JP6006741B2 - Communications system - Google Patents

Description

  The present invention relates to a communication system having a plurality of base stations.

  To cope with the rapid increase in traffic in recent mobile communication systems, small cell base stations (also called “small cell base stations” or “small cell base stations”) whose cells (wireless communication areas) are narrower than conventional macro cell base stations ) Is growing. Since the small cell base station is deployed in multiple stations for traffic countermeasures, it is assumed that the small cell base station is installed in the cell of the conventional macro cell base station. For this reason, there is a problem that inter-cell interference occurs between the macro cell base station and the small cell base station. As a technique for reducing this inter-cell interference, an inter-cell interference control technique in the time domain (subframe unit) on the assumption that the macro cell base station and the small cell base station are time-synchronized with each other is known. (For example, refer to Patent Document 1). This inter-cell interference control technology is a technology based on LTE (Long Term Evolution) -Advanced standards, and is also called eICIC (enhanced Inter-Cell Interference Coordination). In this inter-cell interference control technique, for example, a sub-frame group called ABS (Almost Blank Subframe) in which the macro cell base station does not perform downlink transmission of data area signals (data signals, upper layer control signals) to the mobile station apparatus is set. Then, an ABS pattern table indicating the subframe group is notified to the subordinate small cell base stations. Based on the ABS pattern, the small cell base station performs scheduling for allocating resources to subordinate mobile stations (user terminal devices), and stops downlink transmission of data signals and higher layer control signals to the mobile stations based on the scheduling. To do. Thus, the inter-cell interference between the macro cell base station and the small cell base station can be reduced mutually.

  However, in the inter-cell interference control technique using the conventional ABS, when the subframe that is the target of transmission suspension between the plurality of base stations is a normal subframe, the channel estimation arranged in the subframe is estimated. However, there is a problem that the reference signal used for the transmission cannot be stopped and interference due to the reference signal remains. If interference due to the reference signal remains in this way, inter-cell interference between a plurality of base stations cannot be reliably reduced, and communication quality and transmission speed cannot be improved.

  The present invention has been made in view of the above problems, and an object of the present invention is communication that can reduce interference caused by reference signals between a plurality of base stations that overlap at least part of a wireless communication area. Is to provide a system.

The communication system according to the present invention includes a first base station and a second base station in which at least a part of a wireless communication area overlaps each other, and the first base station and the second base station are respectively time-synchronized with each other. In this state, the communication system performs downlink transmission to the mobile station apparatus using a radio communication frame in which 10 subframes are continuously arranged on the time axis . Sixth array (# 1), third (# 2), fourth (# 3), seventh (# 6), eighth (# 7) and ninth (# 8) Only for the position , a subframe in which transmission of the reference signal can be stopped can be set. 1 unit of frame or multiple units The first base station sets subframes capable of stopping the transmission of the reference signal for all of the predetermined six arrangement positions in the radio communication frame, and the setting is performed. The second base station performs signal transmission stop processing on the subframe, and the second base station performs signal transmission stop processing at the first base station among the predetermined six arrangement positions in the wireless communication frame. For the array positions corresponding to all subframes other than the executed subframe, a subframe capable of stopping the transmission of the reference signal is set, and signal transmission stop processing is executed for the set subframe.
In the communication system, even if a shift amount of the transmission timing of the wireless communication frame is set according to the information of the transmission stop target subframe set in each of the first base station and the second base station. Good.
The communication system further includes a server device capable of communicating with each of the first base station and the second base station, wherein the server device is an interference signal in each of the first base station and the second base station. Receiving the level information, determining the subframe to be stopped based on the information on the interference signal level, and determining the information on the subframe to be stopped for transmission from the first base station and the second base station, respectively. May be sent to .
Also, in the communication system, the first base station, the interference source is a macrocell base station, the second base station located in the cell of the macro cell base station, itself a cell said macrocell It may be an interfered small cell base station smaller than the cell of the base station.
In the communication system, the first base station is an interfered macro cell base station, the second base station is located in a cell of the macro cell base station, and its own cell is the macro cell base station. It may be a small cell base station of an interference source smaller than the cell.
In the communication system, each of the first base station and the second base station is located in a cell of the macro cell base station, and its own cell is smaller than the cell of the macro cell base station and is adjacent to each other. The small cell base station of the interfered source and the interference source may be used.
Further, in the communication system, the sub-frames that can stop transmitting the reference signal, but it may also be a LTE (Long Term Evolution) -Advanced MBSFN ( Multimedia Broadcast Single Frequency Network) standard to conform sub-frame .

