JP5283652B2 - Wireless communication system, interference control method thereof, and base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce interference power from a neighboring cell. <P>SOLUTION: In a radio communication system including a plurality of base stations each communicating with a mobile terminal inside a subordinate cell, at each of the plurality of base stations, interference power received from the mobile terminal inside a neighboring cell is acquired and at each of the plurality of base stations, a notification requesting reduction in interference is transmitted to a base station of the neighboring cell on the basis of the interference power. Information for controlling transmission power of the mobile terminal inside the neighboring cell so as to reduce interference is reported from the base station of the neighboring cell having received the notification requesting the reduction in interference to the mobile terminal and at the mobile terminal inside the neighboring cell, information on transmission power is received to control transmission power of the mobile terminal in accordance with the information. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a radio communication system, an interference control method thereof, and a base station, and more particularly, to a radio communication system having a mobile terminal and a plurality of base stations that communicate with mobile terminals in subordinate cells, an interference control method thereof, and Regarding the base station.

CDMA (Code Division Multiple Access) communication systems are rapidly being put into practical use, and there is a commercial service for wideband CDMA systems (W-CDMA: Wideband-CDMA) for exchanging large data such as moving images as well as voice and still images. Has been started. Specifications of the wideband CDMA system, which has been enacted by the 3GPP standards body of the third generation mobile communication system (3 ^rd Generation Partnership Project), a variety of specifications aimed at systems that currently can be realized more high-quality services Are being reviewed and added.
FIG. 14 is a network configuration diagram of the current 3GPP W-CDMA system. The system includes a host network (CN) 100, a radio network controller (RNC) 101 # to 101 # n, a radio base station (NodeB) 102 # to 102 # n, and a mobile terminal (UE: User Equipment) 103 is composed of four types of nodes. The nodes 100, 101 # 0 to 101 # n, and 102 # 0 to 102 # n are physically connected by an ATM (Asynchronous Transfer Mode) transmission path or the like (wired section). Radio base stations 102 # 0 to 102 # n and mobile terminal 103 are connected by radio signals (radio section). Iu is the interface between the radio network controllers 101 # 0 to 101 # n and the core network 100, Iur is the interface between the radio network controllers 101 # to 101 # n, and Iub is the radio network controllers 101 # to 101 # n is an interface between the radio base stations 102 # 0 to 102 #n, and Uu is an interface between the radio base stations 102 # 0 to 102 #n and the mobile terminal 103.
User data is transmitted from the CN 100 containing the exchange, server, database, etc. to the RNC 101 # 0 to RNC 101 # 1 via the Iu line. When the destination mobile terminal UE 103 is located in the cell 104 # 1 under the RNC 101 # 0, the user data is stored in the NodeB 102 containing the corresponding cell from the RNC 101 # 0 via the Iub line. # 1 is transmitted to the mobile terminal UE 103 via the Uu interface.
In the mobile CDMA communication system composed of a plurality of cells as described above, a signal (uplink signal or reverse link signal) transmitted from a mobile terminal to a connected base station reaches a base station of an adjacent cell. However, when the same frequency band is used in the uplink between cells, the result is an interference signal for adjacent cells. In particular, when a mobile terminal exists in a boundary region where a plurality of cells overlap, an interference signal level to an adjacent cell due to a transmission signal from the mobile terminal increases. FIG. 15 shows an image in which a mobile terminal in one cell interferes with a base station in an adjacent cell for two cells. For ease of explanation, it is assumed that the number of base stations (cells) is 2 and the number of mobile terminals is 3.
The mobile terminal MS1 in the cell CL1 is communicating with the base station BTS1, but the transmission signal from the mobile terminal MS1 reaches the base station BTS2 of the adjacent cell CL2 and becomes an interference signal. Further, the mobile terminals MS2 and MS3 in the cell CL2 are communicating with the base station BTS2, but the transmission signals from the mobile terminals MS2 and MS3 reach the base station BTS1 of the adjacent cell CL1 and become interference signals. In this case, the interference of the mobile terminal MS3 existing in the boundary region where the cells CL1 and CL2 overlap is greater than the interference of the mobile terminal MS2 not existing in the boundary region.
FIG. 16 shows an image of received signal components in base stations BTS1 and BTS2 of cells CL1 and CL2 shown in FIG. As shown in FIG. 16, the received signal power of the base station BTS1 is the sum of the received signal power from the mobile terminal MS1 in the subordinate cell CL1 and the received signal power from the mobile terminals MS2 and MS3 in the adjacent cell (cell CL2). become. In addition, although the thermal noise is included correctly, it is omitted. The received signal power of the base station BTS2 is the sum of the received signal power from the mobile terminals MS2 and MS3 in the subordinate cell CL2 and the received signal power from the mobile terminal MS1 in the adjacent cell (cell CL1).
The maximum allowable received signal power in the base station is considered as a radio resource in the uplink, but the radio resource is limited by the interference signal from the adjacent cell. On the other hand, a mobile terminal in a cell controlled by a base station receiving interference from an adjacent cell gives interference to the adjacent cell and restricts radio resources of the adjacent cell.
In the current 3GPP W-CDMA system, the radio network controller RNC located above the base station BTS performs call admission control (admission control, congestion control: admission control, congestion control) based on the total received signal power of the base station. control) is performed, but control is not performed so that the interference signal power from the adjacent cell is reduced. That is, the base station can control the received signal power from the mobile terminal in the subordinate cell, but cannot control the interference signal power from the adjacent cell.
There is a conventional technique (for example, refer to Patent Document 1) for controlling interference from an adjacent base station. This prior art is a technique for mitigating interference received by a mobile terminal due to a downlink signal from another base station in a communication system in which the frequency band is the same between the uplink and the downlink. is there. That is, the mobile terminal monitors the strength and frequency of interference signals due to downlink signals transmitted from other base stations, and notifies the communicating base station that there is interference when the interference level exceeds a threshold, Further, the interference occurrence time information is notified. Upon receiving the notification, the base station changes the subband (subchannel) used for data transmission to the mobile terminal, thereby canceling the interference received by the mobile terminal. However, if there is no vacant band and the base station cannot solve the problem, the base station is notified of interference information (interference occurrence, interference occurrence time). The host device checks the base station adjacent to the base station, identifies the base station causing the interference based on the interference occurrence time, and uses the subband used for data transmission to the base station causing the interference. To change. The base station that has received the instruction from the higher-level device changes the subband used for downlink data transmission. If there is no subband available, transmission is interrupted.
However, in this conventional technique, the interference given to the base station of the target cell by the uplink signal from the mobile terminal in the cell adjacent to the target cell, particularly the mobile terminal in the adjacent cell existing near the cell edge. It is not something that reduces.

