JP5465616B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system, and more particularly to a wireless communication system that supports multi-point coordinated transmission / reception.

  Conventionally, there is a MIMO (Multi-Input Multi-Output) wireless communication system as a technique for improving communication efficiency between a wireless communication terminal (mobile station) and a base station. In this MIMO wireless communication system, communication is performed via a plurality of paths (streams) between a mobile station and a base station each having a plurality of antennas. In a MIMO wireless communication system, a transmitting apparatus divides data to be transmitted into a plurality of streams in advance and transmits the data from a plurality of antennas in the same frequency band. The receiving device receives and synthesizes signals with a plurality of antennas. Thereby, since a plurality of signals can be transmitted and received in the same frequency band, the amount of data that can be transmitted and received using a limited communication band can be increased, leading to higher communication speed.

  In general, a cell of a certain base station and a cell of a base station adjacent to the base station overlap in the vicinity of each cell edge (boundary of a region where radio waves from the base station reach). For this reason, radio signals from a plurality of base stations interfere with each other in a region where a plurality of cells overlap (hereinafter referred to as a cell edge vicinity region). Furthermore, since the cell edge vicinity region is a region away from the base station, the communication environment is bad and the throughput is reduced.

  In order to solve this and improve the throughput in the region near the cell edge, communication called CoMP (Coordinated Multipoint) has been developed. CoMP is a base station cooperative MIMO technique that significantly improves the throughput particularly in the region near the cell edge by communicating with mobile stations by coordinating adjacent base station antennas (see, for example, Patent Document 1). FIG. 6 shows a communication system 100 based on CoMP according to Patent Document 1. Here, the mobile station 102 is located in the cell edge vicinity region of both the first base station 103 and the second base station 104. The mobile station 102 includes at least two reception antennas, and performs MIMO communication with the first base station 103 and the second base station 104 under the control of the base station control apparatus 101. That is, the base station control apparatus 101 divides data to be transmitted to the mobile station 102 into two, and makes the first base station 103 and the second base station 104 cooperate (synchronize) with each other. The first base station 104 transmits data to the mobile station 102 in the same frequency band through the stream 1 and the second base station 104 through the stream 2.

  Then, the mobile station 102 receives, for example, rake data from the first base station 103 and the second base station 104 and combines them. In this way, in the communication system 100 based on CoMP, a plurality of data can be transmitted and received in the same frequency band, so that the throughput in the cell edge vicinity region can be improved. In other words, the CoMP-based communication system 100 can support a high data transfer rate even in the vicinity of the cell edge.

JP 2008-543141 A

  However, in such a communication system, it is assumed that one mobile station located in the cell edge vicinity region uses communication resources of a plurality of adjacent base stations, but the traffic processing of the base station increases. When using a communication system based on CoMP, communication resources may not be effectively used.

  An object of the present invention made in view of this point is to provide a wireless communication system capable of reducing the processing load on the base station side and effectively utilizing communication resources as the entire wireless communication system. .

The invention of the wireless communication system according to the first aspect for achieving the above object is as follows:
A plurality of base stations, a base station control device that controls the plurality of base stations, and a mobile station that includes a plurality of antennas, the base station control device cooperating with the plurality of base stations, In a wireless communication system that performs wireless communication simultaneously with the mobile station,
At least one base station among a plurality of base stations cooperating with each other that performs radio communication simultaneously with the mobile station, notifies the base station controller of the load state of the own station,
The base station control device determines a magnitude relationship between the load states of the plurality of base stations based on the notifications from the plurality of base stations , and at least between the base station in the maximum load state and the mobile station Controlling a plurality of said base stations to release wireless communication;
It is characterized by this.

The invention according to a second aspect is a wireless communications system according to the first aspect,
The base station controlled by the base station control device that has received the notification to cancel the wireless communication with the mobile station transmits a cancellation request to the mobile station,
The mobile station is characterized by stopping the demodulation of a signal received from the base station upon receiving the cancellation request.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the radio | wireless communications system which can reduce the processing load in the base station side, and can utilize a communication resource effectively as the whole radio | wireless communications system.

