Patent Publication Number: US-2004052232-A1

Title: Method and apparatus for detecting the presence of a wireless local area network using a position location system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This patent application is related to simultaneously filed U.S. patent application Ser. Nos. ______ (Attorney Docket No. PU020076), and ______ (Attorney Docket No. PU020078), which patent applications are incorporated herein by reference in their respective entireties. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention generally relates to communication systems and, more particularly, to a method and apparatus for detecting the presence of a wireless local area network.  
       [0004] 2. Description of the Related Art  
       [0005] Presently, 2.5 generation (2.5G) and third generation (3G) cellular networks can provide wireless data service, such as wireless Internet service, having data rates up to 2 Mbps. On the other hand, wireless local area networks (WLANs), such as IEEE 802.11a, IEEE 802.11b, and HiperLAN/2 wireless networks, for example, can provide data service with rates higher than 10 Mbps. WLAN service is also typically cheaper to implement than cellular service due to the use of unlicensed frequency bands by WLANs. As such, it is desirable to switch from cellular service to WLAN service when a mobile device is within the service area of a WLAN. Switching between cellular service and WLAN service can provide for optimal utilization of the available spectrum, and can reduce the burden on cellular networks during times of peak activity.  
       [0006] Mobile devices typically have limited power resources. Continuously checking for the presence of a WLAN by powering up a complete WLAN subsystem can result in considerable power drain. Thus, there is a need to minimize power used by mobile devices capable of communicating with multiple types of wireless networks, such as cellular and WLAN networks.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention is a method and apparatus for detecting the presence of a wireless local area network (WLAN). Specifically, the present invention determines a position of a mobile device using a position location system. The present invention also receives a position of a WLAN from a location database. The present invention then determines whether the mobile device is within a service area of the WLAN in response to the position of the mobile device and the position of the WLAN. In one embodiment, the mobile device activates WLAN circuitry when the mobile device is within the service area of the WLAN. The mobile device then transfers communications from the wireless communication system to the WLAN. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
     [0009] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
     [0010]FIG. 1 depicts a communication system in accordance with the present invention;  
     [0011]FIG. 2 depicts a high-level block diagram showing one embodiment of a mobile device in accordance with the present invention;  
     [0012]FIG. 3 depicts a flow diagram showing one embodiment of a method for detecting the presence of a WLAN; and  
     [0013]FIG. 4 depicts a flow diagram showing one embodiment of a method for detecting the absence of a WLAN.  
    
    
     DETAILED DESCRIPTION  
     [0014] The present invention is a method and apparatus for detecting the presence of a wireless local area network (WLAN). The present invention will be described within the context of transferring communications in a mobile device from a cellular telephone network to a WLAN when the mobile device is located within the service area of the WLAN. Those skilled in the art, however, will appreciate that the present invention can be advantageously employed in any communication device that is capable of communicating with a WLAN. Thus, the present invention has broad applicability beyond the communication systems described herein.  
     [0015]FIG. 1 depicts a communication system  100  in accordance with the present invention. The communication system  100  comprises a wireless communication network  102 , a plurality of WLAN access points  104  (e.g., WLAN access points  104   1  and  104   2 ), a WLAN location database  112 , a position location system  114 , and a plurality of mobile devices  110  (e.g., mobile devices  110   1  and  110   2 ). The wireless communication network  102  provides service to mobile devices  110  located within a service area  106  (e.g., mobile devices  110   1  and  110   2 ). For example, the wireless communication network  102  can comprise a cellular telephone network providing voice and/or data services to mobile devices  110  within the service area  106 .  
     [0016] The WLAN access points  104   1  and  104   2  provide service to mobile devices  110  located within service areas  108   1  and  108   2 , respectively (e.g., mobile device  110   2  located within service area  108   1 ). For example, the WLAN access points  104  can comprise IEEE 802.11b WLAN access points providing voice and/or data services to mobile devices  110  within the service areas  108 . The location of each of the WLAN access points  104  is stored within the WLAN location database  112 . For example, the WLAN location database  112  can store the coordinates (e.g., longitude and latitude) for each of the WLAN access points  104  along with the extent of the service areas  108 . The communication system  100  is illustratively shown having non-overlapping service areas  108  corresponding to the WLAN access points  104  that are located with the service area  106 . Other arrangements can be used with the present invention, such as overlapping service areas  108 .  
     [0017] The position location system  114  illustratively comprises a satellite positioning system, such as the Global Positioning System (GPS) or the Global Navigation Satellite System (GLONASS). For example, the position location system  114  can comprise an assisted GPS system (AGPS), where the wireless communication system  102  aids in computing position. Such AGPS systems are well known in the art. Although the present invention is described herein as being used with a satellite positioning system, those skilled in the art will appreciate that other position location systems can be used, such as the Long Range Aid to Navigation (LORAN) positioning system.  
