Radio frequency device for receiving TV signals and GPS satellite signals and performing positioning

Abstract

An apparatus and method for determining the position of a user terminal comprise an antenna subsystem which is able to receive signals of GPS and TV, a receiver front end which converts the frequency of the incident signals and filters out unwanted signals so that the desired signals can be sampled, a digital processing component which accommodates the imperfections of the front end and converts the measured signals into a position information. The apparatus is capable of receiving at the user terminal, broadcast television signals from television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signals; receiving at the user terminal global positioning signals from a global positioning satellites; determining a second set of pseudo-ranges between the user terminal and the global positioning satellites based on the global positioning signals; and determining a position of the user terminal based on the first and second sets of pseudo-ranges, locations of the television signal transmitters, and locations of the global positioning satellites.

Description

INCORPORATION BY REFERENCE

[0004] This application hereby incorporates by reference in its entirety for following documents: 1) B. Parkinson and J. Spilker, Jr. Global Positioning System-Theory and Applications, AIAA, Washington, D.C., 1996, Vol. 1, Chapter 17 Tropospheric Effects on GPS by J. Spilker, Jr., 2) J. Spilker, Jr., Digital Communications by Satellite, Prentice-Hall, Englewood Cliffs, N.J., 1977, 1995, and 3) B. W. Parkinson and J. Spilker, Jr., Global Positioning System-Theory and Application, Volume 1, AIAA, Washington, D.C. 1996.

FIELD OF THE INVENTION

[0005] The present invention relates generally to television and position location, and specifically to a radio frequency device that enables reception of GPS signals for position determination as well as the reception of television signals for the purpose of data reception and position determination.

BACKGROUND INFORMATION

[0006] 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).

[0007] 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.

[0008] 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.

[0009] In recent years, there has been a rollout of digital television in Asia, Europe and the Americas. Some of the primary standards around the world are ATSC (e.g. United States), DVB (e.g. Europe) and ISDB (e.g. Japan). All of these different television standards employ an embedded synchronization code which is used to model the transmission channel and mitigate the effects of multipath in a digital TV receiver. In order to be effective for channel modeling and multipath mitigation, these synchronization codes have wide bandwidths, narrow autocorrelation functions, and high power levels, all features which make these synchronization codes ideal for positioning in particular indoors where multipath effects are severe and GPS signals cannot penetrate. In addition, analog television broadcasts have also started in recent years to insert into their broadcasts a synchronization code termed the Ghost-Canceling Reference (GCR), which is used for multipath mitigation on analog signals in TV receivers that digitize the signal. Consequently, the GCR can also be used for precise ranging. Other test signals inserted in the analog broadcasts, such as the multiburst signal, may also be used for positioning.

[0010] 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 technique described the use of the horizontal and vertical synchronization pulses which were intended only for relatively crude synchronization of the TV set sweep circuitry, and cannot achieve the level of positioning accuracy or reliability of the disclosed location technology. Further, in 2006 the Federal Communication Commission (FCC) will consider turning off NTSC transmitters and reassigning that valuable spectrum so that it can be auctioned for other purposes deemed more valuable.

[0011] A strong emphasis is being placed on the mobile user for the type of services that DTV can provide. For example, efforts are underway in Korea and Japan to generate cellular handsets which include television tuners for the purpose of receiving television on the mobile device as well as data conveyed using the DTV channel. A correct design of the receiver architecture, as described in this disclosure will enable data reception, as well as location using TV signals in combination with GPS.

SUMMARY OF THE INVENTION

[0012] The present invention relates to an apparatus and method for determining the position of a user terminal using broadcast television signals and signals from global positioning satellites.

[0013] According to one aspect of the invention, the receiver of the present invention includes an antenna system for receiving television signals and/or GPS signals, a receiver front end for converting the received signals from a first frequency or a second frequency to a third frequency, and a processing component for accepting the signals operating at the third frequency and for converting these signals into a position information.

[0014] In another aspect of the invention, the present invention is a receiver which includes a first antenna for receiving a first signal at a first frequency; a first low noise amplifier for amplifying the first signal; a second antenna for receiving a second signal at a second frequency; a second low noise amplifier for amplifying the second signal; a first frequency converter with an input and an output, the input is coupled to the first low noise amplifier for performing frequency conversion on the first signal; a switch with a first input, a second input and an output, the first switch input is coupled to the first frequency converter output, the second switch input coupled to the second low noise amplifier, and the switch is for selecting between the first signal or the second signal; a bandpass filter coupled to the switch output for filtering the first signal or the second signal; a second frequency converter coupled to the bandpass filter for converting the first signal or the second signal to a post-frequency converter signal at a third frequency; an analog-to-digital converter coupled to the second frequency converter for digitizing the post-converter signal and generating a digitized signal; and a processor coupled to the analog-to-digital converter for accepting the digitized signal and for converting the digitized signal into a position information.

[0015] In yet another aspect of the invention, the present invention is a receiver which includes an antenna system for receiving television signals and GPS signals; a low noise amplifier for amplifying the signals; an I/Q downconverter for downconverting the signals and for generating I and Q components for each of the signals; a first low pass filter coupled to the I/Q downconverter for filtering the I component; a second low pass filter coupled to the I/Q downconverter for filtering the Q component; a first analog-to-digital converter coupled to the first low pass filter for digitizing the I component and generating a digitized I component; a second analog-to-digital converter coupled to the second low pass filter for digitizing the Q component and generating a digitized Q component; a processing component with a first processing input and a second processing input, the first processing input coupled to the first analog-to-digital converter for accepting the digitized I component, the second processing input coupled to the second analog-to-digital converter for accepting the digitized Q component. In a preferred embodiment, the processor converts the digitized I and Q components into a position information.

[0016] In yet another aspect of the invention, the present invention is a receiver which includes an antenna system for receiving television signals and GPS signals, wherein the television signal operates at a first frequency and the GPS signal operates at a second frequency; a tunable bandpass filter having an adjustable passband; a low noise amplifier for amplifying the signals; an I/Q downconverter for downconverting the signals to a third frequency and for generating an I component and a Q component for each of the signals, wherein the I/Q downconverter comprises a first mixer, a local oscillator and a 90° phase shifter with a shifter input and a shifter output, the shifter input coupled to the local oscillator and the shifter output coupled to a second mixer; a first low pass filter for filtering the I component; a second low pass filter for filtering the Q component; a first analog-to-digital converter for digitizing the I component and generating a digitized I component; a second analog-to-digital converter for digitizing the Q component and generating a digitized Q component; and a processing component having a first processing input and a second processing input, the first processing input coupled to the first analog-to-digital converter for accepting the digitized I component, the second processing input coupled to the second analog-to-digital converter for accepting the digitized Q component, wherein the processing component converts the digitized I component and the digitized Q component into a position information.

[0017] In yet another aspect of the invention, the present invention is a method for receiving at the user terminal a plurality of broadcast television signals from television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signals; receiving at the user terminal a plurality of global positioning signals from global positioning satellites; determining a second set of pseudo-ranges between the user terminal and the global positioning satellites based on the global positioning signals; and determining a position of the user terminal based on the first set and the second set of pseudo-ranges, the locations of the television signal transmitters, and the locations of the global positioning satellites. In a preferred embodiment, the method also includes adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

[0018] In yet another aspect of the invention, the present invention is a method for receiving at the user terminal a plurality of broadcast television signals from television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signals; receiving at the user terminal a plurality of global positioning signals from global positioning satellites; determining a second set of pseudo-ranges between the user terminal and the global positioning satellites based on the global positioning signals; and transmitting the first set and second set of pseudo ranges to a location server configured to determine a position of the user terminal based on the first set and second set of pseudo-ranges, locations of the television signal transmitters, and locations of the global positioning satellites. In a preferred embodiment, the method also includes adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

[0019] In yet another aspect of the invention, the present invention is a method for receiving a first set of pseudo-ranges from the user terminal, the first set of pseudo-ranges determined between the user terminal and the television signal transmitters based on a known component of the broadcast television signals transmitted by the television signal transmitters; receiving a second set of pseudo-ranges from the user terminal, the second set of pseudo-ranges determined between the user terminal and the global positioning satellites based on the global positioning signals transmitted by the global positioning satellites; and determining a position of the user terminal based on the first set and second set of pseudo-ranges, locations of the television signal transmitters, and locations of the global positioning satellites. In a preferred embodiment, the method also includes adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

[0020] In yet another aspect of the invention, the present invention is a method for receiving at the user terminal a plurality of broadcast television signals from television signal transmitters; determining by a location server a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; determining by the location server a second set of pseudo-ranges between the user terminal and the global positioning satellites based on the global positioning signals; and determining by the location server a position of the user terminal based on the first set and second set of pseudo-ranges, the locations of the television signal transmitters, and the locations of the global positioning satellites.

