Abstract:
Information on each wireless environment of an adjacent cell is exchanged between adjacent wireless base station in a mobile communication system, where the system enables a plurality of wireless base stations to communicate with each other by using a link between the base stations. Then, the latest information of the information on the wireless environments is stored in a memory at each wireless base station. Each wireless base station performs handover control, transmission power control, traffic control by referencing the memory storage information. That enables usage efficiency of wireless resources to be improved and a communication quality at end users to be improved as a whole of the system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a wireless base station, a method for controlling operations of the wireless base station and a mobile communication system using the wireless base station, and specifically to a wireless base station optimally used in the Beyond3G (B3G) system that performs communication between wireless communication base stations, a method for controlling operations of the wireless base station, and the mobile communication system using the wireless base station. 
         [0003]    2. Description of the Prior Art 
         [0004]    In the W-CDMA (Wideband-Code Division Multiple Access) system, mobile terminals are identified with spread codes in the same frequency. For each of the mobile terminals, power from all the other mobile terminals causes interference. Further, the transmission power control or the handover control for each mobile terminal is performed independently for each wireless base station. These controls do not take account of interference with adjacent cells. That is to say, power control on a certain wireless base station leads much more interference with the adjacent cells, which may degrade system throughput or the wireless capacity of the adjacent cells. Currently, no solution has yet been found to optimally control those kinds of degradation in the entire network. 
         [0005]    Japanese Patent Laid-Open No. 2004-304394 discloses a technique for reserving communication means between wireless base stations to directly exchange information between the wireless base stations. 
         [0006]    The technique disclosed in the abovementioned gazette intends to improve efficiency on a radio channel by reserving means of communication between wireless base stations to enable the wireless base stations to directly exchange information and share the information on the radio channel of each station. As mentioned above, power control on a certain wireless base station leads more interference from the adjacent cells, which may degrade system throughput or the wireless capacity of the adjacent cells. The technique disclosed in the official gazette does not take into account of appropriately controlling the degradation as a whole of a network in such a case. 
         [0007]    The present invention intends to provide a wireless base station that enables efficiency utilizing wireless resources to be improved as a whole of the system and also enables communication quality of end users to be improved, a method for controlling operations of the wireless base station and the mobile communication system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A wireless base station according to the present invention is a wireless base station capable of communicating with an adjacent wireless base station, including handover controlling means for controlling handover by referencing wireless environment information of adjacent cells notified from the adjacent wireless base station. 
         [0009]    Another wireless base station of the present invention is a wireless base station capable of communicating with an adjacent wireless base station, including transmission power controlling means for controlling uplink and downlink transmission power by referencing wireless environment information of adjacent cells notified from the adjacent wireless base station. 
         [0010]    Yet another wireless base station of the present invention is a wireless base station that is adapted to control a handover or a transmission power by informing wireless environment information with an adjacent wireless base station, including means for taking statistics of a handover request frequency for each adjacent wireless base station and controlling a notification frequency of the wireless environment information based on the statistics. 
         [0011]    Yet another wireless base station of the present invention is a wireless base station capable of communicating with an adjacent wireless base station, including traffic controlling means for controlling traffic of communication between wireless base stations by referencing wireless environment information of self-station. 
         [0012]    Yet another wireless base station of the present invention is a wireless base station capable of communicating with an adjacent wireless base station, including means for determining interference from the adjacent cell based on wireless environment information and an average bit rate of the self-station and informing the determination to the adjacent wireless base station. 
         [0013]    A mobile communication system of the present invention includes the above-mentioned wireless base station. 
         [0014]    An operation controlling method of the present invention is an operation controlling method at a wireless base station capable of communicating with an adjacent wireless base station, including a handover controlling step of controlling handover by referencing wireless environment information of adjacent cells notified from the adjacent wireless base station. 
