Patent Description:
In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long-term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower latency and so on (see non-patent literature <NUM>). In addition, successor systems of LTE are also under study for the purpose of achieving further broadbandization and increased speed beyond LTE (referred to as, for example, "LTE-A (LTE-Advanced)," "FRA (Future Radio Access)," "<NUM>," "<NUM>," "<NUM>+ (plus)," "NR (New RAT)," "LTE Rel. <NUM>," "LTE Rel. <NUM> (or later versions)," and so on).

In existing LTE systems (for example, LTE Rel. <NUM> and later versions), carrier aggregation (CA), in which multiple carriers (component carriers (CCs), cells, etc.) are integrated, is introduced in order to achieve broadbandization. Every carrier is configured with the system bandwidth of LTE Rel. <NUM> as one unit. In addition, in CA, multiple CCs under the same radio base station (eNB (eNodeB)) are configured in a user terminal (UE (User Equipment)).

Also, in existing LTE systems (for example, LTE Rel. <NUM> and later versions), dual connectivity (DC), in which multiple cell groups (CGs) formed by different radio base stations are configured in a user terminal, is also introduced. Every cell group is comprised of at least one cell (CC, cell, etc.). In DC, multiple CCs of different radio base stations are integrated, so that DC is also referred to as "inter-eNB CA.

In existing LTE systems (for example, LTE Rels. <NUM> to <NUM>), downlink (DL) and/or uplink (UL) communication are carried out using <NUM>-ms transmission time intervals (TTIs). This <NUM>-ms TTI is the unit of time it takes to transmit one channel-encoded data packet, and serves as the processing unit in scheduling, link adaptation and so on. A TTI of <NUM> is also referred to as a "subframe," a "subframe duration" and so forth.

Non-Patent Literature <NUM> describes sPDCCH design for short TTI.

Non-Patent Literature <NUM> describes DCI and sPDCCH for latency reduction. In the first sTTI, it is considered to share the same legacy PDCCH region between sPDCCH and PDCCH.

Non-Patent Literature <NUM> describes physical layer aspect of processing time for shortened TTI.

Patent Literature <NUM> describes that the frame of a mobile communication system may be configured in a transmission time interval structure shorter than that of a frame of the legacy system.

Patent Literature <NUM> describes that a control channel can be transmitted through two and three OFDM symbols.

Envisaging future radio communication systems (for example, <NUM>, NR and so on), studies are underway to support TTIs (hereinafter also referred to as "short TTIs") that are shorter than the <NUM>-ms TTIs of existing LTE systems (hereinafter also referred to as "long TTIs"), in order to reduce latency (latency reduction).

Furthermore, future radio communication systems are expected to accommodate a variety of services such as high-speed and large-capacity communication (eMBB (enhanced Mobile Broad Band)), massive access (mMTC (massive MTC)) from devices (user terminals) for inter-device communication (M2M (Machine-to-Machine)) such as loT (Internet of Things) and MTC (Machine Type Communication), low-latency and high-reliability communication (URLLC (Ultra-Reliable and Low Latency Communication)), in a single framework. URLLC is required to provide a higher latency-reducing effect than eMBB and mMTC.

In this way, there is a likelihood that a plurality of services with different requirements for latency reduction will be co-present in future radio communication systems. So, for future radio communication systems, research is underway to support multiple TTIs (for example, long TTIs and short TTIs) of different time durations in the same carrier (CC, cell, etc.).

However, the problem when supporting multiple TTIs of varying time durations in the same carrier, lies in how to control communication. For example, when a configuration is used in which a number of short TTIs are included in a long TTI, how to configure these short TTIs is the problem. Furthermore, when downlink control information for controlling the scheduling of each TTI is transmitted via a downlink control channel, how to transmit this downlink control channel is also a problem.

The present invention has been made in view of the above, and it is therefore an object of the present invention to provide a user terminal and a radio communication method that allow adequate communication even when multiple TTIs of varying time durations are used in the same carrier.

According to the present invention, it is possible to communicate adequately even when multiple TTIs of varying time durations are used on the same carrier.

<FIG> is a diagram to explain an example of a transmission time interval (TTI) for existing systems (LTE Rel. <NUM> to <NUM>). As shown in <FIG>, in LTE Rel. <NUM> to <NUM>, a TTI (hereinafter referred to as a "normal TTI") has a time duration of <NUM>. A normal TTI is also referred to as a "subframe," and is comprised of two time slots. A TTI is the unit of time it takes to transmit one channel-encoded data packet (transport block), and serves as the processing unit in scheduling, link adaptation, and so on.

As shown in <FIG>, when normal cyclic prefixes (CPs) are used in the downlink (DL), a normal TTI is comprised of <NUM> OFDM (Orthogonal Frequency Division Multiplexing) symbols (seven OFDM symbols per slot). Each OFDM symbol has a time duration (symbol duration) of <NUM>, and a normal CP of <NUM> is appended. Since the symbol duration and the subcarrier spacing are reciprocal to each other, the subcarrier spacing is <NUM> when the symbol duration is <NUM>.

Also, when normal cyclic prefixes (CPs) are used in the uplink (UL), a normal TTI is comprised of <NUM> SC-FDMA (Single Carrier Frequency Division Multiple Access) symbols (seven SC-FDMA symbols per slot). Each SC-FDMA symbol has a time duration (symbol duration) of <NUM>, and a normal CP of <NUM> is appended. Since the symbol duration and the subcarrier spacing are reciprocal to each other, the subcarrier spacing is <NUM> when the symbol duration is <NUM>.

Note that, when enhanced CPs are used, a normal TTI may include <NUM> OFDM symbols (or <NUM> SC-FDMA symbols). In this case, each OFDM symbol (or each SC-FDMA symbol) has a time duration of <NUM>, and an enhanced CP of <NUM> is appended.

<FIG> is a diagram to show an example of a case where communication is performed using shortened TTIs, the TTI duration of which is made shorter than <NUM>. <FIG> shows a cell (CC #<NUM>) using normal TTIs (<NUM>) and a cell (CC #<NUM>) using shortened TTIs.

When shortened TTIs are used, it may be possible to change the subcarrier spacing (for example, expand the subcarrier spacing) from that of subcarriers of normal TTIs. When TTIs having a shorter time duration than normal TTIs (hereinafter referred to as "shortened TTIs") are used, the time margin for processing in user terminals and radio base stations (for example, coding, decoding, etc.) increases, so that the processing latency can be reduced. Also, when shortened TTIs are used, it is possible to increase the number of user terminals that can be accommodated per unit time (for example, <NUM>). Now, shortened TTIs' configurations and/or others will be described in detail below.

Now, examples of configurations of shortened TTIs will be described with reference to <FIG>. As shown in <FIG>, shortened TTIs have a time duration (TTI duration) shorter than <NUM>. Shortened TTIs may have one TTI duration or a number of TTI durations that, when multiplied, become <NUM>, such as <NUM>, <NUM>, <NUM>, <NUM> and so on. Alternatively, given that a normal TTI contains fourteen symbols when normal CPs are used, normal TTIs may have one TTI duration or a number of TTI durations that, when multiplied, become an integral multiple of <NUM>/<NUM>, such as <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> and <NUM>/<NUM>. Furthermore, given that a normal TTI contains twelve symbols when enhanced CPs are used, normal TTIs may have one TTI duration or a number of TTI durations that, when multiplied, become an integral multiple of <NUM>/<NUM>, such as <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> and <NUM>/<NUM>.

Also when shortened TTIs are used, as in conventional LTE, whether to use normal CPs or use enhanced CPs can be configured by way of higher layer signaling, such as broadcast information and RRC signaling. By this means, it is possible to introduce shortened TTIs while maintaining compatibility (synchronization) with <NUM>-ms normal TTIs.

Note that, although <FIG> illustrate example cases of using normal CPs, the present invention is not limited to these. Shortened TTIs have only to have a shorter time duration than normal TTIs, and the number of symbols in a shortened TTI, the duration of symbols, the duration of CPs and suchlike configurations are not critical. Furthermore, although examples will be described below in which OFDM symbols are used in the DL and SC-FDMA symbols are used in the UL, the present invention is not limited to these.

<FIG> is a diagram to show a first configuration example of shortened TTIs. As shown in <FIG>, in the first configuration example, a shortened TTI is comprised of <NUM> OFDM symbols (or SC-FDMA symbols), which is equal in number to a normal TTI, and each OFDM symbol (each SC-FDMA symbol) has a symbol duration shorter than the symbol duration of a normal TTI (= <NUM>).

As shown in <FIG>, when maintaining the number of symbols in a normal TTI and shortening the duration of symbols, physical layer signal configurations (arrangement of REs and/or others) for normal TTIs can be reused. In addition, when maintaining the number of symbols in a normal TTI, it is possible to include, in a shortened TTI, the same amount of information (the same amount of bits) as in a normal TTI.

Also, since the symbol duration and the subcarrier spacing are each the reciprocal of the other, when the duration of symbols is made short as in <FIG>, the subcarrier spacing becomes wider than the <NUM>-kHz subcarrier spacing of normal TTIs. When the subcarrier spacing becomes wider, it is possible to effectively prevent the inter-channel interference that is caused by the Doppler shift when the user terminal moves, the deterioration of communication quality due to phase noise in user terminals' receivers and so on. In particular, in high frequency bands such as bands of several tens of GHz, the deterioration of communication quality can be effectively prevented by expanding the subcarrier spacing.

<FIG> is a diagram to show a second configuration example of a shortened TTI. As shown in <FIG>, according to the second configuration example, a shortened TTI is comprised of a smaller number of OFDM symbols (or SC-FDMA symbols) than a normal TTI, and each OFDM symbol (each SC-FDMA symbol) has the same symbol duration (= <NUM>) as a normal TTI. In this case, the shortened TTI can be formed with symbol units of a normal TTI (that is, can be formed with a reduced number of symbols). For example, a shortened TTI can be formed by using part of the fourteen symbols included in one subframe. In <FIG>, a shortened TTI is comprised of seven OFDM symbols (SC-FDMA symbols), which is half of a normal TTI.

