Abstract:
The invention concerns methods, a device and computer program products for simplifying handover back to a restricted local access point from an unrestricted global access point as well as to a device implementing a restricted local access point for provision in a wireless network and a wireless network. In the network a restricted local access point hands over a mobile station to an unrestricted global access point and provides data enabling the restricted local access point to be identified as a candidate access point. A device for simplifying handover back determines that the restricted local access point is a candidate for further handover based on this data and informs the mobile station about the restricted local access point via the unrestricted glob access point. Thereby hand over may be considered also to the restricted local access point in addition to other surrounding access points.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of telecommunication. The invention more particularly relates to a method and computer program product for providing access for a limited set of mobile stations to a restricted local access point in a wireless network, a control device for a restricted local access point for provision in a wireless network, a device implementing a restricted local access point for provision in a wireless network and a wireless network. 
       DESCRIPTION OF RELATED ART 
       [0002]    There has for some time been of interest to allow the use of one and the same mobile station at home and in a public wireless network. 
         [0003]    For this reason there has been provided stations that have a dual mode operation, one cellular mode and one cordless mode. The mobile station then switches between modes as it moves between a public cellular network and a cordless base station. This is advantagous if a mobile station is to be provided in two different networks. 
         [0004]    However these stations require exchange of the existing legacy cellular phone owned by the end user and are furthermore costly for the end user because of the dual mode operation. 
         [0005]    It would therefore be of interest to allow a mobile station to be used both at home and in a cellular network and without the user having to acquire a special dual mode mobile station, i.e. through the user using an ordinary mobile station adapted for use in the public cellular network and to use it in his home with a home base station. This also opens the market of public wireless network operators to the home telephony segment. 
         [0006]    The present invention is directed towards providing a mobile station end user with this ability using his ordinary mobile station. 
       SUMMARY OF THE INVENTION 
       [0007]    One object of the present invention is thus directed towards providing a method of providing access for a limited set of mobile stations to a restricted local access point in a wireless network that allows the use of one and the same mobile station for the restricted local access point and the main part of the network. 
         [0008]    This object is according to a first aspect of the present invention achieved through a method of providing access for a limited registered set of mobile stations to a restricted local access point in a wireless network, comprising the steps of:
       attracting mobile stations in an area covered by a restricted local access point, for each mobile station that is attracted,
           determining if the station belongs to the set,   allowing access to the access point in case it does, and   rejecting access to the access point in case it does not.   
               
 
         [0013]    Another object of the present invention is directed towards providing a control device for a restricted local access point for provision in a wireless network that allows the use of one and the same mobile station for the restricted local access point and the main part of the network. 
         [0014]    This object is according to a second aspect of the present invention achieved through a control device for a restricted local access point for provision in a wireless network, said restricted local acces point being implemented by a device comprising a radio communication unit,
       said control device being arranged to
           order the radio communication unit to attract mobile stations in an area covered by the restricted local access point,   for each mobile station that is attracted,
               determine if the station belongs to a limited registered set of mobile stations,   allow access to the access point in case it does, and   reject access to the access point in case it does not.   
               
               
 
         [0021]    Another object of the present invention is directed towards providing a device implementing a restricted local access point for provision in a wireless network that allows the use of one and the same mobile station for the restricted local access point and the main part of the network. 
         [0022]    This object is according to a third aspect of the present invention also achieved through a device implementing a restricted local access point for provision in a wireless network comprising
       a radio communication unit, and   a control device for the restricted local access point being arranged to order the radio communication unit to attract mobile stations in an area covered by the restricted local access point,
           for each mobile station that is attracted,
               determine if the station belongs to a limited registered set of mobile stations,   allow access to the access point in case it does, and   reject access to the access point in case it does not.   
               
               
 
         [0029]    Still another object of the present invention is directed towards providing a wireless network that allows the use of one and the same mobile station for a restricted local access point in the network and the main part of the network. 
