Abstract:
A media independent handover (MIH) device communicates with an 802 technology medium access control (MAC) layer and an 802 technology physical (PHY) layer utilizing an 802 technology management entity (ME) device. Handover information messages are produced by the MIH device. The handover information messages facilitate handover. The 802 technology ME device facilitates encapsulation of the handover information messages. The 802 technology ME device is coupled to the 802 technology MAC layer and the 802 technology PHY layer. The encapsulated handover information messages is sent to other MIH devices messages via the 802 technology ME device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 11/091,159 filed on Mar. 28, 2005 which claims the benefit of U.S. Provisional Application No. 60/569,015, filed May 7, 2004, which is incorporated by reference as if fully set forth herein. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention generally relates to wireless communication systems, and more particularly, to a method and system for implementing a media independent handover between different wireless network types.  
       BACKGROUND  
       [0003]     Typical mobile systems have two main operating modes: Idle mode and Connected mode. In Idle mode, the station (STA) characteristics include: no user service (i.e., no call or transaction in progress); monitoring of paging channels; available service request channels; 100% of the receiver is available for downlink measurements of the radio environment; background coordination; and unscheduled access point (AP) and/or technology reselection. In Connected mode, the STA characteristics include: an active user service (e.g., a call is in progress); handover is possible; limited receiver availability for measurements (since the user service takes priority); and fully coordinated, scheduled AP and/or technology handover.  
         [0004]     Prior to entering Idle mode (e.g., at power-up), the STA must perform selection in order to determine the best AP and technology available for the requested user service. While in the Idle mode, the STA continuously examines neighboring APs and APs with different technologies. Upon determination of a “better” AP, the STA will transition over (i.e., perform “reselection”) to the new AP.  
         [0005]     While in the Connected mode, a handover occurs upon transition from one AP to another AP offering “better” service, including switching to an AP using a different technology. In an ideal case, handover occurs without noticeable interruption of the active user service.  
         [0006]     One goal is to achieve a seamless handover (i.e., to permit mobility of a STA) between different wireless network types, such as between different wireless local area network (WLAN) types or between a WLAN and a cellular system. Current technology does not provide for this type of handover.  
         [0007]      FIG. 1  is a diagram of an existing cellular mobility model  100 , showing a centralized radio resource management (RRM) approach to the mobility issue. A cellular STA  102  (e.g., a 2G mobile station or a 3G user equipment) is freely mobile among a plurality of APs  104 . The APs  104  can include, but are not limited to, GSM base stations and FDD/CDMA Node Bs. The APs  104  are connected together via a radio network  106 . A handover policy function (HPF)  108  is used to direct the handover of the STA  102  among the APs  104  as the STA  102  moves about. The HPF  108  is centrally located (e.g., in a 2G base station controller (BSC) or a 3G radio network controller (RNC)) and is connected to a network  110  (e.g., a switch or a server).  
         [0008]     The HPF  108  provides coordination as the STA  102  moves about the different APs  104 . The STA  102  sends measurements to the HPF  108 , and the HPF  108  makes the final decision regarding handover and which AP  104  the STA  102  should be on.  
         [0009]     In the model  100 , semi-static frequency assignments are made to each AP  104  and some radio planning is required. In Idle mode, both intra-technology (e.g., GSM to GSM) and inter-technology (e.g., GSM to FDDIWCDMA) AP selection/reselection decisions are made in the STA  102  and are supported by system information (from the network  110 ) broadcast by the HPF  108 . In Connected mode, AP handover decisions are made in the HPF  108  and are supported by measurements made by the STA  102  that are sent to the HPF  108  via L3 signaling.  
         [0010]      FIG. 2  is a diagram of an existing WLAN mobility model  200 , showing a distributed RRM approach to the mobility issue. An 802.x STA  202  is freely mobile among a plurality of APs  204 , which can include, but are not limited to 802.11a and 802.16 APs. The APs  204  communicate via a radio network  206  and to a network  208  (e.g., a gateway or router).  
         [0011]     In the model  200 , dynamic frequency assignments are made to each AP  204  and radio planning is not required. The only type of handover supported in the mobility model  200  is an intra-technology (e.g., 802.11a to 802.11a) Idle mode handover, where the AP selection/reselection decision is made autonomously in the STA  202 . The other handover types (Idle mode with inter-technology and Connected mode) are not supported in the mobility model  200 .  
         [0012]     In this distributed RRM approach, the APs  204  can be deployed anywhere and they dynamically manage themselves. There is no centralized point through which RRM is performed, and therefore, no element in the architecture to execute a handover.  
         [0013]      FIG. 3  is a diagram of existing mobile system architectures for cellular and WLAN network types. A GPRS (2G) STA  300  includes a physical layer  302 , a data link layer  304 , and a network layer  306 . The data link layer  304  includes a medium access control (MAC) sublayer  310  and a radio link control (RLC) sublayer  312 . The network layer  306  includes a GSM radio resource (RR) manager  314 , a mobility management (MM) protocol manager  316 , and an Internet Protocol (IP)/convergence manager  318 .  
