Abstract:
Apparatus having corresponding methods and tangible computer-readable media comprise: a measurement module adapted to generate measurements of a wireless television signal received by the apparatus and measurements of a wireless satellite positioning signal received by the apparatus; a location module adapted to determine a location of the apparatus based on the measurements of the wireless television signal and the measurements of the wireless satellite positioning signal; and a time module adapted to provide a clock control signal for the apparatus based on at least one of the measurements of the wireless television signal, and the measurements of the wireless satellite positioning signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a CIP of 10/867,577 Jun. 14, 2004 
         [0002]    which is a CIP of 10/210,847 Jul. 31, 2002 now 6,861,984 
         [0003]    which is a CIP of 09/887,158 Jun. 21, 2001 ABN 
         [0004]    which claims the benefit of 60/265,675 Feb. 2, 2001 
         [0005]    which claims the benefit of 60/281,270 Apr. 3, 2001 
         [0006]    which claims the benefit of 60/281,269 Apr. 3, 2001 
         [0007]    which claims the benefit of 60/293,812 May 25, 2001 
         [0008]    which claims the benefit of 60/293,813 May 25, 2001 
         [0009]    which claims the benefit of 60/293,646 May 25, 2001. 
         [0010]    This application is a CIP of 11/068,570 Feb. 28, 2005 
         [0011]    which is a CIP of 09/932,010 Aug. 17, 2001 now 7,126,536 
         [0012]    and which is a CIP of 10/159,478 May 31, 2002 now 7,463,195. 
         [0013]    This application is a CIP of 11/284,800 Nov. 22, 2005 
         [0014]    which is a CIP of 10/054,302 Jan. 22, 2002 now 6,559,800. 
         [0015]    This application is a CIP of 12/263,731 Nov.  3 ,  2008 . 
         [0016]    This application is a CIP of 12/117,676 May  8 ,  2008 . 
         [0017]    This application is a CIP of 12/209,971 Sep. 12, 2008. 
         [0018]    This application claims the benefit of 61/058,281 Jun.  3 ,  2008 . 
         [0019]    This application claims the benefit of 61/075,160 Jun. 24, 2008. 
         [0020]    This application claims the benefit of 61/105,063 Oct. 14, 2008. 
         [0021]    The disclosures of all of the above are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0022]    The present disclosure relates generally to the determination of frequency, location and time. More particularly, the present disclosure relates to determining frequency, location and time based on television signals, satellite positioning signals, signals of opportunity, and the like. This knowledge of frequency, location and time has many applications. For example, knowledge of frequency, location and time can be used to fulfill the requirements of consumer wireless mobile telephone base stations referred to as “femtocells.” 
         [0023]    Wireless mobile telephones are gaining in popularity. However, many consumers have retained their conventional wired telephones, in part due to their superior reliability compared to wireless mobile telephones. In particular, wireless mobile telephone signals are often attenuated or blocked inside buildings, leading to dropped calls, reduced data rates, and the like. 
         [0024]    To address these reliability problems, consumer wireless mobile telephone base stations, referred to as “femtocells,” are being introduced to the marketplace.  FIG. 1  shows a prior art wireless mobile telephone system  100  that includes a femtocell  102 . Referring to  FIG. 1 , wireless mobile telephone system  100  also includes a “macrocell”  104 , which includes a conventional wireless mobile telephone antenna  106  and a conventional wireless mobile telephone base station  108 , which is in turn connected to the public switched telephone network (PSTN)  110 . 
         [0025]    Femtocell  102  also includes a conventional wireless mobile telephone antenna  128 . Femtocell  102  is generally connected to PSTN  110  by a broadband connection to the Internet  114 . A wireless mobile telephone  116  can communicate with other telephones connected to PSTN  110  by exchanging wireless mobile telephone signals  118  with macrocell  104  and femtocell  102 . 
         [0026]    A key requirement for any sort of base station, whether it be a macrocell  104  or a femtocell  102 , is precise knowledge of frequency and time. This knowledge is required to synchronize the bases stations, which otherwise would interfere with each other. In addition, precise knowledge of time is required for operations such as handovers from one base station to another. The precise determination of time in turn involves precise knowledge of location. 
