JP6551529B2 - Radio base station, inter-cell interference coordination method and program - Google Patents

Description

  TECHNICAL FIELD The present invention relates to control of a wireless communication network, and more particularly, to a technique for allocating wireless resources.

  In LTE (Long Term Evolution), a method called CRE (Cell Range Expansion) is used in order to allow a pico cell with a small communication area to have a small transmission power of a radio signal and to accommodate more UEs (User Equipment). CRE is a technique that makes it difficult for handover to occur and widens the communication area of a pico cell by setting a small value to a cell-specific offset value (CIO: Cell Individual Offset) used in handover determination.

  However, UEs present in a communication area expanded by CRE receive a large interference from neighboring cells such as macro cells, which causes a problem of reduced performance. As a means to solve this problem, an inter-cell interference suppression method called enhanced Inter Cell Interference Coordination (eICIC) has been proposed. In eICIC, a cell (for example, a macro cell) serving as an interference source is referred to as an “aggressor cell”, and a cell (for example, a pico cell) that receives interference from an aggressor cell such as a macro cell is referred to as a “victim cell”.

  The eICIC suppresses data transmission in the time indicated by the Almost Black Subframe (ABS) pattern to the UE where the base station of the aggressor cell is connected to the own station, while the base station of the victim cell is in the own cell. This is a scheme for improving the performance of a victim UE by communicating with a UE that is present in the UE and that receives large interference from an aggressor cell (hereinafter referred to as a victim UE) (see Patent Document 1).

  The procedure for realizing eICIC will be briefly described.

  When the base station of the aggressor cell determines that the start of aggressor ICIC processing is necessary according to a request from the UE, etc., it determines an ABS pattern indicating what subframe pattern the own cell suppresses transmission of. Subsequently, the base station of the aggressor cell suppresses data transmission of its own cell based on the determined ABS pattern. Also, the base station of the aggressor cell notifies the victim cell of the determined ABS pattern using the X2 message. The base station of the victim cell transmits to the victim UE based on the ABS pattern received from the base station of the aggressor cell.

Special table 2014-522215 gazette

  When there are multiple victim cells in the aggressor cell, it is necessary to assign an ABS in consideration of the location of the victim cell. Consider the case where the radio signals of the two victim cells are close enough to interfere and far enough not to interfere.

  FIG. 14 shows the case where two victim cells are close, and FIG. 15 shows the case where two victim cells are not close.

  First, the case where two victim cells are close to each other will be described with reference to FIG.

  As shown in FIG. 14, the network includes a macro cell radio base station (hereinafter referred to as a macro base station) 151, a pico cell radio base station (hereinafter referred to as a pico base station) 251 and 254, and a network 351. And. The macro base station 151 is a base station of the macro cell 152 which becomes an aggressor cell. The macro cell 152 is an area covered by the macro base station 151. The pico base stations 251 and 254 are pico cell base stations serving as victim cells. The macro base station 151 and the pico base stations 251 and 254 are connected via the network 351. A network 351 is a network for exchanging X2 messages between base stations.

  The pico cells 252 and 255 are communication areas of the pico base stations 251 and 254 before applying the CRE. The pico cells 253 and 256 are communication areas of the pico base stations 251 and 254 after application of CRE. The UEs 401 and 402 are located in areas where the picocell 253 and the picocell 256 overlap each other. Each of the UEs 401 and 402 belongs to both the pico cell 253 by the pico base station 251 and the pico cell 256 by the pico base station 254. Here, it is assumed that the pico base station 251 communicates with the UE 401 and the pico base station 254 communicates with the UE 402.

  In the case shown in FIG. 14, a case is considered where the macro base station allocates an ABS to only one subframe (this subframe is referred to as “subframe # 1”) among frames composed of a plurality of subframes.

  At this time, the pico base station 251 allocates data for the UE 401 to subframe # 1 and transmits it. The pico base station 254 allocates and transmits data for the UE 402 in subframe # 1. The UE 401 receives interference from data transmitted from the pico base station 254 for the UE 402, and thus can not improve the performance despite using the ABS. Similarly to the UE 401, the performance of the UE 402 can not be improved because of interference of radio waves output from the pico base station 251. In this case, it is desirable that the number of subframes allocated as an ABS be increased to two and that different pico base stations 251 and pico base stations 254 be allocated different ABSs.

  Next, the case where the two victim cells are not close will be described with reference to FIG.

  In this case, since the UE 401 does not receive the interference of the radio signal from the pico base station 254 and the UE 402 similarly does not receive the interference of the radio signal from the pico base station 251, the performance degradation due to the interference from other pico cells occurs. Absent. In the case shown in FIG. 14, the number of subframes assigned as the ABS may be two, as in the case shown in FIG. However, since the ABS adversely affects the performance of the UE in the aggressor cell, it is better that the number of ABS is small. Therefore, in the case shown in FIG. 14, it is desirable to assign the same ABS to the pico base stations 251 and 254 in order to suppress the influence on the performance of the UE in the aggressor cell.

  The base station of the aggressor cell needs to determine the ABS pattern, but allocating many subframes as ABS loses the opportunity of data transmission to UEs present in its own cell, so allocates as little ABS as possible Is desirable. On the other hand, as a victim cell, it is desirable that more subframes be allocated as an ABS in order to improve the performance to the victim UE.