JP 2003-259414 A

From the above, an object of the present invention is to reduce interference power from adjacent cells.
Another object of the present invention is to request the neighboring base station to reduce interference when the total interference power received from mobile terminals in neighboring cells is larger than a set value, thereby reducing the interference power.
Another object of the present invention is to determine a mobile terminal that may exist at a cell boundary and generate a large interference signal, and reduce interference power by reducing the interference signal from the mobile terminal. It is.
Another object of the present invention is to improve the throughput of the entire system by reducing and controlling the interference signal that the mobile terminal in communication with each base station gives to the base station in the adjacent cell.

A first aspect of the present invention is a wireless communication system having a mobile terminal and a plurality of base stations that communicate with mobile terminals in subordinate cells, and each of the plurality of base stations moves in all adjacent cells. an interference power measurement unit for measuring total interference power received from the terminal, based on the total interference power, the reduce interference request unit to request to reduce interference to the base station of the adjacent cell, the base station of the adjacent cell And a control unit for notifying a mobile terminal in a subordinate cell of the information that controls transmission power so as to reduce interference, and the mobile terminal is requested to reduce the interference. A receiving unit configured to receive information for controlling the transmission power notified from the base station;
Each of the plurality of base stations further includes a comparison unit that compares the total interference power with a set value, and the interference reduction request unit determines whether the base station of an adjacent cell is in accordance with a comparison result by the comparison unit. To reduce interference.
Each of the plurality of base stations includes an interference mobile terminal determination unit that determines a mobile terminal related to interference with the base station of the adjacent cell that has requested reduction of the interference, and the control unit includes the determined mobile terminal Information for controlling transmission power so as to reduce interference.
A second aspect of the present invention is a method of reducing interference in a radio communication system having a plurality of base stations that communicate with mobile terminals in subordinate cells, and each of the plurality of base stations is a mobile terminal in all adjacent cells. get the total interference power received from each of the plurality of base stations, and sends the notification to request reduction of interference to the base station of the neighboring cell based on the total interference power, requesting a reduction of the interference The base station of the adjacent cell that has received the notification to notify the mobile terminal in the adjacent cell of information for controlling the transmission power of the mobile terminal so as to reduce interference, and the mobile terminal in the adjacent cell , Receiving information on the transmission power, and controlling the transmission power of the mobile terminal according to the information.
In the interference reduction method, each of the plurality of base stations compares the total interference power with a set value, and transmits a notification requesting reduction of the interference according to the comparison result.
In the interference reduction method, a mobile terminal related to interference with the base station of the neighboring cell that requested the reduction of the interference is determined, and the interference is reduced to the determined mobile terminal in each of the plurality of base stations. Information for controlling the transmission power is notified.
A third aspect of the present invention is a base station used in a radio communication system having a plurality of base stations that communicate with mobile terminals in subordinate cells, and measures the total interference power received from mobile terminals in all adjacent cells. an interference power measurement section, based on the total interference power, the reduce interference request unit to request to reduce interference to the base station of the adjacent cell, it is required to reduce the interference from the base station of the adjacent cell, under A control unit for notifying mobile terminals in the cell of information for controlling transmission power so as to reduce interference.

