Abstract:
Method and Apparatus thereof, for controlling intercell interference in a radio communications system having a plurality of user equipment and a plurality of access nodes including the steps of: a user equipment of said plurality connected to a serving access node, upon determining that an access node of said plurality is causing interference, transmitting a request to said serving access node; said serving access node forwarding said request to an apparatus controlling said interfering access node over an X2 interface, and said apparatus, instructing said interfering access node to execute said request.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is used in radio communications systems to ensure that interference caused therein is controlled and the adverse effects are reduced. 
       SUMMARY OF THE INVENTION 
       [0002]    In today&#39;s radio communications systems, the number of devices that use radio connections has increased dramatically over the past years. This increase in number has lead to an increase in the number of access nodes or base stations used throughout such radio communications systems in order to provide these devices with access to a PSTN/ISDN (Public Switched Telephone Network/Integrated Services Digital Network) and/or the internet. In the following description, the radio communications systems described, relates to systems using radio technologies known within the 3 rd  and 4 th  generation (3G, 4G) groups of radio technologies such as, for example, UMTS (Universal Mobile Telecommunications System), LTE (Long Term Evolution), or LTE-A (Long Term Evolution-Advanced), or HSPA (High Speed Packet Access). A particular feature of some of these radio communications systems that comprise devices that are situated within a small area, for example a building, is that access nodes or base stations are provided so as to cover the small area. These access nodes or base stations control a small cell which lies within a larger cell controlled by another access node or base station. In order to differentiate between these two cells, the small cell is defined as a “femto cell” while the larger one is defined as a “macro cell”. Access nodes or base stations that control femto cells are defined as HeNBs (Home-evolved Node Bs), while those controlling macro cells are defined as Macro-eNBs. 
         [0003]    In such an environment, HeNBs and Macro-eNBs use a segregated system architecture, whereby shared elements between the two architectures is limited to the OAM (Operations Administration Maintenance) and EPC (Evolved Packet Core) planes. Due to the fact that HeNBs are arbitrarily deployed within the radio communications systems and co-exist within an overlay of Macro eNBs, interference caused by radio signals emitted by the different access nodes or base stations (HeNBs, Macro-eNBs) can seriously affect communications within the radio system, in addition the EPC does not have the functionality to resolve any co-existence issues between HeNBs and Macro-eNBs. Usually, the HeNB to HeNB and the HeNB to Macro-eNB neighbourhood environment can be analysed by a HeNB UE (User Equipment) in the auto-configuration phase by monitoring the radio neighbourhood and any co-existence conflicts can be avoided. However, a problem arises in such a radio communications system, when HeNBs are used in a CSG (Closed Subscriber Group) environment. In such a situation, UEs connected to a Macro-eNB that are located in close proximity to a HeNB that is part of a CSG, will be affected by the interference generated by the HeNB. This problem can have a major impact on the quality of a communication in cases of co-channel deployment whereby both HeNBs and Macro-eNBs share a common spectrum. 
         [0004]    A need therefore exists for a technique that can reduce the effects of such interference in radio communications systems comprising of both HeNBs and Macro-eNBs. 
         [0005]    With the present invention, the above mentioned issues are resolved, allowing for a common radio spectrum to be shared between HeNBs and Macro-eNBs whilst at the same time reducing the effects of interference and thus increasing the efficiency of the radio communications system. 
         [0006]    The technique is achieved by the teachings contained in the independent claims. 
         [0007]    According to the independent method claim, a method is provided for controlling intercell interference in a radio communications system having a plurality of user equipment and a plurality of access nodes, comprising the steps of: a serving access node upon receiving a request from a user equipment directed to an access node of said plurality, forwarding the request to an apparatus controlling the access node, and the apparatus instructing said access node to execute the request. 
         [0008]    According to the independent apparatus claim, an apparatus having means arranged for controlling intercell interference in a radio communications system comprises: transceiver means arranged to allow bi-directional communications with an access node, control means arranged to control the access node, and further transceiver means arranged to allow bi-directional communications with a further access node over an X2 interface, the further access node not being under the control of the apparatus. 