         [0027]    The information required for this precise determination of time and location is generally acquired from satellite positioning systems such as the Global Positioning System (GPS). Referring again to  FIG. 1 , GPS satellites  120  provide GPS signals  122  that can be used to obtain precise knowledge of time and location. Base stations generally include GPS antennas to obtain GPS signals  122 . In system  100 , macrocell  104  includes a GPS antenna  124 , and femtocell  102  includes a GPS antenna  126 . 
         [0028]    Conventional femtocells rely upon GPS signals to obtain precise knowledge of time and location. However, GPS signals are often attenuated or blocked indoors, where femtocells are usually deployed. The required GPS signals can only be obtained by locating the femtocell near a window with a suitable view of the GPS satellites, connecting an expensive GPS antenna to the femtocell, and the like. 
       SUMMARY 
       [0029]    In general, in one aspect, an embodiment features an apparatus comprising: a measurement module adapted to generate measurements of a wireless television signal received by the apparatus and measurements of a wireless satellite positioning signal received by the apparatus; a location module adapted to determine a location of the apparatus based on the measurements of the wireless television signal and the measurements of the wireless satellite positioning signal; and a time module adapted to provide a clock control signal for the apparatus based on at least one of the measurements of the wireless television signal, and the measurements of the wireless satellite positioning signal. 
         [0030]    Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise an oscillator adapted to provide one or more clock signals based on the clock control signal. Some embodiments comprise a receiver adapted to receive the wireless television signal and the wireless satellite positioning signal. Some embodiments comprise a transceiver adapted to transceive wireless mobile telephone signals based at least one of the clock signals. Some embodiments comprise a time base module adapted to provide a periodic time base signal based on one or more of the clock signals; wherein the transceiver is further adapted to transceive the wireless mobile telephone signals based on the periodic time base signal. Some embodiments comprise a network interface adapted to transceive network signals representing the wireless mobile telephone signals. 
         [0031]    In general, in one aspect, an embodiment features a method comprising: generating measurements of a wireless television signal received by an apparatus and measurements of a wireless satellite positioning signal received by the apparatus; determining a location of the apparatus based on the measurements of the wireless television signal and the measurements of the wireless satellite positioning signal; and providing a clock control signal for the apparatus based on at least one of the measurements of the wireless television signal, and the measurements of the wireless satellite positioning signal. 
         [0032]    Embodiments of the method can include one or more of the following features. Some embodiments comprise providing one or more clock signals based on the clock control signal. Some embodiments comprise receiving the wireless television signal and the wireless satellite positioning signal. Some embodiments comprise transceiving wireless mobile telephone signals based at least one of the clock signals. Some embodiments comprise providing a periodic time base signal based on one or more of the clock signals; and transceiving the wireless mobile telephone signals based on the periodic time base signal. Some embodiments comprise transceiving network signals representing the wireless mobile telephone signals. 
         [0033]    In general, in one aspect, an embodiment features tangible computer-readable media embodying instructions executable by a computer to perform a method comprising: generating measurements of a wireless television signal received by an apparatus and measurements of a wireless satellite positioning signal received by the apparatus; determining a location of the apparatus based on the measurements of the wireless television signal and the measurements of the wireless satellite positioning signal; and causing the apparatus to provide a clock control signal for the apparatus based on at least one of the measurements of the wireless television signal, and the measurements of the wireless satellite positioning signal. 
         [0034]    Embodiments of the tangible computer-readable media can include one or more of the following features. In some embodiments, the method further comprises: causing the apparatus to provide one or more clock signals based on the clock control signal. In some embodiments, the method further comprises: causing the apparatus to transceive wireless mobile telephone signals based at least one of the clock signals. In some embodiments, the method further comprises: causing the apparatus to provide a periodic time base signal based on one or more of the clock signals; and causing the apparatus to transceive the wireless mobile telephone signals based on the periodic time base signal. In some embodiments, the method further comprises: causing the apparatus to transceive network signals representing the wireless mobile telephone signals. 
