Abstract:
Apparatus having corresponding methods and computer-readable media comprise a first receiver to receive a wireless television signal; a first measurement unit to generate a measurement of the wireless television signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal; a second receiver to receive a wireless local area network (WLAN) signal; and a second measurement unit to generate a measurement of the WLAN signal; wherein a position of a transmitter of the WLAN signal is determined based on the position of the apparatus and the measurement of the WLAN signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject matter of all of the foregoing are incorporated herein by reference. 
     BACKGROUND 
     The present invention relates generally to position determination. More particularly, the present invention relates to position determination using wireless local area network (WLAN) signals and television signals. 
     There have long been methods of two-dimensional latitude/longitude position location systems using radio signals. In wide usage have been terrestrial systems such as Loran C and Omega, and a satellite-based system known as Transit. Another satellite-based system enjoying increased popularity is the Global Positioning System (GPS). 
     Initially devised in 1974, GPS is widely used for position location, navigation, survey, and time transfer. The GPS system is based on a constellation of 24 on-orbit satellites in sub-synchronous 12 hour orbits. Each satellite carries a precision clock and transmits a pseudo-noise signal, which can be precisely tracked to determine pseudo-range. By tracking 4 or more satellites, one can determine precise position in three dimensions in real time, world-wide. More details are provided in B. W. Parkinson and J. J. Spilker, Jr., Global Positioning System-Theory and Applications, Volumes I and II, AIAA, Washington, D.C. 1996. 
     GPS has revolutionized the technology of navigation and position location. However in some situations, GPS is less effective. Because the GPS signals are transmitted at relatively low power levels (less than 100 watts) and over great distances, the received signal strength is relatively weak (on the order of −160 dBw as received by an omni-directional antenna). Thus the signal is marginally useful or not useful at all in the presence of blockage or inside a building. 
     There has even been a proposed system using conventional analog National Television System Committee (NTSC) television signals to determine position. This proposal is found in a U.S. patent entitled “Location Determination System And Method Using Television Broadcast Signals,” U.S. Pat. No. 5,510,801, issued Apr. 23, 1996. However, the present analog TV signal contains horizontal and vertical synchronization pulses intended for relatively crude synchronization of the TV set sweep circuitry. 
     SUMMARY 
     In general, in one aspect, the invention features an apparatus comprising: a first receiver to receive a wireless television signal; a first measurement unit to generate a measurement of the wireless television signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal; a second receiver to receive a wireless local area network (WLAN) signal; and a second measurement unit to generate a measurement of the WLAN signal; wherein a position of a transmitter of the WLAN signal are determined based on the position of the apparatus and the measurement of the WLAN signal. 
     In some embodiments, the second receiver is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, the measurement of the WLAN signal includes at least one of: a measurement of the received power level of the WLAN signal; and a media access control (MAC) address of the transmitter of the WLAN signal. Some embodiments comprise a transmitter to transmit a signal representing the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise a position unit to determine the position of the apparatus. Some embodiments comprise a transmitter to transmit a signal representing the position of the apparatus and the measurement of the WLAN signal. Some embodiments comprise a WLAN position unit to determine the position of the transmitter of the WLAN signal. Some embodiments comprise a database to store the position of the transmitter of the WLAN signal. Some embodiments comprise a transmitter to transmit a signal representing the position of the transmitter of the WLAN signal. Some embodiments comprise a third receiver to receive a satellite positioning signal; and a third measurement unit to generate a measurement of the satellite positioning signal; wherein the position unit determines the position of the apparatus based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features an apparatus comprising: first receiving means for receiving a wireless television signal; first measuring means for generating a measurement of the wireless television signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal; second receiving means for receiving a wireless local area network (WLAN) signal; and second measuring means for generating a measurement of the WLAN signal; wherein a position of a transmitter of the WLAN signal are determined based on the position of the apparatus and the measurement of the WLAN signal. 