         [0030]    This object is according to a fourth aspect of the present invention also achieved through a wireless network comprising:
       a number of unrestricted global access points,   at least one device implementing a restricted local access point that comprises a radio communication unit, and   a control device for the restricted local access point being arranged to
           order the radio communication unit to attract mobile stations in an area covered by the restricted local access point,   for each mobile station that is attracted,
               determine if the station belongs to a limited registered set of mobile stations,   allow access to the access point in case it does, and   reject access to the access point in case it does not.   
               
               
 
         [0039]    Yet another object of the present invention is directed towards providing a computer program product that allows the use of one and the same mobile station for a restricted local access point in a wireless network and in a main part of the network. 
         [0040]    This object is according to a fifth aspect of the present invention achieved through a computer program product for providing access for a limited registered set of mobile stations to a restricted local access point in a wireless network, comprising computer program code to make a control device for the restricted local access point perform, when the code is loaded into said device:
       order a radio communication unit of the restricted local access point to attract mobile stations in an area covered by the restricted local access point,   for each mobile station that is attracted.
           determine if the station belongs to a limited registered set of mobile stations,   allow access to the access point in case it does, and   reject access to the access point in case it does not.   
               
 
         [0046]    An unrestricted global access point is here defined as an access point which when provided in a network allows all mobile stations in the network to essentially communicate on equal terms, while a restricted local access point is here defined as an access point that has a separate set of rules relating to a limited set of mobile stations within the network and is mainly intended to allow these stations to communicate with a specific restricted local access point. Alternatively a restricted local access point can be restricted only in the sense of having lower output power, thus creating a range of coverage restricted to its close vicinity. 
         [0047]    The present invention has many advantages. It allows an ordinary mobile station to be used both for a restricted local access point and in the main part of the network. Another advantage is that only the mobile stations registered to a restricted local access point may use it. This avoids that mobile stations nearby occupy the access point, while the calls of registred mobile stations are ensured to pass through the restricted local access point. 
         [0048]    It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]    The present invention will now be described in more detail in relation to the enclosed drawings, in which: 
           [0050]      FIG. 1  schematically shows a wireless network comprising three ordinary unrestricted global access points and three restricted local access points, where each restricted local access point is being provided in a house, as well as a number of related entities of the network, 
           [0051]      FIG. 2  shows a block schematic of different units of a restricted local access point, 
           [0052]      FIG. 3  schematically outlines different location areas of the wireless network according to a first embodiment of the present invention 
           [0053]      FIGS. 4A and 4B  shows different signals exchanged between two different mobile stations and a restricted local access point according to the first embodiment, where one mobile station is allowed access and one is not. 
           [0054]      FIG. 5  shows a flow chart of a number of method steps performed in the restricted local access point according to the first embodiment of the present invention, 
           [0055]      FIG. 6  schematically outlines different network identities used according to a second embodiment of the present invention, and 
           [0056]      FIGS. 7A and 7B  show different signals exchanged between two different mobile stations, the restricted local access point and a traffic control unit in the network according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0057]    In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. 
         [0058]    The present invention is described in the non-limiting, context of a wireless network in the form of a Public Land Mobile Network that is here a GSM (Global System for Mobile communications) network  10  shown in  FIG. 1 . Here it should be realised that the network is in no way limited to GSM, but can be any type of public land mobile network, like GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System). It can also be based on for instance WLAN (Wireless Local Area Network) technology. The network  10  here includes at least one first traffic control unit  12 , which in the case of GSM is an MSC (Mobile Services Switching Centre). If the network was a GPRS network this unit would be a SGSN (Serving GPRS Support Node) instead. To the first traffic control unit  12 , there is connected a VLR  14  (Visiting Location Register), which will be described in more detail later in relation to a second embodiment of the present invention. The first traffic control unit  12  is furthermore connected to a first, second and third unrestricted global access point  18 ,  20  and  22  in the form of base stations via a second traffic control unit  13  in the form of a BSC (Base Station Controller). It is possible to combine GPRS and GSM networks. In this case the second traffic control unit  13  would be connected to both an MSC and a SGSN. The base stations  18 ,  20 ,  22  are ordinary base stations, which any mobile station being allowed to communicate in the network  10  can use for communication. In  FIG. 1  two such ordinary mobile stations  54  and  56  are shown as communicating with a first base station  18 . The network  10  also includes an Operation and Maintenance service centre  16 , where customer service is handled. This service centre  16  is also connected to the both the traffic control units  12  and  13 . It may also be connected to unrestricted global access points (not shown). The service centre  16  and the first traffic control unit  12  are furthermore both connected to an external communication network  17 , which is here the Internet. It should be realised that the first traffic control unit  12  may be connected to several second traffic control units  13 , and that there may be several more first traffic control units  12  in the wireless network  10  in order to control communication with mobile stations via one or more access points. It should also be realised that the network need not be provided with a central traffic control unit at all. What has been described so far is well known within the art. 
