Patent Publication Number: US-7904084-B2

Title: Intelligent access point scanning with self-learning capability

Description:
CLAIM OF BENEFIT TO PRIOR APPLICATIONS 
     This Application is a continuation application of U.S. Patent Application entitled “Intelligent Access Point Scanning with Self-Learning Capability,” filed on Aug. 26, 2005, now issued as U.S. Pat. No. 7,515,575, and having Ser. No. 11/212,353. U.S. patent application Ser. No. 11/212,353 is incorporated herein by reference. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to commonly owned U.S. application Ser. No. 11/013,883, now issued as U.S. Pat. No. 7,640,008, entitled “Apparatus And Method For Extending The Coverage Area Of A Licensed Wireless Communication System Using An Unlicensed Wireless Communication System,” filed Dec. 15, 2004, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to telecommunications and, more particularly, to techniques for accessing unlicensed wireless communication services. 
     BACKGROUND 
     Licensed mobile access (LMA) communication systems provide mobile wireless communications over large areas to individuals using wireless handsets. Licensed wireless systems include cellular telephone systems and/or Personal Communication Services (PCS) telephone systems. Wireless handsets include cellular telephones, PCS telephones, wireless-enabled personal digital assistants, wireless modems, and the like. 
     Licensed mobile access communication systems utilize public wireless signal frequencies that are licensed from a government entity. Licensees pay large fees for access to these frequencies, and make large capital investments in base station and switching equipment which is required to support communications over extended geographical areas. As a result, the cost of licensed wireless communication service is generally higher than voice and data services over wired communication networks such as the public switched telephone network (PSTN) and private cable systems, which do not pay license fees and which have lower and/or fully amortized capital costs. 
     Typically, licensed wireless base stations are installed approximately a mile apart from one another and mobile subscribers are handed off from one base station to another as the subscribers move through the coverage areas (cells) of each base station. The quality of the link between the wireless transceiver and any base station is dependent on factors such as weather conditions, distance between the base station and the subscriber, and multipath interference. In contrast, the quality of wired communication services is not affected by any of the aforementioned factors. As a result, the quality and reliability of service (e.g., voice quality, speed of data transfer and bit-error rate) in licensed wireless systems is generally inferior to the quality of service afforded by wired connections. Furthermore, in many areas, the availability of wired communication services is greater than the availability of licensed wireless communication services. Thus, the user of licensed wireless communication systems pays relatively high fees for limited availability and relatively low quality service. 
     As noted above, wired connections are extensively deployed and generally perform at a lower cost with higher quality voice and higher speed data services. The problem with wired connections is that they constrain the mobility of a user. To bridge the gap, unlicensed mobile access (UMA) technology has been developed to enable dual-mode (LMA and UMA) wireless handsets to access voice and data services provided by core mobile network through unlicensed wireless access points, such as IEEE 802.11 (e.g., Wi-Fi) access points or Bluetooth access points, for example. This technology is designed to seamlessly handover a licensed wireless connection to an unlicensed wireless connection whenever an unlicensed wireless link to a wired network is available. The unlicensed wireless connections operate over limited ranges (e.g., up to 100 meters) and provide high quality and high reliability links to wired Internet Protocol (IP) access networks. 
     UMA technology is described in detail in commonly owned copending U.S. Pat. No. 7,640,008, entitled “Apparatus And Method For Extending The Coverage Area Of A Licensed Wireless Communication System Using An Unlicensed Wireless Communication System,” filed Dec. 15, 2004 and incorporated herein by reference. In addition, a standard specification for UMA technology has been adopted by the European Telecommunications Standards Institute (see, ETSI TS 143 318 v6.0.0 2005-01) with respect to GSM and GPRS communication services. 
