JP6144508B2 - Communication control method - Google Patents

Description

  The present invention transmits a data signal to a user apparatus using a non-protected subframe and a protected subframe for inter-cell interference control, and uses the first transmission power in the non-protected subframe, The present invention relates to a communication control method in a macro base station that uses a second transmission power lower than a first transmission power in a ted subframe.

  In LTE (Long Term Evolution) Advanced in 3GPP (Third Generation Partnership Project), OFDMA (Orthogonal Frequency Division Multiplexing Access) using MU-MIMO (multi-user multiple-input multiple-output) is proposed. In downlink transmission of MU-MIMO, not only one base station communicates with multiple user equipments (UE, user equipment), but also simultaneously transmits different data streams (layers, ranks) to one user equipment. Is possible.

  On the other hand, in recent years, heterogeneous radio base stations (macro base stations, pico base stations, femto base stations, remote radio heads, etc.) with different transmission power (transmission capabilities) have been installed in multiple layers. A network (Heterogeneous Network, HetNet) has been proposed (for example, Non-Patent Document 1).

  In a heterogeneous network, a base station having a higher transmission power (transmission capability) (for example, a macro base station) is compared with a base station having a lower transmission power (transmission capability) (for example, a pico base station) by cell search or It is assumed that it is easy to be selected as a wireless connection destination of the user apparatus at the handover stage. Therefore, it is assumed that connections from user apparatuses concentrate on a base station with high transmission power, and that the communication load tends to be excessive.

  Therefore, a technique called cell range expansion has been proposed. The cell range expansion is a technique for adding an offset value (bias value) to reception quality or reception power from a low power base station, which is an index for cell selection by a user apparatus. The reception quality or reception power from the low power base station to which the offset value is added (or added in decibels) is compared with the reception quality or reception power from the macro base station. As a result, the reception quality or reception power from the low power base station tends to be better than the reception quality or reception power from the macro base station. As a result, since the user apparatus selects to connect to the low power base station rather than the macro base station, it is considered that the cell range of the low power base station is expanded and the communication load of the macro base station is reduced.

  However, when the cell range of a low-power base station is expanded by cell range expansion (CRE), the user equipment at the end of the cell of the low-power base station may cause large interference due to radio waves from surrounding macro base stations. There is a possibility of receiving. Therefore, a technique called enhanced inter-cell interference coordination or enhanced inter-cell interference control, which is an extension of inter-cell interference coordination or inter-cell interference control, has been proposed. This technology is abbreviated as eICIC. eICIC is described in Non-Patent Document 2, for example.

  FIG. 1 is a graph illustrating time variation of downlink transmission power of a macro base station and a low power base station in time domain-based eICIC. In time domain-based eICIC, a macro base station and a low power base station use the same frequency band, but different unit times (for example, subframes) are used in different applications. As is apparent from FIG. 1, the low-power base station can continuously transmit downlink data. However, the macro base station can transmit downlink data only intermittently. As a result, a period during which only the low-power base station transmits a downlink data signal (protected subframe, PSF) and a period during which both the macro base station and the low-power base station transmit downlink data signals (non-conversion). Protected subframe (NSF) occurs. A non-protected subframe is a transmission of a downlink data signal from a macro base station to a user apparatus connected to the macro base station, and a user apparatus (for example, a center of a low power base station cell). Even if there is no CRE, it is used for transmission of a downlink data signal to a user apparatus connected to a low power base station. A protected subframe is a transmission of a downlink data signal from a low power base station to a user equipment (eg, a user equipment connected to the low power base station for CRE) at the end of a cell of the low power base station. Used for. Therefore, it is assumed that the interference by the radio wave from the macro base station to the user equipment at the end of the cell of the low power base station is prevented.

  In order to further improve the transmission efficiency from the macro base station, the downlink data from the macro base station is not stopped in the protected subframe, but the downlink data is transmitted at a low transmission power from the macro base station in the protected subframe. A modification of eICIC that transmits a signal has been proposed (Non-Patent Document 3). FIG. 2 is a graph illustrating the time change of the transmission power of the downlink data signal of the macro base station and the low power base station in a modification of the time domain based eICIC. In this case, transmission power from the macro base station is reduced in the protected subframe, but data transmission from the macro base station is allowed. Such resource groups with reduced transmission power can be used for wireless transmission to user equipment geographically close to the macro base station. By reducing the transmission power at the macro base station, even if the low power base station uses these specific resource groups for the user equipment connected to the low power base station, the interference given to those user equipments Is considered small. This modification of eICIC is called FeICIC (Further eICIC). Hereinafter, in this specification, a modification of the eICIC is referred to as a transmission power reduction type ICIC.

  In LTE Advanced, a user apparatus determines channel state information (channel state information, CSI) from SINR (signal to noise interference ratio) in the user apparatus, and feeds back the determined channel state information to a base station. Based on the channel state information fed back from each user apparatus, the base station determines downlink transmission parameters suitable for the user apparatus. Usually, a base station uses CSI fed back from each user apparatus as a downlink transmission parameter for the user apparatus. A set of channel quality indicator (CQI), precoding matrix indicator (PMI), and rank indicator (rank indicator, RI) is known as CSI fed back from user equipment ( Non-patent document 4).

3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Further advancements for E-UTRA physical layer aspects (Release 9); 3GPP TR 36.814 V9.0.0 (2010-03); Section 9A, Heterogeneous Deployments R1-103264, 3GPP TSG RAN WG1 Meeting # 61, Montreal, Canada, May 10-14, 2010, Source: NTT DOCOMO, Title: "Performance of eICIC with Control Channel Coverage Limitation", Agenda Item: 6.8, Document for: Discussion and Decision 3GPP, R1-113482, 3GPP TSG-RAN WG1 # 66bis, Zhuhai, China, 10th-14th October, 2011, Source: Ericsson, ST-Ericsson, Title: "System performance evaluations on FeICIC", Agenda Item: 7.3.1, Document for: Discussion and Decision 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10); 3GPP TS 36.213 V10.8.0 (2012-12)

  In order for the user equipment to determine CQI, the user equipment calculates SINR. For this reason, the base station notifies the UE of the power ratio between the reference signal (eg, cell-specific RS (CRS)) and the data channel (Physical Downlink Shared Channel (PDSCH)). In particular, in the transmission power reduction ICIC, the macro base station reduces the PDSCH transmission power in the protected subframe and transmits the PDSCH in the non-protected subframe. Therefore, in order for the user equipment to determine the appropriate CSI for each of the protected and non-protected subframes, the macro base station shall be able to determine for each of the protected and non-protected subframes. The power ratio information should be transmitted to the user equipment.

  However, at present, it is not standardized that the macro base station transmits the power ratio information to the user equipment for each of the protected subframe and the non-protected subframe. For non-protected subframes, CRS and PDSCH power ratio information is required to be transmitted from the macro base station to the user equipment, but for protected subframes, CRS and PDSCH power ratio information is user equipment. Not sent to. Therefore, for the protected subframe, the user equipment cannot determine an appropriate CSI, and can determine an appropriate CSI only for a non-protected subframe. The macro base station receives the appropriate CSI from the user equipment only for the non-protected subframe. Therefore, the macro base station can perform appropriate downlink transmission in the non-protected subframe, but cannot determine an appropriate downlink transmission parameter in the protected subframe. Since the transmission power is low in the protected subframe, when an appropriate downlink transmission parameter is used in the non-protected subframe, the block error rate of the data signal in the user apparatus tends to increase.

  Therefore, the present invention determines an appropriate downlink transmission parameter for a protected subframe in a macro base station that performs transmission power reduction type ICIC, and reduces a block error rate of a data signal in a user apparatus. A communication control method is provided.

  The communication control method according to the first aspect of the present invention transmits a data signal to a user equipment using a non-protected subframe and a protected subframe for inter-cell interference control, and in the non-protected subframe, A communication control method in a macro base station that uses a first transmission power and uses a second transmission power lower than the first transmission power in a protected subframe, and is used for transmission to the user apparatus Based on the step of receiving a channel quality indicator indicating the power modulation / coding scheme from the user apparatus and the ratio of the second transmission power to the first transmission power, the lower the ratio, the lower the transmission efficiency. As described above, the transmission efficiency is lower than the modulation / coding scheme indicated in the channel quality indicator received from the user equipment The tone and coding scheme, and determining to use to send data signals to the user equipment in the protection Ted subframe.

