Patent Description:
3rd Generation Partnership Project Radio Access Network Long Term Evolution (3GPP-LTE) (hereinafter, referred to as "LTE") employs Orthogonal Frequency Division Multiple Access (OFDMA) as the downlink communication scheme and employs Single Carrier Frequency Division Multiple Access (SC-FDMA) as the uplink communication scheme (see, Non-Patent Literatures (hereinafter, abbreviated as NPL) <NUM>, <NUM> and <NUM>, for example). In addition, a Periodic Sounding Reference signal (P-SRS) is used in the uplink of LTE as a reference signal for measuring uplink reception quality.

In order for terminals to transmit the P-SRS to a base station, an SRS transmission subframe shared by all terminals (hereinafter, referred to as "common SRS subframe") is configured. This common SRS subframe is defined by a combination of a predetermined periodicity and a subframe offset on a per cell basis. The information about the common SRS subframe is broadcasted to the terminals in the cell. For example, when the periodicity is <NUM> subframes, and the offset is <NUM>, a third subframe in a frame (formed of <NUM> subframes) is configured as a common SRS subframe. In the common SRS subframe, all the terminals in the cell stop the transmission of data signals at the last SC-FDMA symbol of the subframe and use this period as a transmission resource for reference signals.

In addition, each terminal is specifically configured with an SRS transmission subframe by a higher layer (RRC layer above the physical layer) (hereinafter, referred to as "specific SRS subframe"). Each terminal transmits a P-SRS in the configured specific SRS subframe. In addition, each terminal is configured with parameters on the SRS resource (hereinafter, may be referred to as "SRS resource parameter") and also notified of the parameter. The parameters on the SRS resource include the bandwidth and band position of the SRS (or position where SRS band starts), Cyclic Shift, Comb (which corresponds to identification information on the subcarrier group), and/or the like. The terminal transmits an SRS using the resource in accordance with the notified parameters. In addition, SRS frequency hopping may be configured in some cases.

In addition, the introduction of a dynamic aperiodic SRS (hereinafter, referred to as "A-SRS") into the uplink of LTE-Advanced, which is an advanced version of LTE (hereinafter, referred to as "LTE-A"), has been discussed. The transmission timing of an A-SRS is controlled by trigger information (e.g., <NUM>-bit information). This trigger information is transmitted to a terminal from a base station on a physical layer control channel (i.e., PDCCH) (e.g., see NPL <NUM>). More specifically, the terminal transmits an A-SRS only in response to an A-SRS transmission request made by the trigger information (i.e., A-SRS transmission request). In addition, studies have been carried out on defining, as the A-SRS transmission timing, the first common SRS subframe located at or after a k-th subframe (e.g., k=<NUM>) from the subframe in which the trigger information is transmitted. As described above, although a P-SRS is transmitted periodically, it is possible to cause a terminal to transmit an A-SRS frequently within a short period only during a data burst in the uplink transmission, for example.

Moreover, LTE-A provides control information formats for various types of data assignment reporting. The control information formats in the downlink include: DCI format 1A for allocation of resource blocks consecutive in number (Virtual RBs or Physical RBs); DCI format <NUM>, which allows allocation of RBs not consecutive in number (hereinafter, referred to as "non-contiguous bandwidth allocation"); DCI formats <NUM> and 2A for assigning a spatial-multiplexing MIMO transmission; a downlink assignment control information format for assigning a beam-forming transmission ("beam-forming assignment downlink format:" DCI format 1B); and a downlink assignment control information format for assigning a multi-user MIMO transmission ("multi-user MIMO assignment downlink format:" DCI format 1D), and/or the like. Meanwhile, the uplink assignment formats include DCI format <NUM> for assigning a single antenna port transmission and DCI format <NUM> for assigning an uplink spatial-multiplexing MIMO transmission. DCI format <NUM> is used for only terminals configured with an uplink spatial-multiplexing MIMO transmission.

In addition, DCI format <NUM> and DCI format 1A are adjusted in size by padding so that each format consists of the same number of bits. DCI format <NUM> and DCI format 1A are also called DCI format <NUM>/1A in some cases. DCI formats <NUM>, <NUM>, 2A, 1B and 1D are used depending on the downlink transmission mode configured for each terminal (i.e., non-contiguous bandwidth allocation, spatial-multiplexing MIMO transmission, beam-forming transmission or multi-user MIMO transmission) and are configured for each terminal. Meanwhile, DCI format <NUM>/1A can be used independently of the transmission mode and thus can be used for terminals in any transmission mode, i.e., DCI format <NUM>/1A is a format commonly usable in all terminals. In addition, when DCI format <NUM>/1A is used, single-antenna transmission or transmit diversity is used as the default transmission mode.

A terminal receives DCI format <NUM>/1A, and the DCI formats that are dependent on the downlink transmission mode. In addition, a terminal configured with an uplink spatial-multiplexing MIMO transmission receives DCI format <NUM> in addition to the abovementioned DCI formats.

The use of DCI format <NUM> and DCI format <NUM>, which are control information formats used for uplink data (PUSCH) assignment reporting, for reporting the A-SRS trigger information has been discussed. The field for reporting an A-SRS trigger is added to DCI format <NUM> in addition to an RB reporting field, MCS reporting field, HARQ information reporting field, transmission power control command reporting field and terminal ID field. In addition to the fields described above, DCI format <NUM> includes an MCS reporting field for the second transport block (data codeword) to be spatially multiplexed, and precoding information for spatial multiplexing.

The DCI described above is transmitted to a base station to a terminal via a PDCCH. The base station in this case assigns a plurality of terminals to a single subframe, so that the base station simultaneously transmits a plurality of PDCCHs using different resources. The base station transmits the PDCCHs while including CRC bits which have been masked (or scrambled) using the terminal ID of the transmission destination in each of the PDCCHs in order to identify the terminal of the transmission destination of each of the PDCCHs. Each terminal then detects the PDCCH intended for the terminal by blind-decoding the PDCCHs by demasking (or descrambling) CRC bits with the terminal ID of the terminal in the PDCCHs which may have been transmitted for the terminal.

As described above, a terminal transmits an A-SRS in the first common SRS subframe located at or after a k-th subframe (e.g., k=<NUM>) from the subframe in which the terminal receives the trigger information. More specifically, let us suppose a case where the periodicity of common SRS subframes is equal to Np subframes. In this case, when receiving an A-SRS trigger during a period from a subframe located Np + k + <NUM> subframes before a certain common SRS subframe until a subframe located k subframes before the common SRS subframe among Np subframes, the terminal uses the common SRS subframe to transmit an A-SRS. Stated differently, when requesting a terminal to transmit an A-SRS in subframe n, which is a common SRS subframe, the base station notifies the terminal of the A-SRS transmission request by the A-SRS trigger information during a period from a subframe corresponding to subframe n - (Np+k+<NUM>) until a subframe corresponding to subframe n - k among Np subframes (hereinafter, referred to as "effective period").

At least two kinds of DCI formats, which are DCI format <NUM> and DCI format <NUM>, can be used for an A-SRS transmission request. A base station can request each terminal to transmit an A-SRS of a different A-SRS configuration (e.g., A-SRS bandwidth, cyclic shift, Comb, the number of antennas and/or the like) using each of the DCI formats.

Meanwhile, each terminal detects the DCI intended for the terminal by blind-decoding PDCCHs. For this reason, a terminal may erroneously detect DCI that is intended for a different terminal or DCI that has not been transmitted. Such erroneous detection of DCI is called a "false alarm" or "false detection" and means that DCI intended for a different terminal or a signal that has not been transmitted intentionally (i.e., noise components) is erroneously detected as the DCI intended for the terminal. Each terminal makes CRC judgment for a plurality of PDCCH resource candidates after demasking the CRC part of each PDCCH using the terminal ID of the terminal (i.e., blind-decoding). During the blind-decoding, when the result of CRC is OK, the terminal detects the DCI as being intended for the terminal regardless of whether or not the bit sequence is actually correct or is intended for the terminal. For example, even when nothing is actually transmitted on the blind-decoding target PDCCH resource, the terminal blind-decodes noise components as a signal. In this case, a random bit sequence appears as the decoding result, and the result of CRC becomes OK depending on the combination of bits.