     A dual-mode wireless handset is capable of switching automatically and seamlessly between licensed and unlicensed mobile access networks. However, dual-mode operation exacts a cost in battery power, consumed by the unlicensed radio transceiver to support scanning for unlicensed wireless access points (UWAPs) while the handset is operating in cellular voice or data mode. For example, if the unlicensed radio is turned on every 2.5 seconds for access point scanning (a typical default scanning rate), the average current drain might be 2.2 milliamperes (ma) for a typical IEEE 802.11 chipset (e.g., the Broadcom BCM4317 b chipset). The average current drain of the cellular radio in standby mode might be 2.5 ma, so the total power consumption of the dual-mode handset could be approximately twice that of a standalone cellular handset. Decreasing the default scan rate of the unlicensed radio will reduce the power consumption, but decreasing the scan rate too much will introduce delays (latency) in acquiring and accessing unlicensed wireless access points that are unacceptable to mobile subscribers. The UMA standard does not specify any mechanism for power management for the unlicensed radio subsystem in a dual-mode handset. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     In one embodiment, a method for intelligent access point scanning with self-learning capability includes detecting the identifier of a licensed mobile access cell (LMAC), obtaining a probability measure for accessing an unlicensed mobile access network (UMAN) through an unlicensed wireless access point (UWAP) within the licensed mobile access cell, and scanning for the unlicensed wireless access point with a scan rate that is determined by the probability measure. In one embodiment, the method also includes modifying the probability measure to reflect the results of the scan. 
     In one embodiment, an apparatus includes a wireless interface to communicate with a licensed mobile access service and with unlicensed wireless access points. The apparatus also includes a memory to store a table of LMAC identifiers and a processing device coupled with the memory and the wireless interface. The processing device is configured to detect an LMAC identifier, to obtain a probability measure from the table for accessing the UMAN through a UWAP within the LMAC, and to scan for the UWAP with a scan rate that is determined by the probability measure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a dual-mode system in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 2  illustrates a method in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 3  illustrates a dual-mode wireless handset in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 4A  illustrates a data table in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 4B  illustrates a lookup table in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 4C  illustrates scan functions in one embodiment of intelligent access point scanning with self-learning capability. 
         FIG. 5  illustrates another method in one embodiment of intelligent access point scanning with self-learning capability. 
     
    
    
     DETAILED DESCRIPTION 
     Methods and apparatus for intelligent access point scanning with self-learning capability are described. In the following description, numerous specific details are set forth, such as examples of specific commands, named components, connections, data structures, etc., in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art that embodiments of present invention may be practiced without these specific details. In other instances, well known components or methods have not been described in detail but rather in a block diagram in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the spirit and scope of the present invention. 
     Embodiments of the present invention include circuits and components, to be described below, which perform operations. Alternatively, the operations of the present invention may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the operations. Alternatively, the operations maybe performed by a combination of hardware and software. 
     Embodiments of the present invention may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present invention. A machine-readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to: magnetic storage media (e.g., floppy diskette); optical storage media (e.g., CD-ROM); magneto-optical storage media; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; electrical, optical, acoustical or other form of propagated signal; (e.g., carrier waves, infrared signals, digital signals, etc.); or other type of medium suitable for storing electronic instructions. 
     Some portions of the description that follow are presented in terms of algorithms and symbolic representations of operations on data bits that may be stored within a memory and operated on by a processor. These algorithmic descriptions and representations are the means used by those skilled in the art to effectively convey their work. An algorithm is generally conceived to be a self-consistent sequence of acts leading to a desired result. The acts are those requiring manipulation of quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, parameters, or the like. 
     The term “coupled to” as used herein may mean coupled directly to or indirectly to through one or more intervening components. Any of the signals provided over various buses described herein may be time multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit components or blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be one or more single signal lines, and each of the single signal lines may alternatively be buses. 
     In the following description, embodiments of the invention may be described in the context of a GSM/GPRS cellular radio system for clarity and simplicity of explanation. One having skill in the art will appreciate that embodiments of the invention may be practiced in the context of other licensed wireless communication systems and technologies such as, for example, CDMA (code division multiple access), FDMA (frequency division multiple access) and TDMA (time division multiple access) systems using non-GSM protocols. 
       FIG. 1  illustrates a system  100  in which embodiments of the present invention may be practiced. It will be appreciated by those skilled in the art that other system configurations may also be used to practice embodiments of the invention. In  FIG. 1 , a UMA-enabled dual-mode wireless handset (handset)  101  is equipped to communicate over a licensed mobile access network (LMAN)  102  operated by a cellular service provider. When the handset is within range of a licensed mobile access cell (LMAC)  103  of a cellular base transceiver station (BTS)  104 , it accesses the core mobile network  105  of the service provider through a private network  106  and a base station controller (BSC)  107  operated by the service provider, and updates its location with the core mobile network  105 . 
