Abstract:
A method and system for switching a base station from an inactive operational mode to a more active operational mode in a hierarchically structured mobile communication network preferably a WiMAX or LTE network, with at least one small cell base station and at least one macro cell base station in a radio access network includes:
   a) determining a current operational mode of the at least one small cell base station;   b) switching the small cell base station from an inactive operational mode to a more active operational mode depending on the determined current operational mode;   c) checking whether at least one predefined criteria in addition to a parameter indicating the current operational mode of the small cell base station is fulfilled; and   d) depending on the checking result of step c) transmitting a switching signal from a higher level network entity to the small cell base station.

Description:
The present invention relates to a method for switching a base station from an inactive operational mode to a more active operational mode in a hierarchically structured mobile communication network, preferably a WiMAX or LTE network, with at least one small cell base station, and at least one macro cell base station in a radio access network comprising the steps of a) determining a current operational mode of the at least one small cell base station, b) switching the at least one small cell base station from an inactive operational mode to a more active operational mode depending on the determined current operational mode. 
     The invention relates also to a system for switching a base station from an inactive operational mode to a more active operational mode in a hierarchically structured mobile communication network, preferably a WiMAX or LTE network and preferably for performing a method according to one of the claims  1 - 13 , comprising at least one small cell base station, at least one macro cell base station and a radio access network connected to the macro cell base station. 
     BACKGROUND OF THE INVENTION 
     Hierarchically structured mobile communication networks are inter alia used for voice communication and recently more and more for data communication, for example between two mobile stations or between a mobile station and the internet, for receiving and sending of E-mails or the like. A hierarchically structured mobile communication network may include one or more base stations that provide services to a certain coverage area. Due to the hierarchically structure of the mobile communication network a macro cell base station covers a plurality of small cell base stations within the macro cell base station coverage area. A small cell base station within the macro cell base station coverage area may be connected to a mobile communication core network or the macro cell base station for providing services. The base stations are part of a more complex radio access network with a plurality of differently located macro cell base stations and small cell base stations preferably with at least partially overlapping coverage areas to provide uninterruptable services when changing the coverage area. Macro cell base stations and small cell base stations may be directly connected to each other and also have a connection to the mobile communication core network providing further services. Small cell base stations have in general smaller coverage areas than macro cell base stations and may even be installed by customers of an operator providing services. 
     In order to save energy the current draft standard of IEEE 802.16m according to IEEE, “IEEE P802.16m/D8, Part 16: Air Interface for Broadband Wireless Access Systems, Advanced Air Interface” of August 2010 supports a so called low-duty-mode (M. Einhaus, L. Fan, T. Ikeda, A. Maeder, J. Zhou, Y. Zhou “Method for operating a WiMAX femtocell base station and femtocell base station”, PCT/EP 2009/007670) for reduced energy consumption and for reduction of interferences between different small cell base stations and/or macro cell base stations. In the low-duty-mode the base station preferably avoids air interface transmissions including in particular a transmission of frame preambles, pilots and broadcast channels if there is no operational need, for example if there is no mobile station within the coverage area of the base station. 
     However, if a mobile station enters the coverage area of a small cell base station which is currently in the low-duty-mode an air interface of the small cell base station is offline although the low-duty-mode allows a basic default transmission pattern to provide at least visibility via the air interface to mobile stations scanning for small cell base station reference signals, in particular for frame preambles of radio frames. This only provides a very slow connectivity between the mobile station and the small cell base station in the low-duty-mode, since the reference signals are broadcasted in relatively long time intervals, so that the mobile station needs time to identify the reference signal of the small cell base station and then to transmit a corresponding signal to activate the small cell base station. After the wake-up or activation of the base station the connection has to be established between the mobile station and the small cell base station in an active operational mode. This is a very time consuming procedure. 
