for uplink grant consists of multiple bits and includes information indicating a frequency allocation resource, a modulation and coding scheme, and/or the like.

In addition, when the information on the coverage enhancement level or the number of repetitions required for PUSCH transmission is transmitted via a downlink control channel for MTC, the information mentioned herein is also included in the DCI for uplink grant. Note that, the information on the coverage enhancement level or the number of repetitions required for PUSCH transmission may be indicated to control section <NUM> of terminal <NUM> via higher-layer signaling.

Control signal generating section <NUM> generates a control information bit sequence (control signal) using information received from control section <NUM> and outputs the generated control signal to coding section <NUM>. Note that, there is a situation where a control signal is transmitted to multiple terminals <NUM>, so that control signal generating section <NUM> includes the terminal ID of each terminal <NUM> in the control signal for terminal <NUM> and generates a bit sequence. For example, a cyclic redundancy check (CRC) bit masked with the terminal ID of the destination terminal is added to the control signal.

Coding section <NUM> encodes the control signal (coded bit sequence) received from control signal generating section <NUM> in accordance with the coding level indicated by control section <NUM> and outputs the coded control signal to modulation section <NUM>.

Modulation section <NUM> modulates the control signal received from coding section <NUM> and outputs the modulated control signal (symbol sequence) to mapping section <NUM>.

Mapping section <NUM> maps the control signal received from modulation section <NUM> to a radio resource indicated by control section <NUM>. Note that, the control channel to which the control signal is mapped may be an MTC PDCCH or Enhanced PDCCH (EPDCCH). Mapping section <NUM> outputs, to IFFT section <NUM>, a signal in the downlink subframe including the MTC PDCCH or EPDCCH to which the control signal is mapped.

IFFT section <NUM> applies IFFT processing to the signal received from mapping section <NUM>, thereby transforming a frequency-domain signal into a time-domain signal. IFFT section <NUM> outputs the time-domain signal to CP adding section <NUM>.

CP adding section <NUM> adds a CP to the signal received from IFFT section <NUM> and outputs the CP added signal (OFDM signal) to transmission section <NUM>.

Transmission section <NUM> applies radio frequency (RF) processing such as digital-to-analog (D/A) conversion or up-conversion to the OFDM signal received from CP adding section <NUM> and transmits the processed radio signal to terminal <NUM> via antenna <NUM>.

Receiving section <NUM> applies RF processing such as down conversion or analog-to-digital (A/D) conversion to the uplink signal (PUSCH) received from terminal <NUM> via antenna <NUM> and outputs the received signal thus obtained to CP removal section <NUM>. The uplink signal (PUSCH) transmitted from terminal <NUM> includes a signal that has been subjected to repetition processing over multiple subframes.

CP removal section <NUM> removes the CP added to the received signal received from receiving section <NUM> and outputs the signal after CP removal to FFT section <NUM>.

FFT section <NUM> applies FFT processing to the signal received from CP removal section <NUM> to transform the signal into a frequency-domain signal sequence and extract a signal corresponding to a PUSCH subframe and outputs the extracted signal to combining section <NUM>.

Combining section <NUM> coherently combines a data signal and a signal portion corresponding to DMRS using symbol level combining for PUSCH transmitted by repetition over multiple subframes. Combining section <NUM> outputs the combined signal to demapping section <NUM>.

Demapping section <NUM> extracts a PUSCH subframe portion assigned to terminal <NUM> from the signal received from combining section <NUM>, using information on the number of DMRSs and DMRS mapping that is received from control section <NUM> and used in PUSCH repetition by terminal <NUM>. In addition, demapping section <NUM> separates the extracted PUSCH subframe portion for terminal <NUM> into DMRS and a data symbol (SC-FDMA data symbol) and outputs the DMRS and data symbol to channel estimating section <NUM> and equalizing section <NUM>, respectively.

Channel estimation section <NUM> performs channel estimation using DMRS received from demapping section <NUM>. Channel estimation section <NUM> outputs the obtained channel estimate to equalizing section <NUM>.

Equalizing section <NUM> equalizes the data symbol received from demapping section <NUM>, using the channel estimate received from channel estimation section <NUM>. Equalizing section <NUM> outputs the equalized data symbol to demodulation section <NUM>.

Demodulation section <NUM> applies inverse discrete Fourier transform (IDFT) processing to the frequency-domain SC-FDMA data symbol received from equalizing section <NUM> to transform the symbol into a time-domain signal and then performs data modulation. More specifically, demodulation section <NUM> converts a symbol sequence into a bit sequence based on the modulation scheme indicated to terminal <NUM> and outputs the bit sequence thus obtained to decoding section <NUM>.

Decoding section <NUM> performs error correction decoding on the bit sequence received from demodulation section <NUM> and outputs the decoded bit sequence to determining section <NUM>.

Determining section <NUM> performs error detection on the bit sequence received from decoding section <NUM>. The error detection is performed using a CRC bit added to the bit sequence. Determining section <NUM> extracts the received data and outputs an ACK when the detection result of the CRC bit indicates no error. Meanwhile, determining section <NUM> outputs a NACK when the detection result of the CRC bit indicates error. Such an ACK or NACK to be outputted from determining section <NUM> is used in retransmission control processing in a processing section (not illustrated).

