JP2008252330A - Communication control method, communication system, and radio base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication control method, a communication system, and a radio base station by which a hand-over can speedily be made to an adjacent radio base station and stable communication can be carried out. <P>SOLUTION: The communication control method of the communication system includes a plurality of radio base stations 1 having adaptive array antennas. When a radio communication device 3 in communication with a first radio base station 1-1 enters an interference area of interference with a second radio base station adjacent to the first radio base station 1-1, transmission of the first radio base station 1-1 is controlled so as to perform a hand-over to the second radio base station 1-2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication control method, a communication system, and a radio base station.

  Conventionally, a cellular system is known as a mobile communication system, and recently, standardization of high-speed wireless communication such as WiMAX (Worldwide Interoperability for Microwave Access) has been promoted.

  In a cellular system, radio waves from adjacent radio base stations are prevented from interfering with each other by using different frequency bands in adjacent radio base stations. For this reason, in the cellular system, a wireless communication network is constructed using a plurality of different frequency bands.

  On the other hand, WiMAX employs TDD (Time Division Duplexing) in which uplink and downlink are time-divided and transmitted / received on the same frequency. For this reason, in WiMAX, by synchronizing the frame structure between the radio base stations, the transmission wave from the other terminal becomes the interference wave of the radio base station transmission wave of the terminal communicating with the other radio base station. I try not to be.

  However, in a wireless communication system using a wideband frequency such as WiMAX, it is difficult to assign different frequency bands to adjacent wireless base stations as in a cellular system from the viewpoint of effective use of a finite frequency. Is assumed. For this reason, when the same frequency band is used between adjacent radio base stations, the radio base stations are frame-synchronized, so that a communication interference region is generated between adjacent radio base stations.

  As described above, when a communication interference area occurs, terminals existing in this area receive transmission waves from adjacent radio base stations at the same time. It is difficult to separate the transmitted waves, and there is a concern that the radio waves cannot be handed over to an adjacent radio base station and become disconnected.

In order to reduce the insensitive area due to interference, an adaptive array is applied to a plurality of radio base station antennas to form nulls in the direction of the plurality of radio base stations (for example, Patent Document 1).
JP-A-11-308037

  However, the one disclosed in Patent Document 1 relates to a site diversity system for simultaneous transmission / reception of multiple stations that combines radio waves transmitted simultaneously from a plurality of radio base stations at a terminal to improve transmission quality. Not applicable to systems communicating with stations.

  Therefore, an object of the present invention made in view of such circumstances is to provide a communication control method, a communication system, and a radio base station that can quickly perform handover to an adjacent radio base station and can communicate stably.

An invention of a communication control method according to claim 1 for achieving the above object is a communication control method in a communication system including a plurality of radio base stations provided with an adaptive array antenna,
In the first radio base station in communication with the radio communication device, the presence or absence of reception of a transmission signal from the radio communication device is detected,
When the transmission signal from the radio communication apparatus cannot be received, the transmission of the first radio base station so that the radio communication apparatus hands over to the second radio base station adjacent to the first radio base station. It is characterized by controlling.

The invention according to claim 2 is the communication control method according to claim 1,
When the transmission signal from the wireless communication apparatus cannot be received, the transmission of the first wireless base station is stopped or the transmission output is reduced.

Further, the invention of the communication control method according to claim 3 is a communication control method in a communication system including a plurality of radio base stations provided with an adaptive array antenna and a communication control device for controlling the plurality of radio base stations. And
For each radio base station, an interference table in which position information indicating an interference area that receives communication interference from an adjacent radio base station is associated with at least a weighting factor for the radio base station to direct a beam to the interference area. Remember
While the wireless communication device is communicating with the first wireless base station among the plurality of wireless base stations, the wireless communication device acquires at least the weighting factor applied by the first wireless base station, and the acquired weighting factor and the Based on the comparison with the weighting factor of the corresponding radio base station stored in the interference table, it is determined whether the radio communication device is located in the interference area,
As a result, when the wireless communication device is located in an interference area, the transmission of the first wireless base station is performed so that the wireless communication device is handed over to the second wireless base station adjacent to the first wireless base station. It is characterized by controlling.