     In addition to the above mentioned low-duty-mode, in PCT/EP2010/002636 a radio interface listen mode and a radio interface off mode is defined, so wake-up conditions of the small cell base station and corresponding procedures may vary according to the current suboperational mode of the base station. For example a small cell base station in the radio interface off mode cannot be activated according to the same procedure as a small cell base station in the low-duty-mode. Another problem is that a switching from an inactive operational mode to a more active operational mode of the base station may not be required, if only a transmission of a low traffic volume is requested or if a hand-over to a small cell base station may decrease a quality of service of the active connection between the mobile station and the base station, so that a direct connection between the mobile station and a small cell base station is not required or may not be beneficial and a connection between a macro cell base station and a mobile station may be sufficient in these cases. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide a method and a system for switching a base station from an inactive operational mode to a more active operational mode avoiding unnecessary activation of a base station in an inactive operational mode. 
     It is a further objective of the present invention to provide a method and a system for switching a base station from an inactive operational mode to a more active operational mode with a faster connection establishment between the mobile station and the base station. 
     It is a further objective of the present invention to provide a method and a system for switching the base station from an inactive operational mode to a more active operational mode with a fast and reliable switching between different inactive and/or an active operational mode. 
     In accordance with the invention the aforementioned objectives are accomplished by a method of claim  1  and a system of claim  14 . 
     According to claim  1  a method for switching a base station from an inactive operational mode to a more active operational mode in a hierarchically structured mobile communication network, preferably a WiMAX or LTE network, with at least one small cell base station and at least one macro cell base station in a radio access network comprising the steps of a) determining a current operational mode of the at least one small cell base station, b) switching the at least one small cell base station from an inactive operational mode to a more active operational mode depending on the determined current operational mode 
     is characterized by the steps of 
     c) checking whether at least one predefined criteria in addition to a parameter indicating the current operational mode of the at least one small cell base station is fulfilled and d) depending on the checking result of step c) transmitting a switching signal from a higher level network entity, preferably the at least one macro cell base station, to the at least one small cell base station. 
     According to claim  14  a system for switching a base station from an inactive operational mode to a more active operational mode in a hierarchically structured mobile communication network, preferably a WiMAX or LTE network and preferably for performing a method according to one of the claims  1 - 13 , comprising at least one small cell base station and at least one macro cell base station in a radio access network, 
     is characterized in that 
     the at least one small cell base station is formed such to switch from an inactive operational mode to a more active operational mode depending on the determined current operational mode, when a checking is performed whether at least one predefined criteria in addition to a parameter indicating the current operational mode of the at least one small cell base station is fulfilled and depending on the checking result a higher level network entity, preferably the at least one macro cell base station, is formed such to transmit a switching signal to the at least one small cell base station. 
     Of course the method and the system is not limited to small cell base stations but also to base stations in general having at least one inactive and one more active operational mode. 
     According to the invention it is first been recognized that transmitting a switching signal from a higher level network entity, for instance a mobility management entity, preferably located in the mobile communication core network, or a macro call base station, to the at least one small cell base station based on the predefined criteria and based on a current operational mode of the at least one small cell base station provides a flexible and reliable switching or “wake-up” from an inactive to an active or more active operational mode of the small cell base station. 
     According to the invention it has further been first recognized that a wake-up of a base station, in particular the at least one small cell base station having different inactive operational modes may be easily performed since a predefined criteria and/or a current operational mode allows different criteria for different operational modes taking into account the different characteristics of the different inactive operational modes. 
     According to the invention it has also been first recognized that a faster connection establishment compared to conventional methods or systems is provided due to an adaption of the switching depending on the inactive operational mode of the preferably small cell, base station. 
     According to the invention it has further been recognized that the method and the system reduce the energy consumption and interference in mobile communication networks since a wake-up of small cell base stations, meaning preferably the switching from an inactive operational mode to a more active operational mode, is based on predefined criteria including the current operational mode and further criteria for example the type of a requested service. This enables a switching only to a more active operational mode if necessary. This further provides an increase of a quality of service for certain network traffic types like voice data traffic or the like between the at least one small cell base station and the at least one macro cell base station and/or a further with the radio access network and further network connected to the radio access network like a core network. 