In addition, a base station may intentionally or unintentionally reports a plurality of A-SRS transmission requests within an effective period. Accordingly, there is a possibility for a terminal to detect a plurality of A-SRS transmission requests within an effective period for a certain common SRS subframe.

However, no studies have been carried out on the operation of terminals upon detection of a plurality of A-SRS transmission requests. For this reason, there is a concern that a base station may perform an erroneous reception quality measurement as a result of different understanding of A-SRS configuration between the base station and the terminal. In addition, the terminal may unnecessarily interfere with a different cell in this case. In particular, A-SRS transmission performed by a terminal using an SRS resource allocated to a different terminal affects not only the reception quality measurement of the terminal but also the reception quality measurement of the different terminal, thus possibly degrading the system throughput.

It is an object of the present invention to provide a communication apparatus and an SRS transmission method each of which is capable of preventing degradation in the system throughput by reducing the possibility of occurrence of a difference in understanding of the presence or absence of SRS transmission or understanding of an SRS resource between the SRS transmission side and reception side.

<CIT> relates to a "periodic SRS" signaling mechanism in which an UE transmits SRS in accordance with a predetermined subframe period and a predetermined transmission offset. In this context, the UE receives a configuration from a base station indicating UE-specific SRS transmission timing factors, including transmission periodicity and transmission offset. Then, the UE determines whether UE-specific and cellspecific SRS transmission instances align, based on the received configuration. If the UE-specific transmission instances do align, then the UE transmits the UE-specific SRS during the cellspecific SRS transmission instances. Otherwise, the UE performs a predetermined action, including: declaring a mis-configuration, selectively dropping UE-specific SRS transmissions, and transmitting the SRS using frequency hopping.

<CIT> relates to a communication system supporting several combinations for the SRS transmission BW, which corresponds to configurations adopted in 3GPP E-UTRA LTE (cf. e.g. Table <NUM> in D2). The Node B signals a configuration c through a broadcast channel. The Node B then individually assigns to each UE one of the possible SRS transmission BWs by indicating the value of b for configuration c. Therefore, the Node B can multiplex SRS transmissions from UEs in BWs (b=<NUM>, b=<NUM>, b=<NUM>, and b=<NUM>). The SRS transmission parameters are assumed to be configured for each UE by the Node B through higher layer signaling, for example, through the MAC layer or the Radio Resource Control (RRC) layer, and remain valid until reconfigured again through higher layer signaling.

<CIT> relates to LTE user equipments transmitting sounding reference signals (SRS) according to both cell specific and UE specific signaling from base station. The cell specific configuration indicates subframes where LTE UEs in the cell can transmit SRS. The UE specific signaling informs each LTE UE the particular subframe where each LTE UE should transmit SRS among subframes configured by cell specific configuration. That is a base station notifies each user equipment terminal which subframe is selected for SRS transmission.

The object of the present invention is attained by the subjectmatter of the independent claims. Advantageous embodiments are covered by the dependent claims.

A communication apparatus according to an example useful for understanding the present invention includes: a detection section that detects control information indicating whether or not to request transmission of a sounding reference signal (SRS); and a control section that controls the transmission of the SRS based on the detected control information, in which, when detecting a plurality of pieces of the control information within a predetermined period, the control section controls the transmission of the SRS based on a piece of the control information that is detected first.

A communication apparatus according to an example useful for understanding the present invention includes: a detection section that detects control information indicating whether or not to request transmission of a sounding reference signal (SRS); and a control section that controls the transmission of the SRS based on the detected control information, in which, when detecting a plurality of pieces of the control information within a predetermined period, the control section controls the transmission of the SRS based on a piece of the control information that is detected last.

A communication apparatus according to a further example useful for understanding the present invention includes: a detection section that detects control information indicating whether or not to request transmission of a sounding reference signal (SRS); and a control section that controls the transmission of the SRS based on the detected control information, in which, when detecting a plurality of pieces of the control information within a predetermined period, the control section performs control in such a way that the SRS is not transmitted.

A communication apparatus according to yet another example useful for understanding the present invention includes: a detection section that detects control information indicating whether or not to request transmission of a sounding reference signal (SRS); and a control section that controls the transmission of the SRS based on the detected control information, in which, when detecting a plurality of different pieces of the control information within a predetermined period, the control section performs control in such a way that the SRS is not transmitted.

A communication apparatus according to an even further example useful for understanding the present invention includes: a detection section that detects control information indicating whether or not to request transmission of a sounding reference signal (SRS); and a control section that controls the transmission of the SRS based on the detected control information, in which, when detecting at least one piece of the control information that requests the transmission of the SRS and subsequently detecting a piece of the control information that requests no transmission of the SRS, within a predetermined period, the control section performs control in such a way that the SRS is not transmitted, and when further detecting, within the predetermined period, at least one piece of the control information that is different from the at least one piece of the control information and that requests the transmission of the SRS, the control section performs control in such a way that the SRS is transmitted, based on the piece of the control information that requests the transmission of the SRS and that is detected last.

A communication apparatus according to another example useful for understanding the present invention includes: a transmission section that transmits control information indicating whethe90or or not to request transmission of a sounding reference signal (SRS) to a communication counterpart; and a detection section that detects the SRS transmitted at a predetermined timing based on the control information from the communication counterpart, in which the transmission section transmits only one piece of the control information before the predetermined timing within a predetermined period.

A communication apparatus according to a further example useful for understanding the present invention includes: a transmission section that transmits control information indicating whether or not to request transmission of a sounding reference signal (SRS) to a communication counterpart; and a detection section that detects the SRS transmitted at a control predetermined timing based on the information from the communication counterpart, in which the transmission section transmits identical pieces of the control information when transmitting a plurality of pieces of the control information to the communication counterpart before the predetermined timing within a predetermined period.

An SRS transmission control method according to yet another example useful for understanding the present invention includes: detecting control information indicating whether or not to request transmission of a sounding reference signal (SRS); and controlling the transmission of the SRS based on the detected control information and a predetermined rule when a plurality of pieces of the control information is detected before a predetermined timing at which the SRS is transmitted within a predetermined period, or a plurality of pieces of the control information is detected within the predetermined period.

According to the present invention, it is possible to provide a communication apparatus and an SRS transmission method each of which is capable of preventing degradation in the system throughput by reducing the possibility of occurrence of a difference in understanding of the presence or absence of SRS transmission or understanding of an SRS resource between the SRS transmission side and reception side.

Throughout the embodiments, the same elements are assigned the same reference numerals and any duplicate description of the elements is omitted.

A communication system according to Embodiment <NUM> of the present invention includes base station <NUM> and terminals <NUM>. Base station <NUM> is an LTE-A compliant base station and each terminal <NUM> is an LTE-A compliant terminal.

<FIG> is a main configuration diagram of base station <NUM> according to Embodiment <NUM> of the present invention. In base station <NUM>, transmission processing section <NUM> transmits control information indicating whether or not to request a sounding reference signal (SRS) transmission to terminal <NUM>, and reception processing section <NUM> detects an SRS transmitted from terminal <NUM> at a predetermined timing based on the control information. In Embodiment <NUM>, configuration section <NUM> controls the transmission of a transmission request, and only one piece of control information is transmitted within an effective period. Base station <NUM> instructs terminal <NUM> to transmit an SRS, using an A-SRS transmission request transmitted from transmission processing section <NUM>.

<FIG> is a main configuration diagram of terminal <NUM> according to Embodiment <NUM> of the present invention. In terminal <NUM>, reception processing section <NUM> detects control information indicating whether or not transmission of a sounding reference signal (SRS) is requested, and transmission signal forming section <NUM> transmits an A-SRS under the control of transmission controlling section <NUM> based on the control information. Transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of an "SRS transmission execution rule" and the reception condition of trigger information.

