Abstract:
The present invention provides a method for performing inter-technology handovers of a communication unit between a first Radio Access Network (RAN) and a second RAN. The communication unit includes a single transceiver. An inter-RAN tunnel is established between the first RAN and the second RAN. When the communication unit determines that it may be moving out of the service area of the first RAN, the communication unit sends a handover request message to the first RAN. The handover request message includes a request for a second RAN that the communication unit can communicate with. The communication unit is then able to perform some handover communication with the second RAN prior to actually handing off to the second RAN, by utilizing the inter-RAN tunnel between the first RAN and the second RAN.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to wireless communication systems, and more particularly to handovers between communication systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    When a mobile phone is operating on one radio technology and comes to the end of the coverage area for that technology, the connection for the mobile phone must be handed over to another radio technology. Such handovers are very important in real-time services, such as voice calls. 
         [0003]    When there is only a single transceiver in a mobile phone, such that it cannot communicate on two technologies simultaneously, it must leave the first technology, initiate a session on the second technology, and an authenticated context must be established before the service can be continued on the second technology. This establishment time on the second technology can take as long as several seconds, and thus is not useful for real-time service inter-technology handovers. 
         [0004]    One solution to this problem is to use a very slow handover between the two systems. This is not very practical, since it leads to discontinuity in voice calls and the potential for members of the call to end the call, thinking that the other party has ended the conversation. 
         [0005]    A second proposed solution is to predefine a communication protocol between the disparate technologies. This protocol for exchanging calls is specific to each technology pair, and would need to be tailored and modified for each and every technology to have an associated protocol with every other communication technology in existence. If one technology changed, or a new technology came online, major changes would be necessary to all other communication networks. 
         [0006]    A further way of dealing with this problem is to simply drop the call. This is not much of a solution to the problem, however. 
         [0007]    Therefore, a need exists for a method of performing handover of voice calls from a network using a first technology to a network using a second technology when a mobile unit includes a single transceiver. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a solution to the problems of the prior art by using a generic tunneling approach to send signaling between a mobile phone and a second RAN using a technology different than the first RAN that the mobile unit is currently using. Signaling and data are sent in both directions between the second RAN and the mobile phone using the radio link of the first RAN. 
         [0009]    The present invention thereby provides for inter-technology handovers in a way that allows independence of the radio technologies and their evolution paths. Changes in a radio technology do not impact other technologies with which inter-technology handovers are executed. 
         [0010]    Because the mobile can begin to exchange signaling with another RAN before actually acquiring the radio channels of that RAN, handover delays for single radio mobiles can be shortened significantly to support real time services such as voice. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]      FIG. 1  depicts a communication system that includes a first radio access network (RAN), a second RAN, an inter-RAN tunnel, and a radio interface tunnel in accordance with an exemplary embodiment of the present invention. 
           [0012]      FIG. 2  depicts a message flow between a communication unit, a first RAN, and a second RAN in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The present invention provides a method for performing inter-technology handovers using generic tunneling. The present invention can be better understand in reference to  FIGS. 1 and 2   
         [0014]      FIG. 1  depicts a communication system  100  that includes a first radio access network (RAN)  101 , a second RAN  103 , an inter-RAN tunnel  113 , and a radio interface tunnel  115 . User equipment  105  is coupled to communication system  100  via RAN  101 .  FIG. 1  depicts a high-level view of the generic tunneling approach proposed by the present invention. 
         [0015]    First RAN  101  and second RAN  103  are radio access networks. Radio access networks manage the radio resources and provide access to a core network or a packet-switched network. First RAN  101  and second RAN  103  are preferably the ground-based infrastructure required for delivery of third-generation (3G) wireless communications services, including high-speed mobile access to the Internet. First RAN  101  and second RAN  103  preferably manage a wide range of tasks for each 3G user, including access, roaming, transparent connection to the public switched telephone network and the Internet, and Quality of Service (QoS) management for data and Web connections. 
         [0016]    Inter-RAN tunnel  113  provides communication between first RAN  101  and second RAN  103 . Inter-RAN tunnel  113  is a generic tunnel that facilitates communication between UE  105  and second RAN  103 . In accordance with an exemplary embodiment of the present invention, UE  105  is communicating over the air with first RAN  101 . Upon leaving the service area of first RAN  101  and traveling into the service area of second RAN  103 , UE  105 , which in this exemplary embodiment has a single transceiver, cannot simultaneously communicate with both first RAN  101  and second RAN  103 . In accordance with an exemplary embodiment of the present invention, UE  105  utilizes radio interface tunnel  115  to send and receive handover information to first RAN  101 . First RAN  101  forwards this information to second RAN  103  via inter-RAN tunnel  113 . 
         [0017]    Radio interface tunnel  115  is defined by the radio interface technology between first RAN  101  and UE  105 . Each over-the-air technology preferably defines radio interface tunnel  115  to suit the design of the particular radio interface. 
         [0018]    Radio interface tunnel  115  preferably provides for communication from UE  105  to first RAN  101  and from first RAN  101  to UE  105 . In an exemplary embodiment, UE  105  sends various messages to first RAN  101  via radio interface tunnel  115 , such as a request for a list of RANs available for handover, a request for a set of control information for the available RAN, a request to send content to a different RAN, a request for an estimate of the time a handover would require, and various acknowledgements of messages received from first RAN  101 . 
         [0019]    In an exemplary embodiment, first RAN  101  sends various message to UE  105  via radio interface tunnel  115 , such as a list of RANs available to handover to, a set of control information for an available RAN, content from second RAN  103 , the approximate time until there is a probable need for a handover to a different technology, and various acknowledgement messages. 