<FIG> is a block diagram illustrating a configuration of terminal <NUM> according to Aspect <NUM> of this disclosure. In <FIG>, terminal <NUM> includes antenna <NUM>, receiving section <NUM>, CP removal section <NUM>, FFT section <NUM>, extraction section <NUM>, control section <NUM>, DMRS generating section <NUM>, coding section <NUM>, modulation section <NUM>, multiplexing section <NUM>, DFT section <NUM>, repetition section <NUM>, mapping section <NUM>, IFFT section <NUM>, CP adding section <NUM>, and transmission section <NUM>.

Receiving section <NUM> applies RF processing such as down-conversion or A/D conversion to the radio signal (MTC PDCCH or EPDCCH) received from base station <NUM> via antenna <NUM> and obtains a baseband OFDM signal. Receiving section <NUM> outputs the OFDM signal to CP removal section <NUM>.

CP removal section <NUM> removes the CP added to the OFDM signal received from receiving section <NUM> and outputs the signal after CP removal to FFT section <NUM>.

FFT section <NUM> applies FFT processing to the signal received from CP removal section <NUM>, thereby transforming the time-domain signal into a frequency-domain signal. FFT section <NUM> outputs the frequency-domain signal to extraction section <NUM>.

Extraction section <NUM> performs blind-decoding on the frequency-domain signal (MTC PDCCH or EPDCCH) received from FFT section <NUM> and attempts to decode the control signal intended for terminal <NUM> of extraction section <NUM>. The CRC masked with the terminal ID of the terminal is added to the control signal intended for terminal <NUM>. Accordingly, extraction section <NUM> extracts the control information if CRC detection is OK as a result of blind-decoding and outputs the extracted control information to control section <NUM>.

Control section <NUM> controls PUSCH transmission based on the control signal received from extraction section <NUM>. More specifically, control section <NUM> indicates the resource allocation for PUSCH transmission to mapping section <NUM> based on the PUSCH resource allocation information included in the control signal. Moreover, control section <NUM> indicates the coding and modulation schemes for PUSCH transmission respectively to coding section <NUM> and modulation section <NUM> based on the coding and modulation scheme included in the control signal.

Moreover, when information on the coverage enhancement level or information on the number of repetitions required for PUSCH transmission is included in the control signal, control section <NUM> determines the number of repetitions for PUSCH repetition transmission and whether or not to increase the number of DMRSs, based on the information, and indicates the information indicating the determined number of repetitions and the information indicating whether or not to increase the number of DMRSs to repetition section <NUM> and DMRS generating section <NUM>, respectively.

Moreover, when the information on the coverage enhancement level or the information on the number of repetitions required for PUSCH transmission is indicated by base station <NUM> via higher-layer signaling, control section <NUM> determines the number of repetitions for PUSCH repetition transmission and whether or not to increase the number of DMRSs based on the indicated information and indicates the determined pieces of information to repetition section <NUM> and DMRS generating section <NUM>, respectively. Moreover, control section <NUM> may indicate the information on the number of DMRSs to be increased or the positions of DMRSs indicated by base station <NUM> via higher-layer signaling to DMRS generating section <NUM>.

DMRS generating section <NUM> generates DMRSs in accordance with the determination whether or not to increase the number of DMRSs, the number of DMRSs to be increased, the positions of DMRSs, and the DMRS pattern that are indicated by control section <NUM> and outputs the generated DMRSs to multiplexing section <NUM>.

Coding section <NUM> adds a CRC bit masked with the terminal ID of terminal <NUM> to the transmission data to be received (uplink data), performs error correction coding on the data, and outputs the coded bit sequence to modulation section <NUM>.

Modulation section <NUM> modulates the bit sequence received from coding section <NUM> and outputs the modulated signal (data symbol sequence) to multiplexing section <NUM>.

Multiplexing section <NUM> time-multiplexes the data symbol sequence received from modulation section <NUM> with the DMRSs received from DMRS generating section <NUM> and outputs the multiplexed signal to DFT section <NUM>.

DFT section <NUM> applies DFT to the signal received from multiplexing section <NUM> to generate a frequency-domain signal and outputs the generated frequency-domain signal to repetition section <NUM>.

When terminal <NUM> of repetition section <NUM> is in the MTC coverage enhancement mode, repetition section <NUM> performs repetition for the signal received from DFT section <NUM> over multiple subframes based on the number of repetitions indicated by control section <NUM> and generates a repetition signal. Repetition section <NUM> outputs the repetition signal to mapping section <NUM>.

Mapping section <NUM> maps the signal received from repetition section <NUM> to a PUSCH time and frequency resource indicated by control section <NUM>. Mapping section <NUM> outputs the PUSCH signal to which the signal is mapped to IFFT section <NUM>.

IFFT section <NUM> generates a time-domain signal by applying IFFT processing to the frequency-domain PUSCH signal received from mapping section <NUM>. IFFT section <NUM> outputs the generated signal to CP adding section <NUM>.