Hereinafter, a description will be provided on an FDD system in which the uplink and downlink are separated in the frequency domain.

<FIG> is a block diagram illustrating a configuration of base station <NUM> according to Embodiment <NUM> of the present invention. In <FIG>, base station <NUM> includes configuration section <NUM>, coding and modulation sections <NUM> and <NUM>, transmission processing section <NUM>, RF transmitting section <NUM>, antenna <NUM>, RF receiving section <NUM>, reception processing section <NUM>, data receiving section <NUM>, and SRS receiving section <NUM>.

Configuration section <NUM> generates "A-SRS transmission rule configuration information" for configuring configuration target terminal <NUM> with correspondence between control information formats (DCI formats) used for requesting A-SRS transmission and resources used by configuration target terminal <NUM> for the A-SRS transmission (i.e., A-SRS resource). The A-SRS transmission rule configuration information includes identification information for a plurality of control information formats (DCI formats) and information about the A-SRS resource corresponding to the identification information on each of the control information formats. This A-SRS resource is a resource for configuration target terminal <NUM> to map an A-SRS as described above. The information about the A-SRS resource includes parameters for configuration target terminal <NUM> to transmit an A-SRS, such as the frequency band (or RB position where the SRS band starts), frequency bandwidth (or the number of RBs), Cyclic Shift, transmission Comb, the number of antennas, the number of times the transmission is to be performed, frequency hopping, and component carrier. More specifically, configuration target terminal <NUM> is configured with a combination of the identification information on each of a plurality of control information formats (DCI formats) and the abovementioned parameters corresponding to the identification information on a corresponding one of the control information formats by the A-SRS transmission rule configuration information. The A-SRS resources in accordance with the number of bits used as the trigger information for the DCI formats (i.e., the number of A-SRS resource candidates that can be reported using the trigger information) are associated respectively with bit states that can be expressed by the number of bits. In the case of <NUM> bit, for example, one bit state is used to report "no SRS transmission request," so that the number of resource types that can be reported is limited to only one. For this reason, the other bit state is associated with resource A. In the case of <NUM> bits, three resource types can be reported, so that three bit states are associated with three resources B, C, and D, respectively.

Configuration section <NUM> generates uplink assignment control information or downlink assignment control information that includes trigger information requesting an A-SRS transmission for configuration target terminal <NUM> (hereinafter, simply referred to as "trigger information").

The A-SRS transmission rule configuration information generated by configuration section <NUM> in the manner described above is subjected to transmission processing as control information of the RRC layer in coding and modulation section <NUM>, transmission processing section <NUM>, and RF transmitting section <NUM> and thereafter transmitted to configuration target terminal <NUM>. The control information including trigger information for A-SRS transmission is subjected to transmission processing in coding and modulation section <NUM>, transmission processing section <NUM>, and RF transmitting section <NUM> as control information of layers <NUM> and <NUM> and thereafter transmitted to configuration target terminal <NUM>. When the trigger information consists of <NUM> bit (e.g., DCI format <NUM>), the bit value "<NUM>" indicates an A-SRS transmission request using resource A, and the bit value "<NUM>" indicates no A-SRS transmission request. When the trigger information consists of <NUM> bits (e.g., DCI format <NUM>), among four bit states, state <NUM> indicates no A-SRS transmission request, and states <NUM>, <NUM> and <NUM> indicate an A-SRS transmission request using resources B, C, and D, respectively. Configuration section <NUM> configures resources A, B, C and D.

Configuration section <NUM> generates assignment control information including trigger information, resource (RB) allocation information, and MCS information for one or more transport blocks (TBs) The assignment control information may be assignment control information on an uplink resource for assigning uplink data (e.g., Physical Uplink Shared Channel (PUSCH)) or on a downlink resource for assigning downlink data (e.g., Physical Downlink Shared Channel (PDSCH)). The assignment control information for assigning uplink data includes DCI formats <NUM> and <NUM>, and the assignment control information for assigning downlink data includes DCI format 1A, <NUM>, 1B, 1D, <NUM>, 2A and/or the like.

Configuration section <NUM> generates control information including trigger information indicating a transmission request to a terminal in order that the control information can be transmitted within the effective period corresponding to the subframe in which the terminal is caused to transmit an A-SRS. Embodiment <NUM> assumes that base station <NUM> transmits control information including trigger information indicating an SRS transmission request to one target terminal only once within a single effective period.

Configuration section <NUM> transmits the A-SRS transmission rule configuration information to configuration target terminal <NUM> via coding and modulation section <NUM> and also outputs the information to reception processing section <NUM>. Configuration section <NUM> transmits the assignment control information including trigger information to configuration target terminal <NUM> via coding and modulation section <NUM> and also outputs the information to transmission processing section <NUM>. Configuration section <NUM> outputs information indicating the format of the assignment control information including trigger information to reception processing section <NUM>.

The configuration information is reported to terminal <NUM> from base station <NUM> as higher layer information (i.e., via RRC signaling). Meanwhile, the assignment control information (including trigger information) is reported to terminal <NUM> from base station <NUM> using Physical Downlink Control Channel (PDCCH). Specifically, the reporting intervals for the configuration information are relatively long (i.e., reported between relatively long intervals) while the reporting intervals for the assignment control information are relatively short (i.e., reported between relatively short intervals).

Coding and modulation section <NUM> encodes and modulates the configuration information and assignment control information received from configuration section <NUM> and outputs the resultant modulation signal to transmission processing section <NUM>.

Coding and modulation section <NUM> encodes and modulates data signals to be received and outputs the obtained modulation signal to transmission processing section <NUM>.

Transmission processing section <NUM> maps the modulation signals to be received from coding and modulation sections <NUM> and <NUM> to the resource indicated by the resource allocation information to be received from configuration section <NUM>, thereby forming a transmission signal. For this processing, when the transmission signal is an OFDM signal, the modulation signal is mapped to the resource indicated by the downlink resource allocation information to be received from configuration section <NUM>, then transforms the signal into a time waveform by inverse fast Fourier transform (IFFT) processing, and adds a cyclic prefix (CP) to the resultant signal, thereby forming an OFDM signal.

RF transmitting section <NUM> performs radio transmission processing (such as up-conversion and digital to analog (D/A) conversion) on the transmission signal to be received from transmission processing section <NUM>.

RF receiving section <NUM> performs radio reception processing (such as down-conversion and analog to digital (A/D) conversion) and outputs the resultant received signal to reception processing section <NUM>.

Reception processing section <NUM> identifies the resource to which the uplink data signal and ACK/NACK information are mapped, on the basis of the uplink resource allocation information received from configuration section <NUM> and extracts signal components mapped to the identified resource from the received signal.

In addition, reception processing section <NUM> identifies the resource to which an A-SRS is mapped, on the basis of the A-SRS transmission rule configuration information, trigger information, and the information on the DCI format used for the A-SRS transmission request received from configuration section <NUM> and extracts signal components mapped to the identified resource from the received signal. More specifically, reception processing section <NUM> receives the A-SRS on the identified resource in the first common SRS subframe located at or after a k-th subframe (k=<NUM> in this case) from the subframe in which the trigger information is transmitted.

When the received signal is a spatially multiplexed signal (i.e., transmitted by a plurality of codewords (CWs)), reception processing section <NUM> demultiplexes the received signals for each CW. In addition, when the received signal is an OFDM signal, reception processing section <NUM> transforms the received signal into a time-domain signal by performing inverse discrete Fourier transform (IDFT) processing on the extracted signal components.

The uplink data signal and ACK/NACK information extracted by reception processing section <NUM> as described above are outputted to data receiving section <NUM>, and the A-SRS signal is outputted to SRS receiving section <NUM>.

Data receiving section <NUM> decodes the signal received from reception processing section <NUM>. Thus, the uplink data and ACK/NACK information are obtained.