[0021] In yet another aspect of the invention, the present invention is a method for receiving at the user terminal a plurality of broadcast television signals from television signal transmitters; determining by the user terminal a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; determining by the user terminal a second set of pseudo-ranges between the user terminal and the global positioning satellites based on the global positioning signals; and determining by the user terminal a position of the user terminal based on the first set and second set of pseudo-ranges, the locations of the television signal transmitters, and the locations of the global positioning satellites.

[0022] 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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 depicts an implementation of the present invention including a user terminal that communicates over an air link with a base station.

[0024] FIG. 2 illustrates an operation of an implementation of the invention.

[0025] FIG. 3 depicts the geometry of a position determination using 3 DTV transmitters.

[0026] FIG. 4 shows a time switching sequence for an integrated TV/GPS receiver according to some implementations.

[0027] FIG. 5 shows a receiver capable of processing both television signals and GPS signals for position determination according to some implementations.

[0028] FIG. 6 shows an embodiment for performing a coherent digital downconversion.

[0029] FIG. 7 shows an architecture for implementing a phase-locked loop to acquire the incident carrier signal.

[0030] FIG. 8 shows a direct downconversion architecture for processing the TV signals.

[0031] FIG. 9 shows real available circuit components which can be combined to implement the direct downconversion architecture illustrated in FIG. 8.

[0032] FIG. 10 shows a circuit for coupling the antenna to the low noise amplifier, which passes the desired channel and rejects interfering signals

[0033] FIG. 11 shows a voltage-controlled tuning filter which is a component of the circuit of FIG. 10.

[0034] FIG. 12 shows the group delay (phase) at various settings of the tunable circuit illustrated in FIG. 10.

[0035] FIG. 13 shows the amplitude response of a band-pass SAW filter.

[0036] FIG. 14 shows an antenna suitable for a small, low-cost mobile device and which receives television signals over a wide range of UHF frequencies.

[0037] FIG. 15 shows the amplitude response of the antenna in FIG. 14, without the use of any tuning circuitry.

[0038] FIG. 16 shows the directional gain plot of the antenna in FIG. 14.

[0039] 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 OF THE PREFERRED EMBODIMENT

[0040] In general, in one aspect, the invention features a method and apparatus for receiving TV and GPS signals in such a way that both signals can be used for determining the position of a user terminal. It comprises an antenna subsystem which is able to receive signals of GPS and TV, a receiver front end which converts the frequency of the incident signals and filters out unwanted signals so that the desired signals can be sampled, a digital processing component which accommodates the imperfections of the front end and converts the measured signals into position information. The method for positioning comprises receiving at the user terminal a first set of broadcast television signals from television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the television signal transmitters based on a known component of the broadcast television signal; receiving at the user terminal a second set of global positioning signals from a set of global positioning satellites; determining a second set of pseudo-range between the user terminal and the global positioning satellites based on the global positioning signals; and determining a position of the user terminal based on the firstand second set of pseudo-ranges, the locations of the set of television signal transmitters, and the locations of the set of global positioning satellites.

[0041] Particular implementations of the system can include one or more of the following features. The antenna subsystem can consist of two separate antennas, the first to receive the first set of TV signals, and the second to receive the second set of GPS signals. The antenna subsystem can also consist of a single antenna coupled to a tunable component which can be activated or deactivated in order to cause the antenna to resonate in the TV or GPS band respectively. Determining a position of the user terminal comprises adjusting the first set of pseudo-ranges based on a difference between thetransmitter clocks driving the broadcast television signals and a known time reference; adjusting the second set of pseudo-ranges based on the relative radial velocities between the global positioning satellites and the user terminal; and determining the position of the user terminal based on the adjusted first and second sets of pseudo-ranges, the location of the television signal transmitters, and the location of the global positioning satellites. The broadcast television signal is an American Television Standards Committee (ATSC) digital television signal, and the known component in the broadcast television signal is a known digital sequence in the ATSC frame. The known digital sequence is a synchronization code. The synchronization code is a Field Synchronization Segment within an ATSC data frame. The synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame. The broadcast television signal is a European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signal. The known component in the broadcast television signal is a scattered pilot carrier. The broadcast television signal is a Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal. The broadcast television signal is an analog television signal. The known component in the analog broadcast television signal is selected from the group comprising a a horizontal blanking pulse; a ghost canceling reference signal; and a vertical interval test signal such as the multiburst testing signal.

[0042] 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 commonly-owned copending U.S. Non-provisional patent application Ser. No. 09/887,158, “Position Location using Broadcast Digital Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed Jun. 21, 2001, 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-Terrestrial (DVB-T) signal are disclosed in commonly-owned copending U.S. Non-provisional patent application Ser. No. 09/932,010, “Position Location using Terrestrial Digital Video Broadcast Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed Aug. 17, 2001, 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 commonly-owned copending U.S. Non-provisional patent applications Ser. No. (TBS, Attorney Docket Number RSM031001), “Position Location using Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) Broadcast Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed (TBS) 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 commonly-owned copending U.S. Non-provisional patent applications Ser. No. 10/054,302, “Position Location using Broadcast Analog Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed Jan. 22, 2002, and Ser. No. (TBS, Attorney Docket Number RSM008001), “Position Location Using Ghost Canceling Reference Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed (TBS), the disclosures thereof incorporated by reference herein in their entirety.

[0043] 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 and clock offsets 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 Segment Synchronization within a Data Segment within an ATSC data frame. Suitable components within the ETSI DVB-T 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; and the vertical interval test signals such as the multiburst.

[0044] In most urban regions there are a sufficient number of TV signals broadcast from different locations to permit a user terminal to measure pseudo-ranges from 3 or more different angles to determine the position of the user terminal. However in some regions hills, buildings, other obstructions, or even the body of a user may block one of the TV signals. Alternatively, the user terminal may simply be located in a rural region too distant from the required number of TV transmitters. In such cases the remaining pseudo-ranges can be supplied using a standard global positioning system (GPS) receiver. Techniques for augmenting position location using broadcast television signals with GPS signals are disclosed in U.S. Provisional patent application Serial No. (TBS, Attorney Docket Number 6743PRO), “DTV Position Location Augmented by GPS,” by James J. Spilker, filed Mar. 4, 2002, the disclosure thereof incorporated by reference herein in its entirety. A user terminal using these techniques can determine its position using 3 or more broadcast television signals, 3 or more GPS signals, or any combination thereof.

[0045] Digital television (DTV) is growing in popularity. As of Feb. 28 2001, approximately 1200 DTV construction permits for US DTV stations had been acted on by the FCC. Over 1600 DTV transmitters are expected in the United States. Other regions are implementing similar DTV systems. The Japan Broadcasting Corp. (NHK) has defined a terrestrial DTV signal for Japan, referred to herein as the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal. These new DTV signals permit multiple TV signals to be transmitted in the assigned 6 MHz channel. Besides enabling High Definition Television, these new ISDB-T DTV signals are also designed for use by the mobile user, and have the ability to transmit data reliably at reduced rates to small handheld devices. Cellular phone and PDA devices will soon be released in Asia which included TV micro-tuners for the purpose of receiving data broadcast over the DTV spectrum. In a device which already includes a TV micro-tuner, the TV position location capability can be added with very small cost. By correct design of the device, one can also add GPS location technology for a very small incremental cost.

[0046] Referring to FIG. 1, an example implementation 100 includes a user terminal 102 that communicates over an air link with a base station 104. In some implementations, user terminal 102 is a wireless telephone and base station 104 is a wireless telephone base station. In some implementations, base station 104 is part of a mobile MAN (metropolitan area network) or WAN (wide area network).

[0047] FIG. 1 is used to illustrate various aspects of the invention but the invention is not limited to this implementation. For example, the phrase “user terminal” is meant to refer to any object capable of implementing the position location techniques described herein. Examples of user terminals include PDAs, mobile phones, cars and other vehicles, and any object which could include a chip or software implementing the position location techniques described herein. Further, the term “user terminal” is not intended to be limited to objects which are “terminals” or which are operated by “users.”

