Abstract:
A method and apparatus for implementing a handoff between radio access networks (RANs) deployed under different radio access technologies (RATs) are disclosed. A wireless transmit/receive unit (WTRU) is equipped with at least two radio units to support the RATs. Each RAN sends a list of co-located RANs in the coverage area of the RAN to the WTRU. The WTRU stores the list and determines whether handoff criteria is met by one of the co-located RANs. The WTRU then initiates a handoff from a current RAN to a target RAN if the handoff criteria is met by the target RAN. Alternatively, the WTRU may send a measurement report to the current RAN, whereby the current RAN determines whether handoff criteria is met by a selected one of the co-located RANs and initiate a handoff to the selected RAN if the handoff criteria is met.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. provisional application Nos. 60/682,516 filed May 19, 2005,60/694,953 filed Jun. 29, 2005, which are 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 implementing a handoff between radio access networks (RANs) deployed under different radio access technologies (RATs).  
       BACKGROUND  
       [0003]     Different types of wireless access systems have been developed to provide different types of services. Some examples of the wireless access systems include wireless local area networks (WLANs), (such as IEEE 802-based networks), and cellular networks, (such as universal mobile telecommunication systems (UMTS) terrestrial radio access network (UTRAN), an evolved UTRAN (E-UTRAN), a GPRS/EDGE radio access network (GERAN), or the like). Each of these networks have been developed and tailored to provide specific applications.  
         [0004]     With the pervasive adoption of wireless communication networks in enterprise, residential and public domains, continuous connectivity can be supported as the users of such networks move from one network to another. With an emerging “always-on” scenario, wireless transmit/receive units (WTRUs), (i.e., mobile stations (MS)), are required to support multiple heterogeneous networks. Thus, a seamless handoff between these networks is desired.  
       SUMMARY  
       [0005]     The present invention is related to a method and apparatus for implementing a handoff between RANs deployed under different RATs. A WTRU is equipped with at least two radio units to support the RATs. Each RAN sends a list of co-located RANs in the coverage area of the RAN to the WTRU. The WTRU stores the list and determines whether handoff criteria is met by one of the co-located RANs. The WTRU then initiates a handoff from a current RAN to a target RAN if the handoff criteria is met by the target RAN. Alternatively, the WTRU may send a measurement report to the current RAN, whereby the current RAN determines whether handoff criteria is met by a selected one of the co-located RANs and initiates a handoff to the selected RAN if the handoff criteria is met. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     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:  
         [0007]      FIG. 1  shows a handoff process in a wireless communication system configured in accordance with the present invention;  
         [0008]      FIG. 2  is a signaling diagram of a process of a location-based WTRU-initiated handoff from an E-UTRAN to an I-WLAN in accordance with the present invention;  
         [0009]      FIG. 3  is a signaling diagram of a process of a power-based WTRU-initiated handoff from an E-UTRAN to an I-WLAN in accordance with the present invention;  
         [0010]      FIG. 4  is a signaling diagram of a process of a power-based WTRU-initiated handoff from an E-UTRAN to an I-WLAN without broadcasting in accordance with the present invention;  
         [0011]      FIG. 5  is a signaling diagram of a process of a WTRU-initiated handoff from an I-WLAN to an E-UTRAN in accordance with the present invention;  
         [0012]      FIG. 6  is a signaling diagram of a process of a WTRU-initiated handoff from an I-WLAN to an E-UTRAN without broadcasting in accordance with the present invention; and  
         [0013]      FIG. 7  is a signaling diagram of a process of a power-based E-UTRAN-initiated handoff from an I-WLAN to an E-UTRAN in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     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, or any other type of device capable of operating in a wireless environment.  
         [0015]     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components.  
         [0016]      FIG. 1  shows a handoff process in a wireless communication system  100  including a plurality of RANs  110   a ,  110   b , deployed under different RATs, and a core network  120  which may be an all IP network (AIPN). The core network  120  is connected to other networks, such as a public switching telephone network (PSTN)  130 , the Internet  140 , or the like. Each of the RANs  110   a ,  110   b  may be a generic access network (GAN), a GERAN, a UTRAN, an E-UTRAN, an IEEE-based interworking WLAN (I-WLAN) or any type of wireless access network.  
         [0017]     In order to optimize mobility among diverse RANs  110   a ,  110   b , the core network  120  provides open interfaces for mobility management (MM)  122  that allow the operator of the core network  120  to direct WTRUs  150  towards the most suitable RANs  110   a ,  110   b . The core network  120  also provides open interfaces that allow the WTRUs  150  to access other AIPN services, such as session control (SC)  124 , authentication, authorization and accounting (AAA)  126  and a policy control  128 .  
