Patent ID: 12225551

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the claimed invention will be described in detail with reference to the accompanying drawings. Throughout the embodiments, the same elements are assigned the same reference numerals, and any duplicate description of the elements is omitted.

Embodiment 1

(Overview of Communication System)

A communication system according to Embodiment 1 includes base station100and terminal200. This communication system is an LTE-Advanced system, for example. In addition, base station100is a base station compliant with the LTE-Advanced system, and terminal200is a terminal compliant with the LTE-Advanced system, for example.

In Embodiment 1, when transmitting EPDCCH intended for terminal200, base station100can apply soft combining for transmitting EPDCCH (i.e., control information) over a plurality of subframes (see,FIG.2). Receiver side (i.e., terminal200) performs reception processing after combining control information transmitted over a plurality of subframes. The EPDCCH transmitted over a plurality of subframes is formed of a bit sequence that includes an information bit and a redundancy bit and that is generated by performing error correction coding on the information bit. In addition, upon reception of the EPDCCH transmitted over a plurality of subframes, terminal200determines the timing of data reception or transmission upon completion of EPDCCH reception and ACK/NACK (i.e., response signals) transmission or reception.

Higher layer signaling previously configures terminal200with subframes to which soft combining of EPDCCH is applied. The configuration of the subframes may be different for each terminal. In addition, a single frame may include both of the subframes to which soft combining is applied and to which no soft combining is applied. This configuration allows switching between soft combining of EPDCCH and non soft combining thereof depending on reception quality of each subframe in such a way that soft combing is applied to a subframe subject to a large amount of interference while no soft combining is applied to a subframe subject to a small amount of interference.

It should be noted herein that base station100and terminal200can transmit and receive control information (i.e., DL assignment or UL grant) using a PDCCH region or EPDCCH region, but the transmission and reception of control information only in an EPDCCH region will be described hereinafter for simplicity of description.

FIG.3is a block diagram illustrating a main configuration of base station100according to Embodiment 1.

In base station100, configuration section102configures an EPDCCH set formed of ECCEs to which control information (assignment information) transmitted over a plurality of subframes is assigned in the plurality of subframes. Signal assignment section105assigns the control information to any of the ECCEs in on a PRB pair in each of the plurality of subframes.

FIG.4is a block diagram illustrating a main configuration of terminal200according to Embodiment 1.

In terminal200, configuration section205identifies the ECCE to which control information (assignment information) transmitted over a plurality of subframes is assigned and which forms an EPDCCH set configured in the plurality of subframes. Control signal receiving section206receives control information assigned to any of the ECCEs on a PRB pair in each of the plurality of subframes.

(Configuration of Base Station100)FIG.5is a block diagram illustrating a configuration of base station100according to Embodiment 1. InFIG.5, base station100includes assignment information generating section101, configuration section102, error correction coding section103, modulation section104, signal assignment section105, transmission section106, reception section107, demodulation section108, and error correction decoding section109.

Assignment information generating section101determines a resource (i.e., RB) to which data signals are assigned, when downlink data signals (DL data signals) to be transmitted and uplink data signals (UL data signals) to be assigned to uplink are present, and generates assignment information (DL assignment and UL grant). The DL assignment includes information on the assignment of DL data signals. The UL grant includes information on the assignment resource of UL data signals transmitted from terminal200. The DL assignment is outputted to signal assignment section105, and the UL grant is outputted to signal assignment section105and reception section107.

Configuration section102configures each terminal200with one or more EPDCCH search spaces. More specifically, configuration section102configures each terminal200with a PRB pair number for locating an EPDCCH search space, an ECCE index for each aggregation level, and the search space (EPDCCH) assignment method (i.e., localized assignment or distributed assignment). An EPDCCH search space is formed of a plurality of assignment candidates (i.e., EPDCCH candidates). Each “assignment candidate” is formed of the same number of ECCEs as the aggregation level.

Configuration section102assigns an ECCE index for each search space when configuring terminal200with a plurality of EPDCCH search spaces.

Configuration section102configures terminal200to which soft combining is applied, with the subframes to which soft combining is applied (see,FIG.2). In addition, configuration section102configures terminal200to which soft combining is applied, with an EPDCCH set for the plurality of subframes to which soft combing is applied. During this processing, the PRB pair corresponding to the ECCEs forming the EPDCCH set is located in each of the plurality of subframes. Accordingly, in each of the subframes used for soft combining, the search space described above is configured on the basis of the configured EPDCCH set.

Configuration section102outputs information on the configured search space and information on the subframe numbers to which soft combining of EPDCCH is applied to signal assignment section105. The information on the search space includes a PRB pair number, the number of PRB pairs and/or the like, for example. In addition, configuration section102outputs information on the PRB pair configured in the search space, and information on the EPDCCH assignment method to error correction coding section103as control information.

Error correction coding section103takes transmission data signals (i.e., DL data signals), and the control information received from configuration section102as input and performs error correction coding on the input signals and outputs the resultant signals to modulation section104.

Modulation section104performs modulation processing on the signals received from error correction coding section103and outputs the modulated data signals to signal assignment section105.

Signal assignment section105assigns the assignment information (DL assignment and UL grant) received from assignment information generating section101to any of the ECCEs (ECCE in units of assignment candidates) corresponding to the PRB pair number indicated by the search space information received from configuration section102. During this assignment, when soft combining is configured for the assignment information, signal assignment section105assigns the assignment information to any of the ECCEs on a PRB pair in each of a plurality of subframes corresponding to the subframe numbers indicated by the information on soft combining received from configuration section102. Accordingly, the assignment information is assigned to the PRB pair on which ECCE is located (e.g., seeFIG.1). In addition, signal assignment section105assigns the data signals received from modulation section104to a downlink resource corresponding to the assignment information (DL assignment) received from assignment information generating section101.

Transmission signals are thus formed by assignment of the assignment information and data signals to a predetermined resource. The transmission signals thus formed are outputted to transmission section106. In addition, signal assignment section105notifies receiving section107of the ECCE index of ECCE used for transmission of DL assignment. It should be noted herein that, when soft combining is applied, signal assignment section105notifies receiving section107of the ECCE index of ECCE in the end subframe (may be referred to as “last subframe,” hereinafter) among the plurality of subframes used for the transmission of DL assignment.