         [0035]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0036]      FIG. 1  shows a prior art wireless mobile telephone system that includes a femtocell. 
           [0037]      FIG. 2  shows elements of a wireless mobile telephone system that includes a femtocell according to embodiments of the present disclosure. 
           [0038]      FIG. 3  shows elements of the femtocell of  FIG. 2  according to embodiments of the present disclosure. 
           [0039]      FIG. 4  shows a process for wireless mobile telephone system of  FIGS. 2 and 3  according to embodiments of the present disclosure. 
           [0040]      FIG. 5  shows a process for setting the frequency of the femtocell oscillator of  FIG. 3  according to embodiments of the present disclosure. 
           [0041]      FIG. 6  shows a process for the femtocell of  FIGS. 2 and 3  to obtain knowledge of absolute time according to embodiments of the present disclosure. 
           [0042]      FIG. 7  shows a process for the femtocell of  FIGS. 2 and 3  to determine its location according to embodiments of the present disclosure. 
           [0043]      FIG. 8  shows a frame matching process for the femtocell of  FIGS. 2 and 3  according to embodiments of the present disclosure. 
           [0044]      FIG. 9  shows a process for the femtocell of  FIGS. 2 and 3  to acquire precise timing according to embodiments of the present disclosure. 
       
    
    
       [0045]    The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
       DETAILED DESCRIPTION 
       [0046]    Embodiments of the present disclosure provide precise determination of location and time based on television signals, satellite positioning signals, signals of opportunity, and the like, for use in consumer wireless mobile telephone base stations referred to as “femtocells.” 
         [0047]    Embodiments of the present disclosure are described in terms of the use of DTV and GPS signals. However, if GPS signals are not available, DTV signals can be used alone or in combination with other signals, herein referred to collectively as signals of opportunity. The DTV signals can include, for example, Advanced Television Systems Committee DTV (ATSC) signals, Digital Video Broadcasting (DVB) DTV signals, Integrated Services Digital Broadcasting (ISDB) DTV signals, and the like. The signals of opportunity can include, for example, mobile telephone signals, analog TV signals, Digital Audio Broadcast (DAB) signals, VHF Omni-directional Radio (VOR) signals, FM radio signals, and the like. 
         [0048]      FIG. 2  shows elements of a wireless mobile telephone system  200  that includes a femtocell  202  according to embodiments of the present disclosure. Although in the described embodiments, the elements of wireless mobile telephone system  200  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, the elements of wireless mobile telephone system  200  can be implemented in hardware, software, or combinations thereof. 
         [0049]    Referring to  FIG. 2 , wireless mobile telephone system  200  also includes a “macrocell”  204 , which includes a conventional wireless mobile telephone antenna  206  and a conventional wireless mobile telephone base station  208 , which is in turn connected to the public switched telephone network (PSTN)  210 . 
         [0050]    Femtocell  202  also includes a conventional wireless mobile telephone antenna  228 . Femtocell  202  is generally connected to PSTN  210  by a broadband connection to the Internet  214 , although other sorts of connections can be used instead. A wireless mobile telephone  216  can communicate with other telephones connected to PSTN  210  by exchanging wireless mobile telephone signals  218  with macrocell  204  and femtocell  202 . 
         [0051]    In order to obtain wireless GPS signals  222 , macrocell  204  includes a GPS antenna  224 , and femtocell  202  includes a GPS antenna  226 . Femtocell  202  also includes a digital television (DTV) antenna  248  in order to obtain wireless DTV signals  230  transmitted by DTV transmitters  232 . Femtocell  202  can also include additional antennas  234  in order to obtain other signals such as signals of opportunity  236  and the like. 
         [0052]    Wireless mobile telephone system  200  also includes one or more monitor units  238  and one or more femtocell servers  240 . Each monitor unit  238  includes a GPS antenna  244  to obtain wireless GPS signals  222  and a DTV antenna  246  to obtain wireless DTV signals  230 . Each monitor unit  238  can also include additional antennas  234  to obtain other signals such as signals of opportunity  236  and the like. Femtocell  202 , monitor units  238 , and femtocell servers  240  can communicate using Internet  214 , by other techniques, by combinations thereof, and the like. 