SRS receiving section <NUM> measures the reception quality of each frequency resource on the basis of the A-SRS signal received from reception processing section <NUM> and outputs the reception quality information. When a plurality of A-SRS signals transmitted from different terminals <NUM> are code-multiplexed using an orthogonal sequence and/or the like, SRS receiving section <NUM> performs demultiplexing processing on the code-multiplexed A-SRS signals.

<FIG> is a block diagram illustrating a configuration of terminal <NUM> according to Embodiment <NUM> of the present invention. Terminal <NUM> is an LTE-A compliant terminal in Embodiment <NUM>.

In <FIG>, terminal <NUM> includes antenna <NUM>, RF receiving section <NUM>, reception processing section <NUM>, reference signal generating section <NUM>, data signal generating section <NUM>, transmission controlling section <NUM>, transmission signal forming section <NUM>, and RF transmitting section <NUM>.

RF receiving section <NUM> performs radio receiving processing (such as down-conversion and analog to digital (A/D) conversion) on the radio signal received via antenna <NUM> and outputs the resultant received signal to reception processing section <NUM>.

Reception processing section <NUM> extracts the configuration information, assignment control information, and data signal in the received signal. Reception processing section <NUM> outputs the configuration information and assignment control information to transmission controlling section <NUM>. In addition, reception processing section <NUM> outputs the DCI format identification information of the assignment control information in which the trigger information has been included to transmission controlling section <NUM>. Reception processing section <NUM> performs error detection processing on the extracted data signal and outputs ACK/NACK information in accordance with the result of error detection to data signal generating section <NUM>. Reception processing section <NUM> detects DCI by blind-decoding and extracts the assignment control information from the detected DCI.

Reference signal generating section <NUM> generates a reference signal upon reception of an instruction to generate a reference signal from transmission controlling section <NUM> and outputs the reference signal to transmission signal forming section <NUM>.

Data signal generating section <NUM> takes the ACK/NACK information and transmission data as input and generates a data signal by encoding and modulating the ACK/NACK information and transmission data on the basis of MCS information to be received from transmission controlling section <NUM>. In the case of Non-MIMO transmission, a data signal is generated by single codeword (CW), while a data signal is generated by two codewords in the case of MIMO. When the received signal is an OFDM signal, data signal generating section <NUM> performs CP removal processing and FFT processing.

Transmission controlling section <NUM> determines whether or not to perform SRS transmission, on the basis of the "SRS transmission execution rule" and the reception condition of the trigger information. The "SRS transmission execution rule" in Embodiment <NUM> indicates that an SRS is transmitted in accordance with the assignment control information that includes the trigger information indicating a transmission request and that is detected first within an effective period. More specifically, upon detection of trigger information indicating a transmission request for a common SRS subframe of subframe number n, once, transmission controlling section <NUM> disregards trigger information and assignment control information included in DCI even when detecting DCI including trigger information indicating a transmission request after the detection of the first trigger information within the effective period in which an A-SRS of subframe number n can be requested (i.e., during a period from subframe n-(Np+k+<NUM>) until subframe n-k).

When determining to perform SRS transmission, transmission controlling section <NUM> configures a resource for terminal <NUM> to map an A-SRS signal. Specifically, transmission controlling section <NUM> identifies the resource on the basis of the configuration information (A-SRS transmission rule configuration information), and DCI format identification information of the assignment control information in which the trigger information has been included, which are to be received from reception processing section <NUM>. In addition, when multiple bits are included as trigger information, SRS resource reporting information included in the trigger information is used for identifying the resource.

Transmission controlling section <NUM> configures the first common SRS subframe located at or after a k-th subframe from the subframe in which the assignment control information including the trigger information is transmitted, to be the transmission subframe for an A-SRS. Upon receipt of the trigger information, transmission controlling section <NUM> outputs an instruction to generate a reference signal to reference signal generating section <NUM> and outputs information about the identified SRS resource to transmission signal forming section <NUM>.

Transmission controlling section <NUM> identifies a "data mapping resource" to which the data signal is mapped, on the basis of the assignment control information to be received from reception processing section <NUM> and outputs information about the data mapping resource (hereinafter, referred to as "data mapping resource information") to transmission signal forming section <NUM> and also outputs MCS information included in the assignment control information to data signal generating section <NUM>.

Transmission signal forming section <NUM> maps the A-SRS signal to be received from reference signal generating section <NUM> to the SRS mapping resource. Transmission signal forming section <NUM> maps the data signal to be received from data signal generating section <NUM> to the data mapping resource indicated by the data mapping resource information. The transmission signal is formed in the manner described above. In the case of Non-MIMO transmission, a single codeword data signal is assigned to a single layer, while a two codeword data signal is assigned to a plurality of layers in the case of MIMO transmission. When the transmission signal is an OFDM signal, transmission signal forming section <NUM> performs discrete Fourier transform (DFT) processing on the data signal and thereafter maps the processed data signal to the data mapping resource. Meanwhile, a CP is added to the formed transmission signal.

RF transmitting section <NUM> performs radio transmission processing (such as up-conversion and digital to analog (D/A) conversion) on the transmission signal formed by transmission signal forming section <NUM> and transmits the processed signal via antenna <NUM>.

A description will be provided with reference to <FIG>, regarding the operation of base station <NUM> and terminal <NUM> configured in the manner described above. This description assumes that the assignment control information of DCI format <NUM> and DCI format <NUM> includes trigger information. <FIG> describe the processing related to the uplink data assignment and A-SRS transmission request in base station <NUM> and to the data transmission and A-SRS transmission in terminal <NUM>. The data assignment reporting and data transmission are performed on a per subframe basis.

As illustrated in <FIG>, base station <NUM> transmits at most one piece of DCI that includes an A-SRS transmission request to each terminal <NUM> within an effective period corresponding to one common SRS subframe.

Meanwhile, transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of the "SRS transmission execution rule" and the reception condition of the trigger information in terminal <NUM>. Specifically, the "SRS transmission execution rule" in Embodiment <NUM> indicates that an SRS is transmitted in accordance with the assignment control information which includes trigger information indicating a transmission request and which is detected first within an effective period. More specifically, even if DCI that includes an A-SRS transmission request is detected after detection of first DCI that includes an A-SRS transmission request within a single effective period, the DCI detected after the first DCI is disregarded. Stated differently, when a plurality of pieces of DCI that include trigger information indicating an A-SRS transmission request are detected within a single effective period, no A-SRS is transmitted on the SRS resource requested by a piece of DCI that includes an A-SRS transmission request and that is detected after the first DCI, but an A-SRS is transmitted on the SRS resource requested by the first piece of DCI that includes an A-SRS transmission request and that is detected first (see, <FIG>).

The control of SRS transmission according to the "SRS transmission execution rule" described above makes it possible to reduce the probability of terminal <NUM> erroneously detecting DCI or the probability of terminal <NUM> transmitting an A-SRS using an SRS resource different from an SRS resource requested by base station <NUM>, due to erroneous detection of A-SRS trigger information. In this situation, when terminal <NUM> erroneously detects DCI that includes an A-SRS transmission request before base station <NUM> transmits DCI that includes an A-SRS transmission request, terminal <NUM> wrongly transmits an A-SRS. However, when base station <NUM> reports an A-SRS transmission request using an earliest possible subframe within an effective period, the probability of terminal <NUM> erroneously detecting DCI before base station <NUM> reports an A-SRS transmission request within the effective period can be reduced. In addition, this configuration provides an advantage in that the processing of terminal <NUM> becomes very simple because terminal <NUM> needs to prepare for A-SRS transmission only according to the first trigger information.