     [0018] In accordance with the present invention, each of the mobile devices  110  is capable of detecting the presence of a WLAN. As described below, the present invention can determine the position of each of the mobile devices  110  using the position location system  114 . Based on the current position of a given mobile device  110   i  and positions of the WLAN access points  104  stored in the WLAN location database  112 , the mobile device  110   i  can determine the presence of a WLAN. As such, the present invention enables each of the mobile devices  110  to communicate with one or more of the WLAN access points  104 , rather than the wireless communication network  102 , when the mobile device  110  is located within the service areas  108 . For example, mobile device  110   2 , which is located within service area  108   1 , is capable of communicating with WLAN access point  104   1  and wireless communication system  102 . Thus, mobile device  110   2  can transfer communications between WLAN access point  104   1  and wireless communication system  102  as desired. Mobile device  110   1 , however, will continue to communicate with the wireless communication system  102  until the mobile device  1101  moves within one or more of the service areas  108  of the WLAN access points  104 .  
     [0019] The decision to switch between the wireless communication system  102  and the WLAN can be made at the mobile device  110  or by the intelligence in the wireless communication system  102 . For the wireless communication system  102  to make the decision, the wireless communication system  102  requires precise knowledge of the location of the mobile device  110  and the location of the WLAN access points  104 . The location of the mobile device  110  can be obtained precisely, for example, by using a Global Positioning System (GPS) receiver in the mobile device  110 , and sending the coordinates to the wireless communication system  102  as described in more detail below. Alternatively, the decision to switch can be made by the mobile device  110 , for example, by scanning for the presence of a WLAN. Such systems are described in commonly assigned patent application Ser. Nos. ______ (Attorney Docket No. PU020076) and ______ (Attorney Docket No. ______ PU020078), which are incorporated by reference in their respective entireties.  
     [0020]FIG. 2 depicts a high-level block diagram showing one embodiment of a mobile device  110  in accordance with the present invention. The mobile device  110  comprises a wireless transceiver  206  coupled to an antenna  202 , a position location receiver  208  coupled to an antenna  204 , a controller  210 , wireless baseband circuitry  212 , and WLAN baseband circuitry  214 . Wireless baseband circuitry  212  processes signals associated with a wireless communication system, such as cellular telephone signals. WLAN baseband circuitry  214  processes signals associated with a WLAN, such as IEEE 802.11b WLAN signals. Wireless transceiver  206  transmits and receives radio frequency (RF) signals that are processed by the wireless baseband circuitry  212  or the WLAN baseband circuitry  214  through the controller  210 . The position location receiver  208  receives signals from a position location system, such as GPS signals. For example, the mobile device  110  can comprise a cellular telephone having a GPS receiver (e.g., a cellular telephone capable of enhanced  911  services) and a WLAN plug-in card (e.g., a personal computer memory card internal association (PCMCIA) plug-in card). In another example, the mobile device  110  can comprise a personal digital assistant (PDA) or a laptop computer with a WLAN and GPS plug-in cards.  
     [0021] The controller  210  can comprise a processor coupled between the wireless baseband circuitry  212 , the WLAN baseband circuitry  214 , the wireless transceiver  206 , and the position location receiver  208 . In this embodiment, the controller  210  is programmed to perform various control functions in accordance with the present invention. Those skilled in the art will appreciate, however, that the invention can be implemented in hardware, for example, as an application specific integrated circuit (ASIC). As such, the process steps described herein are intended to be broadly interpreted as being equivalently performed by software, hardware, or a combination thereof. Furthermore, although the controller  210  is depicted as a separate functional block, those skilled in the art will appreciate that the wireless baseband circuitry  212  and/or the WLAN baseband circuitry  214  can be adapted to perform the functions of the controller  210 .  
     [0022]FIG. 3 depicts a flow diagram showing one embodiment of a method  300  for detecting the presence of a WLAN. The method  300  can be best understood with simultaneous reference to FIGS. 1 and 2. The method  300  begins at step  302 , and proceeds to step  304 , where the position of a mobile device (e.g., mobile device  110   2 ) is determined using the position location system  114 . The mobile device  110  can calculate position solely from GPS signals transmitted by the position location system  114 , or with the addition of aiding information from the wireless communication system  102  (e.g., the position location system  114  comprises an AGPS system). At step  306 , the mobile device  110  transmits the calculated position to the wireless communication system  102 . The mobile device  110  can transmit position only during a data communication between the mobile device  110  and the wireless communication system  102 . Alternatively, the mobile device  110  can initiate a communication with the wireless communication system  102  to transmit position thereto.  