As shown in <FIG>, when maintaining the duration of symbols and reducing number of symbols, the amount of information (the amount of bits) to be included in a shortened TTI can be reduced lower than a normal TTI. Therefore, a user terminal can perform receiving processes (for example, demodulation, decoding and so on) for information included in shortened TTIs in a shorter time than normal TTIs, so that the processing latency can be shortened. Moreover, by making the duration of symbols the same as in existing systems, shortened-TTI signals and normal-TTI signals can be frequency-multiplexed in the same system band (or carrier, cell, CC, etc.), so that compatibility with normal TTIs can be maintained.

For example, when frame configuration type <NUM> (FDD) is employed, a downlink control channel (also referred to as an "sPDCCH," for example) and/or a downlink shared channel (also referred to as an "sPDSCH," for example) may be transmitted using shortened sTTIs (sTTIs) for existing systems, which are comprised of two symbols and/or one slot. Also, in frame configuration type <NUM> (FDD), an uplink control channel (also referred to as an "sPUCCH," for example) and/or an uplink shared channel (also referred to as an "sPUSCH," for example) can be transmitted using sTTIs comprised of, at least one of, two symbols, four symbols and one slot. Alternatively, when frame configuration type <NUM> (TDD) is employed, it is possible to transmit at least one of an sPDCCH, an sPDSCH, an sPUCCH and an sPUSCH by using sTTIs comprised of one slot.

In this way, for the future radio communication systems, studies are under way to support multiple TTIs of varying time durations in the same carrier. However, the problem when supporting multiple TTIs of varying time durations in the same carrier lies in how to control communication. For example, when a configuration is used in which a number of short TTIs (shortened TTIs) are included in a long TTI (normal TTI), how to configure these short TTIs is the problem. In addition, when downlink control information (sDCI) for controlling the scheduling of each short TTI is transmitted via a downlink control channel (sPDCCH), how to transmit this downlink control channel is the problem.

So, the present inventors have focused on the point that the time field where an existing downlink control channel, which is transmitted every long TTI, is allocated changes every long TTI, and come up with the idea of controlling the allocation of a downlink control channel for short TTIs depending on in which time field the existing downlink control channel is allocated.

To be more specific, depending on in which time field a downlink control channel (PDCCH) is allocated, a user terminal controls receipt of a downlink control channel (sPDCCH) for short TTIs. Note that saying that a user terminal controls receipt of an sPDCCH based on the time field a PDCCH is allocated, may refer to using configurations that allow the user terminal to control the sPDCCH's receiving processes based on sPDCCH allocation information, which is reported from the radio base station depending on the time field the PDCCH is allocated.

Also, the present inventors have come up with the idea of controlling the allocation pattern of multiple short TTIs contained in a long TTI based on at least one of the time field in which an existing downlink control channel is allocated, whether or not a downlink control channel for short TTIs is allocated in the time field of the existing downlink control channel, and the TTI duration of the downlink control channel for short TTIs.

Now, embodiments of the present invention will be described below in detail with reference to the accompanying drawings. According to the present embodiment, a short TTI (second TTI) can be configured in any way as long as its time duration is shorter than a long TTI (first TTI). Although examples in which a short TTI is comprised of fewer symbols than a long TTI, and in which each symbol has the same symbol duration as in a long TTI will be described below, these example can be adequately applied even when a short TTI adopts a symbol duration that is different from that of a long TTI.

Also, according to the present embodiment, long TTIs and/or short TTIs can be applied to DL communication, in which user terminals receive signals from radio base stations, UL communication, in which user terminals transmit signals to radio base stations, and side-link (SL) receipt or transmission in inter-terminal communication (D2D (Device to Device) communication), in which signals are transmitted and received between user terminals. In the following description, when reference is made simply to "DL communication," this may include SL receipt. Likewise, in case reference is made simply to "UL communication," this may include SL transmission. Following this manner, when simply "DL data" and/or "UL data" are mentioned, SL data may be included.

Also, a user terminal, according to the present embodiment, may be a user terminal to use long TTIs and short TTIs, or may be a user terminal to use either long TTIs or short TTIs.

In accordance with a first aspect of the present invention, the method for configuring sTTIs and an sPDCCH in the event a downlink control channel (sPDCCH) for short TTIs (sTTIs) can be allocated to an existing PDCCH field will be described. In the following description, a case where the time field for an sTTI is constituted by two symbols and a case where the time field for an sTTI is constituted by seven symbols (one slot) will be exemplified, but the number of symbols applicable to sTTIs is not limited to this.

<FIG> is a diagram to show an example of the method of configuring an existing PDCCH, an sPDCCH and sTTIs in a subframe. An existing PDCCH is placed in a predetermined number of symbols (for example, any of one to three symbols) from the top of a subframe, per long TTI. In the case shown in <FIG>, an existing PDCCH is allocated to the first symbol of a subframe (CFI=<NUM>).

The sTTIs, in which the TTI duration is two symbols, can be placed from the top of the subframe. In this case, up to seven sTTIs (sTTI #<NUM> to #<NUM>) can be placed in one subframe (long TTI). In addition, downlink control information that commands scheduling of sTTIs can be transmitted using the sPDCCH allocated to the first-half symbol of each sTTI.

In this case, the radio base station controls allocation so that a PDCCH and an sPDCCH are multiplexed in the first-half symbol (symbol #<NUM>) of sTTI #<NUM> located at the top of the subframe. The PDCCH and the sPDCCH can be multiplexed based on at least one of FDM, TDM, CDM and so on. Also, assume that the PDCCH and the sPDCCH are transmitted using the same antenna port, and a user terminal may demodulate the sPDCCH using the same cell-specific reference signal (CRS) as that of the PDCCH. In this case, transmission encoding diversity technique such as SFBC and/or others may be used depending on the number of CRS-transmitting antenna ports. Also, in the event an sPDCCH is multiplexed over a PDCCH symbol, the sPDCCH may be formed with units of resource element groups (REGs), like the PDCCH, and the same interleaving as that applied to the PDCCH may be applied to the sPDCCH. By making these arrangements, an sPDCCH and a PDCCH can be readily multiplexed on the same symbol so as not to collide with each other.

<FIG> shows a case where a given sTTI (here sTTI #<NUM>) provided in a subframe is placed across the slot boundary (placed to cross the slot boundary) in the subframe (pattern <NUM>-<NUM>-<NUM>). In this way, sTTIs can be allocated flexibly regardless of slot boundaries.

<FIG> shows a case where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>) (pattern <NUM>-<NUM>-<NUM>). In this case, the existing PDCCH is placed in two symbols constituting sTTI #<NUM>, which is located at the top of the subframe. The radio base station can control the allocation so that data is not allocated to (scheduled in) this sTTI #<NUM>. The user terminal can control the receiving operation on assumption that no data is allocated to this sTTI #<NUM>.

The radio base station may execute allocation so that a PDCCH and an sPDCCH are multiplexed in sTTI #<NUM> (symbols #<NUM> and #<NUM>). In this case, the radio base station may transmit an sPDCCH, which commands allocation of data to sTTI #<NUM> (symbols #<NUM> and #<NUM>), using symbol #<NUM> and/or symbol #<NUM> of sTTI #<NUM>. The user terminal can perform receiving processes on assumption that scheduling-commanding downlink control information that addresses sTTI #<NUM> is included in the sPDCCH that is transmitted in sTTI #<NUM> (symbol #<NUM> and/or symbol #<NUM>).

For example, <FIG> shows a case where downlink control information that commands scheduling of sTTI #<NUM> is included in the sPDCCH allocated to sTTI #<NUM> (symbols #<NUM> and #<NUM>) and transmitted, and where no sPDCCH is allocated to sTTI #<NUM>. In this case, it is possible to make the resource for allocating an sPDCCH in sTTI #<NUM> (symbol #<NUM>) unnecessary, so that the efficiency of the use of resources can be improved.

<FIG> shows a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>) (pattern <NUM>-<NUM>-<NUM>). In this case, the existing PDCCH is placed in two symbols constituting sTTI #<NUM>, which is located at the top of the subframe, and the first-half symbol of sTTI #<NUM>. Consequently, the radio base station can control the allocation so that data is not allocated to (scheduled in) this sTTI #<NUM>. The user terminal can control the receiving operation on assumption that no data is allocated to this sTTI #<NUM>.

The radio base station may execute allocation so that a PDCCH and an sPDCCH are multiplexed in sTTI #<NUM> (symbols #<NUM> and #<NUM>) and in the first-half field (symbol #<NUM>) of sTTI #<NUM>. In this case, the radio base station may transmit an sPDCCH that schedules sTTI #<NUM> (symbol #<NUM>) by using part or all of symbols #<NUM> and #<NUM>, which constitute sTTI #<NUM>, and symbol #<NUM>, which constitutes sTTI #<NUM>. The user terminal can perform receiving processes on assumption that downlink control information to command scheduling for sTTI #<NUM> is included in the sPDCCH that is transmitted in one of symbols #<NUM> to #<NUM>.

Note that control may be exerted here so that sTTI #<NUM> is not used (for example, no sPDCCH is allocated) when an existing PDCCH is allocated to two or more symbols from the top of a subframe (CFI=<NUM> or greater).

<FIG> above show cases where a given sTTI (for example, sTTI #<NUM>) is placed across the boundary between two slots constituting a subframe (slot boundary), but it is equally possible to place an sTTI not to cross the slot boundary. By this means, scheduling can be readily controlled in units of slots. For example, even if there is a user terminal that executes frequency hopping (also referred to as "interleaving," "distribution," and so on) of allocating PRBs between slots, there is no need to change the PRBs constituting a predetermined sTTI that crosses the slot boundary (for example, sTTI #<NUM>) between symbols, so that degradation of demodulation performance can be prevented.

<FIG> is a diagram to show examples of methods of configuring sPDCCHs and sTTIs where no sTTI crosses the slot boundary. <FIG> shows cases where an existing PDCCH is allocated to the first one symbol of a subframe (CFI=<NUM>).