  The present invention has been made to solve the problems of the above-described techniques, and it is a wireless base station that suppresses inter-cell interference and can improve data transmission efficiency, an inter-cell interference coordination method, and a wireless It is an object to provide a storage medium for causing a base station to execute.

The wireless base station of the present invention for achieving the above object
A wireless base station,
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station A determination unit that determines whether or not there is interference from
When there are a plurality of other wireless base stations transmitting the wireless signal determined to be receiving the interference by the determination unit, the second cells formed by each of the plurality of other wireless base stations are close to each other And a allocator for allocating, in the time axis direction, transmission suppression timing indicating a time during which the wireless base station suppresses data transmission according to the determination.
When the plurality of second cells are in proximity as a result of the determination, the assignment unit assigns the transmission suppression timing to be different among the plurality of other wireless base stations, and the plurality of second cells are In the case where they are not close to each other, the transmission suppression timing is assigned to be the same among the plurality of other radio base stations.

The inter-cell interference adjustment method of the present invention is an inter-cell interference adjustment method by a radio base station,
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station To determine if they are receiving
When there are a plurality of other wireless base stations transmitting wireless signals determined to be receiving the interference, whether or not the second cells formed by each of the plurality of other wireless base stations are close to each other To determine
As a result of the determination, when the plurality of second cells are in close proximity, the wireless base station assigns transmission suppression timings indicating times for suppressing data transmission to be different among the plurality of other wireless base stations, When the plurality of second cells are not close to each other, the transmission suppression timing is assigned to be the same among the plurality of other radio base stations.

Furthermore, the program recorded in the storage medium of the present invention is stored in the radio base station.
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station Procedures to determine whether or not there is interference from
When there are a plurality of other wireless base stations transmitting wireless signals determined to be receiving the interference, whether or not the second cells formed by each of the plurality of other wireless base stations are close to each other The procedure for determining
As a result of the determination, when the plurality of second cells are in close proximity, the wireless base station assigns transmission suppression timings indicating times for suppressing data transmission to be different among the plurality of other wireless base stations, When the plurality of second cells are not in proximity, a procedure is performed to assign the transmission suppression timing to be the same among the plurality of other wireless base stations.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the interference between cells, the efficiency of data transmission can be improved.

It is a figure which shows an example of the network structure of 1st Embodiment. FIG. 2 is a block diagram illustrating a configuration example of a macro base station illustrated in FIG. 1. It is a figure which shows an example of the format of the message for a pico base station to transmit measurement information to a macro base station. It is a figure which shows an example of the data storage format in each field of UE1 measurement information-UEn measurement information shown in FIG. It is a figure which shows an example of the table which the measurement result storage part shown in FIG. 2 memorize | stores. It is a flowchart which shows the operation | movement procedure by the macro base station in 1st Embodiment. It is a flowchart which shows the operation | movement procedure by the macro base station in 1st Embodiment. It is a flowchart which shows the procedure of a specific process of step S901 shown to FIG. 6A. It is a figure which shows an example of the victim cell list in 1st Embodiment. It is a flowchart which shows the procedure of a specific process of step S1002 shown in FIG. It is a flowchart which shows the procedure of a specific process of step S904 shown to FIG. 6A. It is a block diagram which shows one structural example of the macro base station in 3rd Embodiment. It is a figure which shows an example of the adjacent cell information in 3rd Embodiment. It is a flow chart which shows a procedure which creates a neighboring cell related list in a 3rd embodiment. In the related art network configuration, it is a diagram showing a case where a plurality of pico cells overlap a macro cell. It is a figure which shows a case different from the case shown in FIG. 14 regarding related technology.

First Embodiment
The network configuration of this embodiment will be described. FIG. 1 is a diagram showing an example of a network configuration according to the present embodiment.

  As shown in FIG. 1, the network of this embodiment is configured to include a macro base station 101, pico base stations 201 and 204, and a network 301. The macro base station 101, the pico base station 201, and the pico base station 204 are connected to each other via a network 301 so that they can communicate with each other. A network 301 is a network for exchanging X2 messages between base stations. The macro base station 101, the pico base station 201, and the pico base station 204 are connected to an EPC (Evolved Packet Core) 501.

  The macro base station 101 is a base station that covers the macro cell 102 having a wider communication area than the pico cells 202 and 205 by the pico base stations 201 and 204, and is a cell that behaves as an aggressor cell of eICIC.

  The pico base stations 201 and 204 are base stations having pico cells 202 and 205 whose communication area is narrower than that of the macro cell 102. However, in this embodiment, the pico base stations 201 and 204 use the CRE to increase the number of UEs that can be accommodated in the pico cell of the own station, and extend the communication area from the pico cells 202 and 205 to the pico cells 203 and 206. There is. In the example illustrated in FIG. 1, the picocell 203 includes a UE 401 communicably connected to the pico base station 201, and the picocell 206 includes a UE 402 communicably connected to the pico base station 204.

  The pico cell is an example of a cell having a smaller communication area than the macro cell. The pico base station is an example of a small cell radio base station which is a small cell radio base station.

  Next, the configuration of the macro base station shown in FIG. 1 will be described.

  FIG. 2 is a block diagram showing one configuration example of the macro base station shown in FIG. In the following, the configuration and operation regarding inter-cell interference adjustment by the macro base station will be described in detail, and the detailed description of techniques related to general wireless communication with the UE will be omitted.