[0048] Position Location Performed by a Location Server

[0049] FIG. 2 illustrates an operation of implementation 100. User terminal 102 receives broadcast signals from one or more TV transmitters 106A and 106B through 106N (step 202). Referring to FIG. 1, TV transmitter 106A is a ETSI transmitter, TV transmitter 106B is a NTSC transmitter, and TV transmitter 106N is a ATSC transmitter, although other combinations are contemplated, including transmitters of the ISDB signal used in Japan.

[0050] Various methods can be used to select which TV channels to use in position location. In one implementation, a location server 110 tells user terminal 102 of the best TV channels to monitor. In some implementations, user terminal 102 exchanges messages with location server 110 by way of base station 104. In some implementations user terminal 102 selects TV channels to monitor based on the identity of base station 104 and a stored table correlating base stations and TV channels. In some implementations, user terminal 102 can accept a location input from the user that gives a general indication of the location of the user terminal, such as the name of the nearest city; and uses this information to select TV channels for processing. In some implementations, user terminal 102 scans available TV channels to assemble a fingerprint of the location based on power levels of the available TV channels. User terminal 102 compares this fingerprint to a stored table that matches known fingerprints with known locations to select TV channels for processing. This selection is based on the power levels of the DTV channels, as well as the directions from which each of the signals are arriving, so as to minimize the dilution of precision (DOP) for the position calculation.

[0051] User terminal 102 determines a pseudo-range between the user terminal and each TV transmitter 106 (step 204). Each pseudo-range represents the time difference (or equivalent distance) between a time of transmission from a transmitter 108 of a component of the TV broadcast signal and a time of reception at the user terminal 102 of the component, as well as a clock offset at the user terminal.

[0052] User terminal 102 transmits the pseudo-ranges to location server 110. In some implementations, location server 110 is implemented as a general-purpose computer executing software designed to perform the operations described herein. In another implementation, location server is implemented as an ASIC (application-specific integrated circuit), or some other sort of device. In some implementations, location server 110 is implemented within or near base station 104.

[0053] The TV signals are also received by a plurality of monitor units 108A through 108N. Each monitor unit 108 can be implemented as a small unit including a transceiver and processor, and can be mounted in a convenient location such as on a utility pole, TV transmitter 106, or base station 104. In some implementations, monitor units 108 are implemented on satellites.

[0054] Each monitor unit 108 measures, for each of the TV transmitters 106 from which it receives TV signals, a time offset between the local clock of that TV transmitter and a reference clock. In some implementations the reference clock is derived from GPS signals. The use of a reference clock permits the determination of the time offset for each TV transmitter 106 when multiple monitor units 108 are used, since each monitor unit 108 can determine the time offset with respect to the reference clock. Thus, offsets in the local clocks of the monitor units 108 do not affect these determinations. Monitor units 108 are described in detail in U.S. Ser. Nos. 09/887,158, 09/932,010, and 10/054,302, the disclosures thereof incorporated by reference herein in their entirety.

[0055] In another implementation, no external time reference is needed. According to this implementation, a single monitor unit 108 receives TV signals from all of the same TV transmitters as does user terminal 102. In effect, the local clock of the single monitor unit functions as the time reference.

[0056] In some implementations, each time offset is modeled as a fixed offset. In another implementation each time offset is modeled as a second order polynomial fit of the form

Offset=a+b(t−T)+c(t−T)2  (1)

[0057] that can be described by a, b, c, and T. In either implementation, each measured time offset is transmitted periodically to the location server using the Internet, a secured modem connection, as part of the actual DTV broadcast data, or the like. In some implementations, the location of each monitor unit 108 is determined using GPS receivers.

[0058] Location server 110 receives information describing the phase center (i.e., the location) of each TV transmitter 106 from a database 112. In some implementations, the phase center of each TV transmitter 106 is measured by using monitor units 108 at different locations to measure the phase center directly. In another implementation, the phase center of each TV transmitter 106 is measured by surveying the antenna phase center.

[0059] In some implementations, location server 110 receives weather information describing the air temperature, atmospheric pressure, and humidity in the vicinity of user terminal 102 from a weather server 114. The weather information is available from the Internet and other sources such as NOAA. Location server 110 determines tropospheric propagation velocity from the weather information using techniques such as those disclosed in B. Parkinson and J. Spilker, Jr. Global Positioning System-Theory and Applications, AIAA, Washington, D.C., 1996, Vol. 1, Chapter 17 Tropospheric Effects on GPS by J. Spilker, Jr.

[0060] Location server 110 can also receive from base station 104 information which identifies a general geographic location of user terminal 102. For example, the information can identify a cell or cell sector within which a cellular telephone is located. This information is used for ambiguity resolution.

[0061] User terminal 102 receives GPS signals from one or more GPS satellites 120 (step 206). User terminal 102 also receives almanac data describing Doppler shifts and pseudo-noise numbers for GPS satellites 120, as described below. User terminal 102 determines a pseudo-range between the user terminal and each GPS satellite 120 (step 208). Each pseudo-range represents the time difference (or equivalent distance) between a time of transmission from a GPS satellite 120 of a component of the GPS signal and a time of reception at the user terminal 102 of the component, as well as a clock offset at the GPS satellite. User terminal 102 transmits the pseudo-ranges to location server 110.

[0062] Location server 110 determines a position of the user terminal based on the pseudo-ranges, a location of each of the TV transmitters 106, and a location of the GPS satellites 120 (step 210). FIG. 3 depicts the geometry of a position determination using three transmitters 302. Transmitters 302 can be all TV transmitters, all GPS transmitters, or any combination thereof. Transmitter 302A is located at position (x1, y1, z1). The range between user terminal 102 and transmitter 302A is r1. Transmitter 302B is located at position (x2, y2, z2). The range between user terminal 102 and transmitter 302B is r2. Transmitter 302N is located at position (x3, y3, z3). The range between user terminal 102 and transmitter 302N is r3.

[0063] Location server 110 may adjust the value of each pseudo-range according to the tropospheric propagation velocity and the time offset for the corresponding transmitter 302. Location server 110 uses the phase center information from database 112 to determine the position of each transmitter 302.

[0064] User terminal 102 makes three or more pseudo-range measurements to solve for three unknowns, namely the position (x, y) and clock offset T of user terminal 102. It is assumed that the altitude of the user terminal is known to within the necessary degree of accuracy and only the latitude and longitude of the user terminal need to be precisely determined. Of course, it is possible to solve for position of the user terminal in three dimensions, namely (x, y, z) assuming that four or more transmitters are available, and the geometry of those transmitters is sufficient. It would be clear to one skilled in the art how to adjust the techniques described herein for a 3-Dimensional position fix.

[0065] The three pseudo-range measurements pr1, pr2 and pr3 are given by

pr 1 =r1+T  (2)

pr 2 =r2+T  (3)

pr 3 =r3+T  (4)

[0066] The three ranges can be expressed as

r 1 =|X−X1|  (5)

r 2 =|X−X2|  (6)

r 3 =|X−X3|  (7)

[0067] where X represents the three-dimensional vector position (x, y, z) of user terminal, X1 represents the three-dimensional vector position (x1, y1, z1) of transmitter 302A, X2 represents the three-dimensional vector position (x2, y2, z2) of transmitter 302B, and X3 represents the three-dimensional vector position (x3, y3, z3) of transmitter 302N. These relationships produce three equations in which to solve for the three unknowns x, y, and T. Notice that in the case that only latitude and longitude are required, location server 110 assumes some estimate for z and does not solve for it as for the other unknown co-ordinates. In one implementation, using a terrain map, the initial estimate of z can be iteratively refined based on the computed values for x and y. In another implementation, location server 110 actively solves for z. Location server 110 solves these equations according to conventional well-known methods. In an E911 application, the position of user terminal 102 is transmitted to E911 location server 116 for distribution to the proper authorities. In another application, the position is transmitted to user terminal 102.

