JP6057788B2 - Radio base station for radio communication system, radio terminal connection control method in radio communication system - Google Patents

Description

  The present invention relates to a radio base station for a radio communication system including a plurality of radio base stations having different cell radii, a radio terminal connection control method in the radio communication system, and the like.

In 3GPP (3 ^rd Generation Partnership Project) is a standardization project organization of a wireless communication system, LTE (Long Term Evolution) standardization of LTE-Advanced having evolved has been promoted as a fourth-generation mobile communication system.

  Conventional radio that covers a wide area only with macrocells, which are large-output base stations with a large area radius, in response to diversification of requirements such as increase in communication capacity required for wireless communication services and improvement of indoor dead zones It is difficult to satisfy only with a communication system. As a solution to this problem, a heterogeneous network is expected in which a small output base station (small cell) represented by a pico cell or a femto cell having a smaller area radius than a macro cell is arranged in a conventional wireless communication system. .

  Since the small cell is mainly intended to improve indoor communication quality, it is generally arranged to overlap with a large-power base station with a large cell radius such as a macro cell. Overlapping frequency bands are used.

  On the other hand, the uplink transmission power of a wireless terminal that provides a service on a wireless communication system is such that the propagation loss between the base station and the wireless terminal increases as the reception quality determined by the base station apparatus that provides the communication service increases. The uplink transmission power is also controlled to be large. Therefore, when a plurality of cells having different cell radii are arranged hierarchically, when a wireless terminal that is far from the macro cell performs communication in the vicinity of an area where a small cell having a small area radius is installed, Since the uplink transmission power of the wireless terminal becomes a very strong interference signal with respect to the small cell, the reception quality of the uplink signal in the small cell is greatly deteriorated, resulting in a problem that the uplink throughput is lowered. The same problem occurs between picocells and femtocells that are classified as small cells having different cell radii.

  As a method for solving this problem, in Patent Document 1 below, when a small cell detects uplink radio wave interference, the amount of interference is measured, and a criterion for strong interference is determined from a predetermined threshold value and a comparison determination processing result. If determined, the cell radius is increased by increasing the transmission power of the small cell, the probability of connecting the wireless terminal transmitting the uplink interference signal to the small cell is increased, and the wireless terminal that is the interference source is As a result, the uplink interference signal is reduced.

JP 2012-114512 A

  However, in the above method, since the transmission power of the small cell is increased, there is a problem in that a downlink interference signal is given from the small cell to all wireless terminals existing in the vicinity of the small cell. Furthermore, increasing the transmission power of the small cell also increases the probability that an unspecified number of wireless terminals will connect to the small cell at the same time. This increases the number of users connected to the small cell, resulting in excessive user accommodation. It becomes a factor of decreasing the throughput in the small cell.

  The present invention has been made in view of this problem, and in a wireless communication system composed of a plurality of base stations having different cell radii for a wireless terminal, a plurality of neighboring base stations transmit uplink interference power to the base station. It is possible to specify a base station to which a wireless terminal that exerts the influence is connected, or, further, the own base station performs measurement control on the wireless terminal, so that only the wireless terminal that transmits uplink interference power can It is intended to provide a radio base station for a radio communication system for reducing uplink interference power by accommodating (changing a connection destination to the base station), a radio terminal connection control method in the radio communication system, and the like.

The present invention relates to a radio base station for a radio communication system composed of a plurality of radio base stations capable of communicating with each other and having different cell radii for a radio terminal, and measures received power from surrounding radio base stations. Further, the peripheral radio base station measurement function unit for detecting the system information and measurement result broadcasted by the peripheral radio base station, the system information and measurement result broadcasted by the peripheral radio base station, and the radio measured by the own radio base station By estimating the uplink transmission power of a wireless terminal in the vicinity of the own radio base station communicating with the neighboring radio base station from the uplink interference power received from the terminal, a plurality of neighboring radio base stations to the own radio base station A radio base station or the like for a radio communication system including an interference detection function unit that determines a radio base station to which a radio terminal serving as an interference source that exerts uplink interference power is connected.
In addition, the wireless communication apparatus further includes an interference control function unit that controls the wireless terminal that transmits the uplink interference power via the wireless base station to which the wireless terminal is connected to connect the wireless terminal to the own wireless base station. There are radio base stations.