According to the present invention, interference power from adjacent cells can be reduced. Further, according to the present invention, when the total interference power received from the mobile terminal of the adjacent cell is larger than a set value, it is possible to reduce the interference power by requesting the adjacent base station to reduce the interference, Throughput of the entire system can be improved. Furthermore, according to the present invention, it is possible to determine the mobile terminal that is present at the cell boundary and generates a large interference signal, and reduce the interference signal from the mobile terminal, thereby reducing the interference power.
According to the present invention, when the total adjacent received signal power (interference power) increases, the interference power from the adjacent cell that gives large interference is reduced, so that the throughput of the entire system can be improved. Can do.

It is a network block diagram which can apply this invention. It is an image figure in which the mobile terminal in an adjacent cell gives interference to the base station of a focused cell in three cells. It is a breakdown explanatory drawing of received signal power. 3 is a processing flow of a base station receiving interference in the first embodiment. It is a processing flow of the base station which accommodates the mobile terminal which has given interference in 1st Example. It is explanatory drawing of the discrimination method of the mobile terminal which may have given interference. It is explanatory drawing of an example of a common pilot signal in a W-CDMA system. It is a processing flow for discriminating a mobile terminal that may be causing interference. It is the structure of the base station of 1st Example. It is explanatory drawing of 2nd Example. 6 is a processing flow of a base station receiving interference in the second embodiment. 10 is another processing flow of the base station receiving the interference in the second embodiment. It is a block diagram of the base station of 2nd Example. It is a network configuration diagram of the current 3GPP specification W-CDMA system. It is an image figure where the mobile terminal in one cell gives interference to the base station of an adjacent cell about two cells. It is a figure explaining that the interference from an adjacent cell has restrict | limited the radio | wireless resource.

(A) First embodiment
(a) Network Configuration FIG. 1 is a network configuration diagram to which the present invention can be applied. A large number of base stations BTS1 to BTSn are connected to the core CN, and each base station communicates wirelessly with mobile terminals MSij in the cells CL1 to CLn. It can be done. The core network CN has functions of both the core network and the radio network controller shown in FIG. In addition, each base station is connected to an adjacent base station by wire (or, for example, wireless using a microwave band), and includes an interface that communicates with each other. The network configuration in FIG. 1 is, for example, the network proposed in 3GPP TR 25.897 V0.3.0 (2003-08).
FIG. 2 shows an image in which the mobile terminals MS2j and MS3k in the adjacent cells CL2 and 3 interfere with the base station BTS1 of the target cell CL1 in the three cells CL1 to CL3. In FIG. 2, the number of cells is shown as 3 for ease of explanation. In these three cells, the same frequency band is used in the uplink.
When attention is paid to the base station BTS1 of the cell CL1, the mobile terminals MS21 and MS22 in the adjacent cell CL2 are communicating with the base station BTS2, but the uplink signals transmitted from the mobile terminals MS21 and MS22 are transmitted to the base of the target cell CL1. It reaches the station BTS1 and becomes an interference signal. In this case, the mobile terminal MS23 that does not exist at the cell edge or the mobile terminal that exists at the cell edge opposite to the target base station BTS1 does not interfere with the base station BTS1, or the interference power is weak. Similarly, the mobile terminal MS32 in the adjacent cell CL3 is communicating with the base station BTS3, but the uplink signal transmitted from the mobile terminal MS32 reaches the base station BTS1 of the cell of interest CL1 and becomes an interference signal. .

