Patent Publication Number: US-9906922-B2

Title: Region determination control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior application Ser. No. 13/741,243, filed Jan. 14, 2013, and entitled “REGION DETERMINATION CONTROL,” which is assigned to the assignee hereof, and expressly incorporated herein by reference. 
    
    
     BACKGROUND 
     When performing positioning in an indoor environment, determining a region, including disambiguating between different regions of the indoor environment is useful, if not critical. Indoor regions may be different floors of a building or portions of floors in a building or different portions of a floor. In this case, signals from wireless transceiver access points (APs) in different regions can be received by a single mobile station (MS). Even though the MS is in a first region, the signal strength received from an AP in a second, different, region may be stronger than the signal strength of a signal received from an AP in the first region. This is especially true near portals such as staircases and elevator shafts, e.g., due to waveguide effects of these structures. Consequently, region determination is performed to determine in which region the MS resides. Region determining, including disambiguating between different indoor regions of a structure, can be a time-consuming, highly power-consuming process. 
     SUMMARY 
     An example method, in a mobile device, of controlling region determination by the mobile device, includes: determining a present pressure at the mobile device; determining, based on the present pressure and a reference pressure, that the mobile device moved from a first region to a second region within a structure, the first region and the second region being different regions of the structure and vertically displaced from each other; and performing region determination in response to determining that the mobile device moved from the first region to the second region. 
     Implementations of such a method may include one or more of the following features. The determining that the mobile device moved from the first region to the second region within the structure includes: determining a present altitude based on the present pressure and the reference pressure; and making a comparison between the present altitude and a reference altitude associated with a reference region that is a region of the structure in which the mobile device was most-recently determined to be; where the region determination is performed in response to the comparison being indicative of the mobile device being outside the reference region. The region determination is performed in response to the present altitude differing from the reference altitude by more than a region-change-indicative magnitude. 
     Implementations of the example method may include one or more of the following features. The determining that the mobile device moved from the first region to the second region within the structure includes: determining a present altitude based on the present pressure and the reference pressure; and making a comparison between the present altitude and a reference altitude associated with a reference region that is a fixed region of the structure; where the region determination is performed in response to the comparison being indicative of the mobile device being outside a region of the structure in which the mobile device was most-recently determined to be. The region determination is performed in response to a first difference differing by more than a region-change-indicative magnitude from a second difference, the first difference being between the present altitude and the reference altitude, and the second difference being between (1) a previously-determined altitude at the mobile device associated with the region of the structure in which the mobile device was most-recently determined to be and (2) the reference altitude. 
     Implementations of the example method may include one or more of the following features. The method further includes: determining a position of the mobile device; and in response to the position of the mobile device being in an area of unreliable pressure measurements, either (1) disregarding the present pressure or (2) disregarding a present altitude determined from the present pressure. The method further includes reducing a frequency of passive measurements by the mobile device in response to determining that the mobile device is unlikely to move between regions of the structure soon. The determining that the mobile device is unlikely to move between regions of the structure soon comprises determining that a present position of the mobile device is displaced from a vertical transition of the structure by more than a threshold distance. The method further includes turning off recurring passive measurements by the mobile device in response to determining that the mobile device is displaced from a vertical transition of the structure by more than a threshold distance. The method further includes performing a passive measurement in response to the mobile device having moved from being in the first region to being in the second region. The mobile device is configured to perform passive measurements at a first rate or a second rate, with the first rate being higher than the second rate, the method further comprising setting a rate of passive measurements by the mobile device to the first rate, in response to determining at least one of that the mobile device is within a threshold distance of a vertical transition of the structure or that the mobile device moved from being in the first region to being in the second region. 
     An example of a mobile device includes: a pressure sensor configured to measure a present pressure at the mobile device; and a region determination module configured to: determine, based on the present pressure and a reference pressure, that the mobile device moved from a first region to a second region within a structure, the first region and the second region being different regions of the structure and vertically displaced from each other; and perform region determination in response to determining that the mobile device moved from the first region to the second region. 
     Implementations of such a mobile device may include one or more of the following features. To determine that the mobile device moved from the first region to the second region, the region determination module is configured to: determine a present altitude based on the present pressure and the reference pressure; and make a comparison between the present altitude and a reference altitude associated with a reference region that is a region of the structure in which the mobile device was most-recently determined to be; where the region determination module is configured to perform the region determination in response to the comparison being indicative of the mobile device being outside the reference region. The region determination module is configured to perform the region determination in response to the present altitude differing from the reference altitude by more than a region-change-indicative magnitude. 
     Implementations of the example mobile device may include one or more of the following features. To determine that the mobile device moved from the first region to the second region, the region determination module is configured to: determine a present altitude based on the present pressure and the reference pressure; and make a comparison between the present altitude and a reference altitude associated with a reference region that is a fixed region of the structure; where the region determination module is configured to perform the region determination in response to the comparison being indicative of the mobile device being outside a region of the structure in which the mobile device was most-recently determined to be. The region determination module is configured to perform the region determination in response to a first difference differing by more than a region-change-indicative magnitude from a second difference, the first difference being between the present altitude and the reference altitude, and the second difference being between (1) a previously-determined altitude at the mobile device associated with the region of the structure in which the mobile device was most-recently determined to be and (2) the reference altitude. 
     Implementations of the example mobile device may include one or more of the following features. The mobile device further includes a position module configured to determine a position of the mobile device, where in response to the position of the mobile device being in an area of unreliable pressure measurements, either (1) disregarding the present pressure or (2) disregarding a present altitude determined from the present pressure. The mobile device further includes a measurement module configured to reduce a frequency of passive measurements in response to the mobile device being unlikely to move between regions of the structure soon. The mobile device is unlikely to move between regions of the structure soon if a present position of the mobile device is displaced from a vertical transition of the structure by more than a threshold distance. The mobile device further includes a measurement module configured to turn off recurring passive measurements in response to the mobile device being displaced from a vertical transition of the structure by more than a threshold distance. The measurement module is configured to perform a passive measurement in response to the mobile device having moved from being in the first region to being in the second region. The mobile device further includes a measurement module configured to set a rate of passive measurements to a first rate or a second rate, with the first rate being higher than the second rate, and to set the rate of passive measurements to the first rate in response to the mobile device being within a threshold distance of a vertical transition of the structure or the mobile device having moved from being in the first region to being in the second region. 