  In the present invention, it is possible to efficiently identify a base station to which a wireless terminal that exerts uplink interference power from a plurality of neighboring base stations on its own base station is connected, or, only a wireless terminal that transmits uplink interference power is self-identified. Uplink interference power can be reduced by accommodating the base station (changing the connection destination to the base station).

It is a figure which shows an example of a structure of the radio | wireless communications system containing the radio base station by this invention. It is a figure which shows an example of a structure of the mobile communication network containing the radio | wireless communications system in Embodiment 1 of this invention. It is a figure which shows the communication state of the radio | wireless terminal in the radio | wireless communications system in Embodiment 1 of this invention. It is a figure which shows an example of the internal structure of the wireless base station in Embodiment 1 of this invention, and a connection with a peripheral device. It is a follow chart which shows an example of the interference electric power estimation information generation process in the wireless base station in Embodiment 1 of this invention. It is a figure which shows an example of the preservation | save table of the uplink interference power estimation information in Embodiment 1 of this invention. It is a figure which shows an example of the communication path establishment sequence between the cells in Embodiment 1 of this invention. It is a figure which shows an example of the sequence of the specific process of the uplink interference source (wireless terminal) in Embodiment 1 of this invention. It is a flowchart which shows an example of the interference measurement process of the uplink interference source (radio | wireless terminal) in Embodiment 1 of this invention. It is a figure which shows an example of the interference control parameter table stored in the memory | storage device in Embodiment 1 of this invention. It is a figure which shows an example of the information element contained in the cell measurement request | requirement and cell measurement report in Embodiment 1 of this invention. It is a figure which shows an example of the sequence of the interference control process of the uplink interference source (wireless terminal) in Embodiment 1 of this invention. It is a flowchart which shows an example of the interference control process with respect to the uplink interference source (wireless terminal) in Embodiment 1 of this invention. It is a figure which shows an example of the information element contained in the measurement parameter update request message in Embodiment 1 of this invention. It is a figure for demonstrating the improvement condition (effect) of the uplink communication quality state in Embodiment 1 of this invention. It is a figure which shows an example of the sequence of the identification of the interference apparatus (radio | wireless terminal) and interference control process in Embodiment 2 of this invention. It is a figure which shows an example of the information element contained in the measurement parameter update request message in Embodiment 2 of this invention. It is a flowchart which shows an example of the interference control determination process with respect to the uplink interference source (wireless terminal) in Embodiment 2 of this invention.

  In the present invention, a small base station having a small cell measures received power from a peripheral base station having a different cell radius, such as a macro base station having a macro cell. By estimating the uplink transmission power of a wireless terminal in the vicinity of a small base station that communicates with the neighboring base station from the measured uplink interference power, a wireless that exerts the uplink interference power on the small base station from a plurality of neighboring base stations It is possible to specify a base station to which a terminal is connected, or further, by realizing a means for the small base station to perform measurement control for the wireless terminal, only the wireless terminal that transmits uplink interference power can be Radio base station for radio communication system accommodated in station and reducing uplink interference power, radio terminal connection control in radio communication system To provide law and the like.

Hereinafter, a radio base station for a radio communication system according to the present invention, a radio terminal connection control method in the radio communication system, and the like will be described with reference to the drawings according to each embodiment. In each embodiment, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.
In the following, for convenience of explanation, a macro radio base station and a small radio base station are called a macro cell, a small cell (a radio base station is called a cell), and a cell of the radio base station is called a service area.

Embodiment 1 FIG.
FIG. 1 is a diagram showing an example of the configuration of a radio communication system including a (radio) base station according to the present invention. In FIG. 1, service areas 12a and 12b constructed by signals transmitted from macro cells 10a and 10b having different cell radii, and a service area 12c constructed by signals transmitted from the small cell 11 are hierarchically arranged. . The wireless terminal (terminal) 13a receives signals transmitted from the macro cell 10a, the wireless terminal (terminal) 13b receives signals transmitted from the macro cells 10a and 10b, and the wireless terminal 13c is a service capable of receiving signals transmitted from the small cell 11. It exists in the area 12c. The macro cells 10a and 10b and the small cell 11 are connected via a wired network 14a including a network device 14.