         [0020]    In accordance with an exemplary embodiment, first RAN  101  defines the protocol to be used for radio interface tunnel  115  and second RAN  103  defines the signaling and procedures to be used for inter-RAN tunnel  113 . Inter-RAN tunnel  113  preferably utilizes a simple, standard protocol in order to enlarge the number of technologies that can communicate with other RANs and the applicability of the present invention. 
         [0021]    User equipment (UE)  105  is a portable communication device that allows communication between itself and other users of communication networks. UE  105  can be a communication unit, a mobile phone, a cellular phone, a pager, or any other communication device that is capable of two-way communication. In accordance with an exemplary embodiment, UE  105  includes a single transceiver, and therefore is not able to tune away from first. RAN  101  for a long enough period to search for other available RANs. 
         [0022]      FIG. 2  depicts a message flow  200  between communication unit  105 , first RAN  101 , and second RAN  103  utilizing generic tunnels in accordance with an exemplary embodiment of the present invention. 
         [0023]    Inter-RAN Tunnel Setup message  201  begins inter-RAN tunnel establishment. Inter-RAN Tunnel Setup message  201  preferably includes an identification of the RAN and the type of RAN. Although Inter-RAN Tunnel Setup message  201  is depicted as flowing from second RAN  103  to first RAN  101 , it can alternately be initiated by first RAN  101 . 
         [0024]    Inter-RAN Tunnel Setup Ack message  203  completes inter-RAN tunnel establishment. Inter-RAN Tunnel Setup Ack message  203  preferably includes the ID of the RAN and the type of RAN. Inter-RAN Tunnel Setup Ack message  203  completes the establishment of a generic tunnel, inter-RAN tunnel  113 , between first RAN  101  and second RAN  103 . Both first RAN  101  and second RAN  103  will receive and store the RAN ID and RAN type of the other RAN. 
         [0025]    Available RANs Request message  301  requests a list of available RANs with a RAN-ID and a RAN-Type for each. 
         [0026]    Available RANs Response message  303  provides a list of available RANs with a RAN-ID and a RAN-Type for each. As an example, available RANs response message  303  could include the RAN ID and RAN type of second RAN  103 . 
         [0027]    Control Information Request message  205  is sent from first RAN  101  to second RAN  103  and requests a set of control information from second RAN  103  in the format used by that RAN type. When first RAN  101  receives Control Information Request message  205  from UE  105 , it preferably formats an inter-RAN Control Information Request to be sent to another RAN. When first RAN  101  receives a Control Information Response from another RAN, it can pass that information on to any mobile requesting the information. 
         [0028]    Control Information Response message  207  provides a set of control information for second RAN  103  in the format used by that RAN type, and can be sent autonomously. Control Information Response message  207  preferably includes RAN-ID, RAN-Type, and RAN-Info. 
         [0029]    Control Information Request message  205  and Control Information Response message  207  complete the function of obtaining control information for UE  105 . 
         [0030]    Control Information Request message  305  requests a set of control information for the indicated RAN in the format used by that RAN type. Control Information Request message  305  preferably includes RAN-ID. 
         [0031]    Control Information Response message  307  provides a set of control information for the RAN indicated in the format used by that RAN type. Control Information Response message  307  preferably includes RAN-ID. 
         [0032]    Send to RAN Request message  309  is used to send content to a different RAN, returns an Ack/Nack. Send to RAN Request message  309  preferably includes RAN-ID, Mobile-ID, Seq-No, and content. 
         [0033]    Send to RAN Ack message  311  is used to Ack/Nack content sent from the mobile to a different RAN via the serving RAN. Send to RAN Ack message  311  preferably includes Ack/Nack and Seq-No. 
         [0034]    Send to RAN Request message  213  is used to forward signaling/data to the targeted RAN from a mobile, returns an Ack/Nack. Send to RAN Request message  213  preferably includes Mobile-ID, Seq-No, and signaling/data. 
         [0035]    Send to RAN Response message  215  is used to Ack/Nack a Send to RAN Request message. Send to RAN Response message  215  preferably includes Mobile-ID, SeqNo, and Ack/Nack. 
         [0036]    Send to Mobile Request message  209  is used to send signaling/data to the mobile via a different RAN, returns an Ack/Nack. Send to Mobile Request message  209  preferably includes Mobile-ID, Seq-No, and signaling/data. 
         [0037]    Send to Mobile Response message  211  is used to Ack/Nack a Send to Mobile Request message. Send to Mobile Response message  211  preferably includes Mobile-ID, SeqNo, and Ack/Nack. 
         [0038]    Send to Mobile Request message  209  and Send to Mobile Response message  211  provide the ability to support a bidirectional flow of content between another non-serving RAN and UE  105 . 
         [0039]    Send to Mobile Ack message  313  is used to Ack/Nack content sent from a different RAN to the mobile via the serving RAN. Send to Mobile Ack message  313  preferably includes Ack/Nack and Seq-No. 
         [0040]    Send to Mobile Request message  315  is used to send content received from a different RAN to the mobile, returns an Ack/Nack. Send to Mobile Request message  315  preferably includes RAN-ID, Mobile-ID, Seq-No, and signaling/data. 
         [0041]    Request Indication of Handover Need message  317  requests an estimate of the time to handover in seconds. 
         [0042]    Indication of Handover Need message  319  is used to indicate the approximate time in seconds until there is a probable need for handover to a different technology. Indication of Handover Need message  319  preferably includes seconds. Indication of Handover Need message  319  can also be sent autonomously by RAN  101  to indicate to UE  105  that a handover to another RAN is recommended. 
         [0043]    While this invention has been described in terms of certain examples thereof, it is not intended that it be limited to the above description, but rather only to the extent set forth in the claims that follow.