  The communication control method according to the second aspect of the present invention transmits a data signal to a user apparatus using a non-protected subframe and a protected subframe for inter-cell interference control, and in the non-protected subframe, A communication control method in a macro base station that uses a first transmission power and uses a second transmission power lower than the first transmission power in a protected subframe, and is used for transmission to the user apparatus Receiving a rank indicator indicating the number of power ranks from the user equipment; receiving a channel quality indicator indicating the modulation and coding scheme to be used for transmission to the user equipment; and the user Regardless of the number of ranks indicated in the rank indicator received from the device, a single rank is And determining to use the transmission of the data signal to the user equipment at Tech Ted subframe.

  The communication control method according to the third aspect of the present invention transmits a data signal to a user apparatus using a non-protected subframe and a protected subframe for inter-cell interference control, and in the non-protected subframe, A communication control method in a macro base station that uses a first transmission power and uses a second transmission power lower than the first transmission power in a protected subframe, and is used for transmission to the user apparatus Receiving a rank indicator indicating the number of power ranks from the user equipment; receiving a channel quality indicator indicating the modulation and coding scheme to be used for transmission to the user equipment; and the user Received from the user device when the rank number received from the device is 2 Comparing the acquired value obtained from two channel quality indicator indexes for the two ranks indicated by the channel quality indicator to a threshold, and if the acquired value is lower than the threshold, a single rank And decides to use to transmit a data signal to the user equipment in the protected subframe, and if the acquired value is higher than the threshold, two ranks are given to the user equipment in the protected subframe. Determining to use for transmission of the data signal.

  A communication control method according to a fourth aspect of the present invention transmits a data signal to a user apparatus using a non-protected subframe and a protected subframe for inter-cell interference control, and in the non-protected subframe, A communication control method in a macro base station that uses a first transmission power and uses a second transmission power lower than the first transmission power in a protected subframe, and is used for transmission to the user apparatus Receiving a rank indicator indicating the number of power ranks from the user equipment; receiving a channel quality indicator indicating the modulation and coding scheme to be used for transmission to the user equipment; and the user Received from the user device when the rank number received from the device is 2 A first comparison step of comparing an acquired value obtained from two channel quality indicator indexes for two ranks indicated by the channel quality indicator with a first threshold; and the acquired value is greater than the first threshold If lower, a first decision step to decide to use a single rank for transmission of data signals to the user equipment in protected subframes, and the acquired value is higher than the first threshold In a case, based on a ratio of the second transmission power to the first transmission power, the two channel quality indicator indexes for two ranks indicated by the channel quality indicator received from the user equipment are corrected. Thus, the lower the ratio, the lower the two channel quality indicator indexes after correction. Obtaining the latter two channel quality indicator indexes, using the two channel quality indicator indexes after the correction, using a modulation and coding scheme corresponding to the two channel quality indicator indexes after the correction, and Estimate a virtual signal-to-noise interference ratio or a virtual channel capacity assumed in the user equipment when transmitting a data signal to the user equipment in protected subframes using two ranks A second comparison step of comparing the virtual signal-to-noise interference ratio or the virtual channel capacity with a second threshold; and the virtual signal-to-noise interference ratio or the virtual channel If the capacity is lower than the second threshold, a single rank is assigned to the protected sub If it is decided to use for transmission of a data signal to the user equipment in a frame and the virtual signal-to-noise interference ratio or the virtual channel capacity is higher than the second threshold, two A second determination step of determining a rank to use for transmitting a data signal to the user equipment in a protected subframe.

  In the communication control method according to the first aspect of the present invention, the ratio is based on a ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe. A modulation / coding scheme having lower transmission efficiency than the modulation / coding scheme indicated in the channel quality indicator received from the user equipment is transmitted to the user equipment in the protected subframe so that the lower the transmission efficiency is, the lower the transmission efficiency is. Decide to use for data signal transmission. A low ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe means that the second transmission power in the protected subframe is low, and thus the user This means that the block error rate of the data signal in the apparatus tends to increase. The low transmission efficiency of the modulation / coding scheme means that at least one of the modulation level and the code rate is small, so that the block error rate of the data signal in the user equipment can be reduced. Means. The block error rate of the data signal in the user apparatus in the protected subframe can be reduced by selecting the modulation / coding scheme so that the transmission efficiency becomes lower as the ratio is lower.

  In the communication control method according to the second aspect of the present invention, a single rank is converted into a data signal to the user equipment in the protected subframe regardless of the rank number indicated in the rank indicator received from the user equipment. Decide to use for sending. If the number of ranks (streams) is large, the transmission efficiency is high, but the block error rate of the data signal in the user apparatus tends to increase. Regardless of the number of ranks indicated in the rank indicator received from the user equipment, a single rank is used to transmit data signals to the user equipment in the protected subframe, thereby allowing the user in the protected subframe. It can be expected that the block error rate of the data signal in the apparatus is reduced.

  In the communication control method according to the third aspect of the present invention, when the obtained value obtained from the two channel quality indicator indexes for the two ranks received from the user equipment is lower than the threshold, the single rank Is used to transmit the data signal to the user equipment in the protected subframe, and if the acquired value is higher than the threshold value, the two ranks are assigned to the data signal to the user equipment in the protected subframe. Decide to use for sending. In short, if the quality value (acquired value) that is expected to be obtained in two ranks is lower than the threshold, the single rank is decided to be used for transmission of the data signal to the user equipment in the protected subframe. If the quality values (acquired values) that are expected to be obtained in the two ranks are higher than the threshold, the two ranks are determined to be used for transmission of the data signal to the user equipment in the protected subframe. Using a single rank can reduce the block error rate of the data signal at the user equipment in the protected subframe when the quality value expected to be obtained in two ranks is lower than the threshold. it can. When the quality value expected to be obtained in two ranks is higher than the threshold value, the transmission rate of the data signal in the protected subframe can be secured high by using the two ranks.

  In the communication control method according to the fourth aspect of the present invention, when the acquired values obtained from the two channel quality indicator indexes for the two ranks received from the user apparatus are lower than the first threshold, A rank is determined to be used for transmission of the data signal to the user equipment in the protected subframe. In short, if the quality value (acquired value) that is expected to be obtained in two ranks is lower than the threshold value, a single rank is decided to be used for transmission of the data signal to the user equipment in the protected subframe. . Therefore, it is possible to reduce the block error rate of the data signal in the user apparatus in the protected subframe. If the acquired value obtained from the two channel quality indicator indexes for the two ranks received from the user equipment is higher than the first threshold, the two ranks are used to the user equipment in the protected subframe. When transmitting a data signal, a virtual signal-to-noise interference ratio or a virtual channel capacity assumed in the user apparatus is estimated. If the virtual signal-to-noise interference ratio or the virtual channel capacity is lower than the second threshold, a single rank is used to transmit the data signal to the user equipment in the protected subframe. Determined, and if the virtual signal-to-noise interference ratio or virtual channel capacity is higher than the second threshold, two ranks are used to transmit the data signal to the user equipment in the protected subframe Decide to do. By using a single rank when the virtual signal-to-noise interference ratio or virtual channel capacity assumed to be obtained in two ranks is lower than the second threshold, The block error rate of the data signal in the user apparatus can be reduced. If the virtual signal-to-noise interference ratio or virtual channel capacity that is assumed to be obtained in two ranks is higher than the threshold, the use of two ranks allows the data signal in the protected subframe to be A high transmission speed can be secured.

It is a graph which illustrates the time change of the transmission power of the downlink data signal of a macro base station and a low power base station in time domain base eICIC. It is a graph which illustrates the time change of the transmission power of the downlink data signal of a macro base station and a low power base station in the modification (transmission power reduction type ICIC) of time domain base eICIC. It is a block diagram which shows the radio | wireless communications system which concerns on various embodiment of this invention. It is a block diagram which shows the macro base station which concerns on various embodiment of this invention. It is a table | surface which shows the example of MCS designated by the index which CQI fed back from a user apparatus to a base station, and an index. FIG. 6 is a diagram illustrating a process of converting a precoding matrix to generate a precoding matrix for a single rank when a precoding matrix for two ranks is requested from a user apparatus.

Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings.
Common Items of Various Embodiments FIG. 3 is a block diagram of a wireless communication system according to various embodiments of the present invention. The wireless communication system includes a macro base station (macro eNodeB (evolved Node B)) 100, a pico base station 200, and a user equipment (UE, User Equipment) 300.