         [0018]     A WTRU  150  is a multi-mode WTRU equipped with at least two radio units configured to support communication with at least two different RATs. For example, the WTRU  150  may include one radio unit for an E-UTRAN and the other radio unit for an I-WLAN. The WTRU  150  establishes a connection to one of the RANs and may perform a handoff to a target RAN if handoff criteria is met by the target RAN.  
         [0019]     The handoff may be initiated manually or automatically. In the manual handoff process initiated by a user of the WTRU  150 , the user knows the existence of alternative RATs in its current geographic location and switches between them. The automatic handoff process may be initiated by the WTRU  150  or by the RAN  110   a ,  110   b  or the core network  120 .  
         [0020]     In the WTRU-initiated handoff, the WTRU  150  detects the existence of alternative RATs and initiates a handoff process based on the preference of the user of the WTRU  150 . The WTRU  150  receives necessary information, (such as handoff policies, resource status, or the like), from the network, (i.e., an RAN  110   b  or the core network  120 ). The WTRU  150  tracks the locations of coverage areas of the RANs  110   a ,  110   b  and initiates the handoff process based on a predetermined handoff criteria.  
         [0021]     In a system initiated handoff, the core network  120 , (or the RAN  110   a ,  110   b ), recognizes that the WTRU  150  is capable of supporting multiple RATs and requests necessary information, (such as power measurements), from the WTRU  150 . The core network  120 , (or the RAN  110   a ,  110   b ), tracks the location of the WTRU  150  and initiates the handoff procedures based on a set of criterion, (such as the mobility of the WTRU  150 , requested bandwidth, applications, load balancing, subscriber&#39;s profile, the measurement reports provided by the WTRU  150 , or the like), once the WTRU  150  is within the coverage area of a target RAN.  
         [0022]     Hereinafter the present invention will be explained with reference to an E-UTRAN and an IEEE-based I-WLAN. However, it should be noted that the present invention is applicable to any type of RANs using any type of RATs.  
         [0023]      FIG. 2  is a signaling diagram of a process  200  of a WTRU-initiated handoff from an E-UTRAN  160  to an I-WLAN  170  based on location in accordance with the present invention. The WTRU  150  is currently attached to the E-UTRAN  160  and is listening to an E-UTRAN channel, such as a broadcast control channel (BCCH) (step  202 ). The E-UTRAN  160  sends, (i.e., broadcasts, multicasts or unicasts), a list of RANs, (e.g., I-WLANs, a UTRAN, a GERAN or a GAN), available within the coverage area of the E-UTRAN  160  (step  204 ). The WTRU  150  receives the list and stores it (step  206 ). The WTRU  150  then sends a request for the location of service areas of the RANs in the list to the E-UTRAN  160  (step  208 ). The E-UTRAN  160  then retrieves the location information and sends it to the WTRU  150  (steps  210 ). The list may include information about the service area locations, radio technologies used by the listed RANs, supported frequencies and data rates, or the like.  
         [0024]     The WTRU  150  constantly monitors its location as it moves around the coverage area of the E-UTRAN  160 . If its location is within a range of the coverage area of an alternative RAN, (such as the I-WLAN  170 ), the WTRU  150  triggers a handoff procedure (step  212 ). If the WTRU  150  determines that the WTRU  150  is within the range of the coverage area of the I-WLAN  170 , the WTRU  150  sends a message to the I-WLAN  170  to initiate a WLAN service (step  214 ). When the I-WLAN  170  receives the message, the I-WLAN  170  initiates an authentication procedure to authenticate the WTRU  150  and may allocate a new IP address depending on the interworking case (step  216 ). Authentication messages are exchanged between the I-WLAN  170  and the E-UTRAN  160  (step  218 ). Once the WTRU  150  is authenticated, the I-WTRU  170  sends an access grant message to the WTRU  150  indicating that access to the WLAN services is granted (step  220 ). The WTRU  150  then initiates a handoff to the I-WLAN  170  by sending a handoff initiation message to the E-UTRAN  160  (step  222 ). Control messages for routing data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  224 ). Once a new route is established, the E-UTRAN  160  sends a handoff complete message to the WTRU  150  (step  226 ) and services provided to the WTRU  150  are resumed via the I-WLAN  170  (step  228 ).  
         [0025]     The process  200  is applicable to a handoff between any types of RANs. For example, the process  200  may be applied to a handoff from a UTRAN to an I-WLAN. In such case, the UTRAN sends a list of available RANs in the coverage area of the UTRAN and the WTRU triggers a handoff from the UTRAN to the I-WLAN using the list based on location of the WTRU and the I-WLAN.  