To place the sTTIs not to cross the slot boundary, a structure is employed here in which predetermined sTTIs are placed at the top of the subframe (first-half slot) and at the top of the second-half slot. In this case, if sTTIs that each correspond to two symbols are placed in each slot (seven symbols), one symbol remains. Consequently, one of the sTTIs may be associated with three symbols and configured. Alternatively, all sTTIs may be made two symbols, and the user terminal may perform receiving processes on assumption that symbols not belonging to any sTTI are blank (meaning that no sPDSCH or sPDCCH is placed).

<FIG> shows a structure in which three symbols are associated with sTTI #<NUM> and sTTI #<NUM>, placed at the end of each slot (pattern <NUM>-<NUM>-<NUM>), a structure in which three symbols are associated with sTTI #<NUM> and sTTI #<NUM>, placed in the middle of each slot (pattern <NUM>-<NUM>-<NUM>), and a structure in which three symbols are associated with sTTI #<NUM> and sTTI #<NUM>, placed at the top of each slot (pattern <NUM>-<NUM>-<NUM>). In this way, by placing the same number of sTTI symbols in the first-half slot and in the second-half slot, the location of the symbol where the user terminal starts blind decoding the sPDCCH in each sTTI can be made common between slots. This makes it possible to reduce the processes the user terminal has to perform in relationship to blind decoding of the sPDCCH, to reduce the circuit scale, and to reduce the battery consumption. Obviously, the number of sTTI symbols to place in the first-half slot and the second-half slot may be configured separately.

Also, when an sTTI is associated with three symbols, it naturally follows that this sTTI can be configured to transmit DL data using more than two symbols. In this case, the sTTI may be configured so that an sPDCCH is allocated to one of two symbols (for example, the first symbol), and DL data is allocated to two symbols (for example, the second and third symbols) (see <FIG>). That is, instead of allocating DL data, an sPDCCH alone may be allocated to the first symbol. In this case, a lot of resources can be reserved to map the sPDCCH, so that the sPDCCH's received quality can be improved. Also, given that no sPDCCH is multiplexed over the symbols of DL data, the efficiency of DL data resources can be improved compared to when other two-symbol sTTIs are used.

Alternatively, when an sTTI is associated with three symbols, the number of symbols to use for DL transmission (sPDCCH, DL data and so on) may be kept at two (for example, the first and second symbols from the top), and the rest of the symbols (for example, the third symbol from the top) may not be used (see <FIG>). In this case, the sTTI, regardless of where it is located, can be subject to receiving and demodulation processes as a two-symbol sTTI, so that it is possible to reduce the processes in the user terminal, reduce the circuit scale, and reduce the battery consumption. Note that, in the following description, the structures of <FIG> can be used when an sTTI is associated with three symbols.

<FIG> shows cases where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>).

In this case, in patterns <NUM>-<NUM>-<NUM> and <NUM>-<NUM>-<NUM>, an existing PDCCH is placed in the two symbols that constitute sTTI #<NUM>, located at the top of a subframe. Consequently, the radio base station can control the allocation so that data is not allocated to this sTTI #<NUM>. The user terminal can control the receiving operation on assumption that no data is allocated to this sTTI #<NUM>.

Note that the radio base station may execute allocation so that a PDCCH and an sPDCCH are multiplexed in sTTI #<NUM> (symbols #<NUM> and #<NUM>). In this case, the radio base station may transmit an sPDCCH (sDCI) that schedules sTTI #<NUM> (symbols #<NUM> and #<NUM>) by using symbol #<NUM> and/or symbol #<NUM> of sTTI #<NUM>. The user terminal can perform receiving processes on assumption that scheduling-commanding downlink control information that addresses sTTI #<NUM> is included in the sPDCCH that is transmitted in sTTI #<NUM> (symbol #<NUM> and/or symbol #<NUM>).

Furthermore, in pattern <NUM>-<NUM>-<NUM>, sTTI #<NUM>, located at the top of a subframe, can be associated with three symbols, so that the radio base station can allocate data to this sTTI #<NUM> (for example, symbol #<NUM>). In this case, the radio base station can transmit an sPDCCH that commands allocation of data to sTTI #<NUM> (symbol #<NUM>), by using symbol #<NUM> and/or symbol #<NUM> of sTTI #<NUM>.

<FIG> shows a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>).

In this case, in pattern <NUM>-<NUM>-<NUM>, too, an existing PDCCH is placed in symbols that constitute sTTI #<NUM>, located at the top of a subframe. Consequently, the radio base station can control the allocation so that data is not allocated to this sTTI #<NUM>. The user terminal can control the receiving operation on assumption that no data is allocated to this sTTI #<NUM>.

The radio base station may transmit an sPDCCH that commands allocation of data to sTTI #<NUM> by using at least one of symbols #<NUM> to #<NUM>. The user terminal can perform receiving processes on assumption that downlink control information to command scheduling of sTTI #<NUM> is included in the sPDCCH that is transmitted in at least one of symbols #<NUM> to #<NUM>.

Note that, although the user terminal learns the number of PDCCH symbols in each subframe based on the PCFICH (CFI) transmitted in the first symbol of each subframe, the user terminal may learn the number of PDCCH symbols, semi-statically, based on RRC signaling, instead of the CFI. At this time, based on the number of PDCCH symbols learned, the user terminal may select an sTTI pattern, in which the number of PDCCH symbols matches the number learned, from sTTI patterns including the sTTI patterns described so far, and perform receiving processes accordingly. In this case, the location of the symbol where the sPDCCH receiving and decoding processes start in each sTTI can be determined based on the sTTI pattern.

<FIG> is a diagram to show examples of methods of configuring an existing PDCCH, an sPDCCH and sTTIs (one slot) in a subframe. <FIG> shows a case where an existing PDCCH is allocated to the first one symbol of a subframe (CFI=<NUM>), a case where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>), and a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>).

If the TTI duration of sTTIs is made one slot, sTTIs (here, sTTIs #<NUM> and #<NUM>) to be placed in a subframe can be placed not to cross the slot boundary in the subframe. Thus, even when short TTIs are used, scheduling can be controlled on a per slot basis.

sTTIs of a TTI duration of one slot (seven symbols) can be placed in both the first-half slot (first slot) and the second-half slot (second slot) that constitute a subframe. In this case, a structure is employed in which two sTTIs (sTTIs #<NUM>-#<NUM>) are placed in one subframe (long TTI). An sPDCCH to transmit downlink control information that commands scheduling of sTTIs can be allocated to symbols constituting each sTTI.

The radio base station can control the allocation so that an existing PDCCH and an sPDCCH are multiplexed in sTTI #<NUM>, which is placed in the first-half slot. The PDCCH and the sPDCCH can be multiplexed using at least one of FDM, TDM, CDM and others. Furthermore, the field (time field) where the sPDCCH is allocated may be configured in association with the field (CFI) where the PDCCH is allocated.

Meanwhile, the sPDCCH-allocating field in sTTI #<NUM>, placed in the second-half slot, may be determined independently of the PDCCH-allocating field. <FIG> shows a case where the sPDCCH-allocating field in sTTI #<NUM> is one symbol (here, symbol #<NUM>) irrespective of the PDCCH-allocating field (CFI).

Note that the field for allocating an sPDCCH, provided in sTTI #<NUM>, needs not be one symbol, and can be changed as appropriate. For example, as shown in <FIG>, in sTTI #<NUM>, an sPDCCH may be placed up to the second symbol or the third symbol from the top of the second-half slot. The sPDCCH-allocating field provided in sTTI #<NUM>, which is placed in the second-half slot, may be configured via higher layer signaling such as RRC signaling, or may be configured in alignment with the allocation field (for example, the CFI) in sTTI #<NUM>, which is placed in the first-half slot.

In existing systems, the number of OFDM symbols occupied by the PDCCH is determined depending on, for example, the number of RBs (NRBDL) occupied by DL transmission (see <FIG>). For example, when the number of RBs is ten or less, the number of PDCCH symbols is two or more, and four at maximum (one is not applicable). Therefore, according to the first aspect of the present invention, it is possible to identify the field for allocating an sPDCCH (that is, judge whether or not this field is two symbols or greater), located at the top of a subframe, based on the number of RBs configured for use for DL transmission. For example, if the number of RBs configured for use for DL transmission is ten or less, the user terminal can judge that the sPDCCH-allocating field configured in sTTI #<NUM> is two symbols or greater (one symbol is not applicable), and control receiving processes accordingly.

In accordance with a second aspect of the present invention, the method of configuring sTTIs and sPDCCHs for use when a downlink control channel (sPDCCH) for short TTIs (sTTIs) is not allocated to an existing PDCCH field (that is, not transmitted in the time field of an existing PDCCH) will be described. In the following description, a case where the time field for an sTTI is constituted by two symbols and a case where it is constituted by seven symbols (one slot) will be exemplified, but these cases are by no means limiting. According to the second aspect, an sPDCCH and a PDCCH can be multiplexed so as to be orthogonal to each other in time, so that the sPDCCH can be precoded differently than the PDCCH, the sPDCCH can adopt a channel structure that is totally different from that of the PDCCH, and so on. By this means, more flexible sTTI control can be performed.

<FIG> is a diagram to show examples of methods of configuring an existing PDCCH, sPDCCHs and sTTIs in a subframe. <FIG> shows a case where an existing PDCCH is allocated to the first one symbol of a subframe (CFI=<NUM>), a case where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>), and a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>).

sTTIs can be placed from the symbol after the time field (for example, symbol) the PDCCH is allocated. For example, if the CFI shows <NUM>, it is possible to start placing sTTIs from symbol #<NUM>. In this case, up to six sTTIs (sTTIs #<NUM> to #<NUM>) can be placed in one subframe, not including the PDCCH-allocating field (here, symbol #<NUM>). Also, sPDCCHs, which transmit downlink control information that commands scheduling of sTTIs, can be allocated from the top symbol (or the first-half symbol) of each sTTI. Obviously, sPDCCHs can be allocated in the second-half symbol, not the top symbol, of each sTTI.