[0068] Now, since we cannot assume a high quality oscillator in the user device, techniques for projecting the measurements at the user terminal 102 to a common instant in time (common time instant) are described. Note that this is not necessary if the clock of the user terminal 102 is stabilized or corrected using a signal from the cellular base station or a DTV transmitter 106. When the user clock is not stabilized, or corrected, the user clock offset can be considered to be a function of time, T(t). For a small time interval, Δ, the clock offset, T(t), can be modeled by a constant and a first order term. Namely, 1$\begin{array}{cc}T\left(t+\Delta \right)=T\left(t\right)+\frac{\partial T}{\partial t}\Delta & \left(8\right)\end{array}$

[0069] We now reconsider equations (2a)-(4a) treating the clock offset as a function of time. Consequently, the pseudorange measurements are also a function of time. For clarity, we assume that the ranges remain essentially constant over the interval Δ. The pseudorange measurements may be described as:

pr 1 (t1)=r1+T(t1)  (2b)

pr 2 (t2)=r2+T(t2)  (3b)

prN (tN)=rN+T(tN)  (4b)

[0070] In one embodiment, the user terminal 102 commences with an additional set of pseudorange measurements at some time Δ after the initial set of measurements. These measurements may be described: 2$\begin{array}{cc}\mathrm{pr1}\left(\mathrm{t1}+\Delta \right)=\mathrm{r1}+T\left(\mathrm{t1}\right)+\frac{\partial T}{\partial t}\Delta & \text{(2c)}\\ \mathrm{pr2}\left(\mathrm{t2}+\Delta \right)=\mathrm{r2}+T\left(\mathrm{t2}\right)+\frac{\partial T}{\partial t}\Delta & \text{(3c)}\\ \mathrm{prN}\left(\mathrm{tN}+\Delta \right)=\mathrm{rN}+T\left(\mathrm{tN}\right)+\frac{\partial T}{\partial t}\Delta & \text{(4c)}\end{array}$

[0071] The user terminal 102 then projects all the pseudorange measurements to some common point in time (common time instant) so that the effect of the first order term is effectively eliminated. For example, consider if some common reference time t0 is used. Applying equations (2b-4b) and (2c-4c) it is straightforward to show that we can project the measurements to a common instant of time as follows:

pr 1 (t0)=pr1(t1)+[pr1(t1+Δ)−pr1(t1)](t0−t1)/Δ  (2d)

pr 2 (t0)=pr2(t2)+[pr2(t2+Δ)−pr2(t2)](t0−t2)/Δ  (3d)

prN (t0)=prN(tN)+[prN(tN+Δ)−prN(tN)](t0−tN)/Δ  (4d)

[0072] These projected pseudorange measurements are communicated to the location server where they are used to solve the three unknowns x, y, and T. Note that the projection in equations (2d-4d) is not precise, and second order terms are not accounted for. However the resulting errors are not significant. One skilled in the art will recognize that second order and higher terms may be accounted for by making more than two pseudorange measurements for each projection. Notice also that there are many other approaches to implementing this concept of projecting the pseudorange measurements to the same instant of time. One approach, for example, is to implement a delay lock loop such as those disclosed in J. J. Spilker, Jr., Digital Communications by Satellite, Prentice-Hall, Englewood Cliffs, N.J., 1977, 1995 and B. W. Parkinson and J. J. Spilker, Jr., Global Positioning System-Theory and Application, Volume 1, AIAA, Washington, D.C. 1996, both incorporated by reference herein. A separate tracking loop can be dedicated to each DTV transmitter 106 These tracking loops effectively interpolate between pseudorange measurements. The state of each of these tracking loops is sampled at the same instant of time. In some implementations, user terminal 102 does not compute pseudo-ranges, but rather takes measurements of the signals that are sufficient to compute pseudo-range, such as a set of correlator outputs, and transmits these measurements to location server 110. Location server 110 then computes the pseudo-ranges based on the measurements, and computes the position based on the pseudo-ranges, as described above.

[0073] Position Location Performed by User Terminal

[0074] In some implementations, the position of user terminal 102 is computed by user terminal 102. In this implementation, all of the necessary information is transmitted to user terminal 102. This information can be transmitted to user terminal by location server 110, base station 104, one or more TV transmitters 106, GPS satellites 120, or any combination thereof. User terminal 102 then measures the pseudo-ranges and solves the simultaneous equations as described above. This implementation is now described.

[0075] User terminal 102 receives the time offset between the local clock of each TV transmitter 106 and a reference clock. User terminal 102 also receives information describing the phase center of each TV transmitter 106 from a database 112.

[0076] User terminal 102 receives the tropospheric propagation velocity computed by location server 110. In some implementation, user terminal 102 receives weather information describing the air temperature, atmospheric pressure, and humidity in the vicinity of user terminal 102 from a weather server 114, and determines tropospheric propagation velocity from the weather information using conventional techniques.

[0077] User terminal 102 can also receive from base station 104 information which identifies the rough location of user terminal 102. For example, the information can identify a cell or cell sector within which a cellular telephone is located. This information is used for ambiguity resolution.

[0078] User terminal 102 receives TV signals from one or more TV transmitters 106 and determines a pseudo-range between the user terminal 102 and each TV transmitter 106. User terminal 102 receives GPS signals from one or more GPS satellites 120 and almanac data describing Doppler shifts and pseudo-noise code numbers for the GPS satellites, as described below, and determines pseudo-ranges between the user terminal 102 and the GPS satellites 120. User terminal 102 then determines its position based on the pseudo-ranges, the locations of the TV transmitters 106, and the locations of the GPS satellites 120.

[0079] In any of these implementations, the position of user terminal 102 can be determined using a TV transmitter and the offset T computed during a previous position determination for that TV transmitter. The values of T can be stored or maintained according to conventional methods.

[0080] In some implementations, base station 104 determines the clock offset of user terminal 102. In this implementation, only two transmitters are required for position determination. Base station 104 transmits the clock offset T to location server 110, which then determines the position of user terminal 102 from the pseudo-range computed for each of the transmitters.

[0081] Receiver Signal Processing Architecture

[0082] The signal processing for both TV and GPS signals can be performed either using correlation of short samples of the received digitized signals or by using a delay-lock loop or time-gated delay lock loop. Such delay lock loop techniques are disclosed in commonly-owned copending U.S. Non-provisional patent application Ser. No. 10/054,262, “Time-Gated Delay Lock Loop Tracking Of Digital Television Signals,” by James J. Spilker and Matthew Rabinowitz, filed Jan. 22, 2002, the disclosure thereof incorporated by reference herein in its entirety.

[0083] FIG. 4 shows a time switching sequence for an integrated TV/GPS receiver according to some implementations. The receiver time sequences over the various signal sources changing the TV channel frequencies to examine three TV signals (TVa, TVb, and TVc) in this example and then switching to the GPS band to examine one or more GPS signals. Of course when tuned to the GPS band, the receiver can correlate any of the GPS satellites and multiple GPS satellites concurrently.

[0084] FIG. 5 shows a receiver 500 capable of processing both television signals and GPS signals for position determination according to some implementations. A TV antenna 502 receives the TV signals. In other implementations, the same antenna can be used for both the GPS and the TV signal. This antenna may be coupled to a tuning circuit 503 (not shown) to form an antenna system in order to resonate at the different frequencies of the television signals or the GPS signals. Alternately, this antenna can have two feeds, one which outputs a signal in the GPS band and one which outputs a signal in the TV band, with a switch determining which feed outputs to the LNA in the receiver front end. A low noise amplifier and RF filter 504 amplifies and filters the received TV signals. The RF filter is tunable over the required range for the set of TV channels that is selected. This could, for example, be just the UHF channels in the range 450 MHz through 7 MHz. The low noise amplifier includes an automatic gain control function. In one embodiment, a frequency converter includes a mixer 506, a local oscillator 507 (not shown) and a frequency synthesizer 508. The mixer 506 combines the resulting signal with the output of a frequency synthesizer 508 to up-convert the signal to an IF frequency where a narrow bandwidth SAW filter 510 can be employed. In a preferred embodiment, the local oscillator 507 operates in conjunction with the frequency synthesizer 508. A switch 512 passes the TV signal to SAW filter 510. In order to make use of GPS the IF frequency is at or near to the GPS L1 frequency of 1575.42 MHz. Other implementations use the L2 frequency of 1227.6 MHz, which will shortly have a new civil signal, or the new L5 signal in the 1.1 GHz region. In other implementations, a different IF frequency can be used and the GPS signal as well as the TV signal will initially be up-converted or down-converted before bandpass filtering.

[0085] In one embodiment, a frequency converter includes a mixer 514 and a local oscillator 516. The mixer 514 combines the filtered signal with the output of a local oscillator 516 to down-convert the filtered signal to a post-frequency converter signal at a convenient IF frequency. In another embodiment, the local oscillator 516 is driven by the frequency synthesizer 508. In one embodiment, the IF frequency is 44 MHz, a standard TV IF frequency. Filter/ADC 518 then filters and digitizes the signal. The signal can then be IF sampled at, for example, 27 Msps using a 10 bit ADC. The digitized signal is fed to a processor 524 for processing. A controller 526 controls filter/amplifier 504, frequency synthesizer 508, and switch 512.