  FIG. 2 shows an example of the configuration of a mobile communication network including the radio communication system according to Embodiment 1 of the present invention. The mobile communication network in LTE / LTE-Advanced is an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) composed of a macro cell (eNB) 10 and a small cell (HeNB) 11, a radio terminal (UE) 13, and a call of UE 13 EPC (Evolved Packet Core) constructed from MME (Mobility Management Entity) 20 in charge of connection and mobility management, S-GW (Serving Gateway) 21 for transferring user data, and P-GW (Packet Data Network Gateway) 22 ) Exists.

  FIG. 3 shows a communication state of radio terminal 13a in the radio communication system according to Embodiment 1 of the present invention. The radio terminal 13a communicates with the macro cell 10a with the main signal power 30a, and at the same time gives the interference power 30b to the small cell 11. An area 12d is a boundary area between the macro cell 10a and the small cell 11, and the wireless terminal 13a is located in an area where both the macro cell 10a and the small cell 11 can communicate.

  FIG. 4 is a diagram showing an example of the internal configuration of the radio base station and the connection with peripheral devices in Embodiment 1 of the present invention. The small cell 11 is connected to the macro terminal 10a (10b) and the network device 14 via the wired network 14a, a wired interface (I / F) unit 100, and a wireless terminal 13c through the wireless lines (30a, 30b). A wireless interface (I / F) unit 101 that performs wireless communication, a modem unit 102 that performs wireless control for wireless connection, and a storage device 103 that stores internal information necessary for operation of the small cell 11.

Furthermore, as a function related to the present invention, a peripheral cell measurement function unit 104 having a function of detecting a plurality of cells existing in the vicinity and acquiring / analyzing measurement results in the cells and broadcasted system information, a wireless terminal The received power including the uplink interference power is measured from the network (if the uplink interference measurement and the neighboring cell measurement process can be performed at the same time, it may be performed by the neighboring cell measurement function unit 104), and interference is detected from a plurality of neighboring cells. The interference detection function unit 105 that identifies the cell to which the source wireless terminal 13a is connected, and whether or not the wireless terminal 13a can be connected to the small cell 11 when the interference detection function unit 105 determines that interference suppression is necessary. An interference control function unit 106 having a measurement control function for determining and connecting the wireless terminal 13a to the small cell 11 is provided.
Each radio base station including the macro cell has basically the same configuration as described above.

  FIG. 5 is a follow chart showing an example of interference power estimation information generation processing in the radio base station according to Embodiment 1 of the present invention. 6 shows a flow of processing for generating interference power estimation information used in the interference detection function unit 105 to identify a cell to which a radio terminal serving as an uplink interference source is connected. The neighboring cell measurement function unit 104 starts detection processing of cells existing in the vicinity of the own cell after the device (wireless base station) is activated and at a constant cycle. This process is performed by measuring the received power from the neighboring cell by measuring the received signal, and in order to detect the presence of the neighboring cell that matches or overlaps the frequency band used by the own cell, the downlink synchronization signal ( The reference signal is measured, and peripheral cells are specified (Primary / Secondary Synchronization Signal (first / second synchronization signal) acquisition and Physical Cell ID (physical layer cell ID) specification) are performed (S100).

  Furthermore, when a neighboring cell is detected (S100a), the neighboring cell measurement function unit 104 acquires system information (Master Information Block / System Information Block (master information block / system information block)) of each neighboring cell (S101). ). It also measures the received power in its own cell.

  Usually, each cell (10a, 10b, 11) in the wireless communication system exchanges system information and measurement information (including transmission / reception status such as transmission / reception power including transmission source and transmission destination) between the cells, Necessary information is stored in the storage device and updated as appropriate.

  Next, from the reference signal power value (Reference Signal Power) indicating the downlink transmission power value of the cell included in the detected system information of the neighboring cell and the downlink signal power (Reference Signal Received Power: RSRP) measured by the small cell 11 Then, a Pathloss calculation indicating the amount of propagation loss of downlink signal power from the cell is performed (S102).

  In order to estimate the uplink interference power transmitted by the radio terminal 13a, the estimated value of the uplink interference power from the radio terminal communicating with the detected cell is calculated based on the calculation method shown in the following formula (1) (S103).