When detecting a different piece of DCI that includes an A-SRS transmission request after detecting a first piece of DCI that includes an A-SRS transmission request within a single effective period, terminal <NUM> may treat data assignment according to the different piece of DCI (i.e., information about data assignment such as data RBs, MCS, transmission power control, and/or the like) as valid information and disregards only the A-SRS trigger information included in the different piece of DCI. Specifically, the assignment reporting information on the data assignment and the A-SRS trigger information in a piece of DCI may be treated, independently. In this case, no A-SRS is transmitted using the SRS resource indicated by the DCI that includes an A-SRS transmission request and that is detected after the first DCI, but an A-SRS is transmitted using the SRS resource requested by the DCI that includes an A-SRS transmission request and that is detected first within a single effective period, while uplink data (PUSCH) is transmitted according to the data assignment information indicated by the DCI that includes an A-SRS transmission request and that is detected after the first DCI. Stated differently, the information other than the A-SRS trigger information in the information included in the assignment reporting information in DCI (i.e., RB allocation, MCS reporting information, and/or the like) is treated as valid regardless of the state of any A-SRS trigger information detected before the DCI, and the A-SRS trigger information detected before the DCI is determined to be valid or invalid depending on the presence or absence of the A-SRS trigger information detected before the DCI.

The A-SRS and A-SRS trigger information are newly introduced in LTE-Advanced. Meanwhile the assignment reporting information other than A-SRS trigger information in DCI is already defined in LTE. Specifically, the processing circuit configured to perform the operation relating to the assignment reporting information in DCI has been already implemented in LTE base stations and LTE terminals before LTE-Advanced. Thus, determining validity or invalidity of the assignment reporting information and A-SRS trigger information in a piece of DCI independently makes it possible to continue using the processing circuit that has been already implemented in LTE without any modification as described above. Accordingly, the man-hours required for implementation can be reduced since it requires only addition of the processing part corresponding to the A-SRS related part.

In Embodiment <NUM>, the "SRS transmission execution rule" indicates that an A-SRS is transmitted according to the assignment control information that includes trigger information indicating a transmission request and that is detected last within an effective period. The base station and terminal according to Embodiment <NUM> are similar to base station <NUM> and terminal <NUM> according to Embodiment <NUM> in their basic configurations, so that Embodiment <NUM> will be described with reference to <FIG> and <FIG>.

In base station <NUM> according to Embodiment <NUM>, configuration section <NUM> generates DCI that includes trigger information indicating an A-SRS transmission request in one or more subframes within an effective period for each terminal <NUM>. Specifically, base station <NUM> according to Embodiment <NUM> is capable of reallocating an A-SRS resource to each terminal <NUM> within an effective period corresponding to a certain common SRS subframe in accordance with the A-SRS assignment state for a plurality of terminals <NUM> in the common SRS subframe.

In terminal <NUM> according to Embodiment <NUM>, transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of the "SRS transmission execution rule" and the reception condition of trigger information. The "SRS transmission execution rule" in Embodiment <NUM> indicates that an A-SRS is transmitted according to the assignment control information that includes trigger information indicating a transmission request and that is detected last within an effective period. Specifically, when detecting a first piece of DCI that includes trigger information indicating a transmission request in an effective period corresponding to a common SRS subframe of subframe number n and detecting a different piece of DCI that includes trigger information indicating a transmission request in a different subframe transmitted after the subframe in which the first piece of DCI is detected (i.e., during a period from the initial detection timing until a subframe corresponding to subframe n-k) in the same period, transmission controlling section <NUM> overwrites the information about the SRS resource indicated by the previous trigger information with the information about the SRS resource indicated by the trigger information in the piece of DCI detected this time. Accordingly, transmission controlling section <NUM> can hold the latest information about the SRS resource in each effective period. Transmission controlling section <NUM> outputs an instruction to generate a reference signal to reference signal generating section <NUM> and also outputs the updated information about the SRS resource to transmission signal forming section <NUM> in accordance with the result of overwriting the information.

The operation of base station <NUM> and terminal <NUM> according to Embodiment <NUM>, which are configured in the manner described above, will be described with reference to <FIG>. In <FIG>, base station <NUM> transmits DCI that includes trigger information indicating an A-SRS transmission request in one subframe and also transmits DCI that includes trigger information indicating an A-SRS transmission request in a subsequent subframe in a single effective period.

In <FIG>, terminal <NUM> correctly detects all pieces of DCI and receives trigger information indicating an A-SRS transmission request in two subframes. Terminal <NUM> then transmits an A-SRS according to the "SRS transmission execution rule" and the assignment control information that includes trigger information indicating a transmission request and that is detected last within the effective period.

In <FIG>, terminal <NUM> fails to detect DCI that includes trigger information indicating an A-SRS transmission request and that is transmitted first within a single effective period. Specifically, terminal <NUM> fails to recognize that the DCI is intended for terminal <NUM> because the result of error detection does not indicate OK as a result of the presence of a bit error. In this effective period, however, the DCI that indicates trigger information indicating an A-SRS transmission request and that is transmitted after the DCI that has resulted in detection failure is correctly detected. Thus, terminal <NUM> transmits an A-SRS according to the A-SRS trigger information included in the correctly detected DCI.

As described above, base station <NUM> transmits DCI that includes trigger information indicating an A-SRS transmission request in a plurality of subframes within a single effective period, while the transmission of SRS is controlled according to the "SRS transmission execution rule. " Thus, terminal <NUM> can correctly transmit an A-SRS even when failing to detect DCI transmitted during an early stage of the effective period, as long as terminal <NUM> can detect DCI transmitted after the earlier DCI. As a result, base station <NUM> can measure appropriate channel quality.

In addition, base station <NUM> can change an SRS resource by transmitting a plurality of pieces of trigger information within an effective period. Specifically, base station <NUM> can request A-SRS transmission to be performed using an SRS resource different from the SRS resource reported by first trigger information, by transmitting second trigger information indicating the different SRS resource, after the first trigger information. For example, when base station <NUM> needs a certain terminal <NUM> with higher priority to perform A-SRS transmission using an SRS resource (e.g., resource A) after transmitting an A-SRS transmission request with the same SRS resource (resource A) to a different terminal <NUM>, base station <NUM> transmits A-SRS trigger information indicating a different SRS resource (e.g., resource B) for overwriting the previously indicated SRS resource. The different SRS resource may be indicated by using a different DCI format or using the same DCI format but reporting a different state of the A-SRS trigger information. As described above, base station <NUM> can reallocate an SRS resource to terminal <NUM> by overwriting an SRS resource that has been reported to terminal <NUM> with a different resource. Accordingly, it is possible to prevent a collision between SRS resources allocated to a plurality of terminals <NUM>.

As described above, when terminal <NUM> erroneously detects DCI, an A-SRS may be transmitted using a wrong SRS resource. However, when terminal <NUM> correctly receives DCI that includes trigger information indicating an A-SRS transmission request and that is transmitted in the last subframe within the effective period, terminal <NUM> does not transmit an A-SRS using a wrong SRS resource. Alternatively, reporting DCI that includes trigger information indicating an A-SRS transmission request from base station <NUM>, using a latest possible subframe in the effective period makes it possible to reduce the probability of terminal <NUM> erroneously detecting DCI or the probability of terminal <NUM> transmitting an A-SRS using an SRS resource different from the SRS resource required by base station <NUM>, due to erroneous detection of A-SRS trigger information.

In Embodiment <NUM>, the "SRS transmission execution rule" indicates that upon detection of a plurality of pieces of DCI each of which includes trigger information indicating an A-SRS transmission request within an effective period, no A-SRS is transmitted in any common SRS subframe corresponding to the effective period. The base station and terminal according to Embodiment <NUM> are similar to base station <NUM> and terminal <NUM> according to Embodiment <NUM> in their basic configurations, so that Embodiment <NUM> will be described with reference to <FIG> and <FIG>.

In base station <NUM> according to Embodiment <NUM>, configuration section <NUM> generates DCI that includes trigger information indicating an A-SRS transmission request in one or two subframes within an effective period for each terminal <NUM>. The number of times this trigger information is generated is controlled in accordance with the A-SRS assignment state for a plurality of terminals <NUM> in a certain common SRS subframe. For example, when base station <NUM> needs a certain terminal <NUM> with higher priority to perform A-SRS transmission using an SRS resource (e.g., resource A) after transmitting an A-SRS transmission request using the same SRS resource (resource A) to a different terminal <NUM>, base station <NUM> transmits A-SRS trigger information indicating an A-SRS transmission request again within the same effective period to cancel the previously made A-SRS transmission request.