     In some embodiments, the second receiving means is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, the measurement of the WLAN signal includes at least one of: a measurement of the received power level of the WLAN signal; and a media access control (MAC) address of the transmitter of the WLAN signal. Some embodiments comprise transmitting means for transmitting a signal representing the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise positioning means for determining the position of the apparatus. Some embodiments comprise transmitting means for transmitting a signal representing the position of the apparatus and the measurement of the WLAN signal. Some embodiments comprise means for determining the position of the transmitter of the WLAN signal. Some embodiments comprise means for storing the position of the transmitter of the WLAN signal in a database. Some embodiments comprise transmitting means for transmitting a signal representing the position of the transmitter of the WLAN signal. Some embodiments comprise third receiving means for receiving a satellite positioning signal; and third measuring means for generating a measurement of the satellite positioning signal; wherein the positioning means determines the position of the apparatus based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features a method comprising: receiving a wireless television signal at a receiver; generating a measurement of the wireless television signal; wherein a position of the receiver is determined based on the measurement of the wireless television signal; receiving a wireless local area network (WLAN) signal; and generating a measurement of the WLAN signal; wherein a position of a transmitter of the WLAN signal are determined based on the position of the receiver and the measurement of the WLAN signal. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, the measurement of the WLAN signal includes at least one of: a measurement of the received power level of the WLAN signal; and a media access control (MAC) address of the transmitter of the WLAN signal. Some embodiments comprise transmitting a signal representing the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise determining the position of the receiver. Some embodiments comprise transmitting a signal representing the position of the receiver and the measurement of the WLAN signal. Some embodiments comprise determining the position of the transmitter of the WLAN signal. Some embodiments comprise storing the position of the transmitter of the WLAN signal in a database. Some embodiments comprise transmitting a signal representing the position of the transmitter of the WLAN signal. Some embodiments comprise receiving a satellite positioning signal; generating a measurement of the satellite positioning signal; and determining the position of the receiver based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features computer-readable media embodying instructions executable by a computer to perform a method comprising: generating a measurement of a wireless television signal received at a receiver; wherein a position of the receiver is determined based on the measurement of the wireless television signal; and generating a measurement of a wireless local area network (WLAN) signal; wherein a position of a transmitter of the WLAN signal are determined based on the position of the receiver and the measurement of the WLAN signal. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, the measurement of the WLAN signal includes at least one of: a measurement of the received power level of the WLAN signal; and a media access control (MAC) address of the transmitter of the WLAN signal. Some embodiments comprise causing transmission of a signal representing the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise determining the position of the receiver. Some embodiments comprise causing transmission of a signal representing the position of the receiver and the measurement of the WLAN signal. Some embodiments comprise determining the position of the transmitter of the WLAN signal. Some embodiments comprise storing the position of the transmitter of the WLAN signal in a database. Some embodiments comprise causing transmission of a signal representing the position of the transmitter of the WLAN signal. Some embodiments comprise generating a measurement of a satellite positioning signal; and determining the position of the receiver based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features an apparatus comprising: a first receiver to receive a wireless television signal; and a first measurement unit to generate a measurement of the wireless television signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal; and a transmitter to transmit a wireless local area network (WLAN) signal, wherein the WLAN signal comprises a position signal representing the position of the apparatus. 
     In some embodiments, the transmitter is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise a position unit to determine the position of the apparatus based on the wireless television signal. Some embodiments comprise a second receiver to receive a satellite positioning signal; and a second measurement unit to generate a measurement of the satellite positioning signal; wherein the position of the apparatus is determined based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features an apparatus comprising: first receiving means for receiving a wireless television signal; and first measuring means for generating a measurement of the wireless television signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal; and transmitting means for transmitting a wireless local area network (WLAN) signal, wherein the WLAN signal comprises a position signal representing the position of the apparatus. 
     In some embodiments, the transmitting means is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise positioning means for determining the position of the apparatus based on the wireless television signal. Some embodiments comprise second receiving means for receiving a satellite positioning signal; and second measuring means for generating a measurement of the satellite positioning signal; wherein the position of the apparatus is determined based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features a method comprising: receiving a wireless television signal at a receiver; and generating a measurement of the wireless television signal; wherein a position of the receiver is determined based on the measurement of the wireless television signal; and transmitting a wireless local area network (WLAN) signal, wherein the WLAN signal comprises a position signal representing the position of the receiver. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise determining the position of the receiver based on the wireless television signal. Some embodiments comprise receiving a satellite positioning signal; and generating a measurement of the satellite positioning signal; wherein the position of the receiver is determined based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features computer-readable media embodying instructions executable by a computer to perform a method comprising: generating a measurement of a wireless television signal received at a receiver; wherein a position of the receiver is determined based on the measurement of the wireless television signal; and causing transmission of a wireless local area network (WLAN) signal, wherein the WLAN signal comprises a position signal representing the position of the receiver. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise determining the position of the receiver based on the wireless television signal. Some embodiments comprise generating a measurement of a satellite positioning signal; wherein the position of the receiver is determined based on the measurement of the wireless television signal and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features an apparatus comprising: a first receiver to receive a wireless television signal; a first measurement unit to generate a measurement of the wireless television signal; a second receiver to receive a wireless local area network (WLAN) signal; and a second measurement unit to generate a measurement of the WLAN signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal and the measurement of the WLAN signal. 