  Advantageous Effects of Invention According to the present invention, there is an effect that interference due to reference signals between a plurality of base stations having at least a part of a wireless communication area can be reduced.

Explanatory drawing which shows an example of schematic structure of the mobile communication system provided with the macrocell base station and small cell base station which concern on embodiment of this invention. Explanatory drawing which shows the mode of a three-dimensional arrangement | positioning of a macrocell base station and a small cell base station. Explanatory drawing which shows an example of the format of the radio communication frame of a LTE downlink. Explanatory drawing which shows an example of the format of the sub-frame which comprises a radio | wireless communication frame. Explanatory drawing which shows an example of the mode of the transmission stop in the sub-frame by ABS employ | adopted with the conventional intercell interference control technique (eICIC). (A) And (b) is explanatory drawing which shows an example of the mode of the signal in the sub-frame in two types of ABS. Explanatory drawing which shows an example of the shift of the radio | wireless communication frame in the small cell base station in this embodiment. Explanatory drawing which shows the other example of the shift of the radio | wireless communication frame in the small cell base station in this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory diagram showing a schematic configuration of a mobile communication system in which a macro cell base station and a small cell base station according to an embodiment of the present invention are arranged. FIG. 2 is an explanatory diagram illustrating a three-dimensional arrangement of macro cell base stations and small cell base stations.

  In FIG. 1, the mobile communication system of the present embodiment is a communication system compliant with LTE (Long Term Evolution) / LTE-Advanced standard specifications, and a macro cell base station 10 as a first base station and its macro cell base A small cell base station 20 as a second base station located in a cell (hereinafter referred to as a “macro cell”) 10A, which is a radio communication area of the station 10, and the base stations 10 and 20 via a communication line And a server device 40 capable of communication. A cell (hereinafter referred to as “small cell” as appropriate) 20 </ b> A that is a radio communication area of the small cell base station 20 is included inside the cell 10 </ b> A of the macrocell base station 10.

  In recent years, in large urban areas, communication traffic in indoor offices of medium- and high-rise buildings has increased rapidly, and means for efficiently carrying communication traffic in the height direction is required. Therefore, as shown in FIG. 2, a three-dimensional space cell configuration in which the small cell 20A is installed in the height direction in the building is effective.

  In FIG. 1, a user terminal device (UE) 30 that is a mobile station is a user terminal device (MUE) that is located in a cell 10 </ b> A of the macrocell base station 10 and is connected to the macrocell base station 10. Wireless communication for telephone or data communication is possible through the network. Since this user terminal device 30 is located in a position near the boundary between the macro cell 10A and the small cell 20A, the user terminal device 30 is likely to receive interference from the small cell 20A.

  A user terminal device (UE) 31 that is a mobile station is a user terminal device (HUE) that is located in the outer edge of the cell 20A of the small cell base station 20 and connected to the small cell base station 20, Wireless communication for telephone or data communication via the cell base station 20 is possible. Since this user terminal device 31 is located near the boundary between the small cell 20A and the macro cell 10A, the user terminal device 31 is susceptible to interference from the macro cell 10A.

  When the user terminal devices 30 and 31 are located in the macro cell 10A or the small cell 20A, the user terminal devices 30 and 31 use a predetermined communication method and wireless communication resources between the macro cell base station and the small cell base station corresponding to the cell in which the user terminal device 30 or 31 is located. Wireless communication. The user terminal devices 30 and 31 are configured by using hardware such as a computer device having a CPU, a memory, etc., an external communication interface unit for a core network, a wireless communication unit, and the like, and a base station by executing a predetermined program Wireless communication with 10, 20, etc. can be performed.

  The macrocell base station 10 is a wide-area base station that covers a macrocell that is a wide area having a radius of about several hundred m to several km that is installed outdoors in a mobile communication network. Sometimes referred to as “Macro e-Node B”, “MeNB” or the like. The macrocell base station 10 is connected to other base stations via a wired communication line, for example, and can communicate with a predetermined communication interface. The macrocell base station 10 is connected to a core network of a mobile communication network via a communication line 50 such as a line termination device and a dedicated line, and is connected to a predetermined node with various nodes such as the server device 40 on the core network. Communication is possible through the communication interface.

