JP2011082944A - Radio communication system, network-side device, small-cell base station, transmission power control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the drop of a communication speed of a wireless terminal connected to a large-cell base station even when the number of small-cell base stations in a large cell is changed. <P>SOLUTION: A large-cell base station 100 that forms a large cell includes: an upper-limit value-determining unit 124 that determines an upper-limit value I<SP>cap</SP>for the amount of interference received by the large-cell base station 100 from one wireless terminal, on the basis of a tolerance value I<SP>total</SP>for the total amount of interference received by the large-cell base station 100 from wireless terminals connected to small-cell base stations within the large cell, and the number of small-cell base stations within the large cell; and a wired communication unit 140 that transmits, to the small-cell base stations, upper-limit value information indicating the upper-limit value I<SP>cap</SP>determined by the upper-limit value-determining unit 124. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio communication system, a network side device, a small cell base station, and a transmission power control method for controlling uplink transmission power of a radio terminal connected to a small cell base station.

  In recent years, a small cell base station, which is a small base station that forms a small cell that is a communication area with a radius of several meters to several tens of meters and can be installed indoors, has attracted attention. By installing a small cell base station, traffic distribution of a large cell base station that forms a large cell, which is a communication area with a radius of about several hundred meters, and coverage of a dead zone in the large cell can be realized.

  For the large cell base station, the communication carrier decides the installation location in consideration of inter-cell interference, but the user can install the small cell base station at an arbitrary location. For this reason, a small cell base station may be installed in the large cell which a large cell base station forms.

  When a wireless terminal connected to a small cell base station in this situation (hereinafter referred to as “small cell terminal” as appropriate) uses the same frequency band for communication as a wireless terminal connected to the large cell base station, When the base station receives interference from the small cell terminal, the communication speed of the wireless terminal connected to the large cell base station decreases.

  In order to suppress interference from a small cell terminal to a large cell base station, the following uplink transmission power control method has been proposed (see Non-Patent Document 1). In the method described in Non-Patent Document 1, an upper limit value of the amount of interference from a small cell terminal to a large cell base station is incorporated in the small cell base station. The small cell base station determines the maximum value of the transmission power of the small cell terminal according to the upper limit value and the propagation loss from the small cell terminal to the large cell base station, and does not exceed the determined maximum value. Control transmission power of small cell terminals.

3GPP TR25.967, “Home Node B Radio Frequency (RF) Requirements (FDD)”, Section 7.3, “Control of HNB uplink interference”, March 2009

  As described above, the user can arbitrarily install the small cell base station, and the number of small cell base stations in the large cell changes.

  However, the method described in Non-Patent Document 1 does not consider the case where the number of small cell base stations in a large cell changes, and thus the following problem occurs. Specifically, when the number of small cell base stations in a large cell increases, the total amount of interference from the small cell terminal to the large cell base station increases, and the communication speed of the wireless terminal connected to the large cell base station greatly decreases. There was a problem.

  Therefore, the present invention provides a wireless communication system, a network side device, and a network side device capable of suppressing a decrease in communication speed of a wireless terminal connected to the large cell base station even when the number of small cell base stations in the large cell changes. It is an object to provide a small cell base station and a transmission power control method.

In order to solve the above-described problems, the present invention has the following features. First, the first feature of the present invention is that a large cell base station (large cell base station 100) and a small cell (small cell SC) smaller than a large cell (large cell LC) formed by the large cell base station. And a wireless terminal (wireless terminal 300) connected to the small cell base station, and a wireless communication system (wireless communication system 1) compatible with LTE. Then, the network side device (upper device 500) consisting of at least one of the large cell base station or the upper device of the large cell base station has an upper limit value of an interference amount received by the large cell base station from the wireless terminal ( A transmission unit (wired communication unit 140) that transmits upper limit value information indicating an upper limit value I ^cap ) to the small cell base station, and the small cell base station receives the upper limit value information from the network side device. Department (Yes A communication unit 240), so as not to exceed the maximum value of the transmission power determined based on the upper limit value information received by the reception unit (the maximum value p ^MAX), transmission power control for controlling transmission power of said wireless terminal And a transmission power control unit 223. Here, the propagation loss means a combination of distance attenuation, shadowing loss, and feature passing loss.

  A second feature of the present invention relates to the first feature of the present invention, wherein the upper limit value determination unit includes the small cell base having wireless terminals connected in all the small cell base stations in the large cell. The gist is to determine, as the upper limit value, a result obtained by dividing the allowable value of the total interference amount by the number of stations.

  A third feature of the present invention relates to the first feature or the second feature of the present invention, wherein the higher-level apparatus receives information on an installation status of the small cell base station and information on a communication status of the small cell base station. The network side device includes an acquisition unit (acquisition unit 121) that acquires information related to the number of the small cell base stations in the large cell using information managed by the host device. This is the gist.

  A fourth feature of the present invention relates to any one of the first to third features of the present invention, wherein the large cell base station measures an interference measurement unit (interference unit) that measures the total amount of interference received by the large cell base station. And the network side device includes an allowable value determining unit (allowable value determining unit 123) that determines an allowable value of the total interference amount based on the measurement value obtained by the interference measuring unit. This is the gist.