Transmission section106performs radio transmission processing such as up-conversion on the received signals and transmits the resultant signals to terminal200via an antenna.

Reception section107receives, via an antenna, the signals transmitted from terminal200and outputs the received signals to demodulation section108. More specifically, reception section107demultiplexes the received signals into signals corresponding to the resource indicated by the UL grant received from assignment information generating section101, then performs reception processing such as down-conversion on the signals obtained by demultiplexing and outputs the processed signals to demodulation section108. Reception section107extracts (i.e., receives) A/N signals from signals corresponding to a PUCCH resource associated with the ECCE index received from signal assignment section105.

Demodulation section108performs demodulation processing on the received signals and outputs the resultant signals to error correction decoding section109.

Error correction decoding section109decodes the received signals to obtain the received data signals from terminal200.

(Configuration of Terminal200)

FIG.6is a block diagram illustrating a configuration of terminal200according to Embodiment 1. InFIG.6, terminal200includes reception section201, signal demultiplexing section202, demodulation section203, error correction decoding section204, configuration section205, control signal receiving section206, error correction coding section207, modulation section208, signal assignment section209, and transmission section210.

Reception section201receives, via an antenna, signals transmitted from base station100, then performs reception processing such as down-conversion on the received signals and outputs the processed signals to signal demultiplexing section202.

Signal demultiplexing section202extracts control signals for resource assignment from the received signals to be received from reception section201and outputs the extracted signals to control signal receiving section206. In addition, signal demultiplexing section202extracts, from the received signals, signals corresponding to the data resource indicated by the DL assignment outputted from control signal receiving section206(i.e., DL data signals) and outputs the extracted signals to demodulation section203. When soft combining of EPDCCH is applied, signal demultiplexing section202extracts signals corresponding to the data resource (DL data signals) from the received signals on the basis of the last subframe among the plurality of subframes used for soft combining.

Demodulation section203demodulates the signals outputted from signal demultiplexing section202and outputs the demodulated signals to error correction decoding section204.

Error correction decoding section204decodes the demodulated signals outputted from demodulation section203and outputs the resultant received data signals. In particular, error correction decoding section204outputs the “information on the PRB pair configured in the search space” and “information on the subframes to which soft combining of EPDCCH is applied” to configuration section205.

Configuration section205identifies the search space configured for the terminal using the EPDCCH (i.e., terminal200). Configuration section205first identifies the PRB pair to be configured in the search space, on the basis of the information received from error correction decoding section204, for example. Configuration section205then identifies the EPDCCH to which soft combining is applied, on the basis of the information on the subframes to which soft combining of EPDCCH is applied. Configuration section205then determines the ECCE index of the search space corresponding to the PRB pair. Accordingly, configuration section205identifies the ECCE to which the EPDCCH to be transmitted over a plurality of subframes is assigned (i.e., ECCE forming the EPDCCH set configured in the plurality of subframes). In this processing, when a plurality of EPDCCH search spaces are configured, configuration section205allocates an ECCE index to each search space. Moreover, configuration section205identifies which ECCE index is configured as an EPDCCH candidate for each aggregation level according to rules that are previously determined for each terminal200and is common to base station100and terminal200. For example, configuration section205identifies the ECCE index serving as an EPDCCH candidate for each aggregation level on the basis of the UE ID (i.e., terminal specific ID) and whether or not soft combining is applied. Configuration section205then outputs the information on the PRB pair and ECCE configured as the search space to control signal receiving section206.

Control signal receiving section206performs blind-decoding on the ECCE corresponding to the PRB pair indicated by the information received from configuration section205, thereby detecting the control signals (DL assignment or UL grant) intended for terminal200. More specifically, control signal receiving section206receives the control signals assigned to one of a plurality of assignment candidates forming the search space configured by configuration section205. When soft combining of EPDCCH is applied, control signal receiving section206receives the control signals assigned to any of ECCHs on a PRB pair in a plurality of subframes. Control signal receiving section206outputs the detected DL assignment intended for terminal200to signal demultiplexing section202and outputs the detected UL grant intended for terminal200to signal assignment section209. Control signal receiving section206outputs the ECCE index of the ECCE on which the DL assignment is detected to signal assignment section209.

Error correction coding section207takes the transmission data signals (UL data signals) as input and performs error correction coding on the transmission data signals and outputs the resultant signals to modulation section208.

Modulation section208modulates the signals received from error correction coding section207and outputs the modulated signals to signal assignment section209.

Signal assignment section209assigns the signals received from modulation section208, according to the UL grant received from control signal receiving section206and outputs the resultant signals to transmission section210. When soft combining of EPDCCH is applied, signal assignment section209determines the transmission subframe for the signals on the basis of the last subframe among the plurality of subframes to which soft combining is applied. In addition, signal assignment section209assigns the A/N signals received from error correction decoding section204to a predetermined resource. More specifically, when transmission data signals are present, signal assignment section209multiplexes the A/N signals with the transmission data signals and outputs the resultant signals to transmission section210. Meanwhile, when no transmission data signals are present, signal assignment section209identifies the PUCCH resource on the basis of the ECCE index received from control signal receiving section206, then assigns the A/N signals to the identified PUCCH resource and outputs the resultant signals to transmission section210. During this processing, when soft combining of EPDCCH is applied, signal assignment section209determines the transmission subframe for the A/N signals on the basis of the last subframe among the plurality of subframes to which soft combining is applied.

Transmission section210performs transmission processing such as up-conversion on the received signals and transmits the processed signals.

(Operations of Base Station100and Terminal200)

A description will be provided regarding operations of base station100and terminal200configured in the manner described above.

Hereinafter, a description will be provided for (1) PDSCH timing, (2) uplink A/N signal (UL ACK/NACK) timing, and (3) PUSCH timing when soft combining of EPDCCH is applied.

(PDSCH Timing)

Base station100and terminal200configure the transmission timing of PDSCH specified by the DL assignment notified using the EPDCCH to which soft combining is applied (i.e., subframe on which the PDSCH is located) to be the last subframe among the plurality of subframes on which EPDCCH to be soft-combined is located.