CP adding section <NUM> adds a CP to the time-domain signal received from IFFT section <NUM> and outputs the CP added signal to transmission section <NUM>.

Transmission section <NUM> applies RF processing such as D/A conversion or up-conversion to the signal received from CP adding section <NUM> and transmits the radio signal to base station <NUM> via antenna <NUM>.

Hereinafter, a detailed description will be given of base station <NUM> and terminal <NUM> configured in the manner described above.

Base station <NUM> indicates the coverage enhancement level (large, middle, small, or no coverage enhancement) or the number of repetitions (NRep) to terminal <NUM> before PUSCH transmission and reception.

For example, the large coverage enhancement level (15dB, 18dB) and the number of repetitions (NRep)=<NUM> may be associated with each other, while the middle coverage enhancement level (10dB, 12dB) and the number of repetitions (NRep)=<NUM> may be associated with each other, and the small coverage enhancement level (5dB, 6dB) and the number of repetitions (NRep)=<NUM> may be associated with each other.

The coverage enhancement level (large, middle, small, or no coverage enhancement) or the number of repetitions (NRep) may be indicated to terminal <NUM> by base station <NUM> via a higher layer (RRC signaling) or using a downlink control channel for MTC. In addition, the number of repetitions can be found from the coding rate configured in terminal <NUM>, so that base station <NUM> may indicate the MCS to terminal <NUM>, thus, implicitly indicating the number of repetitions without explicit indication.

Base station <NUM> (control section <NUM>) does not increase the number of DMRSs used in PUSCH repetition performed by terminal <NUM>, when terminal <NUM> is configured with the coverage enhancement mode and also configured with the middle or small coverage enhancement level. Meanwhile, terminal <NUM> (control section <NUM>) does not increase the number of DMRSs mapped to PUSCH, when the coverage enhancement level or the number of repetitions (NRep) indicated by base station <NUM> is the middle or small coverage enhancement level or the number of repetitions corresponding to any one of these levels (e.g., <NUM> times or <NUM> times).

More specifically, when the coverage enhancement mode (repetition transmission) is applied to terminal <NUM> and the coverage enhancement level is smaller than a determined value (e.g., 15dB or 18dB), base station <NUM> and terminal <NUM> configure the number of DMRSs configured for the normal terminal (predefined number of DMRSs).

In this case, as illustrated in <FIG>, DMRS is mapped to one symbol of each slot (third and tenth SC-FDMA symbols) in one subframe, for example.

Meanwhile, base station <NUM> (control section <NUM>) increases the number of DMRSs used in PUSCH repetition performed by terminal <NUM>, for terminal <NUM> configured with the coverage enhancement mode and also configured with the large coverage enhancement level. Moreover, terminal <NUM> (control section <NUM>) increases the number of DMRSs to be mapped to PUSCH, when the coverage enhancement level or the number of repetitions (NRep) indicated by base station <NUM> is the large coverage enhancement level or the number of repetitions corresponding to this level (e.g., <NUM> times).

In other words, when the coverage enhancement mode (repetition transmission) is applied to terminal <NUM> and the coverage enhancement level is equal to or larger than a determined value (e.g., 15dB or 18dB), base station <NUM> and terminal <NUM> configure the number of DMRSs obtained by adding a predetermined number of DMRSs to the number of DMRSs configured for the normal terminal (i.e., predefined number of DMRSs).

In Aspect <NUM>, the DMRS to be added is mapped on a per-symbol basis in one subframe.

In <FIG>, for example, in addition to the existing DMRS mapped to one symbol of each slot (third and tenth SC-FDMA symbols) in one subframe, DMRSs are added to the first and eighth SC-FDMA symbols or the fifth and twelfth SC-FDMA symbols. In other words, twice the existing number of DMRSs is mapped in <FIG> compared with <FIG>.

Note that, it is also possible to add a DMRS only to one symbol in one subframe (i.e., to add a DMRS only in any one of slots) (increased one and half times the existing number of DMRSs) when the number of DMRSs is increased. For example, in addition to the third and tenth SC-FDMA symbols, a DMRS symbol may be mapped to any one of the first, fifth, eighth, and twelfth SC-FDMA symbols illustrated in <FIG>.

The granularity of DMRS increase by adding a DMRS on a per-symbol basis is <NUM>% (≈<NUM>/<NUM>). In other words, the overhead for DMRS increases by <NUM>% when a DMRS is added to one symbol in one subframe. Accordingly, when the number of DMRSs is doubled (i.e., added to two symbols) as illustrated in <FIG>, the overhead for DMRS increases by <NUM>%.

Adding DMRS on a per-symbol basis as in Aspect <NUM> brings the advantage of keeping peak to average power ratio (PAPR) low.

Moreover, the same sequence as the existing DMRS sequence may be used for the sequence to add DMRS. In this case, base station <NUM> can perform coherent combining for the added DMRS in addition to channel estimation and coherent combining over multiple subframes, so that the channel estimation accuracy can be improved.