  A fifth feature of the present invention is according to the first feature of the present invention, wherein the upper limit value determining unit includes the number of all the small cell base stations in the large cell, and the number of all the small cell base stations in the large cell. The gist is to determine, as the upper limit value, a result obtained by dividing an allowable value of the total interference amount by a multiplication result with a coefficient representing a ratio of the small cell base stations having wireless terminals connected to the small cell base station. To do.

  A sixth feature of the present invention relates to any one of the first to fifth features of the present invention, wherein the small cell base station transmits the propagation loss value to the network side device, and the network side device The propagation loss value is received from the small cell base station, and the upper limit value determining unit includes an allowable value of the total interference amount, the number of the small cell base stations in the large cell, and the small cell base station. The gist is to determine the upper limit value based on the propagation loss value received from.

  A seventh feature of the present invention is that the small cell base station controls transmission power of a wireless terminal connected to a small cell base station that forms a small cell smaller than a large cell formed by the large cell base station. In the wireless communication system supporting the above, an upper limit of the amount of interference that the large cell base station receives from the wireless terminal, which is a network side device composed of at least one of the large cell base station or a higher-level device of the large cell base station The gist of the present invention is to include a transmitter that transmits upper value information indicating a value to the small cell base station.

  An eighth feature of the present invention is a small cell base station that forms a small cell smaller than a large cell formed by a large cell base station in a radio communication system compatible with LTE, the large cell base station, Alternatively, a receiving unit that receives upper limit value information indicating an upper limit value of the amount of interference received by the large cell base station from the wireless terminal from a network side device that is composed of at least one of the higher-level devices of the large cell base station, and the receiving unit And a transmission power control unit that controls transmission power of the wireless terminal so as not to exceed a maximum value of transmission power determined based on the received upper limit value information.

  According to a ninth aspect of the present invention, there is provided a small cell base station that forms a small cell smaller than a large cell formed by the large cell base station. A transmission power control method for controlling transmission power of a wireless terminal to be connected, wherein a network side device comprising at least one of the large cell base station or an upper device of the large cell base station is connected to the large cell from the wireless terminal. Transmitting the upper limit value information indicating the upper limit value of the interference amount received by the base station to the small cell base station; receiving the upper limit value information from the network side device; and The cell base station comprising a step of controlling the transmission power of the radio terminal so as not to exceed a maximum value of the transmission power determined based on the received upper limit value information. And effect.

  According to the present invention, even when the number of small cell base stations in a large cell changes, a wireless communication system, a network side device that can suppress a decrease in communication speed of a wireless terminal connected to the large cell base station, A small cell base station and a transmission power control method can be provided.

It is a schematic block diagram of the radio | wireless communications system which concerns on 1st Embodiment and 2nd Embodiment of this invention. It is a block diagram which shows the structure of the large cell base station which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the small cell base station which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the high-order apparatus which concerns on 1st Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 1 which concerns on 1st Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 2 which concerns on 1st Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 3 which concerns on 1st Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 4 which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the high-order apparatus which concerns on 2nd Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 1 which concerns on 2nd Embodiment of this invention. It is a sequence diagram which shows the operation | movement pattern 2 which concerns on 2nd Embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) First Embodiment In the following first embodiment, (1.1) schematic configuration of radio communication system, (1.2) detailed configuration of radio communication system, (1.3) operation of radio communication system (1.4) The effect of the first embodiment will be described.

(1.1) Schematic Configuration of Radio Communication System FIG. 1 is a schematic configuration diagram of a radio communication system 1 according to the first embodiment. The wireless communication system 1 is, for example, a configuration based on LTE Release 9 which is a 3.9th generation (3.9G) mobile phone system, or LTE-Advanced which is positioned as a 4th generation (4G) mobile phone system. It has a configuration based on.

  As shown in FIG. 1, the wireless communication system 1 includes a large cell base station 100 that forms a large cell LC and small cell base stations 200a to 200c that form small cells SC1 to SC3, respectively. However, since the small cell base stations are arbitrarily installed by the user, the number of small cell base stations of the large cell LC is not limited to the number shown in FIG. 1 and changes with the passage of time.

  The large cell LC is a communication area having a radius of about several hundred meters, for example, and is called a macro cell. Each of the small cells SC <b> 1 to SC <b> 3 is a communication area having a radius of, for example, about several meters to several tens of meters, and is called a femto cell. In LTE and LTE-Advanced, the small cell base station is referred to as a home eNodeB (HeNB), and the large cell base station is referred to as a macro eNodeB (MeNB).

  A radio terminal 300a is connected to the small cell base station 200a, a radio terminal 300b is connected to the small cell base station 200b, and a radio terminal 300c is connected to the small cell base station 200c. A radio terminal 400 is connected to the large cell base station 100. In the first embodiment, the large cell base station 100 constitutes a network side device.

  The small cell base station 200a controls the transmission power of the radio terminal 300a, the small cell base station 200b controls the transmission power of the radio terminal 300b, and the small cell base station 200c controls the transmission power of the radio terminal 300c.