         [0009]    Advantageous embodiments of the present invention are described by the dependent claims, wherein: 
         [0010]    The request is directed to the access node upon the user terminal determining that the access node is causing interference. The request comprises a specific action to be executed by the interfering access node as well as additional information specifically relating to the serving access node, wherein the access node is part of a closed subscriber group. The specific action can be at least one of the following: a transmit power adjustment, a load balancing adjustment, an intercell interference coordination adjustment. 
         [0011]    It is further pointed out that the invention may be realized by means of a computer program respectively software. According to a further refinement of the invention there is provided a computer-readable medium on which there is stored a computer program element for executing the steps of the method claim  1 . 
         [0012]    The program may be implemented as a computer readable instruction code in any suitable programming language, such as, for example, JAVA, C++, and may be stored on a computer-readable medium (removable disk, volatile or non-volatile memory, embedded memory/processor, control processor etc.). The instruction code is operable to program a computer or any other programmable device to carry out the intended functions. The program element may be available from a network, such as the World Wide Web, from which it may be downloaded. 
         [0013]    Furthermore, the invention may also be realized by means of one or more specific electronic circuits respectively hardware. Furthermore, the invention may also be realized in a hybrid form, i.e. in a combination of software modules and hardware modules. 
         [0014]    The computer-readable medium may be readable by a computer or a processor. The computer-readable medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium. The computer-readable medium may include at least one of the following media: a computer-distributable medium, a program storage medium, a record medium, a computer-readable memory, a random access memory, an erasable programmable read-only memory, a computer-readable software distribution package, a computer-readable signal, a computer-readable telecommunications signal, computer-readable printed matter, and a computer-readable compressed software package. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0016]      FIGS. 1   a  and  1   b  depict a radio communications system wherein interference affects user equipments. 
           [0017]      FIG. 2  depicts a flowchart showing the steps performed by the inventive method. 
           [0018]      FIG. 3  depicts a block diagram of a radio communications system wherein the invention is implemented. 
           [0019]      FIG. 4  shows a schematic block diagram of an apparatus in which the invention can be implemented. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1   a  illustrates an environment wherein a radio communications system  1000  comprises of a plurality of access nodes  100  and  200 . Access nodes  100  are Macro-eNBs while access nodes  200  are HeNBs. Radio communications system  1000  also comprises of a plurality of UEs  10  that are connected to the different access nodes  100 ,  200 . An access node  200  can form a CSG in which only authorised UEs  10  are permitted to access. 
         [0021]      FIG. 1   b  illustrates a section of radio communications system  1000  wherein a transmitted signal from access node  200  forming a CSG with UE  10 - 1 , interferes with UE  10 - 2  connected via a radio connection with its serving access node  100  and consequently causes degradation to signals received and/or transmitted by UE  10 - 2 . UE  10 - 2  which is being interfered with detects the interference and the origin of the interference. UE  10 - 2  determines the origin of the interference as it can detect the PCI (Physical Cell Identity) of access node  200 , as the PCI is part of the information that is broadcast by access node  200 . 
         [0022]    The steps executed by the invention are shown in  FIG. 2 . In step  1 , the serving access node  100  upon receiving a request from UE  10 - 2  that is directed to access node  200 , forwards the request to an apparatus  300  that controls access node  200  over an X2 interface, and in step  2  the apparatus  300  instructs access node  200  to execute the request. The request is directed to access node  200  when UE  10 - 2  determines that access node  200  is causing interference to it. The received request comprises a specific action to be executed by the interfering access node  200  as well as additional information specifically relating to the serving access node  100 . The specific action to be executed can be at least one of the following: a transmit power adjustment, a load balancing adjustment, an intercell interference coordination adjustment to be executed by access node  200 . 