         [0015]    Another operation controlling method of the present invention is an operation controlling method at a wireless base station capable of communicating with an adjacent wireless base station, including a transmission power controlling step of controlling uplink and downlink transmission power by referencing wireless environment information of adjacent cells notified from the adjacent wireless base station. 
         [0016]    Yet another operation controlling method of the present invention is an operation controlling method at a wireless base station that is adapted to control a handover or a transmission power by informing wireless environment information between adjacent wireless base station, including a statistics taking step of taking statistics of a handover request frequency for each adjacent wireless base station and a controlling step of controlling a notification frequency of the wireless environment information based on the statistics. 
         [0017]    Yet another operation controlling method of the present invention is an operation controlling method at a wireless base station capable of communicating with an adjacent wireless base station, including a traffic controlling step of controlling traffic of communication between wireless base stations by referencing wireless environment information of self-station. 
         [0018]    Yet another operation controlling method of the present invention is an operation controlling method at a wireless base station capable of communicating with an adjacent wireless base station, including a step of determining interference from the adjacent cell based on wireless environment information and an average bit rate of the self-station and an informing step of informing the determination to the adjacent wireless base station. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a diagram showing an example of a configuration of a mobile communication system to which an embodiment of the present invention is applied; 
           [0020]      FIG. 2  is a functional block diagram of a wireless base station of the embodiment of the present invention; 
           [0021]      FIG. 3  is a diagram showing an example of contents of the adjacent cell information memory  150  in the wireless base station  100 ; 
           [0022]      FIG. 4  is a sequence diagram showing a reporting operation of various measured values between the wireless base stations; 
           [0023]      FIG. 5  is a diagram showing an example of information included in the measured value-reporting request  500  of  FIG. 4 ; 
           [0024]      FIG. 6  is an operational flowchart of handover control in an embodiment of the present invention; 
           [0025]      FIG. 7  is another operational flowchart of handover control in an embodiment of the present invention; 
           [0026]      FIG. 8  is an operational sequence diagram when a soft handover succeeded in an embodiment of the present invention; 
           [0027]      FIG. 9  is an operational sequence diagram when a soft handover failed in an embodiment of the present invention; 
           [0028]      FIG. 10  is an operational flowchart of a transmission power control in an embodiment of the present invention; 
           [0029]      FIG. 11  is an operational flowchart of a statistical processing and transferring of measured value of an adjacent cell to each other in an embodiment of the present invention; 
           [0030]      FIG. 12  is an operational flowchart of traffic control of a communication between wireless base stations in an embodiment of the present invention; and 
           [0031]      FIGS. 13A and 13B  are tables for describing control operations for identifying interference of an adjacent cell in an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Embodiments of the present invention will be described with reference to drawings below.  FIG. 1  is a system block diagram of the embodiment of the present invention. Referring to  FIG. 1 , the reference numerals  100 ,  101 ,  102  indicate wireless bases station devices conforming to the Beyond 3G system. The wireless base station devices have an antenna  120  for a cell  30 , an antenna  121  for a cell  31  and an antenna  122  for a cell  32 , respectively. The wireless base station  100 ,  101 ,  102  have memories  150 ,  151 ,  152  for storing various types of information respectively. The memories will be detailed later. 
         [0033]    The wireless base station devices  100 ,  101 ,  102  are connected with an access gateway  300  via wired links  20 ,  21 ,  22 , respectively. The access gateway  300  is a node for controlling each of the wireless base stations  100 ,  101 ,  102 . 
         [0034]    Each of the wireless base stations  100 ,  101 ,  102  has a rooting function, and is adapted to be able to exchange required information between base stations via the links  140 ,  141  between the wireless base stations or the like. The reference numeral  400  indicates a mobile terminal, which is assumed to be moving from the cell  30  to the cell  31 . Each cell of the wireless base station devices  100 ,  101 ,  102  is assumed to be adjacent to each other. 
         [0035]    A specific example of operations in the embodiment will be described below.  FIG. 2  is an outlined functional block diagram of the wireless base station  100  in the embodiment of the present invention. The other wireless base stations  101  and  102  have the same configuration. 