     In some embodiments, the second receiver is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise a position unit to determine the position of the apparatus based on the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise a transmitter to transmit a signal representing the position of the apparatus. Some embodiments comprise a third receiver to receive a satellite positioning signal; and a third measurement unit to generate a measurement of the satellite positioning signal; wherein the position of the apparatus is determined based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. Some embodiments comprise a position unit to determine the position of the apparatus based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features an apparatus comprising: first receiving means for receiving a wireless television signal; first measuring means for generating a measurement of the wireless television signal; second receiving means for receiving a wireless local area network (WLAN) signal; and second measuring means for generating a measurement of the WLAN signal; wherein a position of the apparatus is determined based on the measurement of the wireless television signal and the measurement of the WLAN signal. 
     In some embodiments, the second receiving means is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise positioning means for determining the position of the apparatus based on the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise transmitting means for transmitting a signal representing the position of the apparatus. Some embodiments comprise third receiving means for receiving a satellite positioning signal; and third measuring means for generating a measurement of the satellite positioning signal; wherein the position of the apparatus is determined based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. Some embodiments comprise positioning means for determining the position of the apparatus based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features a method comprising: receiving a wireless television signal at a receiver; generating a measurement of the wireless television signal; receiving a wireless local area network (WLAN) signal; and generating a measurement of the WLAN signal; wherein a position of the receiver is determined based on the measurement of the wireless television signal and the measurement of the WLAN signal. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise a position unit to determine the position of the receiver based on the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise a transmitter to transmit a signal representing the position of the receiver. Some embodiments comprise receiving a satellite positioning signal; and generating a measurement of the satellite positioning signal; wherein the position of the receiver is determined based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. Some embodiments comprise determining the position of the receiver based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     In general, in one aspect, the invention features computer-readable media embodying instructions executable by a computer to perform a method comprising: generating a measurement of a wireless television signal received at a receiver; and generating a measurement of a wireless local area network (WLAN) signal; wherein a position of the receiver is determined based on the measurement of the wireless television signal and the measurement of the WLAN signal. 
     In some embodiments, the WLAN signal is compliant with all or part of IEEE standard 802.11, including draft and approved amendments 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. Some embodiments comprise determining the position of the receiver based on the measurement of the wireless television signal and the measurement of the WLAN signal. Some embodiments comprise causing transmission of a signal representing the position of the receiver. Some embodiments comprise generating a measurement of a satellite positioning signal; wherein the position of the receiver is determined based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. Some embodiments comprise determining the position of the receiver based on the measurement of the wireless television signal, the measurement of the WLAN signal, and the measurement of the satellite positioning signal. In some embodiments, the wireless television signal comprises at least one of: an American Television Standards Committee (ATSC) digital television (DTV) signal; a Digital Video Broadcasting-Terrestrial (DVB-T) signal; a Digital Video Broadcasting-Handheld (DVB-H) signal; an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; and a National Television System Committee (NTSC) analog television signal. 
     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 
         FIG. 1  shows a system for surveying WLAN nodes using wireless television signals by remotely sensing the WLAN nodes according to some embodiments of the present invention. 
         FIG. 2  shows a process for the system of  FIG. 1  according to some embodiments of the present invention. 
         FIG. 3  shows a system for surveying WLAN nodes using wireless television signals by equipping each WLAN node with a television position unit according to some embodiments of the present invention. 
         FIG. 4  shows a process for the system of  FIG. 3  according to some embodiments of the present invention. 
         FIG. 5  shows a system for determining the position of an apparatus using WLAN signals and wireless television signals according to some embodiments of the present invention. 
         FIG. 6  shows a process for the system of  FIG. 5  according to some embodiments of the present invention. 