The invention according to claim 4 is the communication control method according to claim 3,
In the first radio base station in communication with the radio communication device, the presence or absence of reception of a transmission signal from the radio communication device is detected,
When a transmission signal from the wireless communication apparatus cannot be received, it is determined whether or not the wireless communication apparatus is located in an interference area.

The invention according to claim 5 is the communication control method according to claim 3 or 4,
When the wireless communication device is located in an interference area, the transmission of the first wireless base station is stopped or the transmission output is reduced.

Furthermore, an invention of a communication system according to claim 6 that achieves the above object is a communication system including a plurality of radio base stations provided with an adaptive array antenna and a communication control device that controls the plurality of radio base stations. And
Each of the plurality of radio base stations
A communication control device communication means for transmitting a weighting factor applied to beam generation to the communication control device and receiving an interference region determination result from the communication control device,
The communication control device includes:
Receiving means for receiving the weighting factor transmitted from each radio base station;
For each of the radio base stations, position information indicating an interference area that receives communication interference from an adjacent radio base station and at least a weighting factor for the radio base station to direct a beam to the interference area are stored correspondingly. An interference table;
While the wireless communication device is communicating with the first wireless base station among the plurality of wireless base stations, the wireless communication device acquires at least the weighting factor applied by the first wireless base station, and the acquired weighting factor and the Interference region determination means for determining whether or not the wireless communication device is located in an interference region based on a comparison with a weighting factor of a corresponding wireless base station stored in an interference table;
A transmission means for transmitting an interference area determination result by the interference area determination means to the first radio base station;
When the interference region determining means determines that the wireless communication device is located in the interference region, the wireless communication device is handed over to the second wireless base station adjacent to the first wireless base station. The first radio base station is configured to control transmission.

Furthermore, the invention of the radio base station according to claim 7 that achieves the above object is a radio base station comprising an adaptive array antenna,
Signal detection means for detecting whether or not a transmission signal is received from a wireless communication device in communication;
A transmission control means for controlling transmission so that the radio communication apparatus is handed over to an adjacent radio base station when the signal detection means cannot receive a transmission signal from the radio communication apparatus;
It is characterized by having.

  According to the present invention, during communication with a wireless communication device, when the wireless communication device is located in the interference area, transmission is controlled so that handover is performed to an adjacent wireless base station. By reducing the time (disconnection time) existing in the area, the wireless communication apparatus can be quickly handed over to an adjacent wireless base station, and stable communication can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram for explaining the principle of a communication system according to an embodiment of the present invention. The communication system shown in FIG. 1 includes a plurality of radio base stations 1-1, 1-2,... And a communication control apparatus 2 that controls them. Each radio base station 1-1, 1-2,... (Hereinafter, also referred to as a radio base station 1 when referring to one radio base station) uses the same frequency band, The wireless base station 1 is configured to wirelessly communicate with a terminal (wireless communication device) 3 existing in the communication area of the wireless base station 1 by TDD synchronized with the frame, and each wireless base station 1 has a plurality of antennas. An adaptive array antenna that controls the directivity of the antenna to improve the link status is employed for the terminal 3 that is communicating.

  In the present embodiment, for example, as shown in FIG. 1A, when the radio base station 1-1 is not able to receive a transmission signal from the terminal 3 while communicating with the terminal 3, this is indicated. The communication control device 2 is notified, and the communication control device 2 determines whether or not the terminal 3 is located in the interference area. As a result, as shown in FIG. 1A, when the terminal 3 is located in an interference area with the adjacent radio base station 1-2, the fact is transmitted to the radio base station 1-1 in communication. Thereby, in the radio base station 1-1, the transmission to the terminal 3 is stopped or the transmission output is reduced, and the terminal 3 is handed over to the radio base station 1-2 as shown in FIG. To control.

  FIG. 2 is a functional block diagram showing a schematic configuration of a main part of each radio base station 1 and communication control apparatus 2 in the communication system shown in FIG. Each wireless base station 1 is configured in the same manner, and controls the overall operation of a terminal communication unit 11 that communicates wirelessly with a terminal, a communication control device communication unit 12 that communicates with the communication control device 2 in a wired or wireless manner. And control means 13. The terminal communication unit 11 includes a beam generation unit 15 that controls the directivity of the antenna based on a weighting factor calculated based on a received signal from a terminal that is in communication.