[0086] A GPS antenna 520, such as a patch antenna, receives the GPS signals. A low noise amplifier and RF filter 522 amplifies and filters the received GPS signals. Switch 512 passes the GPS signal to SAW filter 510. Mixer 514 combines the filtered signal with the output of a local oscillator 516 to down-convert the filtered signal to a convenient IF or baseband frequency. Filter/ADC 518 then filters and digitizes the signal. The signal can then be IF sampled at, for example, 27 Msps using a 10 bit ADC. GPS can be sampled at substantially lower sampling rates and with fewer bits without significantly affecting performance. The digitized signal is fed into a processing component 524 for digital processing. In accordance with the knowledge of one skilled in the art, it is clear that the processing component 524 may be a processor, a MicroProcessor, a DSP or may be implemented largely in hardware.

[0087] In one embodiment, the receiver front end comprises at least one low noise amplifier and RF filter 504, 520, at least one mixer 506, 514, a frequency synthesizer 508, at least one local oscillator 516, a filter 510, a Analog to Digital Converter (ADC) 518 and a controller 526. In some implementations, the entire RF section is fabricated as a single integrated circuit, with the exception of the SAW filter 510 (or similar high selectivity bandpass filter) and the processing component 524 which are fabricated as separate integrated circuits.

[0088] We will now explore some of the components of FIG. 5 in more detail. We begin with the digital processing section. In one embodiment of the invention, there is a second IF at a center frequency of 44 MHz, the signal is sampled at a rate of 27 MHz, and a coherent down-conversion architecture is used, where carrier acquisition is performed on the sampled signal. None of these assumptions are crucial to ideas discussed, as one skilled in the art will recognize.

[0089] FIG. 6 illustrates a coherent down-converter which takes a real valued signal output from the ADC, and generates a complex valued baseband signal. The second IF signal has a spectrum that lies between [41, 47] MHz, which after undersampling at 27 MHz by the A/D converter, gets translated to [7, 13] MHz band. There is also a reversal of the spectrum so that the pilot signal is at the lower end of the spectrum, in the vicinity of 7 MHz. Due to the large offsets of the pilot frequency between various analog and digital channels, the coherent downconverter needs frequency aiding i.e. an external algorithm supplies an estimate of the pilot frequency, accurate enough for it to lie within the tracking range of the PLL. In one embodiment, this information on the frequency offset of each channel is measured at the monitor unit and passed to the mobile device. The downconversion is done in two stages. The first stage (utilizing the first downconversion unit 610) consists of mixing the real-valued input signal with quadrature outputs of a Numerically Controlled Oscillator (NCO), whose frequency is adjusted to lie 700 kHz below the estimated pilot frequency. The spectrum of the signal is translated such that the pilot signal lies at 700 kHz. The downconversion to 700 kHz prior to recovering the carrier enables us to design a single, fixed coefficient filter to extract the pilot signal. The Pilot frequency output from the A/D varies over a range of several hundred kHz as we tune through different channels. So it is necessary to bring it down to a fixed value by correctly setting the frequency of the first downconversion.

[0090] After the first downconversion, the signal is branched into 2 paths, namely through the carrier acquisition unit 640 and second downconversion unit 680. Carrier acquisition unit 640 (a.k.a. carrier recovery) consists of a narrow bandpass filter 642 and a phase-locked loop (PLL) 650 which is illustrated in FIG. 7. The purpose of the PLL 650 is to reproduce the vestigial sideband (VSB) carrier with the help of the pilot signal present in the received signal. The PLL 650 includes a phase detector 651, loop filter 655 and an NCO 657. The NCO 657 is programmed to generate a 700 kHz signal. The phase detector is simply a complex mixer which multiplies the I/Q outputs of the filtered Pilot signal with I/Q outputs of the NCO 657. The resulting signal is passed through a loop filter, which is implemented in one embodiment as a second order Infinite Impulse Response (IIR) Filter. The loop filter coefficients are designed to satisfy closed loop stability, the desired tracking range and acceptable phase noise of the NCO. The output of the loop filter 655 is then scaled by constant and added to the phase word of the numerically controlled oscillator (NCO), which determines the rate of the NCO, and maintains lock in the filtered pilot signal.

[0091] The second downconversion unit 680 consists of a complex mixer which mixes the I-Q outputs of the first stage of downconversion with the I-Q outputs of the PLL. The resulting signal is converted to baseband and has a spectrum in the range [0, 6] MHz.

[0092] Many alternative techniques exist to implementing the signal processing, which do not change the fundamental idea of the invention. We will not explore in detail the alternative techniques that can be used for processing the GPS signals, since these techniques are well understood in the art. We will focus instead on alternative methods and architectures for processing the TV signals. One alternative is to convert the TV signal output from the SAW filter 510 to baseband instead of to some IF frequency. This approach would typically make use of an inphase and a quadrature mixer, instead of a single mixer 514. Some of the issues associated with the conversion of an analog signal to baseband will now be discussed in the context of the direct down-conversion architecture of FIG. 8.

[0093] The receiver architecture 800 shown in FIG. 8 is well-suited to integrating the TV receiver component into an Application Specific Integrated Circuit (ASIC). The tunable bandpass filter 810 removes unwanted interference signals so that the Low Noise Amplifer (LNA) 830 is not saturated, and inter-modulation products do not disrupt system performance. The tunable bandpass filter 810 has an adjustable passband which can be adjusted to select an instantaneous desired frequency band. The attenuator 820 at the front end is designed to improve the dynamic range of the circuit, by attenuating signals when the mobile device is close to a TV transmitter and receiving a very powerful signal. The LNA 830 amplifies the signal. The signal is then passed to an I/Q downconverter 850 which includes mixers 851, 852, a 90° phase shifter 853 and a local oscillator 854. The mathematics associated with the downconversion is analyzed below. The output of the I/Q downconverter 850 is an I component of the signal and a Q component of the signal. The Local Oscillator (LO) signal driving the mixers 851, 852 and the 90° phase shifter 853 converts the signal down to baseband, or a very low Intermediate Frequency (IF) so that it can be filtered with low-pass filters 861, 862 that can be implemented on an Integrated Circuit (IC). The Automatic Gain Control (AGC) 871, 872 adjusts the magnitude of the signal so as to make better use of the available bits of the Analog to Digital Converter (ADC) 881, 882. The outputs of the ADCs 881, 882 are digitized I components and digitized Q components. In this embodiment, the outputs of the ADC 881, 882 are inputs to a processing component 890. In accordance with the knowledge of one skilled in the art, it is clear that the processing component 890 may be a processor, a MicroProcessor, a DSP or may be implemented largely in hardware. The receiver architecture 800 being described here is atypical for two reasons: Firstly, it does not require the use of an off-chip Surface Accoustic Wave (SAW) SAW filter which most TV receivers employ. Secondly, the receiver is designed to receive only Ultra-High Frequency (UHF) DTV channels, so that the full tuning range can be covered by a single Voltage-Controlled Oscillator (VCO). Of course, additional direct down-conversion paths can be added to receive VHF signals as well as UHF.

[0094] FIG. 9 illustrates some off-the-shelf parts which may be used to implement the front end of the direct downconversion receiver. In FIG. 9 we assume the use of a diversity antenna with multiple elements which can be switched in and out, depending on the measured post-correlation signal strength. The diversity antenna need not be implemented as a switch between multiple antennas, but may also be implemented simply by varying the voltage that drives a tuning circuit which couples to the antenna. In order to illustrate how this circuit may be constructed with off-the-shelf elements, the key components in the bill of materials for the circuit of FIG. 9 are listed below. The total cost of these off-the-shelf parts, including the necessary passive components, is estimated to be roughly $10 in large volumes. There are of course many ways in which the performance of this circuit may be enhanced, without altering the fundamental concept.