(b) Received signal power The total received signal power P received by the base station BTS1 is the received signal power Pa from the mobile terminal in the own cell CL1, and the mobile terminals in the adjacent cells CL2 and CL3, as shown in FIG. (P = Pa + Pother) (where thermal noise is ignored). The host device in the core performs call admission control, and monitors whether the difference between the maximum allowable received signal power Pmax and the total received signal power P in the base station BTS1 is equal to or less than a set value. If it is, the acceptance of the new call requested from the mobile terminal in the base station BTS1 is rejected, and if it is above, the call is accepted. Therefore, if the total adjacent received signal power Pother increases, reducing this power Pother leads to efficient use of radio resources.

(c) Processing of Base Station Receiving Interference FIG. 4 is a processing flow of the base station receiving interference in the first embodiment.
In the base station BTS1, the total adjacent received signal power Pother from all adjacent cells is measured (step 201). The interference power Pother is measured by measuring the total received signal power of the base station BTS1, and measuring the total received signal power from all mobile terminals in the subordinate cell as the desired power, and the total received signal of the base station BTS1. This is obtained by subtracting the desired power from the power.
Next, the total adjacent received signal power Pother and the threshold power Pth are compared (step 202). If the total adjacent received signal power is equal to or greater than the threshold power (Pother ≧ Pth), the base station BTS1 A flag signal Fint for requesting interference reduction is transmitted (step 203). As will be described later, the adjacent base stations BTS2 and BTS3 that have received the flag signal Fint are uplink for a certain period of time with respect to the mobile terminals located near the cell edge on the target base station BTS1 side among the subordinate mobile terminals. Control to reduce the data rate during transmission or not allow transmission. As a result, the total adjacent received signal power Pother is reduced.
Thereafter, the process waits for a predetermined time to elapse (step 204). If the predetermined time elapses, the processes after step 201 are repeated. In step 202, if the total adjacent received signal power is smaller than the threshold power (Pother <Pth), since the interference is small, the process waits for a predetermined time without doing anything (step 204). The subsequent processing is repeated.

(d) Processing of base station accommodating mobile terminal giving interference FIG. 5 shows a processing flow of a base station accommodating a mobile terminal giving interference in the first embodiment, for example, base station BTS2. is there.
The base station BTS2 monitors whether the flag signal Fint has been received (step 301). If the flag signal Fint is not received, the base station BTS2 waits for a predetermined time to elapse (step 304). Repeat the process.
On the other hand, if the flag signal Fint is received in step 301, a mobile terminal that may be interfering with the base station BTS1 that transmitted the flag signal Fint is determined (step 302). That is, the mobile terminal existing near the cell edge on the base station side that transmitted the flag signal Fint is identified.
When the determination of the mobile terminal that interferes with the base station BTS1 is completed, the adjacent base station BTS2 temporarily lowers the uplink data transmission rate of the mobile terminal by the scheduling function, or temporarily transmits the uplink data. Control to stop (step 303). Thereafter, the process waits for a predetermined time to elapse (step 304), and if the time elapses, the processing after step 301 is repeated.
The uplink data transmission limit ends when the flag signal Fint is no longer received and when the mobile terminal no longer exists at the cell edge. It should be noted that it can be ended when a certain time has elapsed after the start of transmission restriction.
As described above, if the flag signal Fint requesting interference reduction is received, the uplink data transmission rate of the mobile terminal that may be causing interference may be temporarily reduced, or uplink data transmission may be temporarily performed. Since it stops, the interference with the base station BTS1 can be reduced.

(e) Discrimination of mobile terminal at cell edge FIG. 6 is an explanatory diagram of a method of discriminating a mobile terminal giving interference.
As shown in FIG. 6, when the mobile terminal MS22 in communication with the base station BTS2 is present in or near the boundary region of the cells CL1 and CL2 of the base stations BTS1 and BTS2, downlink signals are received from both base stations. . Each downlink signal includes a common pilot signal (CPICH signal). The mobile terminal MS22 measures the reception powers P1 and P2 of the common pilot signals from the base stations BTS1 and BTS2, and if the absolute value of the difference ΔP between the two reception powers is less than or equal to the set value, it exists near the cell edge. It is determined that there is a possibility of interference with the transmission source base station BTS1 of the flag signal Fint. If it is equal to or greater than the set value, it is determined that there is no interference with the transmission source base station BTS1 of the flag signal Fint.
FIG. 7 is an explanatory diagram showing an example of a common pilot signal transmitted from each base station in the W-CDMA system. One frame is 10 msec and is composed of 15 slots S0 to S14. However, the present invention does not depend on the downlink physical channel configuration.
The primary common control physical channel P-CCPCH and the common pilot channel CPICH (CPICH in this example indicates the primary common pilot channel P-CPICH) are both downlink common channels, and one exists in each cell. Of these, the primary common control channel P-CCPCH is used to transmit BCH (broadcast information), and the BCH includes information on base stations, base station codes of adjacent base stations, and the like. On the other hand, the common pilot channel CPICH transmits a common pilot signal, and is transmitted by spreading the common pilot signal with a base station code (for example, a cell-specific scramble code of a cell under the base station) and a CPICH channelization code. To do. On the reception side, control such as channel estimation and reception power measurement is performed using the common pilot signal. In FIG. 7, S-SCH is a secondary synchronization channel.
The mobile terminal MS22 (see FIG. 6) separates the common pilot signal transmitted from the communicating base station BTS2 using the base station code of the communicating base station BTS2 and the CPICH channelization code, and receives the common pilot signal. The power P2 is measured. Further, the base station code of the adjacent base station BTS1 is obtained from the BCH (broadcast information) transmitted by the primary common control channel P-CCPCH, and the base station code and the CPICH channelization code are used to obtain the base station code from the adjacent base station BTS1. The transmitted common pilot signal is separated, and the received power P1 of the common pilot signal is measured.