  Each communication element (the macro base station 100, the pico base station 200, and the user apparatus 300) in the wireless communication system performs wireless communication according to a predetermined radio access technology (for example, LTE). In the present embodiment, a mode in which the wireless communication system operates in accordance with LTE will be described as an example, but this is not intended to limit the technical scope of the present invention. The present invention can be applied to other radio access technologies with necessary design changes.

  Macro base station (first radio base station, high power base station) 100 and pico base station (second radio base station, low power base station) 200 are connected to each other by wire or wirelessly. The macro base station 100 forms a macro cell (first cell) Cm, and each pico base station 200 forms a pico cell (second cell) Cp. The pico cell Cp is a cell formed in the macro cell Cm formed by the macro base station 100 connected to the pico base station 200 that forms the pico cell Cp. In one macro cell Cm, a plurality of pico cells Cp can be formed.

  Each radio base station (macro base station 100, pico base station 200) can perform radio communication with the user apparatus 300 located in the cell of the base station itself. In other words, the user apparatus 300 can wirelessly communicate with a base station (macro base station 100, pico base station 200) corresponding to a cell (macro cell Cm, pico cell Cp) in which the user apparatus 300 is located.

  Since the macro base station 100 has a higher radio transmission capability (such as maximum transmission power and average transmission power) than the pico base station 200, the macro base station 100 can perform radio communication with a user apparatus 300 located farther away. Therefore, the macro cell Cm has a larger area than the pico cell Cp. For example, the macro cell Cm has a radius of several hundred meters to several tens of kilometers, and the pico cell Cp has a radius of several meters to several tens of meters.

  As understood from the above description, the macro base station 100 and the pico base station 200 in the radio communication system are heterogeneous in which a plurality of types of radio base stations having different transmission powers (transmission capabilities) are installed in multiple layers. Configure the network (Heterogeneous Network, HetNet).

  Considering that the pico cell Cp is formed in multiple layers (overlaid) inside the macro cell Cm, when the user apparatus 300 is located in the pico cell Cp, the user apparatus 300 is configured to form the pico cell Cp. It can be understood that wireless communication is possible with at least one of the base station 200 and the macro base station 100 forming the macro cell Cm including the pico cell Cp.

  A wireless communication method between each base station and the user apparatus 300 is arbitrary. For example, OFDMA (Orthogonal Frequency Division Multiple Access) may be employed in the downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) may be employed in the uplink.

  In this wireless communication system, the transmission power reduction ICIC described above with reference to FIG. 2 is used. That is, the macro base station 100 transmits a data signal to the user apparatus 300 using the non-protected subframe and the protected subframe, and uses the first transmission power in the non-protected subframe, and the protected subframe. Then, the second transmission power lower than the first transmission power is used.

  On the other hand, the pico base station 200 transmits a data signal to the user apparatus 300 with substantially the same transmission power in both the non-protected subframe and the protected subframe.

  Each user apparatus 300 calculates SINR in the user apparatus 300 and determines CSI based on the SINR. Each user apparatus 300 transmits (feeds back) CSI to the base station to which the user apparatus 300 is connected. The SINR calculation and CSI feedback are repeated. In accordance with the CSI fed back from each user apparatus 300, the base station determines downlink transmission parameters suitable for the user apparatus 300. Usually, a base station uses CSI fed back from each user apparatus as a downlink transmission parameter for the user apparatus. The CSI fed back from the user equipment includes CQI, PMI, and RI.

  CQI indicates an index (0 to 15) of a modulation and coding scheme (MCS) to be used for transmission to the user apparatus. Based on the CQI fed back from the user apparatus, the base station determines a downlink modulation / coding scheme for the user apparatus. Usually, the base station uses the modulation / coding scheme indicated in the CQI received from the user equipment for the user equipment.

  PMI indicates the codebook index of the transmission weight matrix to be used for transmission to the user equipment. Based on the PMI fed back from the user apparatus, the base station selects a downlink precoding matrix for the user apparatus. Normally, the base station uses the precoding matrix indicated in the PMI received from the user equipment for that user equipment.

  RI indicates the spatial multiplexing number (number of ranks) to be used for transmission to the user apparatus. Based on the fed back RI, the base station determines the number of ranks for the user equipment. Normally, the base station uses the number of ranks indicated in the RI received from the user equipment for that user equipment.

  When the rank number (stream number) indicated by RI is 1, the user equipment feeds back the CQI for a single rank (stream) to the base station, and the precoding matrix for the single rank is obtained. The indicated PMI is fed back to the base station. When the rank number indicated by RI is 2, the user equipment feeds back the CQI for the first rank and the CQI for the second rank to the base station, and the precoding matrix for the two ranks. Is fed back to the base station.

  As described above, when calculating the SINR, the user apparatus considers the power ratio between CRS and PDSCH notified from the base station. For this reason, each base station repeatedly transmits information indicating the power ratio between CRS and PDSCH to the user apparatus with which the base station communicates. However, in this embodiment, the macro base station 100 transmits information on the power ratio of CRS and PDSCH to the user apparatus regarding the non-protected subframe, but information on the power ratio of CRS and PDSCH regarding the protected subframe. Is not sent to the user equipment. Therefore, the CSI fed back from the user apparatus 300 to the macro base station 100 is appropriate for the non-protected subframe, but is not appropriate for the protected subframe.

  The macro base station 100 corrects the CSI (CSI appropriate for the non-protected subframe) received from the user apparatus 300, and transmits the corrected CSI to the user apparatus 300 in the protected subframe. use.

  FIG. 4 is a block diagram showing a configuration of macro base station 100 according to various embodiments of the present invention. The macro base station 100 includes a plurality of transmission / reception antennas 112, a radio communication unit 110, a control unit 120, and a memory 130.

  The wireless communication unit 110 is an element for performing wireless communication with the mobile terminal 300. The wireless communication unit 110 converts a radio wave received by the transmission / reception antenna 112 from the mobile terminal 300 into an electric signal, and converts the electric signal into a radio wave. A transmission circuit for transmitting by the transmission / reception antenna 112 and a variable amplifier for controlling transmission power.

  The radio communication unit 110 may transmit a signal to a mobile terminal 300 that is located in the macro cell Cm of the macro base station 100 and is connected to the macro base station 100 using MIMO (multiple-input and multiple-output) technology. it can. Therefore, the wireless communication unit 110 uses a plurality of antennas for wireless transmission. As illustrated in FIG. 4, the wireless communication unit 110 includes a plurality of transmission / reception antennas 112, but may include a plurality of transmission-dedicated antennas and at least one reception-dedicated antenna.

  The control unit 120 is a CPU (central processing unit), executes a computer program, and operates according to the computer program. Although the macro base station 100 includes other elements, description of these other elements is omitted.

  When determining the first transmission power and the second transmission power, the control unit 120 of the macro base station 100 uses the first transmission power for data transmission in the non-protected subframe, and in the protected subframe. The variable amplifier of the wireless communication unit 110 is controlled so that the second transmission power is used for data transmission. Further, when determining the first transmission power and the second transmission power, the control unit 120 stores the first transmission power and the second transmission power in the memory 130.

  The CSI (including CQI, PMI, and RI) fed back from the user apparatus 300 is received by the wireless communication unit 110 and supplied to the control unit 120. This CSI is appropriate for non-protected subframes, but is not appropriate for protected subframes. The control unit 120 corrects the CSI (CSI suitable for the non-protected subframe) fed back from the user device 300 and supplied from the wireless communication unit 110, and the corrected CSI is the user device in the protected subframe. Used to transmit a data signal to 300. In other words, the control unit 120 determines transmission parameters more appropriate for the protected subframe based on the CSI fed back from the user apparatus 300, and determines those transmission parameters for the user apparatus 300 in the protected subframe. Used to send data signals to Details of this communication control method in the macro base station 100 will be described in association with the following various embodiments.

  The control unit 120 may use the CSI fed back from the user apparatus 300 and supplied from the wireless communication unit 110 as a transmission parameter for transmission of a data signal to the user apparatus 300 in a non-protected subframe. Alternatively, the control unit 120 corrects the CSI fed back from the user apparatus 300 and supplied from the wireless communication unit 110, and uses the corrected CSI as a transmission parameter and other transmission parameters as non-protected subframes. You may use for the transmission of the data signal to the user apparatus 300. FIG.

First Embodiment A communication control method according to a first embodiment of the present invention includes a step of receiving a CQI indicating an MCS to be used for transmission to a user apparatus 300 from the user apparatus 300, and non-protected Calculating a ratio of the second transmission power for the protected subframe to the first transmission power for the subframe, and an MCS having lower transmission efficiency than the MCS indicated in the CQI received from the user equipment 300 Determining to use for transmission of data signals to user equipment 300 in protected subframes.