         [0036]    Referring to  FIG. 2 , the wireless base station  100  has a wireless communication unit  130  for communicating with the mobile terminal  400  via the antenna  120 , a communication unit  160  between base stations for communicating with an adjacent base station via the link  140  between base stations, a wireless environment measuring unit  170  for measuring a wireless environment of the cell  30 , a memory  150  for temporally storing various types of information, a controlling unit (CPU as a computer)  180  for controlling each of the units  130 ,  160 ,  170 ,  150 , and a ROM  190  storing a controlling operation of the controlling unit  180  as a program in advance. 
       &lt;Updating of Adjacent Cell Information&gt; 
       [0037]    First, an updating operation of adjacent cell information will be described below. In  FIG. 1 , the amount of uplink interference and downlink transmission power for each base station are periodically transferred to each other via the links  140 ,  141  between the base stations and save them in the adjacent cell information memories  150 ,  151 ,  152  of respective wireless base stations to realize a handover, in which influence by adjacent cell interference between wireless base stations  100 ,  101 ,  102  is restricted.  FIG. 3  shows detailed contents of the adjacent cell information memory  150  of the wireless base station  100  as an example. They are the same as those of the adjacent cell information memories  151 ,  152  of the other wireless base stations  101 ,  102 . 
         [0038]    In  FIG. 3 , the adjacent cell information memory  150  has an uplink interference level region and a downlink transmission power region of the wireless base station  101  that is an adjacent cell, and an uplink interference level region and a downlink transmission power region of the wireless base station  102  that is also an adjacent cell. The contents of the regions are updated at any time by transferring a measured value to each other. 
         [0039]    In the operations of transferring a measured value to each other, a measured value reporting requests  500 ,  501  from the base station  100  are sent to the base stations  101 ,  102  as shown in the sequence diagram of  FIG. 4 . The measured value reporting requests has a destination address, a self-measured value, a reporting request type, and a measurement request type as shown in  FIG. 5 . 
         [0040]    To the destination address, a destination address to which the measured value reporting request is sent is set. In this embodiment, addresses of the base stations  101 ,  102  are set to the destination address respectively. To the self-measured value, each measured value for the uplink interference level and the downlink transmission power of the self station  100  is set. 
         [0041]    To the measured value reporting request, an information request type indicating whether it is “periodical information” or “on-demand” is further set. The base station  101  or  102  that received the request performs the measured value report according to the reporting request type. If the information request type is “periodical information”, the measured value is notified of according to the time set ( 511  of  FIG. 4 ). If the information request type is “on-demand”, the immediately preceding measured value is notified once ( 510  of  FIG. 4 ). 
         [0042]    The measurement request type is for indicating the type of the measured value, including the uplink interference level and the downlink transmission power, each of which designates an uplink total interference level of the cell and the downlink total transmission power value of the cell. 
       &lt;Handover Control&gt; 
       [0043]    Next, handover control of the mobile terminal will be described with reference to flowcharts of  FIGS. 6 and 7 . First, referring to  FIG. 6 , the wireless base station  100  shown in  FIG. 1  periodically refers to the adjacent cell information memory  150 . If the uplink total interference level or the downlink total transmission power of the adjacent wireless base station  101  is equal to a predetermined value (step  1 ) or more than that, the wireless base station  100  adds a plus offset to a handover threshold (increases the threshold) for the mobile terminal  400  to reduce handover to the adjacent cell of the mobile terminal  400  under the cell  130  (step  2 ), and notifies the mobile terminal  400  of the further updated handover threshold (step S 3 ). 