Furthermore, in Aspect <NUM>, DMRS is added only to terminal <NUM> configured with the large coverage enhancement level, and no DMRS is added to terminal <NUM> configured with the middle or small coverage enhancement level.

In this configuration, the DMRS increase improves the channel estimation accuracy and thus can improve the PUSCH transmission quality in terminal <NUM> configured with the large coverage enhancement level.

Moreover, no DMRS is added for terminal <NUM> configured with the middle or small coverage enhancement level, so that there is no decrease in the number of data bits for PUSCH data. In other words, degradation in the data transmission quality due to an increase in the number of DMRSs does not occur. Moreover, as described above, the PUSCH transmission quality can be improved by multiple subframe channel estimation and symbol level combining without any increase in the number of DMRSs in terminal <NUM> configured with the middle or small coverage enhancement level (see <FIG>).

As described above, according to Aspect <NUM>, the channel estimation accuracy in base station <NUM> can be improved without degradation of the transmission quality in PUSCH.

Hereinafter, a description will be given of reasons for additionally mapping a DMRS in the first, fifth, eighth or twelfth SC-FDMA symbol when the number of DMRSs is increased as illustrated in <FIG>.

When uplink control information is multiplexed in PUSCH, as illustrated in <FIG>, a response signal (ACK/NACK) for a downlink data signal is multiplexed on SC-FDMA symbols adjacent to SC-FDMA symbols where DMRSs are mapped (the third and tenth SC-FDMA symbols) (i.e., the second, fourth, ninth, and eleventh SC-FDMA symbols). Moreover, a Rank Indicator (RI) indicating a rank (number of layers) for Multiple-Input Multiple-Output (MIMO) multiplexing for downlink data is multiplexed on SC-FDMA symbols adjacent to the SC-FDMA symbols where an ACK/NACK is mapped (i.e., the first, fifth, eighth and twelfth SC-FDMA symbols).

The MTC coverage enhancement is expected to be used in an environment where the received power of a desired signal transmitted from terminal <NUM> to base station <NUM> and/or base station <NUM> to terminal <NUM> is very small. For this reason, the MTC coverage enhancement mode does not aim to increase the communication capacity using MIMO, so that it is expected that no MIMO multiplexing is used in the MTC coverage enhancement mode. In other words, RI indicating a rank (number of layers) for MIMO multiplexing is always one, so that there is no need for terminal <NUM> to feedback the case where RI><NUM>.

In this respect, the additional DMRS may be mapped to a symbol where RI is mapped in Aspect <NUM>. For example, as illustrated in <FIG>, when the DMRSs to be added are mapped to the first, fifth, eighth or twelfth SC-FDMA symbol, among <NUM> resource elements (REs) forming each SC-FDMA symbol, the RI not used in the MTC coverage enhancement mode is replaced with DMRS in <NUM> REs. Thus, the number of resources for PUSCH data to be replaced with DMRS is only the remaining <NUM> REs.

As described above, mapping the DMRSs to be added to the first, fifth, eighth and twelfth SC-FDMA symbols which have been used for RI transmission can suppress a decrease in the number of data bits for PUSCH data due to addition of DMRS. In other words, the influence on PUSCH data can be minimized.

Moreover, as illustrated in <FIG>, mapping the DMRSs to be added to the first, fifth, eighth and twelfth SC-FDMA symbols results in mapping the DMRSs to the symbols on both sides of each SC-FDMA symbol where ACK/NACK is mapped, so that the transmission quality of ACK/NACK can be kept high.

Next, a description will be given of a method of configuring DMRS increase and DMRS mapping. The following three options are considered as the method of configuring DMRS increase and DMRS mapping.

In Option <NUM>, base station <NUM> indicates in advance a PUSCH coverage enhancement level (large, middle, small, or no coverage enhancement) or the number of repetitions (NRep) to terminal <NUM> via RRC signaling.

Terminal <NUM> determines whether or not to increase the number of DMRSs based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. More specifically, terminal <NUM> increases the number of DMRSs when the large coverage enhancement level or the number of repetitions corresponding to this level (e.g., <NUM> times) is indicated by base station <NUM>.

Moreover, when a candidate for the number of symbols used for addition of DMRS is configurable, terminal <NUM> may determine the number of symbols used for DMRS based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. Alternatively, base station <NUM> may indicate the position of an SC-FDMA symbol for DMRS increase to terminal <NUM> via RRC signaling.

In Option <NUM>, base station <NUM> indicates in advance a PUSCH coverage enhancement level (large, middle, small, or no coverage enhancement) or the number of repetitions (NRep) to terminal <NUM> via a downlink control channel for MTC.

Moreover, when a candidate for the number of symbols used for addition of DMRS is configurable, terminal <NUM> may determine the number of symbols used for DMRS based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. Alternatively, base station <NUM> may indicate in advance the position of an SC-FDMA symbol for DMRS increase to terminal <NUM> via RRC signaling.

In Option <NUM>, base station <NUM> does not explicitly indicate the number of repetitions (NRep) to terminal <NUM>. Base station <NUM> indicates only the MCS to terminal <NUM> via a downlink control channel for MTC.