  FIG. 5 is a table showing an example of MCS specified by the index (0 to 15) indicated by the CQI fed back from the user apparatus 300 and the index (CQI index). The larger the CQI index, the higher the transmission efficiency. As the transmission efficiency is higher, the block error rate in the user apparatus 300 tends to increase. In other words, the use of MCS with low transmission efficiency is expected to reduce the block error rate in the user apparatus 300.

  The control unit 120 of the macro base station 100 uses the first transmission power and the second transmission power stored in the memory 130 to calculate the ratio of the second transmission power to the first transmission power.

  A low ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe means that the second transmission power in the protected subframe is low, and thus the user This means that the block error rate of the data signal in the apparatus 300 tends to increase. Therefore, in the step of determining the MCS, the control unit 120 of the macro base station 100 is based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe. Thus, the MCS is determined so that the transmission efficiency decreases as the ratio decreases. As is clear from FIG. 5, the low transmission efficiency of MCS is that at least one of the modulation level and the code rate is small, so that the data signal block in the user apparatus 300 is low. This means that the error rate can be reduced. By selecting the MCS so that the transmission efficiency becomes lower as the ratio is lower, the block error rate of the data signal in the user apparatus 300 in the protected subframe can be reduced.

  Even if the CQI index of the CQI received from the user apparatus 300 is 11, for example, the control unit 120 selects an MCS corresponding to the CQI index 10 or lower. In addition, when the power ratio is lower, the control unit 120 selects an MCS corresponding to a smaller CQI index. For example, if the power ratio is 50%, the MCS corresponds to the CQI index 7, and if the power ratio is 20%, the MCS corresponds to the CQI index 5. In order to determine the MCS used for data transmission in the protected subframe from the CQI index of the CQI received from the user apparatus 300 in consideration of the power ratio, an equation may be used, A table may be used.

  When the CQI received from the user apparatus 300 indicates two CQI indexes for the two ranks, the control unit 120 considers the power ratio in the same manner as described above, and the CQI for each rank. An MCS having lower transmission efficiency than the MCS corresponding to the index may be determined to be used for transmission of the data signal to the user apparatus 300 in the protected subframe of that rank.

Second Embodiment A communication control method according to a second embodiment of the present invention includes a step of receiving an RI indicating the number of ranks to be used for transmission to the user apparatus 300 from the user apparatus 300; Receiving a CQI indicating the MCS to be used for transmission to the user apparatus 300 from the user apparatus 300; receiving a PMI indicating the precoding matrix to be used for transmission to the user apparatus 300; Determining to use a single rank for transmission of data signals to the user equipment 300 in the protected subframe, regardless of the number of ranks indicated in the RI received from the user equipment 300. The step of receiving RI, the step of receiving CQI, and the step of receiving MI may be simultaneous.

  In this communication control method, the control unit 120 of the macro base station 100 assigns a single rank to the user apparatus 300 in the protected subframe regardless of the rank number indicated in the RI received from the user apparatus 300. To be used for transmitting the data signal. If the number of ranks (streams) is large, the transmission efficiency is high, but the block error rate of the data signal in the user apparatus 300 tends to increase. Regardless of the number of ranks indicated in the RI received from the user equipment 300, a single rank is used for transmission of data signals to the user equipment 300 in the protected subframe, thereby protecting the protected subframe. It can be expected that the block error rate of the data signal in the user apparatus 300 is reduced.

  Furthermore, in the communication control method according to the second embodiment, when the rank number indicated by the RI received from the user apparatus 300 is 2, 2 for two ranks indicated by the CQI received from the user apparatus 300 A step of determining a higher CQI index among the two CQI indexes, and a PMI received from the user apparatus 300 indicates a precoding matrix for two ranks, the higher CQI index of the precoding matrices Selecting a matrix component corresponding to a rank corresponding to, and using the selected matrix component as a precoding matrix for a single rank for transmitting data signals to user equipment 300 in protected subframes Determining to do. This will be described in more detail with reference to FIG.

  When the user apparatus 300 transmits RI indicating the rank number 2, the user apparatus transmits PMI indicating the precoding matrix for the two ranks. When a single rank is determined to be used for transmission of a data signal to the user apparatus 300 in the protected subframe even though the rank number indicated by the RI received from the user apparatus 300 is two Cannot use the precoding matrix for the two ranks indicated in the PMI as it is for transmission of the data signal to the user equipment 300 in the protected subframe. Therefore, the control unit 120 converts the precoding matrix for two ranks to obtain a precoding matrix for a single rank.

  Think of the precoding matrix for two ranks as the set of precoding matrices for the first rank of the two ranks and the precoding matrix for the second rank of the two ranks. Can do. The upper part of FIG. 6 shows an example of a precoding matrix for two ranks when the base station has two transmit antennas. Each of the matrix elements a, b, c, and d is one of 1, -1, j, and -j. Among the precoding matrices, one matrix component (column component) a, c in the vertical direction corresponds to a precoding matrix for the first rank, and the other column components b, d are precoding for the second rank. Corresponds to coding matrix. Therefore, the control unit 120 decides to use one of these components as a precoding matrix for a single rank for transmission of a data signal to the user apparatus 300 in the protected subframe.

  When the user apparatus 300 transmits RI indicating the rank number 2, the user apparatus transmits CQI indicating two CQI indexes for two ranks. The control unit 120 determines the higher CQI index among the two CQI indexes for the two ranks indicated by the CQI. Thereafter, a matrix component corresponding to the rank corresponding to the higher CQI index is selected from the precoding matrices for the two ranks indicated by the PMI received from the user apparatus 300. For example, if the CQI index for the first rank is 3 and the CQI index for the second rank is 5, the column components b and d for the second rank are selected. Then, the control unit 120 determines to use the selected column component as a precoding matrix for a single rank for transmission of the data signal to the user apparatus 300 in the protected subframe. The lower part of FIG. 6 shows a precoding matrix for a single rank composed of column components b and d for the second rank.

  If the CQI index for the first rank is higher than the CQI index for the second rank, the column components a, c for the first rank are selected. Then, the precoding matrix for a single rank configured from the first rank column components a and c is used to transmit the data signal to the user apparatus 300 in the protected subframe.

  As understood from FIG. 5, the higher the CQI index, the higher the transmission efficiency. As the transmission efficiency is higher, the block error rate in the user apparatus 300 tends to increase. Using the matrix component corresponding to the rank corresponding to the higher CQI index may cause an increase in the block error rate in the user apparatus 300. Therefore, in order to reduce the block error rate of the data signal in the user equipment 300 in the protected subframe, the lower one of the precoding matrices for two ranks indicated by the PMI received from the user equipment 300 The matrix components corresponding to the ranks corresponding to the CQI indices of the other can be used as a precoding matrix for a single rank for transmitting data signals to the user equipment 300 in the protected subframe.

  However, in the communication control method of this embodiment, a single rank is used for transmitting a data signal to the user apparatus 300 in the protected subframe, so that the user apparatus 300 in the protected subframe. It can be expected that the block error rate of the data signal will be reduced. Of the precoding matrices for two ranks indicated by the PMI received from the user apparatus 300, a matrix component corresponding to the rank corresponding to the higher CQI index is used as a precoding matrix for a single rank. By using the transmission of the data signal to the user apparatus 300 in the protected subframe, the transmission efficiency of the data signal to the user apparatus 300 in the protected subframe can be improved.

Third Embodiment In the second embodiment, when the rank number indicated by the RI received from the user apparatus is 1, the MCS indicated in the CQI received from the user apparatus 300 (indicated in the CQI) Single MCS corresponding to a single CQI indicator for a single rank) and the modified MCS of the data signal to the user equipment 300 in a protected subframe using a single rank It may be used for transmission. The third embodiment of the present invention is such a modification based on the second embodiment.

  In the communication control method according to the third embodiment of the present invention, in addition to the communication control method according to the second embodiment, when the rank number indicated by the RI received from the user apparatus 300 is 1, As in the first embodiment, it is determined to use an MCS having lower transmission efficiency than the MCS indicated in the CQI received from the user apparatus 300 for transmission of the data signal to the user apparatus 300 in the protected subframe. Comprising steps.

  The control unit 120 of the macro base station 100 uses the first transmission power and the second transmission power stored in the memory 130 to calculate the ratio of the second transmission power to the first transmission power.