FIG. 8 is a processing flow for determining a mobile terminal that may be causing interference.
Each mobile terminal communicating with the base station BTS2, for example, the mobile terminal MS22 measures the received power of the common pilot signal transmitted via the common pilot channel CPICH of the base station BTS2 in communication (step 401). Next, the base station code (scramble code) of the adjacent base station BTS1 is obtained from the BCH (broadcast information) transmitted by the PCCPCH (step 402), and the base station code and the CPICH channelization code are used for the adjacent base station. The common pilot signal transmitted from BTS1 is separated, and the received power P1 of the common pilot signal is measured (step 403).
When the measurement of the received power P1, P2 is completed, the mobile terminal calculates the absolute value of the difference ΔP between the received power P2, P1 of the common pilot signal from the communicating base station BTS2 and the adjacent base station BTS1 (ΔP = | P2-P1 |), step 404), it is determined whether the difference ΔP is greater than or equal to a threshold value (step 405). If the difference ΔP is equal to or greater than the threshold value, it is determined that it does not exist in the vicinity of the adjacent base station BTS1, and the base station name of the adjacent base station is added to the determination result and notified to the communicating base station BTS2 (step 406). ). Although the determination result is notified to the communicating base station BTS2 here, the determination result in this case does not necessarily have to be notified, and may not be notified.
On the other hand, if the difference ΔP is less than or equal to the threshold value, it is determined that the cell exists near the cell edge, and the base station name of the adjacent base station is added to the determination result and notified to the communicating base station BTS 2 (step 407). . Alternatively, only a flag signal indicating that there is a possibility of causing interference to neighboring cells is transmitted.
Based on the determination result received from each mobile terminal, the base station BTS2 identifies the mobile terminal that is interfering with the transmission source base station BTS1 of the flag signal Fint, and the uplink data transmission rate of the mobile terminal is determined by the scheduling function. Temporarily lower or uplink data transmission is temporarily stopped.

(f) Configuration of Base Station FIG. 9 shows the configuration of the base station according to the first embodiment.
The reception radio unit 11 amplifies the radio signal received by the antenna 10 and down-converts the frequency from the high frequency band to the base band. The total received signal power measuring unit 12 measures the total received signal power P from the output signal of the receiving radio unit 11, and the demodulating unit 13 despreads with a scramble code specific to each terminal after orthogonal demodulation, and further, a predetermined channelization code (1) User data and control signals, (2) Signals for measuring the total received signal power from subordinate mobile terminals, (3) Cell edge notification signals from mobile terminals, etc. To separate. The total received signal power from all mobile terminals in communication is hereinafter referred to as desired signal power (or desired power).
The signal for measuring the desired signal power is obtained by despreading the received signal with a despread code unique to the mobile terminal. The decoding unit 14 performs decoding processing and error detection correction processing on the demodulated data and control signal, and outputs the obtained data and control information.
The desired signal power calculation unit 15 measures the desired signal power Pa using the signal obtained by despreading, and the interference power calculation unit 16 calculates the following equation: Pother = P−Pa (1)
Thus, the received signal power Pother received from the mobile terminals in all adjacent cells is calculated as interference power. The received signal power Pother is hereinafter referred to as total adjacent received signal power. The comparison unit 17 compares the total adjacent received signal power Pother and the threshold power Pth and inputs the comparison result to the flag generation unit 18. The flag generation unit 18 refers to the comparison result, and if the total adjacent received signal power is equal to or greater than the threshold power (Pother ≧ Pth), generates a flag signal Fint requesting the adjacent base station to reduce interference, and the adjacent base station communication interface Input to the unit 19. The transmission unit 19a of the adjacent base station communication interface unit 19 adds the transmission source base station ID to the flag signal Fint and transmits it to all adjacent base stations. If the total adjacent received signal power is equal to or lower than the threshold power, no flag signal is generated.