  As shown in FIG. 2, the macro base station 101 includes an X2 interface unit 601, a storage unit 611, and a control unit 612. The storage unit 611 includes a measurement result storage unit 604 and a victim cell storage unit 605. The control unit 612 includes an Aggressor ICIC start determination unit 602 and an ABS pattern generation unit 603.

The X2 interface unit 601 is a network interface unit for exchanging the X2 message with the pico base stations 201 and 204, and is connected to the network 301.
When the X2 interface unit 601 receives neighboring cell measurement information from another cell, the X2 interface unit 601 stores the neighboring cell measurement information in the measurement result storage unit 604.

  Further, the X2 interface unit 601 receives the X2 message requesting the start of the “aggressor eICIC” for prompting the macro base station to execute the eICIC from the base station (for example, the pico base station) of another cell. Analyze the X2 message. As an X2 message for requesting initiation of aggressor e ICIC, for example, there is LOAD INFORMATION which is an X2 message including Invoke Indication IE in which "ABS Information" is set as a value. When the X2 interface unit 601 analyzes the X2 message and specifies the cell that has requested the ABS information, the X2 interface unit 601 registers the specified cell in the victim cell storage unit 605.

  The neighboring cell measurement information is information obtained by collecting the result of the pico base station measuring the signal strength of the neighboring cell with respect to the UE present in the own cell. This information can be obtained, for example, by the base station setting a measurement configuration in the RRC (Radio Resource Control) message to the UE and instructing the UE to perform measurement. The pico base stations 201 and 204 transmit neighboring cell measurement information to the macro base station 101 via the network 301.

  Here, a specific example of a message format used when the pico base station transmits neighboring cell measurement information to the macro base station will be described. FIG. 3 is a diagram illustrating an example of a message format for the pico base station to transmit neighboring cell measurement information to the macro base station.

  As shown in FIG. 3, this message includes a transmission source cell identifier 701, a data attribute 702, a data length 703, and UEk identifier 704-k and UEk measurement information for each UEk (k is an integer from 1 to n). And 705-k. In the present embodiment, n is an integer of 2 or more.

  The transmission source cell identifier 701 is an identifier for identifying a transmission source cell. For example, ECGI (E-UTRAN Cell Global Identifier) corresponds to the source cell identifier 701. The data attribute 702 is an identifier indicating that the content of data after this field is neighboring cell measurement information. A data length 703 indicates the data length after this field.

  Each of the UE1 identifier 704-1 to UEn identifier 704-n is an identifier of the UE that has reported each result of the UE1 measurement information 705-1 to UEn measurement information 705-n. UE1 measurement information 705-1 to UEn measurement information 705-n is information indicating the signal strength of a cell measured by UE1 to UEn.

  The UE1 measurement information 705-1 to UEn measurement information 705-n illustrated in FIG. 3 will be described with reference to FIG. FIG. 4 is a diagram showing an example of a data storage format in each field of UE1 measurement information to UEn measurement information shown in FIG.

  As shown in FIG. 4, UEk measurement information 705-k, which is the result of measurement by UEk, includes the number of measurement cells 801, cell identifiers (cell 1 identifier 802-1 to cell m identifier 802-m), and signal strength information. (Cell 1 signal strength 803-1 to cell m signal strength 803-m). In the present embodiment, m is an integer of 2 or more.

  In the measurement information illustrated in FIG. 4, the cell 1 identifier 802-1, the cell 2 identifier 802-2, ..., and the cell m identifier 802-m are identifiers of cells observed in UEk. In the present embodiment, it is assumed that the serving cell of the UE has been removed from the observation result. The cell 1 signal strength 803-1, the cell 2 signal strength 803-2, ..., and the cell m signal strength 803-m are information on the signal strength of each cell observed in UEk.

  The signal strength is RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), or both.

  The measurement result storage unit 604 stores the result of each of the UE1 to UEn being measured for each of the cells 1 to m. The measurement result corresponds to the number of UEs stored in the storage unit, and m corresponds to the number of cells stored in the storage unit. n is not limited to 2 or more, the number of UEs may be one, and the number of UEs is not limited. Further, m is not limited to two or more, and the number of cells may be one, and the number of cells is not limited.

The measurement result storage unit 604 stores peripheral cell measurement information received from the X2 interface unit 601 in a table format. FIG. 5 is a diagram showing an example of a table stored in the measurement result storage unit. As shown in FIG. 5, the measurement result storage unit 604 stores the source cell, the UE identifier, the identifier of the observed cell, and the information on the signal strength of the cell in the form of a table.
The transmission source cell is an identifier of a pico cell of a pico base station that is a transmission source of measurement information. The UE identifier is an identifier of a UE connected to the pico base station of the transmission source cell. The identifier of the observed cell is an identifier indicating another cell in which the UE whose signal source is the serving cell has observed the signal strength.

  For example, the case where the transmission source cell is Cell1 will be described with reference to FIG. FIG. 5 shows that the source cell Cell1 is in a connected state with the UEs of the UE identifiers UE1 to UE3. In FIG. 5, the result of measuring the signal strength of each of the cells Cell2, Cell3, ..., Cell5 by the UE with the identifier UE1 corresponding to the transmission source cell Cell1 is recorded in the table, and the UE with the identifier UE2 is the cell Cell2 The result of measuring the signal strength of each of Cell4, ..., Cell6 is recorded in the table, and the result of measuring the signal strength of each of Cell2, Cell3, ..., Cell5 by the UE of identifier UE3 is in the table It is recorded.