  In the following, when the small cells SC1 to SC3 are not distinguished, they are simply referred to as “small cell SC”, and when the small cells base stations 200a to 200c are not distinguished, they are simply referred to as “small cell base station 200”. When 300a to 300c are not distinguished, they are simply referred to as “wireless terminal 300”.

  The small cell base station 200 is configured to be small enough to be installed in an arbitrary place (specifically, indoors) by the user. The small cell base station 200 is installed in the large cell LC for the purpose of distributing the traffic of the large cell base station 300 and covering the dead zone in the large cell LC.

  The small cell base station 200 and the large cell base station 300 are connected to the core network 10 which is a wired communication network. The core network 10 is provided by a telecommunications carrier and includes a router or the like not shown.

  A host device 500 is connected to the core network 10. The host device 500 is a device that can transmit and receive control signals to and from the large cell base station 100 and the small cell base station 200. The host apparatus 500 manages information on the installation status of the small cell base station 200 and information on the communication status of the large cell base station 100 and the small cell base station 200. In LTE and LTE-Advanced, the host device 500 corresponds to an MME (mobility management entity) or a serving gateway.

  When the small cell base station 200 and the radio terminal 300 use the same frequency band for communication as the large cell base station 100 and the radio terminal 400, the radio signal transmitted by the radio terminal 300 interferes with the large cell base station 100. give. In the example of FIG. 1, the radio signal transmitted by the radio terminal 300 interferes with the large cell base station 100. As a result, the uplink communication speed between the radio terminal 400 and the large cell base station 100 decreases.

  The small cell base station 200 controls the transmission power of the radio terminal 300 by a method described later so that the total interference received by the large cell base station 100 from the radio terminal 300 is equal to or less than a predetermined amount.

(1.2) Detailed Configuration of Radio Communication System Next, a detailed configuration of the radio communication system 1 will be described.

(1.2.1) Configuration of Large Cell Base Station FIG. 2 is a block diagram showing the configuration of the large cell base station 100.

  As illustrated in FIG. 2, the large cell base station 100 includes an antenna unit 101, a wireless communication unit 110, a control unit 120, a storage unit 130, and a wired communication unit 140.

  The wireless communication unit 110 is configured using, for example, a radio frequency (RF) circuit, a baseband (BB) circuit, and the like, and transmits and receives wireless signals to and from the wireless terminal 400. In addition, the wireless communication unit 110 performs encoding and modulation of a transmission signal and demodulation and decoding of a reception signal.

  The control unit 120 is configured using, for example, a CPU, and controls various functions included in the large cell base station 100. The storage unit 130 is configured using a memory, for example, and stores various types of information used for controlling the large cell base station 100 and the like. The wired communication unit 140 communicates with other large cell base stations or small cell base stations 200 via the core network 10.

  The control unit 120 includes an acquisition unit 121 and an upper limit determination unit 124.

The acquisition unit 121 includes an allowable value of the total interference amount received by the large cell base station 100 from the radio terminal 300 (hereinafter, allowable value I ^total ) and the number of small cell base stations 200 in the large cell LC (hereinafter, small cell base). Station number). When the allowable value I ^total is fixed and stored in the storage unit 130, the acquisition unit 121 acquires the allowable value I ^total from the storage unit 130. The acquisition unit 121 acquires the number of small cell base stations using a list generated by the higher-level device 500. Details of the list will be described later.

  Here, the interference amount is an interference amount in resource block (RB) units, which are radio resource allocation units. As the amount of interference, IoT (Interference over Thermal) which is a ratio of interference power and noise power can be used.

The control unit 120 may include an interference measurement unit 122 and an allowable value determination unit 123 in order to make the allowable value I ^total variable. The interference measurement unit 122 measures the total amount of interference received by the large cell base station 100. The allowable value determination unit 123 determines the allowable value I ^total based on the measurement value obtained by the interference measurement unit 122. Details of such a method will be described later.

The upper limit determination unit 124 determines an upper limit value (hereinafter, upper limit value I ^cap ) of the amount of interference received by the large cell base station 100 from one radio terminal 300 based on the allowable value I ^total and the number of small cell base stations. To do. Details of the determination method of the upper limit value I ^cap will be described later.

The wired communication unit 140 transmits upper limit value information indicating the upper limit value I ^cap determined by the upper limit value determination unit 124 to the small cell base station 200. The upper limit value information means the upper limit value I ^cap or its index. In the following ^description , the upper limit value I ^cap is used as it is as upper limit value information. In the first embodiment, the wired communication unit 140 corresponds to a transmission unit that transmits upper limit information to the small cell base station 200.

(1.2.2) Configuration of Small Cell Base Station FIG. 3 is a block diagram showing the configuration of the small cell base station 200.

  As illustrated in FIG. 3, the small cell base station 200 includes an antenna unit 201, a wireless communication unit 210, a control unit 220, a storage unit 230, and a wired communication unit 240.

  The wireless communication unit 210 is configured using, for example, a radio frequency (RF) circuit, a baseband (BB) circuit, or the like, and transmits and receives wireless signals to and from the wireless terminal 300. In addition, the wireless communication unit 210 performs encoding and modulation of a transmission signal and demodulation and decoding of a reception signal.