     
    
    
     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 
     Embodiments of the present invention provide techniques for position determination using wireless local area network (WLAN) signals and wireless television signals. Broadcast television signals can be used to determine the position of a user terminal. Techniques for determining the position of a user terminal using the American Television Standards Committee (ATSC) digital television (DTV) signal are disclosed in U.S. Pat. No. 6,861,984, “Position Location using Broadcast Digital Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. Techniques for determining the position of a user terminal using the European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting (DVB) signal are disclosed in U.S. Non-provisional patent application Ser. No. 09/932,010, “Wireless Position Location Using the Japanese ISDB-T Digital TV Signals,” the disclosure thereof incorporated by reference herein in its entirety. Techniques for determining the position of a user terminal using the Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal are disclosed in U.S. Pat. No. 6,952,182, “Position Location using Terrestrial Digital Video Broadcast Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. Techniques for determining the position of a user terminal using the NTSC (National Television System Committee) analog television (TV) signal are disclosed in U.S. Pat. No. 6,559,800 and U.S. Pat. No. 6,522,297, the disclosures thereof incorporated by reference herein in their entirety. 
     Each of these television signals includes components that can be used to obtain a pseudo-range to the transmitter of the television signal. When multiple such pseudo-ranges are known, and the locations of the transmitters are known, the position of the user terminal can be determined with accuracy. Suitable components within the ATSC digital television signal include synchronization codes such as the Field Synchronization Segment within an ATSC data frame and the Synchronization Segment within a Data Segment within an ATSC data frame. Suitable components within the ETSI DVB and ISDB-T digital television signals include scattered pilot carriers. Suitable components within the NTSC analog television signal include the horizontal synchronization pulse, the horizontal blanking pulse, the horizontal blanking pulse and horizontal synchronization pulse taken together, the ghost canceling reference signal, the vertical interval test signal, and other chirp-type signals. 
     Positioning techniques using television signals should revolutionize the technology of navigation and position location. The ubiquitous availability of television signals allows for coverage anywhere that television is available. In fact, with the use of time-gated delay-lock loops, it is possible to use television signals for positioning even beyond those areas where television reception is available. Details are provided in, for example, U.S. Pat. No. 6,753,812, “Time-Gated Noncoherent Delay Lock Loop Tracking of Digital Television Signals,” the disclosure thereof incorporated by reference herein in its entirety. 
     In some cases it is desirable to augment the television signals with other sorts of signals for more accurate positioning. For example, one or more GPS signals can be used. Techniques for determining the position of a user terminal using television and GPS signals are described in U.S. patent application Ser. No. 10/159,478, “Position Location using Global Positioning Signals Augmented by Broadcast Television Signals,” filed May 31, 2002, the disclosure thereof incorporated by reference herein in its entirety. 
     Another wireless signal that can be used to augment television signals for positioning is the wireless local area network (WLAN) signal, also referred to as “WiFi,” which is specified by IEEE standard 802.11. WLAN signals are especially useful in urban centers where WLAN nodes exist in high density. However, it is necessary to survey the locations of the WLAN nodes in order to maintain an accurate database of the location of all WLAN nodes. One conventional way to survey WLAN node locations is using a GPS-located WLAN receiver. But GPS is most affected by blockage in those environments where WLAN nodes are most prevalent. This weakness results in a very unreliable positioning system. 
     Some embodiments of the present invention provide techniques for surveying WLAN nodes using wireless television signals by remotely sensing the WLAN nodes. According to these embodiments, one or more wireless television signals are used to determine the position of a portable survey unit, which can be implemented as a laptop computer or the like. In some embodiments, the wireless television signals can be augmented by other signals, such as GPS signals. The survey unit receives and measures one or more WLAN signals. For example, the survey unit can measure the received power level of each WLAN signal, and the media access control (MAC) address of the WLAN node transmitting each WLAN signal. The position of the survey unit and the measurements of each WLAN signal are used to determine the position of the transmitter of the WLAN signal (that is, the WLAN node). In some embodiments, the survey unit determines the positions of the WLAN nodes. In other embodiments, the survey unit transmits the measurements to a WLAN position unit, which determines the positions of the WLAN nodes. Once the position and identity of the WLAN node are known, WLAN signals transmitted by the WLAN node can be used for positioning. 