         [0053]      FIG. 3  shows elements of femtocell  202  of  FIG. 2  according to embodiments of the present disclosure. Although in the described embodiments, the elements of femtocell  202  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, the elements of femtocell  202  can be implemented in hardware, software, or combinations thereof. 
         [0054]    Referring to  FIG. 3 , femtocell  202  includes a receiver  302 , a measurement module  304 , a time module  306 , an oscillator  308 , a location module  310 . Receiver  302  includes a DTV radio-frequency (RF) module  320 , a DTV baseband (BB) module  322 , a GPS RF module  324 , and a GPS baseband module  326 . Femtocell  202  can also include a time base module  328 . Femtocell  202  also includes a wireless mobile telephone transceiver  312 , a network interface  314  in communication with Internet  214 , and a communications module  316  to provide communications between wireless mobile telephone transceiver  312  and network interface  314 . Femtocell  202  also includes wireless mobile telephone antenna  228 , GPS antenna  226 , and DTV antenna  248 . 
         [0055]    Receiver  302 , wireless mobile telephone transceiver  312 , and network interface  314  can be implemented according to conventional techniques. Measurement module  304 , time module  306 , and time base module  328  can be implemented as a digital signal processor. The digital signal processor can be implemented as a field-programmable gate array (FPGA), which can also include DTV baseband module  322  and GPS baseband module  326 . Location module  310  and communications module  316  can be implemented as software executing on a processor. Oscillator  308  can be implemented as a voltage-controlled temperature-compensated crystal oscillator (VCTCXO). 
         [0056]      FIG. 4  shows a process  400  for wireless mobile telephone system  200  of  FIGS. 2 and 3  according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  400  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  400  can be executed in a different order, concurrently, and the like. 
         [0057]    Referring to  FIG. 4 , femtocell  202  acquires precise frequency (step  402 ). In particular, time module  306  of femtocell  202  provides a clock control signal  330  for oscillator  308  of femtocell  202  based on one or more wireless DTV signals  230  received by femtocell  202 . 
         [0058]      FIG. 5  shows a process  500  for controlling the frequency of femtocell oscillator  308  of  FIG. 3  according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  500  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  500  can be executed in a different order, concurrently, and the like. 
         [0059]    Referring to  FIG. 5 , measurement module  304  of femtocell  202  measures the pilot frequency offset (PFO) of one or more DTV channels (step  502 ). Monitor unit  238  measures the PFO of the same DTV channels (step  504 ). Femtocell server  240  acquires the measurements made by monitor unit  238  (step  506 ). Femtocell  202  requests the measurements made by monitor unit  238  from femtocell server  240  (step  508 ). Femtocell  202  responds by sending the measurements to femtocell  202  (step  510 ). 
         [0060]    Femtocell  202  sets the frequency of oscillator  308  according to the PFO measurements (step  510 ). In particular, for each of the DTV channels, time module  306  of femtocell  202  determines the difference between the PFO measured by femtocell  202  and the PFO measured by monitor unit  238 . The PFO differences are used to generate clock control signal  330 , which sets the frequency of oscillator  308 . In some embodiments, clock control signal  330  is implemented as a pulse-width modulated signal. Based on clock control signal  330 , oscillator  308  provides one or more clock signals  332 . 
         [0061]    In some embodiments, femtocell  202  includes a time base module  328  that provides a time base signal  334  based on one or more of clock signals  332 . For example, time base signal  334  can take the form of a pulse-per-second waveform that accurately provides one pulse each second. Time base signal  334  is useful for wireless telephone technologies such as time division multiple access (TDMA) and the like. The phase of time base signal  334  is set according to absolute time, which can be acquired by femtocell  202  as described below. 
         [0062]    Referring again to  FIG. 4 , after acquiring precise frequency, femtocell  202  obtains knowledge of rough absolute time (step  404 ).  FIG. 6  shows a process  600  for femtocell  202  of  FIGS. 2 and 3  to obtain knowledge of rough absolute time according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  600  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  600  can be executed in a different order, concurrently, and the like. 