     The handset  101  is also equipped to communicate over an unlicensed mobile access network (UMAN)  108  with unlicensed wireless access points (UWAPs) (e.g., Wi-Fi and Bluetooth access points) such UWAP  109  with access to the core mobile network  105  through a broadband IP network  110 . The UMAN includes a UMA network controller (UNC)  111 , operated by the service provider, which routes voice and data communications to the core mobile network  105 . 
     When the handset  101  is connected to the licensed mobile access network  102 , it scans for unlicensed wireless access points to which the handset is allowed to connect (e.g., unencrypted public or private access points or encrypted access points for which the wireless handset has a pass phrase, such as a WEP pass phrase in an IEEE 802.11 wireless network) in a manner described in detail below. When the handset  101  moves within range of such an unlicensed wireless access point, and detects the access point, the handset negotiates a connection. 
     Upon connecting, the handset registers with the UMA Network Controller  111  over the broadband IP network  110 , to be authenticated and authorized to access voice and data services over the broadband IP network  110  via the unlicensed wireless connection  112 . Upon UMA registration, the handset may optionally decide to update its location with core mobile network  105 , and from that point on all mobile voice and data traffic is routed to the handset  101  via the UMAN  108  rather than the LMAN  102 . 
     In one embodiment, dual-mode wireless handset  101  may be equipped with a transceiver for a licensed wireless communication service (e.g., GSM/GPRS, CDMA, FDMA and the like) that provides licensed mobile access (LMA) to the core mobile network  105  of the licensed wireless communication service through licensed mobile access network (LMAN)  102 . Handset  101  may also be equipped with a transceiver for an unlicensed wireless connection (e.g., IEEE 802.11 and/or Bluetooth) that provides unlicensed mobile access (UMA) to the core mobile network  105  of the licensed wireless communication service via unlicensed wireless access points such as UWAP  109  and wired IP access networks such as IP access network  110 . 
     In LMA mode, when the handset comes within range of a licensed mobile access cell (LMAC), it identifies its current location by an identifier of the LMAC. In one embodiment, each LMAC may be identified by a location area identifier (LAI), which is common to a group of LMACs, and by a cell identifier (CI) within the LAI. Together, the LAI and the CI may make up a global cell identifier (GCI) that uniquely identifies each LMAC. 
     In one embodiment, when the handset is in LMA mode and within range of an LMAC, it detects the identifier of the LMAC and compares the identifier with a table of LMAC identifiers to determine whether the handset has previously been within range of the LMAC and whether the handset has successfully accessed a UWAP within range of the LMAC. If the data in the table contains a record of the LMAC, the handset obtains a parameter from the table that is indicative of the likelihood of successfully accessing a UWAP within the LMAC. 
     As described in greater detail below, the parameter may represent a “credit score” or probability measure for accessing a UWAP within the LMAC, based on prior experience within the LMAC. The parameter may then be used to enter a lookup table that specifies a scan rate that the unlicensed transceiver will use to search for a UWAP. The higher the parameter value, the greater the probability of finding a UWAP within the LMAC that can successfully register the wireless handset with the UMAN. 
     Each time a search for a UWAP within a particular LMAC is successful, and a connection to the UMAN is established, the credit score for that LMAC may be increased, resulting in an increased scan rate the next time the wireless handset roams onto that LMAC. Conversely, if the search for a UWAP is unsuccessful, or the wireless handset is unable to connect to the UMAN through a UWAP, the credit score for that LMAC may be decreased, resulting in a decreased scan rate the next time the wireless handset roams onto that LMAC. 
       FIG. 2  illustrates one embodiment  200  of this method. In step  201 , the handset detects the identifier of a licensed mobile access cell. In step  202 , the handset obtains the probability measure associated with the licensed mobile access cell for accessing an unlicensed wireless access point to the unlicensed mobile access network. In step  203 , the handset scans for an unlicensed wireless access point to the unlicensed wireless access network with a scan rate determined by the probability measure. 
       FIG. 3  illustrates a dual-mode wireless handset  300  in one embodiment of intelligent access point scanning with self-learning capability. Wireless handset  300  includes a processing device  301  which may be a general-purpose processor (e.g., a microprocessor), special purpose processor such as a digital signal processor (DSP) or other type of device such as a controller or field programmable gate array (FPGA). Processing device  301  may be coupled with a wireless interface  302 , which may include a licensed mobile access transceiver  303  (e.g., a GSM or CDMA transceiver or the like) adapted to communicate wirelessly with a licensed mobile access network, and an unlicensed mobile access transceiver  304  (e.g., an IEEE 802.11 or Bluetooth transceiver or the like) adapted to communicate with an unlicensed mobile access network. 