<FIG> shows cases where a given sTTI (sTTI #<NUM> in the event of CFI=<NUM> and <NUM>, sTTI #<NUM> in the event of CFI=<NUM>, and so on), provided in a subframe, is placed across the slot boundary (to cross the slot boundary) in the subframe. By this means, sTTIs can be allocated flexibly irrespective of slot boundaries.

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is thirteen. In this case, one of the sTTIs may be configured in association with three symbols. For example, a structure may be employed here in which sTTI #<NUM>, which is placed first among a number of sTTIs, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>). Alternatively, a structure may be employed in which an sTTI that comes after sTTI #<NUM> (for example, sTTI #<NUM>) is associated with three symbols (pattern <NUM>-<NUM>-<NUM>).

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is twelve. In this case, a structure may be employed in which sTTIs #<NUM> to #<NUM> are each associated with two symbols (pattern <NUM>-<NUM>-<NUM>).

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is eleven. In this case, one of the sTTIs may be configured in association with three symbols. For example, a structure may be employed here in which sTTI #<NUM>, which is placed first among a number of sTTIs, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>). Alternatively, a structure may be employed in which an sTTI that comes after sTTI #<NUM> is associated with three symbols.

Although cases have been described above with reference to <FIG> where sTTIs are placed across the boundary between two slots that constitute a subframe (slot boundary), it is equally possible to arrange sTTIs so that no one sTTI crosses the slot boundary (sTTIs are confined and placed within slots). By this means, scheduling can be readily controlled in units of slots. For example, even if there is a user terminal that executes frequency hopping (also referred to as "interleaving," "distribution," and so on) of allocating PRBs between slots, there is no need to change the PRBs of a predetermined sTTI that crosses the slot boundary (for example, sTTI #<NUM>) between symbols, so that degradation of demodulation performance can be prevented.

<FIG> is a diagram to show examples of methods of configuring sPDCCHs and sTTIs, for use when sTTIs are placed to be confined within each slot. <FIG> shows cases where an existing PDCCH is allocated to the first one symbol of a subframe (CFI=<NUM>).

When sTTIs are to be placed not to cross slot boundaries, in the first-half slot of a subframe, sTTIs are placed in fields other than the field where the PDCCH is allocated. In the second-half slot of the subframe, sTTIs can be placed from the first symbol (symbol #<NUM> in <FIG>).

In the event of CFI=<NUM>, the number of symbols where sTTIs can be placed in the first-half slot is six. In this case, a structure may be employed in which sTTIs #<NUM> to #<NUM>, placed in the first-half slot, are each associated with two symbols. Meanwhile, the number of symbols where sTTIs can be placed in the second-half slot is seven. In this case, one of sTTIs #<NUM> to #<NUM>, placed in the second-half slot, may be configured in association with three symbols.

<FIG> shows a structure in which sTTI #<NUM>, placed at the top of the second-half slot, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>), a structure in which sTTI #<NUM>, placed at the center of the second-half slot, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>), and a structure in which sTTI #<NUM>, placed at the end of the second-half slot, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>). The pattern to apply may be configured on a fixed basis, or may be configured in a variable manner. Also, different patterns may be applied on a per user terminal basis. In this case, it is possible to distribute sPDCCH resources, and improve the capacity per carrier.

In the event of CFI=<NUM>, the number of symbols where sTTIs can be placed in the first-half slot is five (see <FIG>). In this case, one of sTTIs #<NUM> and #<NUM>, placed in the first-half slot, may be configured in association with three symbols. Also, the number of symbols where sTTIs can be placed in the second-half slot is seven as in the event of CFI=<NUM>. In this case, one of sTTIs #<NUM> to #<NUM>, placed in the second-half slot, may be configured in association with three symbols.

<FIG> shows a structure, in which sTTI #<NUM>, placed at the end of the first-half slot, and sTTI #<NUM>, placed at the end of the second-half slot, are each associated with three symbols, (pattern <NUM>-<NUM>-<NUM>), a structure, in which sTTI #<NUM>, placed at the end of the first-half slot, and sTTI #<NUM>, placed at the center of the second-half slot, are each associated with three symbols (pattern <NUM>-<NUM>-<NUM>), and a structure, in which sTTI #<NUM>, placed at the end of the first-half slot, and sTTI #<NUM>, placed at the top of the second-half slot, are each associated with three symbols (pattern <NUM>-<NUM>-<NUM>).

Also, <FIG> shows a structure, in which sTTI #<NUM>, placed at the top of the first-half slot, and sTTI #<NUM>, placed at the end of the second-half slot, are each associated with three symbols (pattern <NUM>-<NUM>-<NUM>), a structure, in which sTTI #<NUM>, placed at the top of the first-half slot, and sTTI #<NUM>, placed at the center of the second-half slot, are each associated with three symbols (pattern <NUM>-<NUM>-<NUM>), and a structure, in which sTTI #<NUM>, placed at the top of the first-half slot, and sTTI #<NUM>, placed at the top of the second-half slot, are each associated with three symbols (pattern <NUM>-<NUM>-<NUM>). The pattern to apply may be configured on a fixed basis, or may be configured in a variable manner.

In the event of CFI=<NUM> (see <FIG>), the number of symbols where sTTIs can be placed in the first-half slot is four. In this case, a structure may be employed in which sTTIs #<NUM> and #<NUM>, placed in the first-half slot, are associated with two symbols. Meanwhile, the number of symbols where sTTIs can be placed in the second-half slot is seven. In this case, one of sTTI #<NUM> to #<NUM>, placed in the second-half slot, may be configured in association with three symbols.

<FIG> shows a structure, in which sTTI #<NUM>, placed at the end of the second-half slot, is associated with three symbols (pattern <NUM>-<NUM>), a structure, in which sTTI #<NUM>, placed at the center of second-half slot, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>), and a structure, in which sTTI #<NUM>, placed at the top of second-half slot, is associated with three symbols (pattern <NUM>-<NUM>-<NUM>). The pattern to apply may be configured on a fixed basis, or may be configured in a variable manner.

<FIG> is a diagram to show examples of methods of configuring an existing PDCCH, sPDCCHs and sTTIs (one slot) in a subframe. <FIG> shows a case where an existing PDCCH is allocated to the first symbol of a subframe (CFI=<NUM>), a case where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>), and a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>).

<FIG> shows cases where a given sTTI (here, sTTI #<NUM>) provided in a subframe is placed across the slot boundary (to cross the slot boundary) within the subframe.

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is thirteen. In this case, one of two sTTIs #<NUM> and #<NUM> can be configured in association with seven symbols, and the other sTTI can be configured in association with six symbols. For example, sTTI #<NUM>, which is the first one to be placed between two sTTIs, can be configured in association with seven symbols (pattern <NUM>-<NUM>-<NUM>).

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is twelve. In this case, one of two sTTIs #<NUM> and #<NUM> can be configured in association with seven symbols, and the other sTTI can be configured in association with five symbols. For example, sTTI #<NUM>, which is the first one to be placed between two sTTIs, can be configured in association with seven symbols (pattern <NUM>-<NUM>-<NUM>). Alternatively, two sTTIs #<NUM> and #<NUM> may be each associated with six symbols.

In the event of CFI=<NUM>, the number of symbols where the PDCCH is not allocated (and where sTTIs can be placed) is eleven. In this case, one of two sTTIs #<NUM> and #<NUM> can be configured in association with seven symbols, and the other sTTI can be configured in association with four symbols. For example, sTTI #<NUM>, which is the first one to be placed between two sTTIs, can be configured in association with seven symbols (pattern <NUM>-<NUM>-<NUM>). Alternatively, one of two sTTIs #<NUM> and #<NUM> may be associated with six symbols, and the other one may be associated with five symbols.

In this manner, the sTTI that is located in the first half is associated with seven symbols, so that the capacity of the first-half sTTI contained in a subframe can be increased. It then follows that, when the radio base station determines the scheduling of data on a per subframe basis, by allowing more to be scheduled in the first-half sTTI of each subframe, it is possible to reduce delays in scheduling as viewed from user terminals.

Although cases have been described above with reference to <FIG> where sTTIs are placed across the boundary between two slots that constitute a subframe (slot boundary), it is equally possible to arrange sTTIs so that no one sTTI crosses the slot boundary.

<FIG> is a diagram to show an example of a method for configuring sPDCCH and sTTI when no sTTI crosses the slot boundary. <FIG> shows a case where an existing PDCCH is allocated to the first symbol of a subframe (CFI=<NUM>), a case where an existing PDCCH is allocated from the top of a subframe to the second symbol (CFI=<NUM>), and a case where an existing PDCCH is allocated from the top of a subframe to the third symbol (CFI=<NUM>).

To place sTTIs not to cross the slot boundary, in the first-half slot of a subframe, an sTTI is placed in fields (for example, symbols) other than the field where the PDCCH is allocated. In the second-half slot of the subframe, one sTTI (for example, sTTI #<NUM>) can be placed.

In the event of CFI=<NUM>, the number of symbols where an sTTI can be placed in the first-half slot is six. In this case, sTTI #<NUM>, placed in the first-half slot, can be associated with six symbols (pattern <NUM>-<NUM>-<NUM>). Meanwhile, the number of symbols where an sTTI can be placed in the second-half slot is seven. In this case, sTTI #<NUM>, placed in the second-half slot, is configured in association with seven symbols.

In the event of CFI=<NUM>, the number of symbols where an sTTI can be placed in the first-half slot is five. In this case, sTTI #<NUM>, placed in the first-half slot, can be configured in association with five symbols (pattern <NUM>-<NUM>-<NUM>). Meanwhile, the number of symbols where an sTTI can be placed in the second-half slot is seven. In this case, sTTI #<NUM>, placed in the second-half slot, is configured in association with seven symbols.

In the event of CFI=<NUM>, the number of symbols where an sTTI can be placed in the first-half slot is four. In this case, sTTI #<NUM>, placed in the first-half slot, can be configured in association with four symbols (pattern <NUM>-<NUM>-<NUM>). Meanwhile, the number of symbols where an sTTI can be placed in the second-half slot is seven. In this case, sTTI #<NUM>, placed in the second-half slot, is configured in association with seven symbols.