         [0063]    Referring to  FIG. 6 , each monitor unit  238  obtains knowledge of absolute time (step  602 ). For example, monitor units  238  can be locked to GPS time using GPS signals  222 . Each femtocell server  240  obtains knowledge of rough absolute time from one or more monitor units  238 . For example, femtocell server  240  requests rough absolute time by sending a message to a monitor unit  238  (step  604 ), and monitor unit  238  responds with a message indicating rough absolute time (step  606 ). Femtocell server  240  then determines rough absolute time according to the messages. The determination can account for the time of transit of the messages. For example, the messages can be implemented according to Network Time Protocol (NTP) or the like. 
         [0064]    Femtocell  202  acquires knowledge of rough absolute time from femtocell server  240 . For example, femtocell  202  requests rough absolute time by sending a message to a femtocell server  240  (step  608 ), and femtocell server  240  responds with a message indicating rough absolute time (step  610 ). For example, femtocell  202  can acquire knowledge of rough absolute time from femtocell server  240  in the manner described above for femtocell server  240 . In some embodiments, femtocell  202  acquires knowledge of rough absolute time only during initialization. In other embodiments, femtocell  202  acquires knowledge of rough absolute time at other times. 
         [0065]    Referring again to  FIG. 4 , after acquiring knowledge of rough absolute time, femtocell  202  then determines the location of femtocell  202  (step  406 ). In some embodiments, femtocell  202  determines its location only during initialization. In other embodiments, femtocell  202  determines its location at other times as well. 
         [0066]      FIG. 7  shows a process  700  for femtocell  202  of  FIGS. 2 and 3  to determine its location according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  700  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  700  can be executed in a different order, concurrently, and the like. 
         [0067]    Embodiments of the present disclosure employ DTV signals  230  to determine the location of femtocell  202  with a high degree of precision by generating pseudoranges based on known digital sequences repeated within the DTV signals  230 . In some cases, this requires resolution of ambiguities associated with these signals. For example, ambiguities of 24.2 ms are associated with measurements of the PN511 sequence present in the ATSC DTV signal. Fine timing knowledge can be used to resolve these ambiguities. Femtocell  202  can obtain this fine timing knowledge by one or more techniques. Two such techniques are described below. Other techniques can be used, either alone or in combination. 
         [0068]    In some embodiments, when both ATSC and NTSC TV signals are present, femtocell  202  can employ the beat frequency of the two TV signals to obtain fine timing knowledge. Further details of this technique are provided in U.S. patent application Ser. No. 12/117,676 filed May 8, 2008 and entitled “Reliable Positioning and Time Transfer Using Television Synchronization Signals,” the disclosure thereof incorporated by reference herein in its entirety. 
         [0069]    In some embodiments, femtocell  202  employs a technique referred to herein as “frame matching,” which does not require the use of NTSC TV signals.  FIG. 8  shows a frame matching process  800  for femtocell  202  of  FIGS. 2 and 3  according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  800  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  800  can be executed in a different order, concurrently, and the like. 
         [0070]    According to frame matching, referring to  FIG. 8 , DTV program data is captured by both monitor unit  238  (step  802 ) and femtocell  202  (step  804 ). Femtocell  202  acquires the DTV program data captured by monitor unit  238 . For example, monitor unit  238  pushes the captured data to femtocell server  240  (step  806 ), and, in reply to a request for the data (step  808 ), femtocell server  240  sends the data to femtocell  202  (step  810 ). Femtocell  202  then obtains fine timing knowledge by matching the program data captured by femtocell  202  to the program data captured by monitor unit  238  (step  812 ). Further details of this technique are provided in U.S. patent application Ser. No. 12/209,971 filed Sep. 12, 2008 and entitled “Location Identification Service Based on Broadcast Digital and Analog Television Signals” and U.S. Provisional Patent Application Ser. No. 61/105,063 filed Oct. 14, 2008 and entitled “Hybrid Absolute Time Transfer Methods,” the disclosures thereof incorporated by reference herein in their entirety. 
