Abstract:
In a wireless communications system including a third generation partnership project (3GPP) long term evolution (LTE) network, at least one alternative wireless network, and a wireless transmit/receive unit (WTRU), the 3GPP LTE network sends an indication of the availability of the alternative network or a list of available alternative networks in an area where the WTRU is located. The WTRU receives the information and initiates a handover procedure to the alternative wireless network based on the information. The WTRU may request a list of alternative wireless networks from the 3GPP LTE network, or may send capability information to the 3GPP LTE network. The alternative wireless network may be a 3GPP network, an interworking wireless local area network (I-WLAN), or a fixed broadband network.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/785,558 filed Mar. 24, 2006, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention is related to wireless communication systems. More particularly, the present invention is related to a method and apparatus for performing a handover procedure between a third generation partnership project (3GPP) long term evolution (LTE) network and an alternative wireless network. The alternative wireless network includes a 3GPP network, an interworking wireless local area network (I-WLAN), a fixed broadband network, or the like. 
       BACKGROUND 
       [0003]    A plurality of heterogeneous wireless communication networks currently co-exist. Each network uses a different radio access technology (RAT) adapted for the specific services provided by the particular network. 3GPP systems are the dominant types of currently deployed wireless communication systems. LTE is an evolution of the radio interface and the radio network architecture of 3GPP systems. The 3GPP is now considering an LTE of 3GPP systems to provide a new radio access network for higher data rates, lower latency, better packet optimization, improved system capacity, and better coverage. 
         [0004]      FIG. 1  shows a proposed architecture of the 3GPP LTE system  100 . The 3GPP LTE system  100  includes a global system for mobile communication (GSM) enhanced data rates for GSM evolution (EDGE) radio access network (GERAN)  102 , a universal terrestrial radio access network (UTRAN)  104 , an evolved radio access network (RAN)  106 , an interworking wireless local area network (I-WLAN)  108 , a serving global packet radio service (GPRS) support node (SGSN)  110 , an evolved packet core  112 , a home subscriber server (HSS)  114 , and a policy and charging rules function (PCRF)  116 . The 3GPP LTE system  100  may also include an IP server  118 , (e.g., IP multimedia subsystem (IMS), packet switched streaming (PSS), or the like). In the 3GPP LTE system  100 , the evolved RAN  106  and the evolved packet core  112  are added to the conventional 3GPP LTE system  100 , and R1, R2, R3, Gx+ and AAA interfaces are newly defined. 
         [0005]    Besides the 3GPP and 3GPP LTE networks, non-3GPP systems, (such as fixed broadband systems (FBSs)), have also been proposed and deployed. The non-3GPP systems include WiMAX, (i.e., IEEE 802.16), HIPERMAN, WiBro, or the like. 
         [0006]    As a plurality of heterogeneous networks are concurrently deployed, multi-mode wireless transmit/receive units (WTRUs) having at least two radio units to support at least two different RATs have become available. Depending on the capability of the WTRU, the multi-mode WTRU may communicate with two RANs simultaneously and may selectively receive a service through one of the RANs. The multi-mode WTRU may also select a preferred RAN among a plurality of available RANs and may perform a handover from one RAN to another. 
         [0007]    Since the 3GPP LTE networks, (including an I-WLAN), and the non-3GPP networks are concurrently deployed, it would be desirable to support a handover between the 3GPP LTE network and the non-3GPP network, or between the 3GPP LTE network and the I-WLAN, for service continuity or a better service experience. 
       SUMMARY 
       [0008]    The present invention is related to a method and apparatus for performing a handover procedure between a 3GPP LTE network and an alternative wireless network, such as a 3GPP network, an I-WLAN, a fixed broadband network, or the like. The 3GPP LTE network sends an indication of the availability of the alternative network, or a list of available alternative networks in an area where the WTRU is located, to the WTRU. The WTRU receives the information and initiates a handover procedure to the alternative wireless network based on the information. The WTRU may request a list of alternative wireless networks from the 3GPP LTE network or may send capability information to the 3GPP LTE network. The alternative wireless network may be a 3GPP network, an I-WLAN, or a fixed broadband network. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0010]      FIG. 1  shows a 3GPP LTE system architecture; 
           [0011]      FIG. 2  is a flow diagram of a process for performing a handover procedure between a 3GPP LTE network and an alternative network in accordance with the present invention; 
           [0012]      FIG. 3  is a signaling diagram of an exemplary process for performing a handover procedure between a 3GPP LTE network and an I-WLAN in accordance with the present invention; 
           [0013]      FIG. 4  is a signaling diagram of an exemplary process for performing a handover procedure between a 3GPP LTE network and an FBS in accordance with the present invention; and 
           [0014]      FIG. 5  is a block diagram of a WTRU configured in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    When referred to hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. 
         [0016]      FIG. 2  is a flow diagram of a process  200  for performing a handover procedure between a 3GPP LTE network and an alternative network in accordance with the present invention. The 3GPP LTE network transmits an indication of an availability of alternative networks, (e.g., I-WLAN, non-3GPP networks, or 3GPP networks), and/or a list of available alternative networks to the WTRU (step  202 ). The 3GPP LTE network may transmit both the indication and the list simultaneously. The 3GPP LTE network may transmit the indication and/or the list by broadcasting, multicasting or unicasting. The 3GPP network includes, but is not limited to, a UTRAN, a GERAN, a GSM network, a GPRS network, or the like. 
         [0017]    The WTRU receives the indication and/or the list and stores the list (step  204 ). Optionally, the WTRU may report its capability to support multiple RATs to the 3GPP LTE network (step  206 ). If the 3GPP LTE network broadcasts only the indication of the availability of the alternative wireless network, the WTRU may optionally request a complete list of the available alternative networks and attributes of the alternative networks (step  208 ). Upon receipt of the capability information or the request, the 3GPP LTE network may generate information regarding available alternative networks based on the capability information and send it to the WTRU (step  210 ). Steps  206 - 210  are optional. 