It is a figure which shows schematic structure of the radio | wireless communications system which concerns on one embodiment of this invention. It is a schematic flowchart which shows the control by the base station control apparatus in the radio | wireless communications system which concerns on one embodiment of this invention. It is a figure for demonstrating the reception process by the mobile station in the radio | wireless communications system which concerns on one embodiment of this invention. It is a figure which shows the control by the base station control apparatus in the radio | wireless communications system which concerns on one embodiment of this invention. It is a figure which shows the other control by the base station control apparatus in the radio | wireless communications system which concerns on one embodiment of this invention. It is a figure which shows schematic structure of the communication system based on the conventional CoMP.

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

  FIG. 1 is a diagram showing a schematic configuration of a radio communication system according to an embodiment of the present invention. The radio communication system 10 includes, for example, a mobile station 12 that is a mobile phone terminal, a first base station 13 and a second base station 14 that communicate with the mobile station 12 by CoMP, a first base station 13, and a second base station 14. And a base station control device 11 that performs cooperative control or the like. The base station control device 11 is, for example, an EMS (Element Management System) server. The mobile station 12 includes a plurality of antennas and supports communication by CoMP. The first and second base stations 13 and 14 are base stations compatible with, for example, LTE (Long Term Evolution).

  In the wireless communication system 10, when the mobile station 12 is located in a region near the cell edge of the first base station 13 and the second base station 14, communication based on CoMP is performed between the first base station 13 and the second base station 14. Done. In communication based on CoMP, the base station controller 11 divides data to be transmitted to the mobile station 12 (for example, moving image data) into two parts, and coordinates (synchronizes) the first base station 13 and the second base station 14 with each other. The first base station 13 transmits data to the mobile station 12 in the same frequency band through the stream 1 and the second base station 14 through the stream 2. Here, the data transmitted through the streams 1 and 2 respectively constitute one moving image data.

  FIG. 2 is a schematic flowchart showing control by the base station control apparatus in the radio communication system according to the present embodiment. From the first base station 13 (hereinafter referred to as “BS1”) and the second base station 14 (hereinafter referred to as “BS2”), the base station controller 11 is notified that the respective load states (traffic) have exceeded a predetermined threshold. Notice. The base station control apparatus 11 shall grasp the latest load states of the BS1 and BS2 based on these notifications. The load state (traffic) includes the load on the processor of the base station control device, the data transfer amount (throughput), and the like. Now, it is assumed that communication traffic in BS1 and BS2 is equal to or less than a predetermined threshold. When detecting that the mobile station 12 has moved to the area near the cell edge of BS1 and BS2, the base station controller 11 controls the BS1 and BS2 to start communication by CoMP with the mobile station 12 (steps). S101).

  If the base station controller 11 does not receive a notification that the traffic has exceeded a predetermined threshold value from either BS1 or BS2 (steps S102 and S103), the base station controller 11 controls BS1 and BS2 so as to continue communication using CoMP. (Step S104).

  On the other hand, if the base station controller 11 receives a notification from the BS 2 that the traffic has exceeded the predetermined threshold (Yes in step S103), the base station controller 11 controls the BS 2 to request the mobile station 12 to cancel the channel. Is transmitted (step S105). The mobile station 12 that has received the channel release request releases the channel that has been communicating with the BS 2 until then.

  Next, the control by the base station control device 11 when receiving a notification from the BS 1 that traffic has exceeded a predetermined threshold will be described (Yes in step S102). In this case, if the notification that the predetermined threshold value is exceeded is not received from BS2 (No in step S106), the base station control device 11 controls BS1 to transmit a channel release request to the mobile station 12 (Step S107). The mobile station 12 that has received the channel release request releases the channel that has been communicating with the BS 1 until then.

  On the other hand, when the notification that the predetermined threshold value is exceeded is also received from BS2 (Yes in step S106), the base station control device 11 determines the magnitude relationship between the traffic of BS1 and the traffic of BS2 (step S108). ). As a result, when it is determined that the traffic of BS2 is larger than the traffic of BS1 (Yes in step S108), the base station controller 11 controls BS2 to cause the mobile station 12 to transmit a channel release request. (Step S109). The mobile station 12 that has received the channel release request releases the channel that has been communicating with the BS 2 until then.

  On the other hand, if it is determined in step S108 that the traffic of BS1 is larger than the traffic of BS2 (No in step S108), the base station control device 11 controls BS1 and requests the mobile station 12 to cancel the channel. Is transmitted (step S110). The mobile station 12 that has received the channel release request releases the channel that has been communicating with the BS 1 until then.

  In steps S105 and S109, the mobile station 12 that has received the channel release request transmitted from the BS2 performs a process for not demodulating the data from the BS2. Specifically, as shown in FIG. 3, the data received from BS1 and BS2 is separated by the MIMO reception process, and the data received from BS1 after the time specified by the channel release request is deleted without demodulation. To do. Even when the channel release request transmitted from BS1 is received in steps S107 and S110, the mobile station 12 performs the same processing in order not to demodulate the data from BS1. This is because these data are no longer necessary for the mobile station 12.

  Although not shown, the base station controller 11 transmits data that was scheduled to be transmitted from the base station (BS1 or BS2) that transmitted the channel release request from the base station (BS1 or BS2) that maintains communication. Let

  Hereinafter, an example of control in the wireless communication system according to the embodiment of the present invention will be described with reference to the schematic sequence diagram shown in FIG. This control corresponds to the control up to steps S101 to S107 in FIG. Here, the dashed arrow in FIG. 4 indicates wireless communication, and the solid arrow indicates, in principle, wired communication.

  The base station control device 11 synchronizes the timings of the adjacent BS 1 and BS 2 that perform communication based on CoMP with the mobile station 12. Here, each of BS1 and BS2 grasps whether or not the traffic of its own station exceeds a predetermined threshold, and notifies the base station control device 11 when the traffic exceeds the threshold. To do. That is, in the case where communication based on CoMP is performed between BS1 and BS2 and the mobile station 12, if there is no notification from BS1 and BS2, the base station controller 11 uses the traffic of BS1 and BS2 as traffic information. Holds information that the value is equal to or less than the threshold value. During communication based on CoMP, the mobile station 12 performs normal MIMO reception.

  Now, for example, if communication requests from terminals in the cell of BS1 are concentrated and the traffic of BS1 exceeds a predetermined threshold, BS1 informs the base station controller 11 that the traffic of its own station has exceeded the threshold. Make a notification. Receiving the notification, the base station control device 11 updates the traffic information (corresponding to Yes in step S102 in FIG. 2).

  In this state, as the latest traffic information, the base station control device 11 grasps that the traffic of BS1 exceeds a predetermined threshold and the traffic of BS2 is equal to or lower than the predetermined threshold (step S106 in FIG. 2). Corresponding to No). Then, the base station control device 11 transmits a transmission request for channel release request to the BS 1 (corresponding to step S107 in FIG. 2). In addition, the base station control device 11 notifies the BS 2 that the channel used for communication between the BS 1 and the mobile station 12 has been released.

  The BS 1 that has received the channel release request effectively uses the channel (communication resource) that has been used for communication with the mobile station 12 until then, for example, by assigning it to another terminal. In addition, the mobile station 12 is requested to cancel the channel used for communication with the BS1. The mobile station 12 separates the respective data received from BS1 and BS2 by the MIMO reception process, and after the transmission of the channel release request by BS1, until the reception of the request, via the channel that is the target of the release request The data received from BS1 is deleted without being demodulated. The data to be deleted may be determined based on, for example, the time stamp at the time of transmission included in the cancellation request transmitted from the BS 1 and the reception time of the cancellation request in the mobile station 12.

