Patent Publication Number: US-2006009216-A1

Title: Multiple mode scanning

Description:
FIELD OF THE DISCLOSURE  
      This disclosure relates generally to communication devices and scanning for service using a multiple mode communication device.  
     BACKGROUND OF THE DISCLOSURE  
      Some communication devices, such as cellular telephones, cordless telephones, computers with communication access, and hybrids or combinations of these devices, can operate in more than one mode to communicate with more than one communication network. In order for a single communication device to operate in multiple modes, the communication device searches for available communication networks upon power up and sometimes after power up.  
      Scanning for available communication networks on all modes where the communication device is operational, however, is a time-consuming and power-consuming operation. There is an opportunity for a scanning mechanism that reduces power consumption and quickly finds an available communication network. The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a block diagram of a communication device for multiple mode scanning according to a preferred embodiment.  
       FIG. 2  shows a flowchart for a power up scan by a communication device for multiple mode scanning according to the preferred embodiment.  
       FIG. 3  shows a flowchart for a power down by a communication device for multiple mode scanning according to the preferred embodiment.  
       FIG. 4  shows a flowchart of a scan after power up by a communication device for multiple mode scanning according to the preferred embodiment.  
       FIG. 5  shows a sample scan list according to the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A method for scanning of channels by a multi-mode communication device includes the steps of making a scan list operative for more than one mode, modifying the scan list to remove all non-current-mode systems, and sequentially scanning a highest priority channel on the modified scan list. If the communication device has recently found service on a particular system in a first mode, the communication device will only search for systems that are associated with that first mode. This use of a modified scan list applies both to power up scanning situations and scanning after power up situations. Modifying a scan list to remove all non-current mode systems allows the multi-mode communication device to avoid scanning for systems that are geographically unavailable and instead acquire a system in less time and with less power consumption.  
      In this Detailed Description, the term “multiple mode” refers not only to different radio access technologies (RATs, also called air interfaces), but also to similar air interface protocols used at different frequency bands. For example, code division multiple access (CDMA) cellular phone systems operate at the 800 MHz frequency band and the 1900 MHz frequency band in the United States. Additionally in the United States, a Global System for Mobile communication (GSM) cellular phone system operates at the 1900 MHz frequency band. In Europe, there are GSM cellular phone systems operating on the 900 MHz and 1800 MHz frequency bands. Depending on the implementation, a communication device with multiple mode scanning may treat the CDMA 800 cellular phone system, the CDMA 1900 cellular phone system, the GSM 900 cellular phone system, and the GSM 1800 cellular phone system as four separate modes. Alternately, the communication device with multiple mode scanning may treat the CDMA 800 and CDMA 1900 cellular phone systems as a first mode and treat the GSM 900 and GSM 1800 cellular phone systems as a second mode. Still further, another embodiment of the communication device with multiple mode scanning may group the CDMA 1900 and GSM 1800 cellular phone systems in a first mode and the CDMA 800 and the GSM 900 cellular phone systems in a second mode.  
      As another example, a communication device with multiple mode scanning may treat a 900 MHz cordless phone system, a 46/49 MHz cordless phone system, and a CDMA 1900 cellular phone system as three separate modes. Alternately, a communication device with multiple mode scanning may treat the two cordless phone systems as a first mode and the cellular phone system as a second mode.  
       FIG. 1  shows a block diagram of a communication device  100  for multiple mode scanning according to a preferred embodiment. This communication device  100  is a dual-mode cellular radiotelephone with a first mode having CDMA 800 and CDMA 1900 capabilities and a second mode having GSM 900 and GSM 1800 capabilities. Other cellular phone modes, such as Time Division Multiple Access (TDMA), Advanced Mobile Phone System (AMPS), etc., can be substituted or added to create a tri-mode or other variants of a multi-mode communication device. It is also appropriate to use multiple mode scanning with other types of multi-mode communication devices, such as a cordless-cellular telephone, an FM/AM/satellite radio, or a laptop computer with WLAN-cellular transceivers.  
      For scanning, several hardware components, such as radio-frequency assemblies and base-band assemblies, must be active and supplied with power. Radio-frequency assemblies commonly include an amplifier, mixer, demodulator, and oscillator. Base-band assemblies usually have a digital signal processor, microprocessor, and memory.  