  The victim cell storage unit 605 stores the information of the cell requiring the ABS information. A cell requiring ABS Information corresponds to a victim cell. The victim cell storage unit 605 stores a victim cell list S1. The victim cell list S1 is a list for registering a victim cell. In the victim cell list S1, the identifier of the victim cell and the number of the subframe of the ABS allocated to the victim cell are registered corresponding to the victim cell.

  Further, in the storage unit 611, in addition to the victim cell list S1, the ABS pattern generation unit 603 assigns an ABS to all of the victim cells to which no ABS is assigned, or to one victim cell being assigned. Various tables for recording information used for processing are stored. As a table stored in the storage unit 611, for example, there are a proximity cell relation list S2, a first subframe list S3, a second subframe list S4, and a third subframe list S5.

  The neighboring cell relation list S2 is a list for registering combinations of pico cells that are close enough to interfere with each other. The first sub-frame list S3 is a list indicating sub-frame numbers that can be assigned as an ABS. The “subframes that can be assigned as ABS” mentioned here includes subframes that have already been assigned as ABS.

  The second subframe list S4 is a list indicating the numbers of subframes already assigned as ABS. The third sub-frame list S5 is a list showing the numbers of all ABSs assigned to the neighboring cells of one victim cell to which the ABS is not assigned.

  In addition, at least one of the fourth and fifth subframe lists S6 and S7 is stored in the storage unit 611. The fourth sub-frame list S6 is a list indicating the ABS numbers assigned to cells that are assigned to other victim cells but that are not adjacent to one victim cell to which the ABS is not assigned. The fifth sub-frame list S7 is a list indicating the numbers of sub-frames not assigned as ABSs to any cells among assignable ABSs. The fourth and fifth sub-frame lists S6 and S7 are obtained from the first to third sub-frames S3 to S5 described above.

  The victim cell list S1, the neighboring cell relation list S2, the first subframe list S3, and the second subframe list S4 are lists used for all victim cells to which no ABS is assigned. The third sub-frame list S5 to the fifth sub-frame list S7 are lists prepared for each cell to be subjected to allocation processing among victim cells to which the ABS has not been allocated. A detailed description of these lists is provided below.

  The Aggressor e ICIC start determination unit 602 determines the presence or absence of operation start as an aggressor cell. As a case where it is determined that the operation is started, for example, a case may be considered in which an X2 message requesting ABS Information is received from the base station of another cell via the X2 interface unit 601. Not limited to this case, the Aggressor ICIC start determination unit 602 may determine the presence or absence of operation start as an aggressor cell by analysis of collected information and other methods. Upon determining the start of the operation as an aggressor cell, the Aggressor eICIC start determination unit 602 transmits aggressor cell start information, which is information indicating that the operation has been started as an aggressor cell, to the ABS pattern generation unit 603.

  Upon receiving the aggressor cell start information from the aggressor eICIC start determination unit 602, the ABS pattern generation unit 603 generates an ABS pattern using the information stored in the measurement result storage unit 604 and the information stored in the victim cell storage unit 605. Generate The ABS pattern is a pattern in which a subframe to which ABS is assigned is represented by “1” and a subframe to which ABS is not assigned is represented by “0” in one frame. For example, in the ABS pattern “0010100101...” From the beginning of the frame, it means that the ABS is assigned to the position where the subframe number is “3, 5, 8, 10,. The ABS pattern generation unit 603 transmits the generated ABS pattern to the pico base station of the victim cell via the X2 interface unit 601 and the network 301. The ABS corresponds to transmission suppression timing indicating a time in which the macro base station 101 suppresses transmission of data to the UE connected to the macro base station 101.

When there are a plurality of picocells that interfere with the wireless signal transmitted by the own station, the ABS pattern generation unit 603 is closer to the plurality of picocells so that the wireless signals transmitted by the plurality of pico base stations corresponding to the plurality of picocells Then, according to the determination, the transmission suppression timing for suppressing the interference of the radio signal of the own station is allocated in the time axis direction. Specifically, as a result of the determination, when a plurality of pico cells are in close proximity, the ABS pattern generation unit 603 allocates different ABSs among the plurality of pico base stations. Further, when a plurality of pico cells are not in close proximity, the ABS pattern generation unit 603 allocates the same ABS among a plurality of pico base stations. The ABS pattern generation unit 603 corresponds to an allocation unit that allocates the ABS to the pico base station.
Details of the operation of the ABS pattern generation unit 603 will be described later.

  Each configuration in control unit 612 in the functional block diagram shown in FIG. 2 may be realized by a dedicated integrated circuit such as an application specific integrated circuit (ASIC) for executing a function. It may be realized by a CPU (Central Processing Unit) and a memory provided in advance. Specifically, the control unit 612 is provided with a memory for storing a program and a CPU for executing processing in accordance with the program, and the CPU executes the program, whereby an ABS pattern generation unit 603 and an Aggressor ICIC start determination unit 602 is configured virtually. The memory is, for example, a flash memory.