  The control unit 220 is configured using a CPU, for example, and controls various functions provided in the small cell base station 200. The storage unit 230 is configured using a memory, for example, and stores various types of information used for controlling the small cell base station 200 and the like. The wired communication unit 240 communicates with the large cell base station 100 via the core network 10. In the first embodiment, the wired communication unit 240 corresponds to a receiving unit that receives upper limit information.

  The control unit 220 includes a propagation loss estimation unit 221, a maximum value determination unit 222, and a transmission power control unit 223.

The propagation loss estimation unit 221 estimates a propagation loss value PL _UP indicating a propagation loss from the radio terminal 300 to the large cell base station 100. Details of the method for estimating the propagation loss value PL _UP will be described later.

The maximum value determination unit 222 determines the transmission power of the wireless terminal 300 based on the upper limit value information (upper limit value I ^cap ) received by the wired communication unit 240 and the propagation loss value PL _UP estimated by the propagation loss estimation unit 221. The maximum value p ^MAX is determined. Here, the maximum value p ^MAX is a maximum value of transmission power in resource block (RB) units. Details of the determination method of the maximum value p ^MAX will be described later.

The transmission power control unit 223 controls the transmission power of the radio terminal 300 so as not to exceed the maximum value p ^MAX determined by the maximum value determination unit. Specifically, the transmission power control unit 223 determines the transmission power of the radio terminal 300 so as not to exceed the maximum value ^pMAX , and generates a notification of the determined transmission power. The wireless communication unit 210 transmits a transmission power notification to the wireless terminal 300.

  Note that the wireless terminal 300 that has received the transmission power notification transmits a wireless signal with the transmission power in accordance with the notification.

(1.2.3) Configuration of Host Device FIG. 4 is a block diagram showing the configuration of the host device 500.

  As illustrated in FIG. 4, the upper device 500 includes a wired communication unit 510, a control unit 520, and a storage unit 530.

  The wired communication unit 510 performs communication with the large cell base station 100 and the small cell base station 200 via the core network 10. The control unit 520 is configured using, for example, a CPU, and controls various functions that the host device 500 has. The storage unit 530 is configured using, for example, a memory, and stores various types of information used for controlling the host device 500 and the like.

  The storage unit 530 stores information on the installation status of the small cell base station 200 and information on the communication status of the small cell base station 200. The information on the installation status of the small cell base station 200 includes information on the number of small cell base stations 200 in the large cell LC. The information on the communication status of the small cell base station 200 includes information for identifying the small cell base station 200 where the connected wireless terminal 300 is present among all the small cell base stations 200 in the large cell LC.

  The control unit 520 includes an information management unit 521 and a list generation unit 522.

  The information management unit 521 manages information stored in the storage unit 530. Specifically, the information management unit 521 creates information stored in the storage unit 530 and updates information stored in the storage unit 530. Information stored in the storage unit 530 is periodically updated.

  Based on the communication status information of the small cell base station 200, the list generation unit 522 is information on the small cell base station 200 in which the connected wireless terminal 300 is present among all the small cell base stations 200 in the large cell LC. Generate a list containing. Alternatively, in a case where information on the communication status cannot be obtained, the list generation unit 522 uses the information on the installation status of the small cell base station 200 to obtain information on all the small cell base stations 200 in the large cell LC. Generate a list containing. The wired communication unit 510 transmits the generated list to the large cell base station 100.

  The information management unit 521 and the list generation unit 522 manage and update the list by the following method, for example. Specifically, (a) the cell ID of the small cell base station 200 adjacent to the large cell base station 100 is notified from the large cell base station 100 to the host apparatus 500, or (b) the small cell base station The information management unit 521 and the list generation unit 522 manage the list by any method in which the cell ID of the large cell base station 100 adjacent to the 200 is notified from the small cell base station 200 to the host apparatus 500. The large cell base station 100 and the small cell base station 200 detect which cell (base station) is adjacent using a measurement report from a wireless terminal in order to enable handover. Maintains a list of base stations. Since the host device 500 is involved in the handover, the host device 500 can know from which cell to which cell the handover has occurred. Therefore, it is possible to maintain a list of which cell is adjacent to which cell after the handover occurs. Note that the host device 500 can grasp the small cell base station to which the wireless terminal is connected by measuring the communication status of the small cell base station 200.

(1.3) Operation of Radio Communication System Next, operation patterns 1 to 4 of the radio communication system 1 according to the first embodiment will be described. The operation patterns 1 to 4 are not limited to being performed individually, but can be performed by switching as appropriate.

(1.3.1) Operation pattern 1
FIG. 5 is a sequence diagram showing the operation pattern 1.

The operation includes an operation (steps S11 to S15) for estimating the propagation loss value PL _UP and other operations (steps S111 to S118). The operations in steps S111 to S118 are executed periodically. The operations in steps S11 to S15 are executed periodically or when a trigger is generated.

  First, steps S111 to S118 will be described.