FIG.7illustrates a configuration example of PDSCH timing. As illustrated inFIG.7, when soft combining using two subframes, namely, subframes #0 and #1 is applied, base station100locates PDSCH for terminal200on subframe #1, which is the last subframe among the two subframes. More specifically, as illustrated inFIG.7, a resource in subframe #1 is specified as a PDSCH resource in the DL assignment notified using the EPDCCH located in subframes #0 and #1.

In other words, base station100(i.e., signal assignment section105) assigns the downlink data (PDSCH) the assignment of which is indicated by EPDCCH (DL assignment) to the last subframe among the plurality of subframes used for soft combining.

Meanwhile, inFIG.7, terminal200(i.e., control signal receiving section206) performs blind-decoding on the ECCEs located in subframes #0 and #1 to which soft combining is applied, thereby detecting the DL assignment intended for terminal200. Terminal200(i.e., signal demultiplexing section202) extracts PDSCH (DL data signals) in subframe #1 on the basis of the detected DL assignment.

During this processing, detection of DL assignment to be notified using EPDCCH to which soft combining is applied is performed after reception of the last subframe in terminal200. Upon detection of the DL assignment, terminal200identifies that PDSCH is assigned to the PRB pair specified by the DL assignment and starts reception processing on the PDSCH.

For this reason, if PDSCH is located in a subframe ahead of the last subframe, terminal200needs to store, in a buffer, received signals on all the PRB pairs that may have been assigned to PDSCH until completion of identifying (detecting) the PRB pair assigned to PDSCH.

On the other hand, PDSCH is located in the last subframe among the plurality of subframes to which soft combining is applied in Embodiment 1. Accordingly, the period for saving, in a buffer, the received signals that are received from the reception timing of PDSCH to the completion of EPDCCH detection can be minimized. To put it differently, the period for saving, in a buffer, the received signals that are received from the reception timing of PDSCH to the completion of EPDCCH detection when soft combining of EPDCCH is applied can be the same as the period used when no soft combining of EPDCCH is applied (non soft combining). Thus, it is possible to prevent an increase in the size of the buffer to be included in terminal200.

(UL ACK/NACK Timing) In LTE-Advanced, after reception of PDSCH, terminals perform reception determination (i.e., error determination) and transmit uplink A/N signals (UL ACK/NACK) to base station100(not illustrated). In addition, the subframe used for transmitting uplink A/N signals is previously defined. More specifically, the fourth subframe following the subframe to which PDSCH is assigned is configured as the subframe used for transmitting uplink A/N signals in a frequency division duplex (FDD) system. In a time division duplex (TDD) system, the subframe used for transmitting uplink A/N signals is defined for each TDD UL-DL configuration (i.e., timing configuration in units of subframes for downlink communication (DL) and uplink communication (UL) per frame). In both of the FDD system and TDD system, the transmission timing of uplink A/N signals is always configured to be the fourth or after the fourth subframe following the transmission of PDSCH.

In Embodiment 1, the transmission timing of uplink A/N signals (i.e., subframe used for transmission of UL ACK/NACK) is defined according to the reception subframe for PDSCH (i.e., subframe in which PDSCH is transmitted). The transmission timing of uplink A/N signals is configured to be the fourth subframe following the reception subframe for PDSCH in the FDD system, while the transmission timing of uplink A/N signals is defined according to each TDD UL-DL configuration in the TDD system, using the subframe on which PDSCH is received, as the basis. Uplink A/N signals are transmitted in a PUSCH region when there is PUSCH transmission or transmitted in a PUCCH region when there is no PUSCH transmission.

In LTE-Advanced, when uplink A/N signals are transmitted in a PUCCH region, a PUCCH resource associated with the smallest ECCE number among the ECCEs forming EPDCCH on which DL assignment is located (i.e., EPDCCH subframe on which PDSCH is transmitted) (i.e., implicitly indicated resource) is specified so that the PUCCH resource is automatically (implicitly) assigned to avoid a PUCCH resource collision between terminals.

Thus, base station100and terminal200identify the PUCCH resource associated with the ECCE number of EPDCCH located in the subframe on which PDSCH is transmitted, when soft combining of EPDCCH is applied.

In other words, terminal200transmits A/N signals (response signals) for the downlink data on PUCCH associated with the ECCE located in a subframe to which the downlink data (PDSCH) is assigned among the plurality of subframes used for soft combining, the assignment of the downlink data (PDSCH) being indicated by EPDCCH (DL assignment). Accordingly, when the ECCE number to be assigned varies depending on the subframe, the ECCE associated with the PUCCH resource used for transmission of A/N signals is not necessarily the smallest ECCE number among the ECCEs forming EPDCCH. Likewise, base station100(i.e., reception section107) receives A/N signals (response signals) for the downlink data on PUCCH associated with the ECCE located in a subframe to which the downlink data (PDSCH) is assigned among the plurality of subframes used for soft combining, the assignment of the downlink data (PDSCH) being indicated by EPDCCH (DL assignment).

For example, when PDSCH is located in the last subframe among the plurality of subframes to which soft combining of EPDCCH is applied, base station100and terminal200use the ECCE number of the EPDCCH located in the last subframe and thereby identify the PUCCH resource to which the uplink A/N signals for the PDSCH are assigned. More specifically, PDSCH is located in subframe #1, which is the last subframe among subframes #0 and #1 to which soft combining of EPDCCH is applied inFIG.7. Accordingly, base station100and terminal200identify the PUCCH resource associated with the ECCE number of the EPDCCH located in subframe #1, in subframe #5, which corresponds to the fourth subframe following subframe #1, as the PUCCH resource to which the uplink A/N signals for the PDSCH are assigned inFIG.7.

Accordingly, even when an EPDCCH search space is shared between a terminal to which soft combining of EPDCCH is applied and a terminal to which no soft combining of EPDCCH is applied, base station100assigns the ECCE numbers used in the EPDCCH intended for these terminals in the subframe to which the PDSCH intended for both of the terminals is assigned. Thus, in this subframe, the ECCE numbers are assigned considering a PUCCH resource collision between the terminals, so that PUCCH resources are automatically (implicitly) assigned in a way that avoids a PUCCH resource collision between the terminals.