  A low ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe means that the second transmission power in the protected subframe is low, and thus the user This means that the block error rate of the data signal in the apparatus 300 tends to increase. Therefore, in the step of determining the MCS, the control unit 120 of the macro base station 100 is based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe. Thus, the MCS is determined so that the transmission efficiency decreases as the ratio decreases. As is clear from FIG. 5, the low transmission efficiency of MCS means that at least one of the modulation multi-level number and the coding rate is small, so that the block error rate of the data signal in the user apparatus 300 can be reduced. . By selecting the MCS so that the transmission efficiency becomes lower as the ratio is lower, the block error rate of the data signal in the user apparatus 300 in the protected subframe can be reduced.

  Even if the CQI index of the CQI received from the user apparatus 300 is 11, for example, the control unit 120 selects an MCS corresponding to the CQI index 10 or lower. In addition, when the power ratio is lower, the control unit 120 selects an MCS corresponding to a smaller CQI index. For example, if the power ratio is 50%, the MCS corresponds to the CQI index 7, and if the power ratio is 20%, the MCS corresponds to the CQI index 5. In order to determine the MCS used for data transmission in the protected subframe from the CQI index of the CQI received from the user apparatus 300 in consideration of the power ratio, an equation may be used, A table may be used.

Fourth Embodiment In the second embodiment, if the number of ranks indicated by the RI received from the user apparatus is 2, then two for the two ranks indicated in the CQI received from the user apparatus 300 The MCS for a single rank is obtained from two MCSs corresponding to one CQI indicator, and the obtained MCS is transmitted to the user equipment 300 in a protected subframe using the single rank. May be used for The fourth to sixth embodiments of the present invention are such modifications based on the second embodiment.

  In the communication control method according to the fourth embodiment of the present invention, in addition to the communication control method according to the second embodiment, when the rank number indicated by the RI received from the user apparatus 300 is 2, the user The average value of the two CQI indexes for the two ranks indicated by the CQI received from the apparatus 300 or the MCS corresponding to the higher CQI index of the two CQI indexes is a protected sub using a single rank. Deciding to use to transmit a data signal to the user equipment 300 in a frame.

  When the user apparatus 300 transmits RI indicating the rank number 2, the user apparatus transmits CQI indicating two CQI indexes for two ranks. However, the control unit 120 of the macro base station 100 transmits a single rank to the user apparatus 300 in the protected subframe regardless of the rank number indicated in the RI received from the user apparatus 300. Decide to use. Therefore, the control unit 120 calculates the average value of the two CQI indexes indicated by the CQI. If the average CQI index is not an integer, the control unit 120 rounds up or rounds down the average CQI index to a whole number. Alternatively, the control unit 120 may determine the higher CQI index of the two CQI indexes for the two ranks indicated by the CQI. Then, the control unit 120 determines to use the MCS corresponding to the CQI index obtained in this way for transmission of the data signal to the user apparatus 300 in the protected subframe using a single rank. .

  As understood from FIG. 5, the higher the CQI index, the higher the transmission efficiency. As the transmission efficiency is higher, the block error rate in the user apparatus 300 tends to increase. In order to reduce the block error rate of the data signal in the user apparatus 300 in the protected subframe, the lower of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 is lower. The MCS corresponding to the CQI index can be used to transmit a data signal to the user equipment 300 in a protected subframe using a single rank.

  However, in the communication control method of this embodiment, a single rank is used for transmitting a data signal to the user apparatus 300 in the protected subframe, so that the user apparatus 300 in the protected subframe. It can be expected that the block error rate of the data signal will be reduced. The average value of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or the MCS corresponding to the higher CQI index of the two CQI indexes is protected using the single rank. By using the transmission of the data signal to the user apparatus 300 in the subframe, the transmission efficiency of the data signal to the user apparatus 300 in the protected subframe can be improved.

Fifth Embodiment In the communication control method according to the fifth embodiment of the present invention, in addition to the communication control method according to the second embodiment, the rank number indicated by the RI received from the user apparatus 300 is 2, based on the ratio of the second transmission power to the first transmission power, two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 are corrected, and the ratio is low. The step of obtaining the two corrected CQI indexes so that the two corrected CQI indexes become lower and the higher of the average value of the two corrected CQI indexes or the two corrected CQI indexes. Determining to use the MCS corresponding to the CQI index for transmission of the data signal to the user equipment 300 in a protected subframe using a single rank.

  The control unit 120 of the macro base station 100 uses the first transmission power and the second transmission power stored in the memory 130 to calculate the ratio of the second transmission power to the first transmission power. Based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the control unit 120 determines that the corrected two CQI indexes are lower as the ratio is lower. Two CQI indexes indicated by the CQI received from the user apparatus 300 are corrected so as to be lower, and two corrected CQI indexes are obtained.

  Even if one CQI index of the CQI received from the user apparatus 300 is 11, for example, the control unit 120 determines the corrected CQI index to be 10 or less. When the power ratio is lower, the control unit 120 determines a smaller CQI index as a corrected CQI index. For example, if the power ratio is 50%, the control unit 120 determines the corrected CQI index as 7, and if the power ratio is 20%, determines the corrected CQI index as 5. It is. In order to determine the corrected CQI index from the CQI index of CQI received from the user apparatus 300 in consideration of the power ratio, a mathematical formula or a table may be used.

  Thereafter, the control unit 120 calculates the average value of the two corrected CQI indexes. If the average CQI index is not an integer, the control unit 120 rounds up or rounds down the average CQI index to a whole number. Alternatively, the control unit 120 may determine the higher CQI index of the two corrected CQI indexes. Then, the control unit 120 determines to use the MCS corresponding to the CQI index obtained in this way for transmission of the data signal to the user apparatus 300 in the protected subframe using a single rank. .

  This embodiment is similar to the fourth embodiment. However, in this embodiment, according to the power ratio, the MCS corresponding to the CQI index lower than the CQI index finally obtained in the fourth embodiment (the MCS finally determined in the fourth embodiment) MCS with lower transmission efficiency) is used for transmission of data signals to user equipment 300 in protected subframes using a single rank. Therefore, it is expected to reduce the block error rate of the data signal in the user apparatus 300 in the protected subframe.

Sixth Embodiment In the communication control method according to the sixth embodiment of the present invention, in addition to the communication control method according to the second embodiment, the rank number indicated by the RI received from the user apparatus 300 is 2, obtaining an average value of two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or a higher CQI index of the two CQI indexes as a representative CQI index; Based on the ratio of the second transmission power to the first transmission power, the representative CQI index is corrected, and the corrected representative CQI index is obtained so that the lower the ratio, the lower the corrected representative CQI index. The step and the MCS corresponding to the corrected representative CQI index are transmitted to the user apparatus 300 in the protected subframe using a single rank. And determining to use the.

  The control unit 120 of the macro base station 100 calculates the average value of the two CQI indexes indicated by the CQI received from the user apparatus 300. If the average CQI index is not an integer, the control unit 120 rounds up or rounds down the average CQI index to a whole number. Alternatively, the control unit 120 may determine the higher CQI index of the two CQI indexes. In this way, the control unit 120 obtains a single representative CQI index.

  Thereafter, based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the controller 120 corrects the representative CQI after correction as the ratio decreases. The representative CQI index is corrected so that the index becomes lower, and a corrected representative CQI index is obtained.

  Even if the representative CQI index is 11, for example, the control unit 120 determines the corrected representative CQI index to be 10 or less. When the power ratio is lower, the control unit 120 determines a smaller CQI index as a corrected representative CQI index. For example, if the power ratio is 50%, the control unit 120 determines the corrected representative CQI index as 7, and if the power ratio is 20%, determines that the corrected representative CQI index is 5. As is. In order to determine the corrected representative CQI index from the CQI index of the CQI received from the user apparatus 300 in consideration of the power ratio, a mathematical formula or a table may be used. .

  Then, the control unit 120 uses the MCS corresponding to the representative CQI index after correction obtained in this way for transmission of the data signal to the user apparatus 300 in the protected subframe using a single rank. Decide to do.

  That is, in this embodiment, the correction process and the process of selecting the average or higher one are opposite to the fifth embodiment. Similar to the fifth embodiment, in this embodiment, according to the power ratio, the MCS corresponding to a CQI index lower than the CQI index finally obtained in the fourth embodiment (fourth embodiment). MCS having a transmission efficiency lower than that of the MCS finally determined in step (1) is used for transmission of a data signal to the user apparatus 300 in a protected subframe using a single rank. Therefore, it is expected to reduce the block error rate of the data signal in the user apparatus 300 in the protected subframe.

