Patent Publication Number: US-2012026918-A1

Title: Method and system of managing neighbor relation table in wireless communication system having self-organizing network function

Description:
TECHNICAL FIELD 
     The present invention relates to a wireless communication system, and more particularly, to a method of automatically managing a neighbor relation table (NRT) in a wireless communication system having a self-organizing network (SON) function and a system thereof. 
     BACKGROUND ART 
     Universal Mobile Telecommunication Service (UMTS) systems are a third generation asynchronous mobile telecommunication system using Wide band Code Division Multiple Access (WCDMA) based on Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS). Third Generation Partnership Project (3GPP) in charge of UMTS standard is discussing Long Term Evolution (LTE) as a next generation wireless communication system of the UMTS systems. The LTE is a technology of implementing high-speed packet based communication with transmission speed of approximately maximum 300 Mbps, and aims to be used commonly in year 2010. There have been many attempts to do this. For example, there is an attempt to reduce the number of nodes located on a communication line by simplifying a structure of a network or an attempt to approach the wireless protocols to a wireless channel as far as possible. In the meantime, a SON for base station management aims at constructing a network more stably and efficiently. In particular, with visualization in introduction of Femto cells and next generation 4G in a wireless communication system field, there is growing interest in an SON with an automation function such as self-configuration or self-optimization. Nodes such as the Femto cells are not installed at an optimal position designated by a service provider but are installed by a user. Accordingly, cell planning for the nodes can not be performed. The nodes themselves detect the environment and collect information to perform optimization. 
     Accordingly, in this case, the SON may be defined as a network that enables nodes to access/set a network by themselves, and to suitably perform cell optimization and operation according to a peripheral wireless environment when installing the nodes indoors and outdoors. However, since parts capable of applying a self-organizing function are very diverse in a field of a wireless communication system, the SON can be differently defined according to characteristics, types, and objects of a network to be self-organized. In addition to a configuration of the network, self-organizing concept is applicable to a individual management algorithm and optimization. In spite of the foregoing requirements, there has not been proposed a specific method of managing neighbor base stations and system thereof. 
     The present invention has been made in view of the above problems, and provides a method of automatically managing an NRT in a wireless communication system having an SON function using adding and removing algorithm of the NRT according to the cases which can be occurred in base station management in a network manager, and a system thereof. 
     In accordance with an aspect of the present invention, a method of managing a neighbor relation table by a base station in a wireless communication system having a self-organizing network function includes: receiving a neighbor base station report from a terminal; comparing the neighbor base station report with a stored neighbor relation table; calculating a statistic value of a new base station, in case it is determined that the new base station exists in the step of comparing the neighbor base station report; and adding the new base station to the stored neighbor relation table when the statistic value is equal to or greater than a first reference value. The method further includes, after adding the new base station, calculating a statistic value of a base station included in the stored neighbor relation table except for the new base station; and removing base stations equal to or greater than a second value from the stored neighbor relation table when the statistic value is equal to or greater than the second value. 
     In the method of automatically managing an NRT in a wireless communication system having an SON function, a base station, and a system thereof, since a network may be configured more stably or efficiently in an SON, total service quality may be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a concept diagram illustrating a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 2  is a view illustrating an NRT stored in a base station in a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 3  is a block diagram illustrating a configuration of a network manager and a base station in a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 4  is a block diagram illustrating a configuration of a network manager and a base station in a wireless communication system according to another exemplary embodiment of the present invention; and 
         FIG. 5  is a flowchart illustrating a method of managing an NRT in a wireless communication system according to another exemplary embodiment of the present invention. 
     
    
    
     MODE FOR THE INVENTION 
     Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. 
     Terms of an embodiment of the present invention are based on a 3GPP LTE system standard. 