(PUSCH Timing)

In LTE-Advanced, terminals transmit PUSCH after receiving UL grant. The subframe used for transmission of PUSCH is previously determined. More specifically, the fourth subframe following the subframe to which UL grant is assigned is configured as the subframe on which PUSCH is transmitted in the FDD system, while the subframe on which PUSCH is transmitted is defined according to each TDD UL-DL configuration in the TDD system. In addition, when the number of UL subframes is greater than the number of DL subframes in a single frame, PUSCH on a plurality of UL subframes may be specified in a single DL subframe. However, in this case as well, the subframe on which PUSCH is transmitted is always configured to be the fourth subframe following the subframe to which UL grant is assigned or a subframe after the fourth subframe.

Moreover, after detection of UL grant, terminals identify that the PRB pair specified by the UL grant is assigned to PUSCH and determine the size and transmission method of data (PUSCH). Accordingly, unless at least a certain interval after the last subframe (i.e., detection of UL grant) among the subframes to which soft combining is applied is provided (four subframes or more in LTE-Advanced), PUSCH transmission processing cannot be prepared in terminals.

In this respect, the transmission timing of PUSCH specified by the UL grant transmitted using EPDCCH to which soft combining is applied is identified using, as the basis, the last subframe among the plurality of subframes on which the EPDCCH to be soft-combined is located in Embodiment 1. Since the transmission timing of PUSCH (i.e., subframe on which PUSCH is transmitted and received) is identified using the last subframe used for soft combining, the interval from the detection timing of UL grant until preparation for PUSCH transmission can be the same as the interval used when no soft combining of EPDCCH is applied.

In particular, in the TDD system, there is a subframe on which no UL grant is transmitted among DL subframes in accordance with an association between transmission and reception timing of UL grant and transmission and reception timing of PUSCH (i.e., UL grant-PUSCH timing) defined for each UL-DL configuration. In this respect, in the TDD system, the last subframe among the plurality of subframes used for soft combining is made the same as the transmission subframe for EPDCCH including UL grant (i.e., subframe in which EPDCCH including UL grant is transmitted).

FIG.8illustrates subframes in case of UL-DL configuration #1, for example. As illustrated inFIG.8, subframes #0, #4, #5, and #9 are DL subframes, while subframes #1 and #6 are special subframes (i.e., subframes that can be used for EPDCCH and PDSCH transmission), and subframes #2, #3, #7, and #8 are UL subframes UL-DL configuration #1. Moreover, UL grant-PUSCH timing is previously defined as illustrated inFIG.8, and the subframes on which UL grant can be located are subframes #1, #4, #6, and #9, and for the UL grant notified in each of the subframes, PDSCH is assigned to UL subframes #7, #8, subframe #2 of the next frame (not illustrated), and subframe #3 of the next frame.

Meanwhile, as illustrated inFIG.8, when soft combining is applied, there is a case where UL grant is located in a subframe on which no UL grant is transmitted. In this respect, in Embodiment 1, when soft combining of EPDCCH including UL grant is applied, the last subframe among the subframes on which EPDCCH to be soft-combined is located is configured as a subframe capable of transmitting UL grant when no soft combining is applied.

In this configuration, soft combining can be utilized without changing PUSCH timing from the UL grant detection timing.

For example, only subframes #1, #4, #6, and #9 are configured as the last subframe used for soft combining inFIG.8. More specifically, soft combining of EPDCCH including UL grant is configured in each of subframes #0 and #1 and subframes #5 and #6 inFIG.8. As illustrated inFIG.8, EPDCCH including UL grant is located in subframes #0 and #5 on which no UL grant is located when no soft combining is applied. In this case as well, the transmission timing of PUSCH indicated by the UL grant notified using the EPDCCH is identified on the basis of the last subframe among the subframes in which the EPDCCH is transmitted. In sum, when soft combining including UL grant is applied, the PUSCH timing specified by the UL grant transmitted using EPDCCH to which soft combining is applied (i.e., first transmission subframe for PUSCH) is defined using, as the basis, the last subframe on which EPDCCH to be soft combined is located. Accordingly, soft combining can be utilized without any change in the relationship between the detection timing of UL grant and the PUSCH timing compared to a case where no soft combining is applied.

It should be noted that, when the subframe specified as a subframe to which soft combining of EPDCCH is applied is common to DL assignment and UL grant, regarding UL grant, it is possible to employ a configuration in which soft combining is performed on condition that the abovementioned last subframe is configured as a subframe capable of transmitting UL grant when no soft combining is applied, and no soft combining is performed when this condition is not satisfied.

Hereinabove, a description has been provided regarding the timing of signals (i.e., PDSCH, UL ACK/NACK, and PUSCH) when soft combining of EPDCCH is applied.

Next, a description will be provided regarding switching between soft combining and non soft combining.

For example, in a subframe to which soft combining of EPDCCH is applied, the EPDCCH candidates in the same subframe may be divided into an EPDCCH candidate for soft combining and an EPDCCH candidate for non soft combining. This configuration make it possible to flexibly switch between soft combining and non soft combining depending on instant channel quality by selecting the EPDCCH candidate to be used in the same subframe.

In the following example, the number of EPDCCH candidates for soft combining is referred to as “K1” and the number of EPDCCH candidates for non soft combining is referred to as “K2.”FIG.9Aillustrates an example of the relationship between the aggregation level (L), the number of PRB pairs, and the number of EPDCCH candidates in LTE-Advanced.

FIG.9Billustrates an example in which the EPDCCH candidates inFIG.9Aare divided into EPDCCH candidates for soft combining and EPDCCH candidates for non soft combining when switching between soft combining and non soft combining is employed.

Application of one of three methods 1 to 3 may be possible for utilizing EPDCCH for non soft combining, for example.

(Method 1)

In Method 1, EPDCCH for non soft combining can be located in any subframe, but PDSCH notified by the EPDCCH is located in the subframe corresponding to the last subframe among the subframes to which soft combining is applied, and PUSCH notified by the EPDCCH is located in a subframe identified using the last subframe as the basis.

In Method 1, terminal200monitors (i.e., blind-decodes) K2 EPDCCH candidates in subframes other than the last subframe and monitors K1+K2 EPDCCH candidates in the last subframe.

According to Method 1, each of the PDSCH timing and PUSCH timing for soft combining can be used when no soft combining is applied, which makes the scheduling simple. In particular, in UL HARQ, since the UL HARQ process number is determined depending on the subframe, it is possible to switch between soft combining and non soft combining without changing the UL HARQ process number.