  Next, the operation of the ABS pattern generation unit 603 of the macro base station of the present embodiment will be described with reference to the flowcharts of FIGS. 6A to 11. Here, it is assumed that the measurement result storage unit 604 stores RSRP from each observation cell in each UE.

  6A and 6B are flowcharts for explaining the procedure of the inter-cell interference adjustment method of this embodiment.

  When the ABS pattern generation unit 603 is notified of the start of the operation as an aggressor cell from the aggressor eICIC start determination unit 602, the ABS pattern generation unit 603 first executes initialization processing (step S901). A specific process of the initialization process in step S901 will be described with reference to FIG.

  In the initialization process of step S901, the ABS pattern generation unit 603 first sets identifiers of all the victim cells in the victim cell list S1 (step S1001).

  FIG. 8 shows an example of victim cell list S1. The victim cell list S1 includes a column 1101 in which an identifier of a victim cell is registered, and a column 1102 in which an ABS assigned to the victim cell is registered. The identifier of the victim cell registered in the victim cell storage unit 605 is set in the column 1101, and in the initial stage, the empty state is set in the column 1102.

  Next, the ABS pattern generation unit 603 executes creation processing of the neighboring cell relationship list S2 (step S1002). Cells adjacent to each other are registered in pairs in the adjacent cell relation list S2 so that radio signals cause interference with each other. For example, in the case where the cell X100 and the cell X200 are paired and registered in the neighboring cell relation list S2, hereinafter, the cell is expressed as a cell pair (X100, X200).

  The specific process of step S1002 will be described with reference to FIG.

  In the process of step S1002, the ABS pattern generation unit 603 first sets the neighboring cell relation list S2 to an empty state (step S1201). Next, the ABS pattern generation unit 603 extracts the measurement result of one UE, for example, the measurement result 1201 shown in FIG. 5 from the measurement results stored in the measurement result storage unit 604 (step S1202). Next, the ABS pattern generation unit 603 selects one cell from the plurality of cells measured by the UE among the extracted measurement results of one UE (step S1203). Next, the ABS pattern generation unit 603 compares the RSRP value of the selected cell with a preset threshold, and checks whether the RSRP value is larger than the threshold (step S1204). This threshold is a value serving as a determination reference of whether or not the selected cell is close enough to cause interference with the transmission source of the measurement result (serving cell of the UE).

  The ABS pattern generation unit 603 determines that the observed cell is close to the serving cell of the selected UE when the RSRP value is larger than the threshold, and when the RSRP value is equal to or smaller than the threshold, the observed cell is It is determined that it is not close to the serving cell of the selected UE. If the RSRP value of the observed cell is larger than the threshold, the ABS pattern generation unit 603 may select the cell pair (serving cell of the selected UE, observed cell) or the cell pair whose order is reversed (observed cell, selected cell). It is checked whether the serving cell of the UE is registered in the neighboring cell relation list S2 (step S1205).

  When neither of the two types of cell pairs is registered in the neighboring cell relationship list S2, the ABS pattern generation unit 603 adds the cell pair (serving cell of the selected UE, observed cell) to the neighboring cell relationship list S2. (Step S1206).

  For all the observed cells, the ABS pattern generation unit 603 performs the processes of Steps S1204 to S1206 described above, and the process related to the measurement result acquired from one UE ends (Steps S1203 to S1207). The ABS pattern generation unit 603 performs processing on measurement results acquired from one UE on all UEs in all transmission source cells (steps S1202 to S1208).

  It returns to the explanation of the flow shown in FIG. When the process of creating the proximity cell relationship list S2 in step S1002 ends, the ABS pattern generation unit 603 sets a first subframe list S3 that is a list indicating subframe numbers that can be assigned as ABS (step S1003). ). The subframe that can be assigned as an ABS is a subframe that the macro base station 101 can assign as an ABS. Subframes that can be assigned as ABS can be set by the network administrator.

  Next, the ABS pattern generation unit 603 sets the second subframe list S4, which is a list for recording the number of subframes assigned to the victim cell, to an empty state (step S1004). Thus, the initialization process shown in step S901 of FIG. 6A is completed.

  When the initialization process of step S901 is completed, the ABS pattern generation unit 603 sequentially executes the processes of steps S903 to S912 for all of the victim cells registered in the victim cell list S1. The ABS pattern generation unit 603 refers to the victim cell list S1 and selects one victim cell vc from among the ABS unassigned victim cells that are the victim cells to which the ABS is not assigned (step S903). The ABS unassigned victim cell is a victim cell in which no subframe is set in the column 1102 in the victim cell list S1 described with reference to FIG.

  Next, the ABS pattern generation unit 603 registers all the ABS numbers assigned to neighboring cells of the selected victim cell vc in the third subframe list S5 (step S904). The specific process of step S904 will be described with reference to FIG.

  In the process of step S904, the ABS pattern generation unit 603 first sets an empty state in the third sub-frame list S5 and initializes it (step S1301). Next, the ABS pattern generation unit 603 selects one cell pair from among the cell pairs registered in the neighboring cell relation list S2 (step S1302). Then, the ABS pattern generation unit 603 checks whether or not the victim cell vc selected in Step S903 is included in the selected cell pair (Step S1303). When the victim cell vc is not included in the selected cell pair, the ABS pattern generation unit 603 selects another cell pair from the cell pairs registered in the neighboring cell relation list S2, and performs the process of step S1303. Do.