	LNA	1	BFP420
	switch	2	HSMP-3893
	mixer	2	BFP420
	baseband	1	RF2670
	ADC	1	THS0842
	synth	1	LMX2316
	VCO	1	BFP420
	varactor	1	MA4ST083

[0095] While the direct downconversion architecture is difficult to implement for a data reception receiver, it is more straightforward to use this architecture for a navigation receiver since there is so much processing gain available in the digital signal processing of a navigation receiver. We will illustrate in this section how imperfections in analog circuitry of the direct downconversion architecture affect the sampled signal. We model the signal incident at the first mixer stage with inphase and quadrature components as follows:

s (t)=ci(t) cos (ω0t+φ)−Cq(t) sin (ω0t+φ)

[0096] where ci and cq represent only the useful synchronization signal. For this explanation, the data signal is considered as interference and is ignored The signal is mixed with in-phase reference signal m1(t)=cos (ω1t+δt) and filtered by the low-pass filter to produce 3$s_1\left(t\right)=\frac{c_i\left(t\right)}{2}\cos \left(\mathrm{\Delta \omega }t+\delta t-\phi \right)+\frac{c_q\left(t\right)}{2}\sin \left(\mathrm{\Delta \omega }t+\delta t-\phi \right)$

[0097] where Δω=1071−ω0 and δ is the frequency error in generating the reference signal. In one embodiment, Δω may is roughly 3 MHz for a 6 MHz VSB (Vestigial Sideband) signal. In this way, a lowpass filter with a single-sided bandwidth of only 3 MHz can be used to filter a 6 MHz channel. Similarly, the signal is mixed with quadrature reference signal m2(t)=sin (ω1t+δt+α) and filtered by the low-pass filter to produce 4$s_2\left(t\right)\approx \frac{c_i\left(t\right)}{2}\sin \left(\mathrm{\Delta \omega }t+\delta t-\phi \right)-\frac{c_q\left(t\right)}{2}\cos \left(\mathrm{\Delta \omega }t+\delta t-\phi \right)+\frac{\alpha }{2}{c}_i\left(t\right)$

[0098] where α arises since the “quadrature” reference signal is an analog signal and is not exactly 90 degrees offset in phase relative to the in-phase reference signal. The in-phase and quadrature signals are then respectively amplified by the AGC and sampled by the in-phase and quadrature A/D converters. One could also use a single A/D converter with a switch to sample in-phase and quadrature channels alternatively. Although the signal is digitized, we continue to use analog notation for simplicity. In one embodiment, frequency and phase lock on the signal is established with the anolog mixer, however we assume that this is not done in this description. The digitized version of s1(t) is mixed with m3(t)=cos (Δωt+γt+θ) to produce 5$s_3\left(t\right)=\frac{c_i\left(t\right)}{4}\left\{\cos \left(2\mathrm{\Delta \omega }t+\delta t+\gamma t+\theta -\phi \right)+\cos \left(\delta t-\gamma t-\theta -\phi \right)\right\}+\frac{c_q\left(t\right)}{4}\left\{\sin \left(2\mathrm{\Delta \omega }t+\delta t+\gamma t+\theta -\phi \right)+\sin \left(\delta t-\gamma t-\theta -\phi \right)\right\}$

[0099] where γ and θ are respectively the frequency and phase offset in the reference signal m3(t). Similarly, the digitized version of s2(t) is then mixed with m4(t)=sin (Δωt+γt+θ) to produce 6$s_4\left(t\right)=\frac{c_i\left(t\right)}{4}\left\{\cos \left(2\mathrm{\Delta \omega }t+\delta t+\gamma t+\theta -\phi \right)+\cos \left(\delta t-\gamma t-\theta -\phi \right)\right\}+\frac{c_q\left(t\right)}{4}\left\{\sin \left(2\mathrm{\Delta \omega }t+\delta t+\gamma t+\theta -\phi \right)+\sin \left(\delta t-\gamma t-\phi -\theta \right)\right\}+\frac{\alpha }{2}{s}_3\left(t\right)$

[0100] We then combine the in-phase and quadrature signals to produce the downconverted sampled signal Ssamp(t)=s3(t)+s4(t)= 7$\frac{c_i\left(t\right)}{2}\cos \left(\delta t-\gamma t-\phi -\theta \right)+\frac{c_q\left(t\right)}{2}\sin \left(\delta t-\gamma t-\phi -\theta \right)+\frac{\alpha }{2}{s}_3\left(t\right).$

[0101] Notice that the degree of rejection of the unwanted component 8$\frac{\alpha }{2}{s}_3\left(t\right)$

[0102] is determined by the magnitude of α, or the precision with which the 90 degree analog phase lag can be implemented. We expect α≦3° which results in roughly 25 dB of rejection of s3(t). While this disturbance signal would have a detrimental effect on the reception of digital television, it does not significantly effect the navigation receiver performance due to the processing gain of the correlation processing. Consequently, we will treat this term as negligible and ignore it in subsequent discussion.

[0103] Many different approaches exist for correlating with the downconverted signal and extracting timing information. One approach which considerably mitigates the effects of multipath is to sample an entire autocorrelation function, rather than to use only early and late samples as in a standard DLL (Delay-locked loop)j implemented in hardware. Multipath effects can be mitigated by selecting the earliest correlation peak. In the case that position can be computed with a brief delay a simple approach is to use a software receiver, which samples a sequence of the down-converted signal, and then processes the sample in firmware on a DSP. We will describe the correlation processing in the context of a non-coherent software receiver which doesn't acquire the incident pilot signal.

[0104] A nominal offset frequency for the downconverted sampled signal is assumed. If the signal is downconverted to baseband as with the discussion above, the nominal offset is 0 Hz. The process generates the complete autocorrelation function based on sampled signal ssamp(t). Although we will not describe details, note that there are many techniques for the process to be implemented more efficiently such as using a low duty factor reference signal. Let T1 be the period of data sampled, ωin be the nominal offset of the sampled incident signal, and let ωoffset be the largest possible offset frequency, due to Doppler shift and oscillator frequency drift. The process implements the pseudocode listed below.

[0105] Rmax=0

[0106] Create a complex code signal

s code (t)=Cl(t)+jCq(t)

[0107] where C1 is the function describing the in-phase baseband signal and Cq is the function describing the quadrature baseband signal.

[0108] Compute F(scode)*where F is the Fourier transform operator, and * is the conjugate operator.

[0109] For ω=ωin−ωoffset to ωin+ωoffset step 9$\frac{\pi }{2T_i}$

[0110] Create a complex mixing signal 10$s_{\mathrm{mix}}\left(t\right)=\cos \left(\mathrm{\omega t}\right)+j\sin \left(\omega t\right),t=\left[0\dots T_i\right]$

[0111] Combine the incident signal s(t) and the mixing signal Smax(t) scomb(t)=ssamp(t)smix(t)

[0112] Compute the correlation function 11$\begin{array}{c}\begin{array}{c}R\left(\tau \right)=F^{-1}\left\{{F\left(s_{\mathrm{code}}\right)}^{*}F\left(s_{\mathrm{comb}}\right)\right\}\\ \mathrm{If}{\max }_r\left|R\left(\tau \right)\right|>R_{\max },R_{\max }\leftarrow {\max }_r\left|R\left(\tau \right)\right|,R_{\mathrm{store}}\left(\tau \right)=R\left(\tau \right)\end{array}\\ \mathrm{Next}\omega \end{array}$

[0113] Upon exit from the process, Rstore(τ) will store the correlation between the incident sampled signal ssamp(t) and the complex code signal scode(t). Rstore(τ) may be further refined by searching over smaller steps of ω. The initial step size for ω must be less then half the Nyquist rate 12$\frac{2\pi }{T_i}.$

[0114] The time offset τ that produces the maximum correlation output is used as the pseudo-range.

[0115] Now that we have considered the signal processing in some detail, we will consider certain hardware components in FIG. 5 which are crucial to system performance, and the characteristics of which need to be accommodated in the signal processing.

[0116] The tunable architecture of the receiver 800 must enables one to selectively pass and reject portions of the broadcast television spectrum. FIG. 10 describes the basic architecture of the tunable bandpass filter 810 which is crucial to this function. The tunable bandpass filter 810 must enable rapid and stable frequency selection such that the front-end may be controlled to operate in a ‘frequency hopping’ manner. Channels are selected for analysis, the filters are tuned, analysis is performed and the filters are re-tuned until all channels of interest have been analyzed. Hence, the settling time of this filter (and all tuning components) should be rapid. Various architectures may be implemented without changing the fundamental concept. The architecture described in FIG. 10 makes use of two sections of voltage tunable filters (a voltage controlled bandpass filter 811 and a voltage controlled bandreject filter 812)to pass the selected channel signal and remove unwanted interference. In one embodiment, the tunable section is implemented as described in FIG. 11. In this architecture use is made of a set of inductors and variactors, the capacitance of which is varied by changing the input voltage signals. The tunable range of frequencies is determined by the magnitude of the inductances and the range of capacitance values of the tunable variactors. In one embodiment where use is made of UHF TV signals, the range of tunable frequencies is from 450 MHz to 850 MHz. However, this system could be optionally designed to operate over alternate frequency spectra, not necessarily containing Broadcast Television stations.

[0117] The frequency of interest is initially selected by some algorithm. The filters are tuned by voltages applied by external control circuitry. The voltages are also selected algorithmically, potentially as a simple look-up table. Once a short period of time (the settling time) has passed, the filters are assumed to be tuned and on-frequency. Signals pass through the voltage tunable band-pass filter (B) which provides signal selectivity. Using foreknowledge of the filters band shaping capabilities, this band-pass filter is tuned to pass as much of the desired signal while attenuating known undesired signals maximally. If there is no particular undesired signal within the filters range, the signal is ‘centered’ in the filters pass band. The signals are further processed through the use of a band-reject filter (C) which is coupled to ground and thereby creates a notch filter which enables placing significant attenuation on particular frequencies which are sources of in-band interference. The signal stream with the desired signals accentuated while possibly interfering energy is attenuated are passed to an impedance transforming network to best couple them to the input of an amplifier (D). In one embodiment, the amplifier is a component of a computer controlled single-chip TV tuner. The signals are filtered and downconverted before being sampled in the A/D.

[0118] Notice that in the process of downconversion and filtering, group delay is caused on each of the channels, which will differ for one channel to another and will differ greatly from the group delay on any GPS signals that are used in the position computation. We will consider some of the causes of group delay for the architecture illustrated in FIG. 8. FIG. 12 illustrates the group delay which is caused by the preselection filter operating at three different tuned frequencies, namely 600 MHz, 782 MHz and 470 MHz corresponding to mid, high and low channels in the UHF band. Note that group delays on the order of 14 nanoseconds occur at the frequency being tuned. Each nanosecond of group delay corresponds spatially to roughly 1 foot of ranging error. Consequently, any differential group delay between the TV signals and between TV and GPS signals needs to be actively corrected for. Consequently, the cumulative group delay on each channel must be measured and stored in a database so that it can be actively subtracted out from the pseudorange measurement for that channel. For example, if the cumulative group delay on a particular channel is measured as 20 nanoseconds, this number will be stored in a database (a simple lookup table) associated with that channel. When the pseudorange for that channel is calculated per equation 2d,3d,4d or the like, that result will then be decreased by 20 nanoseconds (or roughly 20 feet, if working in units of distance).

[0119] Since group delay is inversely proportional to a filter's passband, most of the group delay on a channel arises from the SAW filter, which has a very narrow passband. FIG. 13 illustrates the group delay of a typical SAW filter with a passband of 20 MHz, centered on a frequency of 1220 MHz. Note that the group delay is on the order of 75 ns. By using the same SAW filter for both the TV and GPS signals, the same group delay will be caused by the SAW filter on all channels, and can therefore be ignored since it is a common-mode error. This is one of the key advantages of using a single SAW filter for both the GPS and TV signals.

[0120] Now consider the antenna which collects the wide frequency range of TV signals. There exists a fundamental trade-off between the volume of an antenna and the bandwidth with which that antenna can resonate. Consequently, the design of a small antenna to fit into a mobile wireless device which can capture a wide span of TV frequencies is a challenge. FIG. 14 shows the design of such an antenna in one embodiment. The antenna is attached to a ground plane for testing, and is laid next to a cellular phone for size comparison. Note that this antenna structure is designed to be lined on the inside of the plastic housing of a wireless device at low cost. The amplitude response of the antenna is illustrated in FIG. 15. Note that the antenna resonates well over the UHF band from 473 MHz to 741 MHz. FIG. 16 illustrates the gain pattern of the antenna in terms of azimuth and elevation, measured at 700 MHz. The antenna has a fairly uniform gain pattern with respect to azimuth and elevation and will therefore be largely insensitive to changes in orientation. Within roughly 30 degrees of orientation tilt, the antenna has a loss of less than 4 dB. This level of reception is sufficient not only for the reception of a TV signal for positioning, but in many cases for the reception of a data signal as well.

[0121] GPS Receiver Aiding in a Hybrid TV/GPS Handset

[0122] Because GPS satellites 120 move rapidly in their orbits, their signals are subject to large Doppler shifts caused by the large relative radial velocities between the GPS satellites and the stationary or slowly moving user terminals 102. These Doppler shifts can range over +/−5.5 kHz. In addition each GPS satellite 120 has a different pseudo-noise (PN) code. Thus in order to obtain accurate pseudo-range measurements with GPS signals, it is necessary to determine the Doppler shifts of the GPS satellites 120 and the PN codes.

[0123] GPS satellites 120 transmit an almanac which gives approximate satellite orbits and velocities as well as clock offsets and other factors for up to 32 GPS satellites. The entire almanac of information for 32 satellites comprises only 1 KB of information. With this information and knowledge of very crude position information and user terminal clock time, user terminal 102 can estimate the Doppler information for the GPS satellites 120 in view, and their corresponding PN codes, quite easily to much greater precision than needed for initial acquisition by a noncoherent delay lock tracking loop for GPS.

[0124] In fact a larger frequency uncertainty is caused by the handset local oscillator which may have a stability of only 5 parts per million. This frequency uncertainty by itself contributes a frequency error of approximately +/−7.9 kHz unless corrected. Corrections to the user terminal clock can be obtained by either tracking the TV pilot carrier or by correction using the cell phone signals.

[0125] In some implementations location server 110 periodically downloads to the user terminal the GPS almanac data via a cell phone data link.

[0126] In some implementations user terminal 102 computes GPS satellite Doppler from GPS satellite almanac data. Based on its approximate position (within 100 km or so), user terminal 102 can determine which GPS satellites 120 are visible at any given time. Monitor stations 108 collect the almanac data for all GPS satellites, and transfer them to user terminal 102. User terminal 102 then determines satellite visibility and Doppler. The GPS system updates the almanac data about once a week. The GPS satellite Doppler ranges from −5,500 to +5,500 Hz (at 1.575420 GHz). A typical GPS receiver only needs Doppler to within 500 Hz. Provided with good user terminal position and time estimates, user terminal 102 can compute Doppler to within 1 Hz with almanac data that is a week old. Therefore, assuming that the monitor stations 108 always have the latest almanac data, monitor stations 108 need to upload fresh almanac data to user terminals 102 only once a week.

[0127] Although the official GPS constellation consists of 24 satellites, in reality there can be up to 28 satellites. Each GPS satellite 120 has a satellite ID called the satellite PN (pseudo-noise) number, which ranges from 1 through 32. The number of bits for one set of almanac data is:

[0128] Satellite ID=6 bits (to account for PRN 1-32)

[0129] Almanac=182 bits

[0130] Total=188 bits.

[0131] The entire set of almanac data for 28 satellites needs 28×188=5,264 bits per week.

[0132] The GPS standard already provides means of moving this type of information to a user terminal 102. GPS “assistance data” can be delivered in two ways: short message cell broadcast (SMCB) and radio resource location protocol (RRLP) messages in the control channels. SMCB can be used for almanac, ephemeris, ionospheric, and DGPS correction data. The contents of these messages are described in GSM spec 04.35, section 4.2. These messages might be available to battery pack accessories on some user terminals, since the protocol is based on a form of SMS.

[0133] RRLP messages can carry everything a SMCB message can carry, but can also carry “acquisition assistance” information, which includes code offsets and Doppler data. These messages are described in GSM spec 04.31, annex A.4.2.4. These messages would generally not be available to a battery pack accessory.

[0134] In other implementations, monitor stations 108 upload satellite Doppler to user terminals 102. In this option, monitor stations 108 keep the almanac data and compute GPS satellite visibility and Doppler estimates. In some implementations, monitor stations 108 use their own location (instead of the user terminal location, which neither the monitor station nor the user terminal knows at the time) in the estimation. One Hertz resolution of the Doppler is adequate (considering the uncertainty due to the local oscillator in the user terminal). Furthermore, the maximum numbers of Doppler sets is the number of visible satellites, not the number of satellites in constellation. The number of bits required for every contact is:

[0135] Satellite ID=6 bits (to account for PRN 1-32)

[0136] Doppler=14 bits (to account for +/−5,500 Hz in 1-Hz resolution)

[0137] Total=20 bits.

[0138] Assuming a maximum of 12 visible satellites; 12*20=240 bits per contact.

[0139] Alternate Embodiments

[0140] The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof. 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).

[0141] In contrast with systems that utilize heavily augmented GPS receivers, which must attempt to track an extremely low level GPS signal in urban indoor areas, some implementations of the present invention use the various TV signals to determine position in urban areas and utilize the GPS signals only in more remote areas or in hilly or mountainous regions where the TV signals are almost completely blocked. In those regions, GPS does not generally suffer the severe building attenuation, and serves a very useful function. Thus relatively simple and low cost GPS receivers suffice.