Uplink interference power estimate =
min {P _CMAX , 10 log (number of RBs) + P _CELL + P _UE + α × Pathloss ± Δ} (1)
Where P _CMAX : UE (terminal) maximum transmission power P _CELL : Correction value notified by system information in a cell P _UE : Correction value notified for each UE α: Weight coefficient for Pathloss
Pathloss: Propagation loss amount obtained from the reference signal power value notified by the system information and the reference signal power measurement result Δ: Estimated effective range

The above formula (1) is a schematic formula for calculating the uplink transmission power value of the wireless terminal in LTE / LTE-Advanced. P _CMAX is the maximum transmission power determined by the capability of the wireless terminal 13a, and a system-specific value is used. The number of RBs (Resource Blocks) indicates the number of radio resources used during uplink transmission, and is 180 kHz per RB in LTE / LTE-Advanced.

P _CELL and α are correction values used in the cell, and are values that can be obtained when system information is acquired. The P _UE is a correction value individually notified to the wireless terminal. In the uplink interference power estimation information generation process, it is assumed that a value stored in the storage device 103 is used, but the neighboring cell passes through S1 / X2. The value obtained directly by (see FIG. 2) or the information obtained by the OAM (Operation, Administration and Maintenance) function may be used.
S1 is an interface (communication path) between the EPC MME 20 and S-GW 21 shown in FIG. 2 and the small cell 11 and the macro cell 10, and X2 is an interface (communication path) between the small cell 11 and the macro cell 10. is there.

  Δ is an effective range in consideration of fluctuations in the actually measured uplink interference power amount and a Pathloss measurement error caused by a difference in installation position between the wireless terminal 13a and the small cell 11, and the measurement result of the uplink interference power amount indicates the uplink interference It is determined that there is a radio terminal 13b serving as an uplink interference source under a cell that falls within the range of the power estimation value ± Δ.

That is, for example, P _CELL , α, and P _CMAX are obtained from system information to be acquired, P _UE and Δ are stored in advance in, for example, the storage device 103, the number of RBs is obtained from the measurement result of uplink interference power, and Pathloss is calculated Ask.

  An example of a storage table for uplink interference power estimation information generated in this process is shown in FIG. FIG. 6 shows a calculation result assuming a radio bandwidth defined by the LTE system: 20 MHz, and can be expanded by the use bandwidth. Each of RB (number) 1 to 100 includes an uplink interference power estimation value, a minimum estimation range (Min), and a maximum estimation range (Max), and is stored in, for example, the storage device 103. In addition, as a method for determining the estimated uplink interference power value shown in FIG. 6, a previously obtained table value stored in the storage device 103 may be directly used without using the calculation formula defined in the above formula (1). By performing the above processing on all the detected neighboring cells, it is possible to identify a cell that communicates in all the detected cells and is connected to a wireless terminal that exerts uplink interference power on the own cell (S104). .

  FIG. 7 shows a procedure for establishing a communication path between the small cell (HeNB) 11 and the macro cell (eNB) 10 (10a, 10b). (A) of FIG. 7 is an establishment procedure by the X2 interface for establishing a direct communication path between cells, and (b) is a communication path establishment procedure by the S1 interface via the MME 20 which is the network device 14. In (a), a communication path is established by X2 SETUP RQUEST (request) (200) and X2 SETUP RESPONSE (response) (201) between the small cell (HeNB) 11 and the macro cell (eNB) 10, and in (b) Communicate by S1 SETUP RQUEST (request) (300, 302) and S1 SETUP RESPONSE (response) (301, 303) between the MME 20, the small cell (HeNB) 11 and the macro cell (eNB) 10 (10a, 10b). Establish a road. By this procedure, the small cell (HeNB) 11 can communicate with surrounding cells including the macro cells (eNB) 10a and 10b. In the description of the present embodiment, the description will be made on the assumption of (a).

  Next, the flow of processing for identifying a radio terminal that is an uplink interference source in Embodiment 1 will be described using FIG. The interference detection function unit 105 of the small cell (HeNB) 11 performs an uplink interference power measurement process and measures the uplink interference power 30b (400).