     Processing device  301  may also be coupled with a memory  305 , which may be any combination of volatile and/or non-volatile memory capable of storing data and/or instructions. Memory  305  may include an area of memory configured as a data table  306  to hold information relating to licensed mobile access cells as described in greater detail below. Memory  305  may also include an area of memory configured as a lookup table  307 , which may be used to associate the credit scores (i.e., probability measures) of each LMAC in data table  306  with a UWAP scan rate. Handset  300  may also include a user interface  308  coupled with the processing device  301  to enable voice and data input and output for a user of the wireless handset  300 . 
       FIG. 4A  illustrates an exemplary logical structure of data table  306 . Physical structures of data tables in memory are known in the art and, accordingly, are not described in detail. Data table  306  may include a list  401  of n LMAC identifiers LMAC(i) (e.g., LMAC( 1 ), LMAC ( 2 ), . . . , LMAC (n)), which may be global cell identifiers, for example. The LMAC identifiers may consist of two parts: a first part common to a local group of LMACs, denoting an LMA service area (e.g., a local area identifier, LAI(i) for example), and a second part that identifies a particular LMAC within the local group of LMACS (e.g., a cell identifier, CI(i) for example). 
     Data table  306  may also contain a list  402  of n credit scores CS(i) (e.g., CS( 1 ), CS( 2 ), . . . , CS(n)) corresponding to the list  401  of LMAC identifiers LMAC(i), where each credit score in the list denotes a probability measure for successfully connecting with a UMAN through a UWAP in the corresponding LMAC. Data table  306  may also contain a list  403  of timestamps T(i) (e.g., T( 1 ), T( 2 ), . . . , T(n)), one for each LMAC identifier in the list  401  of LMAC identifiers, denoting the latest (i.e., most recent) time that the wireless handset has made a successful UMA connection to the UMAN through a UWAP in the corresponding LMAC. Each timestamp T(i) may include both time and date information. Timestamps T(i) may be derived from an internal clock (not shown) in handset  300 . Alternatively, timestamps T(i) may be derived from system clocks in LMAN  102  and/or UMAN  108  as are known in the art. 
       FIG. 4B  illustrates an exemplary logical structure of lookup table  307 . Physical structures of lookup tables in memory are known in the art and, accordingly, are not described in detail. Lookup table  307  may have an entry column  404  and an output column  405 . The entry column of lookup table  307  may be a list of credit scores ranging from zero to a maximum value m, and the output column of lookup table  307  may be a list of scan rates ranging from a minimum scan rate corresponding to a credit score of zero, to a maximum scan rate corresponding to the maximum credit score m. In one embodiment, the minimum scan rate corresponding to a credit score of zero may be a zero scan rate (i.e., no scan). 
     Lookup table  307  may define any arbitrary functional relationship between credit scores and scan rates. For example, there may be a linear relationship as illustrated by curve  406  in  FIG. 4C , or a nonlinear relationship as illustrated by curve  407  in  FIG. 4C . It will be appreciated that while curves  406  and  407  are illustrated as continuous curves, the actual values of scan rates may be discrete values corresponding to discrete values of credit scores in lookup table  307 . 
       FIG. 5  is a flowchart illustrating a method in one embodiment of intelligent access point scanning with self-learning capability. The method begins when handset  300  scans for an LMAC such as LMAC  103  (step  501 ). If an LMAC is not detected at step  502 , the handset  300  scans for a UWAP at a default rate (step  503 ). If a UWAP is not detected within a specified time period ΔT (e.g., 10 minutes) at step  504 , the handset  300  continues to scan at the default scan rate (step  505 ) and checks whether a new LMAC has been detected (step  506 ). 