         [0059]    In  FIG. 1  there are also shown three different buildings  24 ,  34  and  44 , where a first building  24  includes a first restricted local access point  26  connected to a modem  28 . The modem  28  is connected to the external network  17  as well as a to a computer  30  also provided in the first building. There is also provided a first user mobile station  32  communicating with the first restricted local access point  26 . The first user mobile station  32  belongs to a limited set of mobile stations associated with the first restricted local access point  26 . The second building  34  includes a second restricted local access point  36  connected to a modem  38 , which in turn is connected to the external network  17 . Here a computer  40  is connected to the second restricted local access point  36  for connection to the modem  38 . The reason for this is that this modem is of a type which only allows one other device to be connected to it. In this second building  34  there is a second user mobile station  42  that belongs to a limited set of mobile stations associated with the second restricted local access point  36 . Finally the third building  44  includes a third restricted local access point  46  connected to a modem  48 . The modem  48  is connected to the external network  17 , as well as to a computer  50  also provided in the third building  44 . There is finally provided a third user mobile station  52  communicating with the third restricted local access point  46 , where this third user mobile station  52  belongs to a limited set of mobile stations associated with the third restricted local access point  46 . 
         [0060]    It should here be realised that the restricted access points  26 ,  36  and  46  for the first, second and third user mobile stations  32 ,  42 ,  52  act as access points within the network  10  and are controlled by the first and second traffic control units  12  and  13 . The external network  17  is in this case just a channel that is used for providing this communication between the network  10  and the restricted local access points. The external network may also provide other types of communication with for instance the service centre  16 . The reason for using the Internet is that many households have easy access to it. For this reason it is also evident that the external network can be any network that is provided for a household and can for instance be a cable TV network instead. In case the household has direct access to a LAN network, a modem might also not be needed. There are thus several ways in which this channel may be provided. 
         [0061]      FIG. 2  shows a block schematic of some relevant units of a device implementing the first restricted local access point  26  and the different other devices it communicates with in the first building. It should be realised that the other restricted local access points may be provided in the same way. This device  26  comprises an antenna  58  communicating with the first user mobile station  32 , which antenna is connected to a radio circuit  60 , which may be provided in the form of an ordinary mobile station chipset. The radio circuit  60  is connected to a control unit  62  and to a signal conversion unit  64  converting circuit switched voice to packet based voice. The signal conversion unit may use UMA/GAN (Unlicensed Mobile Access/Generic Access Network), which is a standard for making GSM calls over 802.11 or Bluetooth, where GSM protocols are tunneled over unlicensed bands. Both the control unit  62  and the signal conversion unit  64  are connected to an interface  66  that in turn is connected to the modem  28 . 
         [0062]    The purpose of providing a restricted local access point in this way, is to let the operator of the network  10  simulate a home base station within his own network, where an end user can use his ordinary cellular phone also via this restricted local access point. At the same time the user is automatically allowed to use the mobile station in the rest of the public wireless network  10  whenever there is no or insufficient contact with the restricted local access point. In this way it is for instance possible to delete a fixed land line network connection for an end user. The operator may then also provide different billing strategies for calls made via a restricted local access point and via other access points in the network. For the user of the mobile station, the mobile station is thus to resemble a cordless phone when inside the building and an ordinary mobile station when being provided outside the building. There is furthermore no need for the end user to keep track of several different phone numbers. However the restricted local access point is controlled by the operator of the network. 