     [0023] At step  308 , the position of the mobile device  110  is compared to positions of services areas  108  corresponding to WLAN access points  104 . As described above, the coordinates of WLAN access points  104  are stored within the WLAN location database  112 . At step  310 , the wireless communication system  102  determines whether the mobile device  110  is within one or more of the service areas  108 . If the mobile device  110  is within one or more of the service areas  108 , the method  300  proceeds to step  312 . Otherwise, the method proceeds to step  315 .  
     [0024] At step  315 , the mobile device determines whether to calculate position again. If the mobile device  110  is to calculate position again, the method  400  returns to step  304 . The mobile device  110  can calculate position periodically, in response to a specific request from a user, or in response to a data communication between the mobile device and wireless communication system  102 . If the mobile device  100  is not to calculate position again, the method  400  proceeds to end step  318 .  
     [0025] At step  312 , the wireless communication system  102  transmits an indication of the presence of a WLAN to the mobile device  110 . In the present example, the wireless communication system  102  would send an indication to the mobile device  110   2  that the mobile device  110   2  is within the service area  108   1  of the WLAN access point  104   1 . Again, the wireless communication system  102  can either send the indication during a data communication between the mobile device  110  and the wireless communication system  102 , or can send the indication by initiating a data communication with the mobile device  110 . At step  313 , the mobile device  110  determines whether to connect to the WLAN. If the mobile device  110  is to connect to the WLAN, the method  300  proceeds to step  314 . If the mobile device  110  determines not to connect to the WLAN, the method  300  proceeds to step  304 . For example, the mobile device  110  may determine not to connect to the WLAN if the signal quality received from the WLAN is below a predetermined threshold.  
     [0026] At step  314 , the mobile device  110  activates the WLAN baseband circuitry  214  to connect with the WLAN. At step  316 , the mobile device  110  transfers communications therein to the WLAN if connection to the WLAN is possible. Hitherto, the mobile device  110  has been communicating with the wireless communication system  102 . The method  300  ends at step  318 .  
     [0027]FIG. 4 depicts a flow diagram showing one embodiment of a method  400  for detecting the absence of a WLAN. Again, the method  400  can best be understood with simultaneous reference to FIGS. 1 and 2. In the present example, it is assumed that one of the mobile devices  110  (e.g., mobile device  110   1 ) has been communicating with a WLAN. The method  400  begins at step  402 , and proceeds to steps  404  and  406 . At step  404 , the position of the mobile device  110  is determined using the position location system  114 . At step  408 , the position of the mobile device  110  is compared to the service area of the WLAN. If the position is within one or more of the service areas  108  corresponding to the WLAN access points  104 , the method  400  proceeds to step  409 . If the position is outside of the service areas  108 , the method  400  proceeds to steps  412  and  414 .  
     [0028] At step  409 , a number of methods can be initialized to determine when to again check the position of the mobile device. A delay can be initialized, after which a position check can be repeated, the user could prompt a position check, or, based on increasing error rate, a position check could be prompted by the WLAN signal quality measurements, indicated by dashed path  420 . Any of these methods can be used to trigger the reexamination of the mobile device&#39;s position.  
     [0029] At step  415 , the mobile device  110  determines whether to calculate position again. If the mobile device  110  is to check position again, the method returns to step  404 . The mobile device  110  can calculate position periodically, in response to a specific request from a user, in response to a data communication between the mobile device  110  and the WLAN, or in response to increasing error rates. While the mobile device  110  is waiting to check position again, the mobile device  110  checks whether the WLAN link is still active at step  418 . For example, the WLAN link could have been deactivated in response to a parallel process started at step  406 . If the WLAN is still active, the method  400  proceeds to step  404 . Otherwise, the method  400  proceeds to end step  416 .  
     [0030] At step  406 , the mobile device  110  determines the quality of the signal received by the WLAN. As the mobile device  110  moves away from one of the WLAN access points  104 , the quality of the signal will be decreasing. At step  410 , the mobile device  110  determines whether the quality of signal is below a predetermined threshold. If the quality of signal is above the predetermined threshold, (i.e., adequate quality of signal), the method  400  continues to monitor signal quality. If the quality of signal is below the predetermined threshold, the method  400  proceeds to parallel steps  412  and  414 . If the quality of signal is marginal, a signal  420  can be sent to trigger a check of position. The test for signal quality  406  can have some hysteresis—it should take several packet failures before determining that the signal quality is below threshold.  
     [0031] At step  412 , the mobile device  110  deactivates the WLAN baseband circuitry  214 . At step  414 , the mobile device  110  transfers communications therein to the wireless communication system  102 . In the present example, the mobile device  110   1  would determine position to be outside of the service areas  108 , or would sense a decrease in quality of signal from one or more of the WLAN bases stations  104 . Hitherto, the mobile device  110   1  has been communicating with the WLAN. Thus, the mobile device  110   1  would transfer communications therein to the wireless communication network  102 . The method ends at step  416 .  
     [0032] While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.