Seventh Embodiment In the communication control method according to the seventh to eleventh embodiments of the present invention, when the number of ranks indicated by the RI received from the user apparatus 300 is 2, two ranks are protected. It is characterized in that it is determined whether to use the data signal transmission to the user equipment 300 in a frame or to use a single rank.

  The communication control method according to the seventh embodiment of the present invention includes a step of receiving an RI indicating the number of ranks to be used for transmission to the user apparatus 300 from the user apparatus 300, and a transmission to the user apparatus 300. A CQI indicating MCS to be performed from the user apparatus 300, and when the number of ranks indicated by the RI received from the user apparatus 300 is 2, two CQIs received from the user apparatus 300 indicate two ranks Obtaining an obtained value (a quality value expected to be obtained at two ranks) from the two CQI indexes, and comparing the obtained value with a threshold value. The step of receiving RI and the step of receiving CQI may be simultaneous.

  In the step of obtaining the acquisition value, the control unit 120 of the macro base station 100 determines the higher of the average value of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or the higher of the two CQI indexes. The CQI index is obtained as the acquired value. When the acquired value is lower than the threshold, the control unit 120 determines to use a single rank for transmission of the data signal to the user apparatus 300 in the protected subframe, and the acquired value is higher than the threshold. The two ranks are determined to be used for transmission of the data signal to the user equipment 300 in the protected subframe.

  In short, if the quality value (acquired value) that is expected to be obtained in two ranks is lower than the threshold, the control unit 120 transmits a single rank to the user apparatus 300 in the protected subframe. If the quality value (acquired value) that is expected to be obtained in the two ranks is higher than the threshold, the two ranks are used for transmission of the data signal to the user equipment 300 in the protected subframe. Decide to use. Reducing the block error rate of the data signal at the user equipment 300 in the protected subframe by using a single rank when the quality value expected to be obtained in two ranks is lower than the threshold Can do. When the quality value expected to be obtained in two ranks is higher than the threshold value, the transmission rate of the data signal in the protected subframe can be secured high by using the two ranks.

Eighth Embodiment A communication control method according to an eighth embodiment of the present invention is a modification of the seventh embodiment, and an acquired value for determining the number of ranks is the same as that of the seventh embodiment. Different. In the eighth embodiment, the control unit 120 of the macro base station 100 uses the first transmission power and the second transmission power stored in the memory 130 to perform the second transmission for the first transmission power. Calculate the power ratio. Based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the control unit 120 determines that the corrected two CQI indexes are lower as the ratio is lower. Two CQI indexes indicated by the CQI received from the user apparatus 300 are corrected so as to be lower, and two corrected CQI indexes are obtained. This method is the same as the method described above in connection with the fifth embodiment.

  Thereafter, the control unit 120 calculates the average value of the two corrected CQI indexes. If the average CQI index is not an integer, the control unit 120 rounds up or rounds down the average CQI index to a whole number. Alternatively, the control unit 120 may determine the higher CQI index of the two corrected CQI indexes.

  Then, the control unit 120 uses the CQI index obtained in this way as the acquired value. That is, when the acquired value (the quality value expected to be obtained with two ranks) is lower than the threshold value, the control unit 120 converts the single rank to the data signal to the user apparatus 300 in the protected subframe. If the acquired value is higher than the threshold, the two ranks are determined to be used for transmitting the data signal to the user equipment 300 in the protected subframe. Reducing the block error rate of the data signal at the user equipment 300 in the protected subframe by using a single rank when the quality value expected to be obtained in two ranks is lower than the threshold Can do. When the quality value expected to be obtained in two ranks is higher than the threshold value, the transmission rate of the data signal in the protected subframe can be secured high by using the two ranks.

  The threshold value in this embodiment may be different from the threshold value in the seventh embodiment. In this embodiment, since the acquisition value is determined in consideration of the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the acquired value is determined in the protected subframe. The expected quality value (acquired value) can be appropriately predicted.

Ninth Embodiment A communication control method according to a ninth embodiment of the present invention is a modification of the seventh embodiment, and an acquired value for determining the number of ranks is the same as that of the seventh embodiment. Different. In the eighth embodiment, the control unit 120 of the macro base station 100 calculates the average value of two CQI indexes indicated by the CQI received from the user apparatus 300. If the average CQI index is not an integer, the control unit 120 rounds up or rounds down the average CQI index to a whole number. Alternatively, the control unit 120 may determine the higher CQI index of the two CQI indexes. In this way, the control unit 120 obtains a single representative CQI index.

  Thereafter, based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the controller 120 corrects the representative CQI after correction as the ratio decreases. The representative CQI index is corrected so that the index becomes lower, and a corrected representative CQI index is obtained. This method is the same as the method described above in connection with the sixth embodiment.

  Then, the control unit 120 uses the corrected representative CQI index obtained in this way as the acquired value. That is, when the acquired value (the quality value expected to be obtained with two ranks) is lower than the threshold value, the control unit 120 converts the single rank to the data signal to the user apparatus 300 in the protected subframe. If the acquired value is higher than the threshold, the two ranks are determined to be used for transmitting the data signal to the user equipment 300 in the protected subframe. Reducing the block error rate of the data signal at the user equipment 300 in the protected subframe by using a single rank when the quality value expected to be obtained in two ranks is lower than the threshold Can do. When the quality value expected to be obtained in two ranks is higher than the threshold value, the transmission rate of the data signal in the protected subframe can be secured high by using the two ranks.

  The threshold value in this embodiment may be different from the threshold value in the seventh embodiment. In this embodiment, the correction process and the process of selecting the average or higher one are opposite to those in the ninth embodiment. In this embodiment, since the acquisition value is determined in consideration of the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the acquired value is determined in the protected subframe. The expected quality value (acquired value) can be appropriately predicted.

Tenth Embodiment A communication control method according to a tenth embodiment of the present invention is a modification of the seventh embodiment, and an acquired value for determining the number of ranks is the same as that of the seventh embodiment. Different. In the tenth embodiment, the control unit 120 of the macro base station 100 uses the first transmission power and the second transmission power stored in the memory 130 to perform the second transmission for the first transmission power. Calculate the power ratio. Based on the ratio of the second transmission power for the protected subframe to the first transmission power for the non-protected subframe, the control unit 120 determines that the corrected two CQI indexes are lower as the ratio is lower. Two CQI indexes indicated by the CQI received from the user apparatus 300 are corrected so as to be lower, and two corrected CQI indexes are obtained. This method is the same as the method described above in relation to the fifth embodiment and the eighth embodiment.

Thereafter, the control unit 120 uses the MCS corresponding to the two corrected CQI indexes from the two corrected CQI indexes and uses the two ranks, and the user apparatus in the protected subframe. When transmitting a data signal to 300, a virtual SINR assumed in the user apparatus 300 is estimated. This estimation method is known and may be, for example, a method reverse to the method in which the user apparatus determines CQI from SINR. Further, the control unit 120 may estimate the virtual channel capacity C (bits / second) from the virtual SINR according to the following equation based on the Shannon-Hartley theorem.
C = B log ₂ (1 + SINR)
Here, B is the bandwidth (Hz) of the channel.

  Then, the control unit 120 uses the virtual SINR or virtual channel capacity obtained in this way as the acquired value. That is, when the acquired value (the quality value expected to be obtained with two ranks) is lower than the threshold value, the control unit 120 converts the single rank to the data signal to the user apparatus 300 in the protected subframe. If the acquired value is higher than the threshold, the two ranks are determined to be used for transmitting the data signal to the user equipment 300 in the protected subframe. Reducing the block error rate of the data signal at the user equipment 300 in the protected subframe by using a single rank when the quality value expected to be obtained in two ranks is lower than the threshold Can do. When the quality value expected to be obtained in two ranks is higher than the threshold value, the transmission rate of the data signal in the protected subframe can be secured high by using the two ranks. The threshold value in this embodiment may be different from the threshold values in the seventh to ninth embodiments.

Eleventh Embodiment The communication control method according to the eleventh embodiment of the present invention is a combination of the seventh embodiment and the tenth embodiment, and a single rank is assigned to the protected sub. It has two decision steps for deciding whether to use it for transmitting data signals to the user equipment in frames.