         [0071]    Referring now to  FIG. 7 , DTV signals  230  and GPS signals  222  are measured both by monitor unit  238  (step  702 ) and by measurement module  304  of femtocell  202  (step  704 ). For monitor unit  238 , the measurements of DTV signals  230  can include, for each of the DTV channels observed, the pilot frequency offset (PFO), the fractional symbol rate offset (FSRO), which is also sometimes referred to as the fractional code rate offset (FCRO), and a time of transmission (TOT) of a component of the respective DTV signal from DTV transmitter  232 . For example, the component of an ATSC DTV signal can be the embedded PN511 sequence, and the FSRO can be measured by determining the rate of repetition of the PN511 sequence. 
         [0072]    For femtocell  202 , the measurements of DTV signals  230  can include, for each of the DTV channels observed, the pilot frequency offset (PFO) and a time of reception (TOR) of a component of the respective DTV signal at femtocell  202 . The measurements of GPS signals  222  can include ionospheric delay model parameters, and satellite ephemeris for each GPS satellite  220  in view. 
         [0073]    All of these measurements can be collected by a single monitor unit  238 . If the monitor units  238  have a common time base, some of the measurements can be captured by each of a plurality of monitor units  238 . For example, monitor units  238  can be locked to GPS time. Further details of monitor units  238  are provided in U.S. Pat. No. 7,471,244 issued Dec. 30, 2008 and entitled “Monitor Units for Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. Femtocell  202  can decode the ionospheric delay model parameters and satellite ephemeris for GPS satellites  220  when the GPS signals are received with sufficient power. Alternatively, the ionospheric delay model parameters and the ephemerides received by monitor unit  238  can be sent to femtocell  202 . 
         [0074]    Femtocell  202  acquires the measurements of DTV signals  230  and GPS signals  222  from one or more monitor units  238 . For example, each monitor unit  238  time-tags its measurements, and pushes the time-tagged measurements to femtocell server  240  (step  706 ). Subsequently, femtocell  202  requests one or more of the time-tagged measurements from femtocell server  240  (step  708 ). In response to the request, femtocell server  240  identifies the most recent time-tagged measurements based on the time tags and the local clock of femtocell server  240 , and sends the time-tagged measurements to femtocell  202  (step  710 ). 
         [0075]    After acquiring the measurements of DTV signals  230  and GPS signals  222  from one or more monitor units  238 , location module  310  of femtocell  202  determines the location of femtocell  202  based on the measurements of DTV signals  230  and GPS signals  222 . In particular, location module  310  generates a pseudorange based on each of the signals  230 ,  222  (step  712 ). For each GPS signal  222  used, a pseudorange can be obtained according to conventional techniques. 
         [0076]    For each DTV signal  230  used, the location determination involves the fractional symbol rate offset (FSRO) and time of transmission (TOT) measured by monitor unit  238 , and the time of reception (TOR) measured by femtocell  202 . The TOR of each DTV signal  230  can be determined using correlation techniques, for example by correlating the PN511 sequence of a captured ATSC DTV signal with a stored PN511 sequence. The correlation peak indicates the TOR of the DTV signal  230 . Each DTV pseudorange is then generated by taking the difference between the TOR and TOT for one of the DTV signals. Further details of this technique are provided in U.S. patent application Ser. No. 10/867,577 filed Jun. 14, 2004 and entitled “Position Location using Broadcast Digital Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. Other techniques can be used as well. 
         [0077]    After generating the pseudoranges, femtocell  202  determines its location based on the pseudoranges and the locations of the respective DTV transmitters and GPS satellites  220  (step  714 ). The location determination can also employ aiding information and the like provided over Internet  214  via network interface  314 , communications module  316 , and path  338 . Further details of this technique are provided in U.S. patent application Ser. No. 12/263,731 filed Nov. 3, 2008 and entitled “Position Location using Global Positioning Signals Augmented by Broadcast Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. Other techniques can be used as well. 