  The communication control device 2 includes a radio base station communication unit 21 including a transmission unit and a reception unit that communicate with the radio base station 1, an interference area determination unit 22, an interference table 23, and a control unit 25 that controls the whole. is doing.

  In the present embodiment, the interference table 23 includes position information indicating an interference area by the radio base station 1-1 and the radio base station 1-2 adjacent to each other, and the radio base station 1-1 transmits a beam to the interference area. The first weighting factor for directing and the second weighting factor for directing the beam by the radio base station 1-2 are associated with each other and stored in, for example, the recording format shown in FIG.

  Here, the recording format shown in FIG. 3 has the number of radio base stations related to the position information, an identifier corresponding to the number of radio base stations, and a data pointer. The weighting factor of each radio base station is stored at the address indicated by the data pointer following the identifier. For example, as shown by addresses P1 and P2, an address holding a base station identifier, position information, carrier band information, the number of antennas, and a data pointer is provided, and the data pointer corresponds as shown by addresses P3 and P4. A weighting factor is stored in association with the identifier of the antenna arranged in the radio base station. In addition, an index file for each identifier of the radio base station may be generated separately and linked to information having a weighting factor related to each radio base station. For example, the address P1 is linked to the identifier 1 of the radio base station as weight information.

  In the present embodiment, in order to determine whether the terminal 3 is located in the interference area with respect to the weighting factor of the radio base station in communication with the terminal 3, the radio base station in communication with the terminal 3 In order to make it possible to easily search for the presence of the first weighting factor, a set of data pointers (for example, addresses P1) is preferably created for each radio base station. Further, since the propagation characteristics vary depending on the carrier frequency, for example, as shown in FIG. 4, the propagation characteristics are structured so that the search can be branched according to the carrier frequency.

  The specific operation of the present embodiment will be described below with reference to the flowchart shown in FIG.

  For example, when the radio base station 1-1 communicates with the terminal 3, the radio base station 1-1 is applied to direct the beam to the terminal 3 by the beam generation means 15 based on the received signal from the terminal 3. A weighting factor to be calculated is calculated (step S51), a band is allocated to the terminal 3 (step S52), and communication is started.

  Thereafter, during communication, when the terminal communication means 15 of the radio base station 1-1 does not receive the transmission signal from the terminal 3 (step S53), the weighting factor applied to the beam generation at that time Is transmitted to the communication control device 2 by the communication control device communication means 12, and the communication control device 2 is inquired as to whether or not the terminal 3 is located in the interference region.

  When the communication control device 2 receives the interference area inquiry from the radio base station 1-1 via the radio base station communication means 21, at that time, the adjacent radio base station 1-2 applies the beam generation to the beam. Weighting coefficient obtained from the radio base station 1-2 via the radio base station communication means 21. Then, in the interference area determination means 22, the actual weighting factor acquired from the radio base station 1-1 and the radio base station 1-2, and the first weighting factor and the second weighting factor stored in the interference table 23 Based on the comparison, it is searched whether there is the same combination, and if it is the same combination, it is determined that it is located in the interference region.

  Here, if it is determined that the terminal 3 is located in the interference area with the radio base station 1-2, the fact is transmitted to the radio base station 1-1 via the radio base station communication means 21. To do. As a result, the terminal control means 11 of the radio base station 1-1 controls the transmission so as to stop the transmission to the terminal 3 or reduce the transmission output (step S55), as shown in FIG. Thus, the terminal 3 is prompted to perform a handover to the radio base station 1-2.