  Similarly to the seventh embodiment, the communication control method according to the eleventh embodiment of the present invention includes the step of receiving from the user apparatus 300 RI indicating the number of ranks to be used for transmission to the user apparatus 300. Receiving the CQI indicating the MCS to be used for transmission to the user apparatus 300 from the user apparatus 300, and receiving from the user apparatus 300 when the number of ranks indicated by the RI received from the user apparatus 300 is 2. Obtaining an obtained value (a quality value expected to be obtained at two ranks) from two CQI indexes for the two ranks indicated by the CQI performed, and comparing the obtained value with a threshold value. The step of receiving RI and the step of receiving CQI may be simultaneous.

  In the step of obtaining the acquisition value, the control unit 120 of the macro base station 100 determines the higher of the average value of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or the higher of the two CQI indexes. A CQI index may be obtained as an acquired value. Or similarly to 8th Embodiment, the control part 120 correct | amends two CQI indexes based on the ratio of the said electric power, and average value of two CQI indexes after correction | amendment, or two after correction | amendment The higher CQI index of the CQI indexes may be obtained as the acquired value. Alternatively, as in the ninth embodiment, the control unit 120 uses the average value of the two CQI indexes or the representative CQI index that is the higher CQI index of the two CQI indexes based on the power ratio. Thus, the corrected representative CQI index may be obtained.

  When the acquired value is lower than the threshold value (first threshold value), the control unit 120 determines to use the single rank for transmission of the data signal to the user apparatus 300 in the protected subframe. On the other hand, when the acquired value is higher than the threshold value, as in the tenth embodiment, the control unit 120 temporarily uses the MCS corresponding to the two corrected CQI indexes and uses the two ranks. Then, when a data signal is transmitted to the user apparatus 300 in the protected subframe, a virtual SINR or a virtual channel capacity assumed in the user apparatus 300 is estimated.

  The control unit 120 compares the virtual SINR or the virtual channel capacity with the second threshold value. When the virtual SINR or the virtual channel capacity is lower than the second threshold, the control unit 120 uses the single rank to transmit the data signal to the user apparatus 300 in the protected subframe. If the virtual SINR or the virtual channel capacity is higher than the second threshold, the two ranks are used for transmission of the data signal to the user equipment 300 in the protected subframe. Decide as follows.

  In the communication control method according to this embodiment, when the acquired values obtained from the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 are lower than the first threshold, Are used to transmit data signals to the user equipment 300 in the protected subframe. In short, if the quality value (acquired value) that is expected to be obtained in two ranks is lower than the threshold value, the single rank is decided to be used for transmission of the data signal to the user equipment 300 in the protected subframe. To do. Therefore, the block error rate of the data signal in the user apparatus 300 in the protected subframe can be reduced. If the acquired value obtained from the two CQI indices for the two ranks indicated by the CQI received from the user equipment 300 is higher than the first threshold, the two ranks are used to protect the user in the protected subframe. When transmitting a data signal to the apparatus 300, a virtual SINR or a virtual channel capacity assumed in the user apparatus 300 is estimated. If the virtual SINR or the virtual channel capacity is lower than the second threshold, decide to use a single rank to transmit the data signal to the user equipment 300 in the protected subframe; If the virtual SINR or the virtual channel capacity is higher than the second threshold, the two ranks are determined to be used for transmission of the data signal to the user equipment 300 in the protected subframe. By using a single rank when the virtual SINR or virtual channel capacity assumed to be obtained in two ranks is lower than the second threshold, the user equipment 300 in the protected subframe The block error rate of the data signal can be reduced. When the virtual SINR or virtual channel capacity that is assumed to be obtained by two ranks is higher than the threshold, the data signal transmission rate in the protected subframe is increased by using the two ranks. Can be secured.

Modifications of Seventh to Eleventh Embodiments As described above, in the communication control method according to the seventh to eleventh embodiments, when the rank number indicated by the RI received from the user apparatus 300 is 2, 2 It is determined whether one rank is used for transmitting data signals to the user equipment 300 in protected subframes or a single rank is used.

  If the number of ranks indicated by the RI received from the user apparatus 300 is 2, but the single rank is determined to be used for transmission of the data signal to the user apparatus 300 in the protected subframe, the second rank Similar to the method described above in connection with the embodiment, the control unit 120 converts the precoding matrix for two ranks indicated by the PMI received from the user apparatus 300 to convert the precoding matrix for a single rank. A coding matrix may be obtained.

  If the number of ranks indicated by the RI received from the user apparatus 300 is 2, but it is determined that a single rank is used to transmit the data signal to the user apparatus 300 in the protected subframe, the fourth rank Similar to the method described above with reference to the embodiment, the control unit 120 may determine whether the average value of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or the higher of the two CQI indexes. The MCS corresponding to the other CQI index may be determined to be used for transmission of data signals to the user equipment 300 in protected subframes using a single rank.

  If the number of ranks indicated by the RI received from the user apparatus 300 is 2, but it is determined that a single rank is used to transmit the data signal to the user apparatus 300 in the protected subframe, the fifth rank Similar to the method described above in connection with the embodiment, the control unit 120 determines the two ranks indicated by the CQI received from the user apparatus 300 based on the ratio of the second transmission power to the first transmission power. The two CQI indexes are corrected, and the corrected two CQI indexes are obtained so that the lower the ratio, the lower the two corrected CQI indexes. The average value of the two corrected CQI indexes Alternatively, the MCS corresponding to the higher CQI index of the two corrected CQI indexes is used as the data transmission to the user apparatus 300 in the protected subframe using a single rank. It may decide to use for transmission.

  If the number of ranks indicated by the RI received from the user apparatus 300 is 2, but it is determined that a single rank is used to transmit the data signal to the user apparatus 300 in the protected subframe, the sixth rank Similar to the method described above with reference to the embodiment, the control unit 120 may determine whether the average value of the two CQI indexes for the two ranks indicated by the CQI received from the user apparatus 300 or the higher of the two CQI indexes. The other CQI index is obtained as a representative CQI index, and the representative CQI index is corrected based on the ratio of the second transmission power to the first transmission power. The corrected representative CQI index is obtained so as to be lower, and the MCS corresponding to the corrected representative CQI index is converted to a protected subframe using a single rank. It may decide to use to send data signals to the user equipment 300 in the over arm.

Other Modifications In the macro base station, each function executed by the CPU may be executed by hardware instead of the CPU, or programmable logic such as FPGA (Field Programmable Gate Array), DSP (Digital Signal Processor), etc. May run on the device.

  The above embodiments and modifications may be combined as long as no contradiction arises.

100 macro base station, 110 wireless communication unit, 112 transmission / reception antenna, 120 control unit, 130 memory, 200 pico base station, 300 user equipment.

Claims (15)