     Another example of a mobile device includes: a pressure sensor configured to measure a present pressure at the mobile device; and means for determining region for: determining, based on the present pressure and a reference pressure, that the mobile device moved from a first region to a second region within a structure, the first region and the second region being different regions of the structure and vertically displaced from each other; and performing region determination in response to determining that the mobile device moved from the first region to the second region. 
     Implementations of such a mobile device may include one or more of the following features. For determining that the mobile device moved from the first region to the second region, the means for determining region include means for: determining a present altitude based on the present pressure and the reference pressure; and making a comparison between the present altitude and a reference altitude associated with a reference region that is a region of the structure in which the mobile device was most-recently determined to be; where the means for determining region are configured to perform the region determination in response to the comparison being indicative of the mobile device being outside the reference region. The means for determining region are configured to perform the region determination in response to the present altitude differing from the reference altitude by more than a region-change-indicative magnitude. 
     Implementations of the example mobile device may include one or more of the following features. For determining that the mobile device moved from the first region to the second region, the means for determining region include means for: determining a present altitude based on the present pressure and the reference pressure; and making a comparison between the present altitude and a reference altitude associated with a reference region that is a fixed region of the structure; where the means for determining region are configured to perform the region determination in response to the comparison being indicative of the mobile device being outside a region of the structure in which the mobile device was most-recently determined to be. The means for determining region are configured to perform the region determination in response to a first difference differing by more than a region-change-indicative magnitude from a second difference, the first difference being between the present altitude and the reference altitude, and the second difference being between (1) a previously-determined altitude at the mobile device associated with the region of the structure in which the mobile device was most-recently determined to be and (2) the reference altitude. 
     Implementations of the example mobile device may include one or more of the following features. The mobile device further includes means for determining position for determining a position of the mobile device; where the means for determining region are configured to, in response to the position of the mobile device being in an area of unreliable pressure measurements, either (1) disregard the present pressure or (2) disregard a present altitude determined from the present pressure. The mobile device further includes means for measuring including means for reducing a frequency of passive measurements in response to the mobile device being unlikely to move between regions of the structure soon. The mobile device is unlikely to move between regions of the structure soon if a present position of the mobile device is displaced from a vertical transition of the structure by more than a threshold distance. The mobile device further includes means for measuring including means for turning off recurring passive measurements in response to the mobile device being displaced from a vertical transition of the structure by more than a threshold distance. The means for measuring are configured to perform a passive measurement in response to the mobile device having moved from being in the first region to being in the second region. The mobile device further includes means for measuring including means for setting a rate of passive measurements to a first rate or a second rate, with the first rate being higher than the second rate, and for setting the rate of passive measurements to the first rate in response to the mobile device being within a threshold distance of a vertical transition of the structure or the mobile device having moved from being in the first region to being in the second region. 
     An example of a processor-readable storage medium of a mobile device includes processor-readable instructions configured to cause a processor to: determine, based on a reference pressure and a present pressure measured by a pressure sensor, that the mobile device moved from a first region to a second region within a structure, the first region and the second region being different regions of the structure and vertically displaced from each other; and perform region determination in response to determining that the mobile device moved from the first region to the second region. 
     Implementations of such a storage medium may include one or more of the following features. To determine that the mobile device moved from the first region to the second region, the instructions are configured to cause the processor to: determine a present altitude based on the present pressure and the reference pressure; and make a comparison between the present altitude and a reference altitude associated with a reference region that is a region of the structure in which the mobile device was most-recently determined to be; where the instructions are configured to cause the processor to perform the region determination in response to the comparison being indicative of the mobile device being outside the reference region. The instructions are configured to cause the processor to perform the region determination in response to the present altitude differing from the reference altitude by more than a region-change-indicative magnitude. 
     Implementations of the example storage medium may include one or more of the following features. To determine that the mobile device moved from the first region to the second region, the instructions are configured to cause the processor to: determine a present altitude based on the present pressure and the reference pressure; and make a comparison between the present altitude and a reference altitude associated with a reference region that is a fixed region of the structure; where the instructions are configured to cause the processor to perform the region determination in response to the comparison being indicative of the mobile device being outside a region of the structure in which the mobile device was most-recently determined to be. The instructions are configured to cause the processor to perform the region determination in response to a first difference differing by more than a region-change-indicative magnitude from a second difference, the first difference being between the present altitude and the reference altitude, and the second difference being between (1) a previously-determined altitude at the mobile device associated with the region of the structure in which the mobile device was most-recently determined to be and (2) the reference altitude. 
     Implementations of the example storage medium may include one or more of the following features. The storage medium further includes instructions configured to cause the processor to determine a position of the mobile device; where the instructions are configured to cause the processor to, in response to the position of the mobile device being in an area of unreliable pressure measurements, either (1) disregard the present pressure or (2) disregard a present altitude determined from the present pressure. The storage medium further includes instructions configured to cause the processor to reduce a frequency of passive measurements in response to the mobile device being unlikely to move between regions of the structure soon. The mobile device is unlikely to move between regions of the structure soon if a present position of the mobile device is displaced from a vertical transition of the structure by more than a threshold distance. The storage medium further includes instructions configured to cause the processor to turn off recurring passive measurements in response to the mobile device being displaced from a vertical transition of the structure by more than a threshold distance. The instructions are configured to cause the processor to perform a passive measurement in response to the mobile device having moved from being in the first region to being in the second region. The storage medium further includes instructions configured to cause the processor to set a rate of passive measurements to a first rate or a second rate, with the first rate being higher than the second rate, and to set the rate of passive measurements to the first rate in response to the mobile device being within a threshold distance of a vertical transition of the structure or the mobile device having moved from being in the first region to being in the second region. 
     Items and/or techniques described herein may provide one or more of the following capabilities, as well as other capabilities not mentioned. Location determination within a structure may be achieved using less power than with prior techniques. Passive measurements by a mobile device in a structure may be reduced, thereby reducing power consumption of the mobile device. Anomalous region determination triggers may be ignored to help conserve power. Operation of a pressure sensor may be controlled based on knowledge of connectivity of a region, e.g., to reduce power consumption. Other capabilities may be provided and not every implementation according to the disclosure must provide any, let alone all, of the capabilities discussed. Further, it may be possible for an effect noted above to be achieved by means other than that noted, and a noted item/technique may not necessarily yield the noted effect. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a simplified diagram of a communication system. 
         FIG. 2  is a simplified diagram of access points and a mobile device in a structure shown in  FIG. 1 . 
         FIGS. 3-6  are block diagrams of a base station, a server shown in  FIG. 1 , one of the access points shown in  FIG. 2 , and the mobile device shown in  FIG. 2 . 
         FIG. 7  is a functional block diagram of the mobile device shown in  FIG. 6 . 
         FIG. 8  is a block flow diagram of a process of obtaining and using pressure information to trigger region determination of a mobile device location. 
         FIG. 9  is a block flow diagram of a process of controlling region determination. 
         FIG. 10  is a block flow diagram of a process of determining a reference altitude. 
         FIG. 11  is a block flow diagram of another process of controlling region determination. 
     
    
    
     DETAILED DESCRIPTION 
     Techniques are provided for determining location within a structure, e.g., initiating position determining and/or signal measurements in a structure. For example, determining a region containing a mobile device, including disambiguation between multiple possible regions as appropriate, can be triggered in response to detecting a pressure change indicative of a floor change. Further, signal measurements such as passive measurements for access point signals can be triggered in response to detecting a pressure change indicative of a floor change. Pressure information measured at the mobile device is used by the mobile device to initiate region determination. The mobile device converts the pressure to altitude and uses knowledge of the structure, e.g., a map of the regions, and the determined altitude to determine when to initiate region determination, e.g., in response to a change in altitude exceeding a threshold. The mobile device may ignore some pressure readings, e.g., if the mobile device is in an area of unreliable pressure measurements (e.g., an area of the structure  20  known to have unreliable pressure readings, e.g., transient pressure readings). Other techniques are also possible. 
     Referring to  FIGS. 1-2 , a communication system  10  includes mobile devices  12 , a base transceiver station (BTS)  14 , a network  16 , a server  18 , and wireless transceiver access points (APs)  19  disposed in structures (here buildings)  20 . The system  10  is a communication system in that the system  10  can at least send and receive communications. Although only one server  18  is shown for simplicity, more than one server  18  may be used in the system  10 , e.g., in various locations to provide quicker access as the system  10  may span large regions, e.g., entire countries or continents, or even the planet. 
     The BTS  14  can wirelessly communicate with the mobile devices  12  via antennas. Each of the BTSs  14  may also be referred to as an access point, an access node (AN), a Node B, an evolved Node B (Enb), etc. The BTSs  14  are configured to communicate wirelessly with the mobile devices  12  under the control of the server  18  (via the network  16 ). 
     The mobile devices  12  can be moved to various locations, including into the structures  20  and onto different floors of the structures  20 . The mobile devices  12  may be referred to as access terminals (ATs), mobile stations, user equipment (UE), or subscriber units. The mobile devices  12  are shown here as cellular phones. Other examples of mobile devices include wireless routers, personal digital assistants (PDAs), netbooks, notebook computers, tablet computers, etc. Only one mobile device  12  is shown in  FIG. 2 , and to simplify the discussion below only this mobile device  12  is discussed. 
     Referring also to  FIG. 3 , the BTS  14  comprises a computer system including a processor  40 , memory  42  including software  44 , a transmitter  46 , antennas  48 , and a receiver  50 . While the BTS  14  is shown with a single processor  40  and a single memory  42  (with corresponding software  44 ), the BTS  14  may have a processor  40  and a memory  42  (with corresponding software  44 ) for each sector served by the BTS  14 , e.g., each of three sectors. The transmitter  46 , the antennas  48 , and the receiver  50  form a wireless communication module (with the transmitter  46  and the receiver  50  being a transceiver  51 ) in the BTS  14 . The transmitter  46  and the receiver  50  are configured to communicate bi-directionally with the mobile device  12  via a corresponding antenna  48 . The processor  40  is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor  40  could comprise multiple separate physical entities that can be distributed in the BTS  14 . The memory  42  includes random access memory (RAM) and read-only memory (ROM). The memory  42  is a processor-readable storage medium that stores the software  44  which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor  40  to perform various functions described herein (although the description may refer only to the processor  40  performing the functions). Alternatively, the software  44  may not be directly executable by the processor  40 , but configured to cause the processor  40 , e.g., when compiled and executed, to perform the functions. 
     The mobile device  12  and the BTS  14  are configured to communicate with each other. The mobile device  12  and the BTS  14  can send messages to each other that contain a variety of information. For example, the BTS  14  can collect information from mobile devices  12  and/or from the server  18  and send an altitude map of regional altitude indications and corresponding region indications to the mobile device  12  either directly or through one or more of the APs  19 . The regional altitude indications may indicate differential altitudes. The differential altitudes may be for each region relative to a single, common region such as the ground floor or the top floor of the structure  20 . Also or alternatively, the differential altitudes may be altitude differentials between each region and multiple other regions (e.g., multiple entrance regions, every other region). Also or alternatively, the differential altitudes may include altitude differences between adjacent floors, i.e., between floor n and floor n+1 for n=1 to N−1, where the N th  floor is the top floor. The BTS  14  may be configured to send the regional altitude indications and corresponding region indications in broadcast messages or in a dedicated message as part of an on-going communication with the mobile device  12  specifically. 
     Referring to  FIG. 4 , the server  18  comprises a computer system including a processor  60 , memory  62  including software  64 , a transmitter  66 , and a receiver  68 . The processor  60  is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor  60  could comprise multiple separate physical entities that can be distributed in the server  18 . The memory  62  includes random access memory (RAM) and read-only memory (ROM). The memory  62  is a processor-readable storage medium that stores the software  64  which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor  60  to perform various functions described herein (although the description may refer only to the processor  60  performing the functions). Alternatively, the software  64  may not be directly executable by the processor  60  but configured to cause the processor  60 , e.g., when compiled and executed, to perform the functions. The transmitter  66  and the receiver  68  (together a transceiver  69 ) are configured to send communications to and receive communications from the BTS  14  through the network  16 . The APs  19  are typically hard-wire connected to the network  16 . 
     The server  18  may provide map information to the mobile device  12  through the network  16  and one or more of the APs  19 . The map information provides a layout of the structure  20   2  along with locations of the various APs  19 , and indications of areas (e.g., portions of floors) of unreliable pressure. For example, areas near a vent may cause pressure in the area to differ from the pressure surrounding this area to such a degree that if the mobile device  12  uses measured pressure in this area, then the mobile device  12  may incorrectly determine that the mobile device  12  has likely changed floors. 
     Referring to  FIG. 5 , an example of one of the APs  19  comprises a computer system including a processor  80 , memory  82  including software  84 , a transmitter  86 , antennas  88 , and a receiver  90 . The transmitter  86 , antennas  88 , and the receiver  90  form a wireless communication module (with the transmitter  86  and the receiver  90  being a transceiver). The transmitter  86  is connected to one of the antennas  88  and the receiver  90  is connected to another of the antennas  88 . Other example WTs may have different configurations, e.g., with only one antenna  88 , and/or with multiple transmitters  86  and/or multiple receivers  90 . The transmitter  86  and the receiver  90  are configured such that the AP  19  can communicate bi-directionally with the mobile device  12  via the antennas  88 . The processor  80  is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor  80  could comprise multiple separate physical entities that can be distributed in the AP  19 . The memory  82  includes random access memory (RAM) and read-only memory (ROM). The memory  82  is a processor-readable storage medium that stores the software  84  which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor  80  to perform various functions described herein (although the description may refer only to the processor  80  performing the functions). Alternatively, the software  84  may not be directly executable by the processor  80  but configured to cause the processor  80 , e.g., when compiled and executed, to perform the functions. 
     Referring to  FIG. 6 , the mobile device  12  comprises a computer system including a processor  21 , memory  22  including software  24 , a transceiver  26 , antennas  28 , receivers  30 , and a pressure sensor  32 . The transceiver  26  and antennas  28  form a wireless communication module that can communicate bi-directionally with the BTS  14  and with the APs  19  and/or another entity. Thus, the antennas  28  include an antenna for communicating with the BTS  14  and an antenna for communicating with the APs  19 , and the transceiver  26  includes multiple transceivers, one for communicating with the BTS  14  and one for communicating with the APs  19 . The antennas  28  may include a satellite positioning system (SPS) antenna for receiving SPS signals and the transceiver  26  may include an SPS receiver for processing and transferring the SPS signals to the processor  21 . The processor  21  is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor  21  could comprise multiple separate physical entities that can be distributed in the mobile device  12 . The memory  22  includes random access memory (RAM) and read-only memory (ROM). The memory  22  is a processor-readable storage medium that stores the software  24  which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor  21  to perform various functions described herein (although the description may refer only to the processor  21  performing the functions). Alternatively, the software  24  may not be directly executable by the processor  21  but configured to cause the processor  21 , e.g., when compiled and executed, to perform the functions. 
     Referring to  FIG. 7 , the mobile device  12  includes a measurement module (means for measuring)  110 , a region determination module (means for determining region)  112 , and a position determination module (means for determining position)  114 . The modules  110 ,  112 ,  114  are functional modules implemented by the processor  21  and the software  24  stored in the memory  22 . Thus, reference to any of the modules  110 ,  112 ,  114  performing or being configured to perform a function is shorthand for the processor  21  performing or being configured to perform the function in accordance with the software  24  (and/or firmware, and/or hardware of the processor  21 ). Similarly, reference to the processor  21  performing a measuring, region determination, or position determination function, is equivalent to the measurement module  110 , the region determination module  112 , or the position determination module  114 , respectively, performing the function. The measurement module  110  is configured to obtain pressure measurements, convert these measurements to altitudes, and initiate region determination by the region determination module  112 . The region determination module  112  is configured to determine a region of the structure  20  containing the mobile device  12 , including being configured to disambiguate a region of the structure  20  if appropriate, e.g., if signals are received by the mobile device  12  from APs  19  in different regions. The position determination module  114  is configured to determine a position (location) of the mobile device  12  within a region of the structure  20 . 
     The measurement module  110  is configured to repeatedly measure pressure, e.g., periodically. The measurement module  110  causes the pressure sensor  32  to measure the present pressure at the mobile device  12 . The measurement module  110  converts this pressure to an altitude and stores the altitude in the memory  22 . The measurement module  110  converts pressure to altitude using an arbitrary reference pressure (e.g., that may be measured such as at power-up of the mobile device  12 , or may be pre-programmed and stored in the memory  22 , or otherwise arbitrarily selected). Thus, the determined altitude may not reflect an actual altitude, e.g., above sea level, but is determined for use in relative altitude comparisons. The measurement module  110  includes a filter, e.g., a low-pass Kalman filter, that filters the determined altitudes. The measurement module  110  further can track a variance of the filtered determined altitudes and determine whether the variance over a time window, e.g., 15 seconds (although other window durations may be used), indicates that the determined altitude is stable, e.g., the variance is less than, or less than or equal to, a variance threshold such as 0.1 m (although other thresholds may be used). If the determined altitude is stable (e.g., variance less than or equal to the threshold over the entire time window), then the measurement module  110  stores the altitude in the memory  22  as a reference altitude. Otherwise, e.g., if the variance indicates a non-stable altitude (e.g., the variance exceeds, or meets or exceeds, the threshold or the time window has not been reached since the last reliable region disambiguation), then the module continues to determine the altitude without storing a reference altitude. With a reference altitude stored in the memory  22 , the measurement module  110  compares (makes a comparison of) the present altitude with the reference altitude and determines whether a difference between the present altitude and the reference altitude is high (large) enough to indicate that the mobile device  12  has changed or likely has changed regions in the structure  20 , e.g., if the altitude differential exceeds (or meets or exceeds) a threshold value. The threshold value may be any of a variety of values, and may be fixed or variable (e.g., vary as a function of time and/or location, etc.). For example, the threshold may be a fixed value for all structures  20 , may be a fixed value within any particular structure  20  (e.g., based on information received from an AP  19  in the structure  20 , e.g., as part of map information for the structure), may be different for different present (most-recently determined) regions of the structure (e.g., based on information received from an AP  19  of the structure, e.g., where floors are separated by different heights and/or split-level floors are present), etc. Alternatively, instead of storing a reference altitude and comparing (making a comparison of) a present altitude with the reference altitude, the measurement module  110  may analyze a rate of change of the altitude over the time window. The measurement module  110  determines whether the absolute value of the rate of altitude change is high (large) enough to indicate that the mobile device  12  has changed or likely has changed regions in the structure  20  (e.g., is greater than, or is equal to or greater than, a threshold rate). If, in any case, the module determines that the mobile device  12  has changed or likely has changed regions in the structure  20 , then the measurement module  110  will trigger a position determination and disambiguation, if appropriate, by sending an indication to the position/disambiguation module  112  to determine the position of the mobile device  12 . 
     The measurement module  110  is further configured to take measurements to obtain information for use by the region determination module  112  and the position determination module  114 . For example, the measurement module  110  can perform passive measurements to obtain signal measurements constituting positioning information (e.g., RSSI (received signal strength indication), RTT (round-trip time)). The passive measurement is a measurement in which the mobile device  12  measures or listens on each channel on which the APs  19  and the mobile device  12  are configured to communicate. The mobile device  12  will measure an RSSI for each AP signal that it hears and store information (e.g., identity, locations) for each such AP  19  for use in other measurements. The device  12  can, for example, read beacon frames transmitted by the APs  19  and the mobile device  12  dwells about 100 ms (plus some delta time) for each channel to hear the beacon frames for all APs  19  sending beacon frames on the respective channel. The mobile device  12  is configured to determine or elicit, from the passive measurement (e.g., of the beacon signals), information that indicates APs  19  that are good candidates for active measurements to obtain information for use in determining a region and/or a position of the mobile device  12 . 
     The measurement module  110  can perform the passive measurements on a recurring basis, e.g., at regular periodic intervals, or at non-regular intervals, or combinations of these. The frequency of passive measurements performed by the measurement module  110  may be changed over time. For example, the position determination module  114  may cause the measurement module to perform passive measurements at a relatively high frequency if the mobile device  12  is near (e.g., within a threshold distance of) a vertical transition in the structure  20 , or not to perform the passive measurements or to perform the passive measurements at a relatively low frequency if the mobile device  12  is not near (e.g., beyond a threshold distance of) a vertical transition in the structure  20 . The measurement module  110  may perform the passive measurements at regular intervals, with a constant frequency, or at irregular intervals (e.g., random intervals, pseudo-random intervals, regularly-changing (e.g., increasing or decreasing) intervals, combinations of one or more of these, etc.). 
     The region determination module  112  can determine a region of the structure  20  containing the mobile device  12  and the position determination module  114  can determine a position of the mobile device  12 . The position determination module  114  can perform trilateration using the signal measurements to determine the mobile device&#39;s position in a region, e.g., using RSSI and/or RTT measurements taken by the measurement module  110 , and known locations of the APs  19 . The region determination module  112  can disambiguate between multiple possible disambiguation regions (e.g., floors) within the structure  20 . Thus, the region determination module  112  can determine a region containing the mobile device  12 , and can disambiguate between regions in the structure  20  as appropriate, e.g., where position may be ambiguous due to receipt of signals from APs  19  in different regions, and the position determination module  114  can use location assistance data for that region to perform position determination. Indeed, the position determination module  112  may load the location assistance data for a particular region into the memory  22 , in response to the region determination module  112  determining the region in which the mobile device  12  resides, and then use the loaded assistance data to determine the position of the mobile device  12  within that particular region. The position determination module  114  may even obtain the location assistance data for the particular region only in response to the region determination module  112  determining that the mobile device  12  presently resides in the particular region. 
     The region determination module  112  may work with the measurement module  110  to control operation of the pressure sensor  32 . For example, in response to the region determination module  112  determining that the structure  20  in which the mobile device  12  presently resides has only a single region, e.g., a one-story structure  20  with no vertical transitions, the region determination module  112  can send an indication to the measurement module  110  to turn the pressure sensor  32  off. The region determination module  112  may determine that the structure  20  has only a single region, for example, by examining information provided to the region determination module  112  in a map, or by a disambiguation process returning only a single candidate region. The region determination module  112  can indicate to the measurement module  110  to turn the pressure sensor  32  on, e.g., in response to transitioning to a different structure or in response to more than one candidate region being found during disambiguation. 
     Referring to  FIG. 8 , with further reference to  FIGS. 1-7 , a process  120 , in the mobile device  12 , of controlling region determination by the mobile device  12  while within the structure  20   2  includes the stages shown. The process  120  is, however, an example only and not limiting. The process  120  can be altered, e.g., by having stages altered, added, removed, combined, and/or performed concurrently. 
     At stage  122 , the process  120  includes determining a present pressure at the mobile device  12 . The pressure sensor  32  measures the present pressure at the mobile device  12  and provides an indication of this pressure to the processor  21 . The processor  21  converts this pressure to an altitude using a reference pressure. The mobile device  12  may be configured such that the pressure sensor  32  passively measures the pressure or may be configured such that the pressure sensor  32  actively measures the pressure in response to a command from the processor  21  in accordance with the software  24 . 
     At stage  124 , the process  120  includes determining, based on the present pressure and a reference pressure, that the mobile device  12  moved from a first region to a second region of the structure  20 . The mobile device  12  determines that the mobile device  12  moved from a first region of the structure  20   2  to a second region of the structure  20   2 . The mobile device  21  makes a comparison of the present altitude and a reference altitude stored in the memory  22 , with the reference altitude being based on a pressure at a reference region and the reference pressure. The reference altitude may be the altitude at the mobile device  12  associated with a reference region that is a region of the structure  20   2  in which the mobile device  12  was most-recently determined to be, i.e., the region determined in a most-recent region determination. In this case, the reference region, and reference altitude, are variable and may change over time depending upon the movement of the mobile device  12  within the structure  20   2 . Alternatively, the reference region may be a fixed region such as a ground floor, here Floor 1, of the structure  20   2 . In this case, the reference altitude may be fixed/non-variable, at least for a specified time. 
     At stage  126 , the process  120  includes performing region determination. The mobile device  12  performs region determination in response to (e.g., triggered by) determining that the mobile device moved from the first region to the second region. Here, the region determination module  112  performs region determination in response to the comparison of the present altitude and the reference altitude being indicative of the mobile device  12  having moved from being in the first region of the structure  20   2  to being in the second region of the structure  20   2 . To determine the region of the structure  20   2  in which the mobile device  12  resides, the processor  21  uses known techniques to communicate with the APs and, if appropriate, uses known techniques to disambiguate between regions of the structure  20   2 , e.g., using passive and/or active measurements involving the APs  19 . For example, if the reference altitude is the altitude of the last (most-recently) determined region, then the comparison is indicative of a change in region if a difference between the present altitude and the reference altitude exceeds a threshold. This example is depicted in each of  FIGS. 9 and 11  discussed below. As another example, the reference altitude is fixed and the comparison is indicative of a change in region if a first difference, between the present altitude and the reference altitude, differs from a second difference by more than a threshold. In this example, the second difference is between a previously-determined present altitude (e.g., an altitude associated with a most-recently determined/disambiguated region, i.e., the region of the structure  20  in which the mobile device  12  was most-recently determined to be) and the reference altitude. This example technique could be used as the inquiry of stage  170  discussed below with respect to  FIGS. 9 and 11 . 
     Referring to  FIG. 9 , with further reference to  FIGS. 1-8 , a process  150  of controlling region determination (including disambiguation) by the mobile device  12  while within the structure  20   2  includes the stages shown. The process  150  is an example detailed implementation of the process  120 . The process  150  is, however, an example only and not limiting. The process  150  can be altered, e.g., by having stages altered, added, removed, rearranged, combined, and/or performed concurrently. For example, stage  152  could be eliminated. 
     At stage  152 , the mobile device  12  obtains an altitude threshold A th . The altitude threshold A th  may be structure dependent, or structure independent, e.g., programmed during manufacture of the mobile device  12 . The altitude threshold A th  may be obtained by the mobile device  12  communicating with at least one of the APs  19  (e.g., to obtain altitude difference(s) between the floors) in the structure  20   2 , or with the base station  14 , or obtained by the processor  21  communicating with the memory  22  that stores the altitude threshold A th . The altitude threshold A th  may be the same or different for different regions within the structure  20   2 , e.g., a first value if the mobile device&#39;s last determined/disambiguated region is the first floor and a second value, different from the first value, if the mobile device&#39;s last determined/disambiguated region is the second floor. Alternatively, the altitude threshold A th  may be fixed, e.g., if programmed during manufacture of the mobile device  12 . 
     At stage  154 , the mobile device  12  determines its present position and present region in which the mobile device  12  resides, triggers a passive measurement, and sets a passive measurement rate to high. The region determination module  112  determines the mobile device&#39;s region in the structure  20   2 , disambiguating regions as appropriate, e.g., if the mobile device  12  receives signals from APs  19  in different regions. The position determination module  114  determines the mobile device&#39;s position, e.g., using information from active and/or passive measurements with one or more of the APs  19 , the location(s) of the one or more APs  19 , and one or more known techniques such as trilateration. The processor  21  triggers a passive measurement, e.g., for use in determining the mobile device&#39;s position, and sets (i.e., the measurement module sets, or the means for measuring includes means for setting) a rate of passive measurements to a relatively high value. For example, the processor  21  may be configured to set the passive measurement rate to a first frequency value, a second frequency value, or off, with the first frequency value being higher than the second frequency value such that a first frequency is a relatively higher frequency and a second frequency is a relatively lower frequency. This example is for regularly-spaced in time passive measurements, but rates for non-regularly-spaced measurements may also be set, or parameters inducing different rates set (similarly, a low non-regularly-spaced or regularly-spaced measurement rate can be set at stage  162  discussed below). 
     At stage  156 , an inquiry is made as to whether the mobile device  12  is in an area of unreliable pressure readings. The processor  21  determines (e.g., using a map of the structure  20   2 ) whether the position of the mobile device  12  corresponds to an area of the structure  20   2  known (e.g., as indicated on a map of the structure  20   2 ) to have unreliable pressure readings, e.g., because there is an entity affecting pressure in the area such as a vent or air-conditioning unit. If the processor  21  determines that the mobile device  12  is in an area where pressure measurements taken by the pressure sensor  32  are unreliable (e.g., subject to frequent change), then the process  150  loops at stage  156 . If the processor  21  determines that the mobile device  12  is not in an area where pressure measurements taken by the pressure sensor  32  are unreliable, then the process  150  proceeds to stage  158 . 
     At stage  158 , the mobile device  12  measures the present pressure and determines and stores a reference altitude A r . The pressure sensor  32  measures the pressure at the mobile device  12  and converts this pressure to an altitude using the reference pressure. If this altitude is stable, then the measurement module  110  stores the altitude (i.e., an indication of the stable altitude) in the memory  22  as more fully discussed below with respect to  FIG. 10 . In this example, the stable altitude is stored as a reference altitude A r . 
     At stage  160 , an inquiry is made as to whether the mobile device  12  is unlikely to move between regions of the structure  20   2  soon. In this example, the processor  21  determines whether the mobile device  12  is near/proximate or displaced from a vertical transition of the structure  20   2  and whether the position of the mobile device  12  is accurately known. For example, the processor  21  determines whether the position of the mobile device  12  is outside a threshold distance of any vertical transition of the structure  20   2 , with the mobile device  12  being unlikely to move between vertically displaced regions soon if the mobile device  12  is further than the threshold distance from any such vertical transition. Further, the processor  21  determines whether the position of the mobile device  12  is confidently/accurately known, e.g., whether a confidence in the position determined at stage  154  (or stage  172  discussed below) is greater than a threshold confidence. If the position of the mobile device  12  is confidently/accurately known, and outside of the threshold distance from a vertical transition, then the processor  21  determines that the mobile device is unlikely to move between regions of the structure  20   2  soon, and the process  150  proceeds to stage  162 . If the position of the mobile device  12  is not confidently/accurately known and/or inside of the threshold distance from a vertical transition, then the processor  21  determines that the mobile device is not unlikely to move between regions of the structure  20   2  soon, and the process  150  proceeds to stage  164 . 
     At stage  162 , the mobile device  12  sets a passive measurement rate to low. The processor  21  sets (effectively either changes if high, or leaves alone if already low) a rate of passive measurements (a rate at which the mobile device  12  will perform passive measurements) to a relatively low rate (e.g., a second rate of first and second rates where the first rate is higher than the second rate). That is, the measurement module  110  is configured to reduce (the means for measuring includes means for reducing) a frequency of passive measurements in response to the mobile device being unlikely to move between regions of the structure soon. The relatively low rate would reduce power consumption relative to a higher rate while detecting information often enough to help ensure a high quality user experience. For example, the relatively low rate could be once every 30 seconds. Alternatively, the processor  21  may turn passive measurements off (i.e., the means for measuring includes means for turning off recurring passive measurements and stage  162  potentially includes turning off recurring passive measurements) pending a trigger to induce a passive measurement and/or start recurring passive measurements. From stage  162 , the process  150  proceeds to stage  166  discussed below. 
     At stage  164 , the mobile device  12  sets a passive measurement rate to high. The processor  21  sets (effectively either changes if low, or leaves alone if already high) the rate of passive measurements to a relatively high rate (e.g., the first rate of the first and second rates), e.g., once every six (6) seconds, to provide a compromise between power consumption and delay between a region change and region detection to ensure a high quality user experience. 
     At stage  166 , the mobile device  12  measures the present pressure, converts this pressure to an altitude, and stores this altitude as a present altitude A n  for comparison with the reference altitude A r . The pressure sensor  32  measures the pressure at the mobile device  12  and the measurement module  110  converts the pressure to altitude and stores this altitude (i.e., an indication of this altitude) in the memory  22 . 
     At stage  168 , an inquiry is made as to whether the mobile device  12  is in an area of unreliable pressure readings. Similar to stage  156  discussed above, the processor  21  determines whether the position of the mobile device  12  corresponds to an area of the structure  20   2  known to have unreliable pressure readings. If the processor  21  determines that the mobile device  12  is in an area where pressure measurements taken by the pressure sensor  32  are unreliable, then the region determination module  112  disregards (at least for purposes of the process  150 ) at least one of the pressure measured, or the corresponding altitude determined, at stage  166 , and the process  150  proceeds to stage  172 , bypassing stage  170 . The processor  21  may also turn pressure measurements off until the mobile device  12  is not in an area (i.e., outside of any area) of unreliable pressure. If the processor  21  determines that the mobile device  12  is not in an area where pressure measurements taken by the pressure sensor  32  are unreliable, then the process  150  proceeds to stage  170 . 
     At stage  170 , an inquiry is made as to whether a magnitude of an altitude difference (delta) between the present altitude A n  and the reference altitude A r  is indicative of a region change, i.e., the mobile device  12  moving between first and second regions of the structure  20 , with the first and second regions being vertically displaced with respect to each other. The processor  21  determines a magnitude of a difference between the present altitude A n  and the reference altitude A r  and compares this value with the altitude threshold A th . The altitude threshold Ath is a region-change-indicative magnitude in that if the magnitude of the difference is greater than the altitude threshold A th  (|A n −A r |&gt;A th ), then the altitude difference is indicative of the mobile device  12  having changed regions from the most-recently disambiguated region (i.e., the region the mobile device  12  was determined to be in when the processor  21  most recently performed region disambiguation). In this case, the process  150  returns to stage  154  for position determination, including region disambiguation if appropriate. If the magnitude of the difference of the present altitude A n  and the reference altitude A r  is not greater than the altitude threshold A th , then the altitude difference is indicative of the mobile device  12  not having changed regions from the most-recently disambiguated region. In this case, the process  150  proceeds to stage  172  for position determination. Alternatively, the comparison made during this stage could be whether the magnitude difference between the present altitude A n  and the reference altitude A r  is greater than or equal to the altitude threshold A th . Alternatively still, the comparison made during this stage could be whether an altitude change rate exceeds or falls below a threshold rate. Further, the determination at stage  170  may include some time delay, e.g., being made for the altitude change or altitude change rate over a period of time, e.g., three seconds, before returning to stage  154 . This provides some hysteresis to guard against numerous transition indications if the change or change rate is near the threshold value or if there is rapid altitude change over multiple regions (e.g., floors), e.g., due to transit in an elevator. The hysteresis may also take the form of a variable threshold, e.g., once a first threshold value is exceeded, if the altitude drops below a second threshold value, that is less than the first threshold value, before the position of the mobile device  12  is determined/disambiguated, then the position determination/disambiguation at stage  154  may be terminated, with the process  150  proceeding to stage  156 . 
     At stage  172 , the mobile device  12  determines its position. The position determination module  114  determines the mobile device&#39;s position, e.g., using information from active and/or passive measurements with one or more of the APs  19 , the location(s) of the one or more APs  19 , and one or more known techniques such as trilateration. The process  150  then returns to stage  158  where a new, stable, reference altitude will be determined. 
     Referring to  FIG. 10 , with further reference to  FIGS. 1-9 , a process  180  of determining and storing a reference altitude includes the stages shown. The process  180  is, however, an example only and not limiting. The process  180  can be altered, e.g., by having stages altered, added, removed, combined, and/or performed concurrently. 
     At stage  182 , an altitude filter in the mobile device  12  is initialized. The filter is initialized with one or more appropriate parameters, e.g., noise variance, to implement a low-pass filter. This stage may performed only the first time that the process  180  is performed, or only the first time that the process  182  is performed in a particular structure  20 . 
     At stage  184 , the pressure is measured and converted to an altitude using a reference pressure. The pressure sensor  32  measures the pressure at the mobile device  12  and the processor  21  converts this pressure to an altitude using a reference pressure. The reference pressure is an arbitrary pressure and may be arbitrarily chosen, may be received from a BTS  14 , may be the first pressure measured by the pressure sensor  32  after the mobile device  12  enters the structure  20 , or a pressure determined or chosen in some other way. 
     At stage  186 , an inquiry is made as to whether the determined altitude is stable. The determined altitude is filtered by the altitude filter initialized at stage  182 . For example, the altitude filter may collect altitude values over a period of time such as 15 seconds. If altitude values are not available for the entire period of time, or if the variance of the altitude over the time period exceeds (or, alternatively, meets or exceeds) a threshold variance value, then the process  180  returns to stage  184  where further pressure measurements and altitude determinations are performed. If altitude values are available for the entire period of time, and the variance of the altitude over the time period is less than or equal to (or, alternatively, is less than) the threshold variance value, then the process  180  proceeds to stage  188  where the present altitude (or an altitude associated with the present altitude, e.g., an average of the altitude over the time period) is stored as a reference altitude A r . 
     Referring to  FIG. 11 , with further reference to  FIGS. 1-9 , a process  200  of controlling region determination by the mobile device  12  while within the structure  20   2  includes the stages shown. The process  200  is another example detailed implementation of the process  120 . The process  200  is, however, an example only and not limiting. The process  200  can be altered, e.g., by having stages altered, added, removed, rearranged, combined, and/or performed concurrently. For example, stage  152  could be eliminated. 
     The process  200  is very similar to the process  150  shown in  FIG. 8 . A difference between the process  200  and the process  150  is that in the process  200 , after stage  162 , the process  200  proceeds to stage  165  while in the process  150 , after stage  162 , the process  150  proceeds to stage  166  for measurement of present pressure and determining the present altitude. Stage  165  is similar to stage  168  of the process  150 . If at stage  165  the processor  21  determines that the mobile device  12  is in an area of unreliable pressure readings, then the process  200  bypasses stages  166  and  170  so that a pressure measurement is not taken, while in the process  150  the pressure measurement is taken at stage  166  but disregarded (or the determined altitude is disregarded) if the processor  21  determines that the mobile device  12  is in an area of unreliable pressure readings. 
     Other Considerations 
     One or more dedicated devices may be provided that measure pressure and send communications indicating the pressures, and information from which the region can be determined, to the server  18  and/or the mobile devices  12 . 
     As used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C), or combinations with more than one feature (e.g., AA, AAB, ABBC, etc.). 
     As used herein, including in the claims, unless otherwise stated, a statement that a function or operation is “based on” an item or condition means that the function or operation is based on the stated item or condition and may be based on one or more items and/or conditions in addition to the stated item or condition. 
     A wireless communication network does not have all communications transmitted wirelessly, but is configured to have at least some communications transmitted wirelessly. 
     Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. 
     Further, more than one invention may be disclosed. 
     Substantial variations to described configurations may be made in accordance with specific requirements. For example, customized hardware might also be used, and/or particular elements might be implemented in hardware, software (including portable software, such as applets, etc.), or both. Further, connection to other computing devices such as network input/output devices may be employed. 
     Common forms of physical and/or tangible computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read instructions and/or code. 
     The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and that various steps may be added, omitted, or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims. 
     Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations provides a description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure. 
     Also, configurations may be described as a process which is depicted as a flow diagram or block diagram. Although each may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may have additional stages or functions not included in the figure. Furthermore, examples of the methods may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the tasks may be stored in a non-transitory computer-readable medium such as a storage medium. Processors may perform the described tasks. 
     Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of the invention. Also, a number of operations may be undertaken before, during, or after the above elements are considered. Accordingly, the above description does not bound the scope of the claims.