In this way, scheduling can be controlled in units of slots by confining and configuring sTTIs within slots. Also, the symbols of the sTTI that is placed in the second-half slot can be configured irrespective of the field where the PDCCH is allocated (CFI value). Furthermore, since it becomes easy to schedule DL data in units of slots, it is possible to reduce delays in scheduling as viewed from user terminals.

In accordance with a third aspect of the present invention, the method of reporting the pattern of allocating sTTIs (configuration method) and/or the pattern of allocating sPDCCHs in each sTTI to user terminals will be described.

The pattern of allocating sTTIs and/or the pattern of allocating sPDCCHs can be reported from the radio base station to user terminals by an explicit and/or implicit reporting method. Higher layer signaling (for example, RRC signaling, broadcast information, and so on) and/or downlink control information (for example, existing DCI (slow DCI) and so on) can be used as explicit reporting methods. As for implicit reporting methods, method in which user terminals make decisions based on blind decoding, the conditions of the physical layer, and so on can be used.

For example, a user terminal can identify the field (the number of symbols) where an existing PDCCH is allocated, by using predetermined physical signaling (PCFICH) and/or higher layer signaling. As for the method of reporting the field for allocating an existing PDCCH through higher layer signaling, operations of SCells in existing carrier aggregation can be used. Hereinafter, examples of methods of configuring/reporting resources (time resources and frequency resources) for allocating sPDCCHs will be described with reference to the accompanying drawings. Note that each reporting method may be applied individually or in combination.

The radio base station can configure the allocation of time resources (time-domain resource allocation) for sPDCCHs in user terminals on a semi-static basis or on a fixed basis. For example, the radio base station configures time resource for sPDCCHs in user terminals via higher layer signaling. Alternatively, resources may be configured in advance, on a fixed basis, by specification.

<FIG> show examples of configuring (or re-configuring) time resources for sPDCCHs in user terminals via higher layer signaling. <FIG> shows a case where an sTTI is constituted by two symbols, and <FIG> shows a case where an sTTI is constituted by one slot. Also, <FIG> show cases where sTTIs are allowed to be allocated to the PDCCH field (first aspect).

When sTTIs are each constituted by two symbols, the sPDCCH in each sTTI can be allocated using one or two symbols. When sTTIs are constituted by one slot, the sPDCCH in each sTTI can be allocated using one to three symbols, or one slot. Note that sPDCCHs and DL data (for example, sPDSCH) can be multiplexed using at least one of FDM, TDM and CDM, or using a combination of these.

<FIG> shows a case where, when an sPDCCH is configured in one symbol in sTTIs in which an existing PDCCH is allocated (for example, sTTI #<NUM> to #<NUM>), this one symbol is changed to two symbols by higher layer signaling. Note that, when an sTTI (for example, sTTI #<NUM>) is configured in a field to overlap with the field where an existing PDCCH is allocated, the time resource for the sPDCCH in that sTTI may be configured based on the field the PDCCH is allocated (CFI) (as when allocated in the same field as the existing PDCCH).

<FIG> shows a case where, when an sPDCCH is configured in one symbol in sTTIs in which an existing PDCCH is allocated (for example, sTTI #<NUM> to #<NUM>), this one symbol is changed to three symbols by higher layer signaling. Note that, when an sTTI (for example, sTTI #<NUM>) is configured in a field to overlap with the field where an existing PDCCH is allocated, the time resource for the sPDCCH in that sTTI may be configured based on the field the PDCCH is allocated (CFI) (as when allocated in the same field as the existing PDCCH).

<FIG> show cases where sTTIs are not allowed to be allocated in the PDCCH field (second aspect). <FIG> shows a case where an sTTI is constituted by two symbols, and <FIG> shows a case where an sTTI is constituted by one slot.

When an sTTI is constituted by two symbols, the sPDCCH in each sTTI can be allocated using one or two symbols. If an sTTI is constituted by one slot, the sPDCCH in each sTTI can be allocated using one to three symbols, or one slot. Note that sPDCCHs and DL data (for example, sPDSCH) can be multiplexed using at least one of FDM, TDM and CDM, or using a combination of these.

<FIG> shows a case where, when an sPDCCH is configured in one symbol in sTTIs (for example, sTTI #<NUM> to #<NUM>), this one symbol is changed to two symbols by higher layer signaling. <FIG> shows a case where, when an sPDCCH is configured in one symbol in sTTIs (for example, sTTI #<NUM> to #<NUM>), this one symbol is changed to two symbols by higher layer signaling.

A user terminal can receive the sPDCCH in each sTTI based on information related to allocation of sPDCCHs, which is reported via higher layer signaling.

The radio base station can configure the allocation of time resources for sPDCCHs, in user terminals, on a dynamic basis. For example, the radio base station configures time resources for sPDCCHs, in user terminals, by using downlink control information (also referred to as "slow DCI"), which is contained in an existing PDCCH, other L1/L2 control information, and so on. Note that information related to time resources may be included in downlink control information in the sTTI that overlaps with the field where the PDCCH is allocated.

<FIG> shows an example of a table, in which sCFI values, which report the sPDCCH-allocating field (for example, the number of symbols), and bit values are stipulated. The radio base station can include the sCFI in downlink control information and report this to a user terminal. Based on the sCFI included in the downlink control information, the user terminal identifies the time resource for the sPDCCH allocated in each sTTI.

For example, if an sTTI is constituted by two symbols, if the sCFI value is "<NUM>," the user terminal judges that the sPDCCH is allocated to one symbol in each sTTI, and, if the sCFI value is "<NUM>," the user terminal judges that the sPDCCH is allocated to two symbols in each sTTI (see <FIG>).

Also, if an sTTI is constituted by one slot, if the sCFI value is "<NUM>," the user terminal judges that the sPDCCH is allocated to one symbol in each sTTI, and, if the sCFI value is "<NUM>," the user terminal judges that the sPDCCH is allocated to two symbols in each sTTI (see <FIG>).

In this manner, allocation of sPDCCHs can be controlled dynamically by reporting the time resources for sPDCCHs by using downlink control information (for example, sDCI that is transmitted in the PDCCH).

The value of the sCFI may be reported in the PCFICH, which is included in the first symbol of the subframe. Based on the demodulation result of the PCFICH, the user terminal identifies the CFI value, which represents the number of PDCCH symbols, and the sCFI value, which represents the number of sPDCCH symbols. The values of the CFI and the sCFI may be the same, or may be different. Also, the value of the PCFICH and the corresponding sCFI value may be configured by higher layer signaling such as RRC signaling and so on. By using the PCFICH like this, the signaling overhead incurred by reporting of sCFIs can be reduced.

The radio base station can configure the allocation of frequency resources (frequency-domain resource allocation) for sPDCCHs, in user terminals, in a semi-static manner or in a fixed manner. For example, the radio base station configures the frequency resources for sPDCCHs, in user terminals, via higher layer signaling. Alternatively, sPDCCH frequency resources may be configured in advance, on a fixed basis, by specification. Note that both frequency resources and time resources may be reported via higher layer signaling.

Also, sPDCCH frequency resources may be configured so that common frequency resources are used by predetermined user terminals (that is, the frequency resources may be cell-specific) (see <FIG> shows a structure, in which each sTTI is each constituted by two symbols, and in which the sPDCCH to be transmitted in each sTTI is allocated to predetermined frequency resources per cell.

Alternatively, separate (UE-specific) sPDCCH frequency resources may be configured in each user terminal (see <FIG> shows a structure, in which each sTTI is constituted by two symbols, and in which the sPDCCH to be transmitted in each sTTI is allocated to different frequency resources on a per user terminal basis.

The radio base station can configure the allocation of frequency resources for sPDCCHs, in user terminals, on a dynamic basis. For example, the radio base station configures frequency resources for sPDCCHs, in user terminals, by using downlink control information (also referred to as "slow DCI"), which is contained in an existing PDCCH, or by using other types of L1/L2 control information, and/or the like. Note that information related to frequency resources may be included in downlink control information in the sTTI that overlaps with the field where the PDCCH is allocated. Also, both frequency resources and time resources may be reported in downlink control information.

Similar to above reporting method <NUM>, sPDCCH frequency resources may be configured so that common frequency resources are used by predetermined user terminals (that is, the frequency resources may be cell-specific) (see <FIG> shows a structure, in which each sTTI is each constituted by two symbols, and in which the sPDCCH to be transmitted in each sTTI is allocated to predetermined frequency resources per cell.

In this manner, allocation of sPDCCHs can be controlled dynamically by reporting the frequency resources for sPDCCHs by using downlink control information (for example, sDCI that is transmitted in the PDCCH).

sPDCCH frequency resources may be reported in the PCFICH, which is included in the first symbol of the subframe. Based on the demodulation result of the PCFICH, the user terminal identifies the CFI value, which represents the number of PDCCH symbols, and information related to sPDCCH frequency resources. The information related to sPDCCH frequency resources, corresponding to each PCFICH value, may be reported in advance through higher layer signaling. By using the PCFICH like this, the signaling overhead incurred by reporting of sPDCCH frequency resources can be reduced.

Now, the structure of a radio communication system according to the present embodiment will be described below. In this radio communication system, the radio communication methods according to the above-described embodiments are employed. Note that the radio communication method according to each embodiment described above may be used alone or may be used in combination.

<FIG> is a diagram to show an example of a schematic structure of a radio communication system according to an embodiment of the present invention. A radio communication system <NUM> can adopt carrier aggregation (CA) and/or dual connectivity (DC) to group a plurality of fundamental frequency blocks (component carriers) into one, where the LTE system bandwidth (for example, <NUM>) constitutes one unit. Note that the radio communication system <NUM> may be referred to as "SUPER <NUM>," "LTE-A (LTE-Advanced)," "IMT-Advanced," "<NUM>," "<NUM>," "FRA (Future Radio Access)," "NR (New RAT)" and so on.