In terminal <NUM> according to Embodiment <NUM>, transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of the "SRS transmission execution rule" and the reception condition of the trigger information. In Embodiment <NUM>, the "SRS transmission execution rule" indicates that upon detection of a plurality of pieces of DCI each of which includes trigger information indicating an A-SRS transmission request within an effective period, no A-SRS is transmitted in any common SRS subframe corresponding to the effective period. Specifically, when transmission controlling section <NUM> detects first piece of DCI that includes trigger information indicating a transmission request in an effective period corresponding to a common SRS subframe of subframe number n and detecting a different piece of DCI that includes trigger information indicating a transmission request in a different subframe transmitted after the subframe in which the first piece of DCI is detected (i.e., during a period from the initial detection timing until a subframe corresponding to subframe n-k) in the same period, transmission controlling section <NUM> determines the A-SRS trigger information to be invalid and also invalidates (i.e., cancels) the A-SRS trigger information that is detected before the A-SRS trigger information. In this case, transmission controlling section <NUM> outputs an instruction to cancel the instruction to generate a reference signal to reference signal generating section <NUM>.

The operation of base station <NUM> and terminal <NUM> according to Embodiment <NUM> configured in the manner described above will be described with reference to <FIG>. In <FIG>, base station <NUM> transmits DCI that includes trigger information indicating an A-SRS transmission request in a single subframe and transmits DCI that includes trigger information indicating no A-SRS transmission request in uplink data assignment reporting in subframes other than the single subframe.

In <FIG>, terminal <NUM> correctly receives all pieces of DCI intended for terminal <NUM> without erroneous detection of DCI within the effective period. In addition, terminal <NUM> transmits an A-SRS using an SRS resource according to the A-SRS trigger information indicating a transmission request and detected in the single subframe within the effective period.

Meanwhile, in <FIG>, although base station <NUM> transmits DCI intended for terminal <NUM> in two subframes within a single effective period, terminal <NUM> detects DCI that includes trigger information indicating an A-SRS transmission request in a different subframe (i.e., erroneous detection). Since terminal <NUM> detects two pieces of DCI each of which includes trigger information indicating an A-SRS transmission request within the single effective period, terminal <NUM> transmits no A-SRS according to the "SRS transmission execution rule.

The SRS transmission control according to the "SRS transmission execution rule" as described above can reduce the probability of terminal <NUM> erroneously transmitting an A-SRS due to erroneous detection. Meanwhile, when terminal <NUM> erroneously detects DCI that includes trigger information indicating an A-SRS transmission request although base station <NUM> has not made an A-SRS transmission request even once during a certain effective period, terminal <NUM> erroneously transmits an A-SRS. However, when base station <NUM> makes an A-SRS transmission request even once during a single effective period, erroneous transmission of an A-SRS due to erroneous detection by terminal <NUM> can be prevented. In addition, erroneous transmission of data due to erroneous detection of the second DCI indicating the second A-SRS transmission request can be prevented.

The control of SRS transmission according to the "SRS transmission execution rule" described above allows base station <NUM> to cancel an A-SRS transmission request that has been reported to a certain terminal <NUM>, by intentionally transmitting a plurality of transmission requests. Thus, the resource that has become available because of the cancellation can be allocated to different terminal <NUM> with higher priority. Accordingly, A-SRS resource allocation to terminals <NUM> according to priority is made possible, which in turn makes it possible to reduce the amount of delay in acquiring A-SRS reception quality information for terminal <NUM> with higher priority. As a result, the data transmission delay to terminal <NUM> with higher priority can be reduced.

When detecting a different piece of DCI that includes an A-SRS transmission request after detecting a first piece of DCI that includes an A-SRS transmission request in a single effective period, terminal <NUM> may treat data assignment according to the different piece of DCI as valid and treat only trigger information included in the different piece of DCI as invalid, or may treat both of the data assignment and trigger information as invalid. In the former case, when canceling an A-SRS transmission request that has been reported to certain terminal <NUM>, base station <NUM> can perform new data assignment while canceling only the A-SRS transmission request. The latter case is effective when there is no data to be newly assigned, because base station <NUM> can cancel only an A-SRS transmission request without involving data assignment, and terminal <NUM> transmits no wasteful data. In addition, the former and the latter can be switched according to additional control information transmitted from base station <NUM> to terminal <NUM>.

In Embodiment <NUM>, the "SRS transmission execution rule" indicates that no A-SRS is transmitted upon detection of even one piece of DCI that includes trigger information indicating no A-SRS transmission after detection of a first piece of DCI that includes the trigger information indicating an A-SRS transmission request, or upon detection of a piece of DCI indicating an SRS resource different from the SRS resource indicated by the first piece of DCI within an effective period. In Embodiment <NUM>, when transmitting the first piece of DCI that includes trigger information indicating an A-SRS transmission request, and thereafter reporting data assignment using a different piece of DCI of the same DCI format as that of the first piece of DCI, the base station includes, in the different piece of DCI, trigger information indicating the same SRS resource as the SRS resource indicated by the trigger information in the first piece of DCI. Stated differently, an assumption is made that base station <NUM> repeatedly transmits a piece of DCI that includes the trigger information indicating the same SRS resource in a single effective period. The base station and terminal according to Embodiment <NUM> are similar to base station <NUM> and terminal <NUM> according to Embodiment <NUM> in their basic configurations, so that Embodiment <NUM> will be described with reference to <FIG> and <FIG>.

In base station <NUM> according to Embodiment <NUM>, when generating a first piece of DCI that includes trigger information indicating an A-SRS transmission request to terminal <NUM> in one subframe in a single effective period, configuration section <NUM> includes trigger information indicating the A-SRS transmission request in a different piece of DCI to be transmitted thereafter within the same effective period if a "predetermined condition" is satisfied. The "predetermined condition" is that the DCI format of a different piece of DCI is the same as that of the first piece of DCI. The SRS resource indicated by the trigger information included in the different piece of DCI is also matched with the SRS resource indicated by the trigger information included in the first piece of DCI. Stated differently, base station <NUM> according to Embodiment <NUM> repeatedly transmits a piece of DCI that includes the trigger information indicating the A-SRS transmission request within a single effective period as long as the "predetermined condition" is satisfied, basically.

In terminal <NUM> according Embodiment <NUM>, transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of the "SRS transmission execution rule" and the reception condition of trigger information. In Embodiment <NUM>, the "SRS transmission execution rule" indicates that upon detection of a piece of DCI that includes trigger information indicating no A-SRS transmission request even once after detection of a first piece of DCI that includes trigger information indicating an A-SRS transmission request, or upon detection of a piece of DCI that indicates an SRS resource different from the SRS resource indicated by the first piece of DCI within an effective period, no A-SRS is transmitted in any common SRS subframe corresponding to the effective period. Specifically, when detecting a piece of DCI that includes trigger information indicating a transmission request first in an effective period corresponding to the common SRS subframe of subframe n and thereafter detecting a piece of DCI that includes trigger information indicating no A-SRS transmission request in a different subframe after the subframe in which the first piece of DCI is detected (i.e., period from the initial detection timing to the subframe corresponding to subframe n-k) even once in the effective period, transmission controlling section <NUM> determines that there is no A-SRS transmission. In addition, when detecting a piece of DCI that includes trigger information indicating an A-SRS transmission request using an SRS resource different from the SRS resource indicated by the first piece of DCI, transmission controlling section <NUM> also determines that there is no A-SRS transmission. In this case, transmission controlling section <NUM> outputs an instruction to cancel the instruction to generate a reference signal to reference signal generating section <NUM>.

The operation of base station <NUM> and terminal <NUM> according to Embodiment <NUM> configured in the manner described above will be described with reference to <FIG>.