     Further features, advantages and preferred embodiments are described in the following subclaims. 
     According to a preferred embodiment the inactive operational mode comprises at least two, preferably three, hierarchically structured inactive suboperational modes. This provides a flexible adaption of small cell base stations regarding energy consumption. For example if there is no mobile station to be found within a certain time interval and within the coverage area of the small cell base station the small cell base station may switch from an active operational mode to a first inactive operational mode for example by turning off the air interface of the small cell base station. After a second time interval the base station may also reduce the activity on the interface for a wireless connection between the small cell base station and the macro cell base station. Therefore a plurality of hierarchically structured inactive operational modes allows a flexible scheme for energy saving. Such inactive operational mode may include a low-duty mode, a radio interface listen mode and a radio interface off mode according to A. Maeder, L. Fan, M. Einhaus “Method for operating a base station and a base station”. 
     According to a further preferred embodiment a mobile station connects to at least one of the macro cell base stations and at least the steps c) and d) are performed with the predefined criteria in addition to a parameter indicating a threshold value for a distance between the mobile station and the at least one small cell base station. This provides a further energy reduction of the at least one small cell base station: if the mobile station is connected to a macro cell base station and if the macro cell base station is aware of the current operational mode of the at least one small cell base station the macro cell base station may transmit a switching signal to the at least one small cell base station for switching into a more active operational mode of the small cell base station if the small cell base station is in an inactive operational mode and if the mobile station is within a connection distance of the at least small cell base station and if a predefined criteria for example high priority high volume data traffic is requested by the mobile station. After receiving the switching signal by the at least one small cell base station the at least one small cell base station switches to the more active operational mode and the mobile station recognizes now the at least one small cell base station and connects to the small cell base station for transferring a high priority high volume data. 
     According to a further preferred embodiment the switching signal is included in a paging signal for establishing data traffic between the at least one macro cell base station and a mobile station assigned to the at least one small cell base station. Data traffic means all sorts of data to be transmitted from a mobile station to a base station including pure data traffic, voice traffic, short message services, multimedia message services or the like. When the switching signal is included or embedded in a paging signal the switching signal may easily be provided in preferably standardized paging protocols. For example, the switching signal may be embedded in the Paging_Announce message of the WiMAX forum. A further advantage is, that by including the switching signal in the paging signal a selective activation of small cell base stations is possible. For example paging signals in form of paging messages may selectively sent by a core network to the radio access network comprising the macro cell and small cell base stations based on a type, a requested service and a mode of the small cell base stations. If, for example, the small cell base station is in a low-duty-mode the small cell base station does not change its current operational mode according to a paging signal when the paging signal is provided such that it is intended for a macro cell base station for macro cell paging. 
     According to a further preferred embodiment the paging signal is sent to the at least one macro cell base station and/or subsidiary to a small cell base station in an active operational mode and/or subsidiary to a small cell base station in an inactive operational mode. This provides a paging in a step-by-step manner. In a first step macro cell base stations are paged, then small cell base stations in an active operational mode and finally small cell base stations in an inactive operational mode. It is further possible that paging can be further differentiated for the different inactive operational modes of the at least one small cell base station. In summary one of the advantages is that only small cell base stations which fulfill a predefined criteria are switched from an inactive operational mode to an active operational mode and only if the small cell base station in an inactive operational mode is a target of the paging signal by embedding a corresponding switching signal. 
     According to a further preferred embodiment the paging signal includes a paging message with at least one base station identity information element, preferably including information about a hierarchical level of the at least one macro cell base station and/or the at least small cell base station and/or the current operational mode of the at least one macro cell base station and/or the at least one small cell base station. By including a paging message in the paging signal with a base station identity information element, a standardized paging message can be easily adapted without a complete restructuring of the paging message and the paging procedure. 