The radio communication system <NUM> shown in <FIG> includes a radio base station <NUM> that forms a macro cell C <NUM>, and radio base stations 12a to 12c that are placed within the macro cell C1 and that form small cells C2, which are narrower than the macro cell C1. Also, user terminals <NUM> are placed in the macro cell C1 and in each small cell C2. A structure may be adopted here in which different numerologies (for example, different TTI durations, and/or processing times, and so on) are used between cells. Note that a "numerology" refers to a set of communication parameters that characterize the design of signals in a given RAT and the design of the RAT.

The user terminals <NUM> can connect with both the radio base station <NUM> and the radio base stations <NUM>. The user terminals <NUM> may use the macro cell C1 and the small cells C2, which use different frequencies, at the same time, by means of CA or DC. Also, the user terminals <NUM> can execute CA or DC by using a plurality of cells (CCs) (for example, two or more CCs). Furthermore, the user terminals can use licensed-band CCs and unlicensed-band CCs as a plurality of cells. Note that a structure may be employed here in which an FDD carrier and/or a TDD carrier, which use shortened TTIs, may be included in one of the cells.

Between the user terminals <NUM> and the radio base station <NUM>, communication can be carried out using a carrier of a relatively low frequency band (for example, <NUM>) and a narrow bandwidth (referred to as, for example, an "existing carrier," a "legacy carrier," and so on). Meanwhile, between the user terminals <NUM> and the radio base stations <NUM>, a carrier of a relatively high frequency band (for example, <NUM>, <NUM>, <NUM> to <NUM> and so on) and a wide bandwidth may be used, or the same carrier as that used in the radio base station <NUM> may be used.

A structure may be employed here in which wire connection (for example, means in compliance with the CPRI (Common Public Radio Interface) such as optical fiber, the X2 interface and so on) or wireless connection is established between the radio base station <NUM> and the radio base station <NUM> (or between two radio base stations <NUM>).

The user terminals <NUM> are terminals to support various communication schemes such as LTE, LTE-A and so on, and may be either mobile communication terminals or stationary communication terminals.

In the radio communication system <NUM>, as radio access schemes, OFDMA (orthogonal Frequency Division Multiple Access) can be applied to the downlink (DL), and SC-FDMA (Single-Carrier Frequency Division Multiple Access) can be applied to the uplink (UL). OFDMA is a multi-carrier communication scheme to perform communication by dividing a frequency bandwidth into a plurality of narrow frequency bandwidths (subcarriers) and mapping data to each subcarrier. SC-FDMA is a single-carrier communication scheme to mitigate interference between terminals by dividing the system bandwidth into bands formed with one or continuous resource blocks per terminal, and allowing a plurality of terminals to use mutually different bands. Note that the uplink and downlink radio access schemes are not limited to the combination of these, and OFDMA may be used in the UL.

In the radio communication system <NUM>, a DL data channel (PDSCH (Physical Downlink Shared CHannel), which is also referred to as, for example, a "DL shared channel"), which is shared by each user terminal <NUM>, a broadcast channel (PBCH (Physical Broadcast CHannel)), L1/L2 control channels and so on are used as DL channels. User data, higher layer control information and SIBs (System Information Blocks) are communicated in the PDSCH. Also, the MIB (Master Information Block) is communicated in the PBCH.

The L1/L2 control channels include DL control channels (PDCCH (Physical Downlink Control CHannel), EPDCCH (Enhanced Physical Downlink Control CHannel), and/or other channels), a PCFICH (Physical Control Format Indicator CHannel), a PHICH (Physical Hybrid-ARQ Indicator CHannel) and so on. Downlink control information (DCI), including PDSCH and PUSCH scheduling information, is communicated by the PDCCH. The number of OFDM symbols to use for the PDCCH is communicated by the PCFICH. HARQ delivery acknowledgement information (ACK/NACK) in response to the PUSCH is communicated by the PHICH. The EPDCCH is frequency-division-multiplexed with the PDSCH (downlink shared data channel) and used to communicate DCI and so on, like the PDCCH.

In the radio communication system <NUM>, a UL data channel (PUSCH (Physical Uplink Shared CHannel), which is also referred to as "UL shared channel" and so on), which is shared by each user terminal <NUM>, a UL control channel (PUCCH (Physical Uplink Control CHannel)), a random access channel (PRACH (Physical Random Access CHannel)) and so on are used as UL channels. User data, higher layer control information and so on are communicated by the PUSCH. Uplink control information (UCI (Uplink Control Information)), including at least one of delivery acknowledgment information (ACK/NACK) and radio quality information (CQI) and so on, is transmitted by the PUSCH or the PUCCH. By means of the PRACH, random access preambles for establishing connections with cells are communicated.

<FIG> is a diagram to show an example of an overall structure of a radio base station according to the present embodiment. A radio base station <NUM> has a plurality of transmitting/receiving antennas <NUM>, amplifying sections <NUM>, transmitting/receiving sections <NUM>, a baseband signal processing section <NUM>, a call processing section <NUM> and a communication path interface <NUM>. Note that one or more transmitting/receiving antennas <NUM>, amplifying sections <NUM> and transmitting/receiving sections <NUM> may be provided.

DL data to be transmitted from the radio base station <NUM> to a user terminal <NUM> is input from the higher station apparatus <NUM> to the baseband signal processing section <NUM>, via the communication path interface <NUM>.

In the baseband signal processing section <NUM>, the DL data is subjected to a PDCP (Packet Data Convergence Protocol) layer process, user data division and coupling, RLC (Radio Link Control) layer transmission processes such as RLC retransmission control, MAC (Medium Access Control) retransmission control (for example, an HARQ (Hybrid Automatic Repeat reQuest) transmission process), scheduling, transport format selection, channel coding, an inverse fast Fourier transform (IFFT) process and a precoding process, and the result is forwarded to the transmitting/receiving sections <NUM>. Furthermore, DL control signals are also subjected to transmission processes such as channel coding and an inverse fast Fourier transform, and forwarded to the transmitting/receiving sections <NUM>.

Baseband signals that are precoded and output from the baseband signal processing section <NUM> on a per antenna basis are converted into a radio frequency band in the transmitting/receiving sections <NUM>, and then transmitted. The radio frequency signals having been subjected to frequency conversion in the transmitting/receiving sections <NUM> are amplified in the amplifying sections <NUM>, and transmitted from the transmitting/receiving antennas <NUM>. The transmitting/receiving sections <NUM> can be constituted by transmitters/receivers, transmitting/receiving circuits or transmitting/receiving apparatus that can be described based on general understanding of the technical field to which the present invention pertains. Note that a transmitting/receiving section <NUM> may be structured as a transmitting/receiving section in one entity, or may be constituted by a transmitting section and a receiving section.

Meanwhile, as for UL signals, radio frequency signals that are received in the transmitting/receiving antennas <NUM> are amplified in the amplifying sections <NUM>. The transmitting/receiving sections <NUM> receive the UL signals amplified in the amplifying sections <NUM>.

In the baseband signal processing section <NUM>, user data that is included in the UL signals that are input is subjected to a fast Fourier transform (FFT) process, an inverse discrete Fourier transform (IDFT) process, error correction decoding, a MAC retransmission control receiving process, and RLC layer and PDCP layer receiving processes, and forwarded to the higher station apparatus <NUM> via the communication path interface <NUM>. The call processing section <NUM> performs call processing such as setting up and releasing communication channels, manages the state of the radio base station <NUM> and manages the radio resources.

The communication path interface section <NUM> transmits and receives signals to and from the higher station apparatus <NUM> via a predetermined interface. Also, the communication path interface <NUM> may transmit and receive signals (backhaul signaling) with other radio base stations <NUM> via an inter-base station interface (which is, for example, optical fiber that is in compliance with the CPRI (Common Public Radio Interface), the X2 interface, etc.).

Note that the transmitting/receiving sections <NUM> transmit DL signals (for example, DL control signals (DL control channels), DL data signals (DL data channels, DL shared channels and so on), DL reference signals (DM-RS, CSI-RS and so on), discovery signals, synchronization signals, broadcast signals and so on), and receive UL signals (for example, UL control signals (UL control channels), UL data signals (UL data channels, UL shared channels and so on), UL reference signals and so on).

To be more specific, the transmitting/receiving sections <NUM> transmit information about the pattern of allocating sTTs (configuration method) and/or the pattern of allocating sPDCCHs in each sTTI. For example, the transmitting/receiving sections <NUM> control transmission of information about time resources and/or frequency resources for sPDCCHs (third aspect).

The transmitting/receiving sections of the present invention are constituted by a transmitting/receiving section <NUM> and/or a communication path interface <NUM>.

<FIG> is a diagram to show an example of a functional structure of a radio base station according to the present embodiment. Note that, although <FIG> primarily shows functional blocks that pertain to characteristic parts of the present embodiment, the radio base station <NUM> has other functional blocks that are necessary for radio communication as well. As shown in <FIG>, the baseband signal processing section <NUM> at least has a control section <NUM>, a transmission signal generation section <NUM>, a mapping section <NUM>, a received signal processing section <NUM> and a measurement section <NUM>.

The control section <NUM> controls the whole of the radio base station <NUM>.

The control section <NUM>, for example, controls generation of signals in the transmission signal generation section <NUM>, allocation of signals in the mapping section <NUM>, and so on. Furthermore, the control section <NUM> controls signal receiving processes in the received signal processing section <NUM>, measurements of signals in the measurement section <NUM>, and so on.

The control section <NUM> controls scheduling (for example, resource allocation) of DL signals and/or UL signals. To be more specific, the control section <NUM> controls the transmission signal generation section <NUM>, the mapping section <NUM> and the transmitting/receiving sections <NUM> to generate and transmit DCI (DL assignment) that includes DL data channel scheduling information and DCI (UL grant) that includes UL data channel scheduling information.

The control section <NUM> controls allocation of a PDCCH, which is transmitted in a first TTI (for example, a long TTI), and an sPDCCH, which is transmitted in a second TTI (for example, a short TTI). For example, the control section <NUM> controls allocation of sTTIs and/or a second downlink control channel based on in which time field a first downlink control channel, which is transmitted every first TTI, is allocated (first aspect and second aspect).