(Method 2)

In Method 2, EPDCCH for non soft combining is located in a subframe other than the subframe corresponding to the last subframe among the subframes to which soft combining is applied. More specifically, when the number of subframes to which soft combining is applied is two, EPDCCH for non soft combining is located in the first subframe.

In this case, terminal200monitors K2 EPDCCH candidates in the subframe other than the last subframe and monitors K1 EPDCCH candidates in the last subframe.

According to Method 2, the number of EPDCCH candidates monitored by terminal200in each subframe can be averaged because the subframes that become monitoring targets for EPDCCH candidates are distributed in accordance with whether or not soft combining is applied.

In addition, a subframe on which EPDCCH for non soft combining is transmitted and a subframe on which PDSCH notified by this EPDCCH is transmitted may be configured as different subframes. This configuration can separate an EPDCCH subframe and a data (PDSCH) subframe, thus allowing the power useable for EPDCCH transmission to be allocated to data transmission when the data transmission requires power.

(Method 3)

In method 3, EPDCCH for non soft combining can be located in any subframe.

In method 3, terminal200monitors K2 EPDCCH candidates in a subframe other than the subframe corresponding to the last subframe among the subframes to which soft combining is applied and monitors K1+K2 EPDCCH candidates in the subframe corresponding to the last subframe.

In addition, PDSCH may be located in any subframe, and PUSCH is located in a subframe identified using the subframe on which EPDCCH is detected, as the basis.

According to method 3, PDSCH/PUSCH can be assigned more flexibly when no soft combining is applied.

Hereinabove, a description has been given regarding switching between soft combining and non soft combining.

As described above, according to Embodiment 1, the transmission timing of each set of signals (resource allocation for each set of signals) when soft combining is applied can be appropriately configured.

It should be noted that, application of soft combining of PDSCH and PUSCH (sometimes, called “TTI bundling”) in combination with soft combining of EPDCCH described above may be possible. In this case, the first subframe of DL data (PDSCH) the assignment of which is indicated using DL assignment may be located in the last subframe among a plurality of subframes on which EPDCCH including the DL assignment is transmitted. In this configuration, the period for saving, in a buffer, the received signals that are received from the reception timing of PDSCH to the completion of EPDCCH detection processing (i.e., signals that may be PDSCH) can be the same as the period used when no soft combining of EPDCCH is applied.

Embodiment 2

In Embodiment 2, a description will be provided regarding resource allocation for EPDCCH (i.e., search space configuration) in a plurality of subframes on which EPDCCH to be soft combined is located.

The base station and terminal according to Embodiment 2 include the same basic configurations as base station100and terminal200according to Embodiment 1. Accordingly, the description will be provided with reference toFIGS.5and6.

In Embodiment 2, a single EPDCCH set is configured in each of a plurality of subframes used for soft combining. More specifically, a plurality of EPDCCH sets respectively configured in a plurality of subframes are connected to each other for soft combining of EPDCCH.

It should be noted that, the number of PRB pairs and a PRB pair number (frequency resource, i.e., PRB pair position) are configured for each EPDCCH set. In addition, the number of PRB pairs determines NECCE, which is the number of ECCEs in an EPDCCH set, and the ECCEs of ECCE #0 to ECCE #NECCE−1 are located.

FIG.10illustrates an example in which soft combining of EPDCCH is performed using two subframes. It should be noted that, the bit sequence of EPDCCH to be transmitted is previously configured as one that is equivalent to at least aggregation level 2 (at least AL2). In FIG. the aggregation levels of EPDCCH #0 and EPDCCH #1 are AL2, and the aggregation level of EPDCCH #2 is AL4.

In Embodiment 2, each EPDCCH is divided into two EPDCCHs, and the two EPDCCHs are respectively located on an ECCE of EPDCCH set 0 (EPDCCH set corresponding to subframe #0) and an ECCE of EPDCCH set 1 (EPDCCH set corresponding to subframe #1). In other words, each EPDCCH is divided in units of ECCEs.

For example, inFIG.10, EPDCCH #0 is divided into EPDCCH #0a and EPDCCH #0b, and EPDCCH #0a and EPDCCH #0b are respectively located on EPDCCH candidates of AL1 (each candidate corresponding to one ECCE) of EPDCCH set 0 and EPDCCH set 1. Likewise, EPDCCH #1 is divided into EPDCCH #1a and EPDCCH #1b, and EPDCCH #1a and EPDCCH #1b are respectively located on EPDCCH candidates of AL1 (each candidate corresponding to one ECCE) of EPDCCH set 0 and EPDCCH set 1. Likewise, EPDCCH #2 is divided into EPDCCH #2a and EPDCCH #2b, and EPDCCH #2a and EPDCCH #2b are respectively located on EPDCCH candidates of AL2 (each candidate corresponding to two ECCEs) of EPDCCH set 0 and EPDCCH set 1.

To put it differently, base station100(i.e., configuration section102) configures an EPDCCH set in each of a plurality of subframes used for soft combining. In addition, base station100(i.e., signal assignment section105) divides EPDCCH (control information) into the same number of EPDCCHs in units of ECCEs as the number of the plurality of subframes and assigns each of the divided EPDCCHs to any of the ECCEs forming the EPDCCH set configured in one of the plurality of subframes.

In this case, the EPDCCH candidate for each terminal200varies depending on the subframe number. Accordingly, as illustrated inFIG.10, the divided EPDCCHs are located on different EPDCCH candidates in subframes #0 and #1, respectively. In LTE-Advanced, studies have been carried on two equations 1 and 2 below as equations for determining EPDCCH candidates for each terminal200.

[1]L⁢{(Yp,k+m′)⁢mod⁢⌊NECCE,p,k/L⌋}+i(Equation⁢1)[2]L⁢{(Yp,k+⌊m′·NECCE,p,kL·Mp(L)⌋)⁢mod⁢⌊NECCE,p,k/L⌋}+i(Equation⁢2)

In equations 1 and 2, L represents aggregation level (AL), Yp,krepresents UE ID (i.e., terminal ID), k represents subframe number, and p represents search space set number. In addition, i takes on the value of 0, 1, . . . , L−1.