     Some embodiments of the present invention provide techniques for surveying WLAN nodes using wireless television signals by equipping each WLAN node with a television position unit. According to these embodiments, one or more wireless television signals are used to determine the position of the WLAN node. In some embodiments, the wireless television signals can be augmented by other signals, such as GPS signals. The WLAN node then transmits a WLAN signal that includes a position signal representing the position of a WLAN node. The WLAN signals transmitted by the WLAN node can be used for positioning. 
     Some embodiments of the present invention provide techniques for determining the position of an apparatus using WLAN signals and wireless television signals. According to these embodiments, an apparatus receives one or more WLAN signals and one or more wireless television signals. The position of the apparatus is then determined based on the wireless television signals and WLAN signals. In some embodiments, the television signals can be augmented by other signals, such as GPS signals. In some embodiments, the apparatus determines its position. In other embodiments, the apparatus transmits measurements of the wireless television signals and WLAN signals to a remote position unit, which determines the positions of the apparatus. 
       FIG. 1  shows a system  100  for surveying WLAN nodes using wireless television signals by remotely sensing the WLAN nodes according to some embodiments of the present invention. Although in the described embodiments, the elements of system  100  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 provided herein. 
     System  100  comprises a survey unit  102 , one or more WLAN nodes  104  to transmit WLAN signals  106 , one or more television transmitters  108  to transmit wireless television signals  110 , a survey position unit  112 , and a WLAN position unit  114 . System  100  can also comprise one or more positioning satellites  116 , such as GPS satellites and the like, to transmit satellite positioning signals  118 . 
     Survey unit  102  comprises a television receiver  120  to receive one or more wireless television signals  110  from television transmitter(s)  108 , and a television measurement unit  124  to generate one or more measurements of each television signal  110 . Survey unit  102  also comprises a WLAN receiver  122  to receive WLAN signal(s)  106  from WLAN node(s)  104 , and a WLAN measurement unit  126  to generate one or more measurements of each WLAN signal  106 . In some embodiments, WLAN receiver  122  is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, survey unit  102  comprises a satellite receiver  128  to receive one or more satellite positioning signals  118  from satellite(s)  116 , and a satellite measurement unit  130  to generate one or more measurements of each satellite positioning signal  118 . 
     Survey position unit  112  determines the position of survey unit  102  based on wireless television signal(s)  110 . In some embodiments, survey position unit  112  also employs other sorts of signals, such as satellite positioning signals  118 , FM signals, and the like, to determine the position of survey unit  102 . In some embodiments, survey position unit  112  is implemented as part of survey unit  102 . In other embodiments, survey position unit  112  is implemented separately. For example, survey position unit  112  can be implemented remotely, and can communicate with survey unit  102  over a wireless link. 
     WLAN position unit  114  determines the position of each WLAN node  104  based on the position of survey unit  102  and the measurements of the respective WLAN signal  106 . In some embodiments, WLAN position unit  114  is implemented as part of survey unit  102 . In other embodiments, WLAN position unit  114  is implemented separately. For example, WLAN position unit  114  can be implemented remotely, and can communicate with survey unit  102  over a wireless link. In some embodiments, the positions of WLAN nodes  104  are recorded in a WLAN node database  132 . 
       FIG. 2  shows a process  200  for system  100  of  FIG. 1  according to some embodiments of the present invention. Although in the described embodiments, the elements of process  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 provided herein. 
     Television receiver  120  of survey unit  102  receives one or more wireless television signals  110  from television transmitter(s)  108  (step  202 ). For example, wireless television signals  110  can comprise analog television signals such as the NTSC analog television signal, digital television signals such as the ATSC, DVB-T, DVB-H, ISDB-T signals, and the like. 
     Television measurement unit  124  generates one or more measurements of each wireless television signal  110  (step  204 ). Techniques for generating measurements of television signals that are useful for positioning are described in detail in the patent documents cited above. For example, television measurement unit  124  generates a pseudorange for each wireless television signal  110 . 
     In embodiments employing satellites  116 , satellite receiver  128  receives one or more satellite positioning signals  118  from satellite(s)  116  (step  206 ), and satellite measurement unit  130  generates one or more measurements of each satellite positioning signal  118  (step  208 ). For example, satellite measurement unit  130  generates a pseudorange for each satellite positioning signal  118 . 
     Survey position unit  112  determines the position of survey unit  102  based on the measurement(s) of wireless television signal(s)  110 , and if used, the measurement(s) of satellite positioning signal(s)  118  (step  210 ). Techniques for determining positions based on measurements of television signals, and satellite positioning signals, are described in detail in the patent documents cited above. 