  Next, another control in the wireless communication system according to the embodiment of the present invention will be described with reference to the schematic sequence diagram shown in FIG. This control corresponds to the control up to steps S101 to S109 in FIG. As in S101 to FIG. 4, a broken line arrow indicates wireless communication, and a solid line arrow indicates, in principle, wired communication. In the figure, the first base station 13 is shown as BS1, and the second base station 14 is shown as BS2.

  As in the case of FIG. 4, the base station controller 11 synchronizes the timings of BS1 and BS2. In addition, the mobile station 12, BS1 and BS2 perform communication based on CoMP, and the mobile station 12 performs MIMO reception. In this state, for example, when communication requests from terminals in the cell of BS1 are concentrated and the traffic of BS1 exceeds a predetermined threshold, BS1 informs the base station controller 11 that the traffic of its own station has exceeded the threshold. Make a notification. Receiving the notification, the base station control device 11 updates the traffic information (corresponding to Yes in step S102 in FIG. 2). When the traffic in BS2 also exceeds a predetermined threshold, BS2 notifies base station controller 11 that the traffic of the local station has exceeded the threshold. Receiving the notification, the base station control device 11 updates the traffic information (corresponding to Yes in step S106 in FIG. 2).

  Then, the base station control device 11 determines the magnitude relationship between the traffic values of BS1 and BS2. If it is determined that the value of BS2 traffic is larger (corresponding to Yes in step S108 in FIG. 2), the base station controller 11 transmits a transmission request for a channel release request to BS2 (corresponding to step S107 in FIG. 2). ). In addition, the base station control device 11 notifies the BS 1 that the channel used for communication between the BS 2 and the mobile station 12 has been released.

  The BS 2 that has received the channel release request effectively uses the channel (communication resource) that has been used for communication with the mobile station 12 so far, for example, by assigning it to another terminal. Also, the mobile station 12 is requested to cancel the channel that has been communicating with the BS 2 (corresponding to step S109 in FIG. 2). The mobile station 12 separates each data received from BS1 and BS2 by the MIMO reception process, and after the transmission of the channel release request by the BS2, until the reception of the request, via the channel that is the target of the release request The data received from BS2 is deleted without being demodulated. The data to be deleted may be determined based on, for example, the time stamp at the time of transmission included in the cancellation request transmitted from the BS 2 and the reception time of the cancellation request in the mobile station 12.

  Thus, according to the radio communication system according to the present embodiment, the base station can perform communication based on CoMP according to the load state. For this reason, in a wireless communication system based on CoMP, it is possible to reduce the processing load on the base station side and to effectively use communication resources.

  Although the wireless communication system according to the embodiment of the present invention has been described above, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. For example, although the above embodiment has been described using two base stations, the above control and the like can also be applied to CoMP communication between three or more base stations. In this case, under the control of the base station control device, for example, leaving one base station and canceling communication between all other base stations and the mobile station, normal communication between the one base station and the mobile station is performed. There may be communication. Alternatively, under the control of the base station control device, communication between one base station and a mobile station may be canceled, and communication using CoMP may be continued between a plurality of other base stations and the mobile station.

DESCRIPTION OF SYMBOLS 10 Wireless communication system 11 Base station control apparatus 12 Mobile station 13 1st base station 14 2nd base station

Claims (2)

A plurality of base stations, a base station control device that controls the plurality of base stations, and a mobile station that includes a plurality of antennas, the base station control device cooperating with the plurality of base stations, In a wireless communication system that performs wireless communication simultaneously with the mobile station,
A plurality of base stations cooperating with each other that perform radio communication simultaneously with the mobile station notify the base station controller of the load state of the own station,
The base station control device determines a magnitude relationship between the load states of the plurality of base stations based on the notifications from the plurality of base stations , and at least between the base station in the maximum load state and the mobile station Controlling a plurality of said base stations to release wireless communication;
A wireless communication system. The base station controlled by the base station control device that has received the notification to cancel the wireless communication with the mobile station transmits a cancellation request to the mobile station,
The radio communication system according to claim 1, wherein the mobile station stops the demodulation of a signal received from the base station upon receiving the cancellation request.

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