         [0014]     A 3GPP (3G) STA  320  includes a physical layer  322 , a data link layer  324 , and a network layer  326 . The data link layer  324  includes a MAC sublayer  330  and a RLC sublayer  332 . The network layer  326  includes a 3G RR controller  334 , a MM protocol manager  336 , and an IP/convergence manager  338 .  
         [0015]     An 802.xx STA  340  includes a physical layer  342 , a data link layer  344 , and a network layer  346 . The data link layer  344  includes a MAC sublayer  350  and a logical link (LLC) sublayer  352 . The network layer  346  includes a mobile IP manager  354  and an IP/convergence manager  356 .  
         [0016]     The RR manager/controller ( 314 ,  334 ) manages the instantaneous radio link, handling all of the information regarding a radio link. The MM protocol ( 316 ,  336 ,  354 ) handles network level issues, such as registration and location updating as the STA moves about the system (i.e., issues outside of the call itself).  
         [0017]     Current WLAN systems offer only a limited mobility capability. Intra-technology (e.g., 802.11 to 802.11) and inter-technology (e.g., 802.11 to 802.16) user transitions are supported using a “break before make” strategy that can be characterized as a reselection operation, as opposed to a handover operation in a typical full mobility system (e.g., GSM). This problem limits the growth of WLAN technologies, as this approach is unsatisfactory for supporting real time services such as voice and video streaming.  
       SUMMARY  
       [0018]     A media independent handover (MIH) device communicates with an 802 technology medium access control (MAC) layer and an 802 technology physical (PHY) layer utilizing an 802 technology management entity (ME) device. Handover information messages are produced by the MIH device. The handover information messages facilitate handover. The 802 technology ME device facilitates encapsulation of the handover information messages. The 802 technology ME device is coupled to the 802 technology MAC layer and the 802 technology PHY layer. The encapsulated handover information messages is sent to other MIH devices messages via the 802 technology ME device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     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:  
         [0020]      FIG. 1  is a diagram of an existing cellular mobility model;  
         [0021]      FIG. 2  is a diagram of an existing WLAN mobility model;  
         [0022]      FIG. 3  is a diagram of existing mobile system architectures for cellular and WLAN network types;  
         [0023]      FIG. 4  is a diagram of a mobility architecture in a WLAN in accordance with the present invention and how it compares to cellular network types;  
         [0024]      FIG. 5  is a diagram of a WLAN mobility model in accordance with the present invention;  
         [0025]      FIG. 6  is a diagram showing construction of a STA architecture to implement a distributed handover policy function of the present invention; and  
         [0026]      FIG. 7  is a diagram showing construction of a STA architecture to implement a centralized handover policy function of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Hereafter, the term “station” (STA) includes, but is not limited to, a wireless transmit/receive unit, a user equipment, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the term “access point” (AP) includes, but is not limited to, a base station, a Node B, a site controller, or any other type of interfacing device in a wireless environment.  
         [0028]      FIG. 4  is a diagram of a mobility architecture in a WLAN and how it compares to cellular network types. The GPRS STA  300  and the 3GPP STA  320  are identical to the STAs described above in connection with  FIG. 3 . An 802.xx STA  400  includes a physical layer  402 , a data link layer  404 , and a network layer  406 . The data link layer  404  includes a MAC sublayer  410  and a LLC sublayer  412 . The network layer  406  includes a media independent handover layer  414 , a mobile IP manager  416 , and an IP/convergence manager  418 . The remainder of the discussion focuses on the media independent handover (MIH) layer  414  and how it operates within a mobility model. The MIH layer  414  performs functions similar to the GSM RR  314  and the 3G RRC  334 .  
         [0029]      FIG. 5  is a diagram of a WLAN mobility model  500  in accordance with the present invention, showing two basic HPF options, distributed and centralized. These options relate to the situations not previously addressed by mobility models, i.e., Idle mode with inter-technology handover and Connected mode handover.  
         [0030]     An 802.x STA  502  is freely mobile among a plurality of APs  504 , which can include, but are not limited to 802.11a and 802.16 APs. The APs  504  communicate via a radio network  506  and to a network  508  (e.g., a gateway or router).  
         [0031]     The model  500  can implement a distributed HPF  510  at the STA  502  and/or a centralized HPF  520  at the network  508 .  
         [0032]     In a distributed HPF setting, the STA makes the selection, reselection, and handover decisions autonomously. This includes Idle mode, inter-technology selection/reselection and both Connected mode handover types.  
         [0033]     In a centralized HPF setting, the HPF located on the system side assists in the selection and reselection processes, and makes the handover decisions supported by information gathered by the STA. The information is communicated from the STA to the HPF via the signaling mechanisms of the present invention (i.e., the MIH layer). This includes Idle mode, inter-technology selection/reselection and both Connected mode handover types.  