  FIG. 9 shows a flow of this interference measurement process 400 that is the serving cell specifying process. In this case, the serving cell specifying process of the interference source (wireless terminal) is performed. The interference detection function unit 105 evaluates the presence of a wireless terminal connected to its own cell, and when there is a wireless terminal (UE) in communication (S200a), it measures the uplink interference power (S200). In this uplink interference power measurement process, measurement can be performed in units of RBs (Resource Blocks) that actually received uplink interference power.

  In order to evaluate whether or not uplink interference suppression is necessary for the measured uplink interference power amount, the uplink set in the interference control parameter table illustrated in FIG. Comparison is made with a threshold value a which is a determination parameter of strong interference power (S201).

Here, the interference control parameter table in FIG. 10 includes a threshold value a that is a determination parameter for uplink strong interference power, a threshold value b that is a determination parameter for uplink communication quality degradation of the own cell, and a threshold value c that is a parameter for determining whether or not a terminal can be accommodated. , The above-described parameter P _UE used for uplink interference power estimation calculation, the above-mentioned Δ that determines the effective range of uplink strong interference power, the offset addition value that is an offset value to be added to the measurement control parameter, and the lowest reception that can be accommodated in the own cell A minimum received signal level which is a signal level value.

  In this evaluation using the threshold value a, for example, when it is determined that the uplink interference power amount is equal to or greater than the threshold value a and the uplink interference power amount is strong interference power, the communication of the radio terminal 13c that is communicating in the own cell. Whether the quality is deteriorated is evaluated using the uplink BLER (Block Error Rate (block error rate)) of the wireless terminal 13c and the threshold value b which is a determination parameter of the uplink communication quality deterioration of the own cell (S202).

  If it is determined that the uplink communication quality of the wireless terminal 13c is deteriorated below the desired quality, that is, if the uplink BLER of the wireless terminal 13c is equal to or greater than the threshold value b, the amount of uplink interference power, the RB (Resource Block receiving the uplink interference power) ) From the number and the uplink interference power estimation value, the nearest neighbor cell of the wireless terminal 13c closest to the condition is determined (S203). Specifically, the uplink interference power amount is within the range of the estimation range (Min) to the estimation range (Max), and the uplink interference power is transmitted through a cell having the smallest error from the uplink interference power estimation value. The wireless terminal is determined as a connected cell.

  Returning to FIG. 8, the small cell (HeNB) 11 acquires the measurement result of the wireless terminal capable of detecting the PCI (Physical Cell ID) which is the cell identifier of the own cell, with respect to the specified macro cell (eNB) 10 a. The cell measurement request is notified (401).

  The macro cell (eNB) 10a that has received the cell measurement request returns a cell measurement response to the small cell (HeNB) 11, and then detects the small cell (HeNB) 11 from the wireless terminal group in communication with the own cell. Search is performed from the measurement information held inside the terminal 13a (402). When valid information has already been acquired from the wireless terminal group, the measurement result reported from the wireless terminal 13a to the small cell (HeNB) 11 and the measurement ID (Measurement ID) used for measurement control of the wireless terminal are stored in the cell. Notification is made in a measurement report (Measurement Result List) (404).

  As an option (Option), when there is no effective measurement information in the macro cell (eNB) 10a, a measurement request is started with respect to the wireless terminal group to obtain a measurement report (403). Even when valid measurement information is already held, the latest measurement information may be acquired again. The small cell (HeNB) 11 that has received the cell measurement report associates the acquired measurement information with the uplink interference power measurement information, stores it in the storage device 103, and updates it (405).

  FIG. 11 shows information necessary for the cell measurement request (401) and the cell measurement report (404) used in this processing. The cell measurement request requires a cell identifier (Physical Cell ID) that identifies the own cell to be measured by the terminal, and the cell measurement report including the measurement result of the wireless terminal includes the user identifier (UE) that performed the measurement. -SAP-ID: User Equipment Service Access Point ID), measurement information (Received Signal Power) on the cell with which the wireless terminal is communicating, and at least the measurement result of the own cell (Physical Cell ID (the interference cell) Cell identifier) and received signal power (measurement result of interfered cell of measurement terminal)).