         [0044]    Referring to  FIG. 7 , when the uplink total interference level or the downlink total transmission power of the self-station in the wireless base station  100  becomes a certain level or more (step S 4 ), the wireless base station  100  refers to the adjacent cell information memory  150 . When the uplink total interference level or the downlink total transmission power in the adjacent wireless base station  101  is lower than the threshold (step S 5 ), the wireless base station  100  adds a minus offset to the handover threshold for the mobile terminal  400  (decreases the threshold) (step S 6 ) and notifies the mobile terminal  400  of the updated handover threshold to encourage the handover to the adjacent cell of the mobile terminal  400  under the cell  130  (step S 7 ). 
       &lt;Control when a Handover Failed&gt; 
       [0045]    A control when a handover of the mobile terminal fails will be described. Assuming that the mobile terminal  400  handovers from the wireless base station (hereinafter referred to as a source base station)  100  to the wireless base station (hereinafter referred to as a target base station)  101  in the system for performing communication between wireless base stations as shown in  FIG. 1 .  FIGS. 8 and 9  are sequence diagrams of processing operations in the case.  FIG. 8  shows a case of a successful handover and  FIG. 9  shows a case of a failed handover. 
         [0046]    Before describing a control in the case of a failed handover, operations in the case of a successful handover will be described for reference. Referring to  FIG. 8 , the mobile terminal  400  sends out a handover request  600  to the wireless base station  100 . The handover request  600  includes a target wireless base station ID that is identification information of the target wireless base station  101  and the mobile terminal ID of itself. 
         [0047]    The wireless base station  100  that received the handover request  600  performs a handover start request  601  to the wireless base station  101 . The wireless base station  101  that received the handover start request  601  activates a handover waiting timer for determining whether the handover has been done properly or not ( 602 ) and sets a wireless link with the designated mobile terminal  400  ( 603 ). The timer stops when the wireless base station  101  receives handover completion information  604  from the mobile terminal  400 . 
         [0048]    When the wireless base station  101  receives the handover completion information  604  from the mobile terminal  400 , it stops the handover waiting timer ( 605 ) and issues the handover completion information  606  to the wireless base station  100 , while sending out a communication channel switching request  607  to the access gateway  300 . In response to that, the access gateway  300  sends out the communication channel switching response  608  to the wireless base station  101 . 
         [0049]    In response to that, the wireless base station  100  deletes the old wireless link with the mobile terminal  400  ( 609 ) and sends out a wireless link deletion response  610  informing accordingly to the wireless base station  101 . The wireless base stations  100  and  101  save the target base station ID and the source base station ID, respectively. 
         [0050]    Referring to  FIG. 9 , the same operational processes as those of  FIG. 8  have the same reference numerals as those in  FIG. 8 . In  FIG. 9 , if the wireless base station  101  cannot receives the handover completion information  604  and the handover waiting timer is timed out ( 702 ) due to a handover failure at the mobile terminal  400  ( 701 ), the wireless base station  101  immediately sends handover failure information  703  to the wireless base station  100  that received a setting request in the wireless section. The wireless base station  100  that received the handover failure information  703  determines it as the handover failure and sends a reconnection call  704 . The wireless base station  100  saves resources (frequency, OVSF (Orthogonal Variable Spreading Factor) code and the like) that have been used by the mobile terminal  400  during the period. 
         [0051]    The reconnected mobile terminal  400  performs reconnection confirming information  705  to the wireless base station  101 . The wireless base station  101  that received the reconnection confirming information sends the reconnection confirming information  706  to the wireless base station  100 . The above-described operational sequence enables the source base station and the target base station to cooperate with each other to cause a network to lead in reconnection in the case of the handover failure. 
       &lt;Transmission Power Control&gt; 
       [0052]    With reference to the flowchart of  FIG. 10 , the transmission power control will be described. The wireless base station  100  periodically refers to the adjacent cell information memory  150  in  FIG. 2 , and if the uplink total interference level or the downlink total transmission power of the adjacent cell is at the defined value or more (step S 8 ), the control described below is performed. 