     According to a further preferred embodiment a mobile station performs a scanning of a current operational mode of at least one of the small cell base stations of at least one macro cell base station and sends a scanning result to the macro cell base station assigned to the mobile station. An advantage is, that this allows a fast switching of an inactive operational mode of a small cell base station to a more active operational mode of the small cell base station. Preferably the scanning result may include the type and the current operational mode of a scanned small cell base station, resulting in an even faster switching from an inactive operational mode to a more active operational mode of the small cell base station. 
     According to a further preferred embodiment the radio access network is connected to a database, wherein the database includes base station assigning information and/or current operational mode information of at least one of the small cell base stations. A database provides in a centralized manner a list of current operational modes of the small cell base stations. A mobile station may, for example, update a current operational mode of a small cell base station scanned by the mobile station by transmitting a scanning result of the scanned small cell base station. Further a macro cell base station may also access the database, so that a mobile station connected to a macro cell base station, for example when transferring low priority and/or low amount of data, may switch a small cell base station to a more active operational mode when the mobile station connected to the macro cell base station is within the coverage area of the small cell base station so that the small cell base station may connect to the mobile station if a high volume of data traffic and/or with a high priority is sent by the mobile station. Further a core network may be connected to the radio access network and may provide mobility management functions by a mobility management function entity which may also have access to the current operational modes of the small cell base stations via the database so that a reliable and flexible switching from inactive operational modes to a more active operational mode of a small cell base station is provided. 
     According to a further preferred embodiment the scanning result is included in the scanning report according to IEEE 802.16m, preferably in the AAI-SCN-REP message. Thus, a standardized message may be used by adding scanning results so that base stations may or may not use the additional information in the scanning report according to IEEE 802.16m, if for example a base station are not upgraded to the latest version of a corresponding protocol of a scanning report or if a base station is not formed such to exploit the additional information in the scanning report therefore providing downward compatibility for base stations with former versions of the corresponding protocol. 
     According to a further preferred embodiment the AAI-SCN-REP message includes an additional information element for indicating scanning of small cell base stations in an inactive operational mode, preferably with size of one bit. The size of one bit minimizes the amount of data to be transferred in the AAI-SCN-REP message needed for indicating a scanning of small cell base stations by a mobile station. When the AAI-SCN-REP message is received by the mobile station the mobile station extracts the additional information element. If the additional information element indicates a scanning the mobile station scans for small cell base stations within its coverage area and determines during the scanning process the current operational mode of a small cell base station. 
     According to a further preferred embodiment the at least one macro cell base station uses an over-the-air-interface for transmitting the switching signal to the at least one small cell base station in an inactive operational mode. This provides a flexible way to transmit the switching signal from the at least one macro cell base station to the at least one small cell base station; cable based or wire line connections between a macro cell base station and a small cell base station have not to be applied. 
     According to a further preferred embodiment the at least one predefined criteria includes network performance information parameters and/or base station type parameters. This provides a plurality of options defining small cell base stations to be switched from an inactive operational mode to more active operational mode according to an actual performance of the radio access network a core network or relevant network parts. 
     According to a further preferred embodiment the network performance information parameters include energy consumption parameters, quality-of-service related parameters, preferably maximum and/or average packet latency and/or guaranteed minimum data rate and/or application type parameters, preferably indicating voice-over-IP, short-message-service, machine-to-machine data and/or timing related parameters like timing information for a regularly scheduled data. This further enhances flexibility and options to configure the switching of small cell base stations from an inactive operational mode to a more active operational mode. 
     There are several ways how to design and further develop the teaching of the present invention in an advantageous way. To this end it is to be referred to the patent claims subordinate to patent claims  1  and  14  on the one hand and to the following explanation of preferred embodiments of the invention by way of example, illustrated by the drawing on the other hand. In connection with the explanation of the preferred embodiments of the invention by the aid of the drawing, generally preferred embodiments and further developments of the teaching will be explained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawing 
         FIG. 1  shows a schematical view of a system according to an embodiment of the present invention; 
         FIG. 2  shows a method according to a second embodiment of the present invention; and 
         FIG. 3  shows a diagram of a part of a method according to a third embodiment of the present invention. 
     