  In step S111, the list generation unit 522 of the higher-level device 500 determines whether the connected wireless terminal 300 among all the small cell base stations 200 in the large cell LC is based on the communication status information of the small cell base station 200. A list L including information of a certain small cell base station 200 is generated.

  In step S <b> 112, the wired communication unit 510 of the higher-level device 500 transmits the list L generated by the list generation unit 522 to the large cell base station 100. The wired communication unit 140 of the large cell base station 100 receives the list L via the core network 10. The storage unit 130 of the large cell base station 100 stores the list L (step S113).

In step S114, the upper limit determination unit 124 of the large cell base station 100 sets the upper limit I ^cap based on the allowable value I ^total and the number of small cell base stations (that is, the number of elements in the list L). Decide every time. Here, as shown in Expression (1), a method is used in which an allowable value I ^total is equally divided by the number of small cell base stations (number of elements in the list L) as an upper limit value I ^cap .

In this manner, the upper limit value I ^cap of the interference power density from one radio terminal 300 is determined for each small cell base station 200 present in the large cell LC.

In step S115, the wired communication unit 140 of the large cell base station 100 transmits information on the upper limit value I ^cap determined by the upper limit value determination unit 124 to each small cell base station 200 via the core network 10. The wired communication unit 240 of the small cell base station 200 receives the information on the upper limit value I ^cap via the core network 10.

In step S116, the maximum value determination unit 222 of the small cell base station 200 receives the information on the upper limit value I ^cap received by the wired communication unit 240 and the propagation loss value PL _UP (path loss from the wireless terminal 300 to the small cell base station 200). : A combination of distance attenuation, shadow ring loss, and feature passage loss), the maximum value p ^MAX of the transmission power density of the wireless terminal 300 is determined according to the following equation (2).

In step S117, the transmission power control unit 223 of the small cell base station 200 defines the transmission power of the wireless terminal 300 as the transmission power density is less than the maximum value p ^MAX.

  In step S <b> 118, the radio communication unit 210 of the small cell base station 200 transmits the transmission power notification obtained by the transmission power control unit 223 to the radio terminal 300. When receiving the notification, the radio terminal 300 transmits a radio signal to the small cell base station 200 with transmission power according to the notification.

  Next, steps S11 to S15 will be described.

  The radio communication unit 110 of the large cell base station 100 periodically transmits a reference signal (Referennce Signal: RS) (step S11). When receiving the reference signal RS, the radio terminal 300 measures a received signal strength (Reference Signal received powe: RSRP) of the reference signal RS (step S12), and notifies the small cell base station 200 of the connection destination (step S12). S12). The radio communication unit 210 of the small cell base station 200 receives RSRP from the radio terminal 300.

In step S14, the propagation loss estimation unit 221 of the small cell base station 200 transmits the reference signal transmission power of the large cell base station 100 and the RSRP notified from the wireless terminal 300 to the wireless terminal 300 from the large cell base station 100. the propagation loss value PL _DOWN of calculating according to the following equation (3).

Propagation loss value PL _DOWN = Transmission power of reference signal of large cell base station 100 / RSRP (3)
Here, in the small cell base station 200, it is assumed that the transmission power of the reference signal of the large cell base station 100 is known, but if it is unknown, the maximum value of the transmission power of the reference signal of the large cell base station 100 is set. Use.

In step S15, the propagation loss estimation unit 221 of the small cell base station 200 estimates a propagation loss value PL _UP from the radio terminal 300 to the large cell base station 100. The propagation loss value PL _DOWN obtained in step S14 is a downlink propagation loss from the large cell base station 100 to the radio terminal 300. When the frequency bands used for uplink and downlink are close, the uplink propagation loss value PL _UP is approximated by the downlink propagation loss value PL _DOWN . When the frequency band to be used is greatly different, the uplink propagation loss value PL _UP is obtained by correcting the downlink propagation loss value PL _DOWN .

(1.3.2) Operation pattern 2
FIG. 6 is a sequence diagram showing the operation pattern 2. In operation pattern 2, an operation different from operation pattern 1 will be described. The operation pattern 1 is an operation in the case where the allowable value I ^total is fixed. However, in the operation pattern 2, the allowable value I ^total is variable.

  In step S201, the interference measurement unit 122 of the large cell base station 100 measures the total amount of interference received by the large cell base station 100. Here, the total amount of interference includes not only the amount of interference from the radio terminal 300 but also the amount of interference from other interference sources.

In step S202, the allowable value determining unit 123 of the large cell base station 100 determines the allowable value I ^total based on the total interference amount measured by the interference measuring unit 122. For example, the allowable value determining unit 123 sets a part (x%) of the total interference received by the large cell base station 100 as the allowable value I ^total .

  Subsequent operations are the same as those in the operation pattern 1.

(1.3.3) Operation pattern 3
FIG. 7 is a sequence diagram showing the operation pattern 3. In the operation pattern 3, operations different from the operation pattern 1 will be described. The operation pattern 3 is an operation when only the list L ′ of the small cell base stations 200 in the large cell LC can be obtained regardless of whether or not there is a connected wireless terminal 300.

  In step S301, the list generation unit 522 of the higher-level device 500 generates a list L ′ including information on all the small cell base stations 200 in the large cell LC based on the information on the installation status of the small cell base station 200. .