       (1) Control Over the Transmission Power of the Mobile Terminal 
       [0053]    If the uplink total interference level of the adjacent cell is at the defined value or more, the mobile terminal communicating near a cell edge of the wireless base station  100  is detected and the uplink transmission power to the mobile terminal is reduced or kept (step S 9 ). That limits the throughput and enables to reduce interference to the adjacent cell. 
       (2) Control Over the Transmission Power of the Wireless Base Station 
       [0054]    If the downlink total transmission power of the adjacent cell is at the defined value or more, the mobile terminal communicating near a cell edge of the wireless base station  100  is detected and the downlink transmission power to the mobile terminal is reduced or kept (step S 10 ). That limits the throughput and enables to reduce interference to the adjacent cell. 
       &lt;Statistical Processing and Transferring of Measured Value to Each Other of the Adjacent Cell&gt; 
       [0055]    Referring to the flowchart of  FIG. 11 , the statistical processing and transferring of measured value to each other of the adjacent cell will be described. In each wireless base station, statistics of the base station ID of the source wireless base station which generates the handover request  600  in  FIG. 8  are taken (step S 11 ), and a handover frequency is determined for each base station ID (step S 12 ). A frequency of the transferring of measured value to each other is weighed with the handover frequency for each base station ID. 
         [0056]    For example, the measured value reporting request  500  and the measured value report  510  or  511  in  FIG. 4  are provided in short cycles for the base station ID whose frequency of the handover request  600  is more than the defined value (step S 13 ) (step S 14 ). For the base station ID whose frequency of the handover request  600  is at the defined value or less, the measured value reporting request  500  and the measured value report  510  or  511  are provided in long cycles (step S 15 ). 
         [0057]    Only the necessary information can be transferred between base stations by introducing statistical processing on the adjacent cell in the wireless base station in such a manner. By minimizing the traffic of the communication between wireless base stations, the capacity for subscribers for the entire system by appropriate wireless environment control can be improved as a whole of the system. 
       &lt;The Case where a Plurality of Cells are Present in Each Wireless Base Station&gt; 
       [0058]    The case where a plurality of cells are present for each wireless base station will be described next. In  FIG. 1 , one wireless base station comprises one cell, but one wireless base station can form a plurality of cells. In such a case, the links between the base stations  140 ,  141  in  FIG. 1  are available as they are. Control that does not depend on the number of cells, which are formed in the wireless base station by modification/addition described below, is enabled. 
         [0000]    (a) Measured Value Reporting Request/Measured Value Report  500 / 501  (see  FIG. 4 ) 
         [0059]    The cell ID is added in addition to the wireless base station ID to each of a request message and an informing message. 
         [0000]    (b) Handover Request  600 , Handover Start Request  601  (see  FIGS. 8 ,  9 ) 
         [0060]    The cell ID is added in addition to the mobile terminal ID and the source base station ID. 
         [0000]    (c) Saving of the Base Station ID  611 / 612  (see  FIG. 8 ) 
         [0061]    The cell ID is also stored at the same time as the base station ID is saved after a handover. 
         [0000]    (e) Statistical Processing of the Adjacent Base Station and the Adjacent Cell 
         [0062]    The base station ID and the cell ID are used for detecting the adjacent cell. 
       &lt;Traffic Deletion of the Communication between Wireless Base Stations&gt; 
       [0063]    Next, the traffic deletion of the communication between wireless base stations will be described. In &lt;handover control&gt; in the embodiment as described above, adjacent cell information may be transferred to each other as required instead of being periodically transferred. 
         [0064]      FIG. 12  shows an operational flowchart in such a case. If only the uplink interference level or the downlink total transmission power of the self-station in the wireless base station  100  becomes at a certain level or more (step S 16 ), the wireless base station  100  sends the measured value-reporting request (on-demand) (step S 17 ). If the uplink total interference level or the downlink total transmission power at the adjacent wireless base station is below the threshold (step S 18 ), the wireless base station  100  adds a minus offset to the handover threshold for the mobile terminal  400  (lowers the threshold) (step S 19 ) and notifies the mobile terminal  400  of the updated handover threshold to encourage handover to the adjacent cell of the mobile terminal  400  under the self-cell  130  (step S 20 ). 