    
    
       FIG. 1  shows a schematically view of a system according to an embodiment of the present invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a system  1  comprising a radio access network  2  and a core network  3 . The core network  3  comprises a security gateway  4  connected to a small cell gateway in form of a femtocell gateway  5 . The femtocell gateway  5  is connected to a mobile management function entity  6  and the mobile management function entity  6  is connected to a status data base  7  for storing current operational status of small cell base stations in form of femtocell base stations. The radio access network  2  comprises a plurality of macro cell base stations  21 ,  22 ,  23  each having a certain coverage area  21   a ,  22   a ,  23   a . Within the coverage area  21   a  of macro cell base station  21  two femtocell base stations  31 ,  32  are located each having a corresponding femtocell coverage area  31   a ,  32   a . Each femtocell base station  31 ,  32  comprises an over-the-air-interface for a communication with a corresponding over-the-air-interface of the macro cell base station  21  for an over-the-air-transmission  40 . 
     In the macro cell base station coverage area  22   a  a femtocell base station  33  having a femtocell coverage area  33   a  is located. Further, in the macro cell base station coverage area  23  two femtocell base stations  34 ,  35  each having a femtocell coverage area  34   a ,  35   a  are located. The macro cell base stations  21 ,  22 ,  23  are connected to the mobility management function entity  6 . The femtocell base stations  31 ,  32 ,  33 ,  34 ,  35  are connected to the security gateway  4 . 
     A mobile station  50  within the coverage area  21   a  of the macro cell base station  21  and a mobile station  51  within the femtocell coverage area  32   a  of the femtocell base station  32  and within the coverage area  21   a  of the macro cell base station  21  are also shown in  FIG. 1 . 
     If the mobile station  50  tries to transmit for example short-message-service (SMS) data the mobile station  50  does not have access to the femtocell base stations  31 ,  32  but only to the macro cell base station  21 . Therefore, the mobile station  50  connects to the macro cell base station  21  to transmit the short-message-service data. 
     In contrast thereto the mobile station  51  is within the femtocell coverage area  32   a  of the femtocell base station  32 . The femtocell base station  32  however is in a low-duty-mode. In order to provide a communication between the mobile station  51  and the femtocell base station  32  the femtocell base station  32  in the low-duty-mode has to switch to a normal active operational mode since in the low-duty mode according to IEEE 802.16m the air interface of the femtocell base station  32  is reduced, e.g. is switched off on some radio frames. 
     In order to “wake-up” the femtocell station  32  the mobile station  51  connects to the macro cell base station  21  when the mobile station  51  is within the corresponding macro cell coverage area  21   a . When the mobile station  51  enters the femtocell coverage area  32   a  the macro cell base station  21  connects to the status database  7  via the mobility management function entity  6  for requesting the current operational mode of the femtocell base station  32 . The mobility management function entity  6  provides the current operational mode of the femtocell base station  32  to the macro cell base station  21  which is a low-duty-mode. The macro cell base station  21  then transmits a switching signal to the femtocell base station  32 . The femtocell base station  32  is then switched from a low-duty-mode to an active operational mode according to the switching signal. The mobile station  51  recognizes that the femtocell base station  32  is now in an active or normal operational mode and connects to the femtocell base station  32  for data transmission. Since the femtocell base station  32  is also directly connected to the mobility management function entity  6  a decision to “wake up” of the femtocell base station  32  may also be performed directly by the mobility management function entity  6 . 
     If the mobile station  51  would like to send low priority and/or low volume data like short-message-service (SMS) data the mobile station  51  sends the SMS data directly to the macro cell base station  21 . The macro cell base station  21  receiving the corresponding transmission request from the mobile station  51  requests the current operational mode of the femtocell base station  32  from the mobility management function entity  6  connected to the status database  7 . The macro cell base station  21  may also provide a mobility management function entity  6  the service requested by the mobile station  51 , i.e. a transmission of short-message-service data. The mobility management function entity  6  then determines that a “wake-up” of the femtocell base station  32  is not necessary since the low amount of SMS data may be handled by the macro cell base station  21  directly. The mobility management function entity  6  therefore does not provide any switching signal to the femtocell base station  32  in low-duty mode or provide a corresponding information to the macro cell base station  21  to avoid an unnecessary “wake-up” of the femtocell base station  32 . In this case the mobility management function entity  6  would first page the mobile station  51  only with the macro cell base station  21 . Similarly voice traffic of the mobile station  51  may also be efficiently handled by the macro cell base station  21  directly due to the low traffic volume and strict requirements on latency, especially during handover. That means that the macro cell base station  21  would not “wake-up” the femtocell base station  32  in its coverage area  21   a  even if it would be possible. 
     In general the type of service or requested traffic like the already mentioned short-message-service, may include quality of service related parameters like maximum/average packet latency, guaranteed minimum data rate, etc., application types such as voice-over-IP, short-message-service, machine-to-machine data, etc. and/or timing-related information for a regularly scheduled data. 
       FIG. 2  shows a method according to a second embodiment of the present invention. 