         [0023]      FIG. 3  depicts a block diagram of a radio communications system  1000  wherein the invention is implemented. System  1000  comprises of a plurality of access nodes  100  and a plurality of access nodes  200 . It further comprises of at least one UE  10 - 2  connected to its serving access node  100  whose coverage defines a macro cell, at least one further UE  10 - 1  connected to its serving access node  200  whose coverage defines a femto cell and forms a CSG with UE  10 - 1  being permitted to access the CSG and apparatus  300 . Access nodes  100 ,  200  are connected to the EPC via S1-MME, S1-U, and S1 interfaces. Access node  100  upon receiving a request from UE  10 - 2 , which is being served by access node  100 , directed to access node  200 , forwards the request to apparatus  300  that controls access node  200  over an X2 interface. Apparatus  300  to which the request is forwarded to, as indicated herein above, is a device that controls numerous access nodes  200 , which can be HeNBs, within radio communications system  1000 . Apparatus  300  may be a HeNB-Gateway (HeNB-GW) having an X2 interface permitting connectivity with macro-eNBs  100  as well as a S1 interface acting as a concentrator and permitting connectivity with the EPC. The concentrator on the HeNB-GW is required for the C-plane and for the S1-MME interface and for the termination of the S1-U interface or for a direct logical U-plane connection between HeNB and the serving gateway of the EPC. A macro-eNB  100  views apparatus  300  as another macro-eNB which covers a multitude of cells. This is similar to a macro-eNB which may comprise 3 or 6 sector cells, however in the case of apparatus  300  it may support up to 20000 cells, wherein each HeNB  200  is considered as a cell. 
         [0024]    Apparatus  300  also comprises an X2 interface permitting a connection with macro-eNBs (or simply eNBs)  100 . As part of this connection, macro-eNBs  100  can address apparatus  300  and transmit reports if necessary to it. The termination of the X2 interface at apparatus  300 , is done within a X2-Management router function, which permits apparatus  300  to perform message discrimination, message reformatting, HeNB identification and when necessary individual message routing to individual HeNBs  200 . 
         [0025]      FIG. 4  shows a schematic block diagram of apparatus  300  in which the invention can be implemented. The apparatus  300  has means arranged for controlling intercell interference in a radio communications system  1000 . It comprises of:
       transceiver means  310  arranged to allow bi-directional communications with an access node  200 ;   control means  320  arranged to control said access node  200 , and   further transceiver means  330  arranged to allow bi-directional communications with a further access node  100  over an X2 interface, said further access node  100  not being under the control of apparatus  300 .       
 
         [0029]    The control means  320  are also further arranged, upon receipt of a request over the X2 interface from the further access node  100 , to instruct access node  200  to execute the received request. The request comprises a specific action to be executed by access node  200  as well as additional information specifically relating to the further access node  100 . The specific action can be at least one of the following: a transmit power adjustment, a load balancing adjustment, an intercell interference coordination adjustment. 
         [0030]    It is noted that the block structure could be implemented by a person skilled in the art as various separate physical units or as one physical unit comprising one or more physical or logical processing units which may be realized as a program code, e.g., software and/or firmware, running on a processing unit, e.g., a computer, microcontroller, ASIC, FPGA and/or any other logic device. 
         [0031]    In this way interference caused to UE  10 - 2  by access node  200  can be reduced. Apparatus  300  upon reception of the transmitted request from the eNB  100  can resolve the address, such as the IP (Internet Protocol address) of the individual HeNB  200  and thus instruct the correct HeNB  200  to execute the request. This has the advantage that within radio communications system  1000 , a connection is established between the femto cells and the macro cells, which allows for a fast exchange of eNB parameters and measurements and at the same time, avoids having to create a full meshed interconnection between eNBs  100  and HeNBs  200  within the radio communications system  1000 . 
         [0032]    As mentioned hereinabove, apparatus  300  may be a HeNB-GW, comprising of an X2 interface which is managed by an X2-Management router function which resides in control means  320 . The functionality of which, is further described herein below. 