         [0026]      FIG. 3  is a signaling diagram of a process  300  of a WTRU-initiated handoff from an E-UTRAN  160  to an I-WLAN  170  based on a power level in accordance with the present invention. The WTRU  150  includes an E-UTRAN radio unit  152 , a WLAN radio unit  154  and a handoff controller  156  so that the WTRU  150  may handoff between the E-UTRAN  160  and the I-WLAN  170 . The WTRU  150  is currently attached to the E-UTRAN  160  and listens to an E-UTRAN channel, (such as a BCCH) (step  302 ). The E-UTRAN  160  sends, (i.e., broadcasts, multicasts or unicasts), a list of other RANs, (e.g., I-WLANs, a UTRAN, GERAN or a GAN), available within the coverage area of the E-UTRAN  160  (step  304 ). The E-UTRAN radio unit  152  of the WTRU  150  receives the list and stores it (step  306 ). The E-UTRAN radio unit  152  then initializes the WLAN radio unit  154  (step  308 ). The list provided by the E-UTRAN  160  preferably includes a frequency list of the I-WLAN  170  so that the WLAN radio unit  154  may search the available WLANs using the frequency list.  
         [0027]     The WLAN radio unit  154  is then initialized and monitors WLAN channels based on the frequency list and measures a power level of signals received from the I-WLAN  170  (step  310 ). The handoff controller  156  triggers a handoff procedure if the measured power level satisfies a predetermined threshold (step  312 ). The WTRU  150  sends a message to the I-WLAN  170  to initiate WLAN services (step  314 ).  
         [0028]     When the I-WLAN  170  receives the message from the WTRU  150 , the I-WLAN  170  initiates an authentication procedure to authenticate the WTRU  150  and may allocate a new IP address depending on the interworking case (step  316 ). Authentication messages are exchanged between the I-WLAN  170  and the E-UTRAN  160  (step  318 ). Once the WTRU  150  is authenticated, the I-WTRU  170  sends an access grant message to the WTRU  150  (step  320 ). The WLAN radio unit  154  then sends a handoff initiate message to the E-UTRAN radio unit  152  (step  322 ). The E-UTRAN radio unit  152  then sends a message to the E-UTRAN  160  to initiate a handoff to the I-WLAN  170  (step  324 ). Control messages for routing of data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  326 ). Once a new route is established, the E-UTRAN  160  sends a handoff complete message to the E-UTRAN radio unit  152 , which forwards it to the WLAN radio unit  154  (steps  328 ,  330 ). Services are then resumed via the I-WLAN (step  332 ).  
         [0029]     The process  300  is applicable to a handoff between any types of RANs. For example, the process  300  may be applied to a handoff from a UTRAN to an I-WLAN. In such case, the UTRAN sends a list of available RANs in the coverage area of the UTRAN and the WTRU triggers a handoff from the UTRAN to the I-WLAN using the list based on measurement results of signals from the UTRAN and/or the I-WLAN.  
         [0030]      FIG. 4  is a signaling diagram of a process  400  of a WTRU-initiated handoff from an E-UTRAN  160  to an I-WLAN  170  without broadcasting based on a power level in accordance with the present invention. The WTRU  150  includes an E-UTRAN radio unit  152 , a WLAN radio unit  154  and a handoff controller  156 . Currently, the WTRU  150  is attached to the E-UTRAN  160  and the WLAN radio unit  154  is powered on (steps  402 ,  404 ). The E-UTRAN radio unit  152  initializes the WLAN radio unit  154  for potential handoff to the I-WLAN  170  (step  406 ). Since the WTRU  150  is not aware of the available RANs in the coverage area of the E-UTRAN  160 , the WLAN radio unit  154  monitors WLAN channels to find any available WLAN services (step  408 ). If the WLAN radio unit  154  finds any WLAN channel, the WLAN radio unit  154  locks onto the WLAN channel and measures a power level of signals via the channel (step  410 ). If the measured power level satisfies a predetermined threshold, the handoff controller  156  triggers a handoff procedure and the WTRU  150  sends a message to the I-WLAN  170  to initiate WLAN services (step  412 ).  