  Next, interference control processing for connecting the radio terminal 13a serving as an uplink interference source to the small cell (HeNB) 11 will be described using FIG. The small cell (HeNB) 11 starts an interference control process in order to evaluate whether or not the radio terminal 13a can be accommodated in the own cell (500). The flow of the interference control process 500 is shown in FIG.

  When there is a radio terminal (UE) that has detected its own cell (S300a), the interference control function unit 106 acquires UE measurement information from the storage device 103 (S300). In order to determine whether or not it can be accommodated in the own cell, it is determined whether or not the terminal set in the terminal measurement result (reception power) that is the measurement result of the own cell and the interference control parameter information (FIG. 10) in the storage device 103 is acceptable. Comparison is made with a threshold value c which is a parameter to be performed (S301). In this evaluation, when it is determined that the mobile station can be accommodated in the own cell, an offset addition value to be added to the difference between the RSRP value that is the measurement result of the cell connected to the wireless terminal 13a and the measurement result RSRP of the own cell and the measurement control parameter (see FIG. 10) is used to calculate an offset value, and an offset value (measurement control parameter) is calculated so that the measurement result of the own cell exceeds the measurement result of the cell connected to the wireless terminal 13a (S302).

  The small cell (HeNB) 11 transmits to the macro cell (eNB) 10a a measurement parameter update request including a measurement control message for transmitting the calculated offset value to the radio terminal 13a to the cell (S303). That is, the UE measurement information is changed (event A3 measurement disclosure). The above process is performed on the measurement information of all UEs (S303a).

  Returning to FIG. 12, the macro cell (eNB) 10a that has received the measurement parameter update request specifies the radio terminal 13a from the UE identifier set in the message, and transparently transmits the measurement control message included in the message to the radio terminal 13a. (502). The wireless terminal 13a that has received the measurement control message performs neighboring cell measurement and event determination processing based on the newly received measurement event and offset value (503). Since the measurement control message uses the Measurement ID (identifier of measurement information that can be assigned to the wireless terminal 13a) value notified by the cell measurement report, it can be normally received and processed by the wireless terminal 13a.

  In the terminal accommodating process 504, since the small cell (HeNB) 11 calculates a value that satisfies the event determination condition as an offset value, the wireless terminal 13a satisfies the event determination condition, and the measurement report (Event A3, PCI = A ) (Handover request) is transmitted to the macro cell (eNB) 10a (504a). The macro cell (eNB) 10a that has received the measurement report performs handover determination (504b), and then between the macro cell (eNB) 10a and the small cell (HeNB) 11, and between the small cell (HeNB) 11 and the wireless terminal 13a. Communication is performed to perform a handover process (504c). Thereby, the radio | wireless terminal 13a used as an uplink interference source can be connected to the small cell (HeNB) 11. Then, the small cell (HeNB) 11 proceeds to interference measurement processing (505).

  FIG. 14 shows information necessary for the measurement parameter update request used for this processing. The measurement parameter update request includes a user identifier (UE-SAP-ID) that is a measurement control target and a measurement control message (Transparent Container) of the wireless terminal. With respect to the content of the measurement control message, the macro cell (eNB) 10a does not process, but only transmits it transparently to the radio terminal 13a. In FIG. 14, the event set in the measurement control message is described assuming a handover process based on EventA3 defined by LTE / LTE-Advanced.

  By performing the above processing, as shown in FIG. 15, from the uplink interference power measured by the small cell (HeNB) 11, a plurality of neighboring cells (macro cells (eNBs) 10a, 10b) to the small cell 11 Therefore, it is possible to identify the cell to which the radio terminal (UE) 13a that exerts the uplink interference power is connected, so that only the radio terminal 13a that transmits the uplink interference power is accommodated in the small cell 11 to reduce the uplink interference power. can do. In FIG. 15, 30 b ′ indicated by a solid line is main signal power, and 30 a ′ indicated by a broken line is interference power.

  In addition, although the case where the process was applied with respect to a macro cell and a small cell was shown in the said embodiment, you may apply between small cells from which a cell radius differs like indoor hierarchical cell arrangement | positioning.