  In step S <b> 302, the wired communication unit 510 of the higher-level device 500 transmits the list L ′ generated by the list generation unit 522 to the large cell base station 100. The wired communication unit 140 of the large cell base station 100 receives the list L ′ via the core network 10. The storage unit 130 of the large cell base station 100 stores the list L ′ (step S303).

In step S304, the upper limit determination unit 124 of the large cell base station 100 sets the upper limit I ^cap based on the allowable value I ^total and the number of small cell base stations (that is, the number of elements in the list L ′). Determine every 200. Here, in Expression (1), “number of elements in list L” is replaced with “k × number of elements in list L ′”. k is a coefficient representing the proportion of small cell base stations having connected wireless terminals among the small cell base stations in the list L ′. If an accurate k value cannot be obtained, the value determined by the system is used.

  Subsequent operations are the same as those in the operation pattern 1.

(1.3.4) Operation pattern 4
FIG. 8 is a sequence diagram showing the operation pattern 4. In the operation pattern 4, an operation different from the operation pattern 1 will be described.

When determining the maximum value p ^MAX as in equation (2), as the wireless terminal 300 is further the farther from the large cell base station 100, the maximum value p ^MAX is increased, the maximum value p ^MAX between the wireless terminal 300 Is unfair (ie, unfair communication speed). In general, from the viewpoint of maintaining the communication speed of the wireless terminal 300, it is better that the maximum value p ^MAX is large. The problem of unfairness of the maximum value p ^MAX can be solved if a control signal from the small cell base station 200 to the large cell base station 100 can be transmitted. The operation pattern 4 is an operation pattern aiming at ensuring fairness of the communication speed.

All the small cell base stations 200 in the large cell LC transmit a propagation loss value PL _UP between the connected radio terminal 300 and the large cell base station 100 to the large cell base station 100 (step S401). When a plurality of radio terminals 300 are connected to one small cell base station 200, the average value of the propagation loss values PL _UP is transmitted to the large cell base station 100.

In step S402, the upper limit determination unit 124 of the large cell base station 100 determines the upper limit I ^cap to be notified to each small cell base station i according to the following equation (4).

Here, PLUP (i) is a propagation loss value PL _UP notified from the small cell base station i. The symbol Σ represents the sum related to the element j other than i in the list L (the same applies to the equation (5) described later).

When the upper limit value I ^cap is determined by Expression (4), the maximum value p ^MAX of the transmission power density of one wireless terminal 300 connected to the small cell base station i is expressed by Expression (5).

Thus, the maximum value p ^MAX is constant regardless of the small cell base station. As a result, fairness regarding the maximum value p ^MAX of the transmission power density of the wireless terminal 300 can be ensured.

Thus, in the operation pattern 4, the small cell base station 200 transmits the propagation loss value PL _UP to the large cell base station 100, and the upper limit value determination unit 124 of the large cell base station 100 determines the allowable value I ^total and the small value. The upper limit value I ^cap is determined based on the number of cell base stations and the propagation loss value PL _UP . Thereby, the upper limit value I ^cap can be determined for each small cell base station 200 so that the maximum value p ^MAX is kept constant between the radio terminals 300.

(1.4) Effects of First Embodiment In the present embodiment, the large cell base station 100 determines the upper limit value I ^cap based on the allowable value I ^total and the number of small cell base stations. The small cell base station 200 determines the maximum value p ^MAX based on the upper limit value I ^cap and the propagation loss value PL _UP and controls the transmission power of the radio terminal 300 so as not to exceed the determined maximum value p ^MAX . As a result, even if the number of small cell base stations 200 in the large cell LC changes, the total amount of interference from the radio terminal 300 to the large cell base station 100 can be kept below the allowable value I ^total , A decrease in communication speed of the wireless terminal 400 connected to the station 100 can be suppressed.

In the present embodiment, the upper limit value determination unit 124 of the large cell base station 100 determines the allowable value I by the number of small cell base stations 200 having wireless terminals 300 connected to all the small cell base stations 200 in the large cell LC. ^The result of dividing ^total is determined as the upper limit value I ^cap . Accordingly, since the upper limit value I ^cap is determined after eliminating the small cell base station 200 that does not have the connected wireless terminal 300, the upper limit value I ^cap can be prevented from becoming unnecessarily low. The upper limit determination section 124 may be divided into uniform tolerance I ^total, it may be divided by the allowable value I ^total uneven.

In the present embodiment, the higher-level device 500 manages information on the installation status of the small cell base station 200 and information on the communication status of the small cell base station 200. The acquisition unit 121 of the large cell base station 100 uses the list based on the information managed by the higher-level device 500 to count the number of all small cell base stations 200 in the large cell LC or all the large cell LCs. The number of small cell base stations 200 having the wireless terminal 300 being connected in the small cell base station 200 is acquired. As a result, the upper limit value I ^cap can be determined in accordance with the real-time communication environment.

In the present embodiment, the large cell base station 100 determines an allowable value I ^total based on the interference measurement unit 122 that measures the total amount of interference received by the large cell base station 100 and the measurement value obtained by the interference measurement unit 122. And an allowable value determining unit 123. As a result, the allowable value I ^total can be determined in accordance with the real-time communication environment.