     WLAN receiver  122  of survey unit  102  receives one or more WLAN signals  106  from each WLAN node  104  (step  212 ). In some embodiments, WLAN signals  106  are compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. 
     WLAN measurement unit  126  generates one or more measurements of each WLAN signal  106  (step  214 ). For example, the measurements can include a measurement of the received power level of each WLAN signal  106  and the like. In order to identify each WLAN node  104 , WLAN measurement unit  126  can also determine the media access control (MAC) address of each WLAN node  104 . 
     WLAN position unit  114  determines the position of each WLAN node  104  based on the position of survey unit  102  and the measurement(s) of the respective WLAN signal  106  (step  216 ). In some embodiments, the positions of WLAN nodes  104  are recorded in WLAN node database  132  (step  218 ). 
     Once the positions of WLAN nodes  104  are established, many techniques exist to use the WLAN nodes  104  for positioning. One approach is to associate each WLAN node  104 , for example by the MAC address of the WLAN node  104 , with a particular radius of detection, and to assume that when survey unit  102  lies within that radius, its WLAN receiver  122  can detect the MAC address. Another approach is to perform a ranging measurement to each WLAN node  304  based on the measured power level of the WLAN signal  106  transmitted by that WLAN node  304 . However, embodiments of the present invention are not limited to these techniques. 
       FIG. 3  shows a system  300  for surveying WLAN nodes using wireless television signals by equipping each WLAN node with a television position unit according to some embodiments of the present invention. Although in the described embodiments, the elements of system  300  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 provided herein. 
     System  300  comprises a WLAN node  304  to transmit WLAN signals  306 , one or more television transmitters  308  to transmit wireless television signals  310 , and a survey position unit  312 . System  300  can also comprise one or more positioning satellites  316 , such as GPS satellites and the like, to transmit satellite positioning signals  318 . 
     WLAN node  304  comprises a television receiver  320  to receive one or more wireless television signals  310  from television transmitter(s)  308 , and a television measurement unit  324  to generate one or more measurements of each wireless television signal  310 . WLAN node  304  also comprises a WLAN transmitter  334  to transmit WLAN signal(s)  306 . In some embodiments, WLAN transmitter  334  is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, WLAN node  304  comprises a satellite receiver  328  to receive one or more satellite positioning signals  318  from satellite(s)  316 , and a satellite measurement unit  330  to generate one or more measurements of each satellite positioning signal  318 . 
     Survey position unit  312  determines the position of WLAN node  304  based on wireless television signal(s)  310 . In some embodiments, survey position unit  320  also employs other sorts of signals, such as satellite positioning signals  318 , FM signals, and the like, to determine the position of WLAN node  304 . In some embodiments, survey position unit  312  is implemented as part of WLAN node  304 . In other embodiments, survey position unit  312  is implemented separately. For example, survey position unit  312  can be implemented remotely, and can communicate with WLAN node  304  over a wireless link. When the position of WLAN node  304  has been determined, WLAN transmitter  334  transmits a WLAN signal  306  comprising a position signal representing the position of WLAN node  304 . 
       FIG. 4  shows a process  400  for system  300  of  FIG. 3  according to some embodiments of the present invention. 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 provided herein. 
     Television receiver  320  of WLAN node  304  receives one or more wireless television signals  310  from television transmitter(s)  308  (step  402 ). For example, wireless television signals  310  can comprise analog television signals such as the NTSC analog television signal, digital television signals such as the ATSC, DVB-T, DVB-H, ISDB-T signals, and the like. 
     Television measurement unit  324  generates one or more measurements of each wireless television signal  310  (step  404 ). Techniques for generating measurement of television signals that are useful for positioning are described in detail in the patent documents cited above. For example, television measurement unit  324  generates a pseudorange for each wireless television signal  310 . 
     In embodiments employing satellites  316 , satellite receiver  328  receives one or more satellite positioning signals  318  from satellite(s)  316  (step  406 ), and satellite measurement unit  330  generates one or more measurements of each satellite positioning signal  318  (step  408 ). For example, satellite measurement unit  330  generates a pseudorange for each satellite positioning signal  318 . 
