JP2016105636A - Mobile terminal device, radio base station, and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide highly efficient local area wireless access.SOLUTION: A mobile terminal device of the present invention includes: a measurement section for measuring the reception power of a discovery signal transmitted at a predetermined interval from a radio base station that can switch itself between a downlink transmission state and a no transmission state; and a control section for controlling the transmission power of an uplink signal to be transmitted to the radio base station, on the basis of path loss calculated using a value of the reception power of the measured discovery signal.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a mobile terminal apparatus, a radio base station, and a radio communication method in a next generation mobile communication system in which a local area is arranged in a wide area.

  In a UMTS (Universal Mobile Telecommunications System) network, Long Term Evolution (LTE) has been studied for the purpose of higher data rate and low delay (Non-patent Document 1). LTE uses a multi-access scheme based on OFDMA (Orthogonal Frequency Division Multiple Access) for the downlink (downlink) and SC-FDMA (single carrier frequency division multiple access) for the uplink (uplink). Is used.

  In addition, a successor system of LTE is also being studied for the purpose of further broadbandization and speedup from LTE (for example, LTE advanced or LTE enhancement (hereinafter referred to as “LTE-A”). In A (Rel-10), carrier aggregation that bundles a plurality of component carriers (CC: Component Carrier) with the system band of the LTE system as one unit is used, and in LTE-A, interference coordination is used. A HetNet (Heterogeneous Network) configuration using technology (eICIC: enhanced Inter-Cell Interference Coordination) has been studied.

3GPP TR 25.913 “Requirements for Evolved UTRA and Evolved UTRAN”

  By the way, in a cellular system such as W-CDMA, LTE (Rel. 8), and a successor system of LTE (for example, Rel. 9, Rel. 10), a wireless communication system (wireless interface) is designed to support a wide area. Has been. In the future, in addition to such cellular environments, it is expected to provide high-speed wireless services by short-range communication in local areas such as indoors and shopping malls. For this reason, the design of a new wireless communication system specialized for the local area is required so that the capacity can be secured in the local area while ensuring the coverage in the wide area.

  The present invention has been made in view of this point, and an object of the present invention is to provide a mobile terminal device, a radio base station, and a radio communication method that can provide highly efficient local area radio access.

  The radio communication method of the present invention is a radio communication method between a radio base station and a mobile terminal apparatus capable of switching between a downlink transmission state and a non-transmission state, and the mobile terminal apparatus performs a predetermined cycle from the radio base station. Measuring received power of a discovery signal to be transmitted, and controlling transmission power of an uplink signal to the radio base station based on a path loss calculated based on the measured received power value of the discovery signal; It is characterized by having.

  The radio base station of the present invention is a radio base station capable of switching between a downlink transmission state and a non-transmission state, a transmission unit that transmits a discovery signal at a predetermined period, and a reception that receives an uplink signal from a mobile terminal device A transmission power of the uplink signal is controlled based on a path loss calculated based on a reception power value of the discovery signal.

  The mobile terminal apparatus of the present invention includes a measurement unit that measures reception power of a discovery signal transmitted at a predetermined period from a radio base station that can switch between a downlink transmission state and a non-transmission state, and the measured discovery signal And a control unit that controls transmission power of an uplink signal to the radio base station based on a path loss calculated based on a received power value.

  A radio communication system according to the present invention is a radio communication system including a radio base station and a mobile terminal device that can switch between a downlink transmission state and a non-transmission state, and the mobile terminal device receives a predetermined period from the radio base station. A measurement unit for measuring the reception power of the discovery signal transmitted in step (b), and controlling the transmission power of the uplink signal to the radio base station based on the path loss calculated based on the measured reception power value of the discovery signal. And a control unit.

  According to the present invention, highly efficient local area wireless access can be provided.

It is explanatory drawing of the system band of a LTE-A system. It is a figure which shows the structure which has arrange | positioned many small cells in a macrocell. It is a figure which shows two types of Heterogeneous Network structure. It is a figure which shows the carrier used by a wide area and a local area. It is a table which shows the difference between a wide area and a local area. It is a figure which shows the arrangement configuration of a discovery signal and DACH. It is a figure for demonstrating the coverage of the up-and-down link of a local area. It is a conceptual diagram of transmission power control in the downlink of a local area. It is a sequence diagram which shows the radio | wireless communication method in the downlink of the local area which concerns on a 1st aspect. It is a sequence diagram which shows the radio | wireless communication method in the downlink of the local area which concerns on a 2nd aspect. It is a figure which shows the transmission power difference of PDSCH / ePDCCH and CSI-RS. It is a figure which shows an example of the arrangement configuration of CSI-RS. It is a figure which shows an example of the arrangement configuration of CSI-RS. It is a figure for demonstrating an example of the system configuration | structure of a radio | wireless communications system. It is a block diagram of a mobile terminal device. It is a block diagram of a wide area base station apparatus. It is a block diagram of a local area base station apparatus.

  FIG. 1 is a diagram illustrating a hierarchical bandwidth configuration defined in LTE-A. The example shown in FIG. 1 is an LTE-A system having a first system band composed of a plurality of fundamental frequency blocks (hereinafter referred to as component carriers) and an LTE having a second system band composed of one component carrier. This is a hierarchical bandwidth configuration when the system coexists. In the LTE-A system, for example, wireless communication is performed with a variable system bandwidth of 100 MHz or less, and in the LTE system, wireless communication is performed with a variable system bandwidth of 20 MHz or less. The system band of the LTE-A system is at least one component carrier with the system band of the LTE system as one unit. In this way, collecting a plurality of component carriers to increase the bandwidth is called carrier aggregation.

  For example, in FIG. 1, the system band of the LTE-A system is a system band (20 MHz × 5 = 100 MHz) including a band of five component carriers, where the system band (base band: 20 MHz) of the LTE system is one component carrier. ). In FIG. 1, a mobile terminal apparatus UE (User Equipment) # 1 is a mobile terminal apparatus compatible with the LTE-A system (also compatible with the LTE system) and can support a system band up to 100 MHz. UE # 2 is a mobile terminal apparatus compatible with the LTE-A system (also supports the LTE system), and can support a system band up to 40 MHz (20 MHz × 2 = 40 MHz). The UE # 3 is a mobile terminal device compatible with the LTE system (not compatible with the LTE-A system), and can support a system band up to 20 MHz (base band).

  By the way, in a future system, as shown in FIG. 2, the structure which arrange | positions innumerable small cell S in the macrocell M is assumed. In this case, it is required to design the small cell S in consideration of the capacity with respect to the network cost. Examples of the network cost include installation costs for network nodes and backhaul links, operation costs for cell planning and maintenance, power consumption on the network side, and the like. In addition, small cells are required to support power saving and random cell planning on the mobile terminal device side as requests other than capacity.

  When arranging a small cell in the macro cell M, as shown in FIGS. 3A and 3B, two types of heterogeneous network (hereinafter referred to as HetNet) configurations are conceivable. In the first HetNet configuration shown in FIG. 3A, the small cells are arranged such that the macro cell M and the small cell S use the same carrier. In the second HetNet configuration shown in FIG. 3B, the small cell S is arranged such that the macro cell M and the small cell S use different carriers. In the second HetNet configuration, since the small cell S uses a dedicated carrier, it is possible to secure capacity in the small cell S while ensuring coverage in the macro cell M. In the future (Rel. 12 and later), this second HetNet configuration is assumed to be important.

  An example of the carrier used in the second HetNet configuration will be described with reference to FIG. Hereinafter, the macro cell M and the small cell S in FIG. 3B are referred to as a wide area and a local area, respectively. The wide area may include sectors and the like in addition to the macro cell, and the local area may include pico cells, nano cells, femto cells, micro cells, and the like in addition to small cells. A radio base station that covers the wide area and the local area (referred to as a coverage range) is referred to as a wide area base station apparatus and a local area base station apparatus.