      A frame generator  101  and a microprocessor  103  combine to generate the necessary communication protocols needed to operate in the GSM 900/1800 and CDMA 800/1900 cellular systems. The microprocessor  103  uses memory  104  such as a random access memory (RAM)  105 , an electrical erasable programmable read-only memory (EEPROM)  107  and a read-only memory (ROM)  109 . Alternate memory devices can be used, and the memories can be consolidated in one package  111 . The microprocessor  103  and the memory  104  work together to execute the steps necessary to generate the protocol and to perform other functions for the communication device, such as writing to a display  113 , accepting information from a keypad  115 , controlling a frequency synthesizer  125 , or performing steps needed to amplify a signal. The frame generator  101 , in conjunction with the microprocessor  103 , processes audio transformed by the audio circuitry  119  from a microphone  117  and to a speaker  121 .  
      A transceiver processes radio frequency signals to and from the communication device  100 . For this dual-mode cellular radiotelephone, two transmitters  123 ,  124  transmit through an antenna  129  using carrier frequencies produced by a frequency synthesizer  125 . Information received by the communication device&#39;s antenna  129  enters receivers  127 ,  128  through a matching network and transmit/receive switch  130 . At least one of the receivers  127 ,  128  demodulates the symbols comprising the message frame using an intermediate frequency (IF) section  126  and the carrier frequencies from frequency synthesizer  125 . The transmitters and receivers are collectively called a transceiver. Those skilled in the art will recognize that other transceiver architectures can be substituted, for example the two transmitters may combined in one subsystem, the two receivers may be combined into a subsystem, or the intermediate frequency section  126  may be eliminated by using a direct conversion receiver. The communication device  100  may optionally include a message receiver and storage device  131  including digital signal processing means. The message receiver and storage device  131  could be, for example, a digital answering machine or a paging receiver.  
      Because this is a multi-mode communication device, upon power-up (and after power-up) the communication device has several options for finding a serving network. Generally speaking for a dual-mode device, there will be classifications available for a home network for a first mode, a home network for a second mode, at least one preferred network for the first mode, at least one preferred network for the second mode, “roam” networks for the first mode, “roam” networks for the second mode, other networks for the first mode, and other networks for the second mode. With more than two modes, there will be opportunities for home, preferred, roam, and other networks in the additional modes.  
      Some service providers operate modes that are exclusive to specific geographic regions. For example, a service provider may operate a CDMA network in North America and operate a GSM network in Western Europe. By using multiple mode scanning during power-up and subsequent to power-up of a communication device, the communication device eliminates spending time and battery power on searching for service that is not available at the geographic location where it is being powered-up. This scanning takes advantage of systems that are not co-located.  
       FIG. 2  shows a flowchart  200  for a power up scan by a communication device for multiple mode scanning according to the preferred embodiment. In a cellular telephone environment, this scan is sometimes referred to as “cell selection.” In step  201 , the flowchart starts power-up scanning upon powering up the communication device. Step  210  deletes any value in memory that is assigned to a “current mode” variable C URRENT M ODE . At this point in time, the communication device is not aware of a current mode. Step  220  determines if the current time is less than a variable L AST P OWER D OWN T IME  plus a variable S AME M ODE T IME O UT . The variable L AST P OWER D OWN T IME  represents the most recent time that the communication device was properly powered down. The variable S AME M ODE T IME O UT  represents a predetermined time interval.  
      If the communication device is starting its scan within the period determined by the variable S AME M ODE T IME O UT  since the communication device last properly powered down, step  225  sets the variable C URRENT M ODE  to the value of variable L AST M ODE . This means that the communication device will scan only for networks that operate using the same mode as the communication device was operating on at the time it powered down. Otherwise, the flowchart goes straight from step  220  to step  230 .  
      The S AME M ODE T IME O UT  variable can be retained in the communication device memory as set by a service provider, or it can be manually adjusted by the user of the communication device, or it can be automatically adjusted depending on some predetermined variables. For example, if the service provider intends the communication device to operate in a first mode in North America and a second mode in Western Europe, the S AME M ODE T IME O UT  variable can be set at six hours, which represents an expected minimum time needed to get from North America to Western Europe. Alternately, if a user intends the communication device to operate in a first mode at home and a second mode at the office, the user can set the S AME M ODE T IME O UT  variable to an expected minimum commute time between home and office.  
      Step  230  assembles a scan list. The scan list is a prioritized list of channels that will be described in more detail with reference to  FIG. 5 . The scan list can be assembled from a variety of sources and ranked according to a variety of preferences. Network identifiers that become items in a scan list are often available from a permanent memory (ROM) in the communication device, from a removable memory such as a subscriber identity module (SIM card) or a removable user identity module (RIUM), or a non-permanent memory (RAM) in the communication device that is downloaded using either a wireless or wired connection. The scan list at this step of the preferred embodiment includes all allowed channels from all modes the communication device can operate on.  