         [0031]     When the I-WLAN  170  receives the message, the I-WLAN  170  initiates an authentication procedure and may allocate a new IP address depending on the interworking case (step  414 ). Authentication messages are exchanged between the I-WLAN  170  and the E-UTRAN  160  (step  416 ). Once the WTRU  150  is authenticated, the I-WTRU  170  sends an access grant message to the WTRU  150  (step  418 ). The WLAN radio unit  154  then sends a handoff initiate message to the E-UTRAN radio unit  152  (step  420 ). The E-UTRAN radio unit  154  then sends a message to the E-UTRAN  160  to initiate the handoff to the I-WLAN  170  (step  422 ). Control messages for routing of data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  424 ). Once a new route is established, the E-UTRAN  160  sends a handoff complete message to the E-UTRAN radio unit  152 , which forwards it to the WLAN radio unit  154  (steps  426 ,  428 ). Services are then resumed via the I-WLAN  170  (step  430 ).  
         [0032]     The process  400  is applicable to a handoff between any types of RANs. For example, the process  400  may be applied to a handoff from a UTRAN to an I-WLAN. In such case, the WTRU monitors I-WLAN channels and triggers a handoff from the UTRAN to the I-WLAN based on measurement results of signals from the UTRAN and/or the I-WLAN.  
         [0033]      FIG. 5  is a signaling diagram of a process  500  of a WTRU-initiated handoff from an I-WLAN  170  to an E-UTRAN  160  in accordance with the present invention. The WTRU  150  includes an E-UTRAN radio unit  152 , a WLAN radio unit  154  and a handoff controller  156 . The WTRU  150  is currently connected to the I-WLAN  170  and listening to an I-WLAN channel (step  502 ).  
         [0034]     The I-WLAN  170  sends, (i.e., broadcasts, multicasts or unicasts), a list of E-UTRAN and other services available within the coverage area of the I-WLAN  170  (step  504 ). The WTRU  150  receives the E-UTRAN list and stores it (step  506 ). The WTRU  150  may send a request for additional information of the E-UTRAN (step  508 ). The I-WLAN  170  then retrieves the requested information and sends it to the WTRU  150  (steps  510 ). The additional information includes, but is not limited to, locations of the E-UTRAN, frequencies supported by the E-UTRAN and data rates.  
         [0035]     A handoff to the E-UTRAN  160  is initiated either by the user or automatically by the handoff controller  156  based on predetermined criteria, such as signal quality (step  512 ). If a handoff is initiated, the WLAN radio unit  154  sends a radio initialization signal to the E-UTRAN radio unit  152  (step  514 ). The E-UTRAN radio unit  152  then initiates an E-UTRAN service initialization procedure, which includes attachment, registration, context activation, or the like (step  516 ). The E-UTRAN  160  then sends a message to the WTRU  150  to grant access to the E-UTRAN  160  (step  518 ). The WLAN radio unit  154  then sends a message to the I-WLAN  170  to initiate a handoff to the E-UTRAN  160  (step  520 ). Control messages for routing of data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  522 ). Once a new route is established, the I-WLAN  170  sends a handoff complete message to the WTRU  150  (step  524 ). The WLAN radio unit  154  forwards the handoff complete message to the E-UTRAN radio unit  152 , which responds with an acknowledgement (ACK) (steps  526 ,  528 ). The WLAN radio unit  154  is then turned off (step  530 ) and services are resumed via the E-UTRAN  160  (step  532 ).  
         [0036]     The process  500  is applicable to a handoff between any types of RANs. For example, the process  500  may be applied to a handoff from an I-WLAN to a UTRAN. In such case, the I-WLAN sends a list of available RANs in the coverage area of the I-WLAN and the WTRU triggers a handoff from the I-WLAN to the UTRAN using the broadcast list.  
         [0037]      FIG. 6  is a signaling diagram of a process  600  of a WTRU-initiated handoff from an I-WLAN  170  to an E-UTRAN  160  without broadcasting in accordance with the present invention. The WTRU  150  includes an E-UTRAN radio unit  152 , a WLAN radio unit  154  and a handoff controller  156 . The WTRU  150  is currently connected to the I-WLAN  170 . A handoff to the E-UTRAN  160  is initiated either by the user or automatically by the handoff controller  156  based on predetermined criteria, such as signal quality (step  602 ). The WLAN radio unit  154  sends a signal to the E-UTRAN radio unit  152  to initialize the E-UTRAN radio unit  152  (step  604 ). Since the WTRU  150  is not aware of the available E-UTRAN, the E-UTRAN radio unit  152  searches a channel of the E-UTRAN  160  and locks onto the E-UTRAN channel once it is found (step  606 ).  