         [0034]      FIG. 6  is a block diagram of a functional architecture for a STA  600  utilizing the distributed HPF of the present invention. The STA  600  includes a physical sublayer management entity (ME)  602  and a MAC sublayer ME  604 . A HPF  606  communicates with both the physical sublayer ME  602  and the MAC sublayer ME  604 . A local management information base  608  stores information accessed by the HPF  606  in making the handover decision. The physical sublayer ME  602  includes a physical layer convergence procedure (PLCP) sublayer  610  and a physical medium dependant (PMD) sublayer  612 . The MAC sublayer ME  604  includes a MAC sublayer  614 .  
         [0035]     Reselection and handover decisions are made autonomously by the STA  600 . The HPF  606  receives measurements and other events (information typically used in making a handover decision) from the MAC sublayer ME  604  and the physical sublayer ME  602 . The HPF  606  processes this information and makes an autonomous decision whether to perform a handover.  
         [0036]     This is a limited handover solution, and is really just an extension of the reselection procedure and would be characterized as such in a typical mobile system. This is an adequate, but sub-optimal solution, mainly due to the use of a “break then make” strategy. With this strategy, when a STA knows that its radio link is deteriorating, it breaks the current link or the link independently fails before the new link is established. The resource availability to complete the handover is not guaranteed, and could lead to dropped calls of the new AP lacks the resources to accommodate the handover. The possibility of dropped calls is an adequate solution for non-real time services, but is an unacceptable solution for real time services such as voice communications. Furthermore, this is a poorly scalable solution, for the same reasons; i.e., as more STAs are added to the system, the performance will deteriorate.  
         [0037]      FIG. 7  is a block diagram of a functional architecture for a STA  700  utilizing the centralized HPF. The STA  700  includes a physical sublayer ME  702  and a MAC sublayer ME  704 . A media independent handover (MIH) layer  706  communicates with both the physical sublayer ME  702  and the MAC sublayer ME  704 . The MIH layer  706  communicates with a MIH layer  708  on the system side. The MIH layer  708  communicates with a system HPF  708 . The physical sublayer ME  702  includes a PLCP sublayer  712  and a PMD sublayer  714 . The MAC sublayer ME  704  includes a MAC sublayer  716 .  
         [0038]     The MIH layer  706  and the system HPF  710  communicate via the MIH layer  708 . The MIH layer  706  sends measurements to the HPF  710  and the HPF  710  sends system information to the MIH layer  706 . The reselection and handover decisions are coordinated between the MIH layer  706  and the HPF  710  based on this exchange of information. This use of both the MIH layer  706 , the MIH layer  708 , and the HPF  710  is analogous to a cellular system type of handover.  
         [0039]     Reselection and handover decisions are coordinated by the HPF  710  and are supported by measurement reports and system signaling received via the MIH layers  706 ,  708 . This is a fast, optimal handover solution due to the centralized decision-making which uses a make then break strategy, guaranteeing resource availability to complete the handover. This is an adequate solution for non-real time services, an acceptable solution for real time services, and is easily scalable, providing a full mobility solution.  
         [0040]     In order to support a full mobility solution, both a mobility protocol (e.g., MM, mobile IP, SIP, etc.) and a resource control protocol (e.g., RRC or MIH layer) are required. The mobility protocol supports functions such as discovery, registration, tunneling, termination (or paging), handover at the network level (between two switches), and security. The resource control protocol supports functions such as system information, termination (or paging), cell selection/reselection, establishment, release, measurement reporting, power control, and handover at the radio level (between two radios). Handover support provided at both levels is required to support a full mobility solution.  
         [0041]     On the network side, both the MIH layer  708  and the HPF  710  can be positioned in any centralized entity, such as an AP, a server, a database, or a router. In a preferred embodiment, the MIH layer  708  and the HPF  710  are located in an AP or an AP controller. The MIH layer  708  and the HPF  710  are separate logical entities. The MIH layer  708  acts as a state machine, gathering the necessary information and passing it to the HPF  710 . The HPF  710  makes the handover decision based upon the information received.  
         [0042]     While the present embodiment has been described in terms of a WLAN, the principles of the present embodiment are equally applicable to any type of wireless communication system. The centralized HPF architecture can be extended to support wireless to wired interworking scenarios, such as a handover policy when connecting a wireless device to a wireline system. An example of this would be using an 802.11-enabled laptop and then docking the laptop and using handover to take advantage of an Ethernet connection to the laptop docking station.  
         [0043]     Although the elements shown in  FIGS. 6 and 7  are illustrated as separate elements, these elements may be implemented on a single integrated circuit (IC), such as an application specific integrated circuit (ASIC), multiple ICs, discrete components, or a combination of discrete components and IC(s). In certain implementations, the functionality of embodiments and features of the invention may be present in discrete component(s)/IC(s) and may be partially/totally disabled or deactivated.  
         [0044]     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.