  In the process of step S1303, if the victim cell vc is included in the selected cell pair, assuming that the cell pair at this time is (vc, X) or (X, vc), the ABS pattern generation unit 603 displays the victim cell list. It is checked with reference to S1 whether or not the ABS is already assigned to the cell X (step S1304). If the ABS is already assigned to the cell X, the ABS pattern generation unit 603 records the subframe number in the third subframe list S5 (step S1305).

  In this way, the ABS pattern generation unit 603 extracts the cell pair including the victim cell vc from the neighboring cell relation list S2, and is already assigned to the neighboring cell of the victim cell vc with reference to the victim cell list S1. All the ABSs are registered in the third subframe list S5 (steps S1302 to S1306).

  In step S904 shown in FIG. 6A, when the creation of the third subframe list S5 is completed for the victim cell vc, the ABS pattern generation unit 603 is an ABS assigned to another victim cell, but the victim cell vc. The ABS assigned to the cell not adjacent to the is registered in the fourth sub-frame list S6 (step S905). The fourth sub-frame list S6 subtracts the third sub-frame list S5 in which the ABS used in the neighboring cells of the victim cell vc is registered from the second sub-frame list S4 in which the assigned ABS is registered. It is determined by If this processing is expressed by a mathematical formula, S6 = S4-S5.

  Next, the ABS pattern generation unit 603 checks whether the fourth sub-frame list S6 is not empty (step S906). If the fourth sub-frame list S6 is not empty, the ABS pattern generation unit 603 allocates an arbitrary sub-frame from the sub-frames registered in the fourth sub-frame list S6 as an ABS for the victim cell vc (step S 907). Then, the ABS pattern generation unit 603 registers the subframe number of the ABS allocated to the victim cell vc in the victim cell list S1 (step S908). Specifically, the ABS pattern generation unit 603 registers the ABS subframe number in the column 1102 column corresponding to the victim cell vc in the column 1101 in the victim cell list S1.

  In this case, although the same ABS as the ABS allocated to the cell not adjacent to the own cell is allocated to the victim cell vc, the radio signals do not interfere with each other.

  On the other hand, if it is determined in step S906 that the fourth sub-frame list S6 is empty, the ABS pattern generation unit 603 sets a list of allocatable sub-frames in the fifth sub-frame list S7 (step S909). The fifth sub-frame list S7 subtracts the second sub-frame list S4, which is a list in which the already allocated ABS is registered, from the first sub-frame list S3, which is a list in which the allocatable ABS is registered. It is determined by If this process is expressed by a mathematical formula, S7 = S3-S4.

  Next, the ABS pattern generation unit 603 checks whether the fifth sub-frame list S7 is not empty (step S910). If the fifth sub-frame is not empty, the ABS pattern generation unit 603 allocates an arbitrary sub-frame from the sub-frames registered in the fifth sub-frame list S7 as an ABS for the victim cell vc (step S911). .

  Next, the ABS pattern generation unit 603 registers the ABS subframe number assigned to the victim cell vc in the victim cell list S1 and the second subframe list S4 (step S912). Specifically, in the victim cell list S1, the ABS pattern generation unit 603 registers the ABS subframe number in the column 1102 corresponding to the victim cell vc in the column 1101.

  In this case, an ABS not assigned to any cell is assigned to the victim cell vc, and the radio signal does not interfere with other cells.

  In this manner, the ABS pattern generation unit 603 performs the processing of the above-described steps S903 to S912 on all the victim cells registered in the victim cell list S1 (steps S902 to S913). When this is completed, the ABS pattern generation unit 603 sets the assigned ABS stored in the second sub-frame list S4 to “1”, and creates an ABS pattern in which the other sub-frames are set to “0”. (Step S914).

  After generating the ABS pattern in step S912, the ABS pattern generation unit 603 transmits an X2 message for notifying the ABS pattern to the victim cell registered in the victim cell list S1 (step S915). As an X2 message for notifying an ABS pattern, for example, there is LOAD INFORMATION which is an X2 message in which an ABS pattern is described in ABS Information IE.

  Here, although a common ABS pattern is notified from the macro base station 101 to the pico base stations 201 and 204 shown in FIG. 1, a number of ABSs corresponding to the number of victim cells are allocated to the ABS pattern. There is. Therefore, even if the pico cells 203 and 206 are close to each other as shown in FIG. 1, the pico base stations 201 and 204 increase the time zone in which data can be transmitted and interfere with radio signals of the pico cells that are close to the own cell. Is suppressed.

  As described above, in the present embodiment, when assigning an ABS to a victim cell vc, if there is an ABS assigned to another victim cell not close to this cell, a subframe assigned to the other cell as an ABS. And the same subframe as the ABS is assigned to the victim cell vc, and an ABS that has not been assigned is assigned to the victim cell vc only when there is no corresponding ABS. If there is an ABS assigned to another victim cell not adjacent to the victim cell vc, that ABS is preferentially assigned to the victim cell.

  By performing the ABS allocation process in this way, different ABSs can be allocated to a plurality of adjacent victim cells, and interference between the victim cells can be suppressed. On the other hand, since a common ABS is assigned to a plurality of victim cells located distant from one another, it is possible to suppress the influence on the performance of the UE connected with the macro base station. By efficiently allocating the ABS, the efficiency of data transmission of each cell can be improved.