In the present embodiment, the upper limit determination unit 124 sets the upper limit I ^cap as a result of dividing the allowable value I ^total by the multiplication result of the number of all the small cell base stations 200 in the large cell LC and the coefficient k. decide. Thereby, even if it is a case where the information of communication status (information of the connected wireless terminal 300) cannot be obtained in the host device 500, the upper limit value I ^cap can be set appropriately.

In the present embodiment, the upper limit determination unit 124 determines the upper limit I ^cap based on the allowable value I ^total , the number of small cell base stations, and the propagation loss value PL _UP . Thereby, the upper limit value I ^cap can be determined for each small cell base station 200 so that the maximum value p ^MAX is kept constant between the radio terminals 300.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. In the first embodiment described above, the upper limit the upper limit I ^cap notifications and the large cell base station 100 to determine the small cell base station 200 of the I ^cap had done, in the second embodiment, the upper limit value I ^{The host} apparatus 500 performs determination of the ^cap and notification of the upper limit value I ^cap to the small cell base station 200. That is, in the second embodiment, the higher-level device 500 constitutes a network side device.

  Hereinafter, the difference between the second embodiment and the first embodiment will be mainly described.

(2.1) Configuration of Host Device FIG. 9 is a block diagram showing the configuration of the host device 500 according to the second embodiment.

As shown in FIG. 9, the higher-level device 500 according to the second embodiment is different from the first embodiment in that the control unit 520 has an upper limit determination unit 524. Further, when the allowable value I ^total is fixed, the storage unit 530 stores the allowable value I ^total in advance. Upper limit determination unit 524 determines upper limit I ^cap according to equation (2). When the allowable value I ^total is variable, the control unit 520 may include an allowable value determining unit 523. Other configurations are the same as those of the first embodiment.

(2.2) Operation of Radio Communication System Next, operation patterns 1 and 2 of the radio communication system 1 according to the second embodiment will be described. The operation patterns 1 and 2 are not limited to being performed individually, but can be performed by switching as appropriate.

(2.2.1) Operation pattern 1
FIG. 10 is a sequence diagram showing an operation pattern 1 according to the second embodiment. In operation pattern 1, it is assumed that the allowable value I ^total is fixed.

  In step S111, the list generation unit 522 of the higher-level device 500, based on the communication status information of the small cell base station 200, includes the small wireless terminals 300 that are connected to all the small cell base stations 200 in the large cell LC. A list L including information on the cell base station 200 is generated.

  In step S <b> 501, the storage unit 530 of the higher-level device 500 stores the list L generated by the list generation unit 522.

In step S502, the upper limit determination unit 524 of the upper device 500 sets the upper limit I ^cap for each small cell base station 200 based on the allowable value I ^total and the number of small cell base stations (that is, the number of elements in the list L). decide. Here, as shown in Equation (1), a method is used in which an allowable value I ^total is equally divided by the number of small cell base stations (number of elements in the list L) as an upper limit value I ^cap . In this way, the upper device 500 determines the upper limit value I ^cap of the interference power density from one radio terminal 300 for each small cell base station 200 present in the large cell LC.

In step S <b> 503, the wired communication unit 510 of the higher-level device 500 transmits information on the upper limit value I ^cap determined by the upper limit value determination unit 524 to each small cell base station 200 via the core network 10. The wired communication unit 240 of the small cell base station 200 receives the information on the upper limit value I ^cap via the core network 10.

  Subsequent operations are the same as the operation pattern 1 according to the first embodiment.

(2.2.2) Operation pattern 2
FIG. 11 is a sequence diagram showing an operation pattern 2 according to the second embodiment. In the operation pattern 2, the allowable value I ^total is assumed to be variable.

  In step S201, the interference measurement unit 122 of the large cell base station 100 measures the total amount of interference received by the large cell base station 100. Here, the total amount of interference includes not only the amount of interference from the radio terminal 300 but also the amount of interference from other interference sources.

  In step S <b> 601, the wired communication unit 140 of the large cell base station 100 transmits the measurement value obtained by the interference measurement unit 122 to the higher-level device 500 via the core network 10. The wired communication unit 510 of the host device 500 receives the measurement value.

In step S602, the allowable value determination unit 523 of the higher-level device 500 determines the allowable value I ^total based on the notified total interference amount. For example, the allowable value determining unit 123 sets a part (x%) of the total interference received by the large cell base station 100 as the allowable value I ^total .

In step S603, the upper limit value determination unit 524 of the higher-level device 500 determines the upper limit value based on the allowable value I ^total determined by the allowable value determination unit 523 and the number of small cell base stations (that is, the number of elements in the list L). I ^cap is determined for each small cell base station 200.

  The subsequent operation is the same as that of the operation pattern 1 according to the second embodiment.

(2.3) Effects of Second Embodiment According to the present embodiment, in addition to the effects obtained in the first embodiment, the following effects can be obtained. Specifically, the number of processes added to the large cell base station 100 can be reduced as compared with the first embodiment.