  The small cell base station 20, unlike a macro cell base station in a wide area, has a wireless communication range of several meters to several hundred meters, and has a small capacity that can be installed indoors such as ordinary homes, stores, offices, etc. It is a base station. Since the small cell base station 20 is provided so as to cover an area smaller than the area covered by the wide-area macro cell base station in the mobile communication network, it is called a “femto base station” or “Home e-Node B”. Or “Home eNB”. The small cell base station 20 is also connected to the core network of the mobile communication network via a communication line 51 such as a line terminating device and a broadband public communication line such as an ADSL (Asymmetric Digital Subscriber Line) line or an optical line. It is possible to communicate with various nodes such as the above server device 40 through a predetermined communication interface.

  In addition, the base station device of each of the macro cell base station 10 and the small cell base station 20 is configured by using hardware such as a computer device having a CPU, a memory, etc., an external communication interface unit for a core network, a wireless communication unit, and the like. By executing a predetermined program, various processes for suppressing interference, which will be described later, are performed, or wireless communication is performed between the user terminal devices 30 and 31 using a predetermined communication method and wireless communication resources. Can be.

  The base station apparatus includes, for example, an antenna, a radio signal path switching unit, a duplexer (DUP), a downlink radio reception unit and an OFDM (Orthogonal Frequency Division Multiplexing) demodulation unit, an interference measurement unit, an uplink radio reception unit, an SC- An FDMA (Single-Carrier Frequency-Division Multiple Access) demodulator is provided. Furthermore, the base station apparatus includes an OFDM modulation unit, a downlink radio transmission unit, a control unit, a synchronization acquisition / cell ID extraction unit, and the like.

The downlink radio receiving unit receives a radio signal including broadcast information modulated by the OFDM scheme for downlink defined in LTE from the surrounding base stations 10 via the antenna and the radio signal path switching unit. The OFDM demodulator demodulates a radio signal modulated by the OFDM method to obtain a received signal. The interference measurement unit functions as a measurement unit that measures the interference signal level. The interference measurement unit measures the signal level of the interference wave transmitted from the neighboring base station (hereinafter referred to as “interference signal level”) from the reception signal demodulated by the OFDM demodulation unit, and the measurement result of the interference signal level. Is passed to the control unit.

The synchronization acquisition / cell ID extraction unit specifies a cell ID (PCI: Physical Cell ID) as base station identification information for identifying a neighboring base station based on the received signal received by the downlink radio receiving unit, and A synchronization acquisition process is performed as a time synchronization process for synchronizing the time with the station. As a method of time synchronization processing, “GPS method”, “network method”, “air listening method”, and the like can be used. The GPS method is a method of synchronizing based on time information of a GPS signal received by a GPS receiver. The network method is a method of synchronizing based on time information received via a mobile communication network. Further, air listening system detects the downlink signal of the peripheral base stations, a method to synchronize the signal as a reference.

  The SC-FDMA demodulator performs SC-FDMA demodulation processing on the received signal received by the uplink radio receiver, and passes the demodulated data to the controller. The OFDM modulation unit modulates the data of the downlink signal transmitted from the control unit to the user terminal device residing in the cell of the local station by the OFDM method so as to be transmitted with a predetermined power. In addition, when the base station apparatus receives information on a subframe to be transmitted from the server apparatus 40, the OFDM modulation unit is controlled to stop downlink transmission only for a specific subframe in the radio communication frame. The downlink radio transmission unit transmits the transmission signal modulated by the OFDM modulation unit via the duplexer, the radio signal path switching unit, and the antenna.

  The control unit of the base station apparatus is configured by a computer device, for example, and controls and executes various processes by reading and executing a predetermined program. Further, the control unit functions as means for transmitting information on the interference signal level measured by the interference measurement unit to the server device in cooperation with the external communication interface unit. The control unit also functions as means for receiving, from the server device, ABS pattern information, which is information on a subframe to be transmitted, in cooperation with the external communication interface unit. Further, the control unit may be a means for controlling to stop the downlink transmission in a specific transmission stop target subframe based on the transmission stop target subframe information (ABS pattern information) received from the server device 40. Function.

  The synchronization acquisition / cell ID extraction unit specifies a cell ID (PCI: Physical Cell ID) as base station identification information for identifying a neighboring base station based on the received signal received by the downlink radio reception unit, and A synchronization acquisition process is performed as a time synchronization process for synchronizing the time with the base station.