      If step  240  determines that the variable C URRENT M ODE  is not empty (i.e., C URRENT M ODE  is set in step  225 ), step  245  removes all entries from the scan list that are not associated with the C URRENT M ODE  variable. Thus, when step  245  has completed, all the networks on the scan list will be associated with the same mode as the communication device was operating on when it last properly powered down; all the networks that were associated with non-C URRENT M ODE  modes will have been removed. If step  240  determines that the variable C URRENT M ODE  is empty, no networks will be removed from the scan list before the flowchart moves to step  247 , where an elapsed scan timer is reset.  
      Next, step  250  sequentially scans channels associated with the networks on the scan list. If step  260  determines that service is not allowed on the channel being scanned, step  263  checks the elapsed scan timer to see whether it has exceeded a predetermined S CAN T IME O UT  variable. In this preferred embodiment, the S CAN T IME O UT  variable equals the S AME M ODE T IME O UT  variable. If the predetermined S CAN T IME O UT  variable has not been exceeded, step  267  checks whether all channels on the scan list have been scanned. If not all the channels on the scan list have been scanned, the flowchart returns to step  250 . If step  260  determines that service is allowed on the channel being scanned, step  270  sets the variable C URRENT M ODE  equal to the value of the mode of the found system. Step  299  ends the flowchart with camping within the found network.  
      If step  263  determines that the elapsed scan timer has exceeded the S CAN T IME O UT  variable, or if step  267  determines that all the channels on the scan list have been scanned with no service allowed, the flow returns to step  210  where the C URRENT M ODE  variable is cleared. During this second pass through the flowchart, a scan list is assembled, potentially modified, and sequentially scanned. If, for example, a user is traveling from North America to Western Europe but does not power down the communication device for a six hour period of time represented by the S AME M ODE T IME O UT , the second pass through the flow chart will check again the current time in step  220  and set (or not set) the C URRENT M ODE  variable according to the flow chart. This allows the communication device, in the event of an unexpected situation or a software bug, to rebuild the scan list and eventually scan all the channels on an unmodified scan list.  
      Thus, the flowchart allows for assembling a scan list, modifying the scan list to remove all non-C URRENT M ODE  systems, and scanning using the modified scan list. By scanning only channels associated with the mode last servicing the communication device, the communication device saves time and battery power. If the communication device supports modes that operate in mutually exclusive geographic areas, this scanning produces a performance improvement over scanning in all modes supported by the communication device.  
       FIG. 3  shows a flowchart  300  for a power down by a communication device for multiple mode scanning according to the preferred embodiment. Upon power down of the communication device, as noted in step  301 , step  310  sets the variable L AST M ODE  to the value in the variable C URRENT M ODE . This allows the communication device to recall the last mode that serviced the communication device. Next, step  320  sets the variable L AST P OWER D OWN T IME  equal to the current time. These two variables, L AST M ODE  and L AST P OWER D OWN T IME , are used in the flowchart of  FIG. 2  to determine whether to modify the scan list in step  245  of  FIG. 2 .  
      If the communication device is powered up within the time period represented by S AME M ODE T IME O UT  since the time represented by the L AST P OWER D OWN T IME  variable, the communication device will scan only for the network represented by the L AST M ODE  variable. This allows the communication device to save time and battery energy in finding a serving system.  
       FIG. 4  shows a flowchart  400  of a scan after power up by a communication device for multiple mode scanning according to the preferred embodiment. A non-power up scanning can occur when a signal is lost or there is another type of abnormal disconnection of the communication device from its serving system. Abnormal disconnection may be caused by network artifacts such as maintenance cycles or signaling errors. Flowchart  400  is essentially a subset of flowchart  200  shown in  FIG. 2 . Thus, it is possible to use flowchart  200  for both power up scanning and scanning after power up. Step  401  starts scanning after a power up. Step  430  assembles a scan list similar to step  230 . Step  445  modifies the scan list to remove all entries corresponding to systems that are not of the type represented by the variable C URRENT M ODE.    
      Next, step  447  resets an elapsed scan timer. Step  450  sequentially scans channels associated with the systems in the modified scan list. Step  460  determines if the current channel allows service. If the current channel does not allow service, step  463  checks the elapsed scan timer to see whether it has exceeded a predetermined S CAN T IME O UT  variable. If the predetermined S CAN T IME O UT  variable has not been exceeded, step  467  checks whether all channels on the scan list have been scanned. If not all the channels on the scan list have been scanned, the flowchart returns to step  450  and scans the next channel in the modified scan list. If step  460  determines that the current channel allows service, step  499  camps the communication device in the system of the current channel.  