         [0078]    In some embodiments, process  700  is repeated one or more times to improve the accuracy of the location determined for femtocell  202 . The location of femtocell  202  can be used to acquire precise timing, as described below. The location of femtocell  202  can also be reported to an E911 server for emergency location purposes over Internet  214  via path  338 , communications module  316 , and network interface  314 . 
         [0079]    In some embodiments, femtocell  202  measures DTV signals  230 , and acquires measurements of DTV signals  230  from femtocell server  240 , for each location determination. GPS satellite ephemeris and ionospheric delay change less frequently, and so are acquired less frequently, for example every two hours. 
         [0080]    Referring again to  FIG. 4 , after determining the location of femtocell  202 , femtocell  202  then acquires precise time (step  408 ). In some embodiments, femtocell  202  repeats this precise time acquisition periodically during operation. For example, precise time acquisition can occur once a minute. Precise time acquisition generally requires approximately 30 seconds. The remaining 30 seconds of each minute can be used to repeat precise frequency acquisition (step  410 ), for example as described above. Of course, other intervals can be used. 
         [0081]      FIG. 9  shows a process  900  for femtocell  202  of  FIGS. 2 and 3  to acquire precise time according to embodiments of the present disclosure. Although in the described embodiments, the elements of process  900  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  900  can be executed in a different order, concurrently, and the like. 
         [0082]    DTV signals  230  and GPS signals  222  are measured both by monitor unit  238  (step  902 ) and by measurement module  304  of femtocell  202  (step  904 ), as described above. Femtocell server  240  acquires the measurements of DTV signals  230  and GPS signals  222  from one or more monitor units  238  (step  906 ), for example as described above. Femtocell  202  requests the measurements from femtocell server  240  (step  908 ), which responds by sending the measurements to femtocell  202  (step  910 ). 
         [0083]    After acquiring the measurements of DTV signals  230  and GPS signals  222  from one or more monitor units  238 , femtocell  202  determines the precise time based on the measurements of DTV signals  230  and GPS signals  222 . In particular, location module  310  generates a respective pseudorange based on each of the signals  230 ,  222  (step  910 ), and determines a clock offset based on the pseudoranges (step  912 ). Alternatively, femtocell  202  can send the measurements of DTV signals  230  and GPS signals  222  to femtocell server  240 , which generates the pseudoranges, determines the clock offset, and sends the clock offset back to femtocell  202 . 
         [0084]    Each pseudorange represents the time of flight of the respective signal  222 ,  230  from its transmitter to femtocell  202 , as well as the clock offset of clock signals  332 . Because the location of femtocell is now known, the time of flight of each signal  222 ,  230  can be calculated and subtracted from the respective pseudorange to obtain the clock offset. In some embodiments, clock offsets are obtained from multiple signals  222 ,  230 . Receiver Autonomous Integrity Monitoring (RAIM) techniques or the like can be used to obtain a single clock offset from these multiple clock offsets. 
         [0085]    Femtocell  202  controls time base module  328  based on the clock offset (step  914 ). In particular, location module  310  sends one or more clock commands  336  to time base module  328 , which adjusts the phase of time base signal  334  based on clock commands  336 . Alternatively, or additionally, pseudorange measurements can be used to steer oscillator  308  as well. 
         [0086]    Thanks to the acquisition of precise time and frequency, clock signals  332  and time base signal  334  are precise enough for use by wireless mobile telephone transceiver  312  for communications with wireless mobile telephone  216  without interference to other base stations  208  and femtocells  202 , and for performing seamless handovers to other base stations  208  and femtocells  202 . In operation, wireless mobile telephone transceiver  312  transceives wireless mobile telephone signals  218 , for example in communication with one or more wireless mobile telephones  216 , based on clock signals  332 , and in some cases, based on time base signal  334 . Network interface  314  transceives network signals representing wireless mobile telephone signals  218  with Internet  214 , which communicates with PSTN  110 . 
         [0087]    Embodiments of the disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments of the disclosure can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the disclosure can be performed by a programmable processor executing a program of instructions to perform functions of the disclosure by operating on input data and generating output. The disclosure can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
         [0088]    A number of implementations of the disclosure have been described. 
         [0089]    Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.