  In FIG. 1, one macro cell base station 10 and one small cell base station 20 are illustrated, but there may be a plurality of macro cell base stations 10 and small cell base stations 20. In addition, FIG. 1 illustrates a case where one user terminal device is located in each of the macro cell 10A and the small cell 20A, but there are a plurality of user terminal devices located in each cell. Also good.

  The server device 40 is configured using hardware such as a computer device having a CPU, a memory, and the like, and an external communication interface unit for a core network. The server device 40 executes various processes for reducing interference described later by executing a predetermined program, or communicates with the macrocell base station 10 and the small cell base station 20 via the communication lines 50 and 51. Can be. Further, the computer device of the server device 40, based on the interference signal level information received from the interfered small cell base station 20, causes interference sources for at least one subframe in the radio communication frame for downlink transmission to the user terminal device. It functions as means for determining whether or not it is necessary to stop downlink transmission from the macro cell base station 10. The computer device of the server device 40 also functions as means for determining at least one transmission stop target subframe in the radio communication frame when it is determined that the downlink transmission needs to be stopped. The computer device of the server device 40 cooperates with the external communication interface unit to receive information on the interference signal level in the interfered small cell base station 20 from the small cell base station 20, and the macro cell base station as an interference source. 10 also functions as means for transmitting the information of the determined subframe to be stopped for transmission.

Next, inter-cell interference control in the mobile communication system having the above configuration will be described.
In recent years, application of an overlay cell configuration in which a small cell 20A is superimposed on a macro cell 10A is effective as a countermeasure against rapidly increasing traffic. However, in the overlay cell configuration, interference occurs between the macro cell 10A and the small cell 20A. Therefore, in order to maximize the application effect, it is necessary to control the interference. An LTE-Advanced standard eICIC (enhanced Inter-Cell Interference Coordination) technique is effective as an interference control method.

FIG. 3 is an explanatory diagram illustrating an example of a format of an LTE downlink radio communication frame.
As shown in FIG. 3, a predetermined length (10 in the illustrated example) of wireless communication frames 100 having a predetermined length (10 msec in the illustrated example), which is one unit of the LTE downlink signal, has a predetermined length (in the illustrated example). Is 1.0 msec). Each subframe 110 is divided into a predetermined number (two in the illustrated example) of a predetermined length (0.5 msec in the illustrated example) of slots. Since a transmission time interval (TTI) that is a minimum time unit of LTE downlink scheduling is one subframe, a resource block (RB) that is a minimum unit of radio resources is transmitted to the scheduled user terminal device for each subframe. Assigned.

  In the wireless communication frame 100 of FIG. 3, the second (# 1), the third (# 2), the fourth (# 3), the seventh (# 6), and the eighth (# 7) from the top. In addition, a subframe capable of stopping the transmission of the cell-specific reference signal (CRS) can be set at the ninth (# 8) arrangement position. A subframe in which the transmission of the reference signal (CRS) can be stopped is an MBSFN (Multimedia Broadcast Single Frequency Network) subframe compliant with the LTE-Advanced standard. Other arrangement positions of the radio communication frame 100, that is, the second (# 0), fifth (# 4), sixth (# 5), and tenth (# 9) arrangement positions from the top are MBSFN. Only normal subframes in which subframes cannot be set and transmission of the reference signal (CRS) cannot be stopped can be set.

  FIG. 4 is an explanatory diagram showing an example of a format of a subframe constituting the wireless communication frame. In FIG. 4, each subframe 110 includes, for example, a total of 144 REs (Resource Elements) of 12 subcarriers (15 kHz) in the frequency direction and 168 FDM symbols in the time axis direction. Here, the “symbol” is a unit of information transmitted by wireless communication. One symbol is generated by one modulation of information to be transmitted, and the information amount (number of bits) of one symbol is determined by the modulation method. Scheduling which frequency / time resource mapping is performed for each user terminal device for each subframe, what modulation format (modulation scheme, coding rate) is used for the data signal to each user terminal device, etc. And the result is notified to the user terminal device.

  As shown in FIG. 4, each subframe 110 includes a control region 110 </ b> A at the head portion to which the RE of the downlink L1 / L2 control channel signal is mapped, and data to which the RE of the data channel signal and the upper control channel signal is mapped. Region 110B.