         [0033]    In order to optimise the specific physical channel connections of the HeNBs, the message format on the S1/X2 Application level, as well as on the S1 interface, is kept the same. The HeNB-GW function is to mimic a 1:many to a 1:1 relation from the EPC point of view, as seen from the Application Protocol layer, because below this layer the S1 interface consists of 2 connections addressing different MMEs (Mobile Management Entities) for load sharing reasons. 
         [0034]    The HeNB-GW for UE associated S1 Application Protocol (S1AP) signalling, only exchanges a S1AP protocol identity (ID) from that exchanged between the HeNB-GW and the EPC to that of the S1AP protocol ID, that is used between a HeNB and the HeNB-GW. Any non UE associated signalling is terminated at the HeNB GW. This results in that the S1AP is identical for both sides of the HeNB-GW. 
         [0035]    The function of the X2 Management Router is to hide Radio Access Network (RAN) communications from the EPC. For the purpose of X2 communication the X2 Management Router resolves the routing of many to many Application Protocol Layer connections, because different neighbour eNBs may have to contact an HeNB via the X2 Management Router. From the HeNBs point of view, the X2 interface still appears as a point to point connection, i.e. the functionality provided by the X2 Management Router is transparent to the HeNBs. 
         [0036]    Automatic X2 establishment is provided by S1 communication between eNBs  100 . This establishment can be intercepted at the HeNB-GW  300 . The X2 Management Router announces itself at the HeNB-GW  300  and informs it about its IP address. Then the HeNB-GW, when intercepting/handling the S1 signaling messages (i.e. eNB CONFIGURATION TRANSFER and MME CONFIGURATION TRANSFER) replaces the TNL (Transport Network Layer) address of the HeNB  100  with the TNL address of the X2 Management Router in the eNB CONFIGURATION TRANSFER reply message (the TNL address information is only carried in the eNB/MME CONFIGURATION TRANSFER replay messages). This ensures that the SCTP (Stream Control Transmission Protocol) association carrying the X2 Application Protocol, which is always bidirectional, is established from the requesting source eNB  100  to the X2 Management Router function and not to the HeNB  200 . Furthermore the HeNB-GW  300  extracts the Global eNB ID and Selected TAI (Timing Advance Index) from both source (i.e. requesting eNB  100 ) and target HeNB  200  of the, to be established, X2 connection and the TNL Address of the target HeNB  200 . All this information can be extracted by the HeNB-GW  300  from the S1 messages and is provided to the X2 Management Router function. The X2 Management Router function can then store and use this information when the source eNB  100  wants to establish the X2 connection. 
         [0037]    For that purpose, the requesting source eNB  100  first has to initiate a SCTP association between itself and the X2 Management Router function. Then the requesting eNB  100  sends the X2AP X2 SETUP REQUEST message to establish the X2AP. The X2 Management Router function uses the saved information in order to identify the proper HeNB  200 , to establish the SCTP association to this HeNB  200  and to maintain the mapping between these SCTP associations for the duration that the X2 interface is active. The received X2AP X2 SETUP REQUEST message comprises the Global eNB ID of the eNB  100  that is requesting X2 establishment. This ID could be used by the X2 Management Router function to find the corresponding entry in the previously generated table and to retrieve the TNL address of the actually targeted HeNB  200 . Then the X2 Management Router function can establish a SCTP association between itself and the target HeNB  200  and then forward the messages received so that the request can be executed by the target HeNB  200 . In this way it is possible to identify the proper TNL address of the target HeNB  200  and create a unique mapping between the established SCTP associations, thus ensuring that in the event of multiple X2 SETUP REQUEST messages being received at the X2 Management Router, the correct target HeNB  200  for each X2 SETUP REQUEST message is chosen. 
         [0038]    Although the invention has been described in terms of preferred embodiments described herein, those skilled in the art will appreciate other embodiments and modifications which can be made without departing from the scope of the teachings of the invention. All such modifications are intended to be included within the scope of the claims appended hereto.