         [0063]    This is thus the functionality that is desired. However, since a restricted local access point is controlled by the network, there has to be provided measures for allowing a first user mobile station associated with the first restricted local access point to communicate with this access point whenever it is possible and also disallow other mobile stations to communicate with it. That is, if the first user mobile station is to use the first restricted local access point, it should be possible to do so if it is close enough. Also other mobile stations that are not associated with it, should be disallowed to use this access point. In order to provide economy, it is furthermore often desirable that such a restricted local access point be provided at a low cost. This also means that it normally is much smaller, weaker in transmission power and provided with fewer traffic channels as compared with an ordinary unrestricted global access point, which furthermore may cover the restricted local access point as an umbrella. Thus an unrestricted global access point may be much stronger than the restricted local access point in the area the restricted local acess point is intended to cover. All in all, there are thus several problems that have to be addressed for realising this functionality when ordinary mobile stations adapted for this type of network are to be used. 
         [0064]      FIG. 3  schematically shows how the different access points of the network of  FIG. 1  have been organised according to a first embodiment of the present invention in order to help solving the problems mentioned above. The whole network  10  has a network identity N 1  and is divided into sectors in the form of location areas, where a first location area LA 1  only includes the first restricted local access point  26 , a second location area LA 2  only includes the second restricted local access point  36  and a third location area LA 3  only includes the third restricted local access point  46 . A fourth location area LA 4  includes all of the unrestricted global access points  18 ,  20  and  22 . It should here be realised that there may be more location areas including several unrestricted global access points. However according to this embodiment each restricted local access point is associated with one location area. There is thus a one-to-one correspondence between a location area and a restricted local access point. Each restricted local access point is thus associated with a corresponding unique location area. 
         [0065]    Now the principles of the present invention will be described with reference also being made to  FIGS. 4A and 4B , which shows signals transmitted between mobile stations and the first restricted local access point according to the first embodiment and  FIG. 5 , which shows a flow chart of a method according to the first embodiment of the present invention. 
         [0066]    The first restricted local access point  26  works on the principle that it is to attract all mobile stations  32 ,  54 ,  56  in the area it covers. It does this by broadcasting information, step  68 . The broadcast information then includes the network identity of the network to which it belongs, which is here N 1 , the location area to which it belongs, which is the location area LA 1  as well as a cell reselect offset CRO, and a link quality value, here in the form of a minimum signal strength value ACCMIN. The minimum signals strength value ACCMIN is also known within the field as RXLEV_ACCESS-MIN. 
         [0067]    As is well known within the art a mobile station constantly monitors the link qualities to different candidate access points in order to determine which access point is preferred. It may do this by comparing link quality values determined for different access points, where a link quality value may be a measured signal strength determined or measured for a candidate access point. It then selects the access point having the best link quality value. 
         [0068]    An access point may also indicate a minimum link quality value level for a mobile station to consider the access point in question, which may be a minimum received signal strength value level. This value level sets the minimum level on the link quality value a mobile terminal dtermines that is to be the base for considering the access point as a candidate. 
         [0069]    What a mobile station  32 ,  54 ,  56  does, when using link quality in the form of signal strength and when it has received this broadcast information, is that it first investigates if the detected signal strength of the restricted local access point is above the received value ACCMIN. If it is, the mobile station  32 ,  54 ,  56  is close enough to the restricted local access point  26 . The value may here be set such that a mobile station will detect a higher level than ACCMIN when it is within 20 or 50 metres from the restricted local access point  26 . Thereafter the mobile station  32 ,  54 ,  56  adds the offset CRO to the same detected signal strength and compares the sum with detected signal strengths of other access points. If now the sum is higher than other detected signal strengths the mobile station  32 ,  54 ,  56  is attracted. 