On the other hand, if the reception unit 19b of the adjacent base station communication interface unit 19 receives the flag signal Fint from the adjacent base station, the reception unit 19b indicates that the flag signal Fint has been received and the transmission source base station name of the flag signal Fint. 20 is notified. Upon receiving this flag signal reception notification, the uplink schedule unit 20 inputs the transmission source base station name of the flag signal Fint to the cell edge neighboring terminal specifying unit 21.
The cell edge neighboring terminal specifying unit 21 receives the cell edge neighborhood determination result sent from the communicating mobile terminal according to the process of FIG. 8, and based on the result, whether each communicating mobile terminal exists at the cell edge. In other words, it is identified whether each mobile terminal in communication is interfering with the base station that transmitted the flag signal Fint, and notifies the uplink scheduling unit 20 of the mobile terminal that is causing interference.
Upon receiving this notification, the uplink schedule unit 20 instructs the control signal generation unit 22 to limit uplink data transmission of the mobile terminal that is causing the interference. The control signal generator 22 generates a control signal for limiting uplink data transmission of the instructed mobile terminal. That is, a control signal for temporarily reducing the uplink data transmission rate or a control signal for temporarily stopping uplink data transmission is created. The multiplexing unit 23 multiplexes the control signal and the user data generated by the user data generation unit 24, and the encoding / modulation unit 25 encodes the multiplexed data and spreads it with a predetermined spreading code, and orthogonalizes it according to the spreading result. After modulation, the transmission radio unit 26 performs frequency up-conversion, high-frequency amplification, etc. on the modulated output signal and transmits the transmission signal from the antenna 27.
A mobile terminal that has received a signal transmitted from the antenna 27 and is limited in uplink data transmission temporarily lowers the uplink data transmission rate or temporarily stops uplink data transmission. The uplink schedule unit 20 controls to release the restriction on the uplink transmission data of the mobile terminal when the flag signal Fint is not received, or when a certain time has elapsed after the transmission rate is lowered or suspended.
According to the first embodiment, it is possible to reduce interference power from adjacent cells. Further, according to the first embodiment, when the total interference power received from the mobile terminal in the adjacent cell is larger than the set value, the interference power can be reduced by requesting the adjacent base station to reduce the interference. And the throughput of the entire system can be improved. Furthermore, according to the first embodiment, interference power can be reduced by determining a mobile terminal that is present at a cell boundary and generating a large interference signal, and reducing the interference signal from the mobile terminal. .

により、すなわち、隣接セル毎の隣接受信信号電力Ｐcell 1〜Pcell Nを総計して総隣接受信信号電力Ｐotherを計算する。（ここで、各端末は、セル固有のスクランブルコードでスクランブルを行なった後、上りデータの送信を行なうものとする。）隣接セルcell １〜cell Ｎのセル毎の隣接受信信号電力Ｐcell 1〜Pcell Nは、各隣接セルのスクランブルコードで受信信号を逆拡散して各基地局の共通パイロットを分離することにより測定する。 (B) Second Example In the first example, the total received signal power (total adjacent received signal power) Pother from mobile terminals in all adjacent cells was measured based on Equation (1). In the second embodiment, the total received signal power (adjacent received signal power) Pcell 1 to Pcell N from the mobile terminals in the cell is measured for every cell of all adjacent cells cell 1 to cell N as shown in FIG. ,

That is, the adjacent received signal power Pcell 1 to Pcell N for each adjacent cell is totaled to calculate the total adjacent received signal power Pother. (Here, each terminal scrambles with a cell-specific scramble code and then transmits uplink data.) Adjacent received signal power Pcell 1 to Pcell for each of adjacent cells cell 1 to cell N N is measured by despreading the received signal with the scramble code of each adjacent cell and separating the common pilot of each base station.