       FIG. 1  is a concept diagram illustrating a wireless communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the wireless communication system according to an exemplary embodiment of the present invention includes a network manager  101 , a plurality of cell areas  101 , and a terminal  102 . In particular, the plurality of cell areas  101  includes a base station for controlling each cell. The network manager  100  includes an SON server. The network manager  101  communicates with respective base stations for controlling the plurality of cell areas  101  using a 1 tf-N interface. In particular, the network manager  101  and the respective base stations exchange information for managing an NRT. In detail, a base station reports a list of neighboring base stations to the network manager  100 . Upon reception of the list of neighboring base stations, the network manager  100  performs given procedures, and transmits a command of adding or removing specific base stations to or from the NRT stored in the base station. Meanwhile, the terminal  102  transmits information regarding base stations for controlling cell areas except for a cell area to which the terminal  102  belongs to a base station for controlling the cell area. Such information transmission is achieved in a form of radio resource control (RRC) messages. Each base station for controlling the plurality of cell areas  101  receives base station operation and management (OAM) information from the network manager  100  or a separate OAM server, and uses it as management information of the NRT. Communication environment information is transmitted and received between base stations through an X2 interface. 
       FIG. 2  is a view illustrating a neighbor relation table stored in a base station in a wireless communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the NRT stored in a base station in the wireless communication system according to an exemplary embodiment of the present invention includes fields about a self cell ID and a target cell ID, and a removal impossible attribute, a handover impossible attribute, and an X2 interface attribute as attributes corresponding to each field. The following is a detailed explanation of each attribute. The removal impossible attribute indicates not to remove base stations with high occurrence possibility of hand-over event closely associated with the base station itself from the NRT although they satisfy the following specific conditions. The hand-over impossible attribute is an attribute of base stations with high possibility to be removed from the NRT without an occurrence possibility of a hand-over event that are even registered as a neighbor base station. The X2 interface attribute is an attribute for indicating presence of an X2 interface being an interface between base stations, and indicates that information exchange is not achieved between base stations not connected by the X2 interface. 
       FIG. 3  is a block diagram illustrating a network manager and a base station in the wireless communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the wireless communication system according to an exemplary embodiment of the present invention includes a network manager  300  and a base station (eNB)  350 . The network manager  300  may include a module controller  301 , an initialization module  302 , a coverage optimization module  303 , a power/interference optimization module  304 , a mobility robustness (MR) module  305 , a mobility load balancing (MLB) module  306 , and a synchronization controller  307 . The base station (eNB)  350  may include an NRT controller  351 , an NRT storage unit  352 , and an NR optimization unit  353 . In the network manager  300 , the module controller  301  transmits collected network quality information itself or network quality information received from a base station to necessary modules. The initialization module  302  creates and transmits new set information of a base station and changed set information of a neighbor base station to the synchronization controller  307 . The coverage optimization module  303  creates change information for system set for maximizing a capacity of a base station. The power/interference optimization module  304  optimizes power consumption of the base station to create set information of a neighbor base station, and transmits it to the synchronization controller  307 . Further, the MR module  305  optimizes hand-over to create base station set information. The MLB module  306  optimizes a balance of a processing load between base stations to create base station set information. The synchronization controller  307  determines whether to change an NRT stored in each station using the base station set information received from the respective modules, and transmits the NRT change presence information to the NRT controller  351  of the base station. 
     Hereinafter, a configuration of the base station  350  will be described. The NRT controller  351  adds or removes a base station to or from the NRT stored in the NRT storage unit  352  using the NRT change presence information received from the network manager  300 . The NR optimization unit  353  optimizes transmitting/receiving signals with a neighbor base station based on information regarding adding or removing of the base station to or from the NRT from the NRT controller  351 , and transmits the optimization information to the network manager  300 . 
       FIG. 4  is a block diagram illustrating a network manager and a base station in the wireless communication system according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the wireless communication system according to another exemplary embodiment of the present invention includes a network manger  401  and a base station  450 . A construction of the network manager was described above, and thus the detailed description is omitted. The base station (Enb)  450  in the wireless communication system according to another exemplary embodiment of the present invention further includes a NR adding/removing module  454  besides an NRT controller  451 , an NRT storage unit  452 , an NRT optimization unit  453 . 