     In order to set up communication channels for, for example a one to one communication between a mobile station  50  and a macro cell base station or a small cell base station in form of a femtocell base station  31 ,  32 ,  33 ,  34 , paging is required. In order to avoid that the base station  31 ,  32 ,  33 ,  34  in an inactive operational mode is switched to an active or normal operational mode when it is not necessary a selective paging is required. One option to provide such a selective paging is to send paging messages selectively based on a type, a requested service and a current operational mode of the small cell base station. Another option to provide such a selective paging is to include an information element in the paging message which is then filtered at the different types of base stations  31 ,  32 ,  33 ,  34 . A further option is that a paging may be done in a step-by-step manner, where for example first macro cell base stations  21 ,  22 ,  23  are paged then femtocell base stations  31 ,  33 ,  35  in a normal operational mode and finally femtocell base stations  32 ,  34  in an inactive operational mode. This can be further divided into different inactive operational modes. 
     In  FIG. 2  there is shown a modified paging message flow in a WiMAX network. An access service network gateway  6   a  serving as a mobility management function entity  6  pages base stations  31 ,  33  in a normal operational mode and base stations  32 ,  34  in an inactive operational mode, for example in an energy-efficiency mode. To perform paging a so called Paging_Announce message is provided including information for the access service network gateway  6   a  and the base stations  31 ,  32 ,  33 ,  34  to perform paging. For paging the access service network gateway  6   a  sends the Paging_Announce messages to the base stations  32 ,  34  in energy efficiency mode so that the base stations  32 ,  34  in energy efficiency mode are waking up, i.e. switching to a normal operational mode. If the access service network gateway  6   a  is aware of the current operational modes of the base stations  32 ,  34  in energy efficient mode the access service network gateway  6   a  may use a base station identification information element to send a paging message for one or more base stations  32 ,  34  complying with the base station identification information element and the current operational mode of the base station  32 ,  34 . If such an information element is not available the decision for switching to a normal operational mode may be done by a corresponding device in a base station  32 ,  34  itself. 
     If the access service network gateway  6   a  uses flood paging an additional information element must be included in the Paging_Announce message. Flood paging means that the access service gateway  6   a  sends the Paging_Announce message to all base stations within a specified tracking or coverage area. In  FIG. 2  the access service network gateway  6   a  sends Paging_Announce messages to all base stations  32 ,  34  in energy efficiency mode. However, in the Paging_Announce message an information element concerning the base station type and the operational mode of the base stations  32 ,  34  is included. All paged base stations  32 ,  34  in energy efficient mode filter the Paging_Announce message and switch to a normal operational mode if the information element comprising type and operational mode correspond to the type and operational mode of base stations  32 ,  34 . Optionally, the base stations  32 ,  34  may respond with a Paging_Response message to the access service network gateway  6   a  to indicate the access service network gateway  6   a  that the paging request sent by the access service network gateway  6   a  could not be performed due to a local filtering, meaning that the Paging_Announce message does not comply with predefined or actual base station characteristics for example type and operational mode of the corresponding base stations  32 ,  34 . 
     If only one access service network gateway  6   a  is involved in the paging procedure, the access service network gateway  6   a  sends a reference point R 6  Paging_Announce message to the relevant base stations  32 ,  34 . If more than one access service network gateway is involved in the paging procedure both reference points R 4  and R 6  Paging_Announce messages are sent to the relevant base stations  32 ,  34 , wherein reference point R 4  Paging_Announce messages are sent between the different access service network gateways  6   a  and the reference point R 6  Paging_Announce messages are sent between the corresponding access service network gateways  6   a  and the base stations  32 ,  34 . 
     In case that a macro cell base station needs to “wake-up” a small cell base station  32 ,  34  in an energy-efficient mode within its coverage area a Paging_Announce message may be send over reference point R 8  which is intra access service network. 
     The above mentioned reference points R 4 , R 6  and R 8  are defined as follows: 
     Reference point R 4  consists of the set of control and data path protocols originating/terminating in an access service network gateway that coordinate mobile stations mobility between access service networks and access service network gateways. R 4  is the only interoperable reference point between the access service network gateways of one access service network or two different access service networks. 
     Reference point R 6  consists of the set of control and data path protocols for communication between a base station and the access service network gateway within a single access service network. The data path consists of intra-access service network data paths between the base station and access service network gateway. The control protocols comprise functions for data path establishment, modification, and release control in accordance with the mobile stations mobility events. However, when protocols and primitives over reference point R 8  are available, MAC states will not be exchanged over reference point R 6 . 
     Reference point R 8  is intra-access service network and consists of the set of control message flows between the base stations to ensure fast and seamless handover. The control plane consists of the inter-base station communication protocol in line with the WiMAX Forum Mobile System Profile and additional set of protocols that allow controlling the data transfer between the base stations involved in handover of a certain mobile stations. 
     In a Paging_Announce message of WiMAX forum the Paging_Announce message may be modified as follows: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 IE 
                 Reference 
                 M/O 
                 Notes 
               