  As shown in FIG. 4, a carrier used in a wide area of the second HetNet configuration (hereinafter referred to as a wide area carrier) has a relatively narrow bandwidth (for example, 2 MHz) in a predetermined frequency band. It is a carrier wave. The wide area carrier is transmitted with a relatively large transmission power so as to cover a wide wide area. This wide area carrier is also called a legacy carrier or a coverage carrier.

  On the other hand, the carrier used in the local area of the second HetNet configuration (hereinafter referred to as a local area carrier) is wide in a different frequency band (in FIG. 4, a higher frequency band than the wide area carrier). A carrier wave having a bandwidth (for example, 3.5 GHz). Since the local area carrier has a wide bandwidth for improving the capacity, it is transmitted with relatively small transmission power. The local area carrier is also called an additional carrier, an extension carrier, a capacity carrier, or the like.

  In such a second HetNet configuration, as shown in FIG. 5, it is assumed that required conditions and the like are different between the wide area and the local area. For example, in a wide area, since the bandwidth is limited, frequency utilization efficiency is very important. On the other hand, in the local area, it is easy to take a wide bandwidth. Therefore, if a wide bandwidth can be secured, the importance of frequency utilization efficiency is not so high as in the wide area. In a wide area, it is necessary to cope with high mobility such as a car, but in a local area, low mobility may be supported. In a wide area, it is necessary to secure wide coverage. On the other hand, it is preferable to secure a wide coverage in the local area, but a shortage of coverage can be covered in the wide area.

  In the wide area, the difference in capability between the wide area base station apparatus and the mobile terminal apparatus is large, so that the maximum transmission power difference between the uplink and downlink is large, and the transmission power of the uplink and downlink is asymmetric. On the other hand, in the local area, since the difference in capability between the local area base station apparatus and the mobile terminal apparatus is small, the maximum transmission power difference between the uplink and downlink is small, and the transmission power of the uplink and downlink is close to symmetry. Furthermore, in a wide area, since the number of connected users per cell is large and cell planning is performed, fluctuations in traffic are small. On the other hand, in the local area, the number of connected users per cell is small and there is a possibility that cell planning is not performed. As described above, since the optimum requirements for the local area are different from those for the wide area, it is necessary to design a radio communication system specialized for the local area.

  In consideration of interference due to power saving and random cell planning, the wireless communication system for the local area is preferably configured so that no transmission is performed when there is no traffic. For this reason, as shown in FIG. 6, the UE-specific design is assumed as much as possible for the wireless communication system for the local area. Specifically, the wireless communication system for the local area includes Cell-specific such as PSS / SSS (Primary Synchronization Signal / Secondary Synchronization Signal), CRS (Cell-specific Reference Signal), and PDCCH (Physical Downlink Control Channel) in LTE. It is designed based on ePDCCH (enhanced Physical Downlink Control Channel), PDSCH (Physical Downlink Shared Channel), and DM-RS (DeModulation-Reference Signal).

  Here, ePDCCH (enhanced downlink control signal) is a downlink control signal that is frequency division multiplexed with PDSCH (downlink data signal). Similar to PDSCH, ePDCCH is demodulated using DM-RS, which is a user-specific demodulation reference signal. In addition, ePDCCH may be called FDM type PDCCH and may be called UE-PDCCH. In FIG. 6, PDSCH, ePDCCH, DM-RS, etc. are described as UE-specific L1 / L2 signals.

  In addition, in the wireless communication system for the local area, as shown in FIG. 6, it is also considered to define a discovery signal (Discovery Signal) in the downlink and to define a DACH (Direct Access Channel) in the uplink. . Here, the discovery signal is a detection signal used for detection of the local area base station apparatus by the mobile terminal apparatus. DACH is a dedicated access channel for the local area base station apparatus. The received power of the discovery signal in the mobile terminal apparatus is transmitted by the DACH.

  As shown in FIG. 6, the downlink discovery signal is transmitted in a relatively long cycle (for example, a cycle of several seconds) so that the mobile terminal apparatus can reduce the number of measurements and save the battery. On the other hand, radio resources are allocated to the uplink DACH in a shorter cycle than the discovery signal. Thereby, an uplink connection is quickly established when traffic occurs in the mobile terminal apparatus.

  Note that the signal arrangement shown in FIG. 6 is merely an example, and the present invention is not limited to this. For example, radio resources may be allocated to the DACH at the same cycle as the discovery signal (for example, a cycle of several seconds). The discovery signal may also be called PDCH (Physical Discovery Channel), BS (Beacon Signal), DPS (Discovery Pilot Signal), or the like. The name of DACH is not particularly limited.

  By the way, in the local area of the second HetNet configuration as described above, the uplink / downlink coverage may be asymmetric. As described with reference to FIG. 5, in the local area, since the difference in capability between the local area base station apparatus and the mobile terminal apparatus is small, the maximum transmission power difference between the upper and lower links becomes smaller, and generally the transmission power of the upper and lower links. Is close to symmetry. However, as shown in FIG. 7, in the uplink of the local area, it is possible to perform transmission power control that increases the transmission power by narrowing the bandwidth of the local area carrier shown in FIG. As a result, as shown in FIG. 7, the uplink transmission power becomes significantly larger than the downlink transmission power, and there is a problem that the uplink and downlink coverage in the local area becomes asymmetric.

  Therefore, the present inventors prevent the uplink / downlink coverage from becoming asymmetric in a local area where the transmission power difference between the local area base station apparatus and the mobile terminal apparatus is small and generally the uplink / downlink transmission power is nearly symmetrical. Therefore, the present invention has been achieved. That is, the essence of the present invention is that the downlink power in the local area is also improved by performing transmission power control for increasing the transmission power by narrowing the bandwidth of the local area carrier shown in FIG. The goal is to make the coverage close to symmetry.

  Hereinafter, the transmission power control method in the downlink of the local area according to the present embodiment will be described. Note that the following description assumes a wireless communication system (see FIG. 14) in which a plurality of local areas are arranged in a wide area. In this wireless communication system, the second HetNet configuration described above is applied, and the local area has a wider bandwidth than the wide area carrier in a frequency band different from the wide area carrier (first carrier). A carrier for use (second carrier) is used.

  FIG. 8 is a conceptual diagram of transmission power control in the downlink of the local area according to the present embodiment. As shown in FIG. 8, in the downlink of the local area, the discovery signal is transmitted with a constant transmission power so that the coverage is maximized. This is because more mobile terminal apparatuses 10 can detect the discovery signal.

  On the other hand, in FIG. 8, the transmission power of downlink signals such as ePDCCH (enhanced downlink control signal) and PDSCH (downlink data signal) is adaptively controlled. For example, for a downlink signal to the mobile terminal apparatus 10 near the local area base station apparatus 30, a high capacity is maintained with a small coverage using a local area carrier (see FIG. 4) with a wide bandwidth and a small transmission power as it is. A city may be secured. On the other hand, for the downlink signal to the mobile terminal apparatus 10 that is further away from the local area base station apparatus 30, the coverage is expanded by narrowing the bandwidth of the local area carrier (see FIG. 4) to increase the transmission power. Capacity may be reduced.

  Next, with reference to FIG.9 and FIG.10, the radio | wireless communication method in the downlink of the local area which concerns on this Embodiment is explained in full detail.

  FIG. 9 is a sequence diagram showing a wireless communication method in the downlink of the local area according to the first aspect. In FIG. 9, the wide area base station apparatus 20 and the local area base station apparatus 30 are connected by a wired interface such as an X2 interface, but may be connected by a wireless interface. The mobile terminal apparatus 10 is connected to the wide area base station apparatus 20 and the local area base station apparatus 30 through a radio interface.

  As shown in FIG. 9, the local area base station device 30 receives control information for discovery signal (DS) transmission from the wide area base station device 20 (step S101). The control information for transmitting the discovery signal includes a radio resource and a signal sequence for transmitting the discovery signal. The signal sequence of the discovery signal is set for each local area, and the local area is identified by this signal sequence.

  The mobile terminal apparatus 10 receives, from the wide area base station apparatus 20, for example, local area control information such as discovery signal (DS) reception control information, DACH transmission control information, and ePDCCH reception control information ( Step S102).