Embodiment 2. FIG.
Hereinafter, the radio base station and the like according to the second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in the operation after the interference measurement process 400 in FIG. FIG. 16 illustrates the sequence of the process of identifying the radio terminal that is the uplink interference source and the interference control process that connects the radio terminal 13a that is the uplink interference source to the small cell (HeNB) 11 in the second embodiment.

  The process of measuring the uplink interference power performed by the interference detection function unit 105 and the process of determining the cell to which the wireless terminal transmitting the uplink interference power is connected are the same as in Embodiment 1 (400).

  The small cell (HeNB) 11 measures the minimum received signal level that can be accommodated in the interference control parameter table in the storage device 103 for the identified macro cell (eNB) 10a to accommodate in the own cell. A parameter change request is set and transmitted (601). FIG. 18 shows information necessary for the measurement parameter change request used for this processing. In the measurement parameter change request, a cell identifier (Physical Cell ID) that identifies the subject cell to be measured, a determination threshold that can be accommodated in the subject cell, the minimum received signal level of the RSRP value that is the measurement result of the wireless terminal 13a, and The maximum number of UEs allowable as a measurement control target is included.

  The macro cell (eNB) 10a that has received the measurement parameter change request searches from the measurement information that internally holds the wireless terminal 13a that detects the small cell (HeNB) 11 from the wireless terminal group in communication with the own cell (602). ). When valid measurement information has already been acquired from the wireless terminal group, the measurement information may be used for interference control processing. In a situation where there is no effective measurement information, a measurement request is started to the wireless terminal group (13) to acquire measurement information (report) (603).

  The interference control function unit 106 of the macro cell (eNB) 10a that has acquired the measurement information from the wireless terminal group (13) starts the interference control processing 604 in order to determine the presence of a wireless terminal that can be connected to the small cell (HeNB) 11. To do.

  The flow of the interference control process (604) is shown in FIG. If there is a wireless terminal that has detected the interfered cell (S400a), the interference control function unit 106 acquires UE measurement information from the storage device 103 (S400). In order to evaluate whether accommodation in the small cell (HeNB) 11 is possible, the minimum power notified by the received power of the small cell (HeNB) 11 that is an interfered cell included in the UE measurement information and the measurement parameter change request The received power level is compared (S401).

  In this evaluation, when it is determined that the small cell (HeNB) 11 can be accommodated, an event determination threshold value that is less than the received power of the small cell (HeNB) 11 measured by the wireless terminal 13a is calculated (S402). That is, the UE measurement information is changed (measurement disclosure of Event A4). The above processing is performed up to the maximum number of UEs that have detected the interfered cell (S403a).

  Returning to FIG. 16, the macro cell (eNB) 10a transmits a measurement control message in which the calculated event determination threshold is set to the wireless terminal 13a (608). The wireless terminal 13a that has received the measurement control message performs neighboring cell measurement and event determination processing based on the newly received measurement event and event determination threshold (609). Since the macro cell (eNB) 10a calculates a value that satisfies an event determination condition that can be handed over to the small cell (HeNB) 11 as an event determination threshold, the wireless terminal 13a satisfies the event determination condition, and the measurement report (handover Request) is transmitted to the macro cell (eNB) 10a, whereby the radio terminal 13a serving as an uplink interference source can be connected to the small cell (HeNB) 11. In FIG. 16, the event set in the measurement control message is described assuming a handover process based on Event A4 defined by LTE / LTE-Advanced.

Embodiment 3 FIG.
Further, in the radio base station or the like in the third embodiment of the present invention, Δ that defines the estimated effective range is set to a small cell (HeNB) 11 in the interference power estimation information generation process (see FIG. 5) described in the first embodiment. It is determined by the amount of propagation loss that is the difference between the received power value of the small cell (HeNB) 11 received from the wireless terminal 13c connected to the mobile terminal and the transmission power value of the own cell.

As a result, the propagation loss amount up to the boundary value of the communication area with the small cell (HeNB) 11 where the transmission power of the own cell actually reaches can be set as the effective range of the estimation information. Thus, it is possible to improve the estimation accuracy of the wireless terminal that is an uplink interference source that can be accommodated in the mobile terminal. Furthermore, by making the mobility between cells continue to be connected to the small cell (HeNB) 11, it is possible to set a communication limit point with the small cell (HeNB) 11 as an estimated effective range.
Other processes are the same as those described in the first embodiment.