  Although the case where one ABS is allocated to the victim cell has been described in the present embodiment, the number of ABSs allocated to the victim cell is not limited to one. Also, the number of ABSs assigned to the victim cell may be changed according to the resource usage in the victim cell.

Second Embodiment
In the first embodiment, in step S914 of the flow shown in FIG. 6B, an ABS pattern is generated using the second subframe list S4, which is a list of already allocated ABSs, and is common to all victim cells. The ABS pattern was notified. In this case, for example, the aggressor cell assigns subframe # 1 to victim cell vc1 and subframe # 2 to victim cell vc2 so that neighboring victim cells vc1 and vc2 do not interfere with each other. It is conceivable to assign At this time, an ABS pattern in which “1” is set in both of the subframes # 1 and # 2 is notified to the victim cells vc1 and vc2. Therefore, each of the victim cells vc1 and vc2 does not recognize that each of the subframes # 1 and # 2 is assigned to itself, and if both subframes # 1 and # 2 are used, the wireless signal is transmitted. May interfere with each other.

  In the present embodiment, in step S914, instead of using the second subframe list S4, a separate ABS pattern is generated for each victim cell using the victim cell list S1.

  The inter-cell interference adjustment method of the present embodiment will be described with reference to FIG.

  The ABS pattern generation unit 603 notifies the victim cell Cell1 of an ABS pattern in which only subframe # 1 is set to “1” by an X2 message. The ABS pattern generation unit 603 notifies the victim cell Cell2 of an ABS pattern in which only subframe # 2 is set to “1” by an X2 message.

  At this time, the pattern set in the Measurement Subset included in the ABS Information IE in the X2 message used in the UE measurement may be a pattern set based on the ABS specific to the victim cell, similar to the ABS pattern. The pattern may be set based on the ABS used in all the victim cells stored in the list S4.

  In the case of this embodiment, each victim cell is notified of an ABS assigned to each victim cell by the aggressor cell so that neighboring cells do not use a common ABS. As a result, in the ABS, it is possible to reliably avoid interference of radio signals between adjacent victim cells.

Third Embodiment
In this embodiment, instead of using the neighboring cell measurement information from each cell, the information of the neighboring cell list notified by the X2 message is used.

  The configuration of the macro base station in the present embodiment will be described.

  FIG. 11 is a block diagram showing a configuration example of a macro base station in the present embodiment. In the present embodiment, detailed description of the same configuration as that of the first embodiment is omitted.

  As shown in FIG. 11, the macro base station includes a storage unit 651 including a victim cell storage unit 605 and a neighboring cell list storage unit 654, a control unit 652 including an ABS pattern generation unit 653 and an aggressor eICIC start determination unit 602, And an X2 interface unit 601.

  Compared to the configuration shown in FIG. 2, an adjacent cell list storage unit 654 is provided in the storage unit 651 instead of the measurement result storage unit 604. When the X2 interface unit 601 receives an X2 message including the Neighbor Information IE from another cell, the X2 interface unit 601 stores information on the adjacent cell list included in the IE in the adjacent cell list storage unit 654. Such X2 messages include, for example, X2 SETUP REQUEST and ENB CONFIGURATION UPDATE messages. The adjacent cell list is information indicating which cell is adjacent to the own cell. On the basis of the information on the adjacent cell list collected, the information on the adjacent cells is stored, for example, in the form of a table shown in FIG. 12 in the adjacent cell list storage unit 654.

  As shown in FIG. 12, the information on the adjacent cell corresponds to the identifier 1501 of the plurality of adjacent cells (Neighbor cells), corresponding to the identifier 1501 of the cell (Served Cell) that has reported the adjacent cell list. , 1504 are described. The adjacent cell list includes information on identifiers of cells adjacent to the Served Cell specified by the identifier 1501.

  The operation of the inter-cell interference adjustment method by the macrocell base station of this embodiment will be described.

  In the present embodiment, in the first embodiment, among the operations described with reference to FIGS. 6A to 10, the processing for generating the proximity cell relationship list S2 described with reference to FIG. Replace with In the following, the detailed description of the same operation as that of the first embodiment is omitted, and the procedure of creating the neighboring cell relationship list S2 will be described with reference to FIG.

  First, the ABS pattern generation unit 653 sets the proximity cell relation list S2 to an empty state and initializes it (step S1601). Next, the ABS pattern generation unit 653 selects an unprocessed Served Cell from the table (see FIG. 12) stored in the adjacent cell list storage unit 654 (step S1602), and sets the identifier of that cell to s. (Step S1603). Next, the ABS pattern generation unit 653 selects one unprocessed Neighbor Cell from the Neighbor Cells corresponding to the selected Served Cell with reference to the table shown in FIG. 12 (step S1604), and identifies the cell. Is set to n (step S1605). Subsequently, the ABS pattern generation unit 653 checks whether or not the cell pair (s, n) and (n, s) are included in the neighboring cell relation list S2 (step S1606). If neither cell pair (s, n) nor (n, s) is included in the adjacent cell relation list S2, the ABS pattern generation unit 653 sets the cell pair (s, n) in the adjacent cell relation list S2 Step S1607).