  Here, the discovery signal reception control information includes a radio resource and a signal sequence for receiving the discovery signal from the local area base station apparatus 30. The control information for receiving the discovery signal may include the transmission power of the discovery signal from the local area base station device 30. Further, the control information for DACH transmission includes radio resources assigned to the DACH, DM-RS sequences, and the like. The ePDCCH reception control information includes radio resources, DM-RS sequences, and the like for receiving downlink control information (DCI: Downlink Control Information) using ePDCCH from the local area base station apparatus 30.

  The mobile terminal apparatus 10 receives a discovery signal from the local area base station apparatus 30 based on the discovery signal reception control information received in step S102, and measures the received power of the discovery signal (step S103). As described above, the discovery signal is transmitted from the local area base station device 30 at a predetermined cycle (for example, a cycle of several seconds). Note that, as the reception power of the discovery signal, for example, the SINR (Signal-to-Interference and Noise power Ratio) of the discovery signal is used.

  The mobile terminal apparatus 10 calculates the path loss of the discovery signal based on the received power of the discovery signal (Step S104). Specifically, the mobile terminal apparatus 10 determines the difference between the transmission power value of the discovery signal received from the wide area base station apparatus 20 in step S102 and the reception power value of the discovery signal measured in step S103. Calculated as path loss.

  The mobile terminal apparatus 10 transmits the reception power or path loss of the discovery signal to the local area base station apparatus 30 using the DACH based on the control information for DACH transmission received in step S102 (step S105). Here, the initial transmission power of DACH may be determined based on the path loss calculated in step S104. For example, the initial transmission power of the DACH may be a value that is equal to or less than the maximum transmission power of the mobile terminal apparatus 10 and a predetermined offset is added to the path loss.

  The local area base station device 30 determines the initial transmission power of the downlink signal for the mobile terminal device 10 based on the path loss of the discovery signal in the mobile terminal device 10 (step S106). For example, the initial transmission power of the downlink signal may be a value that is equal to or less than the maximum transmission power of the local area base station apparatus 30 and a predetermined offset is added to the path loss. Note that examples of downlink signals for which the initial transmission power is determined include frequency-division multiplexed ePDCCH (enhanced downlink control signal) and PDSCH (downlink data signal).

  The path loss of the discovery signal may be calculated by the mobile terminal apparatus 10 and transmitted to the local area base station apparatus 30 or may be calculated by the local area base station apparatus 30. The local area base station device 30 receives the reception power value of the discovery signal from the mobile terminal device 10, calculates the path loss of the discovery signal from the difference between the received reception power value and the transmission power value of the discovery signal, and calculates the calculated path loss. Based on the above, the initial transmission power of the downlink signal is determined.

  The local area base station apparatus 30 transmits a downlink signal with the initial transmission power determined in step S106 (step S107). Specifically, the local area base station device 30 transmits ePDCCH and PDSCH with the initial transmission power indicated by the initial transmission power information from the wide area base station device 20. The mobile terminal apparatus 10 recognizes and receives the PDSCH assigned to itself based on DCI (Downlink Control Information) transmitted using the ePDCCH.

  Note that CSI-RS (Channel State Information Reference Signal) is multiplexed in the downlink signal transmitted from the local area base station apparatus 30. Here, the CSI-RS is a measurement reference signal for measuring a channel state between the local area base station device 30 and the mobile terminal device 10.

  The mobile terminal apparatus 10 measures the received power of the CSI-RS multiplexed on the downlink signal, and generates CSI (Channel State Information) based on the measured received power (step S108). As the received power of CSI-RS, for example, CSI-RS SINR (Signal-to-Interference and Noise power Ratio) is used.

  Here, the CSI is a channel state indicating a channel state between the mobile terminal apparatus 10 and the local area base station apparatus 30, such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), and RI (Rank Indicator). Information. The CQI is a value calculated based on the SINR of the CSI-RS from the local area base station apparatus 30, and each value is associated with a modulation and coding scheme (MCS).

  The mobile terminal apparatus 10 transmits the CSI generated in step S108 to the local area base station apparatus 30 (step S109). The CSI transmission may be performed using PUCCH (Physical Uplink Control Channel, uplink control signal) or may be performed using PUSCH (Physical Uplink Shared Channel, uplink data signal).

  The local area base station apparatus 30 determines the transmission power of the downlink signal based on the CSI received from the mobile terminal apparatus 10 in step S109 and the path loss of the above discovery signal (step S110). Examples of downlink signals for which transmission power is determined include frequency division multiplexed ePDCCH and PDSCH. In addition, the local area base station apparatus 30 may determine the offset value with respect to the transmission power of the present downlink signal based on the above-mentioned CSI and path loss.

  Further, the local area base station apparatus 30 may determine a modulation and coding scheme (MCS) to be applied to the downlink signal based on the CQI received from the mobile terminal apparatus 10 in step S109.

  The local area base station apparatus 30 transmits a downlink signal with the transmission power determined in step S110 (step S111). Moreover, the local area base station apparatus 30 may transmit a downlink signal by MCS determined based on CQI.

  As described above, according to the wireless communication method in the downlink of the local area according to the first aspect shown in FIG. 9, the transmission power of the downlink signal is also reduced in the downlink of the local area based on the path loss of the discovery signal. Adaptively controlled. As described above, by adaptively controlling the transmission power of the local area carrier not only in the uplink in the local area but also in the downlink, it is possible to make the coverage of the uplink and downlink in the local area close to symmetry.

  Also, according to the local area downlink radio communication method according to the first aspect shown in FIG. 9, the local area base station apparatus 30 to which the mobile terminal apparatus 10 is connected determines the transmission power of the downlink signal. For this reason, it is possible to control the transmission power of the downlink signal more quickly than in the case where the transmission power is determined by the wide area base station apparatus 20.

  FIG. 10 is a sequence diagram showing a wireless communication method in the downlink of the local area according to the second aspect. The wireless communication method shown in FIG. 10 differs from the wireless communication method shown in FIG. 9 in that the initial transmission power and transmission power of the downlink signal are determined not by the local area base station device 30 but by the wide area base station device 20. Different. Hereinafter, the description will be focused on the difference from FIG.

  In FIG. 10, it is assumed that the mobile terminal apparatus 10 has established a connection (for example, an upper layer connection such as an RRC connection) with the wide area base station apparatus 20. Also, steps S201 to S204 in FIG. 10 are the same as steps S101 to S104 in FIG.

  As shown in FIG. 10, the mobile terminal apparatus 10 transmits the reception power or path loss of the discovery signal to the wide area base station apparatus 20 using higher layer signaling such as RRC signaling (step S205).

  The wide area base station apparatus 20 determines the initial transmission power of the downlink signal from the local area base station apparatus 30 to the mobile terminal apparatus 10 based on the path loss of the discovery signal in the mobile terminal apparatus 10 (step S206). For example, the initial transmission power of the downlink signal from the local area base station apparatus 30 may be a value that is equal to or less than the maximum transmission power of the local area base station apparatus 30 and a predetermined offset is added to the path loss. Note that downlink signals for which the initial transmission power is determined include ePDCCH and PDSCH that are frequency division multiplexed.

  Note that the path loss of the discovery signal may be calculated by the mobile terminal apparatus 10 and transmitted to the wide area base station apparatus 20, or may be calculated by the wide area base station apparatus 20. The wide area base station apparatus 20 receives the reception power value of the discovery signal from the mobile terminal apparatus 10, calculates the path loss of the discovery signal from the difference between the received reception power value and the transmission power value of the discovery signal, and calculates the calculated path loss. Based on the above, the initial transmission power of the downlink signal is determined.

  The wide area base station apparatus 20 transmits transmission power information indicating the determined initial transmission power to the local area base station apparatus 30 via a wired interface such as an X2 interface (step S207).

  The local area base station device 30 transmits the downlink signal with the initial transmission power indicated by the transmission power information from the wide area base station device 20 (step S208). Specifically, the local area base station device 30 transmits at least one of ePDCCH and PDSCH with the initial transmission power indicated by the transmission power information from the wide area base station device 20.