In <FIG>, base station <NUM> transmits a piece of DCI that includes trigger information indicating the presence of an A-SRS transmission request in a single subframe and repeatedly transmits a piece of DCI that includes trigger information indicating the presence of an A-SRS transmission request after the single subframe in a single effective period. In <FIG>, terminal <NUM> correctly detects all pieces of DCI. Terminal <NUM> transmits an A-SRS according to the "SRS transmission execution rule" under the detection state of the pieces of DCI.

On the other hand, <FIG> illustrates a case where base station <NUM> makes no A-SRS transmission request to terminal <NUM> within a certain effective period. In <FIG>, base station <NUM> transmits DCI that includes trigger information indicating no A-SRS transmission request in two subframes within the effective period. Meanwhile, terminal <NUM> detects two pieces of DCI actually transmitted from base station <NUM> after erroneously detecting a piece of DCI that includes trigger information indicating an A-SRS transmission request. Terminal <NUM> transmits no A-SRS under this detection state of the pieces of DCI according to the "SRS transmission execution rule.

In addition, although the operation is not illustrated in the drawings, when erroneously detecting that the third piece of DCI transmitted from base station <NUM> and thus determining that the third piece of DCI is DCI that includes A-SRS trigger information indicating an A-SRS transmission request using resource B in <FIG>, terminal <NUM> performs no A-SRS transmission because the indicated resource is a resource different from the resource indicated by the previously detected A-SRS trigger information.

The control of SRS transmission according to the DCI transmission rule of base station <NUM> and the "SRS transmission execution rule" of terminal <NUM> in the manner described above, even when erroneously detecting DCI that includes trigger information indicating A-SRS transmission, terminal <NUM> can determine that terminal <NUM> has erroneously detected the DCI because of trigger information included in the DCI to be received by terminal <NUM> after the erroneous detection of DCI. Accordingly, the probability of terminal <NUM> erroneously detecting DCI, or the probability of terminal <NUM> transmitting an A-SRS using an SRS resource different from the SRS resource required by base station <NUM> due to erroneous detection of A-SRS trigger information by terminal <NUM> can be reduced.

As long as base station <NUM> satisfies the abovementioned "predetermined condition," repeatedly transmitting DCI that includes trigger information indicating an A-SRS transmission request in a single effective period allows an A-SRS to be correctly transmitted even when terminal <NUM> erroneously detects DCI that includes trigger information indicating an A-SRS transmission request. As a result, base station <NUM> can measure appropriate channel quality.

In addition, the control of SRS transmission according to the "SRS transmission execution rule" as described above allows base station <NUM> to cancel an A-SRS transmission request that has been reported to a certain terminal <NUM>. For example, when base station <NUM> makes an A-SRS transmission request with a certain SRS resource (e.g., resource A) to first terminal <NUM> first but needs second terminal <NUM> with higher priority to transmit an A-SRS using the same resource (resource A), base station <NUM> transmits assignment control information that is of the same DCI format as that used for the previous A-SRS transmission request and that includes trigger information indicating no A-SRS transmission request to terminal <NUM>, in order to cancel the A-SRS transmission request that has been transmitted to first terminal <NUM>. In this case, according to the "SRS transmission execution rule," first terminal <NUM> transmits no A-SRS. The resource thus made available in this case can be allocated to different terminal <NUM> with higher priority. Thus, A-SRS resource allocation to terminals <NUM> according to priority is made possible, and the amount of delay in acquiring A-SRS reception quality information for terminal <NUM> with higher priority can be reduced. As a result, the data transmission delay to terminal <NUM> with higher priority can be reduced.

The control of SRS transmission according to the "transmission execution rule" described above controls terminals in a way that prevents the terminals from transmitting any A-SRS when the terminals detect DCI that includes trigger information indicating an A-SRS transmission request and thereafter detects DCI that indicates an SRS resource different from the SRS resource indicated by the first DCI within an effective period. Accordingly, it is possible to reduce the probability of a terminal transmitting an A-SRS using a wrong resource due to erroneous detection of DCI that indicates A-SRS trigger information indicating a resource different from a resource actually indicated by the base station within an effective period, thus, reducing the probability of the terminal unnecessarily interfering with a different terminal or a different cell.

It should be noted that, it is possible to use only any one of the two "SRS transmission execution rules" in this embodiment. For example, it is possible to use only the "SRS transmission execution rule" that indicates that no A-SRS is transmitted upon detection of even one piece of DCI that includes trigger information indicating no A-SRS transmission request after detection of the first DCI that includes trigger information indicating an A-SRS transmission request, or to use only the "SRS transmission execution rule" that indicates no A-SRS is transmitted when a terminal receives DCI that includes trigger information indicating an A-SRS transmission request first and thereafter detects DCI that indicates an SRS resource different from the SRS resource indicated by the first DCI. In this case, the DCI that indicates a different SRS resource is DCI that includes trigger information indicating an A-SRS configuration including a different SRS resource.

In Embodiment <NUM>, the "SRS transmission execution rule" indicates that no A-SRS is transmitted upon detection of first DCI that includes trigger information indicating an A-SRS transmission request and detection of even one piece of different DCI that includes trigger information indicating no A-SRS transmission request within an effective period, as in Embodiment <NUM>. However, Embodiment <NUM> is different from Embodiment <NUM> in that the "SRS transmission execution rule" indicates that even upon detection of a different piece of DCI that indicates an SRS resource different from the SRS resource indicated by the first piece of DCI, an A-SRS is transmitted according to the trigger information included in the different piece of DCI when the DCI format of the different piece of DCI is different from the DCI format of the first piece of DCI. As in Embodiment <NUM>, when transmitting a first piece of DCI that includes trigger information indicating an A-SRS transmission request and thereafter reporting data assignment by a piece of DCI different from the first DCI but of the same DCI format as that of the first piece of DCI in an effective period, the base station includes, in the different piece of DCI, trigger information indicating the same SRS resource as the SRS resource indicated by the trigger information in the first piece of DCI in Embodiment <NUM>. Specifically, an assumption is made that base station <NUM> repeatedly transmits DCI that includes trigger information indicating the same SRS resource within a single effective period. The base station and terminal according to Embodiment <NUM> are similar to base station <NUM> and terminal <NUM> according to Embodiment <NUM> in their basic configurations, so that Embodiment <NUM> will be described with reference to <FIG> and <FIG>.

In base station <NUM> according to Embodiment <NUM>, when generating a first piece of DCI that includes trigger information indicating an A-SRS transmission request for terminal <NUM> in one subframe within an effective period, configuration section <NUM> includes trigger information indicating an A-SRS transmission request in a different piece of DCI to be transmitted thereafter within the effective period when a "predetermined condition" is satisfied. The "predetermined condition" is that the DCI format of the different piece of DCI is the same as that of the first piece of DCI. In addition, the SRS resource indicated by the trigger information included in the different piece of DCI is also matched with the SRS resource indicated by the trigger information included in the first piece of DCI. Specifically, base station <NUM> according to Embodiment <NUM> repeatedly transmits DCI that includes trigger information indicating an A-SRS transmission request within a single effective period as long as the "predetermined condition" is satisfied, basically.

However, when reallocating an A-SRS resource used in a previous transmission request to each terminal <NUM>, in accordance with the A-SRS assignment state for terminals <NUM>, configuration section <NUM> changes the DCI format of the assignment control information to another and includes trigger information indicating an A-SRS transmission request in the assignment control information.

In terminal <NUM> according to Embodiment <NUM>, transmission controlling section <NUM> determines whether or not to perform SRS transmission on the basis of the "SRS transmission execution rule" and the reception condition of trigger information. The "SRS transmission execution rule" in Embodiment <NUM> indicates that upon detection of a piece of DCI that includes trigger information indicating no A-SRS transmission request even once after detection of a piece of DCI that includes trigger information indicating an A-SRS transmission request within an effective period, no A-SRS is transmitted in any common SRS subframe corresponding to the effective period. Specifically, when detecting a piece of DCI that includes trigger information indicating an A-SRS transmission request once in an effective period corresponding to a common SRS subframe of subframe number n and detecting a piece of DCI that includes trigger information indicating no A-SRS transmission request in a different subframe transmitted after the common SRS subframe (i.e., during a period from the initial detection timing until a subframe corresponding to subframe n-k) in the same period, transmission controlling section <NUM> determines that no A-SRS transmission is required. In this case, transmission controlling section <NUM> outputs an instruction to cancel the instruction to generate a reference signal to reference signal generating section <NUM>.