     Survey position unit  312  determines the position of WLAN node  304  based on the measurement(s) of wireless television signal(s)  310 , and if used, the measurement(s) of satellite positioning signal(s)  318  (step  410 ). Techniques for determining positions based on measurements of television signals, and satellite positioning signals, are described in detail in the patent documents cited above. In addition, other signals can be used to augment wireless television signal(s)  310 , such as FM signals and the like. 
     WLAN transmitter  334  of WLAN node  304  transmits one or more WLAN signals  306  (step  412 ), where WLAN signal  306  comprises a position signal representing the position of WLAN node  304 . In some embodiments, WLAN signals  306  are compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. 
       FIG. 5  shows a system  500  for determining the position of an apparatus using WLAN signals and wireless television signals according to some embodiments of the present invention. Although in the described embodiments, the elements of system  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 provided herein. 
     System  500  comprises a survey unit  502 , one or more WLAN nodes  504  to transmit WLAN signals  506 , one or more television transmitters  508  to transmit wireless television signals  510 , and a survey position unit  512 . System  500  can also comprise one or more positioning satellites  516 , such as GPS satellites and the like, to transmit satellite positioning signals  518 . 
     Survey unit  502  comprises a television receiver  520  to receive one or more wireless television signals  510  from television transmitter(s)  508 , and a television measurement unit  524  to generate one or more measurements of each television signal  510 . Survey unit  502  also comprises a WLAN receiver  522  to receive WLAN signal(s)  506  from WLAN node(s)  504 , and a WLAN measurement unit  526  to generate one or more measurements of each WLAN signal  506 . In some embodiments, WLAN receiver  522  is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. In some embodiments, survey unit  502  comprises a satellite receiver  528  to receive one or more satellite positioning signals  518  from satellite(s)  516 , and a satellite measurement unit  530  to generate one or more measurements of each satellite positioning signal  518 . 
     Survey position unit  512  determines the position of survey unit  502  based on the measurement(s) of wireless television signal(s)  510  and the measurement(s) of WLAN signals  506 . For example, survey position unit  512  can use a WLAN database  532  that contains the positions and identities of WLAN nodes  504 . 
     In some embodiments, survey position unit  512  also employs other sorts of signals, such as satellite positioning signals  518 , FM signals, and the like, to determine the position of survey unit  502 . In some embodiments, survey position unit  512  is implemented as part of survey unit  502 . In other embodiments, survey position unit  512  is implemented separately. For example, survey position unit  512  can be implemented remotely, and can communicate with survey unit  502  over a wireless link. 
       FIG. 6  shows a process  600  for system  500  of  FIG. 5  according to some embodiments of the present invention. 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 provided herein. 
     Television receiver  520  of survey unit  502  receives one or more wireless television signals  510  from television transmitter(s)  508  (step  602 ). For example, wireless television signals  510  can comprise analog television signals such as the NTSC analog television signal, digital television signals such as the ATSC, DVB-T, DVB-H, ISDB-T signals, and the like. 
     Television measurement unit  524  generates one or more measurements of each wireless television signal  510  (step  604 ). Techniques for generating measurements of television signals that are useful for positioning are described in detail in the patent documents cited above. For example, television measurement unit  524  generates a pseudorange for each wireless television signal  510 . 
     WLAN receiver  522  of survey unit  502  receives one or more WLAN signals  506  from each WLAN node  504  (step  606 ). In some embodiments, WLAN signals  506  are compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, and 802.11w. 
     WLAN measurement unit  526  generates one or more measurements of each WLAN signal  506  (step  608 ). For example, the measurements can include a measurement of the received power level of each WLAN signal  506  and the like. In order to identify each WLAN node  504 , WLAN measurement unit  526  can also determine the media access control (MAC) address of each WLAN node  504 . 
     In embodiments employing satellites  516 , satellite receiver  528  receives one or more satellite positioning signals  518  from satellite(s)  516  (step  610 ), and satellite measurement unit  530  generates one or more measurements of each satellite positioning signal  518  (step  612 ). For example, satellite measurement unit  530  generates a pseudorange for each satellite positioning signal  518 . 
     Survey position unit  512  determines the position of survey unit  502  based on the measurement(s) of wireless television signal(s)  510 , the measurement(s) of WLAN signal(s)  506 , and if used, the measurement(s) of satellite positioning signal(s)  518  (step  614 ). Techniques for determining positions based on measurements of television signals, and satellite positioning signals, are described in detail in the patent documents cited above. 
     Embodiments of the invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention 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 invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention 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). 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.