Moreover, m′ represents the parameter used when cross-carrier scheduling is configured and expressed by the next equation.
[3]
m′=m+Mp(L)·nCI(Equation 3)

Mp(L)represents the number of EPDCCH candidates to be monitored at aggregation level (L) and nCLrepresents the parameter used in configuring cross-carrier scheduling (i.e., carrier indicator field value). In equation 3, m′=m when no cross-carrier scheduling is configured.

Moreover, m is expressed by the next equation.
[4]
m=0,1, . . .Mp(L)−1   (Equation 4)

More specifically, m represents the EPDCCH candidate number for each aggregation level (L).

In Embodiment 2, each of the divided EPDCCHs is located on an EPDCCH candidate represented by m (the same number between the subframes) in each of the subframes to which soft combining is applied.

In this manner, EPDCCH candidate numbers to be used can be shared between subframes. More specifically, in the subframes to which soft combining is applied (two subframes in this embodiment), the number of combinations of EPDCCH candidates that is equal to Mp(L)*Mp(L)patterns can be limited to Mp(L)patterns. Even when an EPDCCH candidate of the same number m is used in subframes, the EPDCCH candidate (ECCE) is different for each subframe. More specifically, even with the EPDCCH candidate of the same number m, the frequency resource allocated to each subframe is different, so that frequency diversity effect can be obtained. In addition, when the number of REs to be actually allocated varies for each ECCE number, the number of REs can be averaged.

Next, a description will be provided regarding methods 1 and 2 for configuring an EPDCCH search space in subframes to which soft combining is applied. It should be noted that, a case where soft combining is applied over two subframes will be described as an example. However, the number of subframes used for soft combining is not limited to two and can be three or more.

(Method 1: When EPDCCH Sets Configured in Two Subframes are the Same)

FIG.11Aillustrates an EPDCCH set configured for non soft combining andFIG.11Billustrates EPDCCH sets configured for soft combining.

As illustrated inFIG.11B, EPDCCH sets 0 and 1 respectively configured in the two subframes to which soft combining is applied (first and second subframes) are assumed to be the same.

Accordingly, as illustrated inFIG.11B, the EPDCCH sets respectively located in the subframes include the same number of PRB pairs (four) and the same PRB numbers (the same PRB pair arrangement positions). However, EREGs corresponding to EPDCCH candidates forming each EPDCCH set are different in each of the subframes.

In this manner, EPDCCH candidates at each aggregation level (AL) are equal to each other between EPDCCH sets (i.e., between subframes to which the same EPDCCH is assigned). Accordingly, all the EPDCCH candidates can be used as search spaces for soft combining of EPDCCH.

In addition, since EPDCCH is located on the same PRB pairs in a plurality of subframes, precoding for demodulation reference signals (DMRS), which are the reference signals used for EPDCCH, can be shared between the subframes. Accordingly, when the moving speed of terminal200is slow, for example, an assumption can be made that channel fluctuation is small between contiguous subframes, so that terminal200can combine the reference signals of a plurality of subframes to improve the channel estimation accuracy.

In addition, LTE-Advanced allows each terminal to be configured with two EPDCCH sets. Thus, it is possible to dynamically switch between soft combining and non soft combining by configuring one EPDCCH set for soft combining and the other EPDCCH for non soft combining.

(Method 2: When EPDCCH Sets Configured in Two Subframes are Different)

FIG.12Aillustrates EPDCCH sets for non soft combining, andFIG.12Billustrates EPDCCH sets configured for soft combining.

As illustrated inFIG.12B, EPDCCH sets 0 and 1 respectively configured in the two subframes to which soft combining is applied (first and second subframes) are different.

In the subframes to which soft combining is applied, a single EPDCCH set is located in each of the subframes as illustrated inFIG.12B, while two EPDCCH sets are located in the subframe to which no soft combining is applied as illustrated inFIG.12A.

As illustrated inFIGS.12A and12B, the number of PRB pairs, the PRB numbers (PRB pair arrangement positions), and the assignment method (distributed assignment or localized assignment) can be configured in each of the EPDCCH sets respectively configured in the plurality of subframes used for soft combining. More specifically, soft combining can be performed using EPDCCH sets that are different in design in Method 2.

For example, inFIG.12B, among the two subframes to which soft combining of EPDCCH is applied, the number of PRB pairs of the EPDCCH set configured in the first subframe is four (N=4) and the number of PRB pairs of the EPDCCH set configured in the second subframe is two (N=2). As described, since the number of PRB pairs is different between the subframes (between the EPDCCH sets), the number of EPDCCH candidates for each aggregation level is also different. For example, as illustrated inFIG.13, the numbers of EPDCCH candidates when the number of PRB pairs N=2 are 4, 2, 1, 1, and 0 for the ALs (L=1, 2, 4, 8, and 16), respectively, while the numbers of EPDCCH candidates when the number of PRB pairs N=4 are 2, 3, 2, 1, and 1 for the ALs (L=1, 2, 4, 8, and 16), respectively.

InFIG.13, with reference to AL1 (L=1, but L=2 when soft combining is applied), the number of EPDCCH candidates when the number of PRB pairs=2 is four (i.e., EPDCCH candidate numbers m=0, 1, 2, and 3), and the number of EPDCCH candidates when the number of PRB pairs=4 is two (i.e., EPDCCH candidate numbers m=0 and 1). In this case, base station100and terminal200use only two EPDCCH candidates (m=0 and 1) common to the two EPDCCH sets as the EPDCCH candidates for soft combining and use the remaining EPDCCH candidates (i.e., two EPDCCH candidates m=2 and 3 when the number of PRB pairs N=2) as the EPDCCH candidates for non soft combining. The same applies to the other ALs.

To put it differently, since the EPDCCH candidates for each AL are different between EPDCCH sets, the EPDCCH candidates of the EPDCCH set smaller in number are used as the search spaces for soft combining in Method 2. In this case, the remaining EPDCCH candidates of the EPDCCH set larger in number can be used as the search spaces for non soft combining.

In addition, according to Method 2, the region used for EPDCCH can be changed for each subframe. For example, when PDSCH is located in the last subframe (e.g., second subframe inFIG.12B) among the subframes used for soft combining, the EPDCCH region located in the last subframe is reduced in size compared with the other subframe (e.g., first subframe inFIG.12B), which makes it possible to ensure the PDSCH region.