FIG. 11 is a processing flow of the base station receiving interference in the second embodiment.
For each cell of all adjacent cells cell 1 to cell N, the adjacent received signal power Pcell 1 to Pcell N from the mobile terminal in the cell is measured (step 501), and the total adjacent received signal power Pother is calculated by the equation (2). (Step 502). Next, the total adjacent received signal power Pother and the threshold power Pth are compared (step 503). If the total adjacent received signal power is greater than or equal to the threshold power (Pother ≧ Pth), the adjacent received signal power Pcell 1 to Pcell N is increased in descending order. Ranking is performed (step 504). Next, a flag signal Fint requesting interference reduction is transmitted to the base stations corresponding to the ranked top m cells, for example, the top two cells (step 505). The adjacent base station that has received this flag signal Fint, during uplink transmission for a certain period of time to a mobile terminal located near the cell edge on the target base station BTS1 side, as in the first embodiment (see the processing flow in FIG. 5). Control to lower the data rate or control not to permit transmission. As a result, the total adjacent received signal power Pother is reduced.
Thereafter, the process waits for a predetermined time to elapse (step 506). If the predetermined time elapses, the processes after step 501 are repeated. In step 503, if the total adjacent received signal power is smaller than the threshold power (Pother <Pth), the process waits for a predetermined time to elapse (step 506), and if it elapses, the processes in and after step 501 are repeated.

FIG. 12 is another processing flow of the base station receiving interference in the second embodiment.
For each cell of all adjacent cells cell 1 to cell N, the adjacent received signal power Pcell 1 to Pcell N from the mobile terminal in the cell is measured (step 601), and the total adjacent received signal power Pother is calculated by equation (2). (Step 602). Next, the total adjacent received signal power Pother and the threshold power Pth1 are compared (step 603), and if the total adjacent received signal power is equal to or higher than the threshold power (Pother ≧ Pth1), the threshold value among the adjacent received signal powers Pcell 1 to Pcell N A power greater than or equal to Pth2 is searched (step 604), and a flag signal Fint for requesting interference reduction is transmitted to the base station of the cell corresponding to the adjacent received signal power equal to or greater than the threshold Pth2 (step 605). Similar to the first embodiment (see the processing flow in FIG. 5), the adjacent base station that has received the flag signal Fint transmits a certain amount of time for uplink transmission to a mobile terminal located near the cell edge on the target base station BTS1 side. Control to lower the data rate or control not to permit transmission. As a result, the total adjacent received signal power Pother is reduced.
Thereafter, the process waits for a predetermined time to elapse (step 606). If the predetermined time elapses, the processes after step 601 are repeated. In step 603, if the total adjacent received signal power is smaller than the threshold power (Pother <Pth2), the process waits for a predetermined time to elapse (step 606), and if it elapses, the processes in and after step 601 are repeated.

FIG. 13 is a block diagram of the base station of the second embodiment. The configuration different from that of the first embodiment of FIG. 9 determines the configuration for calculating the total adjacent received signal power Pother and the destination base station for the flag signal Fint. It is a configuration.
The demodulator 13 despreads the baseband signal after orthogonal demodulation with a cell-specific scramble code to obtain a despread signal, and then further transmits a predetermined channelization code (for example, temporarily to each channel used by each terminal). (1) User data and control signals, (2) Cell edge notification signals from mobile terminals, etc. are separated.
The adjacent reception signal power calculation unit 31 inputs the despread signal obtained by despreading, calculates the adjacent reception signal power Pcell n (n = 1 to N), and the total adjacent reception signal power calculation unit 32 (2 ) To calculate the total adjacent received signal power Pother. The comparison unit 33 compares the total adjacent received signal power Pother and the threshold power Pth1, and inputs the comparison result to the flag generation unit 18 and the flag signal transmission destination base station determination unit 34. If the total adjacent received signal power is equal to or higher than the threshold power (Pother ≧ Pth), the transmission destination base station determination unit 34 determines the transmission destination base station of the flag signal and inputs it to the flag generation unit 18. The transmission destination base station of the flag signal is a base station that ranks the adjacent received signal powers cell 1 to Pcell N in descending order and corresponds to the ranked top m cells. Alternatively, the transmission destination base station of the flag signal is a base station corresponding to a cell having a threshold Pth2 or more among the adjacent received signal powers Pcell 1 to Pcell N.
If the total adjacent received signal power is equal to or greater than the threshold power (Pother ≧ Pth), the flag generation unit 18 generates a flag signal Fint for requesting interference reduction, and the source base station name and destination base station are added to the flag signal Fint. The name is added to the adjacent base station communication interface unit 19, and the transmission unit 19a transmits the flag signal Fint to the transmission destination base station.