               
                   
               
             
             
               
                 ... 
                   
                   
                   
               
               
                 &gt;Target BS Type 
                   
                 O 
                 If flood paging is used, this field 
               
               
                 (new) 
                   
                   
                 indicates whether the message is 
               
               
                   
                   
                   
                 intended for macrocells or 
               
               
                   
                   
                   
                 femtocells. 
               
               
                   
                   
                   
                 1 = macrocell BSs. 
               
               
                   
                   
                   
                 0 = femtocell BSs. 
               
               
                 &gt;Target Femtocell 
                   
                 O 
                 If femtocell BSs support energy- 
               
               
                 BS status (new) 
                   
                   
                 efficiency modes, this TLV 
               
               
                   
                   
                   
                 defines the states of the 
               
               
                   
                   
                   
                 addressed femtocells. 
               
               
                 ... 
               
               
                   
               
             
          
         
       
     
     Further a type-length-value definition of a target femtocell base station status is given below: 
     TLV definition of Target Femtocell BS status: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Type 
                 TBD 
               
               
                   
                   
               
             
             
               
                   
                 Length in octets 
                 1 
               
               
                   
                 Value 
                 0x00 = reserved 
               
               
                   
                   
                 0x01 = normal operation 
               
               
                   
                   
                 0x02 = low-duty mode 
               
               
                   
                   
                 0x04 = radio interface listen mode 
               
               
                   
                   
                 0x08 = radio interface off mode 
               
               
                   
                   
                 0x10-0x80 = reserved 
               
               
                   
                   
                 0xFF = all states 
               
               
                   
                 Description 
                 Bit mask of states which are addressed in 
               
               
                   
                   
                 the femtocell BS. 
               
               
                   
                 Parent TLV 
                 None 
               
               
                   
                   
               
             
          
         
       
     
     In section B of  FIG. 2  the access service network gateway  6   a  sends Paging_Announce messages to base stations  31 ,  33  in normal mode. The corresponding base stations  31 ,  33  are then sending each a MOB_PAG-ADV message to a mobile station  50  for conventional paging. 
       FIG. 3  shows a diagram of a part of a method according to a third embodiment of the present invention. 
     In  FIG. 3  there is shown a base station  32  and a mobile station  51 . The mobile station  51  sends a scanning request for a controlling corresponding base station  32  by means of a AAI-SCN-REQ request message according to IEEE 802.16m. The base station  32  sends a AAI-SCN-RSP response message according to IEEE 802.16m. The mobile station  51  then may perform a scanning for a small cell or femtocell base station in a low duty mode itself or the AAI-SCN-RSP message may include an additional entry to indicate the mobile station  51  to scan explicitly for small or femtocell base stations in an inactive operational mode, preferably in a low-duty-mode. The mobile station  51  then performs a corresponding scanning and may send the scanning result with the current operational mode of a scanned femto or small cell base station included in an AAI-SCN-REP message. The scanning result may be included in the AAI-SCN-REP message according to IEEE 802.16m as a single bit entry indicating the mode of the scanned small cell base station: 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 AAI-SCN-REP modifications 
               
             
          
           
               
                   
                 Size 
                   
                   
               
               
                 Field 
                 (bits) 
                 Value/Description 
                 Condition 
               
               
                   
               
               
                 ... 
                   