For inter-cell interference control, a data signal is transmitted to the user equipment using a non-protected subframe and a protected subframe, the first transmission power is used in the non-protected subframe, and in the protected subframe. A communication control method in a macro base station using a second transmission power lower than a first transmission power,
Receiving from the user device a rank indicator indicating the number of ranks to be used for transmission to the user device;
Receiving from the user equipment a channel quality indicator indicating a modulation and coding scheme to be used for transmission to the user equipment;
Deciding to use a single rank for transmission of data signals to the user equipment in protected subframes regardless of the number of ranks indicated in the rank indicator received from the user equipment ;
Receiving from the user equipment a precoding matrix indicator indicating a precoding matrix to be used for transmission to the user equipment;
When the rank number indicated by the rank indicator received from the user equipment is 2, the higher one of the two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment Determining a channel quality indicator index of
If the precoding matrix indicator received from the user equipment indicates a precoding matrix for two ranks, a matrix component corresponding to a rank corresponding to the higher channel quality indicator index of the precoding matrix A step of selecting
Determining to use the selected matrix component as a precoding matrix for the single rank to be used for transmission of a data signal to the user equipment in a protected subframe. Control method. When the rank number received from the user apparatus is 1 (one), the lower the ratio, the lower the transmission efficiency based on the ratio of the second transmission power to the first transmission power. A modulation / coding scheme having transmission efficiency lower than that of the modulation / coding scheme indicated in the channel quality indicator received from the user apparatus, in the protected subframe using the single rank. The communication control method according to claim 1 , further comprising a step of deciding to use the data signal for transmission to the user apparatus. If the rank indicator received from the user equipment is 2, the average value of two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment or the A modulation / coding scheme corresponding to the higher channel quality indicator index of the two channel quality indicator indexes is used for transmitting a data signal to the user equipment in a protected subframe using the single rank The communication control method according to claim 1 , further comprising a step of deciding to do. When the rank number received by the rank indicator received from the user apparatus is 2, the channel quality indicator received from the user apparatus based on a ratio of the second transmission power to the first transmission power 2 channel quality indicator indexes for the two ranks indicated by the two corrected channel quality indicator indexes so that the lower the ratio, the lower the two corrected channel quality indicator indexes. And getting the steps
The single rank is used for the modulation / coding scheme corresponding to the average value of the two channel quality indicator indexes after correction or the higher one of the two channel quality indicator indexes after correction. The communication control method according to claim 1 , further comprising a step of deciding to use for transmission of a data signal to the user apparatus in the protected subframe. If the rank indicator received from the user equipment is 2, the average value of two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment or the Obtaining a higher channel quality indicator index of the two channel quality indicator indexes as a representative channel quality indicator index;
Based on the ratio of the second transmission power to the first transmission power, the representative channel quality indicator index is corrected so that the lower the ratio, the lower the corrected representative channel quality indicator index. Obtaining the corrected representative channel quality indicator index;
Determining to use a modulation / coding scheme corresponding to the corrected representative channel quality indicator index for transmission of a data signal to the user equipment in a protected subframe using the single rank; and The communication control method according to claim 1 , further comprising: For inter-cell interference control, a data signal is transmitted to the user equipment using a non-protected subframe and a protected subframe, the first transmission power is used in the non-protected subframe, and in the protected subframe. A communication control method in a macro base station using a second transmission power lower than a first transmission power,
Receiving from the user device a rank indicator indicating the number of ranks to be used for transmission to the user device;
Receiving from the user equipment a channel quality indicator indicating a modulation and coding scheme to be used for transmission to the user equipment;
If the rank number received from the user equipment is 2, the acquired value obtained from two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment Comparing to a threshold;
If the acquisition value is lower than the threshold, a single rank is determined to be used for transmitting data signals to the user equipment in protected subframes, and the acquisition value is higher than the threshold. Determining the two ranks to be used for transmission of data signals to the user equipment in protected subframes. Obtaining an average value of the two channel quality indicator indexes for two ranks received from the user equipment or a higher channel quality indicator index of the two channel quality indicator indexes as the acquired value; The communication control method according to claim 6 , further comprising: Based on the ratio of the second transmission power to the first transmission power, correcting the two channel quality indicator indexes for the two ranks received from the user equipment, the lower the ratio, Obtaining the two corrected channel quality indicator indexes such that the two corrected channel quality indicator indexes are low;
And obtaining the higher channel quality indicator index of the two channel quality indicator indexes after correction or the higher of the two channel quality indicator indexes after correction as the acquired value. The communication control method according to claim 6 . Obtaining an average value of the two channel quality indicator indexes for the two ranks received from the user equipment or a higher channel quality indicator index of the two channel quality indicator indexes as a representative channel quality indicator index When,
Based on the ratio of the second transmission power to the first transmission power, the representative channel quality indicator index is corrected so that the lower the ratio, the lower the corrected representative channel quality indicator index. The communication control method according to claim 6 , further comprising: obtaining the corrected representative channel quality indicator index as the acquired value. Based on the ratio of the second transmission power to the first transmission power, correcting the two channel quality indicator indexes for the two ranks received from the user equipment, the lower the ratio, Obtaining the two corrected channel quality indicator indexes such that the two corrected channel quality indicator indexes are low;
From the two corrected channel quality indicator indexes, using a modulation / coding scheme corresponding to the two corrected channel quality indicator indexes and using two ranks, When a data signal is transmitted to the user apparatus, a virtual signal-to-noise interference ratio or a virtual channel capacity assumed in the user apparatus is estimated, and the virtual signal-to-noise interference ratio or the virtual The communication control method according to claim 6 , further comprising a step of obtaining a typical channel capacity as the acquired value. For inter-cell interference control, a data signal is transmitted to the user equipment using a non-protected subframe and a protected subframe, the first transmission power is used in the non-protected subframe, and in the protected subframe. A communication control method in a macro base station using a second transmission power lower than a first transmission power,
Receiving from the user device a rank indicator indicating the number of ranks to be used for transmission to the user device;
Receiving from the user equipment a channel quality indicator indicating a modulation and coding scheme to be used for transmission to the user equipment;
If the rank number received from the user equipment is 2, the acquired value obtained from two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment A first comparison step for comparing the to a first threshold;
A first determining step of determining that a single rank is used to transmit a data signal to the user equipment in a protected subframe if the acquired value is lower than the first threshold;
If the acquired value is higher than the first threshold, the two for the two ranks received from the user equipment based on a ratio of the second transmission power to the first transmission power. Correcting the channel quality indicator index to obtain two corrected channel quality indicator indexes such that the lower the ratio, the lower the corrected two channel quality indicator indexes;
From the two corrected channel quality indicator indexes, using a modulation / coding scheme corresponding to the two corrected channel quality indicator indexes and using two ranks, Estimating a virtual signal-to-noise interference ratio or virtual channel capacity assumed in the user equipment when transmitting a data signal to the user equipment;
A second comparing step of comparing the virtual signal-to-noise interference ratio or the virtual channel capacity with a second threshold;
If the virtual signal-to-noise interference ratio or the virtual channel capacity is lower than the second threshold, a single rank is transmitted to the user equipment in the protected subframe. If the virtual signal-to-noise interference ratio or the virtual channel capacity is higher than the second threshold, two ranks are assigned to the user equipment in the protected subframe. A communication control method comprising: a second determination step of determining to use the data signal for transmission to the network. Receiving from the user equipment a precoding matrix indicator indicating a precoding matrix to be used for transmission to the user equipment;
If the rank indicator received from the user equipment is 2 ranks, but if it is decided to use a single rank to transmit a data signal to the user equipment in a protected subframe, the rank Determining a higher channel quality indicator index of two channel quality indicator indexes for two ranks indicated by the channel quality indicator received from a user equipment;
If the rank indicator received from the user equipment is 2 ranks, but if it is decided to use a single rank to transmit a data signal to the user equipment in a protected subframe, the rank Selecting a matrix component corresponding to a rank corresponding to the higher channel quality indicator index among precoding matrices for two ranks indicated by the precoding matrix indicator received from a user equipment;
Determining to use the selected matrix component as a precoding matrix for the single rank for transmission of data signals to the user equipment in protected subframes. The communication control method according to any one of claims 6 to 11 . If the rank indicator received from the user equipment is 2 ranks, but if it is decided to use a single rank to transmit a data signal to the user equipment in a protected subframe, the rank An average value of two channel quality indicator indexes for two ranks indicated by the channel quality indicator received from a user apparatus or a modulation / code corresponding to a higher channel quality indicator index of the two channel quality indicator indexes scheme and from claim 6 and further comprising the step of determining to use for transmission of the data signal to the user equipment in the protection Ted subframe using the single rank of claim 12 The communication control method according to any one of claims. If the rank indicator received from the user equipment is 2 ranks, but if it is decided to use a single rank to transmit a data signal to the user equipment in a protected subframe, the rank Correcting two channel quality indicator indexes for two ranks indicated by the channel quality indicator received from the user equipment based on a ratio of the second transmission power to a first transmission power; Obtaining two corrected channel quality indicator indexes such that the lower the two are, the lower the corrected two channel quality indicator indexes are;
The single rank is used for the modulation / coding scheme corresponding to the average value of the two channel quality indicator indexes after correction or the higher one of the two channel quality indicator indexes after correction. The communication control method according to any one of claims 6 to 12 , further comprising a step of deciding to use the data signal to be transmitted to the user equipment in the protected subframe. . If the rank indicator received from the user equipment is 2 ranks, but if it is decided to use a single rank to transmit a data signal to the user equipment in a protected subframe, the rank The average value of the two channel quality indicator indexes for the two ranks indicated by the channel quality indicator received from the user equipment or the higher channel quality indicator index of the two channel quality indicator indexes is represented as a representative channel quality indicator. Obtaining as an index;
Based on the ratio of the second transmission power to the first transmission power, the representative channel quality indicator index is corrected so that the lower the ratio, the lower the corrected representative channel quality indicator index. Obtaining the corrected representative channel quality indicator index;
Determining to use a modulation / coding scheme corresponding to the corrected representative channel quality indicator index for transmission of a data signal to the user equipment in a protected subframe using the single rank; and The communication control method according to any one of claims 6 to 12 , further comprising:

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