  The ABS pattern generation unit 653 performs the processing of steps S1605 to S1607 described above on all Neighbor Cells of the selected Served Cell (Steps S1604 to S1608). Furthermore, the ABS pattern generation unit 653 performs the process of steps S1603 to S1608 performed on the served cell on all the served cells registered in the adjacent cell list storage unit 654 (steps S1602 to S1609).

  In this embodiment, not only the same effects as the effects described in the first embodiment can be obtained, but there is also an advantage that the cell interference adjustment method of the present invention can be realized using the X2 message already defined in 3GPP. . Further, this embodiment may be applied to the second embodiment.

  In the first to third embodiments, although the radio base station to which the ABS is allocated is described as a macro base station, it may be a radio base station of a CSG (Closed Subscriber Group) cell, and in the aggressor of eICIC. The present invention is applicable to any base station that performs processing, and is not particularly limited to the size of coverage of the base station. However, the radio base station of the CSG cell has an X2 interface unit.

  In the first to third embodiments, the small cell (small cell), which is a cell having a smaller communication area than the macro cell, has been described as a pico cell, but the small cell may be a femto cell. The present invention is applicable to any base station that performs victim processing, and is not particularly limited to the size of the coverage of the base station.

  Furthermore, FIG. 1 shows the case where the entire pico cell is included in the communication area of the macro cell, but the entire pico cell may not be included in the communication area of the macro cell. By overlapping a part of the communication area of the pico cell with the macro cell, the first to third embodiments are performed even when the radio signal transmitted from the pico base station is affected by the radio signal transmitted from the macro base station. The inter-cell interference adjustment method described in the embodiment can be applied.

  As mentioned above, although the present invention was explained using an embodiment, the technical scope of the present invention is not limited to a statement of the above-mentioned embodiment. It is obvious to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. Therefore, it is needless to say that embodiments with such changes or improvements are also included in the technical scope of the present invention. Further, numerical values, names of respective components, and the like used in the embodiment described above are illustrative and can be changed as appropriate.

  This application claims priority based on Japanese Patent Application No. 2015-165639 filed on August 25, 2015, the entire disclosure of which is incorporated herein.

101 Macro base station 601 X2 interface unit 602 Aggressor eICIC start determination unit 603, 653 ABS pattern generation unit (allocation unit)
604 measurement result storage unit 605 victim cell storage unit 654 adjacent cell list storage unit 611, 651 storage unit 612, 652 control unit

Claims (6)

A wireless base station,
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station A determination unit that determines whether or not there is interference from
When there are a plurality of other wireless base stations transmitting the wireless signal determined to be receiving the interference by the determination unit, the second cells formed by each of the plurality of other wireless base stations are close to each other And a allocator for allocating, in the time axis direction, transmission suppression timing indicating a time during which the wireless base station suppresses data transmission according to the determination.
When the plurality of second cells are in proximity as a result of the determination, the assignment unit assigns the transmission suppression timing to be different among the plurality of other wireless base stations, and the plurality of second cells are If not close, the transmission suppression timing is assigned to be the same among the plurality of other radio base stations ,
The allocation unit
The radio base station determines whether or not the plurality of second cells are close to each other, using information of signal strength measured by a terminal communicably connected to the plurality of other radio base stations. In the radio base station according to claim 1 ,
The allocation unit
A wireless base station which notifies a pattern indicating the transmission suppression timing allocated to the other wireless base station corresponding to the plurality of other wireless base stations. In the radio base station according to claim 1 ,
The allocation unit
A wireless base station that notifies each of the plurality of other wireless base stations of a pattern indicating all of the transmission suppression timings assigned to the plurality of other wireless base stations. The radio base station according to any one of claims 1 to 3 .
The allocation unit
A wireless base station using a method defined by eICIC (enhanced Inter Cell Interference Coordination) when notifying the plurality of other wireless base stations of the transmission suppression timing. An inter-cell interference coordination method by a radio base station
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station To determine if they are receiving
When there are a plurality of other wireless base stations transmitting wireless signals determined to be receiving the interference, whether or not the second cells formed by each of the plurality of other wireless base stations are close to each other Determining the signal strength information measured by the terminal connected to the plurality of other radio base stations ,
As a result of the determination, when the plurality of second cells are in close proximity, the wireless base station assigns transmission suppression timings indicating times for suppressing data transmission to be different among the plurality of other wireless base stations, The inter-cell interference adjustment method which allocates the said transmission suppression timing so that it may become the same among several other wireless base stations, when these several 2nd cells are not close. In the radio base station,
A wireless signal transmitted by the wireless base station is a wireless signal transmitted from another wireless base station forming a second cell in which at least a part of the communication area overlaps with the first cell which is a cell formed by the wireless base station Determining whether or not there is interference from
When there are a plurality of other wireless base stations transmitting wireless signals determined to be receiving the interference, whether or not the second cells formed by each of the plurality of other wireless base stations are close to each other Determining the signal strength information measured by a terminal connected to the plurality of other radio base stations ,
As a result of the determination, when the plurality of second cells are in close proximity, the wireless base station assigns transmission suppression timings indicating times for suppressing data transmission to be different among the plurality of other wireless base stations, A program for causing the transmission suppression timing to be assigned to be the same among the plurality of other wireless base stations when the plurality of second cells are not in proximity.

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