When the number of repetitions can be expressed by using the coding rate in the reception transmission, terminal <NUM> can obtain the coding rate and the number of repetitions in the repetition transmission from the MCS indicated by base station <NUM>. In this case, terminal <NUM> determines whether or not to increase the number of DMRSs based on the obtained number of repetitions. More specifically, terminal <NUM> increases the number of DMRSs when the number of repetitions corresponds to the large coverage enhancement level (e.g., <NUM> times).

Moreover, when a candidate for the number of symbols used for addition of DMRS is configurable, terminal <NUM> may determine the number of symbols used for DMRS based on the obtained number of repetitions. Alternatively, base station <NUM> may indicate in advance the position of an SC-FDMA symbol for DMRS increase to terminal <NUM> via RRC signaling.

The MTC coverage enhancement is expected to be used also in an environment where terminal <NUM> is very distant from base station <NUM>, so that the MTC coverage enhancement may be used in an environment where an extended CP mode is used. <FIG> illustrates a mapping example of the existing DMRSs in an environment where an extended CP mode is used. Meanwhile, <FIG> each indicate a DMRS mapping example when the number of DMRSs illustrated in <FIG> is doubled as in the case of Aspect <NUM>. Thus, even in an environment where an extended CP mode is used, the DMRS increase can improve the PUSCH transmission quality in terminal <NUM> configured with the large coverage enhancement level.

As a variation of the case where the number of DMRSs is increased on a per-symbol basis, DMRSs may be mapped in accordance with a subframe configuration (DMRS mapping pattern) defined by existing PUCCH (Physical Uplink Control Channel) format <NUM> as illustrated in <FIG>. In this case, there is an advantage in that there is no need to specify a new subframe format and the existing standard can be diverted even when the number of DMRSs is increased.

In Aspect <NUM>, the case where the added DMRSs are mapped on a per-symbol basis has been described. Meanwhile, in Aspect <NUM>, a case where the added DMRSs are mapped on a per-resource element (RE) basis will be described.

Note that, the base station and terminal according to Aspect <NUM> will be described with reference to <FIG> and <FIG> because their basic configurations are common to the configurations of base station <NUM> and terminal <NUM> according to Aspect <NUM>, respectively.

As in Aspect <NUM>, when the coverage enhancement mode (repetition transmission) is applied to terminal <NUM> and the coverage enhancement level is smaller than a determined value (e.g., 15dB or 18dB), base station <NUM> and terminal <NUM> configure the number of DMRSs configured for the normal terminal (predefined number of DMRSs). In other words, base station <NUM> (control section <NUM>) and terminal <NUM> (control section <NUM>) do not increase the number of DMRSs mapped to PUSCH, when the coverage enhancement level or the number of repetitions (NRep) configured for terminal <NUM> is the middle or small coverage enhancement level or the number of repetitions corresponding to any one of these levels (e.g., <NUM> times or <NUM> times).

Meanwhile, as in Aspect <NUM>, when the coverage enhancement mode (repetition transmission) is applied to terminal <NUM> and the coverage enhancement level is equal to or larger than a determined value (e.g., 15dB or 18dB), base station <NUM> and terminal <NUM> configure the number of DMRSs obtained by adding a predetermined number of DMRSs to the number of DMRSs configured for the normal terminal (i.e., predefined number of DMRSs). In other words, base station <NUM> (control section <NUM>) and terminal <NUM> (control section <NUM>) increase the number of DMRSs mapped to PUSCH, when the coverage enhancement level or the number of repetitions (NRep) configured for terminal <NUM> is the large coverage enhancement level or the number of repetitions corresponding to this level (e.g., <NUM> times).

In Aspect <NUM>, the DMRS to be added is mapped on a per-RE basis in one subframe.

In <FIG>, for example, in addition to the existing DMRS mapped to one symbol of each slot (third and tenth SC-FDMA symbols) in one subframe, DMRSs are added to <NUM> REs in each of the first, fifth, eighth and twelfth SC-FDMA symbols. In other words, the DMRSs to be added are mapped to <NUM> REs (the same number of REs as that for two symbols), respectively, in <FIG>.

Note that, when the number of DMRSs is added, how DMRSs are mapped is by no means limited to the mapping example illustrated in <FIG>, and the number of DMRSs may be increased on a per-RE basis in one subframe.

The granularity of DMRS increase by adding a DMRS on a per-RE basis is <NUM>% (≈<NUM>/(<NUM>*<NUM>)). In other words, the overhead for DMRS increases by <NUM>% when a DMRS is increased for one RE in one subframe.

As in Aspect <NUM>, adding a DMRS on a per-RE basis allows smaller granularity in terms of the ratio of DMRSs to data in a subframe compared with the case where DMRSs are added on a per-symbol basis as in Aspect <NUM>.

Moreover, a known QPSK symbol pattern may be used between base station <NUM> and terminal <NUM> as a DMRS sequence to be added. In this case, base station <NUM> can perform coherent combining for the added DMRS in addition to channel estimation and coherent combining over multiple subframes, so that the channel estimation accuracy can be improved.