         [0038]     The E-UTRAN radio unit  152  then initiates an E-UTRAN service initialization procedure, which includes attachment, registration, context activation, or the like (step  608 ). If the E-UTRAN  160  determines to grant service to the user, the E-UTRAN  160  sends a message to the WTRU  150  to grant access to the E-UTRAN  160  (step  610 ). The WLAN radio unit  154  then sends a message to the I-WLAN  170  to initiate a handoff to the E-UTRAN  160  (step  612 ). Control messages for routing of data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  614 ). Once a new route is established, the I-WLAN  170  sends a handoff complete message to the WTRU  150  (step  616 ). The WLAN radio unit  154  forwards the handoff complete message to the E-UTRAN radio unit  152 , which responds with an ACK (steps  618 ,  620 ). The WLAN radio unit  154  is then turned off (step  622 ) and services are resumed via the E-UTRAN  160  (step  614 ).  
         [0039]     The process  600  is applicable to a handoff between any types of RANs. For example, the process  200  may be applied to a handoff from an I-WLAN to a UTRAN.  
         [0040]      FIG. 7  is a signaling diagram of a process  700  of an E-UTRAN-initiated handoff from an I-WLAN  170  to an E-UTRAN  160  based on a power level in accordance with the present invention. The WTRU  150  includes an E-UTRAN radio unit  152  and a WLAN radio unit  154 . The WTRU  150  is currently attached to the E-UTRAN  160  and listening to an E-UTRAN channel, (such as a BCCH) (step  702 ). The E-UTRAN  160  sends, (i.e., broadcasts, multicasts or unicasts), a list of RANs, (e.g., I-WANs, a UTRAN, a GERAN or a GAN), available within the coverage area of the E-UTRAN  160  (step  704 ). The WTRU  150  receives the list and stores it (step  706 ). The WTRU  150  sends a request for additional information, such as the location of service areas of the RANs (step  708 ). The E-UTRAN  160  then retrieves the requested information and sends it to the WTRU  150  (steps  710 ). The information may include information about the service area locations, radio technologies used by the RANs, supported frequencies and data rates, or the like.  
         [0041]     The E-UTRAN radio unit  152  then forwards the I-WLAN information to the WLAN radio unit  154  including a frequency list to help the WLAN radio unit searching the available WLANs and initializes the WLAN radio unit (steps  712 ,  714 ). The WLAN radio unit  154  monitors the WLAN channels based on the frequency list and measures a power level of signals from the I-WLAN  170  (step  716 ). The WLAN radio unit  154  then sends the measurement report to the E-UTRAN radio unit  152  (step  718 ) and the E-UTRAN radio unit  152  forwards the measurement report to the E-UTRAN  160  (step  720 ).  
         [0042]     The E-UTRAN  160  selects a target I-WLAN based on the measurement report and initiates a handoff process (step  722 ). The E-UTRAN  160  sends a handoff trigger message including information about the target I-WLAN to the WTRU  150  (step  724 ). The E-UTRAN radio unit  152  forwards the information to the WLAN radio unit  154  (step  726 ). The WLAN radio unit  154  then searches a channel of the target WLAN based on the information and locks onto the target WLAN (step  728 ). The WLAN radio unit  154  sends a message to the I-WLAN  170  to initiate WLAN services (step  730 ).  
         [0043]     When the I-WLAN  170  receives the message, the I-WLAN  170  initiates an authentication procedure and may allocate a new IP address depending on the interworking case. Authentication messages are exchanged between the I-WLAN  170  and the E-UTRAN  160  (step  732 ). Once the WTRU is authenticated, the I-WLAN  170  sends an access grant message to the WTRU  150  (step  734 ). The WLAN radio unit  154  then sends a handoff complete message to the E-UTRAN radio unit  152  (step  736 ). The E-UTRAN radio unit  152  then forwards the handoff complete message to the E-UTRAN  160  (step  738 ). Control messages for routing of data via the I-WLAN  170  are exchanged between the E-UTRAN  160  and the I-WLAN  170  (step  740 ). Once a new route is established, the E-UTRAN  160  then sends an ACK to the E-UTRAN radio unit  152  (step  742 ) and the E-UTRAN radio unit  152  forwards the ACK to the WLAN radio unit  154  (step  744 ). Services are then resumed via the I-WLAN  170  (step  746 ).  
         [0044]     The process  700  is applicable to a handoff between any types of RANs. For example, the process  700  may be applied to a handoff from a UTRAN to an I-WLAN. In such case, the UTRAN sends a list of available RANs in the coverage area of the UTRAN and the WTRU reports measurement results to the UTRAN and the UTRAN triggers a handoff from the UTRAN to the I-WLAN based on the measurement results.  
         [0045]     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.