(3) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

For example, in the first embodiment, performs the notification of the upper limit value I ^cap to the upper limit value I determined and the small cell base station 200 of the ^cap is the large cell base station 100, in the second embodiment, the determination of the upper limit value I ^cap And the upper device 500 notifies the small cell base station 200 of the upper limit value I ^cap . However, makes decisions upper limit I ^cap the large cell base station 100, the notification of the upper limit value I ^cap may be configured to host device 500 performs to the small cell base station 200. Alternatively, it makes decisions upper limit I ^cap host device 500 may be a limit I notice a large cell base station 100 performs configuration of the ^cap to the small cell base station 200. Thus, the network side apparatus for implement | achieving the transmission power control method mentioned above is comprised by a large cell base station and a high-order apparatus.

  In the embodiment described above, the specification of base station communication has not been particularly described. The base station communication specifications will be described below.

  The large cell base station 100 is connected to a neighboring large cell base station via a dedicated line, and can perform base station communication using a high-speed dedicated line. Such an interface between base stations is called an X2 interface. Through the X2 interface, an OI (overload indicator) that is information indicating the amount of interference received by the base station in the uplink can be transmitted and received between the base stations.

  The large cell base station 300 performs transmission power control in the uplink based on the received OI. On the other hand, the small cell base station 200 is connected to the core network 10 of the communication carrier via a general public line such as ADSL or FTTH. In addition, since the small cell base station 200 is installed at an arbitrary location, it is difficult to connect the large cell base stations 200 by a dedicated line like the large cell base stations 300.

  Therefore, even if the small cell base station 200 can receive the OI, since the OI goes through the general public line, there is a high possibility that the transmission delay time of the OI becomes long. However, a transmission power control method in the uplink using OI when there is a large difference in transmission delay time is not generally known.

  In the above-described embodiment, since information on high-speed time fluctuation of the communication path is not used, it is expected to be strong against a control signal reception delay in the small cell base station, and thus such a problem can be solved.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 10 ... Core network, 100 ... Large cell base station, 101 ... Antenna part, 110 ... Wireless communication part, 120 ... Control part, 121 ... Acquisition part, 122 ... Interference measurement part, 123 ... Tolerance determination , 124 ... upper limit determination unit, 130 ... storage unit, 140 ... wired communication unit, 200 ... small cell base station, 201 ... antenna unit, 210 ... wireless communication unit, 220 ... control unit, 221 ... propagation loss estimation unit, 222: Maximum value determination unit, 223 ... Transmission power control unit, 230 ... Storage unit, 240 ... Wired communication unit, 300 ... Large cell base station, 300 ... Wireless terminal, 400 ... Wireless terminal, 500 ... Host device, 510 ... Wired Communication unit, 520 ... control unit, 521 ... information management unit, 522 ... list generation unit, 523 ... tolerance value determination unit, 524 ... upper limit value determination unit, 530 ... storage unit

Claims (4)

A large cell base station,
A small cell base station forming a small cell smaller than the large cell formed by the large cell base station;
A wireless communication system compatible with LTE, comprising a wireless terminal connected to the small cell base station,
The network side device consisting of at least one of the large cell base station or the higher cell base station,
A transmission unit that transmits upper limit value information indicating an upper limit value of an interference amount received by the large cell base station from the wireless terminal to the small cell base station;
The small cell base station is
A receiving unit for receiving the upper limit information from the network side device;
A wireless communication system comprising: a transmission power control unit that controls transmission power of the wireless terminal so as not to exceed a maximum value of transmission power determined based on the upper limit value information received by the reception unit. In the radio communication system corresponding to LTE, in which the small cell base station controls transmission power of a radio terminal connected to a small cell base station that forms a small cell smaller than a large cell formed by the large cell base station, A network side device composed of at least one of a large cell base station or a host device of the large cell base station,
A network side apparatus provided with the transmission part which transmits the upper limit value information which shows the upper limit of the interference amount which the said large cell base station receives from the said radio | wireless terminal to the said small cell base station. In a radio communication system corresponding to LTE, a small cell base station that forms a small cell smaller than a large cell formed by a large cell base station,
Reception of receiving upper limit value information indicating an upper limit value of the amount of interference received by the large cell base station from the wireless terminal from the network side device formed of at least one of the large cell base station or the higher level device of the large cell base station And
A small cell base station comprising: a transmission power control unit that controls transmission power of the radio terminal so as not to exceed a maximum value of transmission power determined based on the upper limit value information received by the reception unit. A small cell base station that forms a small cell smaller than the large cell formed by the large cell base station, and controls transmission power of a wireless terminal connected to the small cell base station in a wireless communication system compatible with LTE A transmission power control method for
The network side apparatus consisting of at least one of the large cell base station or the upper apparatus of the large cell base station receives upper limit value information indicating an upper limit value of the amount of interference received by the large cell base station from the wireless terminal. Transmitting to the base station;
The small cell base station receiving the upper limit information from the network side device;
A transmission power control method comprising: controlling the transmission power of the radio terminal so that the small cell base station does not exceed a maximum value of the transmission power determined based on the received upper limit value information.

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