     Functions of the NR adding/removing module  454  will be explained in detail below. The NR adding/removing module  454  receives self-cell coverage information and cell coverage information of neighbor base stations from a terminal through an RRC message  470 . Meanwhile, the NR adding/removing module  454  may receive the foregoing information from an operation and management (OAM) server. Upon reception of the information, the NR adding/removing module  454  determines to add or remove neighbor base stations to or from the NRT using the RRC message and the OAM information. In particular, the NR adding/removing module  454  calculates the reported number of quality information in the neighbor base stations, the failure number of hand-over to a neighbor base station, and a radio link failure (RLF) through the RRC message and the OAM information, and uses them as upgrade information of the NRT. The following is an explanation of a case considering the reported number of quality information in the neighbor base stations. When an event regarding the neighbor base stations occurs, the terminal reports quality information of all base stations among the neighbor base stations having signal quality greater than a reference value to the NR adding/removing module  454 . Accordingly, the NR adding/removing module  454  determines to add or remove neighbor base stations based on the quality information of all base stations to transmit a base station removing command to the NRT controller  451 . The NRT controller  451  reports changed NRT information to the network manager. 
     Next, a case of considering the failure number of hand-over to a neighbor base station is described herein. A base station collects failure information of hand-over to a neighbor base station over a constant period of time. Further, the base station calculates a statistic value of a hand-over failure rate regarding the neighbor base station through the collected information. When the statistic value is less than or equal to a threshold value, the base station transmits a base station removing command for removing a neighbor base station from the NRT to the NRT controller  451 . The NRT controller  451  reports changed NRT information to the network manager. Finally, a case of considering the rate of a radio link failure is explained. The base station collects failure information of a radio link set to a neighbor base station from the terminal or the OAM server regardless of hand-over event occurrence. Moreover, the base station calculates a statistic value of a radio link set failure regarding the neighbor base station through the collected information. When the statistic value is less than or equal to the threshold value, the base station transmits a base station removing command for removing a neighbor base station from the NRT to the NRT controller  451 . The NRT controller  451  reports changed NRT information to the network manager. 
       FIG. 5  is a flowchart illustrating a method of managing an NRT in the wireless communication system according to another exemplary embodiment of the present invention. The following is a description of a method of managing the NRT in a wireless communication system based on an operation of the NRT controller in a base station according to the embodiment. 
     Referring to  FIG. 5 , D refers to a set of base stations included in a neighbor base station report received from a terminal. A base station determines whether D is included in an NRT ( 501 ). When the D is not included in the NRT at step  501 , i.e., when it is determined that new base stations are included in the D, the base station allocates the new base stations to a set N ( 502 ). A statistic value S i  of all base stations included in the set N is calculated ( 503 ). Next, it is determined whether the new base stations are added to all base stations of the set N ( 504 ). The statistic value S i  of a base station i included in the set N is compared with a reference value T sh  ( 505 ). When it is determined that the statistic value S i  of a base station i is greater than the reference value T sh  at step  505 , the base station adds the base station i to a base station addition list {ADD} ( 506 ), and allocates another base station among the base stations included in the N to the base station i ( 507 ). 
     Then, when it is determined that the new base stations are added to all base stations of the set N at step  504 , the base station executes a command of adding the base station addition list {ADD} to the NRT ( 508 ), and updates the NRT ( 509 ) and reports it to a network manager. The base station allocates base stations except for base stations included in the set N among base stations of the NRT to a removal determination target base station set R ( 510 ). 
     When the D is included in the NRT in step  501 , the base station allocates base stations except for base stations included in the set D among base stations of the NRT to the removal determination target base station set R ( 511 ). Further, a statistic value S i  of all base stations included in the set R is calculated ( 512 ). Next, it is determined whether or not the new base stations are removed from all base stations of the set N ( 513 ). The statistic value S i  of a base station i included in the set R is compared with a reference value T s1  ( 514 ). When it is determined that the statistic value S i  of a base station i is less than the reference value T s1  at step  514 , the base station adds the base station i to a base station removal list {REM} ( 515 ), and allocates another base station among the base stations included in the R to the base station I ( 516 ). 
     Then, when it is determined that the new base stations are removed from all base stations of the set N at step  513 , the base station executes a command removing the base station removal list {REM} from the NRT ( 517 ), and updates the NRT ( 518 ) and reports it to a network manager. 
     Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.