Methods 1 and 2 for configuring search spaces have been described above.

As described above, according to Embodiment 2, the resource allocation for locating EPDCCH when soft combining is applied can be appropriately configured.

It should be noted that, the number of EPDCCH candidates for each AL varies depending on conditions such as a DCI format, bandwidth, subframe type and/or the number of subcarriers in EPDCCH of LTE-Advanced. More specifically, the abovementioned conditions are classified into Cases 1, 2, and 3 in LTE-Advanced. Case 1 supports AL2 (L=2) or above, while Cases 2 and 3 support AL1 (L=1) or above. For this reason, although Embodiment 2 has been described with the case assuming EPDCCH at AL2 or above, EPDCCH at AL1 can be treated as EPDCCH at AL2 or above by application of soft combining. More specifically, in Embodiment 2, it is possible to apply, to all DCI formats, not only Case 1 in which the number of EPDCCH candidates at AL2 or above is prepared, but also Cases 2 or 3 in which the number of EPDCCH candidates at AL1 or above is prepared. In this manner, the AL can be prevented from rising too high in case of soft combining.

Embodiment 3

In Embodiment 2, a description has been given regarding the case where soft combining is performed while a plurality of EPDCCH sets respectively configured in a plurality of subframes to which soft combining is applied are connected to each other. On the other hand, in Embodiment 3, a description will be provided regarding a case where PRB pairs of a single EPDCCH set are distributed into a plurality of subframes to which soft combining is applied.

The base station and terminal according to Embodiment 3 include the same basic configuration as base station100and terminal200according to Embodiment 1. Accordingly, the description will be provided with reference toFIGS.5and6.

More specifically, base station100(i.e., configuration section102) configures a single EPDCCH set entirely for the plurality of subframes used for soft combining. However, the PRB pairs corresponding to the ECCEs forming the single EPDCCH set are distributedly located in the plurality of subframes used for soft combining.

For example, when the number of PRB pairs of the EPDCCH set is N while the number of subframes used for soft combining is M, the number of PRB pairs obtained by dividing N by M (N/M) is located per subframe.

FIG.14illustrates an example in which soft combining of EPDCCH is performed using two subframes (M=2). InFIG.14, the number of PRB pairs of the EPDCCH set is set equal to four (N=4). Accordingly, two PRB pairs (=N/M) are located per subframe inFIG.14. InFIG.14, the aggregation levels of EPDCCHs #0 and #1 are AL1, and the aggregation level of EPDCCH #2 is AL2. Moreover, each EPDCCH is located according to the assignment method of ECCEs in EPDCCH set 0.

InFIG.14, EPDCCH #0 is located on ECCE #0, while EPDCCH #1 is located on ECCE #1, and EPDCCH #2 is located on ECCEs #2 and #3. Each ECCE is located on four PRB pairs of EPDCCH set 0 (e.g., PRB indices #0, #1, #2, and #3). However, PRB indices #0 and #2 are located in subframe #0, and PRB indices #1 and #3 are located in subframe #1 inFIG.14. More specifically, single EPDCCH set 0 is located in a divided manner on a plurality of subframes to which soft combining is applied.

Accordingly, soft combining can be applied even when AL1 is used in Embodiment 3. In addition, since the amount of resource for the EPDCCH region per subframe used for soft combining can be reduced, the resource not used for EPDCCH can be used for PDSCH.

(Variation when N=8)FIG.15illustrates an example of a correspondence between ECCEs and PRB pairs when the number of PRB pairs of a search space set is eight (N=8), and the number of EREGs per ECCE is four. InFIG.15, the PRB pairs on which ECCE is located vary depending on the ECCE. More specifically, an even number (index) ECCE is located on even number PRB pairs, and an odd number ECCE is located on odd number PRB pairs.

A description will be provided regarding variations1and2of dividing an EPDCCH set (PRB pairs) into a plurality of subframes (i.e., two subframes herein) used for soft combining in this case.

(Variation 1)

In Variation 1, in case of soft combining, subframes are separated into a subframe on which even number PRB pairs are located and a subframe on which odd number PRB pairs are located. For example, when soft combining is performed using two subframes, even number PRB pairs are located in the first subframe and odd number PRB pairs are located in the second subframe.

Accordingly, EPDCCH at AL1 formed of single ECCE is located in one of the first and second subframes. To put it differently, no soft combining is applied to EPDCCH at ALL Thus, it is possible to switch between soft combining and non soft combining by selecting a certain AL.

As described above, soft combining can be applied using EPDCCH at AL2 or above in Variation 1. In this respect, Case 1 prepared from the number of EPDCCH candidates at AL2 (see, NPL 1) can be applied to all DCI formats in LTE-Advanced. Accordingly, soft combining can be applied to all EPDCCH candidates.

(Variation 2)

In Variation 2, in case of soft combining, a set of PRB pairs including an even number PRB pair and an odd number PRB pair is located in a single subframe. For example, when soft combining is performed using two subframes, a set of PRB pairs #0, #1, #4 and #5 is located in the first subframe, and a set of PRB pairs #2, #3, #6 and #7 is located in the second subframe inFIG.15.

In this manner, even when EPDCCH at AL1 formed of single ECCE is used, EPDCCH is located in each of the first and second subframes. Accordingly, soft combining can be applied to EPDCCH at ALL The variations of dividing an EPDCCH set (PRB pairs) for a plurality of subframes has been described.

As described above, according to Embodiment 3, resource allocation for locating EPDCCH when soft combining is applied can be appropriately configured as in Embodiment 2.

The embodiments of the claimed invention have been described.

Other Embodiments

(1) When soft combining is applied, the number of EPDCCH candidates for each AL may be changed. For example,FIG.16Aillustrates the number of EPDCCH candidates for each AL before any change is made, andFIG.16Billustrates the number of EPDCCH candidates for each AL after some changes are made (for soft combining). InFIG.16B, the number of EPDCCH candidates for the high AL (L=8) is increased while the number of EPDCCH candidates for the low AL (L=2) is decreased. The increase in the number of EPDCCH candidates for a high AL particularly increases the soft combining effects.

(2) Although the description has been given regarding the case where contiguous subframes are used as the subframes used soft combining as illustrated inFIGS.7and8, for example, the subframes used for soft combining do not have to be necessarily contiguous, and non-contiguous subframes may be used.

(3) The precoding of DMRS in each subframe may be assumed to be the same depending on conditions when soft combining of EPDCCH is performed in Embodiments 2 and 3.

Examples of the conditions include a case where the PRB pairs on which EPDCCH to be soft combined are located are identical between the subframes. For example, in Embodiment 2 (Method 1), since the same EPDCCH set is used in a plurality of subframes used for soft combining, it is possible to assume that the precoding of DMRS is the same in the subframes.

Another example of the conditions is a case where the PRB pairs on which EPDCCH is located are arranged within a constant range in each subframe to which soft combining is applied, for example. The term “within a constant range” as used herein refers to adjacent PRB pair indices, for example.

Still another example of the conditions is a case where the PRB pairs on which EPDCCH is located are arranged within a PRB bundling range in each subframe to which soft combining is applied. The term “PRB bundling range” as used herein refers to a value that is determined according to the bandwidth and includes patterns of one, two, and three PRB pairs.

In Embodiment 3, the PRB pairs (positions) are always different between the plurality of subframes, and it is thus difficult to set the same precoding of DMRS in the subframes. In this respect, when Embodiment 3 is employed, the same PRB pairs may be used between the subframes used for soft combining. For example, in two subframes used for soft combining, the position of the PRB pair used in the second subframe may be shifted in such a way that the PRB pair used in the second subframe is identical with the PRB pair used in the first subframe.

(4) In the embodiments described above, the cases where soft combining is performed over a plurality of subframes (i.e., in the time domain) have been described. However, the embodiments may be applied in the frequency domain (e.g., carrier aggregation). In this case, EPDCCH may be located over a plurality of component carriers (CCs) instead of locating EPDCCH on a plurality of subframes in the embodiments described above. In Embodiment 1, the PUCCH resource is implicitly indicated by the ECCE (index) of EPDCCH located in the last subframe among a plurality of subframes, for example. Meanwhile, the PUCCH resource may be implicitly indicated by the ECCE (index) of EPDCCH located on the PCell among a plurality of component carriers in case of carrier aggregation.

(5) Soft combining of EPDCCH in Embodiment 2 may be applied to two EPDCCH sets in the same subframe. In this configuration, the maximum AL in a single subframe can be made larger, and the reception quality of EPDCCH in a subframe having poor reception quality can be improved.

(6) The embodiments have been described by examples of hardware implementations, but the claimed invention can be also implemented by software in conjunction with hardware.

In addition, the functional blocks used in the descriptions of the embodiments are typically implemented as LSI devices, which are integrated circuits. The functional blocks may be formed as individual chips, or a part or all of the functional blocks may be integrated into a single chip. The term “LSI” is used herein, but the terms “IC,” “system LSI,” “super LSI” or “ultra LSI” may be used as well depending on the level of integration.

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

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

A base station according to this disclosure includes: a configuration section that configures an Enhanced Physical Downlink Control Channel (EPDCCH) set in a plurality of subframes, the EPDCCH set being formed of Enhanced Control Channel Elements (ECCEs) to which control information transmitted over the plurality of subframes is assigned; and an assignment section that assigns the control information to any of the ECCEs on a Physical Resource Block (PRB) pair in each of the plurality of subframes.

In the base station according to this disclosure, the configuration section configures the EPDCCH sets respectively in the plurality of subframes, and the assignment section divides the control information into the same number of pieces of control information as the number of the plurality of subframes in units of the ECCEs and assigns each of the divided pieces of control information to any of the ECCEs forming the EPDCCH sets configured respectively in the plurality of subframes.

In the base station according to this disclosure, the EPDCCH sets configured respectively in the plurality of subframes are the same.

In the base station according to this disclosure, the EPDCCH sets configured respectively in the plurality of subframes are different.

In the base station according to this disclosure, configuration section configures the single EPDCCH set entirely for the plurality of subframes, and PRB pairs corresponding to the ECCEs forming the single EPDCCH set are distributedly located in the plurality of subframes.

In the base station according to this disclosure, the assignment section assigns downlink data to the last subframe among the plurality of subframes, the assignment of the downlink data being indicated by the control information.

The base station according to this disclosure further includes a reception section that receives response signals for downlink data on a Physical Uplink Control Channel (PUCCH) associated with the ECCE located in a subframe to which the downlink data is assigned among the plurality of subframes, the assignment of the downlink data being indicated by the control information.

In the base station according to this disclosure, a transmission subframe for the control information indicating assignment of uplink data is associated with a reception subframe for the uplink data, and the last subframe among the plurality of subframes is the same as the transmission subframe.

A terminal according to this disclosure includes: a configuration section that identifies Enhanced Control Channel Elements (ECCEs) to which control information transmitted over a plurality of subframes is assigned, the ECCEs forming an Enhanced Physical Downlink Control Channel (EPDCCH) set configured in the plurality of subframes; and a reception section that receives the control information assigned to any of the ECCEs on a Physical Resource Block (PRB) pair in each of the plurality of subframes.

A transmission method according to this disclosure includes: configuring an Enhanced Physical Downlink Control Channel (EPDCCH) set in a plurality of subframes, the EPDCCH set being formed of Enhanced Control Channel Elements (ECCEs) to which control information transmitted over the plurality of subframes is assigned; and transmitting the control information assigned to any of the ECCEs on a Physical Resource Block (PRB) pair in each of the plurality of subframes.

A reception method according to this disclosure includes: identifying Enhanced Control Channel Elements (ECCEs) to which control information transmitted over a plurality of subframes is assigned, the ECCEs forming an Enhanced Physical Downlink Control Channel (EPDCCH) set configured in the plurality of subframes; and receiving the control information assigned to any of the ECCEs on a Physical Resource Block (PRB) pair in each of the plurality of subframes.

INDUSTRIAL APPLICABILITY

The claimed invention is useful in mobile communication systems.

REFERENCE SIGNS LIST

100Base station200Terminal101Assignment information generating section102,205Configuration section103,207, Error correction coding section104,208Modulation section105,209Signal assignment section106,210Transmission section107,201Reception section108,203Demodulation section109,204Error correction decoding section202Signal demultiplexing section206Control signal receiving section