         [0070]    When that has been done the mobile station  32 ,  54 ,  56  thus decides that the first restricted local access point  26  is a desirable access point to communicate with, i.e. that it should roam into the area covered by that access point. However, since the location area LA 1  is different from the location area LA 4  of the unrestricted global access points surrounding it, the mobile station  32 ,  54 ,  56  will perform a location update and send a location update message, which is received by the restricted local access point. In this location update message, the mobile station provides a mobile station identifier, which is either an IMSI (International Mobile Subscriber Identity) or a TMSI (Temporary Mobile Subscriber Identity). The location update message is received by the radio communcation unit  60  of the restricted local acces point  26  and forwarded to the control unit  62 . In case the identity in the message is an IMSI, the control unit  62  compares this IMSI with a limited registered set of mobile station identifiers associated with the access point, step  72 . Here the first user mobile station  32  belongs to this set, while mobile stations  54  and  56  do not. If the identifier is in the set, step  74 , the mobile station  32  is allowed to roam into the area covered by the first restricted local access point  26 , step  76 , whereas if it is not, the roaming of the mobile terminal  54   56  into this area is disallowed, step  78 . This response is in GSM a message called “Location Update Rejected” with a cause code “Roaming not allowed in this LA”. In any case the control unit  62  orders the radio communication unit  60  to send the response to the mobile station  32 ,  54 ,  56 . In case a TMSI was received, the control unit  62  would send an Identity Request (IMSI) regarding the TMSI to the first traffic control unit  12 , which in turn would locate a corresponding IMSI that it would send to the control unit  62  of the restricted local access point  26  via the second traffic control unit  13 . The control unit  62  would then perform the comparing and allow or disallow roaming in the way described above. 
         [0071]    The first user mobile station  32  which belongs to a limited set of mobile stations associated with the first restricted local access point, may in this way freely use the first restricted local access point. At the same time other mobile stations not in the set, which may accidentally try to use the first restricted local access point, are not allowed to do so because of the denied roaming. This barring of roaming furthermore stays in place for a long time and the other stations will not try again. 
         [0072]    There are some variations that could be provided in relation to this and other embodiments that should be mentioned here. It is also possible to include a timing advance limitation value in the broadcast information. This timing advance limitation value would then limit the timing advance the mobile station would need to perform in order to time itself to the transmission structure (time slots) of the restricted local access point. The timing advance needed is a strong indication that the distance between access point and mobile station is too long for it to be close. The limit should then be a timing advance of zero. 
         [0073]    A second way to provide the functionality of the present invention will now be described with reference being made to  FIGS. 6 and 7 , where  FIG. 6  shows how the different access points of the network have been organised according to a second embodiment of the present invention and  FIGS. 7A  and B show show signals transmitted between mobile stations, the first restricted local access point and the first traffic control unit. As is shown in  FIG. 6 , all the restricted local access points are provided in a part of the network that has a different network identity N 2 , here a PLMN identity, than the identity of the rest of the network that has a network identity N 1 , also a PLMN identity. The provision of a second network identity can here also be seen as providing a sector of the network for all restricted local access points. Here the first traffic control unit  12  of the network  10  keeps track of the user mobile stations allowed in the part of the network having the second network identity N 2 . With this configuration other mobile stations only belong to the part of the network having the first network identity N 1 , while all user mobile stations are associated with the second network identity N 2 . This means that all user mobile stations within the set may use any restricted local access point. Here broadcasting is made in the same way mentioned earlier, however using the second network identity N 2  instead of the first N 1 . The local area information and offset value CRO may also be omitted or need not be considered. As a station  32  belongs to a certain network having a certain network identity N 2  it always tries to connect to that network. In the case of GSM this means that a SIM—(Subscriber Identity Module) card for the station  32  may have a setting for the network identity N 2  as a home network and a setting for the network identity N 1  as a preferred visitor network. As before each station  32 ,  54 ,  56  that wants to access the network sends a location update message. When the first restricted local access point  26  recieves this message it forwards it to the first traffic control unit  12 , which goes on an checks in the VLR  14  if the station is allowed to use it. The VLR  14  thus defines an own roaming area. All mobile terminals should then as a default have a roaming restriction to this roaming area. The user mobile terminals of the set should then have this this roaming restriction removed in the VLR  14 . If a mobile terminal  54 ,  56  is not allowed to roam, the first traffic control unit  12  therefore sends a roaming rejected signal and if a mobile terminal  32  is allowed to roam, it sends a roaming allowed signal. Here all restricted local access points may be provided in the same location area, which means that all users might be allowed to use all restricted access points. It is of course possible to also here provide location areas that puts restrictions on the use. It is also possible to provide a special zone code if they all have the same location area, where this zone code identifies a sector corresponding to one restricted local access point. This in order to provide multiple sets, where each set is associated with a corresponding restricted local acess point. 