  That is, in the interference area, the terminal 3 receives signals mixedly because the reception strengths of the radio base station 1-1 and the adjacent radio base station 1-2 are approximately the same. However, as described above, when the transmission from the radio base station 1-1 to the terminal 3 is stopped or the transmission output is reduced, the terminal 3 receives the radio base station 1-1. Since the reception intensity becomes low, when the reception intensity from the radio base station 1-2 does not change, the signal of the radio base station 1-1 is buried in the signal of the radio base station 1-2. As a result, the terminal 3 can receive the signal of the radio base station 1-2 instead of receiving the signal of the radio base station 1-1 that has been wirelessly connected so far. On the other hand, a handover request from the radio base station 1-1 is increased. As a result, the terminal 3 can smoothly perform handover from the radio base station 1-1 to the radio base station 1-2.

  The radio base station 1-1 tracks the transmission status of the terminal 3 after reducing or stopping the transmission power to the terminal 3, and when a handover to another radio base station cannot be confirmed for a certain period of time. Returns transmission power and resumes communication. If it is determined in step S54 that the terminal 3 is not located in the interference area with the radio base station 1-2, for example, the terminal control unit 11 of the radio base station 1-1 determines that the terminal 3 The transmission output is controlled to increase.

  Therefore, in the present embodiment, the terminal communication means 11 of each radio base station 1 includes a signal detection means for detecting whether or not a transmission signal is received from a terminal in communication with the radio base station 1, and a terminal in communication And transmission control means for controlling transmission.

  As described above, in the present embodiment, when the radio base station 1-1 cannot receive a transmission signal from the terminal 3 while communicating with the terminal 3, the communication control apparatus 2 stores the interference table 23. With reference to this, it is determined whether or not the terminal 3 is located in the interference area. When the terminal 3 is located in the interference area, the transmission of the radio base station 1-1 is performed so as to be handed over to the adjacent radio base station 1-2. As a result, the time during which the terminal 3 exists in the interference area (disconnection time) can be reduced, and the terminal 3 can be quickly handed over to the adjacent radio base station 1-2. Can be secured.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, in the above embodiment, adjacent radio base stations use the same frequency band. However, even when the used frequency band is different, the transmission wave from the adjacent radio base station becomes an interference wave. The present invention can be applied effectively. Moreover, in the said embodiment, when the transmission signal from the terminal 3 cannot be received on the radio base station 1-1 side communicating with the terminal 3, the communication control device 2 uses the interference table 23 to 3 is determined whether it is located in the interference area, but without using the interference table 23, the radio base station 1-1 side in communication with the terminal 3 can receive the transmission signal from the terminal 3. If not, it can be configured that the transmission to the terminal 3 is controlled and the terminal 3 is prompted to be handed over to an adjacent radio base station, assuming that the terminal is likely to be located in the interference area. Moreover, in the said embodiment, it is applied in the radio base station 1-1, without detecting the presence or absence of reception of the transmission signal from the terminal 3 in the radio base station 1-1 side in communication with the terminal 3. Based on the comparison between the weighting factor and the content stored in the interference table, it can also be determined whether or not the terminal 3 is located in the interference region.

  In the above-described embodiment, the interference table 23 includes position information indicating an interference area by the radio base station 1-1 and the radio base station 1-2 adjacent to each other, and the radio base station 1-1 in the interference area. The first weighting factor for directing the beam and the second weighting factor for directing the beam by the radio base station 1-2 are stored in association with each other. The position information indicating the interference area to be received may be stored in association with at least the weighting factor for the radio base station to direct the beam to the interference area. In this case, based on the comparison between the weighting factor acquired from the wireless base station 1-1 in communication and the weighting factor of the corresponding wireless base station 1-1 stored in the interference table 23, for example, the antenna The difference value of the weighting factor is calculated for each, and if the variance of the difference value of the weighting factor is within a certain value, it may be determined that the terminal 3 is located in the interference region. In this case, it is not possible to limit which adjacent radio base stations transmit radio waves that may cause interference, but there is a possibility that the terminal 3 exists in an area that may cause interference with other radio base stations. Means high. When this determination method is adopted, preferably, when the radio base station 1-1 controls transmission to the terminal 3 and the terminal 3 is handed over to the radio base station 1-2, it is determined as interference. The weighting factor of the radio base station 1-1 and the weighting factor of the handover destination radio base station 1-2 are associated with each other and registered in the interference table 23.