                   
                   
               
               
                 Neighbor_Request_Indication 
                 1 
                 Request indication for 
                 Optional 
               
               
                   
                   
                 system information 
               
               
                   
                   
                 and the list of the 
               
               
                   
                   
                 neighbor Femto ABSs 
               
               
                 If(Neighbor_Request_Indication == 
               
               
                 1) { 
               
               
                 Neighbor_Request_BS_Type 
                 3 
                 Indicates type of 
                 Optional 
               
               
                   
                   
                 neighbor Femto ABSs 
               
               
                   
                   
                 for which system 
               
               
                   
                   
                 information is 
               
               
                   
                   
                 requested. 
               
               
                   
                   
                 Bit #0: CSG-Closed 
               
               
                   
                   
                 Femto ABS 
               
               
                   
                   
                 Bit #1: CSG-Open 
               
               
                   
                   
                 Femto ABS 
               
               
                   
                   
                 Bit #2: OSG Femto 
               
               
                   
                   
                 ABS 
               
               
                 Femto_BS_State (new) 
                 1 
                 Indicates current 
                 Optional 
               
               
                   
                   
                 state of Femto BS. 
               
               
                   
                   
                 0: normal mode 
               
               
                   
                   
                 1: LDM 
               
               
                 for (j=0; j&lt;N_CSG_IDs; j++) { 
                   
                 N_CSG_IDs is the 
                 Optional. 
               
               
                   
                   
                 number of CSG IDs 
                 Sent by AMS 
               
               
                   
                   
                   
                 to aid in 
               
               
                   
                   
                   
                 generation of 
               
               
                   
                   
                   
                 optimized 
               
               
                   
                   
                   
                 neighbor list 
               
               
                   
                   
                   
                 by the ABS 
               
               
                 CSGID 
                 variable 
                 The CSGID within the 
               
               
                   
                   
                 Operator ID. 
               
               
                   
                   
                 It may be part of the 
               
               
                   
                   
                 BS ID, with certain 
               
               
                   
                   
                 bits inside indicating 
               
               
                   
                   
                 its length. 
               
               
                   
                   
                 If the CSG has single 
               
               
                   
                   
                 BS, it may be of 
               
               
                   
                   
                 maximum length 
               
               
                   
                   
                 which is the LSB-24 
               
               
                   
                   
                 bits of the full BS ID. 
               
               
                 } 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
     The mobile station  51  may scan a small cell base station preferably in form of a femtocell base station  32 ,  34  even if the small cell base station  32 ,  34  is in an operational mode where the air interface of the small cell base station  32 ,  34  is reduced but not switched off. The small cell base station  32 ,  34  may preferably include its current operational mode and/or type of operational mode in system information data which is broadcasted by the small cell base station  32 ,  34 , for example on the broadcast channel BCH in LTE or the secondary superframe header S-FH according to IEEE 802.16m. A further option is that the mobile station  51  is formed such that the mobile station  51  may deduce the current operational mode of the small cell or femtocell base station  32 ,  34  from the transmission pattern of the small cell base station  32 ,  34 . The scanning may also be required, if the access service network gateway  6   a  is not connected to a status data base  7  or data in the status data base  7  is inconsistent. 
     In summary the present invention provides a framework for selectively waking-up small cell base stations to reduce energy consumption and interferences in a wireless network. The criteria are based on traffic types and traffic volume and on small cell base station operational modes. One of the advantages of the present invention is that signaling for faster indication of small cell base station modes is defined. A further advantage is that due to the selective signaling unnecessary activation of small cell base station in energy/efficiency modes, like the low-duty mode, is avoided. This reduces further the interference to macro cell base stations and other small cell base stations and provides a reduction in energy consumption for base stations and/or mobile stations. A further advantage is an increase in quality of service for services like voice-over-IP due to a lower latency in hand-over. A further advantage is that modifications concern mainly the radio and access network and/or the core network comprising the mobility management function entity. Alternatively a distributed message filtering system for paging messages is proposed. 
     Many modifications and other embodiments of the invention set in forth herein will come to mind the one skilled in the art to which the invention pertains having benefit of the teaching presented in the foregoing description and the associated drawings. Therefore it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein they are used in a generic and descriptive sense only for purposes of limitation.