  The mobile terminal apparatus 10 measures the received power of the CSI-RS multiplexed on the downlink signal, and generates CSI including CQI and the like based on the measured received power (step S209).

  The mobile terminal apparatus 10 transmits the CSI generated in step S209 to the wide area base station apparatus 20 (step S210). The CSI transmission may be performed using higher layer signaling of RRC signaling.

  The wide area base station apparatus 20 determines the transmission power of the downlink signal from the local area base station apparatus 30 to the mobile terminal apparatus 10 based on the CSI received from the mobile terminal apparatus 10 in step S210 and the path loss of the discovery signal described above. (Step S211). Examples of the downlink signal from the local area base station apparatus 30 that is the target of transmission power include frequency division multiplexed ePDCCH and PDSCH. Note that the local area base station apparatus 30 may determine an offset value for the transmission power of the downlink signal from the current local area base station apparatus 30 based on the above-described CSI and path loss.

  Also, the wide area base station apparatus 20 determines a modulation and coding scheme (MCS) to be applied to the downlink signal from the local area base station apparatus 30 based on the CQI received from the mobile terminal apparatus 10 in step S210. Also good.

  The wide area base station apparatus 20 transmits transmission power information indicating the determined transmission power to the local area base station apparatus 30 via a wired interface such as an X2 interface (step S212). Further, the wide area base station apparatus 20 may transmit MCS information indicating the determined MCS to the local area base station apparatus 30.

  The local area base station apparatus 30 transmits a downlink signal with the transmission power indicated by the transmission power information from the wide area base station apparatus 20 (step S213). Moreover, the local area base station apparatus 30 may transmit the downlink signal containing ePDCCH and PDSCH by MCS which the MCS information from the wide area base station apparatus 20 shows.

  According to the local area downlink radio communication method according to the second aspect shown in FIG. 10, the wide area base station apparatus 20 forming the wide area in which the local area base station apparatus 30 is arranged transmits downlink signals. Determine the power. Thereby, it is possible to determine a more optimal downlink signal transmission power in consideration of the load balance between the local areas. Further, the wide area base station apparatus 20 determines the transmission power of the downlink signal of the subordinate local area base station apparatus 30, thereby enabling the transmission power control of the downlink signal in CoMP (Coordinated Multiple Point). Note that the wireless communication methods in FIGS. 9 and 10 are combined, for example, before step S108 in FIG. 9 and after step S210 in FIG. 10, or before step S209 in FIG. 10 and after step S109 in FIG. May be.

  Next, a CSI reporting method suitable for the transmission power control method in the downlink of the local area according to the present embodiment will be described with reference to FIG.

  FIG. 11 is a diagram illustrating transmission power of a downlink signal adaptively controlled in the local area according to the present embodiment. As shown in FIG. 11, in the local area of the present embodiment, ePDCCH or PDSCH transmission power adaptively increases, while CSI-RS transmission power is kept constant. This is because the CSI-RS is used for channel estimation in the mobile terminal apparatus, and therefore it is preferable to keep the transmission power of the CSI-RS constant so that a change in channel state can be detected.

  In the case illustrated in FIG. 11, the transmission power difference between the CSI-RS in which low transmission power is maintained and the adaptively increased ePDCCH or PDSCH increases. Thereby, the reception power difference between CSI-RS in the mobile terminal device 10, and ePDCCH or PDSCH increases.

  For example, the SINR of CSI-RS deteriorates at -5 dB or less, but due to adaptive control of ePDCCH or PDSCH transmission power, SINR of ePDCCH or PDSCH becomes better at +5 dB or more, and CSI-RS and ePDCCH or PDSCH It is assumed that the received power difference increases. In such a case, the CQI measured using the CSI-RS deviates from the actual reception quality of the ePDCCH or PDSCH, so it is expected that the accuracy of link adaptation (MCS selection) based on the CQI will be reduced. Therefore, it is conceivable to adopt the following CSI reporting method.

  In the first CSI reporting method, the difference (ΔS) between the adaptively controlled ePDCCH or PDSCH transmission power and the CSI-RS transmission power allocated to the same resource block as the ePDCCH or PDSCH is a wide area. The mobile terminal apparatus 10 is notified in advance from the base station apparatus 20 or the local area base station apparatus 30.

  For example, the transmission power difference ΔS may be notified from the wide area base station apparatus 20 in step S102 of FIG. 9 or step S202 of FIG. Alternatively, the transmission power difference ΔS may be notified from the local area base station apparatus 30 in the access procedure triggered by the DACH. The mobile terminal apparatus 10 corrects the CQI value calculated using the SINR of the CSI-RS based on the notified transmission power difference ΔS, and reports the CSI including the corrected CQI. For example, the mobile terminal apparatus 10 corrects the CQI value so as to add ΔS to the SINR of CSI-RS.

  In the first CSI reporting method, it is possible to prevent a CQI with low accuracy from being reported and a decrease in link adaptation (MCS selection) accuracy without changing the configuration of an existing CQI.

  In the second CSI reporting method, the measurement range of CQI (channel quality identifier) using the received power of CSI-RS is extended. For example, it is conceivable to extend the measurement range of CQI so that it can cope with the case where the SINR of CSI-RS is −20 dB. The existing CQI is identified by a CQI index of 16 stages from 0 to 15, and 4 bits are reserved for the CQI index. In the second CSI reporting method, the number of bits for CQI index is further expanded, and a CQI index value corresponding to the expanded measurement range is reported. As a result, even when the CQI measured using CSI-RS deviates to some extent from the actual reception quality of ePDCCH or PDSCH, it can be kept within the CQI measurement range, so link adaptation based on CQI (MCS selection) Accuracy is improved.

  In the second CSI reporting method, it is possible to report CQI with high accuracy without notifying the transmission power difference ΔS between ePDCCH or PDSCH and CSI-RS, and it is possible to prevent a decrease in link adaptation accuracy.

  Next, with reference to FIG.12 and FIG.13, the arrangement structure of CSI-RS suitable for the transmission power control system in the downlink of the local area of this Embodiment is demonstrated.

  FIG. 12 is a diagram illustrating an arrangement configuration example of CSI-RSs in the local area according to the present embodiment. In the local area, the CSI-RS is transmitted using a local area carrier (see FIG. 4) having a wide bandwidth and low transmission power. As described above, CSI-RS does not perform adaptive transmission power like ePDCCH and PDSCH. For this reason, if CSI-RS is transmitted with the local area carrier, the mobile terminal apparatus 10 cannot receive the CSI-RS with sufficient reception power, and the measurement accuracy of the CSI-RS deteriorates. Therefore, as shown in FIG. 12A, it is conceivable to increase the insertion density of CSI-RS.

  FIG. 12A shows an example of an arrangement configuration of CSI-RSs in a subframe when the insertion density is increased. As shown in FIG. 12A, the CSI-RS transmitted in the local area is shorter than the subcarrier interval in which the CSI-RS transmitted in the wide area is arranged in a specific OFDM symbol in the subframe. It is arranged.

  For example, in FIG. 12A, CSI-RSs are arranged for every three subcarriers in the ninth and tenth OFDM symbols from the beginning in the subframe. In the wide area, in the case of 2 antenna ports, CSI-RS is arranged for every 12 subcarriers. For this reason, in the arrangement shown in FIG. 12A, the CSI-RS insertion density in the local area increases more than in the wide area.

  As shown in FIG. 12A, the CSI-RS is reduced in the local area carrier with a wide bandwidth and a small transmission power by reducing the subcarrier interval in which the CSI-RS is arranged and increasing the insertion density of the CSI-RS. Even in the case of transmitting the CSI-RS measurement accuracy in the mobile terminal device 10 can be prevented.

  Moreover, as shown in FIG. 11, when ePDCCH or PDSCH in which transmission power increases adaptively and CSI-RS are arranged in adjacent subcarriers, it is assumed that power boost of ePDCCH or PDSCH may be hindered. The Therefore, it is conceivable to arrange CSI-RS as shown in FIGS. 12B and 12C.

  FIG. 12B shows an example of an arrangement configuration in which a specific OFDM symbol in a subframe is occupied by CSI-RS. As shown in FIG. 12B, CSI-RS transmitted in the local area is arranged on all subcarriers constituting the resource block width in a specific OFDM symbol in the subframe.

  In the arrangement shown in FIG. 12B, ePDCCH or PDSCH whose transmission power is adaptively increased and CSI-RS whose transmission power is constant and low are arranged in adjacent subcarriers in a specific OFDM symbol in the subframe. There is no. For this reason, it can prevent that CSI-RS obstructs the power boost of ePDCCH or PDSCH. Moreover, since CSI-RS is arrange | positioned at all the subcarriers which comprise a resource block width, even when transmitting CSI-RS with the carrier for local areas with wide bandwidth, measurement of CSI-RS in the mobile terminal device 10 Decrease in accuracy can be prevented.

  FIG. 12C shows an example of an arrangement configuration in which frequency division multiplexing of CSI-RS and ePDSCH or PDSCH is avoided in a specific OFDM symbol of a subframe. As shown in FIG. 12C, CSI-RS transmitted in the local area is arranged on some subcarriers constituting the resource block width in a specific OFDM symbol in the subframe. At this time, muting resources (Zero-power CSI-RS) are allocated to the remaining subcarriers so that the PDSCH is not allocated to the remaining subcarriers.

  In the arrangement configuration shown in FIG. 12C, muting resources are arranged in subcarriers in which CSI-RS is not arranged in a specific OFDM symbol in the subframe. For this reason, in a specific OFDM symbol in a subframe, ePDCCH or PDSCH in which transmission power increases adaptively and CSI-RS in which transmission power is constant and low are not arranged in adjacent subcarriers. For this reason, it can prevent that CSI-RS obstructs the power boost of ePDCCH or PDSCH.

  In addition, arrangement | positioning of CSI-RS shown to FIGS. 12A-12C is only an illustration, and is not restricted to this. For example, in FIGS. 12A to 12C, CSI-RSs may be arranged in OFDM symbols other than the ninth and tenth in the subframe. Further, in FIG. 12A, CSI-RS may be arranged in any subcarrier as long as the subcarrier interval in which CSI-RS is arranged is shorter than the wide area. In FIG. 12C, if a muting resource is allocated to a subcarrier in which CSI-RS is not allocated in a specific OFDM symbol in the subframe, CSI-RS may be allocated to any subcarrier.

  Further, in the local area, as shown in FIGS. 12A to 12C, it is considered that no PDCCH is arranged in a maximum of 3 OFDM symbols from the top of the subframe. For this reason, CSI-RS may be arrange | positioned in this resource area | region. Also, the arrangement configuration of DM-RSs that are UE-specific demodulation reference signals is not limited to the arrangement shown in FIGS.

  FIG. 13 is a diagram illustrating an example of an arrangement configuration of CSI-RSs when carrier aggregation is performed in a wide area and a local area. When carrier aggregation is performed between the wide area base station apparatus 20 and the local area base station apparatus 30, it is assumed that the wide area carrier and the local area carrier described in FIG. 4 belong to different component carriers. .

  In such a case, as illustrated in FIG. 13, the CSI-RS transmitted in the local area may be arranged in a subframe different from the subframe in which the CSI-RS transmitted in the wide area is arranged. For example, in FIG. 13, the wide area CSI-RS is arranged in subframes 1 and 3, while the local area CSI-RS is arranged in subframe 2.

  When carrier aggregation is performed, the frequency band is different between the component carrier (CC1) in the wide area and the component carrier (CC2) in the local area. For this reason, it becomes possible to realize frequency hopping in a pseudo manner by arranging CSI-RSs in different subframes between component carriers.

  In addition, arrangement | positioning of CSI-RS shown in FIG. 13 is only an illustration, and is not restricted to this. For example, in FIG. 13, CSI-RSs may be arranged in OFDM symbols other than the ninth and tenth in the subframe. Moreover, CSI-RS may be arrange | positioned in which subcarrier in a specific OFDM symbol.

  Here, the radio communication system according to the present embodiment will be described in detail. FIG. 14 is an explanatory diagram of a system configuration of the wireless communication system according to the present embodiment. Note that the radio communication system illustrated in FIG. 14 is a system including, for example, an LTE system or SUPER 3G. In this wireless communication system, carrier aggregation in which a plurality of basic frequency blocks (component carriers) with the system band of the LTE system as one unit is integrated is applied. Further, this radio communication system may be called IMT-Advanced, or may be called 4G, FRA (Future Radio Access).

  As shown in FIG. 14, the wireless communication system 1 includes a wide area base station apparatus 20 that forms a wide area C1 and a plurality of plural local areas C2 that are arranged in the wide area C1 and that are narrower than the wide area C1. Local area base station apparatus 30. A large number of mobile terminal apparatuses 10 are arranged in the wide area C1 and each local area C2. The mobile terminal apparatus 10 is compatible with the wide area and local area wireless communication systems, and is configured to be able to perform wireless communication with the wide area base station apparatus 20 and the local area base station apparatus 30.

  Communication between the mobile terminal device 10 and the wide area base station device 20 is performed using a wide area carrier (for example, a carrier having a narrow bandwidth in a low frequency band). The mobile terminal apparatus 10 and the local area base station apparatus 30 communicate using a local area carrier (for example, a carrier having a wide bandwidth in a high frequency band). Moreover, the wide area base station apparatus 20 and each local area base station apparatus 30 are wired or wirelessly connected.

  The wide area base station device 20 and each local area base station device 30 are each connected to a higher station device (not shown), and are connected to the core network 40 via the higher station device. The upper station apparatus includes, for example, an access gateway apparatus, a radio network controller (RNC), a mobility management entity (MME), and the like, but is not limited thereto. Further, the local area base station device 30 may be connected to the higher station device via the wide area base station device 20.

  Each mobile terminal apparatus 10 includes an LTE terminal and an LTE-A terminal. In the following, the description will be given as a mobile terminal apparatus unless otherwise specified. For convenience of explanation, it is assumed that the wireless communication with the wide area base station apparatus 20 and the local area base station apparatus 30 is a mobile terminal apparatus, but more generally includes a mobile terminal apparatus and a fixed terminal apparatus. User equipment (UE: User Equipment) may be sufficient. Moreover, the wide area base station apparatus 20 and the local area base station apparatus 30 may be referred to as a wide area transmission point and a local area transmission point, respectively.

  In a radio communication system, OFDMA (Orthogonal Frequency Division Multiple Access) is applied to the downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to the uplink as radio access schemes. OFDMA is a multi-carrier transmission scheme that performs communication by dividing a frequency band into a plurality of narrow frequency bands (subcarriers) and mapping data to each subcarrier. SC-FDMA is a single carrier transmission scheme that reduces interference between terminals by dividing a system band into bands each consisting of one or continuous resource blocks for each terminal, and a plurality of terminals using different bands. .

  Here, a communication channel in the LTE system will be described. The downlink communication channel includes PDSCH (Physical Downlink Shared Channel) shared by each mobile terminal apparatus 10 and downlink L1 / L2 control channels (PDCCH, PCFICH, PHICH). User data and higher control information are transmitted by the PDSCH. PDSCH and PUSCH scheduling information and the like are transmitted by PDCCH (Physical Downlink Control Channel). The number of OFDM symbols used for PDCCH is transmitted by PCFICH (Physical Control Format Indicator Channel). HARQ ACK / NACK for PUSCH is transmitted by PHICH (Physical Hybrid-ARQ Indicator Channel). In the LTE-A system, scheduling information of PDSCH and PUSCH may be transmitted by ePDCCH (Enhanced Physical Downlink Control Channel).

  The uplink communication channel includes a PUSCH (Physical Uplink Shared Channel) as an uplink data channel shared by each mobile terminal apparatus and a PUCCH (Physical Uplink Control Channel) which is an uplink control channel. User data and higher control information are transmitted by this PUSCH. Also, downlink radio quality information (CQI: Channel Quality Indicator), ACK / NACK, and the like are transmitted by PUCCH.

  The overall configuration of the mobile terminal apparatus 10 will be described with reference to FIG. The mobile terminal apparatus 10 includes a format selection unit 101, an uplink signal generation unit 102, an uplink signal multiplexing unit 103, baseband transmission signal processing units 104 and 105, and transmission RF circuits 106 and 107 as transmission processing units. .

  The format selection unit 101 selects a wide area transmission format and a local area transmission format. The uplink signal generation unit 102 generates an uplink data signal and a reference signal. In the case of a wide area transmission format, the uplink signal generation unit 102 generates an uplink data signal and a reference signal for the wide area base station apparatus 20. Further, in the case of the transmission format for the local area, the uplink signal generation unit 102 generates an uplink data signal and a reference signal for the local area base station apparatus 30.

  Uplink signal multiplexing section 103 multiplexes uplink transmission data and a reference signal. The uplink signal for the wide area base station apparatus 20 is input to the baseband transmission signal processing unit 104 and subjected to digital signal processing. For example, in the case of an OFDM uplink signal, a frequency domain signal is converted into a time-series signal by an inverse fast Fourier transform (IFFT), and a cyclic prefix is inserted. The upstream signal passes through the transmission RF circuit 106 and is transmitted from the wide-area transmission / reception antenna 110 via the duplexer 108 provided between the transmission system and the reception system. In the transmission / reception system for the wide area, simultaneous transmission / reception is possible by the duplexer 108.

  The uplink signal for the local area base station apparatus 30 is input to the baseband transmission signal processing unit 105 and subjected to digital signal processing. For example, in the case of an OFDM uplink signal, a frequency domain signal is converted into a time-series signal by an inverse fast Fourier transform (IFFT), and a cyclic prefix is inserted. Then, the upstream signal passes through the transmission RF circuit 107 and is transmitted from the wide-area transmission / reception antenna 111 via the changeover switch 109 provided between the transmission system and the reception system. In the local area transmission / reception system, transmission / reception is switched by the selector switch 109.

  In the present embodiment, the duplexer 108 is provided in the wide area transmission / reception system and the changeover switch 109 is provided in the local area transmission / reception system. However, the present invention is not limited to this configuration. The changeover switch 109 may be provided in the wide area transmission / reception system, or the duplexer 108 may be provided in the local area transmission / reception system. Further, the wide area and local area uplink signals may be transmitted simultaneously from the transmitting and receiving antennas 110 and 111, or may be transmitted separately by switching the transmitting and receiving antennas 110 and 111.

  In addition, the mobile terminal apparatus 10 includes reception RF circuits 112 and 113, baseband reception signal processing sections 114 and 115, a local area control information reception section 116, a discovery signal reception section 117, and a discovery signal measurement section as reception processing sections. 118, and downlink signal demodulation / decoding sections 119 and 120.

  The downlink signal from the wide area base station apparatus 20 is received by the wide area transmission / reception antenna 110. This downstream signal is input to the baseband reception signal processing unit 114 via the duplexer 108 and the reception RF circuit 112, and is subjected to digital signal processing. For example, in the case of an OFDM downlink signal, a cyclic prefix is removed, and a time-series signal is converted to a frequency domain signal by Fast Fourier Transform (FFT).

  The local area control information receiving unit 116 receives local area control information from the wide area downlink signal. Here, discovery signal (DS) reception control information, DACH transmission control information, and ePDCCH reception control information are received as local area control information. The local area control information receiving unit 116 outputs control information for receiving a discovery signal (DS) to the discovery signal receiving unit 117, and outputs control information for DACH transmission to the discovery signal measuring unit 118, and controls for receiving ePDCCH. Information is output to downlink signal demodulation / decoding section 120. The local area control information is received from the wide area base station apparatus 20 by higher layer signaling such as RRC signaling or broadcast information, for example.

  The wide area downlink data signal is input to the downlink signal demodulation / decoding section 119, and is decoded (descrambled) and demodulated by the downlink signal demodulation / decoding section 119. The downlink signal from the local area base station apparatus 30 is received by the local area transmission / reception antenna 111. The downstream signal is input to the baseband reception signal processing unit 115 via the changeover switch 109 and the reception RF circuit 113, and is subjected to digital signal processing. For example, in the case of an OFDM downlink signal, a cyclic prefix is removed, and a time-series signal is converted to a frequency domain signal by Fast Fourier Transform (FFT).

  The discovery signal receiving unit 117 receives the discovery signal from the local area base station apparatus 30 based on the control information for receiving the discovery signal (DS) input from the local area control information receiving unit 116. The control information for receiving the discovery signal includes radio resource information and signal sequence information for receiving the discovery signal from the local area base station apparatus 30. The radio resource information includes, for example, a discovery signal transmission time interval, a frequency position, a code, and the like.

  The discovery signal measuring unit 118 measures the reception power of the discovery signal received by the discovery signal receiving unit 117. As the reception power of the discovery signal, for example, SINR (Signal-to-Interference and Noise power Ratio) may be measured.

  Further, the discovery signal measurement unit 118 may calculate the path loss of the discovery signal based on the reception power of the discovery signal. For example, the discovery signal measurement unit 118 calculates the path loss of the discovery signal based on the difference between the transmission power value of the discovery signal and the measured received power value. In this case, the transmission power of the discovery signal may be received from the wide area base station apparatus 20 as local area control information, or may be received from the local area base station apparatus 30. The calculated path loss is output to uplink transmission power control section 122.

  The reception power of the discovery signal measured by the discovery signal measurement unit 118 or the calculated path loss is transmitted to the local area base station apparatus 30 using the DACH. Transmission using the DACH is performed with the initial transmission power determined by the uplink transmission power control unit 122 described later.

  Transmission using the DACH is performed based on the control information for DACH transmission input from the local area control information receiving unit 116. The control information for DACH transmission includes radio resource information for transmitting to the local area base station apparatus 30 via the DACH, DM-RS sequence information, and the like. The radio resource information includes, for example, a DACH transmission time interval, a frequency position, a code, and the like. The DACH transmission time interval may be set shorter than the discovery signal transmission time interval or the same so that the DACH is transmitted more frequently than the discovery signal. In the DACH, the user ID may be transmitted together with the measurement result of the discovery signal.

  The reception power or path loss of the discovery signal may be transmitted to the local area base station device 30 using an uplink channel other than the DACH (for example, PUCCH or PUSCH) or higher layer signaling. Further, both the reception power of the discovery signal and the path loss may be transmitted to the local area base station apparatus 30. Further, the reception power or path loss of the discovery signal may be transmitted to the wide area base station apparatus 20 using higher layer signaling. Further, both the reception power and the path loss of the discovery signal may be transmitted to the wide area base station apparatus 20 or the local area base station apparatus 30.

  The channel estimation unit 121 performs channel estimation based on the received power of the measurement reference signal (CSI-RS) from the local area base station device 30. For example, SINR (Signal-to-Interference and Noise power Ratio) is used as the received power of CSI-RS.

  In addition, the channel estimation unit 121 generates channel state information (CSI) indicating the estimated channel state. This CSI includes CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), and the like. CSI is transmitted to the local area base station apparatus 30 using PUCCH or PUSCH. The CSI may be transmitted to the wide area base station apparatus 20. Moreover, CQI is calculated based on SINR of CSI-RS. This CQI may be corrected based on a transmission power difference between CSI-RS and ePDCCH or PDSCH notified in advance from the wide area base station apparatus 20 or the local area base station apparatus 30. Alternatively, the CQI may have an extended measurement range (extended feedback bit number) so that the SINR of CSI-RS up to −20 dB can be measured, for example.

  The downlink data signal for the local area is input to the downlink signal demodulation / decoding unit 120, and is decoded (descrambled) and demodulated by the downlink signal demodulation / decoding unit 120. Further, the downlink signal demodulation / decoding section 120 decodes (descrambles) the local area extended downlink control signal (ePDCCH) based on the ePDCCH reception control information input from the local area control information receiving section 116. Demodulate. The control information for ePDCCH reception includes radio resource information, DM-RS sequence information, and the like for receiving ePDCCH from the local area base station apparatus 30. The radio resource information includes, for example, an ePDCCH transmission interval, a frequency position, a code (code), and the like.

  Further, the wide area and local area downlink signals may be received simultaneously from the transmitting and receiving antennas 110 and 111, or may be received separately by switching the transmitting and receiving antennas 110 and 111.

  The uplink transmission power control unit 122 controls the transmission power of the uplink signal for the local area base station device 30. Specifically, the uplink transmission power control unit 122 determines the initial transmission power of the DACH based on the path loss of the discovery signal. For example, the uplink transmission power control unit 122 determines the initial transmission power of the DACH by giving a predetermined offset to the path loss below the maximum transmission power of the mobile terminal apparatus 10. Further, uplink transmission power control section 122 may determine the transmission power of the uplink data signal (PUSCH) based on the channel estimation result of channel estimation section 121. Note that the uplink transmission power control unit 122 may control the transmission power of the uplink data signal (PUSCH) based on instruction information (for example, a TPC command) from the local area base station 30.

  The overall configuration of the wide area base station apparatus 20 will be described with reference to FIG. The wide area base station apparatus 20 includes a local area control information generation unit 201, a downlink signal generation unit 202, a downlink signal multiplexing unit 203, a baseband transmission signal processing unit 204, and a transmission RF circuit 205 as a processing unit of the transmission system. Yes.

  The local area control information generation unit 201 includes, as local area control information, discovery signal (DS) transmission control information, discovery signal (DS) reception control information, DACH transmission control information, and ePDCCH reception control information. Is generated. The local area control information generation unit 201 outputs discovery signal transmission control information to the transmission path interface 211, and downlink signal multiplexing control information for discovery signal reception, control information for DACH transmission, and control information for ePDCCH reception. The data is output to the unit 203. The control information for transmitting the discovery signal is transmitted to the local area base station apparatus 30 via the transmission path interface 211. On the other hand, control information for discovery signal reception, control information for DACH transmission, and control information for ePDCCH reception are transmitted to mobile terminal apparatus 10 via downlink signal multiplexing section 203.

  The downlink signal generation unit 202 generates a downlink data signal (PDSCH) and a reference signal. The downlink signal multiplexing unit 203 multiplexes the local area control information, the downlink data signal (PDSCH), and the reference signal. The downlink signal for the mobile terminal apparatus 10 is input to the baseband transmission signal processing unit 204 and subjected to digital signal processing. For example, in the case of an OFDM downlink signal, a frequency domain signal is converted to a time-series signal by an inverse fast Fourier transform (IFFT), and a cyclic prefix is inserted. The downlink signal is transmitted from the transmission / reception antenna 207 through the transmission RF circuit 205 and the duplexer 206 provided between the transmission system and the reception system.

  In addition, the wide area base station apparatus 20 has a reception RF circuit 208, a baseband reception signal processing unit 209, an uplink signal demodulation / decoding unit 210, a measurement information reception unit 212, and a local area downlink transmission power determination as a reception system processing unit. Part 213 is provided.

  The uplink signal from the mobile terminal apparatus 10 is received by the transmission / reception antenna 207 and input to the baseband reception signal processing unit 209 via the duplexer 206 and the reception RF circuit 208. The baseband received signal processing unit 209 performs digital signal processing on the upstream signal. For example, in the case of an OFDM uplink signal, a cyclic prefix is removed, and a time-series signal is converted to a frequency-domain signal by Fast Fourier Transform (FFT). The uplink data signal is input to the uplink signal demodulation / decoding unit 210, and is decoded (descrambled) and demodulated by the uplink signal demodulation / decoding unit 210.

  The measurement information receiving unit 212 receives measurement information transmitted from the mobile terminal apparatus 10 by higher layer signaling. Specifically, the measurement information receiving unit 212 receives the reception power or path loss of the discovery signal in the mobile terminal apparatus 10. The measurement information reception unit 212 may calculate the path loss based on the difference between the transmission power value of the discovery signal from the local area base station device 30 and the reception power value. The measurement information reception unit 212 outputs the path loss of the discovery signal to the local area downlink transmission power determination unit 213.

  In addition, the measurement information receiving unit 212 acquires channel state information (CSI) estimated based on the received power of the measurement reference signal (CSI-RS) in the mobile terminal apparatus 10. The measurement information reception unit 212 outputs the acquired CSI to the local area downlink transmission power determination unit 213.

  The local area downlink transmission power determination unit 213 determines the transmission power of the downlink signal from the local area base station apparatus 30 to the mobile terminal apparatus 10. Specifically, the local area downlink transmission power determination unit 213 determines the initial transmission power of the downlink signal based on the path loss of the discovery signal. Further, the local area downlink transmission power determination unit 213 determines the transmission power of the downlink signal based on the CSI and the path loss of the discovery signal. The local area downlink transmission power determination unit 213 transmits transmission power information indicating the determined transmission power to the local area base station apparatus 30 via the transmission path interface 211.

  Note that downlink signals for which transmission power is determined include a downlink data signal (PDSCH) from the local area base station apparatus 30 and an extended downlink control signal (ePDCCH). Moreover, the local area downlink transmission power determination part 213 may be abbreviate | omitted when the transmission power of a downlink signal is determined in the local area base station apparatus 30.

  The overall configuration of the local area base station device 30 will be described with reference to FIG. It is assumed that the local area base station device 30 is arranged in the immediate vicinity of the mobile terminal device 10. The local area base station device 30 includes a local area control information reception unit 301, a discovery signal generation unit 302, a downlink signal generation unit 303, a reference signal generation unit 304, a downlink signal multiplexing unit 305, and baseband transmission as a processing unit of the transmission system. A signal processing unit 306 and a transmission RF circuit 307 are provided.

  The local area control information receiving unit 301 receives local area control information from the wide area base station apparatus 20 via the transmission path interface 314. Here, control information for discovery signal transmission is received as local area control information. The local area control information reception unit 301 outputs control information for discovery signal transmission to the discovery signal generation unit 302.

  The discovery signal generation unit 302 is used for detection of the local area base station device 30 in the mobile terminal device 10 based on the control information for discovery signal (DS) transmission input from the local area control information reception unit 301. (Detection signal) is generated. The control information for transmitting the discovery signal includes radio resource information, signal sequence information, and the like for transmitting the discovery signal from the local area base station apparatus 30. The radio resource information includes, for example, a discovery signal transmission interval, a frequency position, a code, and the like. Note that the transmission power of the discovery signal is set to a constant value so as to have a wider coverage than a downstream signal described later.

  The downlink signal generation unit 303 generates a downlink signal for the mobile terminal apparatus 10. Specifically, the downlink signal generation section 303 generates a downlink data signal (PDSCH) and an extended downlink control signal (ePDCCH) that is frequency-division multiplexed on the downlink data signal (PDSCH). The transmission power of the downlink data signal and the downlink control signal is adaptively controlled by a downlink transmission power control unit 315 described later.

  The reference signal generation unit 304 generates a reference signal such as a measurement reference signal (CSI-RS) or a demodulation reference signal (DM-RS), and outputs the reference signal to the downlink signal multiplexing unit 305. The transmission power of the reference signal for measurement (CSI-RS) is set to a constant value because it is used for channel state estimation in the mobile terminal apparatus 10.

  Further, the measurement reference signal (CSI-RS) is multiplexed with the downlink signal by the downlink signal multiplexing unit 305, and is arranged in a predetermined radio resource area by using the predetermined arrangement pattern by the baseband transmission signal processing unit 306. For example, as shown in FIG. 12A, CSI-RSs may be arranged at shorter subcarrier intervals than CSI-RSs transmitted in a wide area in a specific OFDM symbol in a subframe. Moreover, CSI-RS may be arrange | positioned at all the subcarriers which comprise a resource block width in the specific OFDM symbol in a sub-frame, as shown to FIG. 12B. In addition, as shown in FIG. 12C, CSI-RS is arranged on some subcarriers constituting the resource block width in specific OFDM in a subframe, and muting resources are arranged on the remaining subcarriers. Good. Further, when the wide area carrier and the local area carrier belong to different component carriers due to carrier aggregation, the CSI-RS of the local area is arranged as shown in FIG. The subframe may be arranged in a different subframe.

  The downlink signal multiplexer 305 multiplexes the downlink signal generated by the downlink signal generator 303 and the reference signal generated by the reference signal generator 304. The downlink signal multiplexed with the reference signal is input to the baseband transmission signal processing unit 306 and subjected to digital signal processing. For example, in the case of an OFDM downlink signal, a frequency domain signal is converted to a time-series signal by an inverse fast Fourier transform (IFFT), and a cyclic prefix is inserted. Then, the downstream signal passes through the transmission RF circuit 307 and is transmitted from the transmission / reception antenna 309 via the changeover switch 308 provided between the transmission system and the reception system. Note that a duplexer may be provided instead of the changeover switch 308.

  The local area base station apparatus 30 includes a reception RF circuit 310, a baseband reception signal processing unit 311, an uplink signal demodulation / decoding unit 312, and a measurement information reception unit 313 as a reception system processing unit.

  The uplink signal from the mobile terminal apparatus 10 is received by the local area transmission / reception antenna 309 and input to the baseband reception signal processing unit 311 via the changeover switch 308 and the reception RF circuit 310. The baseband received signal processing unit 311 performs digital signal processing on the upstream signal. For example, in the case of an OFDM uplink signal, a cyclic prefix is removed, and a time-series signal is converted to a frequency-domain signal by Fast Fourier Transform (FFT). The uplink data signal is input to the uplink signal demodulation / decoding unit 312, and is decoded (descrambled) and demodulated by the uplink signal demodulation / decoding unit 312.

  The measurement information receiving unit 313 receives the measurement information of the discovery signal. Specifically, the measurement information receiving unit 313 receives the reception power or path loss of the discovery signal transmitted from the mobile terminal apparatus 10. The measurement information receiving unit 313 may calculate the path loss based on the difference between the transmission power value and the reception power value of the discovery signal. The measurement information receiving unit 313 outputs the path loss of the discovery signal to the downlink transmission power control unit 315.

  In addition, the measurement information reception unit 313 receives channel state information (CSI) estimated based on the received power of the measurement reference signal (CSI-RS) in the mobile terminal apparatus 10. The measurement information receiving unit 313 outputs the acquired CSI to the downlink transmission power control unit 315.

  The downlink transmission power control unit 315 controls transmission power of downlink signals for the mobile terminal apparatus 10. Specifically, the initial transmission power of the downlink signal is determined based on the path loss of the discovery signal input from the measurement information receiving unit 313. Further, the downlink transmission power control section 315 determines the transmission power of the downlink signal based on the CSI and the discovery signal path loss. The downlink transmission power control unit 315 controls the downlink signal generation unit 303 so that the downlink signal is transmitted with the determined transmission power. Note that downlink data for which transmission power is determined include a downlink data signal (PDSCH), an extended downlink control signal (ePDCCH), and the like. Note that the downlink transmission power control unit 315 may control the transmission power of the downlink signal based on instruction information (for example, a TPC command) from the mobile terminal apparatus 10 by closed loop control.

  Further, the downlink transmission power control section 315 determines the initial transmission power and transmission power of the downlink signal for the mobile terminal apparatus 10 based on the transmission power information received from the wide area base station apparatus 20 via the transmission path interface 314. May be.

  As described above, according to the radio communication system 1 according to the present embodiment, the transmission power of the downlink signal is adaptively controlled even in the downlink of the local area based on the path loss of the discovery signal. As described above, by adaptively controlling the transmission power of the local area carrier not only in the uplink in the local area but also in the downlink, it is possible to make the coverage of the uplink and downlink in the local area close to symmetry. Therefore, highly efficient local area wireless access specialized for the local area can be provided.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, without departing from the scope of the present invention, the number of carriers, the carrier bandwidth, the signaling method, the type of additional carrier type, the number of processing units, and the processing procedure in the above description can be changed as appropriate. It is. FIG. 4 is merely an example, and a carrier in a high frequency band may be used even in a wide area. Other modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Wireless communication system 10 ... Mobile terminal apparatus 20 ... Wide area base station apparatus 30 ... Local area base station apparatus 40 ... Core network 101 ... Format selection part 102 ... Upstream signal generation part 103 ... Upstream signal multiplexing part 104 ... Baseband transmission Signal processing unit 105 ... baseband transmission signal processing unit 106 ... transmission RF circuit 107 ... transmission RF circuit 108 ... duplexer 109 ... changeover switch 110 ... transmission / reception antenna 111 ... transmission / reception antenna 112 ... reception RF circuit 113 ... reception RF circuit 114 ... baseband Received signal processing unit 115 ... baseband received signal processing unit 116 ... local area control information receiving unit 117 ... discovery signal receiving unit 118 ... discovery signal measuring unit 119 ... downlink signal demodulation / decoding unit 120 ... downlink signal demodulation / decoding unit 121 ... Channel estimation unit 22 ... Uplink transmission power control unit 201 ... Local area control information generation unit 202 ... Downlink signal generation unit 203 ... Downlink signal multiplexing unit 204 ... Baseband transmission signal processing unit 205 ... Transmission RF circuit 206 ... Duplexer 207 ... Transmission / reception antenna 208 ... Reception RF circuit 209 ... baseband received signal processing section 210 ... uplink signal demodulation / decoding section 211 ... transmission path interface 212 ... measurement information receiving section 213 ... local area downlink transmission power determining section 301 ... local area control information receiving section 302 ... discovery signal Generation unit 303 ... Downstream signal generation unit 304 ... Reference signal generation unit 305 ... Downstream signal multiplexing unit 306 ... Baseband transmission signal processing unit 307 ... Transmission RF circuit 308 ... Changeover switch 309 ... Transmission / reception antenna 310 ... Reception RF circuit 311 ... Baseband Received signal processor 312 Uplink signal demodulation and decoding unit 313 ... measurement information receiver 314 ... transmission path interface 315 ... downlink transmission power controller

Claims (10)

A measurement unit that measures reception power of a discovery signal transmitted at a predetermined cycle from a radio base station that can switch between a downlink transmission and a non-transmission state;
A control unit that controls transmission power of an uplink signal to the radio base station based on a path loss calculated based on a measured reception power value of the discovery signal;
A mobile terminal device comprising: A receiving unit that receives the transmission power value of the discovery signal by upper layer signaling;
The movement according to claim 1, wherein the measurement unit calculates the path loss based on a difference between a received transmission power value of the discovery signal and a measured received power value of the discovery signal. Terminal device.   The discovery signal is transmitted in a longer period than a detection signal used for detection of another radio base station that cannot switch between a downlink transmission state and a non-transmission state. The mobile terminal device described.   The mobile terminal apparatus according to claim 1, wherein the transmission unit transmits the measured received power value of the discovery signal by higher layer signaling.   The mobile terminal apparatus according to claim 1, wherein the uplink signal is an access channel for the radio base station. A radio base station that can switch between a downlink transmission state and a non-transmission state,
A transmission unit for transmitting a discovery signal at a predetermined period;
A receiving unit for receiving an uplink signal from a mobile terminal device,
The transmission power of the uplink signal is controlled based on a path loss calculated based on a reception power value of the discovery signal.   The radio base station according to claim 6, wherein the path loss is calculated based on a difference between a transmission power value of the discovery signal and a reception power value of the discovery signal.   The transmission unit transmits the discovery signal at a cycle longer than a detection signal used for detection of another radio base station that cannot switch between a downlink transmission and a non-transmission state. The radio base station according to claim 7.   The radio base station according to claim 6, wherein the uplink signal is an access channel for the radio base station. A wireless communication method between a radio base station and a mobile terminal apparatus capable of switching between a downlink transmission state and a non-transmission state, in the mobile terminal apparatus,
Measuring received power of a discovery signal transmitted from the radio base station at a predetermined period;
Controlling the transmission power of the uplink signal to the radio base station based on the path loss calculated based on the measured received power value of the discovery signal;
A wireless communication method comprising:

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