It is a figure for demonstrating the principle of the communication system which concerns on one embodiment of this invention. It is a functional block diagram which shows schematic structure of the principal part of each wireless base station and communication control apparatus in the communication system shown in FIG. FIG. 3 is a diagram illustrating an example of a recording format of an interference table illustrated in FIG. 2. It is a figure which shows the modification of the recording format shown in FIG. 3 is a flowchart for explaining a specific operation of the communication system shown in FIG. 1.

Explanation of symbols

1-1, 1-2 Wireless base station 2 Communication control device 3 Terminal (wireless communication device)
DESCRIPTION OF SYMBOLS 11 Terminal communication means 12 Communication control apparatus communication means 13 Control means 15 Beam generation means 21 Radio base station communication means 22 Interference area determination means 23 Interference table 25 Control means

Claims (7)

A communication control method in a communication system including a plurality of radio base stations equipped with an adaptive array antenna,
In the first radio base station in communication with the radio communication device, the presence or absence of reception of a transmission signal from the radio communication device is detected,
When the transmission signal from the radio communication apparatus cannot be received, the transmission of the first radio base station so that the radio communication apparatus hands over to the second radio base station adjacent to the first radio base station. The communication control method characterized by controlling.   2. The communication control method according to claim 1, wherein when the transmission signal from the wireless communication apparatus cannot be received, the transmission of the first wireless base station is stopped or the transmission output is reduced. A communication control method in a communication system including a plurality of radio base stations provided with an adaptive array antenna and a communication control device that controls the plurality of radio base stations,
For each radio base station, an interference table in which position information indicating an interference area that receives communication interference from an adjacent radio base station is associated with at least a weighting factor for the radio base station to direct a beam to the interference area. Remember
While the wireless communication device is communicating with the first wireless base station among the plurality of wireless base stations, the wireless communication device acquires at least the weighting factor applied by the first wireless base station, and the acquired weighting factor and the Based on the comparison with the weighting factor of the corresponding radio base station stored in the interference table, it is determined whether the radio communication device is located in the interference area,
As a result, when the wireless communication device is located in an interference area, the transmission of the first wireless base station is performed so that the wireless communication device is handed over to the second wireless base station adjacent to the first wireless base station. The communication control method characterized by controlling. In the first radio base station in communication with the radio communication device, the presence or absence of reception of a transmission signal from the radio communication device is detected,
The communication control method according to claim 3, wherein when the transmission signal from the wireless communication device cannot be received, it is determined whether or not the wireless communication device is located in an interference area.   5. The communication control method according to claim 3, wherein when the wireless communication apparatus is located in an interference area, transmission of the first wireless base station is stopped or transmission output is reduced. A communication system including a plurality of radio base stations provided with an adaptive array antenna and a communication control device for controlling the plurality of radio base stations,
Each of the plurality of radio base stations
A communication control device communication means for transmitting a weighting factor applied to beam generation to the communication control device and receiving an interference region determination result from the communication control device,
The communication control device includes:
Receiving means for receiving the weighting factor transmitted from each radio base station;
For each of the radio base stations, position information indicating an interference area that receives communication interference from an adjacent radio base station and at least a weighting factor for the radio base station to direct a beam to the interference area are stored correspondingly. An interference table;
While the wireless communication device is communicating with the first wireless base station among the plurality of wireless base stations, the wireless communication device acquires at least the weighting factor applied by the first wireless base station, and the acquired weighting factor and the Interference region determination means for determining whether or not the wireless communication device is located in an interference region based on a comparison with a weighting factor of a corresponding wireless base station stored in an interference table;
A transmission means for transmitting an interference area determination result by the interference area determination means to the first radio base station;
When the interference region determining means determines that the wireless communication device is located in the interference region, the wireless communication device is handed over to the second wireless base station adjacent to the first wireless base station. A communication system configured to control transmission in a first radio base station. A wireless base station with an adaptive array antenna,
Signal detection means for detecting whether or not a transmission signal is received from a wireless communication device in communication;
A transmission control means for controlling transmission so that the radio communication apparatus is handed over to an adjacent radio base station when the signal detection means fails to receive a transmission signal from the radio communication apparatus;
A radio base station characterized by comprising:

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