Furthermore, as in Aspect <NUM>, DMRS is added only for terminal <NUM> configured with the large coverage enhancement level, while no DMRS is added for terminal <NUM> configured with the middle or small coverage enhancement level. Thus, the DMRS increase improves the channel estimation accuracy and thus can improve the PUSCH transmission quality in terminal <NUM> configured with the large coverage enhancement level. Moreover, since no DMRS is added to terminal <NUM> configured with the middle or small coverage enhancement level, there is no reduction in the number of data bits for PUSCH data. Meanwhile, as described above, in terminal <NUM> configured with the middle or small coverage enhancement level, the PUSCH transmission quality can be improved by multiple subframe channel estimation and symbol level combining without any increase in the number of DMRSs (see <FIG>).

As described above, according to Aspect <NUM>, the channel estimation accuracy in base station <NUM> can be improved without degradation of the transmission quality in PUSCH as in Aspect <NUM>.

Moreover, as described in Aspect <NUM>, it is expected that no MIMO multiplexing is used in the MTC coverage enhancement. Thus, RI indicating a rank (number of layers) for MIMO multiplexing is always one, so that there is no need for terminal <NUM> to feedback the case where RI><NUM>.

In this respect, in Aspect <NUM>, the added DMRS may be mapped to an RE where an RI is mapped. For example, as illustrated in <FIG>, when the DMRSs to be added are mapped to six REs of each of the first, fifth, eighth, and twelfth SC-FDMA symbols (e.g., see <FIG>), the influence of adding DMRSs on PUSCH data is small compared with Aspect <NUM>. More specifically, although the number of REs to which the added DMRSs are mapped (24REs) in <FIG> is the same as that in Aspect <NUM> (see <FIG>), no resources for PUSCH data are replaced by the added DMRSs in <FIG>. In other words, DMRSs can be added without any decrease in the number of data bits for PUSCH data in <FIG>.

In addition, as in Aspect <NUM>, mapping additional DMRSs to the first, fifth, eighth and twelfth SC-FDMA symbols results in mapping DMRSs to the symbols on both sides of the SC-FDMA symbols where ACK/NACK is mapped, so that the transmission quality of ACK/NACK can be kept high.

Moreover, when a candidate for the number of REs used for addition of DMRS is configurable, terminal <NUM> determines the number of REs used for DMRS based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. Alternatively, base station <NUM> may indicate the position of an RE for DMRS increase or a DMRS sequence pattern to terminal <NUM> via RRC signaling.

Moreover, when a candidate for the number of REs used for addition of DMRS is configurable, terminal <NUM> determines the number of REs used for DMRS based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. Alternatively, base station <NUM> may indicate the position of an RE for DMRS increase or a DMRS sequence pattern to terminal <NUM> via a downlink control channel for MTC or RRC signaling in advance.

When the number of repetitions can be expressed by using the coding rate in the reception transmission, terminal <NUM> can obtain the coding rate and the number of repetitions from the MCS indicated by base station <NUM>. In this case, terminal <NUM> determines whether or not to increase the number of DMRSs based on the obtained number of repetitions. More specifically, terminal <NUM> increases the number of DMRSs when the number of repetitions corresponds to the large coverage enhancement level (e.g., <NUM> times).

Moreover, when a candidate for the number of REs used for addition of DMRS is configurable, terminal <NUM> determines the number of REs used for DMRS based on the obtained number of repetitions. Alternatively, base station <NUM> may in advance indicate the position of an RE for DMRS increase or a DMRS sequence pattern to terminal <NUM> via RRC signaling.

In Aspect <NUM>, a description will be given of a case where a sounding reference signal (SRS) transmitted from a terminal to a base station for measuring the uplink channel quality is used as additional DMRS.

As illustrated in <FIG>, it is specified that an SRS is multiplexed in the last symbol of a subframe and periodically transmitted from terminal <NUM> to base station <NUM>. <FIG> illustrates an example in which one SRS is transmitted per subframe. Normally, base station <NUM> performs scheduling for terminal <NUM> to transmit a PUSCH signal based on the result of channel quality measurement using an SRS.

In Aspect <NUM>, base station <NUM> (control section <NUM>) and terminal <NUM> (control section <NUM>) increase the number of DMRSs to be mapped to PUSCH, when the coverage enhancement level or the number of repetitions (NRep) configured in terminal <NUM> is the large coverage enhancement level or the number of repetitions corresponding to this level (e.g., <NUM> times) as in Aspect <NUM>.

In this case, base station <NUM> performs channel estimation using an SRS in addition to the DMRSs transmitted from terminal <NUM>. More specifically, in base station <NUM> according to Aspect <NUM>, for terminal <NUM> configured with the MTC coverage enhancement mode, demapping section <NUM> separates the extracted PUSCH subframe for terminal <NUM> into an SRS, DMRSs, and data symbols in a subframe in which an SRS is transmitted, and outputs the DMRSs and SRS to channel estimation section <NUM> and outputs the data symbols to equalizing section <NUM>. Channel estimation section <NUM> performs channel estimation using the DMRSs and SRS received from demapping section <NUM>.