On the other hand, if the reception unit 19b of the adjacent base station communication interface unit 19 receives the flag signal Fint from the adjacent base station, the reception unit 19b indicates that the flag signal Fint has been received and the transmission source base station name of the flag signal Fint. 20 is notified. Upon receiving this flag signal reception notification, the uplink schedule unit 20 inputs the transmission source base station name of the flag signal Fint to the cell edge neighboring terminal specifying unit 21.
The cell edge neighboring terminal specifying unit 21 receives the cell edge neighborhood determination result sent from the communicating mobile terminal according to the process of FIG. 8, and based on the result, whether each communicating mobile terminal exists at the cell edge. In other words, it is identified whether each mobile terminal in communication is interfering with the base station that transmitted the flag signal Fint, and notifies the uplink scheduling unit 20 of the mobile terminal that is causing interference.
Upon receiving this notification, the uplink schedule unit 20 instructs the control signal generation unit 22 to limit uplink data transmission of the mobile terminal that is causing the interference. The control signal generator 22 generates a control signal for instructing to temporarily reduce the uplink data transmission rate or to temporarily stop the uplink data transmission in accordance with the instruction, and transmits the control signal to the instructed mobile terminal. To do. The multiplexing unit 23 multiplexes the control signal and the user data generated by the user data generation unit 24, and transmits the multiplexed data to the mobile terminal from the antenna 27 via the encoding / modulation unit 25 and the transmission radio unit 26.
The mobile terminal restricted in uplink data transmission temporarily lowers the uplink data transmission rate or temporarily stops uplink data transmission. If the uplink schedule unit 20 does not receive the flag signal Fint, the uplink schedule unit 20 performs control so as to release the restriction on the uplink transmission data of the mobile terminal.
According to the second embodiment, the same effects as in the first embodiment can be obtained. In addition, according to the second embodiment, when the total adjacent received signal power (interference power) increases, the interference power from adjacent cells giving large interference is reduced. Improvements can be made.

BTS1 to BTS3 Base stations CL1 to CL3 Cell MS11 to MS32 Mobile terminal

Claims (7)

A wireless communication system having a mobile terminal and a plurality of base stations that communicate with mobile terminals in subordinate cells,
Each of the plurality of base stations is
An interference power measurement unit that measures the total interference power received from mobile terminals in all adjacent cells ;
Based on the total interference power, the reduce interference request unit to request to reduce interference to the base station of the adjacent cell,
A control unit for requesting reduction of interference from a base station of an adjacent cell, and notifying information for controlling transmission power so as to reduce interference to a mobile terminal in a subordinate cell, and
The mobile terminal
A wireless communication system, comprising: a receiving unit that receives information for controlling the transmission power notified from the base station requested to reduce the interference. Each of the plurality of base stations includes a comparison unit that compares the total interference power with a set value,
The wireless communication system according to claim 1, wherein the interference reduction request unit requests the base station of an adjacent cell to reduce interference according to a comparison result by the comparison unit. An interference mobile terminal discriminating unit for discriminating a mobile terminal related to interference with the base station of the neighboring cell that requested the reduction of the interference,
The wireless communication system according to claim 1 or 2, wherein the control unit notifies the determined mobile terminal of information for controlling transmission power so as to reduce interference. An interference reduction method in a radio communication system having a plurality of base stations that communicate with mobile terminals in a subordinate cell,
In each of the plurality of base stations, obtain the total interference power received from mobile terminals in all adjacent cells ,
Wherein each of the plurality of base stations, and sends the notification to request reduction of interference to the base station of the neighboring cell based on the total interference power,
The base station of the neighboring cell that has received the notification requesting the reduction of interference notifies the mobile terminal in the neighboring cell of information for controlling the transmission power of the mobile terminal so as to reduce interference,
An interference control method, wherein each mobile terminal in the adjacent cell receives information on the transmission power, and controls the transmission power of the mobile terminal according to the information. In each of the plurality of base stations, the total interference power is compared with a set value,
The interference control method according to claim 4, wherein a notification requesting reduction of the interference is transmitted according to the comparison result. Determining a mobile terminal related to interference with a base station of the neighboring cell that requested reduction of the interference;
The interference control method according to claim 4 or 5, wherein each of the plurality of base stations notifies the determined mobile terminal of information for controlling transmission power so as to reduce interference. A base station used in a radio communication system having a plurality of base stations that communicate with mobile terminals in a subordinate cell,
An interference power measurement unit that measures the total interference power received from mobile terminals in all adjacent cells ;
Based on the total interference power, the reduce interference request unit to request to reduce interference to the base station of the adjacent cell,
A control unit that is requested by an adjacent cell base station to reduce interference and notifies a mobile terminal in a subordinate cell of information for controlling transmission power so as to reduce interference. .

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