A PDCCH (Physical Downlink Control Channel) that is an L1 / L2 control channel is set in the control area 110A of the subframe 110. The PDCCH is used for transmission of control information (DCI: Downlink Control Information) such as determination of uplink / downlink scheduling and uplink power control command. DCI includes a downlink scheduling assignment including PDSCH resource indication, transmission format, HARQ information, and control information related to spatial multiplexing. The DCI also includes an uplink scheduling grant including a PUSCH resource indication, a transmission format, and HARQ related information.

  Also, a physical shared channel (PDSCH) is set in the data area 110B of the subframe 110. The PDSCH is a physical channel for transmitting downlink data, and corresponds to MIMO diversity as a MIMO transmission method, up to four layers of MIMO multiplexing in LTE, and up to eight layers of MIMO multiplexing in LTE-Advanced. Also, SIB that is broadcast information other than MIB, paging information that is a call at the time of incoming call, and other upper layer control messages, for example, RRC (Radio Resource Control Protocol) layer control information are also transmitted by PDSCH. A user terminal apparatus decodes PDSCH based on information, such as a radio | wireless resource allocation position acquired from PDCCH, a modulation system, and data size (TB: Transport Block size).

  In LTE, cell-specific reference signals (CRS) are regularly distributed and arranged in the first, fifth, eighth, and twelfth OFDM symbols among the 14 OFDM symbols in the time domain within the subframe 110. The reference signal CRS has two roles: a reference signal for measuring channel quality information (CSI: Channel State Information) and a reference signal for data demodulation in the user terminal device. The reference signal CRS is applied with a frequency shift of a subcarrier position mapped with different scrambling depending on the cell ID. Further, as described above, transmission of the reference signal CRS mapped in the normal subframe cannot be stopped by the ABS, and transmission of the reference signal CRS mapped in the MBSFN subframe is stopped by the ABS. can do.

  FIG. 5 is an explanatory diagram showing an example of a state of transmission stop in a subframe by ABS employed in the conventional inter-cell interference control technology (eICIC). In ABS, signal transmission is stopped in some subframes (# 1 to # 3 and # 6 to # 8 subframes in the illustrated example) of the macro cell, so that the user terminal device connected to the small cell Interference can be reduced. In addition, by stopping signal transmission in some subframes (# 0, # 4, # 5, and # 9 subframes in the illustrated example) of the small cell, interference in user terminal devices connected to the macrocell Can be reduced.

  FIGS. 6A and 6B are explanatory diagrams showing examples of signals in subframes in two types of ABS. In the ABS employed in the conventional inter-cell interference control technology (eICIC), transmission of a normal subframe is stopped and converted to ABS (hereinafter referred to as “Non-MBSFN ABS”), and MBSFN subframes are used. There are two types of transmissions that stop transmission and become ABS (hereinafter referred to as “MBSFN ABS”).

  In the Non-MBSFN ABS shown in FIG. 6A, CRS used for reception level measurement and channel estimation is transmitted in four OFDM symbols in one normal subframe. On the other hand, in the MBSFN ABS shown in FIG. 6 (b), CRS is transmitted only with the OFDM symbol in the head control area, and not all signals including CRS are transmitted in the data area, which greatly reduces interference between cells. Can be reduced.

  However, in the LTE / LTE-Advanced specification, MBSFN ABS can be applied only with specific 6 subframes in 10 subframes within one frame. Specifically, as described above, the second (# 1), the third (# 2), the fourth (# 3), the second (# 3) from the top in the ten subframe arrangement positions shown in FIG. An MBSFN subframe that can stop transmission of a cell-specific reference signal (CRS) can be set only at the sixth (# 6), eighth (# 7), and ninth (# 8) arrangement positions. is there. Among the ten subframe arrangement positions, the second (# 0), fifth (# 4), sixth (# 5) and tenth (# 9) arrangement positions from the head are MBSFN sub-positions. The frame cannot be set.

  Therefore, when performing inter-cell interference control between a macro cell and a small cell, MBSFN ABS that reduces interference from a macro cell to a small cell or interference from a small cell to a macro cell in the above six MBSFN subframes is possible. However, in the other four normal subframes other than that, only interference reduction by Non-MBSFN ABS, which has little effect on interference in either direction, can be performed. That is, in the conventional inter-cell interference control technology (eICIC), MBSFN ABS cannot be set between the macro cell and the small cell.

  Therefore, in this embodiment, according to the resource allocation (ABS setting) of the macro cell and the small cell, the transmission timing in the small cell is shifted in units of subframes with respect to the transmission timing of the radio communication frame in the macro cell. Communication quality and transmission speed are improved by reducing interference in any direction by MBSFN ABS in all subframes.