As described above, in base station <NUM>, performing channel estimation using an SRS as a demodulation reference signal for data symbols in addition to DMRSs can improve the channel estimation accuracy.

Accordingly, in Aspect <NUM>, the number of demodulation reference signals for data symbols can be increased without newly adding a DMRS, unlike Aspect <NUM> or <NUM>. Thus, the channel estimation accuracy can be improved without changing the coding rate for PUSCH data.

Note that, as illustrated in <FIG>, an SRS is allowed to be transmitted via only one symbol per subframe, so that the channel estimation improvement when one SRS is transmitted per subframe is equivalent to the case where the number of DMRSs is increased one and a half times in Aspect <NUM> or <NUM>.

The channel estimation accuracy in base station <NUM> depends on the SRS transmission period. For example, when the SRS transmission period is every two subframes, only DMRSs for two symbols are present in one subframe in which no SRS is transmitted, as in the conventional case. For this reason, the channel estimation accuracy degrades compared with the case where one SRS is transmitted every subframe.

In this respect, in order to solve the problem that the above channel estimation accuracy is dependent on the SRS transmission period, a DMRS is added to the last symbol as illustrated in <FIG> in a subframe in which no SRS is transmitted, while no DMRS is added in a subframe in which an SRS is transmitted as illustrated in <FIG>.

In this case, control section <NUM> instructs DMRS generating section <NUM> to add and transmit a DMRS in a subframe in which no SRS is transmitted.

DMRS generating section <NUM> generates a DMRS in accordance with the determination whether or not to increase the number of DMRSs, the number of DMRSs to be increased, and the position of a DMRS (subframe, and a symbol position in the subframe) that are indicated by control section <NUM> and outputs the generated DMRS to multiplexing section <NUM>.

Meanwhile, when a DMRS is added to terminal <NUM>, channel estimation section <NUM> in base station <NUM> performs channel estimation using the existing DMRSs (predefined number of DMRSs) and the SRS in a subframe configured to transmit an SRS. Meanwhile, channel estimation section <NUM> performs, in a subframe configured to transmit no SRS, channel estimation using the existing DMRSs and the DMRS added to the position (last symbol) of a subframe where an SRS is supposed to be mapped in a subframe in which an SRS is mapped.

As described above, using an SRS for channel estimation when a DMRS is added can minimize the influence on the data symbol caused by the addition of DMRS and also improve the channel estimation accuracy without dependency on the SRS transmission period.

Next, a description will be given of a method of configuring DMRS increase and DMRS mapping in the variation of Aspect <NUM>. The following three options are considered as the method of configuring DMRS increase and DMRS mapping as in Aspect <NUM>.

Terminal <NUM> determines whether or not to increase the number of DMRSs based on the coverage enhancement level or the number of repetitions indicated by base station <NUM>. More specifically, terminal <NUM> adds a DMRS to the last symbol of a subframe configured to transmit no SRS, when the large coverage enhancement level or the number of repetitions corresponding to this level (e.g., <NUM> times) is indicated by base station <NUM>.

When the number of repetitions can be expressed by using the coding rate in the reception transmission, terminal <NUM> can obtain the coding rate and the number of repetitions from the MCS indicated by base station <NUM>. In this case, terminal <NUM> determines whether or not to increase the number of DMRSs based on the obtained number of repetitions. More specifically, terminal <NUM> adds a DMRS to the last symbol of a subframe configured to transmit no SRS, when the number of repetitions corresponds to the large coverage enhancement level (e.g., <NUM> times).

Each aspect of this disclosure has been described thus far.

Note that, the values used for the number of repetitions, MTC coverage enhancement level, and the number of DMRSs mapped in a subframe are only examples, and are by no means limited to these examples. In addition, the positions where the added DMRSs are mapped in each of the aspects are only examples and are by no means limited to these examples.

Note that, although each aspect has been described with an example in which one mode of this disclosure is implemented by a hardware configuration by way of example, this disclosure can be also implemented by software in concert with hardware.

In addition, the functional blocks used in the description of each aspect are typically implemented as LSI devices, which are integrated circuits. Such integrated circuits may control the functional blocks used in the description of the aspects and be provided with inputs and outputs. The functional blocks may be formed as individual chips, or some or all of the functional blocks may be collectively made into a single chip. In addition, although the term "LSI" is used herein, the terms "IC," "system LSI," "super LSI" or "ultra LSI" may be used as well depending on the level of integration.

The circuit integration is not limited to LSI and may be implemented by a dedicated circuit or a general-purpose processor other than LSI. After fabrication of LSI, a field programmable gate array (FPGA), which is programmable, or a reconfigurable processor which allows reconfiguration of connections and settings of circuit cells in LSI may be used.

Should a circuit integration technology replacing LSI appear as a result of advancements in semiconductor technology or other technologies derived from the technology, the functional blocks may be integrated using such a technology. Another possibility is the application of biotechnology, for example.