      If step  463  determines that the elapsed scan timer has exceeded the S CAN T IME O UT  variable, or if step  467  determines that all the channels on the scan list have been scanned with no service allowed, the flow returns to step  210  in  FIG. 2  where the C URRENT M ODE  variable is cleared. During this pass through the flowchart  200  of  FIG. 2 , a scan list is assembled, potentially modified, and sequentially scanned. If, for example, an unexpected situation or a software bug causes the communication device to improperly assemble the scan list in step  430  or improperly modify the scan list in step  445 , the flow will revert to the full flowchart  200  in  FIG. 2 . If a time period represented by the variable S CAN T IME O UT  has elapsed without the communication system successfully camping on a system, the communication device will rebuild the scan list that includes all the entries and scan through the unmodified scan list.  
      Because the variable C URRENT M ODE  is set during a power-up scan during step  270  shown in  FIG. 2 , any non-power-up scan presumes that the system represented by the C URRENT M ODE  variable will still be available for a subsequent non-power-up scan. By making this presumption, the communication device will find a system more quickly, and with less power consumption, than if the presumption was not made.  
       FIG. 5  shows a sample scan list  500  according to the preferred embodiment. The scan list is a prioritized list of channels that a communication device, such as the communication device  100  shown in  FIG. 1 , can create and maintain in memory  104 . The channels on the scan list can be obtained from sources such as ROM and RAM in the communication device, a SIM card or a RUIM. The example communication device has a first mode of CDMA and a second mode of GSM. The CDMA mode represents two systems, a CDMA800 system and a CDMA1900 system. The GSM mode represents two systems, a GSM900 system and a GSM1800 system. In this preferred embodiment, each system is included as a separate submode in the scan list. Another embodiment can eliminate the submodes, and have only the CDMA and GSM modes, which does not allow for quite as much flexibility in changing mode definitions. For example, if the two modes of a communication device were to change from CDMA800/CDMA1900 and GSM900/GSM1800 to CDMA1900/GSM1800 and CDMA800/GSM900, there would be little change needed to the scan list shown.  
      In this sample, the C URRENT M ODE  variable of the communication device refers to the CDMA mode representing both the CDMA 800 and CDMA 1900 cellular phone networks. Thus, in this sample scan list  500 , the channels associated with non-C URRENT M ODE  systems have been struck-out to show that the scan list has been modified to remove all non-C URRENT M ODE  systems as described in step  245  of  FIG. 2  and step  445  of  FIG. 4 . Because the non-C URRENT M ODE  system channels have been removed, the communication device will first scan for the home network of the CDMA 1900 system. If the scan is unsuccessful, the communication device will scan preferred networks of the CDMA 1900. (The parentheses around a priority number indicates that more than one channel is usually listed under that priority number.) If none of those scans are successful, the communication device will scan for roam networks of the CDMA system. If none of those scans are successful, the communication device will scan for other networks of the CDMA system. If a time period represented by the variable S CAN T IME O UT  has elapsed without the communication system successfully camping on a system, the communication device will rebuild the scan list that includes all the entries and scan through the unmodified scan list.  
      Thus, multiple mode scanning provides a quicker, lower-power-consumption alternative to traditional multi-mode scanning methods. By setting up a scan list, removing non-current mode systems from the scan list to create a modified scan list, and sequentially scanning through the modified scan list until a system is found, a communication device with multiple mode scanning saves battery power and time in locating a serving system.  
      While this disclosure includes what are considered presently to be the preferred embodiments and best modes of the invention described in a manner that establishes possession thereof by the inventors and that enables those of ordinary skill in the art to make and use the invention, it will be understood and appreciated that there are many equivalents to the preferred embodiments disclosed herein and that modifications and variations may be made without departing from the scope and spirit of the invention, which are to be limited not by the preferred embodiments but by the appended claims, including any amendments made during the pendency of this application and all equivalents of those claims as issued.  
      It is further understood that the use of relational terms such as first and second, top and bottom, and the like, if any, are used solely to distinguish one from another entity, item, or action without necessarily requiring or implying any actual such relationship or order between such entities, items or actions. Much of the inventive functionality and many of the inventive principles are best implemented with or in software programs or instructions. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs with minimal experimentation. Therefore, further discussion of such software, if any, will be limited in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention.