Patent Publication Number: US-2011069627-A1

Title: Peer-assisted transmitter signal attribute filtering for mobile station position estimation

Description:
This application claims priority from U.S. Provisional Application No. 61/160,425, filed Mar. 16, 2009, and entitled “Peer Assisted RSSI Filtering”, assigned to the assignee hereof and expressly incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     Subject matter disclosed herein relates to filtering one or more signal attributes for a given transmitter from use in mobile station position estimation. 
     2. Information 
     The position of a mobile station, such as a cellular telephone, may be estimated based on information gathered from various systems. One such system may comprise a cellular communication system comprising a number of terrestrial base stations to support communications for a number of mobile stations. Another such system may comprise a wireless local area network (WLAN) communication system comprising a number of access points (APs) to support communications for a number of mobile stations. Still another example system may comprise a Satellite Positioning System (SPS) comprising a number of satellite vehicles (SVs). A position estimate, which may also be referred to as a position “fix”, for a mobile station may be obtained based at least in part on distances or ranges measured from such a mobile station to one or more transmitters, and also based at least in part on knowledge of the locations of the one or more transmitters. 
     SUMMARY 
     In an aspect, a range may be estimated between a first mobile station and an access point. A confidence value related to the estimated range may be determined based, at least in part, on one or more signal attributes associated with wireless communications among the first mobile station, a second mobile station, and the access point. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Non-limiting and non-exhaustive examples will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures. 
         FIG. 1  is a schematic block diagram depicting an example wireless terminal in communication with an example satellite positioning system and an example wireless communication network. 
         FIG. 2  is a schematic block diagram depicting an example trilateration technique for performing a position fix for a wireless terminal. 
         FIG. 3  is a schematic block diagram depicting an example communication system including a transmitter and a plurality of mobile stations. 
         FIG. 4  is a schematic block diagram of an example technique for filtering transmissions from a given transmitter for mobile station position estimation operations. 
         FIG. 5  is a schematic block diagram of an example process for filtering a signal attribute for a communication from a given transmitter from use in position estimation operations for a given mobile station. 
         FIG. 6  is a schematic block diagram illustrating an example implementation of a mobile station. 
         FIG. 7  is a schematic block diagram depicting an example wireless communication system including a plurality of computing platforms comprising one or more transmitters and one or more mobile stations. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed above, a position of a mobile station, such as a cellular telephone, may be estimated based on information gathered from one or more wireless communication systems. Such wireless systems may comprise a number of transmitters to support communications for a number of mobile stations. A position estimate, which may also be referred to as a position “fix”, for a mobile station may be obtained based at least in part on distances or ranges measured or estimated from the mobile station to one or more transmitters, and also based at least in part on knowledge of the known or estimated locations of the one or more transmitters. Ranges from the mobile stations to the transmitters may be estimated, in some cases, based at least in part on signal strength indicators included in some transmissions, and/or based at least in part on signal strengths measured at receiving mobile stations. For example, estimating the range between a mobile station and an access point may comprise the mobile station measuring a signal strength of a beacon signal transmitted by the access point. 
     As used herein, the term “access point” refers to any device with the ability to receive wireless signals from one or more terminal devices and that may provide access to a network such as a local area network (LAN) or the Internet, for example. An access point may be installed at a fixed terrestrial location, and may facilitate communication in a wireless communication network, such as, for example, a wireless local area network (WLAN). Such a WLAN may comprise a network compliant to or compatible with an IEEE 802.11x standard, although the scope of claimed subject matter is not limited in this respect. Also, in an aspect, an access point may couple a WLAN to the Internet, in an example implementation. In such an implementation, a wireless terminal may gain access to a server located on the Internet by communicating with the access point using protocols compatible with an 802.11x standard. In another aspect, an access point may comprise a femtocell utilized to extend cellular telephone service into a business or home. In such an implementation, one or more wireless terminals may communicate with the femtocell via a code division multiple access (CDMA) cellular communication protocol, for example, and the femtocell would provide the wireless terminals access to a larger cellular telecommunication network by way of another broadband network such as the Internet. Of course, these are merely example implementations utilizing one or more wireless terminals and an access point, and the scope of claimed subject matter is not limited in this respect. 
       FIG. 1  is a schematic block diagram of a satellite positioning system (SPS)  110  and a wireless network  120  in communication with a wireless terminal (e.g., wireless terminal  600 ), which may comprise a mobile station, although the scope of claimed subject matter is not limited in this respect. Wireless network  120 , for this example, may provide voice and/or data communication for a number of wireless terminals including wireless terminal  600 , for example, and may further support position estimation for the wireless terminals in addition to providing voice and/or data communication. Wireless network  120  may comprise any of a number of wireless network types. Wireless network  120  for this example comprises terrestrial-based wireless transmitters  132 ,  134 , and  136  that provide communication for a number of wireless terminals such as, for example, wireless terminal  600 . For simplicity, only a few transmitters  132 ,  134 , and  136  are depicted and one wireless terminal  600  is depicted in  FIG. 1 . Of course, other examples may include additional numbers of transmitters and/or wireless terminals, and the configuration of transmitters depicted in  FIG. 1  is merely an example configuration. 
     In an aspect, SPS  110  may comprise a number of satellite vehicles (SVs), for example, SVs  112 ,  114 , and  116 . For an example, SPS  110  may comprise one or more satellite positioning systems, such as GPS, GLONASS and Galileo, although the scope of claimed subject matter is not limited in this respect. In one or more aspects, wireless terminal  600  may receive signals from SVs  112 ,  114 , and  116 , and may communicate with one or more of transmitters  132 ,  134 , and  136 . For example, wireless terminal  600  may obtain one or more measurements from one or more signals received from one or more of the SVs and/or terrestrial transmitters. However, in some circumstances timing signals from an SPS may not be available. In such a circumstance, wireless terminal  600  may gather propagation delay information and/or signal strength information through communication with one or more of wireless transmitters  132 ,  134 , and/or  136 . Wireless terminal  600  may calculate a position location for the wireless terminal based, at least in part, on timing calibration parameters and/or signal strength estimates and/or measurements obtained through communication with one or more of wireless terminals  132 ,  134 , and/or  136 , and further based, at least in part, on known position locations of the wireless terminals. 
     In another aspect, position fix operations may be performed by a network entity such as, for example, location server  140  depicted in  FIG. 1 , rather than at wireless terminal  600 . Such a calculation may be based, at least in part, on information gathered by wireless terminal  600  from one or more of wireless terminals  132 ,  134 , and/or  136  and/or from SVs  112 ,  114 , and/or  116 . In a further aspect, location server  140  may transmit a calculated position estimate to wireless terminal  600 . 
     In an aspect, one or more of wireless transmitters  132 ,  134 , and  136  may further couple wireless terminal  600  to one or more other systems and networks, such as, for example, a public switched telephone network (PSTN), a local area network (LAN), and/or a wide area network such as the Internet, to name merely a few examples. For the example depicted in  FIG. 1 , wireless terminal  600  may access location server  140  by way of transmitter  134 . Location server  140  may collect and format location data, may provide assistance to wireless transmitters for position fix operations, and/or may perform computations to obtain position estimates for the wireless terminals. 
     In an aspect, the locations of one or more wireless transmitters in a wireless system such as wireless network  120  may be reported to a wireless terminal such as wireless terminal  600  by the transmitters themselves. In another aspect, such location information may be provided as part of an almanac, perhaps referred to as a base station almanac, provided by an almanac server entity, over a communication network, for example. 
       FIG. 2  depicts an example trilateration technique for performing a position fix for wireless terminal  600 . For the present example, wireless terminal  600  may receive wireless signals from a number of transmitters. In this example, wireless transmitters  132 ,  134 , and  136  are shown. In other examples, wireless terminal  600  may receive wireless signals from other number of transmitters. In an aspect, to perform a trilateration position fix, signals from three or more wireless transmitters may be received. The respective strengths of the received signals may be measured or otherwise obtained, and the respective signal strengths may be used to estimate a range, or distance, between the wireless transmitters and the wireless terminal. In general, the closer a receiving device is to the transmitter, the stronger the received signal strength. That is, a wireless terminal in relatively close proximity to a transmitter may expect to receive a signal of relatively high signal strength from the transmitter, and a wireless terminal located a greater distance from the transmitter may expect to receive a signal of lower signal strength. Various mathematical models may be utilized to estimate a range between a wireless terminal and a wireless transmitter, and the scope of claimed subject matter is not limited in this respect. 
     In an aspect, a strength of a signal received at a wireless terminal may be measured by the receiving wireless terminal. In another example, a wireless terminal may transmit a signal to an access point and the access point may measure the signal strength of the received signal and return a signal strength value to the wireless terminal. The scope of claimed subject matter is not limited to any particular technique for obtaining a signal strength value for a communication between a transmitter and a terminal. 
     For the present example, as depicted in  FIG. 2 , wireless terminal  600  may receive a transmission from wireless transmitter  132 , and based at least in part on the strength of the received signal, a range “a” may be estimated. Similarly, a range “b” may be estimated between transmitter  134  and wireless terminal  600  based at least in part on a strength of a signal transmitted by transmitter  134 , and a range “c” may be estimated between transmitter  136  and wireless terminal  600  based at least in part on a strength of a signal transmitted by transmitter  136  received at wireless terminal  600 . If the locations of transmitters  132 ,  134 , and  136  are known, as is assumed for the present example, a trilateration technique may be used to determine an intersection point of all of the arcs formed by ranges “a”, “b”, and “c”, and the intersection point may be designated a position fix for wireless terminal  600 . If the positions of transmitters  132 ,  134 , and  136  are accurate, and if respective ranges “a”, “b”, and “c” are accurate, an accurate position fix may be obtained for terminal  600 . However, if any of the reported positions of the transmitters are inaccurate, such inaccuracy may be reflected in the estimated position of a wireless terminal. Similarly, even if the locations of the transmitters are accurate, any inaccuracies in the range estimations between any of the transmitters and wireless terminal  600  may result in an inaccurate position fix. 
     Although examples described herein discuss estimating ranges between transmitting devices and receiving devices based at least in part on signal strength, the scope of claimed subject matter is not limited in this respect. Estimating ranges between transmitting devices and receiving devices based at least in part on signal strength is merely one example technique for estimating and/or measuring such ranges. Other techniques may include, for example, measuring and/or estimating such ranges based at least in part on signal phase and/or signal timing. Again, the scope of claimed subject matter is not limited in theses respects. 
       FIG. 3  depicts a situation where an obstacle  340  is present between wireless terminal  600  and a wireless transmitter  330 , which may result in a situation where a signal strength measurement for a communication between wireless terminal  600  and wireless transmitter  330  may lead to an inaccurate range measurement. For the present example, wireless terminal  600  comprises a mobile station, and wireless transmitter  330  comprises an access point, although the scope of claimed subject matter is not limited in this respect. 
     As mentioned above, if an obstacle is present between a transmitter and a wireless terminal, or if there is some other situation resulting in an attenuation of the signal between the access point and the mobile station, a signal strength attribute reported in a transmission received at a wireless terminal from the transmitter may indicate a range between the transmitter and the wireless terminal that is greater than it really is. Similarly, signal strength values may be measured at the wireless terminal for a transmission received from the transmitter, and a range between the terminal and the transmitter may be estimated based on the measured signal strength. Again, range estimates using such a signal strength indication or measurement in the presence of an obstacle or other signal attenuation situation may be inaccurate, and it follows that mobile station position fixes based on the inaccurate range estimate may also be undesirably inaccurate. Techniques for evaluating a level of confidence for estimated ranges between the mobile station and the access point are discussed more fully below. 
     In an aspect, to determine whether a likely obstacle condition exists, communications between an access point and two or more mobile stations may be analyzed along with one or more communications between the two or more mobile stations to determine whether it appears that an obstacle or any other signal attenuating condition is present between one of the mobile stations and the access point. If such an obstacle or condition is thought to exist, transmissions from that access point may be excluded from position fix operations involving that particular mobile station. Alternatively, the contributions from the access point in the position fix operation may be discounted if an obstacle or other such condition is thought to exist. 
     In an aspect, a determination may be made as to whether a first mobile station and a second mobile station are approximately equidistant to a transmitter. If the first mobile station and the second mobile station are approximately equidistant to a transmitter, a determination may be made as to whether a signal strength indicator for a communication between the first mobile station and the transmitter has a value at least a threshold value lower than a signal strength indicator value for a communication between the second mobile station and the transmitter. If the indicator value for the transmission for the first mobile station is more than a threshold value less than the indicator for the transmission for the second mobile station, it may be assumed that the difference is due to an obstacle or similar signal attenuating condition. In such a situation, transmissions from the transmitter may lead to inaccurate results if utilized in position fix operations involving the first mobile station and, as a result, contributions from this particular transmitter may be filtered with respect to position fix operations related to the first mobile station. That is, the contributions from the transmitter may be excluded, at least in part, from position fix operations related to the first mobile station. 
     In an aspect, in a situation where it is determined that an obstacle may exist between a given wireless terminal and a particular wireless transmitter, communications to or from the transmitter may be excluded from use in position fix operations involving the particular wireless terminal until the obstacle condition no longer exists (perhaps, for example, by the mobile station moving to a different location). In such a situation, if excluding the transmitter in question brings the total number of transmitters available for a position fix operation below an acceptable level (e.g., below three in the example of  FIG. 2 ), the transmitter with the obstacle condition may be replaced by one or more additional transmitters, if available. If adequate numbers of transmitters are not available, the position fix operation may be postponed until such a time as an adequate number is available. In a further aspect, if an obstacle is thought to exist between a given wireless terminal and a particular wireless transmitter, rather than completely excluding contributions involving the particular wireless transmitter in performing a position fix for the given wireless terminal, the contributions from the particular wireless transmitter may be weighted in a manner so as to de-emphasize the contributions from the particular transmitter. This may be helpful in situations where additional transmitters are not available to replace a transmitter with a suspected obstacle, and a position fix may be obtained, although with a diminished level of confidence with respect to accuracy. 
     As used herein, the term access point is meant to include any wireless communication station and/or device used to facilitate communication in a wireless communications system, such as, for example, a wireless local area network, although the scope of claimed subject matter is not limited in this respect. Similarly, the term access point is meant to include a base station that may facilitate wireless communication in a cellular telephone network, for example. Also, as used herein, the terms access point, wireless transmitter, and base station may be used interchangeably, as each term is meant to include any device used to facilitate communication in a wireless communication system. In another aspect, an access point may comprise a wireless local area network (WLAN) access point, for example. Such a WLAN may comprise a network compatible with one or more versions of IEEE standard 802.11 in an aspect, although the scope of claimed subject matter is not limited in this respect. A WLAN access point may provide communication between one or more mobile stations and a network such as the Internet, for example. 
     As used herein, the term mobile station (MS) refers to a device that may from time to time have a position location that changes. The changes in position location may comprise changes to direction, distance, orientation, etc., as a few examples. In particular examples, a mobile station may comprise a cellular telephone, wireless communication device, user equipment, laptop computer, other personal communication system (PCS) device, personal digital assistant (PDA), personal audio device (PAD), portable navigational device, and/or other portable communication devices. A mobile station may also comprise a processing unit and/or computing platform adapted to perform functions controlled by machine-readable instructions. 
     Returning once more to  FIG. 3 , for the present example, the communication system may comprise a wireless system compliant to and/or compatible with one or more versions of IEEE standard 802.11x. Further example wireless communication systems are mentioned, and the scope of claimed subject matter is not limited to any particular wireless network type. 
     As can be seen in  FIG. 3 , the present example system comprises an access point  330  that may facilitate communications between/among mobile stations  600  and  320  and a network  350 . Network  350  for this example may comprise the Internet, but of course the scope of claimed subject matter is not limited in this respect. For the present example, mobile station  600  may comprise a cellular telephone and mobile station  320  may comprise a notebook computer, although it should be noted that these two device types merely represent two examples of mobile station device types, and the scope of claimed subject matter is not limited in this respect. Other example device types are mentioned, although the list presented is not intended to be an exhaustive list, and other device types are possible in other example implementations of the techniques presented herein in accordance with claimed subject matter. 
     Also depicted in  FIG. 3  is obstacle  340 , which for this example may comprise a wall. However, obstacle  340  in this example is meant to represent any type of obstacle and/or any type of condition that would result in an attenuation of a signal transmitted from access point  330  and received by mobile station  600  that is greater than what might be expected in light of an actual range between access point  330  and mobile station  600 . For example, mobile stations  600  and  320  are depicted as being approximately equidistant from access point  330 . A distance, or range, between mobile station  320  and access point  330  may be expressed as a function of an indicated or measured signal strength based on a range model as follows: 
       Distance=Range(signal strength(AP 330 to mobile station))  (1)
 
     where Range( ) indicates a range function utilized to estimate a range or distance from a signal strength value and where signal strength(AP  330  to mobile station) indicates a reported signal strength for a transmission from AP  330  to either of the mobile stations (which for this example are equidistant to AP  330 ). Alternatively, signal strength(AP  330  to mobile station) may represent a signal strength value directly measured at the receiving mobile station. 
     Now, taking obstacle  340  into consideration, a distance between mobile station  600  and access point  330  may be expressed as: 
       Distance=Range(signal strength(AP 330 to mobile station+Δ))  (2)
 
     That is, obstacle  340  introduces an error in the distance measurement from access point  330  to mobile station  600  as compared with the distance measurement from access point  330  to mobile station  320 . 
     In an example implementation, one possible function that may be utilized to determine a range between a transmitting device and a receiving device such as in equations (1) and (2), above, may be represented as: 
     
       
         
           
             
               
                 
                   d 
                   = 
                   
                     
                       
                         P 
                         Tx 
                       
                        
                       
                         
                           
                             G 
                             Tx 
                           
                           × 
                           
                             G 
                             Rx 
                           
                           × 
                           
                             λ 
                             2 
                           
                         
                         
                           16 
                           × 
                           
                             π 
                             2 
                           
                           × 
                           
                             P 
                             Rx 
                           
                           × 
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     where d represents a distance separating a transmitting device and a receiving device, G Tx  represents a transmitting device antenna gain, G Rx  represents a receiving device antenna gain, λ represents a wavelength with units identical to the units used for d, L represents a system loss factor that is greater than or equal to one, P Rx  represents a power for a signal received at the receiving device, and where P Tx  represents a power for the signal transmitted at the transmitting device. Of course, this is merely one example of a function that may be utilized to determine a range between a transmitting device and a receiving device, and the scope of claimed subject matter is not limited in this respect. 
     As noted above, because the signal strength for a communication from access point  330  to mobile station  600  would indicate a range that is greater than the actual range due to obstacle  340 , a position fix operation performed by mobile station  600  based at least in part on a transmission from access point  330  to mobile station  600  may result in an undesirably inaccurate position fix. 
     In an aspect, a received signal strength indicator (RSSI) may be utilized for one or more communications in evaluating the likelihood of an obstacle. RSSI for the examples described herein may comprise an element of versions of IEEE standard 802.11, although the scope of claimed subject matter is not limited in this respect. RSSI may comprise an integer value reported by a receiving device to a transmitting device to indicate a signal strength for a transmission received from the transmitting device. In this manner, mobile station  600  may transmit a signal to access point  330  that may require an acknowledgement transmission from access point  330 , and mobile station  600  may compute an RSSI value from the received acknowledgement transmission. Additionally, AP  330  may calculate an RSSI value from the transmission received from mobile station  600 , and mobile station  600  may receive an RSSI value back from access point  330  in the acknowledgement transmission in response to the transmission from mobile station  600  or in a subsequent transmission. The RSSI value may indicate the signal strength measured at access point  330  for the signal transmitted by mobile station  600 , and mobile station  600  may utilize this value to estimate a range between mobile station  600  and access point  330 . Alternatively, mobile station  600  may utilize the RSSI value calculated from the acknowledgement transmission received from AP  330  to estimate the range between mobile station  600  and access point  330 . Of course, as explained, such an estimate may assume no significant obstacle or other unusual signal attenuating circumstance. Utilizing RSSI in this manner, a distance, or range, between mobile station  320  and access point  330  may be expressed as a function of RSSI based on a range model as follows: 
       Distance=RSSI(RSSI(mobile station to AP))  (4)
 
     where RSSI( ) indicates a range function utilized to estimate a range or distance from a reported RSSI value and where RSSI(mobile station to AP) indicates the reported RSSI value for a previous transmission from mobile station  320  to AP  330 . The “range” function described herein may comprise any process or technique for estimating a range from a signal strength value. 
     Again, taking obstacle  340  into consideration, a distance between mobile station  600  and access point  330  may be expressed as: 
       Distance=RSSI(RSSI(mobile station to AP+Δ))  (5)
 
     where an error term is again introduced to account for obstacle  340 . If the error term exceeds a pre-selected threshold, it may be assumed that an obstacle exists between mobile station  320  and access point  330 , and the contributions of access point  330  to any position fix operations for mobile station  320  may be excluded or otherwise accounted for in performing position fix operations related to mobile station  320 , at least for a period of time. 
     To summarize an example technique, if mobile station  600  and mobile station  320  are approximately equidistant to access point  330 , and if a relatively large difference in signal strength indications exist between communications from mobile station  600  to access point  330  and from mobile station  320  to access point  330 , it may be assumed that the difference is due to an obstacle or a similar signal attenuating condition. In such a situation, transmissions from access point  330  may not be reliable if utilized in position fix operations involving mobile station  320 . 
     The following example processes depicted in the flow charts of  FIGS. 4 and 5  provide additional explanation of the techniques and general principles of example implementations described. In the discussions to follow in connection with  FIGS. 4 and 5 , it may be helpful to refer to  FIG. 3  for improved understanding. 
       FIG. 4  is a schematic block diagram of an example technique for filtering transmissions from a given transmitter for mobile station position estimation operations. At block  410 , a range may be estimated between a first mobile station and an access point. At block  420 , a confidence value related to the estimated range may be determined based, at least in part, on one or more signal attributes associated with wireless communications among the first mobile station, a second mobile station, and the access point. In an aspect, and as described above, such signal attributes may comprise signal strength attributes, although the scope of claimed subject matter is not limited in this respect. For example, determining the confidence value related to the estimated range between a first mobile station and an access point may comprise determining the confidence value based, at least in part, on first, second, and third wireless signal strength values, respectively for a wireless communication between the first mobile station and the access point, between a second mobile station and the access point, and between the first mobile station and the second mobile station. At least in part in response to the confidence value falling below a pre-selected threshold value, the access point may be excluded, or “filtered”, from being used in position fix operations for the first mobile station. In an aspect, filtering the access point may include eliminating the access point completely from position fix operations related to the first mobile station for a period of time or more. In another aspect, contributions from the access point for position fix operations for the first mobile station may be considered to a lesser extent, such as by de-weighting such contributions, for example. Example implementations in accordance with claimed subject matter may include all of, less than, or more than, blocks  410 - 420 . Further, the order of blocks  410 - 420  is merely an example, and the scope of claimed subject matter is not limited in this respect. 
       FIG. 5  is a schematic block diagram of an example process for filtering a signal attribute for a communication from a given transmitter, access point  330  in this example, from use in position estimation operations for a given mobile station, mobile station  600  in this example, referring back to  FIG. 3 . At block  510 , a signal strength may be estimated for a communication between access point  330  and mobile station  600 . The signal strength may be estimated by directly measuring a transmission from access point  330  received at mobile station  600 , or in an additional example the signal strength may be estimated by receiving an RSSI value transmitted by access point  330  in response to a communication transmitted by mobile station  600  to access point  330 . The scope of claimed subject matter is not limited to any particular technique for estimating a signal strength, and example implementations in accordance with claimed subject matter may utilize any technique for estimating a signal strength for a communication between two devices in a wireless communication system. 
     At block  520 , a communication between access point  330  and mobile station  320  may be sniffed by mobile station  600 . As used herein, the term sniff refers to any technique whereby one wireless terminal receives and analyzes in some way a communication intended for another receiving device. For the present example, and as depicted at block  530 , a signal (SIG) field of the communication between access point  330  and mobile station  320  may be decoded to obtain a data rate for the aforementioned communication. Further, as depicted at block  540 , mobile station  600  may estimate a signal strength for a communication between access point  330  and mobile station  320  by performing a look-up to a local data rate/signal strength table. In such an implementation, the values of the data rate/signal strength table would be stored in a memory at mobile station  600  at an earlier point in time, perhaps as part of the manufacturing process. In this manner, if mobile station  600  has access to a data rate for a particular communication, mobile station  600  may estimate the signal strength for that communication as experienced at the receiving device by performing a simple table look-up. At block  550 , the estimated signal strength for the communication between access point  330  and mobile station  320  may be stored in a memory for later retrieval. Also, obtaining the signal strength value for the wireless communication between mobile station  320  and access point  330  may comprise mobile station  600  sniffing the wireless communication to receive an RSSI value included as part of the wireless communication intended for mobile station  320 . 
     In obtaining the data rate for the communication between access point  330  and mobile station  320 , note that mobile station  600  may obtain such information even if mobile station  600  is unable to decode the communication packet due to low RSSI and/or high data rate. This is possible due to the SIG field of the preamble of the packet being sent at the lowest data rate, for an example implementation. Of course, the scope of claimed subject matter is not limited to these specific details. 
     In another aspect of the present example, a signal strength may be obtained by mobile station  320  for a communication transmitted from mobile station  320  to mobile station  600 , as depicted at block  560 . The signal strength for the communication transmitted by mobile station  320  and received at mobile station  600  may provide an indication as to the range or distance between the two mobile stations. If, as indicated in block  560 , the communication is transmitted from mobile station  320  and received at mobile station  600 , the signal strength may be obtained by direct measurement. If, however, mobile station  600  transmits a signal to mobile station  320  and mobile station  320  responds with an RSSI value, the signal strength is reported by mobile station  320 . In either case, for the present example, a range may be estimated between the two mobile stations, for example, based at least in part on a signal strength value for a wireless communication between mobile station  320  and mobile station  600 . Also, obtaining the signal strength value for a wireless communication between the mobile station  600  and mobile station  320  may comprise mobile station  600  sniffing an acknowledge signal transmitted by mobile station  320  and intended for access point  330  to determine the strength value based at least in part on a measured strength of the acknowledge signal as received at mobile station  600 . 
     At block  570 , a determination may be made as to whether the signal strength for the communication between mobile station  320  and mobile station  600  is greater than a pre-selected threshold. At least in part in response to the threshold being reached or exceeded, the process of the present example proceeds to block  580 . Otherwise, no further action is taken, as indicated at block  575 . That is, no action may be taken in this present example if mobile station  320  is not determined to be sufficiently close in range to mobile station  600  to perform the comparisons utilized in the present example with satisfactory results. In another example, at block  570 , a determination may be made as to whether the estimated range between mobile station  320  and mobile station  600  is within a specified threshold. At least in part in response to the threshold not being reached or exceeded, the process proceeds to block  580 . Otherwise, no further action is taken, as indicated at block  575 . 
     Continuing with the present example, at block  580 , a determination may be made as to whether a difference in signal strengths between the communications from access point  330  to mobile station  320  and from access point  330  to mobile station  600  is greater than a pre-selected threshold value. In particular, it may be determined whether a communication between access point  330  and mobile station  600  has a signal strength more than a threshold level lower than the signal strength of a communication between access point  330  and mobile station  320 . If not, no further action is taken, as depicted at block  575 . However, at least in part in response to communication between access point  330  and mobile station  600  having a signal strength more than a threshold level lower than the signal strength of the communication between access point  330  and mobile station  320 , access point  330  may be filtered from use in position fix operations involving mobile station  600  (block  590 ). In this manner, if mobile station  600  and mobile station  320  are determined to be approximately equidistant to access point  330 , and if the signal strength for a communication between mobile station  600  and access point  330  is at least a threshold value lower than the signal strength for a communication between mobile station  320  and access point  330 , transmissions from access point  330  may be excluded, at least in part, from position fix operations involving mobile station  600 . 
     Example implementations in accordance with claimed subject matter may include all, more than, or fewer than blocks  510 - 590 . Further, the order of blocks  510 - 590  is merely an example order, and the scope of claimed subject matter is not limited in this respect. 
       FIG. 6  is a block diagram illustrating example mobile station  600  that may be adapted to perform any of the example techniques described herein related to wireless terminals. One or more transceivers  670  may be adapted to modulate an RF carrier signal with baseband information, such as voice or data, onto an RF carrier, and demodulate a modulated RF carrier to obtain such baseband information. An antenna  672  may be adapted to transmit a modulated RF carrier over a wireless communications link and receive a modulated RF carrier over a wireless communications link. 
     A baseband processing unit  660  may be adapted to provide baseband information from a processing unit (PU)  620  to transceiver  670  for transmission over a wireless communications link. Here, PU  620  may obtain such baseband information from an input device within a user interface  610 . Baseband processing unit  660  may also be adapted to provide baseband information from transceiver  670  to PU  620  for transmission through an output device within user interface  610 . 
     User interface  610  may comprise a plurality of devices for inputting or outputting user information such as voice or data. Such devices may include, by way of non-limiting examples, a keyboard/keypad, a display/touch screen, a microphone, and a speaker. 
     Transceiver  670  may provide demodulated information to correlator  640 . Correlator  640  may be adapted to derive beacon-related correlation functions from information relating to beacon signals provided by transceiver  670 . This information may be used by mobile station  600  to acquire wireless communications services, for example from a wireless access point such as access point  330 . Channel decoder  650  may be adapted to decode channel symbols received from baseband processing unit  660  into underlying source bits. In one example where channel symbols comprise convolutionally encoded symbols, such a channel decoder may comprise a Viterbi decoder. In a second example, where channel symbols comprise serial or parallel concatenations of convolutional codes, channel decoder  650  may comprise a turbo decoder. 
     Memory  630  may be adapted to store machine-readable instructions which are executable to perform one or more of processes, implementations, and/or examples thereof which are described and/or suggested herein. PU  620  may be adapted to access and execute such machine-readable instructions, thereby enabling mobile station  600  to perform one or more of the processes, implementations, and/or examples described and/or suggested herein, for example, in connection with  FIGS. 1-5 . Of course, mobile station  600  is merely an example, and the scope of claimed subject matter is not limited to the specific configuration of components and/or functional units depicted. 
       FIG. 7  is a schematic diagram illustrating a system that may include one or more devices adapted or adaptable to implement techniques and/or processes described, for example, in connection with example techniques depicted in  FIGS. 1-6 . System  700  may include, for example, a mobile station  702 , an access point  704 , and a mobile station  706 . Mobile stations  702  and  706  may communicate with access point  704  via antenna  708  of access point  704 . 
     Although devices  702  and  706  are depicted as mobile stations, these are merely examples of wireless terminals that may be representative of any device, appliance or machine that may be configurable to exchange data over a wireless communications network. By way of example but not limitation, access point  704  may comprise a stand-alone device including one or more radios, or access point  704  may be implemented as at least a portion of one or more computing devices and/or platforms, such as, e.g., a desktop computer, a laptop computer, a workstation, a server device, or the like, although the scope of claimed subject matter is not limited in this respect. Mobile stations  702  and/or  706  may comprise one or more personal computing or communication devices or appliances, such as, e.g., a personal digital assistant, mobile communication device, or the like. 
     Similarly, the wireless communications depicted between access point  704  and mobile stations  702  and  706 , as shown in  FIG. 7 , is representative of any communication links, processes, and/or resources configurable to support the wireless exchange of data between access point  704  and one or more of mobile stations  702  and  706 . As illustrated, for example, by the dashed lined box illustrated as being partially obscured by mobile station  706 , there may be additional like devices establishing wireless communications with access point  704 . 
     It is recognized that all or part of the various devices and networks, for example, shown in  FIGS. 3 and 7 , and the processes and techniques as further described herein, may be implemented using or otherwise including hardware, firmware, software, or any combination thereof. 
     Thus, by way of example but not limitation, access point  704  may include at least one processing unit  720  that is operatively coupled to memory  722  through bus  728 . 
     Processing unit  720  is representative of one or more circuits configurable to perform at least a portion of a data computing procedure or process. By way of example but not limitation, processing unit  720  may include one or more processors, controllers, microprocessors, microcontrollers, application specific integrated circuits (ASICs), digital signal processors, programmable logic devices, field programmable gate arrays, and the like, or any combination thereof. 
     Memory  722  is representative of any data storage mechanism. Memory  722  may include, for example, primary memory  724  and/or secondary memory  726 . Primary memory  724  may include, for example, a random access memory, read only memory, etc. While illustrated in this example as being separate from processing unit  720 , it should be understood that all or part of primary memory  724  may be provided within or otherwise co-located/coupled with processing unit  720 . 
     Secondary memory  726  may include, for example, the same or similar type of memory as primary memory and/or one or more data storage devices or systems, such as, for example, a disk drive, an optical disc drive, a tape drive, a solid state memory drive, etc. In certain implementations, secondary memory  726  may be operatively receptive of, or otherwise configurable to couple to, computer-readable medium  740 . Computer-readable medium  740  may include, for example, any medium that can carry and/or make accessible data, code and/or instructions for one or more of the devices in system  700 . Computer-readable medium  740  may also be referred to as storage medium. 
     Access point  704  may further include, for example, communication interface  730  that provides for or otherwise supports wireless communication with one or more wireless terminals such as mobile stations  702  and  706 . Communication interface  730  may further support communication with a wired network such as the Internet as depicted in  FIG. 7 . By way of example but not limitation, communication interface  730  may include a network interface device or card, a modem, a router, a switch, a transceiver, a process, and/or the like. 
     The methodologies described herein may be implemented by various means depending upon applications according to particular examples. For example, such methodologies may be implemented in hardware, firmware, software, and/or combinations thereof. In a hardware implementation, for example, a processing unit may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other devices designed to perform the functions described herein, and/or combinations thereof. 
     For an implementation involving firmware and/or software, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory and executed by a processing unit. Memory may be implemented within the processing unit or external to the processing unit. As used herein the term “memory” refers to any type of long term, short term, volatile, nonvolatile, or other memory and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored. 
     If implemented in firmware and/or software, the functions may be stored as one or more instructions or code on a computer-readable medium. Examples include computer-readable media encoded with a data structure and computer-readable media encoded with a computer program. Computer-readable medium may comprise an article of manufacture. Computer-readable media includes physical computer storage media. A storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, semiconductor storage, or other storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer; disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     In addition to storage on computer-readable medium, instructions and/or data may be provided as signals on transmission media included in a communication apparatus. For example, a communication apparatus may include a transceiver having signals indicative of instructions and data. The instructions and data are configured to cause one or more processing units to implement the functions outlined in the claims. That is, the communication apparatus includes transmission media with signals indicative of information to perform disclosed functions. At a first time, the transmission media included in the communication apparatus may include a first portion of the information to perform the disclosed functions, while at a second time the transmission media included in the communication apparatus may include a second portion of the information to perform the disclosed functions. 
     “Instructions” as referred to herein relate to expressions which represent one or more logical operations. For example, instructions may be “machine-readable” by being interpretable by a machine for executing one or more operations on one or more data objects. However, this is merely an example of instructions and claimed subject matter is not limited in this respect. In another example, instructions as referred to herein may relate to encoded commands which are executable by a processing circuit having a command set which includes the encoded commands. Such an instruction may be encoded in the form of a machine language understood by the processing circuit. Again, these are merely examples of an instruction and claimed subject matter is not limited in this respect. 
     “Storage medium” as referred to herein relates to media capable of maintaining expressions which are perceivable by one or more machines. For example, a storage medium may comprise one or more storage devices for storing machine-readable instructions and/or information. Such storage devices may comprise any one of several media types including, for example, magnetic, optical or semiconductor storage media. Such storage devices may also comprise any type of long term, short term, volatile or non-volatile memory devices. However, these are merely examples of a storage medium, and claimed subject matter is not limited in these respects. 
     Some portions of the detailed description included herein are presented in terms of algorithms or symbolic representations of operations on binary digital signals stored within a memory of a specific apparatus or special purpose computing device or platform. In the context of this particular specification, the term specific apparatus or the like includes a general purpose computer/processing unit once it is programmed to perform particular operations pursuant to instructions from program software. Algorithmic descriptions or symbolic representations are examples of techniques used by those of ordinary skill in the signal processing or related arts to convey the substance of their work to others skilled in the art. An algorithm is here, and generally, considered to be a self-consistent sequence of operations or similar signal processing leading to a desired result. In this context, operations or processing involve physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared or otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals, or the like. It should be understood, however, that all of these or similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless specifically stated otherwise, as apparent from the discussion herein, it is appreciated that throughout this specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining” or the like refer to actions or processes of a specific apparatus, such as a special purpose computer or a similar special purpose electronic computing device. In the context of this specification, therefore, a special purpose computer or a similar special purpose electronic computing device is capable of manipulating or transforming signals, typically represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the special purpose computer or similar special purpose electronic computing device. 
     Wireless communication techniques described herein may be in connection with various wireless communication networks such as a wireless wide area network (WWAN), a wireless local area network (WLAN), a wireless personal area network (WPAN), and so on. The term “network” and “system” may be used interchangeably herein. A WWAN may be a Code Division Multiple Access (CDMA) network, a Time Division Multiple Access (TDMA) network, a Frequency Division Multiple Access (FDMA) network, an Orthogonal Frequency Division Multiple Access (OFDMA) network, a Single-Carrier Frequency Division Multiple Access (SC-FDMA) network, a Long Term Evolution (LTE) network, a WiMAX (IEEE 802.16) network, or any combination of the above networks, and so on. A CDMA network may implement one or more radio access technologies (RATs) such as cdma2000, Wideband-CDMA (W-CDMA), to name just a few radio technologies. Here, cdma2000 may include technologies implemented according to IS-95, IS-2000, and IS-856 standards. A TDMA network may implement Global System for Mobile Communications (GSM), Digital Advanced Mobile Phone System (D-AMPS), or some other RAT. GSM and W-CDMA are described in documents from a consortium named “3rd Generation Partnership Project” (3GPP). Cdma2000 is described in documents from a consortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available. A WLAN may comprise an IEEE 802.11x network, and a WPAN may comprise a Bluetooth network, an IEEE 802.15x network, for example. Wireless communication implementations described herein may also be used in connection with any combination of WWAN, WLAN and/or WPAN. 
     A satellite positioning system (SPS) typically includes a system of transmitters positioned to enable entities to determine their location on or above the Earth based, at least in part, on signals received from the transmitters. Such a transmitter typically transmits a signal marked with a repeating pseudo-random noise (PN) code of a set number of chips and may be located on ground based control stations, user equipment and/or space vehicles. In a particular example, such transmitters may be located on Earth orbiting satellite vehicles (SVs). For example, a SV in a constellation of Global Navigation Satellite System (GNSS) such as Global Positioning System (GPS), Galileo, Glonass or Compass may transmit a signal marked with a PN code that is distinguishable from PN codes transmitted by other SVs in the constellation (e.g., using different PN codes for each satellite as in GPS or using the same code on different frequencies as in Glonass). In accordance with certain aspects, the techniques presented herein are not restricted to global systems (e.g., GNSS) for SPS. For example, the techniques provided herein may be applied to or otherwise enabled for use in various regional systems, such as, e.g., Quasi-Zenith Satellite System (QZSS) over Japan, Indian Regional Navigational Satellite System (IRNSS) over India, Beidou over China, etc., and/or various augmentation systems (e.g., an Satellite Based Augmentation System (SBAS)) that may be associated with or otherwise enabled for use with one or more global and/or regional navigation satellite systems. By way of example but not limitation, an SBAS may include an augmentation system(s) that provides integrity information, differential corrections, etc., such as, e.g., Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Multi-functional Satellite Augmentation System (MSAS), GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN), and/or the like. Thus, as used herein an SPS may include any combination of one or more global and/or regional navigation satellite systems and/or augmentation systems, and SPS signals may include SPS, SPS-like, and/or other signals associated with such one or more SPS. 
     As used herein, a mobile station (MS) refers to a device such as a cellular or other wireless communication device, personal communication system (PCS) device, personal navigation device (PND), Personal Information Manager (PIM), Personal Digital Assistant (PDA), laptop or other suitable mobile device which is capable of receiving wireless communication and/or navigation signals. The term “mobile station” is also intended to include devices which communicate with a personal navigation device (PND), such as by short-range wireless, infrared, wireline connection, or other connection—regardless of whether satellite signal reception, assistance data reception, and/or position-related processing occurs at the device or at the PND. Also, “mobile station” is intended to include all devices, including wireless communication devices, computers, laptops, etc. which are capable of communication with a server, such as via the Internet, Wi-Fi, or other network, and regardless of whether satellite signal reception, assistance data reception, and/or position-related processing occurs at the device, at a server, or at another device associated with the network. Any operable combination of the above are also considered a “mobile station.” 
     The terms, “and,” “and/or,” and “or” as used herein may include a variety of meanings that will depend at least in part upon the context in which it is used. Typically, “and/or” as well as “or” if used to associate a list, such as A, B or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B or C, here used in the exclusive sense. Reference throughout this specification to “one example” or “an example” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of claimed subject matter. Thus, the appearances of the phrase “in one example” or “an example” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in one or more examples. Examples described herein may include machines, devices, engines, or apparatuses that operate using digital signals. Such signals may comprise electronic signals, optical signals, electromagnetic signals, or any form of energy that provides information between locations. 
     While there has been illustrated and described what are presently considered to be example features, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from claimed subject matter. Additionally, many modifications may be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular examples disclosed, but that such claimed subject matter may also include all aspects falling within the scope of the appended claims, and equivalents thereof.