  FIG. 7 is an explanatory diagram illustrating an example of a shift of a radio communication frame at the small cell base station in the present embodiment. In the example of FIG. 7, the ABS allocation ratio, which is the ratio of the number of subframes to which ABS is allocated in the macro cell 10A and the number of subframes to which ABS is allocated in the small cell 20A, is 4: 6, 5: 5, or 6: 4. This is a suitable example.

In the example of FIG. 7, the transmission timing of the radio communication frame 100 in the small cell base station 20 is shifted by the time corresponding to two units of the subframe on the time axis with respect to the transmission timing of the radio communication frame in the macrocell base station 10. ing.
The macro cell base station 10 can stop the transmission of the reference signal (CRS) for all six arrangement positions (# 1 to # 3, # 6 to # 8) that can be set in the MBSFN subframe in the radio communication frame 100. A subframe is set. Then, signal transmission stop processing is executed for the set MBSFN subframe.
On the other hand, the small cell base station 20 corresponds to MBSFN subframes other than the subframe in which signal transmission stop processing is executed in the macrocell base station 10 among the six arrangement positions where the MBSFN subframe can be set in the radio communication frame 100. MBSFN subframes that can stop transmission of reference signals (CRS) are set for the arrangement positions (# 2, # 3, # 7, and # 8). Then, signal transmission stop processing is executed for the set MBSFN subframe.
As a result, MBSFN ABS is applied to all 10 subframes constituting the radio communication frame 100, and transmission of not only a data signal and an upper layer control signal in the data area but also a reference signal (CRS) can be stopped. . Therefore, when the ABS allocation ratio is 4: 6, 5: 5, or 6: 4, interference due to the reference signal can be reduced between the macrocell base station 10 and the small cell base station 20.

  FIG. 8 is an explanatory diagram showing another example of shift of the radio communication frame at the small cell base station in the present embodiment. The example of FIG. 8 is also a suitable example when the ABS allocation ratio is 4: 6, 5: 5, or 6: 4.

In the example of FIG. 8, the transmission timing of the radio communication frame 100 in the small cell base station 20 is shifted by the time corresponding to three units of the subframe on the time axis with respect to the transmission timing of the radio communication frame in the macrocell base station 10. ing.
The macro cell base station 10 can stop the transmission of the reference signal (CRS) for all six arrangement positions (# 1 to # 3, # 6 to # 8) that can be set in the MBSFN subframe in the radio communication frame 100. A subframe is set. Then, signal transmission stop processing is executed for the set MBSFN subframe.
On the other hand, the small cell base station 20 corresponds to MBSFN subframes other than the subframe in which signal transmission stop processing is executed in the macrocell base station 10 among the six arrangement positions where the MBSFN subframe can be set in the radio communication frame 100. MBSFN subframes in which transmission of reference signals (CRS) can be stopped are set for the arrangement positions (# 1, # 2, # 6, # 7). Then, signal transmission stop processing is executed for the set MBSFN subframe.
As a result, MBSFN ABS is applied to all 10 subframes constituting the radio communication frame 100, and transmission of not only a data signal and an upper layer control signal in the data area but also a reference signal (CRS) can be stopped. . Therefore, when the ABS allocation ratio is 4: 6, 5: 5, or 6: 4, interference due to the reference signal can be reduced between the macrocell base station 10 and the small cell base station 20.

  In addition, although the said embodiment demonstrated the case where the intercell interference between the macrocell base station 10 and the small cell base station 20 with which a cell overlaps was reduced, this invention is a small cell base with which a cell mutually overlaps. The same applies to the case of reducing inter-cell interference between the stations 20.

Further, although the present embodiment has been described on the assumption that it is applied to LTE / LTE-Advanced, the concept of the present invention can be applied to any system as long as the system uses a channel configuration similar to LTE / LTE-Advanced. The present invention is applicable and is not limited to the configurations of the transmitter and the receiver shown in this embodiment. The signal sequence for cell search, the channel coding scheme used for the sequence and error correction of the references signals that are used to estimate the like of the channel response is as long as it meets these applications, which Such a kind may be sufficient and it is not limited to what is defined by LTE / LTE-Advanced.

  Further, the processing steps described in this specification and the components of the mobile communication system, the base station, and the user terminal device (mobile station device) can be implemented by various means. For example, these steps and components may be implemented in hardware, firmware, software, or a combination thereof.