         [0074]    There are several ways in which mobile stations can be registered for being associated with a set. It is for instance possible to press a button on the device implementing the restricted local access point while the mobile station is switched on nearby. At power on, the mobile station will then perform a so-called IMSI attach, where it provides its identity. The access point will then receive and store the IMSI. 
         [0075]    If two mobile stations are switched on at the same time while the button on the device implementing the access point is held down, the procedure will fail with an indication to the end-user to try again. 
         [0076]    There are several other different ways in which mobile stations can be registered. It is for instance possible to send MMS or SMS messages from the mobile station to the service centre or to use the computer and log into a web site of the operator or even to call the operator in order to indicate the mobile stations that are to be registered in the set. It is also possible to provide one or more SIM-card slots in the device implementing the restricted local access point, where one twin Sim card is inserted for each person that shall be able to use the restricted local access point and the other twin SIM card is provided in the mobile station. 
         [0077]    The identifiers of the registered mobile stations may also be received in a restricted local access point via an ADC (Automatic Device Configuration) that may typically be received by the access point via SMS or using OMA DM (Open Mobile Alliance, Device Management). These are the same types of messages that are normally used to configure a mobile station with settings for various services, such as GPRS settings, WAP, MMS, QoS. Th access point can also receive the information via a UMA bearer via the Internet. It is furthermore possible that it is sent from the traffic control unit of the network. In the case of registrations being provided in the VLR, the VLR may receive them from the service centre or from the restricted local access point that received the information. 
         [0078]    The control of whether roaming is allowed into an area covered by a restricted local access point or not may thus be provided in the access point or centrally in the network or perhaps as a combination of both. 
         [0079]    The control unit according to the present invention can be implemented through one or more processors together with computer program code for performing its function. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier or as program code downloable from a server. 
         [0080]    There are several variations that are possible to make of the present invention. It is for instance possible that more than one mobile station may be registered for use with each restricted local access point. Link quality values have above been exemplified through the use of signal strength. It should also be realised that other link quality vales than signal strength may be used, like bit error rate or signal to interference ratio. As an alternative to providing each restricted local access point with a corresponding location area it is also possible to provide the restricted local access points in the same location area, but being repeated with a wide span between them in the network, e.g. every 10.000 th  ordinary base station. This ensures that two restricted local access points are not close to each other, i.e. it is unlikely that one user of a mobile station associated with one restricted local access point uses the restricted local access point intended for another user. 
         [0081]    The invention also has a number of advantages. It allows an ordinary mobile station to be used both for a restricted local access point and in the main part of the network. Another advantage is that only the mobile stations registered to a restricted local access point may use it. This avoids that mobile stations nearby occupy the access point, while the calls of registred mobile stations are ensured to pass through the restricted local access point. It is furthermore easy to register mobile stations for use with a restricted local access point, since ordinary mobile station device configuration techniques may be used. 
         [0082]    While the invention has been described in connection with what is presently considered to be most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements. Therefore the present invention is only to be limited by the following claims.