The transmission signal generation section <NUM> generates DL signals (DL control channels, DL data channels, DL reference signals such as DM-RSs, and so on) as commanded from the control section <NUM>, and outputs the DL signals to the mapping section <NUM>. The transmission signal generation section <NUM> can be constituted by a signal generator, a signal generating circuit or signal generating apparatus that can be described based on general understanding of the technical field to which the present invention pertains.

The mapping section <NUM> maps the DL signals generated in the transmission signal generation section <NUM> to predetermined radio resources, as commanded from the control section <NUM>, and outputs these to the transmitting/receiving sections <NUM>. The mapping section <NUM> can be constituted by a mapper, a mapping circuit or mapping apparatus that can be described based on general understanding of the technical field to which the present invention pertains.

The received signal processing section <NUM> performs receiving processes (for example, demapping, demodulation, decoding and so on) of received signals that are input from the transmitting/receiving sections <NUM>. Here, the received signals are, for example, UL signals transmitted from the user terminals <NUM> (UL control channels, UL data channels, UL reference signals and so on). For the received signal processing section <NUM>, a signal processor, a signal processing circuit or signal processing apparatus that can be described based on general understanding of the technical field to which the present invention pertains can be used.

The received signal processing section <NUM> outputs the decoded information, acquired through the receiving processes, to the control section <NUM>. For example, the received signal processing section <NUM> outputs at least one of a preamble, control information and UL data, to the control section <NUM>. Also, the received signal processing section <NUM> outputs the received signals, the signals after the receiving processes and so on, to the measurement section <NUM>.

The measurement section <NUM> conducts measurements with respect to the received signal.

The measurement section <NUM> may measure the received power (for example, RSRP (Reference Signal Received Power)), the received quality (for example, RSRQ (Reference Signal Received Quality)), channel states and so on of the received signals. The measurement results may be output to the control section <NUM>.

<FIG> is a diagram to show an example of an overall structure of a user terminal according to the present embodiment. A user terminal <NUM> has a plurality of transmitting/receiving antennas <NUM>, amplifying sections <NUM>, transmitting/receiving sections <NUM>, a baseband signal processing section <NUM> and an application section <NUM>. Note that one or more transmitting/receiving antennas <NUM>, amplifying sections <NUM> and transmitting/receiving sections <NUM> may be provided.

Radio frequency signals that are received in the transmitting/receiving antennas <NUM> are amplified in the amplifying sections <NUM>. The transmitting/receiving sections <NUM> receive the DL signals amplified in the amplifying sections <NUM>. The received signals are subjected to frequency conversion and converted into the baseband signal in the transmitting/receiving sections <NUM>, and output to the baseband signal processing section <NUM>. A transmitting/receiving section <NUM> can be constituted by a transmitters/receiver, a transmitting/receiving circuit or transmitting/receiving apparatus that can be described based on general understanding of the technical field to which the present invention pertains. Note that a transmitting/receiving section <NUM> may be structured as a transmitting/receiving section in one entity, or may be constituted by a transmitting section and a receiving section.

In the baseband signal processing section <NUM>, the baseband signal that is input is subjected to an FFT process, error correction decoding, a retransmission control receiving process and so on. The DL data is forwarded to the application section <NUM>. The application section <NUM> performs processes related to higher layers above the physical layer and the MAC layer, and so on. Also, in the DL data, system information and higher layer control information are also forwarded to the application section <NUM>.

Meanwhile, UL data is input from the application section <NUM> to the baseband signal processing section <NUM>. The baseband signal processing section <NUM> performs a retransmission control transmission process (for example, an HARQ transmission process), channel coding, precoding, a discrete Fourier transform (DFT) process, an IFFT process and so on, and the result is forwarded to the transmitting/receiving sections <NUM>. Baseband signals that are output from the baseband signal processing section <NUM> are converted into a radio frequency band in the transmitting/receiving sections <NUM> and transmitted. The radio frequency signals that are subjected to frequency conversion in the transmitting/receiving sections <NUM> are amplified in the amplifying sections <NUM>, and transmitted from the transmitting/receiving antennas <NUM>.

Note that the transmitting/receiving sections <NUM> receive DL signals (for example, DL control signals (DL control channels), DL data signals (DL data channels, DL shared channels and so on), DL reference signals (DM-RS, CSI-RS and so on), discovery signals, synchronization signals, broadcast signals and so on), and transmit UL signals (for example, UL control signals (UL control channels), UL data signals (UL data channels, UL shared channels and so on), UL reference signals and so on).

To be more specific, the transmitting/receiving sections <NUM> at least receive sPDCCHs, which are transmitted in short TTIs. In addition, the transmitting/receiving sections <NUM> receive information about the allocation pattern of sTTIs (configuration method) and/or the allocation pattern of sPDCCHs in each sTTI. For example, the transmitting/receiving sections <NUM> control receipt of information about time resources and/or frequency resources for sPDCCHs (third aspect).

<FIG> is a diagram to show an example of a functional structure of a user terminal according to the present embodiment. Note that, although <FIG> primarily shows functional blocks that pertain to characteristic parts of the present embodiment, the user terminal <NUM> has other functional blocks that are necessary for radio communication as well. As shown in <FIG>, the baseband signal processing section <NUM> provided in the user terminal <NUM> at least has a control section <NUM>, a transmission signal generation section <NUM>, a mapping section <NUM>, a received signal processing section <NUM> and a measurement section <NUM>.

The control section <NUM> acquires a DL control channel and a DL data channel, transmitted from the radio base station <NUM>, from the received signal processing section <NUM>. To be more specific, the control section <NUM> controls the transmitting/receiving sections <NUM> and the received signal processing section <NUM> to blind-decode the DL control channel and detect the DCI and/or sDCI, transmitted in subframes and/or shortened TTIs, and receive the DL data channel based on the DCI and/or sDCI.

The control section <NUM> controls receipt of a second downlink control channel (sPDCCH) based on in which time field a first downlink control channel (PDCCH), which is transmitted every first TTI (long TTI), is allocated (first aspect and second aspect). For example, the control section <NUM> controls receipt of the second downlink control channel in a first TTI, which includes the time field where the first downlink control channel is allocated, or in a first TTI which does not include the time field where the first downlink control channel is allocated.

The control section <NUM> can determine whether a second TTI is configured over two slots that constitute the first TTI based on the time field where the first downlink control channel is allocated and/or the TTI duration of the second TTI.

In addition, the control section <NUM> can identify the time field and/or the frequency field in which a second downlink control channel, which is transmitted in the second TTI, is allocated, based on higher layer signaling and/or L1/L2 control information.

The transmission signal generation section <NUM> generates UL signals (UL control channels, UL data signals, UL reference signals and so on) as commanded from the control section <NUM>, and outputs these signals to the mapping section <NUM>. The transmission signal generation section <NUM> can be constituted by a signal generator, a signal generating circuit or signal generating apparatus that can be described based on general understanding of the technical field to which the present invention pertains.

The mapping section <NUM> maps the UL signals generated in the transmission signal generation section <NUM> to radio resources as commanded from the control section <NUM>, and output the result to the transmitting/receiving sections <NUM>. The mapping section <NUM> can be constituted by a mapper, a mapping circuit or mapping apparatus that can be described based on general understanding of the technical field to which the present invention pertains.

The received signal processing section <NUM> performs receiving processes (for example, demapping, demodulation, decoding and so on) of received signals that are input from the transmitting/receiving sections <NUM>. Here, the received signals include, for example, DL signals transmitted from the radio base station <NUM> (DL control channels, DL data channels, DL reference signals and so on). The received signal processing section <NUM> can be constituted by a signal processor, a signal processing circuit or signal processing apparatus that can be described based on general understanding of the technical field to which the present invention pertains. Also, the received signal processing section <NUM> can constitute the receiving section according to the present invention.

Based on commands from control section <NUM>, the received signal processing section <NUM> performs blind decoding of a DL control channel, which schedules transmission and/or receipt of a DL data channel, and performs receiving processes for the DL data channel based on this DCI. In addition, the received signal processing section <NUM> estimates channel gain based on the DM-RS or the CRS, and demodulates the DL data channel based on the estimated channel gain.

The received signal processing section <NUM> outputs the decoded information, acquired through the receiving processes, to the control section <NUM>. The received signal processing section <NUM> outputs, for example, broadcast information, system information, RRC signaling, DCI and so on, to the control section <NUM>. The received signal processing section <NUM> may output the decoding result of the data to the control section <NUM>. Also, the received signal processing section <NUM> outputs the received signals, the signals after the receiving processes and so on, to the measurement section <NUM>.

For example, the measurement section <NUM> measures channel states based on reference signals (CSI-RSs) for channel state measurements, transmitted from the radio base station. The measurement section <NUM> may measure, for example, the received signals' received power (for example, RSRP), DL received quality (for example, RSRQ) and so on. The measurement results may be output to the control section <NUM>.

Note that the block diagrams that have been used to describe the above embodiments show blocks in functional units. These functional blocks (components) may be implemented in arbitrary combinations of hardware and/or software. Also, the means for implementing each functional block is not particularly limited. That is, each functional block may be realized by one piece of apparatus that is physically and/or logically aggregated, or may be realized by directly and/or indirectly connecting two or more physically and/or logically separate pieces of apparatus (via wire and/or wireless, for example) and using these multiple pieces of apparatus.

For example, the radio base station, user terminals and so on according to one embodiment of the present invention may function as a computer that executes the processes of the radio communication method of the present invention. <FIG> is a diagram to show an example hardware structure of a radio base station and a user terminal according to one embodiment of the present invention. Physically, the above-described radio base stations <NUM> and user terminals <NUM> may be formed as a computer apparatus that includes a processor <NUM>, a memory <NUM>, a storage <NUM>, communication apparatus <NUM>, input apparatus <NUM>, output apparatus <NUM> and a bus <NUM>.

Furthermore, processes may be implemented with one processor, or processes may be implemented either simultaneously or in sequence, or in different manners, on two or more processors.

