Patent Publication Number: US-2003227873-A1

Title: Method and apparatus for switching between a wireless local area network (WLAN) and a wide area network (WAN) employing operator and user criteria

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
     [0001] This application claims priority from Serial No. 60/385,871 filed on Jun. 5, 2002, which is incorporated by reference as if fully set forth. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates to WLAN-WAN switching. More particularly, the present invention relates to method and apparatus to facilitate such switching taking into account both operator and user criteria and perspective.  
       BACKGROUND  
       [0003] User and service operators have conflicting perspectives as to the optimum utilization of link resources in a communication system. For example, a user, from his perspective, desires to have the cheapest and yet highest quality of service (QoS) available. On the other hand, from the perspective of the service operator there is typically a desire to provide the cheapest or least expensive service and to provide adequate QoS and security to keep most of its subscribers happy. In addition to a conflict of objectives as between the service operator and the user, there are actually conflicts within each of these groups as to their desires. For example, the lowest cost for the user may not be very secure. Likewise “adequate QoS” to support a user application may not be optimum to achieve an overall goal of revenue maximization from the point of view of the service provider.  
       [0004] Present day systems are limited to making fixed triggering assumptions about whether a transfer should be made between systems. Such fixed assumptions as to when to switch and not switch are usually placed on a few specific simulations of expected operational scenarios. While such switching decisions are adequate when the systems are lightly loaded or when the network is operating close to a scenario that has been modeled, such fixed assumptions do not take into account the myriad of other scenarios that will occur in real systems as loading and service applications evolve.  
       [0005] One typical method for selecting a link involves determining exact mathematical relationships between inputs and outputs and their complicated relationships. However, when a parameter falls outside of the boundaries of the equations employed, the system can become very inefficient and in the worst case the network may become unstable due, for example, to excessive switching and very low resource utilization. Adjustments to maintain the stability of the system and strive towards some optimization goals is very complicated and time consuming, necessitating a decision making process that is inherently stable, sensitive to both changing and unforeseen states and is easily modified when necessary.  
       SUMMARY  
       [0006] These attributes are accomplished through the provision of method and apparatus for controlling switching between WLANs and WANs which is implemented in a fuzzy logic design in which input data undergoes a fuzzification process, sorting inputs into membership values with associated linguistic variables. A rules engine operates on the membership values generating output membership data. The output of the rules engine then undergoes “defuzzification” to produce an actionable result. 
     
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
     [0007] The present invention and its objectives and its advantages will be best understood from a consideration of the following figures in which like elements are designated by like numerals, and wherein:  
     [0008]FIG. 1 is a block diagram of a device employing a fuzzy logic design and embodying the principles of the present invention.  
     [0009]FIG. 2 is a plot of showing in relationship the membership function to usable in present network and usable in possible network.  
     [0010]FIG. 3 is a plot of relationship of membership function to cost to user and cost to network.  
     [0011]FIG. 4 is a plot relating membership function to usability need to switch. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS THEREOF  
     [0012]FIG. 1 is a block diagram of a fuzzy logic design system for effecting the decision making process, such as switching between a network “A” and a network “B”.  
     [0013] Input data enters into the fuzzification process at stage  12 . Typical input data, entered at  12   a,  includes but, is not limited to, the following types of information:  
     [0014] Application quality of service (QoS) requirement, for example, latency, fidelity, security.  
     [0015] User service subscription particulars, for example, including: priority, incremental costs.  
     [0016] The state of network A, for example, loading and cost for QoS required.  
     [0017] The state of network B, which may incorporate substantially the same type of criteria as the state of network A.  
     [0018] The cost of switching from the present network, for example, network A, to another network, for example, network B, such cost including, for example, delay in application execution and insufficiencies in channel utilizations during transition.  
     [0019] The input data enters the fuzzification process at stage  12  which sorts the inputs into membership values with associated linguistic variables. The input data may be stored in storage means (not shown) associated with stage  12  to compare current and historic values, for example.  
     [0020]FIG. 2 shows input membership sets which include:  
     [0021] usable in present network  
     [0022] usable in possible network  
     [0023] Regarding the costs to user, FIG. 3 shows the ratio of present to possible cost to networks. Regarding cost to networks, FIG. 3 also shows the ratio of present to possible.  
     [0024] The rules engine  14  operates on the membership values, generating output membership data. FIG. 4 shows the usability need to switch.  
     [0025] The following rules are examples of the rules engine  14 : (typically referred as linguistic rules).  
     [0026] Initialize rules results assume usability need to switch is low.  
     [0027] Rules applied:  
     [0028] If (usable In Present Network is low (FIG. 2) AND usable In Possible Network is adequate or high (also FIG. 2)) THEN usability need to switch is high.  
     [0029] If (usable In Present Network is adequate AND usable In Possible Network is high) THEN usability need to switch is medium.  
     [0030] The output of rules Engine  14  is then passed through the “Defuzzification” process at stage  16  to produce an actionable result, at  16 a.  
     [0031] The following is one example:  
     [0032] Initialize decision  
     [0033] Switch decision IS no (a crisp binary variable of set {yes, no})  
     [0034] Determine if decision should be set to yes  
     [0035] IF (usability Need To Switch IS high) THEN switch decision IS yes; EXIT  
     [0036] IF (usability Need To Switch IS medium)  
     [0037] IF (Cost To User IS Lower OR Cost To Networks IS lower) THEN switch decision IS yes; EXIT  
     [0038] ELSE not a cost benefit to either one EXIT  
     [0039] ELSE usability Need To Switch IS low IF (Cost To User IS lower AND control network is lower) THEN Switch Decision IS yes; EXIT ELSE number not a cost benefit for both; EXIT  
     [0040] The membership sets and rules outlined above are examples of the possibilities. Fuzzy logic facilitates use of additional inputs, rules, and outputs in a straight-forward manner, leading to rapid enhancement of the systems operation as required.  
     [0041] This type of system also lends itself to providing the users and system operators both with the means to determine the most important characteristics of operations to each of them. Even though these goals may be in conflict, the proper set up of the membership functions lead to reasonable and stable operation of the system.