     If a new LMAC is not detected at step  506 , the method continues looping through steps  504  and  505  until a new LMAC is detected at step  506 . If a new LMAC is detected at step  506 , the method continues at step  507  where path loss parameters for the detected LMAC are evaluated (e.g., to determine link quality). If the path loss parameters are below a specified threshold, the method reverts to the “no LMAC detected” mode at step  503 . If the path loss is OK at step  507 , the handset  300  compares the identifier of the detected LMAC to the list  401  of LMAC identifiers (monitored cell list) in data table  306  (step  508 ). At step  509 , if the identifier of the (detected) LMAC matches both the LAI and the CI of an LMAC identifier in the list  401  of LMAC identifiers in data table  306 , the handset  300  scans for a UWAP at a scan rate corresponding to the credit score in the list  402  of credit scores that is associated with the detected LMAC (step  510 ). 
     The scan rate is determined by locating the credit score of the detected LMAC in the list  404  of credit scores in lookup table  307  to a corresponding scan rate in the list of scan rates  405  in lookup table  307 . If a UWAP is located within the specified time ΔT at step  511 , the handset  300  attempts to register with the UMAN  102  at step  512 . If the registration is successful at step  512 , the handset  300  compares the current time (from local or network clocks as described above) with the timestamp in the list of timestamps  403  associated with the detected LMAC (step  513 ). If the registration with the UMAN  102  is the first registration in the last M hours (e.g., 12 hours), then the credit score for the detected LMAC is incremented by one count (step  514 ). Next, the timestamp is updated to the current time at step  515 . If, at step  513 , the registration with the UMAN  102  is not the first registration in the last M hours, the credit score for the detected LMAC is not incremented and the timestamp is updated to the current time at step  515 . 
     Returning to step  511 , if a UWAP is not located within the specified time ΔT, or, if at step  512 , the handset  300  does not register successfully with UMAN  102 , handset  300  scans for a UWAP at the default rate (step  515 ). If the detected LMAC identifier does not change at step  516 , the method continues at step  511 . If the detected LMAC at step  516  changes, the method continues at step  507  as previously described. 
     If, at step  509 , the identifier of the detected LMAC matches only the LAI of an LMAC identifier in the list  401  of LMAC identifiers in data table  306  (e.g., there is an LAI match without a CI match), the method assigns a credit score of 1 to the identified LMAC and the handset  300  scans for a UWAP at a scan rate corresponding to a credit score of 1 in lookup table  307  (step  517 ). The method continues with a return to step  504 , where, if a UWAP is not located within the time ΔT, the method continues at step  505  as previously described. If, at step  504 , a UWAP is located within the time ΔT, and UMA registration is successful at step  518 , the currently detected LMAC is added to the monitored cell list (list  401 ) with a credit score of 2 at step  519 , and the timestamp associated with the detected LMAC is updated to the current time at step  515 . If, at step  518 , the registration with the UMAN is not successful, scanning for a UWAP continues at the default rate at step  505 . 
     If, at step  509 , the identifier of the currently detected LMAC does not match all or a portion of an LMAC identifier in the monitored cell list  401 , the currently detected LMAC is entered in the list with a credit score of 0 and scanning for a UWAP is suspended (step  520 ). At step  521 , an unprompted manual override option may be invoked by the user of handset  300 . If the user invokes a manual override at step  521 , the method continues to scan at the default scan rate at step  503 . Otherwise, the method scans for an LMAC at step  501 . 
     The method  500  may also include an audit of the monitored cell list (step  522 ). In step  522 , each timestamp in the list of timestamps  403  of each LMAC identifier in the list  401  of LMAC identifiers is examined to determine if the timestamp is older than a specified period of time (e.g., M hours) compared to the current time. If the timestamp is older than the specified period of time, then the credit score for the corresponding LMAC identifier is decremented by one count. If the decremented count reduces the credit score of an LMAC identifier in the table of LMAC identifiers to a specified minimum value, then the LMAC identifier is deleted from the table of LMAC identifiers. 
     Step  521  may also include a limit on the number of LMAC identifiers in the table of LMAC identifiers. In step  521 , if the table of LMAC identifiers includes the maximum number of LMAC identifiers n, step  521  may delete the LMAC identifier with the least credit score (probability measure) and, if two or more LMAC identifiers have the same credit score, then the LMAC identifier with the oldest timestamp may be deleted. 
     Thus, embodiments of intelligent access point scanning with self-learning capability have been described. While some specific embodiments of the invention have been shown, the invention is not to be limited to these embodiments. The invention is to be understood as limited only by scope of the appended claims.