In addition, the "SRS transmission execution rule" in Embodiment <NUM> includes a rule indicating that even upon detection of a different piece of DCI indicating an SRS resource different from the SRS resource indicated by the first piece of DCI that includes trigger information indicating an A-SRS transmission request, an A-SRS is transmitted according to the trigger information included in the different piece of DCI when the DCI format of the different piece of DCI is different from the DCI format of the first piece of DCI. Specifically, transmission controlling section <NUM> overwrites the information about the SRS resource indicated by the trigger information included in the piece of DCI detected immediately before the different piece of DCI with the information about the SRS resource indicated by the trigger information included in the different piece of DCI. In this case, transmission controlling section <NUM> outputs an instruction to generate a reference signal to reference signal generating section <NUM> and also outputs the information about the updated SRS resource to transmission signal forming section <NUM>.

The operation of base station <NUM> and terminal <NUM> according to Embodiment <NUM> configured in the manner described above will be described with reference to <FIG>. In <FIG>, base station <NUM> transmits a piece of DCI that includes trigger information indicating an A-SRS transmission request in one subframe and repeatedly transmits a piece of DCI that includes trigger information indicating an A-SRS transmission request in subsequent subframes in a single effective period. In this case, an A-SRS transmission request for a plurality of antennas is made by DCI format <NUM> (i.e., MIMO transmission assignment information). Moreover, an A-SRS transmission request for a plurality of antennas is made using resource A.

In addition, in <FIG>, base station <NUM> transmits a piece of DCI formed by including trigger information indicating an A-SRS transmission request in assignment control information of DCI format <NUM> after repeatedly transmitting a piece of DCI formed by including trigger information indicating an A-SRS transmission request in assignment control information of DCI format <NUM>. This is because terminal <NUM> is caused to transmit an A-SRS using a resource different from a previously requested SRS resource (e.g., single antenna transmission using resource B) due to a change in the propagation path conditions of terminal <NUM> (such as a case where data transmission becomes difficult using spatial multiplexing transmission using a plurality of antennas due to degradation of the quality of propagation path, for example).

Meanwhile, terminal <NUM> detects an A-SRS transmission request using DCI format <NUM> after detecting an A-SRS transmission request using DCI format <NUM>. According to the "SRS transmission execution rule," terminal <NUM> transmits an A-SRS according to the A-SRS trigger information of DCI detected in a later subframe (i.e., trigger information of DCI format <NUM>) under the detection state of DCI.

According to the DCI transmission rule by base station <NUM> and the "SRS transmission execution rule" by terminal <NUM>, base station <NUM> can change the SRS resource to another by transmitting a plurality of pieces of trigger information of different DCI formats within the effective period. Thus, base station <NUM> can cause each terminal <NUM> to transmit an A-SRS using an SRS resource corresponding to a change in the propagation path conditions of each terminal <NUM>. In addition, it is possible to prevent a collision between SRS resources allocated to a plurality of terminals <NUM>.

Moreover, as in Embodiment <NUM>, as long as base station <NUM> satisfies the abovementioned "predetermined condition," repeatedly transmitting a piece of DCI that includes trigger information indicating an A-SRS transmission request within a single effective period allows an A-SRS to be correctly transmitted even when terminal <NUM> fails to detect a piece of DCI that includes trigger information indicating an A-SRS transmission request. As a result, base station <NUM> can measure appropriate channel quality.

As in Embodiment <NUM>, the control of SRS transmission according to the "SRS transmission execution rule" described above allows base station <NUM> to cancel an A-SRS transmission request that has been reported to certain terminal <NUM>.

The description provided above assumes that base station <NUM> repeatedly transmits a piece of DCI that includes trigger information indicating an A-SRS transmission request within a single effective period as long as the "predetermined condition" is satisfied basically, as in Embodiment <NUM>. Meanwhile, when a first piece of DCI that includes trigger information indicating an A-SRS transmission request to terminal <NUM> is generated in one subframe with in an effective period, trigger information indicating an A-SRS transmission request may not be included in a different piece of DCI that is to be transmitted after the first piece of DCI during the effective period and that is of the same format as that of the first piece of DCI as in Embodiment <NUM>. In this case, terminal <NUM> performs no A-SRS transmission when detecting the different piece of DCI that includes trigger information indicating an A-SRS transmission request and that is of the same DCI format as that of the first piece of DCI. However, when further detecting a piece of DCI that includes trigger information indicating an A-SRS transmission request and that is of a DCI format different from that of the first piece of DCI, terminal <NUM> transmits an A-SRS using an SRS resource according to the A-SRS trigger information included in the piece of DCI of the different DCI format.

An SRS resource may be changed to another only upon detection of DCI that includes trigger information indicating an A-SRS transmission request and that is of DCI format <NUM> after detection of DCI that includes trigger information indicating an A-SRS transmission request and that is of a DCI format other than DCI format <NUM>. Specifically, overwriting the SRS resource corresponding to a previous A-SRS transmission request (including the number of antennas) by base station <NUM> is allowed only for A-SRS transmission requests for single antenna transmission. A-SRS transmission requests for single antenna or A-SRS transmission requests using DCI format <NUM> are made when terminal <NUM> in the transmission mode using multiple antenna transmission is caused to fall back to single antenna transmission.

In particular, such an A-SRS transmission request is made when the propagation path conditions of terminal <NUM> are degraded. Terminal <NUM> in a situation where the propagation path conditions are degraded can communicate only in a single antenna transmission mode. Thus, it is necessary to cause terminal <NUM> to perform A-SRS transmission for single antenna transmission as soon as possible. On the other hand, it is also possible to employ a configuration in which changing an SRS resource is not allowed upon detection of DCI that includes trigger information indicating an A-SRS transmission request and that is of a DCI format other than DCI format <NUM> after detection of DCI that includes trigger information indicating an A-SRS transmission request and that is of DCI format <NUM>. With this configuration, the probability of terminal <NUM> performing erroneous transmission after erroneously detecting DCI of a DCI format other than DCI format <NUM> can be reduced.

The term "antenna port" refers to a logical antenna including one or more physical antennas. In other words, the term "antenna port" does not necessarily refer to a single physical antenna, and may sometimes refer to an antenna array formed of a plurality of antennas, and/or the like.

For example, 3GPP LTE does not specify the number of physical antennas forming an antenna port, but specifies an antenna port as a minimum unit allowing each base station to transmit a different reference signal.

In addition, an antenna port may be specified as a minimum unit for multiplication of precoding vector weighting.

(<NUM>) In the embodiments described above, uplink data is transmitted via a Physical Uplink Shared Channel (PUSCH) while downlink data is transmitted via a Physical Downlink Shared Channel (PUSCH), but may be transmitted via another channel.

(<NUM>) The "SRS transmission execution rule" in each of the embodiments described above may be switched to another depending on the cell environment, the communication environment of the terminal, and/or the like. In this case, base station <NUM> may broadcast information indicating which one of the plurality of "SRS transmission execution rules" is to be used to all terminals <NUM> in the cell or may report the information to the terminals <NUM> individually (by RRC signaling).

(<NUM>) The above-noted embodiments have been described by examples of hardware implementations, but the present 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.

Claim 1:
A communication apparatus (<NUM>) comprising:
circuitry (<NUM>, <NUM>) configured to detect control information indicating whether or not to request transmission of a sounding reference signal, SRS, and indicating a transmission parameter of the SRS; and
characterized in that the SRS is an aperiodic SRS; and
a transmitter (<NUM>) configured to transmit the SRS based on the detected control information, when the circuitry detects the control information twice or more within a predetermined period and the control information, which is detected twice or more within the predetermined period, indicates an identical transmission parameter.