         [0018]    The WTRU then initiates a handover procedure to one of the available alternative networks (step  212 ). The WTRU may display the information regarding the alternative networks to the user before initiating a handover procedure. Alternatively, the WTRU may autonomously initiate the handover procedure. 
         [0019]      FIG. 3  is a signaling diagram of an exemplary process  300  for performing a handover procedure between a 3GPP LTE network  354  and an I-WLAN  356  in accordance with the present invention. The WTRU  352  listens to the broadcasting, (e.g., a broadcast control channel (BCCH)), from the 3GPP LTE network  354  (step  302 ). The 3GPP LTE network  354  broadcasts an indication of availability of I-WLAN(s) and/or a list of available I-WLANs in the area on which the WTRU  352  is located (step  304 ). The WTRU  352  receives the indication and/or the list, and stores the list (step  306 ). 
         [0020]    Steps  308 - 312  may optionally be performed. If the 3GPP LTE network  354  sends only the indication of available I-WLAN(s), the WTRU  352  may optionally send a capability report indicating I-WLAN capability of the WTRU  352  and/or a request for a complete list of available I-WLANs to the 3GPP LTE network  354  (step  308 ). In such case, upon receipt of the capability report and/or the request, the 3GPP LTE network  354  retrieves the information of available I-WLANs, (based on the capability report if it is received), (step  310 ), and sends a list of available I-WLANs and their associated attributes to the WTRU  352  (step  312 ). 
         [0021]    The WTRU  352  may scan, (actively or passively), for one of the I-WLANs and if the WTRU  352  is within a range of a target I-WLAN  356 , the WTRU  352  initiates a handover procedure to the target I-WLAN  356  (step  314 ). 
         [0022]    For a handover, the WTRU  352  sends an initial access message to the target I-WLAN  356  (step  316 ). The target I-WLAN  356  initiates an authentication procedure for the WTRU  352  and may allocate a new IP address to the WTRU  352  depending on the interworking case (step  318 ). Authentication data is exchanged between the 3GPP LTE network  354  and the target I-WLAN  356  (step  320 ). Once the WTRU  352  is authenticated, the target I-WLAN  356  sends an access grant message to the WTRU  352  (step  322 ). The target I-WLAN  356  sends a handover complete message to the 3GPP LTE network  354  (step  324 ). The 3GPP LTE network  354  releases a radio resource allocated for the WTRU  352  (step  326 ). The WTRU  352  receives a service via the target I-WLAN  356  (step  328 ). 
         [0023]      FIG. 4  is a signaling diagram of a process  400  for performing a handover procedure between a 3GPP LTE network  454  and an FBS  456  in accordance with the present invention. The WTRU  452  listens to the broadcasting, (e.g., a BCCH), from the 3GPP LTE network  454  (step  40   e ). The 3GPP LTE network  454  broadcasts an indication of availability of FBS(s) and/or a list of available FBSs in the area on which a WTRU  452  is located (step  404 ). The WTRU  454  receives the indication and/or the list, and stores the list (step  406 ). 
         [0024]    Steps  408 - 412  may optionally be performed. If the 3GPP LTE network  454  sends only the indication of available FBSs, the WTRU  452  may optionally send a capability report indicating FBS capability of the WTRU  452  and/or a request for a complete list of available FBSs to the 3GPP LTE network  454  (step  408 ). In such case, upon receipt of the capability report and/or the request, the 3GPP LTE network  454  retrieves the information of available FBSs, (based on the capability report if it is received), and their associated attributes and sends them to the WTRU  454  (steps  410 ,  412 ). 
         [0025]    The WTRU  452  may scan, (actively or passively), for one of the FBSs and if the WTRU  452  is within a range of one of the FBSs, the WTRU  452  initiates a handover procedure (step  414 ). 
         [0026]    The WTRU  452  measures a channel on FBSs and sends a measurement report along with a request for handover to the 3GPP LTE network  454  (step  416 ). The 3GPP LTE network  454  selects a target FBS  456  based on the measurement report and initiates a handover procedure and service forwarding (step  418 ). At step  418 , the 3GPP LTE network  454  also authenticates the WTRU  452  and may allocate a new IP address to the WTRU  452  depending on the interworking case. Service instantiation and authentication are performed between the 3GPP LTE network  454  and the target FBS  456  (step  420 ). Once the service is instantiated, the 3GPP LTE network  454  sends an access grant message to the WTRU  452  (step  422 ). The WTRU  452  then sends an initial access message to the target FBS  456  (step  424 ). The target FBS  456  sends a handover complete message to the 3GPP LTE network  454  (step  426 ). The 3GPP LTE network  454  then releases a radio resource allocated for the WTRU  452  (step  428 ). The WTRU  452  receives a service via the target FBS  456  (step  430 ). 
         [0027]      FIG. 5  is a block diagram of a WTRU  500  configured in accordance with the present invention. The WTRU includes a 3GPP LTE radio unit  502 , at least one alternative radio unit  504  and a handover controller  506 . The 3GPP LTE radio unit  502  is for communication with the 3GPP LTE network. The alternative radio unit  504  is for communication with an alternative wireless network, such as a 3GPP network or a non-3GPP network. For example, the alternative radio unit  504  may be an I-WLAN radio unit or an FBS radio unit. The 3GPP LTE radio unit  502  receives information regarding the alternative wireless network broadcast by the 3GPP LTE network. The handover controller  506  may initiate a handover to the alternative wireless network based on the information as stated above. 
         [0028]    Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0029]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0030]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) module.