         [0065]    The wireless base station  100  sends out the handover start request  601  to the, wireless base station  101  when the mobile terminal  400  performs a handover from the wireless base station  100  to  101 . It can also include a measured value-reporting request along with the measured value of the self-station in the message. That is to say, it can update the adjacent cell information memory by transferring the measured value of the adjacent cell to each other at each time a handover occurs. 
       &lt;Control of Interference Identification of the Adjacent Cell&gt; 
       [0066]    Next, a controlling operation for identifying interference of the adjacent cell will be described with reference to tables in  FIGS. 13A and 13B .  FIG. 13A  shows relationship between the uplink total interference level of the self-cell and the uplink average bit rate of the self-cell. If the uplink total interference level is high and the uplink average bit rate is low, it is determined that it is influenced by the interference from the adjacent cell and notifies the adjacent base station of the fact by the communication between the base stations. The wireless base station that received the information can reduce the adjacent cell interference to the origin of the information by dropping the bit rate (data rate) by a predefined number of percent. 
         [0067]    In the case of a combination of the uplink total interference level and the uplink average bit rate other than those mentioned above, it is assumed that it does not perform any operation in particular (No action). In the case of the self-cell interference (the case where the uplink total interference level is high and the uplink average bit rate is high), it is determined that interference in the self-cell is high, and it can reduce the interference by dropping the bit rate of the mobile terminal in the self-cell. 
         [0068]      FIG. 13B  shows relationship between the downlink total transmission power of the self-cell and the downlink average bit rate of the self-cell. If the downlink total transmission power is high and the downlink average bit rate is low, the mobile terminal determines that it is influenced by the interference from the adjacent cell, and notifies the adjacent base station of the fact via the communication between the base stations. The wireless base station that received the information can reduce the adjacent cell interference to the origin of the information by dropping the bit rate (data rate) by a predefined number of percent. 
         [0069]    In the case of a combination of the downlink total transmission power and the downlink average bit rate other than those mentioned above, it is assumed that it does not perform any operation in particular (No action). In the case of the self-cell interference (the case where the downlink total transmission power is high and the downlink average bit rate is high), it is determined that interference in the self-cell is high, and it can reduce the interference by dropping the bit rate of the mobile terminal in the self-cell. 
         [0070]    It is a matter of course that the operations in the respective embodiments as described above can be adapted to be stored in a recording medium such as a ROM as a program in the operational procedures in advance to cause the CPU (computer) to read and execute. 
         [0071]    As mentioned above, the efficiency utilizing the wireless resources in the W-CDMA mobile communication system can be improved as the whole system, as the wireless environment information such as the uplink interference level of the adjacent cell or the downlink transmission power is notified of between wireless base stations, and handover control, data transmission control, traffic control and the like are performed in consideration of the interference between adjacent cells in the mobile communication system that avails a communication between wireless base stations. That can also improve the communication quality of the end user. 
         [0072]    Specifically, the handover control by using the communication between wireless base stations enables the handover reduction/encouraging control of the mobile terminal in the wireless base station in consideration of wireless environment such as the uplink interference level or the downlink total transmission power of the adjacent cell, thus, an appropriate wireless environment control can be realized as a whole of the system in a plurality of wireless base stations so that the capacity for subscribers of the entire system can be improved. 
         [0073]    Reconnection of the wireless links can be efficiently performed when handover is failed. Thus, call disconnection due to a handover failure can be reduced so that it is expected to improve the quality for the end user. 
         [0074]    Further, only the necessary information can be transferred between base stations as statistical processing on the adjacent cell in the wireless base station is introduced in such a manner. By minimizing the traffic of the communication between wireless base stations, the capacity for subscribers for the entire system by appropriate wireless environment control can be improved as a whole of the system.