Embodiment 4 FIG.
Further, in the radio base station or the like according to the third embodiment of the present invention, the radio terminal 13a serving as an uplink interference source is connected to the small cell (HeNB) 11 in the interference control process described in the first or second embodiment. Threshold value that is a parameter for determining whether or not the wireless terminal can be accommodated as described in Embodiment 1, which is registered in the storage device 103 as an interference control parameter when connection to the small cell (HeNB) 11 fails after processing for c, or the lowest received signal level value that can be accommodated in the own cell described in the second embodiment is corrected (+1 [dB] in a direction in which judgment is more severe).

Thereby, it becomes possible to improve the accuracy of the reference for determining whether or not the small cell (HeNB) 11 can be accommodated.
Other processes are the same as those described in the first and second embodiments.

  The present invention is not limited to the above-described embodiments, and it goes without saying that all possible combinations thereof are included.

  As described above, in a wireless communication network having different cell radii, by efficiently identifying a terminal as an interference source, and further accommodating the wireless terminal in a base station with a small area radius as an interfered source, Interference between different cells can be reduced.

  10, 10a, 10b Macro cell (eNB), 11 Small cell (HeNB), 12a-12c Service area, 12d area, 13a-13c Wireless terminal (UE), 14 Network device, 14a Wired network, 20 MME, 21 S-GW 22 P-GW, 100 wired I / F unit, 101 wireless I / F unit, 102 modem unit, 103 storage device, 104 peripheral cell measurement function unit, 105 interference detection function unit, 106 interference control function unit.

Claims (7)

A radio base station for a radio communication system comprising a plurality of radio base stations capable of communicating with each other with different cell radii for a radio terminal,
Measuring the received power from the surrounding radio base station, and further detecting the system information and measurement results notified by the surrounding radio base station, the surrounding radio base station measurement function unit,
From the system information broadcast by the neighboring radio base station, the measurement result, and the uplink interference power received from the radio terminal measured by the own radio base station, the uplink of the radio terminal near the own radio base station communicating with the neighboring radio base station An interference detection function unit that determines a radio base station to which a radio terminal that is an interference source that exerts uplink interference power from a plurality of neighboring radio base stations to an own radio base station by estimating transmission power, and
A wireless base station for a wireless communication system.   The radio for the radio communication system according to claim 1, wherein the interference detection function unit determines a radio base station to which a radio terminal serving as an interference source is connected based on measurement information of a radio terminal connected to the radio base station. base station.   Claims further comprising an interference control function unit for controlling a wireless terminal that transmits the uplink interference power via a connection-destination wireless base station of the wireless terminal to connect the connection-destination wireless base station to the own wireless base station. Item 3. A radio base station for the radio communication system according to Item 1 or 2.   The said interference control function part makes the radio base station of the connection destination of the radio | wireless terminal used as an interference source perform the interference control which connects this radio | wireless terminal to an own radio | wireless base station instead of an own radio | wireless base station. A radio base station for the radio communication system according to claim 1.   5. The wireless communication system according to claim 3, wherein the interference control function unit changes a parameter for determining whether or not the wireless terminal can be accommodated when connection of a wireless terminal to the wireless base station fails. For wireless base stations. A wireless terminal connection control method in a wireless communication system comprising a plurality of wireless base stations capable of communicating with each other with different cell radii for the wireless terminal,
A step in which the radio base station measures received power from the neighboring radio base station , and further detects system information and measurement results broadcast by the neighboring radio base station ;
Uplink transmission of a radio terminal in the vicinity of the own radio base station communicating with the neighboring radio base station from the system information broadcast by the neighboring radio base station of the radio base station, the measurement result, and the uplink interference power measured by the own radio base station Determining a radio base station to which a radio terminal serving as an interference source exerting an uplink interference power from a plurality of neighboring radio base stations to the own radio base station by estimating power is connected;
A wireless terminal connection control method in a wireless communication system comprising:   7. The method of claim 6, further comprising a step of connecting the wireless terminal that transmits the uplink interference power via the wireless base station that is the connection destination of the wireless terminal to the wireless base station from the wireless base station that is the connection destination. A wireless terminal connection control method in the described wireless communication system.

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