Each function of the radio base station <NUM> and user terminal <NUM> is implemented by allowing predetermined software (programs) to be read on hardware such as the processor <NUM> and the memory <NUM>, and by allowing the processor <NUM> to do calculations, the communication apparatus <NUM> to communicate, and the memory <NUM> and the storage <NUM> to read and/or write data.

The processor <NUM> may control the whole computer by, for example, running an operating system. The processor <NUM> may be configured with a central processing unit (CPU), which includes interfaces with peripheral apparatus, control apparatus, computing apparatus, a register and so on. For example, the above-described baseband signal processing section <NUM> (<NUM>), call processing section <NUM> and so on may be implemented by the processor <NUM>.

Furthermore, the processor <NUM> reads programs (program codes), software modules or data, from the storage <NUM> and/or the communication apparatus <NUM>, into the memory <NUM>, and executes various processes according to these.

The memory <NUM> is a computer-readable recording medium, and may be constituted by, for example, at least one of a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), a RAM (Random Access Memory) and/or other appropriate storage media. The memory <NUM> may be referred to as a "register," a "cache," a "main memory" (primary storage apparatus) and so on. The memory <NUM> can store executable programs (program codes), software modules and so on for implementing the radio communication methods according to embodiments of the present invention.

The communication apparatus <NUM> is hardware (transmitting/receiving apparatus) for allowing inter-computer communication by using wired and/or wireless networks, and may be referred to as, for example, a "network device," a "network controller," a "network card," a "communication module" and so on. The communication apparatus <NUM> may be configured to include a high frequency switch, a duplexer, a filter, a frequency synthesizer and so on in order to realize, for example, frequency division duplex (FDD) and/or time division duplex (TDD). For example, the above-described transmitting/receiving antennas <NUM> (<NUM>), amplifying sections <NUM> (<NUM>), transmitting/receiving sections <NUM> (<NUM>), communication path interface <NUM> and so on may be implemented by the communication apparatus <NUM>.

Furthermore, these pieces of apparatus, including the processor <NUM>, the memory <NUM> and others, are connected by a bus <NUM> for communicating information.

Note that the terminology used in this specification and the terminology that is needed to understand this specification may be replaced by other terms that convey the same or similar meanings. For example, "channels" and/or "symbols" may be replaced by "signals (or "signaling"). " Also, "signals" may be "messages. " A reference signal may be abbreviated as an "RS," and may be referred to as a "pilot," a "pilot signal" and so on, depending on which standard applies. Furthermore, a "component carrier (CC)" may be referred to as a "cell," a "frequency carrier," a "carrier frequency" and so on.

Furthermore, a radio frame may be comprised of one or more periods (frames) in the time domain. Each of one or more periods (frames) constituting a radio frame may be referred to as a "subframe. " Furthermore, a subframe may be comprised of one or more slots in the time domain. Furthermore, a slot may be comprised of one or more symbols in the time domain (OFDM (Orthogonal Frequency Division Multiplexing) symbols, SC-FDMA (Single Carrier Frequency Division Multiple Access) symbols, and so on).

A radio frame, a subframe, a slot and a symbol all represent the time unit in signal communication. A radio frame, a subframe, a slot and a symbol may be each called by other applicable names. For example, one subframe may be referred to as a "transmission time interval (TTI)," or a plurality of consecutive subframes may be referred to as a "TTI," and one slot may be referred to as a "TTI. " That is, a subframe and a TTI may be a subframe (<NUM>) in existing LTE, may have a shorter period than <NUM> (for example, one to thirteen symbols), or may have a longer period than <NUM>.

For example, in LTE systems, a radio base station schedules radio resources (such as the frequency bandwidth and transmission power that can be used in each user terminal) to allocate to each user terminal in TTI units. TTIs may be the time unit for transmitting channel-encoded data packets (transport blocks), or may be the unit of processing in scheduling, link adaptation and so on.

A TTI having a time duration of <NUM> may be referred to as a "normal TTI" (TTI in LTE Rel. <NUM> to <NUM>), a "long TTI," a "normal subframe," a "long subframe," and so on. A TTI that is shorter than a normal TTI may be referred to as a "shortened TTI," a "short TTI," a "shortened subframe," a "short subframe," and so on.

A resource block (RB) is the unit of resource allocation in the time domain and the frequency domain, and may include one or a plurality of consecutive subcarriers in the frequency domain. Also, an RB may include one or more symbols in the time domain, and may be one slot, one subframe or one TTI in length. One TTI and one subframe each may be comprised of one or more resource blocks. Note that an RB may be referred to as a "physical resource block (PRB (Physical RB))," a "PRB pair," an "RB pair," and so on.

Note that the above-described structures of radio frames, subframes, slots, symbols and so on are merely examples. For example, configurations such as the number of subframes included in a radio frame, the number of slots included in a subframe, the number of symbols and RBs included in a slot, the number of subcarriers included in an RB, the number of symbols in a TTI, the symbol duration and the cyclic prefix (CP) duration can be variously changed.

Also, the information and parameters described in this specification may be represented in absolute values or in relative values with respect to predetermined values, or may be represented in other information formats. For example, radio resources may be specified by predetermined indices. In addition, equations to use these parameters and so on may be used, apart from those explicitly disclosed in this specification.

For example, since various channels (PUCCH (Physical Uplink Control Channel), PDCCH (Physical Downlink Control Channel) and so on) and information elements can be identified by any suitable names, the various names assigned to these individual channels and information elements are in no respect limiting.

The information, signals and so on that are input and /or output may be stored in a specific location (for example, in a memory), or may be managed in a control table. The information, signals and so on to be input and/or output can be overwritten, updated or appended. The information, signals and so on that are output may be deleted. The information, signals and so on that are input may be transmitted to other pieces of apparatus.

Reporting of information is by no means limited to the aspects/embodiments described in this specification, and other methods may be used as well. For example, reporting of information may be implemented by using physical layer signaling (for example, downlink control information (DCI), uplink control information (UCI)), higher layer signaling (for example, RRC (Radio Resource Control) signaling, broadcast information (the master information block (MIB), system information blocks (SIBs) and so on), MAC (Medium Access Control) signaling and so on), and other signals and/or combinations of these.

Also, reporting of predetermined information (for example, reporting of information to the effect that "X holds") does not necessarily have to be sent explicitly, and can be sent implicitly (by, for example, not reporting this piece of information, or by reporting a different piece of information).

Decisions may be made in values represented by one bit (<NUM> or <NUM>), may be made in Boolean values that represent true or false, or may be made by comparing numerical values (for example, comparison against a predetermined value).

As used herein, the terms "base station (BS)," "radio base station," "eNB," "cell," "sector," "cell group," "carrier," and "component carrier" may be used interchangeably.

A base station can accommodate one or more (for example, three) cells (also referred to as "sectors"). When a base station accommodates a plurality of cells, the entire coverage area of the base station can be partitioned into multiple smaller areas, and each smaller area can provide communication services through base station subsystems (for example, indoor small base stations (RRHs (Remote Radio Heads)). The term "cell" or "sector" refers to part or all of the coverage area of a base station and/or a base station subsystem that provides communication services within this coverage.

Furthermore, the radio base stations in this specification may be interpreted as user terminals. For example, each aspect/embodiment of the present invention may be applied to a structure in which communication between a radio base station and a user terminal is replaced with communication among a plurality of user terminals (D2D (Device-to-Device)). In this case, user terminals <NUM> may have the functions of the radio base stations <NUM> described above. In addition, wording such as "uplink" and "downlink" may be interpreted as "side. " For example, an uplink channel may be interpreted as a side channel.

Certain actions which have been described in this specification to be performed by base station may, in some cases, be performed by higher nodes (upper nodes). In a network comprised of one or more network nodes with base stations, it is clear that various operations that are performed to communicate with terminals can be performed by base stations, one or more network nodes (for example, MMEs (Mobility Management Entities), S-GW (Serving-Gateways), and so on may be possible, but these are not limiting) other than base stations, or combinations of these.

The aspects/embodiments illustrated in this specification may be applied to systems that use LTE (Long Term Evolution), LTE-A (LTE-Advanced), LTE-B (LTE-Beyond), SUPER <NUM>, IMT-Advanced, <NUM> (4th generation mobile communication system), <NUM> (5th generation mobile communication system), FRA (Future Radio Access), New-RAT (Radio Access Technology), NR (New Radio), NX (New radio access), FX (Future generation radio access), GSM (registered trademark) (Global System for Mobile communications), CDMA <NUM>, UMB (Ultra Mobile Broadband), IEEE <NUM> (Wi-Fi (registered trademark)), IEEE <NUM> (WiMAX (registered trademark)), IEEE <NUM>, UWB (Ultra-WideBand), Bluetooth (registered trademark) and other adequate radio communication methods, and/or next-generation systems that are enhanced based on these.

Reference to elements with designations such as "first," "second" and so on as used herein does not generally limit the number/quantity or order of these elements. These designations are used only for convenience, as a method of distinguishing between two or more elements. In this way, reference to the first and second elements does not imply that only two elements may be employed, or that the first element must precede the second element in some way.

As used herein, the terms "connected" and "coupled," or any variation of these terms, mean all direct or indirect connections or coupling between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The coupling or connection between the elements may be physical, logical or a combination thereof. As used herein, two elements may be considered "connected" or "coupled" to each other by using one or more electrical wires, cables and/or printed electrical connections, and, as a number of non-limiting and non-inclusive examples, by using electromagnetic energy, such as electromagnetic energy having wavelengths in radio frequency fields, microwave regions and optical regions (both visible and invisible).

Claim 1:
A terminal (<NUM>) comprising:
a receiving section (<NUM>) adapted to receive a downlink control channel, PDCCH; and
a control section (<NUM>) adapted to control an allocation pattern of transmission time intervals that is applied to a subframe having two slots, each slot having three transmission time intervals each having a different number of symbols, each slot having seven symbols,
wherein the control section (<NUM>) is adapted to perform a receiving process by selecting one allocation pattern from a plurality of allocation patterns depending on a number of symbols allocated to the PDCCH in one subframe, and
wherein each allocation pattern has a transmission time interval formed with three symbols and two transmission time intervals each formed with two symbols.