A base station of the present disclosure includes: a control section that configures a first number of demodulation reference signals (DMRSs) for a terminal when a coverage enhancement level is smaller than a determined value, and that configures a second number of DMRSs for the terminal when the coverage enhancement level is equal to or larger than the determined value, the terminal being configured to perform repetition of an uplink signal over a plurality of subframes, the uplink signal being formed by time-multiplexing a data symbol with a DMRS in one subframe, the coverage enhancement level corresponding to a number of the plurality of subframes, the second number being larger than the first number; a receiving section that receives the uplink signal including the DMRSs and transmitted from the terminal; and a channel estimation section that performs channel estimation using the DMRS included in the received uplink signal.

In the base station of this disclosure, the second number of DMRSs is obtained by adding additional DMRSs to the first number of DMRSs.

In the base station of this disclosure, the second number of DMRSs is obtained by adding additional DMRS to the first number of DMRSs, and the additional DMRSs is mapped on a per-symbol basis in one subframe.

In the base station off this disclosure, the additional DMRS is mapped to a symbol to which a rank indicator (RI) is mapped.

In the base station of this disclosure, when the terminal is configured with the second number of DMRSs, the DMRSs are mapped in accordance with a DMRS mapping pattern defined by PUCCH (Physical Uplink Control Channel) format <NUM>.

In the base station of this disclosure, the second number of DMRSs is obtained by adding additional DMRS to the first number of DMRSs, and the additional DMRS is mapped on a per-resource element basis in one subframe.

In the base station of this disclosure, the additional DMRS is mapped to a resource element to which a rank indicator (RI) is mapped.

In the base station of this disclosure, the second number of DMRSs is obtained by adding additional DMRS to the first number of DMRSs; and when the terminal is configured with the second number of DMRSs, the channel estimation section performs, in a first subframe in which a sounding reference signal (SRS) is transmitted, channel estimation using the first number of DMRSs and the SRS, and the channel estimation section performs, in a second subframe in which no SRS is transmitted, channel estimation using the first number of DMRSs and the additional DMRS that is mapped to a position of the second subframe where the SRS is mapped in the first subframe.

A terminal of this disclosure includes: a control section that configures a first number of demodulation reference signals (DMRSs) for the terminal when the terminal applies repetition over a plurality of subframes to an uplink signal and a coverage enhancement level corresponding to a number of the plurality of subframes is smaller than a determined value, and that configures a second number of DMRSs for the terminal when the terminal applies the repetition and the coverage enhancement level is equal to or larger than the determined value, the uplink signal being formed by time-multiplexing a data symbol with a DMRS in one subframe, the second number being larger than the first number; and a transmission section that transmits the uplink signal including the DMRSs.

A receiving method of this disclosure includes: configuring a first number of demodulation reference signals (DMRSs) for a terminal when a coverage enhancement level is smaller than a determined value, and configuring a second number of DMRSs for the terminal when the coverage enhancement level is equal to or larger than the determined value, the terminal being configured to perform repetition of an uplink signal over a plurality of subframes, the uplink signal being formed by time-multiplexing a data symbol with a DMRS in one subframe, the coverage enhancement level corresponding to a number of the plurality of subframes, the second number being larger than the first number; receiving the uplink signal including the DMRSs and transmitted from the terminal; and performing channel estimation using the DMRS included in the received uplink signal.

A transmission method of this disclosure includes: configuring a first number of demodulation reference signals (DMRSs) for a terminal when the terminal applies repetition over a plurality of subframes to an uplink signal and a coverage enhancement level corresponding to a number of the plurality of subframes is smaller than a determined value, and configuring a second number of DMRSs for the terminal when the terminal applies the repetition and the coverage enhancement level is equal to or larger than the determined value, the uplink signal being formed by time-multiplexing a data symbol with a DMRS in one subframe, the second number being larger than the first number; and transmitting the uplink signal including the DMRSs.

Claim 1:
A base station (<NUM>) comprising:
circuitry, which, in operation, configures a predefined first number of demodulation reference signals, DMRSs, the first number being a predefined value common to every subframe, or a second number of DMRSs for a terminal (<NUM>), which transmits an uplink signal formed by time-multiplexing a data symbol with a DMRS in one subframe, the second number being larger than the first number;
a receiver (<NUM>), which, in operation, receives the uplink signal including the DMRSs and transmitted from the terminal;
wherein the circuitry, in operation, performs channel estimation using the DMRS included in the received uplink signal, and configures the second number of DMRSs in a second subframe, in which the terminal transmits no sounding reference signal, SRS, the second number of DMRSs being obtained by adding additional DMRSs to the predefined first number of DMRSs,
wherein when the second number of DMRSs is configured for the terminal (<NUM>), the circuitry, in operation, performs, in a first subframe, in which the SRS is transmitted, channel estimation using the first number of DMRSs and the SRS, and the circuitry, in operation, performs, in the second subframe, in which no SRS is transmitted, channel estimation using the first number of DMRSs and the additional DMRS, and
wherein in the second subframe the additional DMRS is mapped to a position of the second subframe where the SRS is mapped in the first subframe.