  For hardware implementation, means such as a processing unit used to realize the above steps and components in an entity (for example, various wireless communication devices, Node B, terminal, hard disk drive device, or optical disk drive device) One or more application specific ICs (ASICs), digital signal processors (DSPs), digital signal processing units (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors , A controller, a microcontroller, a microprocessor, an electronic device, other electronic units designed to perform the functions described herein, a computer, or a combination thereof.

  Also, for firmware and / or software implementation, means such as processing units used to implement the above components may be programs (eg, procedures, functions, modules, instructions) that perform the functions described herein. , Etc.). In general, any computer / processor readable medium that specifically embodies firmware and / or software code is means such as a processing unit used to implement the steps and components described herein. May be used to implement For example, the firmware and / or software code may be stored in a memory, for example, in a control device, and executed by a computer or processor. The memory may be implemented inside the computer or processor, or may be implemented outside the processor. The firmware and / or software code may be, for example, random access memory (RAM), read only memory (ROM), nonvolatile random access memory (NVRAM), programmable read only memory (PROM), electrically erasable PROM (EEPROM) ), FLASH memory, floppy disk, compact disk (CD), digital versatile disk (DVD), magnetic or optical data storage, etc. Good. The code may be executed by one or more computers or processors, and may cause the computers or processors to perform the functional aspects described herein.

  Also, descriptions of embodiments disclosed herein are provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. The present disclosure is therefore not limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

DESCRIPTION OF SYMBOLS 10 Macrocell base station 10A Macrocell 20 Small cell base station 20A Small cell 30 User terminal device (mobile device, mobile station device)
40 Server device 50, 51 Communication line 100 Wireless communication frame 110 Subframe

JP 2012-129793 A

Claims (7)

Comprising a first base station and second base station at least a portion of the wireless communication areas overlap each other, each of the first and second base stations, in a state of being synchronized with each other time, 10 A communication system that performs downlink transmission to a mobile station device by wireless communication frames in which subframes are continuously arranged on a time axis,
Second (# 1), third (# 2), fourth (# 3), seventh (# 6), eighth (# 7) and ninth from the beginning of the wireless communication frame Subframes that can stop transmission of reference signals can be set only for the six arrangement positions of (# 8) ,
The transmission timing of the wireless communication frame transmitted from each of the first base station and the second base station is shifted from each other by a time corresponding to two units or three units of the subframe on the time axis,
The first base station sets a subframe capable of stopping the transmission of the reference signal for all of the predetermined six arrangement positions in the wireless communication frame, and performs a signal transmission stop process for the set subframe. Run
The second base station supports all subframes other than the subframe in which signal transmission stop processing is executed in the first base station among the predetermined six arrangement positions in the wireless communication frame. A sub-frame capable of stopping the transmission of the reference signal is set for the array position to be transmitted, and a signal transmission stop process is executed for the set sub-frame. The communication system of claim 1.
A communication is characterized in that a shift amount of the transmission timing of the wireless communication frame is set in accordance with information of a subframe to be stopped for transmission set in each of the first base station and the second base station. system. The communication system according to claim 1 or 2,
A server device capable of communicating with each of the first base station and the second base station;
The server device
Receiving interference signal level information at each of the first base station and the second base station;
Determining a subframe to be transmitted based on the interference signal level information;
A communication system, wherein information on the subframe to be stopped is transmitted to each of the first base station and the second base station. The communication system according to any one of claims 1 to 3 ,
The first base station is a macrocell base station of an interference source;
The communication system, wherein the second base station is located in a cell of the macro cell base station, and its own cell is an interfered small cell base station smaller than the cell of the macro cell base station. The communication system according to any one of claims 1 to 3 ,
The first base station is an interfered macrocell base station;
The communication system, wherein the second base station is located in a cell of the macro cell base station, and its own cell is a small cell base station of an interference source smaller than a cell of the macro cell base station. The communication system according to any one of claims 1 to 3 ,
Each of the first base station and the second base station is located in the cell of the macro cell base station, and its own cell is smaller than the cell of the macro cell base station and is adjacent to each other. A communication system characterized by being a small cell base station. The communication system according to any one of claims 1 to 6 ,
The subframe capable of stopping the transmission of the reference signal is an MBSFN (Multimedia Broadcast Single Frequency Network) subframe conforming to LTE (Long Term Evolution) -Advanced standards.