[0142] A number of embodiments 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.

[0143] For example, while various signals and signal processing techniques are discussed herein in analog form, digital implementations will be apparent to one skilled in the relevant art after reading this description.

[0144] In some implementations, Location server 110 employs redundant signals available at the system level, such as pseudo-ranges available from the TV transmitters, making additional checks to validate each TV channel and pseudo-range, and to identify TV channels that are erroneous. One such technique is conventional receiver autonomous integrity monitoring (RAIM).

[0145] Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A receiver for processing television signals and GPS signals for position determination comprising: an antenna system for receiving a plurality of signals, at least one television signal and at least one GPS signal, wherein the at least one television signal operates at a first frequency and the at least one GPS signal operates at a second frequency; a receiver front end coupled to the antenna system for converting the plurality of signals from at least one of the first frequency or of the second frequency to a third frequency; and a processing component coupled to the receiver front end for accepting the plurality of signals operating at the third frequency and for converting the plurality of signals into a position information.

2. The receiver of claim 1 wherein the antenna system comprises a tuning circuit for resonating at different frequencies to accept at least one signal of the plurality of signals.

3. The receiver of claim 1 wherein the antenna system comprises a first feed and a second feed, the first feed for operating at the first frequency and the second feed for operating at the second frequency.

4. The receiver of claim 3 wherein the antenna system further comprises a switching means coupled to the receiver front end for selecting between the first frequency and the second frequency.

5. The receiver of claim 1 wherein the receiver front end comprises: a low noise amplifier for amplifying the plurality of signals; a first frequency converter coupled to the low noise amplifier for performing frequency conversion on at least one signal of the plurality of signals; a bandpass filter coupled to the first frequency converter for filtering at least one signal of the plurality of signals; a second frequency converter coupled to the bandpass filter for performing frequency conversion on at least one signal of the plurality of signals; and an analog-to-digital converter coupled to the second frequency converter for digitizing at least one signal of the plurality of signals.

6. The receiver of claim 5 wherein the first frequency converter comprises a first mixer and a frequency synthesizer.

7. The receiver of claim 6 wherein the second frequency converter comprises a second mixer and a local oscillator, the local oscillator being driven by the frequency synthesizer.

8. The receiver of claim 5 wherein the second frequency converter comprises a mixer and a local oscillator coupled to the mixer.

9. The receiver of claim 5 wherein the bandpass filter is a surface acoustic wave filter.

10. The receiver of claim 5 wherein the bandpass filter is a high selectivity bandpass filter.

11. The receiver of claim 5 wherein the plurality of signals comprises: at least one television signal and at least one GPS signal; and the receiver front end includes a switch coupled to the bandpass filter for switching between the at least one television signal and at least one GPS signal.

12. The receiver of claim 11 wherein the receiver front end further includes a controller for controlling at least one of the switch, the first frequency converter or the low noise amplifier.

13. The receiver of claim 11 wherein the low noise amplifier includes a RF filter to filter the at least one television signal.

14. The receiver of claim 5 wherein the low noise amplifier includes a RF filter to filter at least one signal of the plurality of signals.

15. The receiver of claim 1 wherein the processing component comprises a first downconversion unit, a carrier acquisition unit and a second downconversion unit, the carrier acquisition coupled between the first downconversion unit and the second downconversion unit.

16. The receiver of claim 15 wherein the first downconversion unit comprises: a first downconverter input for accepting the plurality of signals; a first numerically controlled oscillator having a first pair of quadrature outputs; at least two mixers for mixing the plurality of signals with the first pair of quadrature outputs to generate a plurality of signals in I and Q form (in phase and quadrature form); and a first downconverter output for outputting the plurality of signals in I and Q form.

17. The receiver of claim 16 wherein the carrier acquisition unit comprises a narrow bandpass filter and a phase locked loop for reproducing a vestigial sideband carrier.

18. The receiver of claim 17 wherein the phase locked loop comprises: a loop filter; a second numerically controlled oscillator having a second pair of quadrature outputs; and a phase detector for mixing the second pair of quadrature outputs with the plurality of signals in I and Q form to generate a resulting signal in I & Q form, the resulting signal in I & Q form is passed to the loop filter.

19. The receiver of claim 18 wherein the second downconversion unit comprises a plurality of mixers for mixing the plurality of signals in I and Q form with the resulting signal in I & Q form.

20. The receiver of claim 1 wherein the first frequency is within the UHF and VHF frequency bands.

21. The receiver of claim 1 wherein the second frequency is selected from a frequency group comprising of 1227.6 MHz, 1575.42 MHz or 1.1 GHz.

22. The receiver of claim 1 wherein the third frequency is either an IF frequency or a baseband frequency.

23. The receiver of claim 1 wherein the position information is a psuedo range.

24. The receiver of claim 1 wherein the position information is a user terminal location.

25. A receiver for processing television signals and GPS signals for position determination comprising: a first antenna for receiving at least one first signal at a first frequency; a first low noise amplifier for amplifying the at least one first signal; a second antenna for receiving at least one second signal at a second frequency; a second low noise amplifier for amplifying the at least one second signal; a first frequency converter having a first frequency converter input and a first frequency converter output, the first frequency converter input coupled to the first low noise amplifier for performing frequency conversion on the at least one first signal; a switch having a first switch input, a second switch input and a switch output, the first switch input coupled to the first frequency converter output, the second switch input coupled to the second low noise amplifier, the switch for selecting between the at least one first signal or the at least one second signal; a bandpass filter coupled to the switch output for filtering the at least one first signal or the at least one second signal; a second frequency converter coupled to the bandpass filter for converting the at least one first signal or the at least one second signal to a post-frequency converter signal at a third frequency; an analog-to-digital converter coupled to the second frequency converter for digitizing the post-converter signal and generating a digitized signal; and a processor coupled to the analog-to-digital converter for accepting the digitized signal and for converting the digitized signal into a position information.

26. The receiver of claim 25 wherein the at least one first signal is a television signal.

27. The receiver of claim 25 wherein the first frequency is in the UHF or VHF frequency band.

28. The receiver of claim 25 wherein the at least one second signal is a GPS signal.

29. The receiver of claim 25 wherein the second frequency is selected from a frequency group comprising of 1227.6 MHz, 1575.42 MHz or 1.1 GHz.

30. The receiver of claim 25 wherein the third frequency is either an IF frequency or a baseband frequency.

31. The receiver of claim 25 wherein the first low noise amplifier includes a RF filter.

32. The receiver of claim 25 wherein the first frequency converter comprises a first mixer and a frequency synthesizer.

33. The receiver of claim 32 wherein the second frequency converter comprises a second mixer and a local oscillator, the local oscillator being driven by the frequency synthesizer.

34. The receiver of claim 25 wherein the second frequency converter comprises a mixer and a local oscillator coupled to the mixer.

35. The receiver of claim 25 wherein the bandpass filter is a surface acoustic wave filter.

36. The receiver of claim 25 wherein the bandpass filter is a high selectivity bandpass filter.

37. The receiver of claim 25 wherein the position information is a psuedo range.

38. The receiver of claim 25 wherein the position information is a user terminal location.

39. A receiver for processing television signals and GPS signals for position determination comprising: an antenna system for receiving a plurality of signals selected from the group comprising at least one television signal and at least one GPS signal, wherein the at least one television signal operates at a first frequency and the at least one GPS signal operates at a second frequency; a low noise amplifier coupled to the antenna system for amplifying the plurality of signals; an I/Q downconverter coupled to the low noise amplifier for downconverting the plurality of signals to a third frequency and for generating an I component and a Q component for each of the plurality of signals; a first low pass filter coupled to the I/Q downconverter for filtering the I component; a second low pass filter coupled to the I/Q downconverter for filtering the Q component; a first analog-to-digital converter coupled to the first low pass filter for digitizing the I component and generating a digitized I component; a second analog-to-digital converter coupled to the second low pass filter for digitizing the Q component and generating a digitized Q component; a processing component having a first processing input and a second processing input, the first processing input coupled to the first analog-to-digital converter for accepting the digitized I component, the second processing input coupled to the second analog-to-digital converter for accepting the digitized Q component.

40. The receiver of claim 39 wherein the processing component converts the digitized I component and the digitized Q component into a position information.

41. The receiver of claim 39 further comprising a tunable bandpass filter having an adjustable passband, the tunable bandpass filter coupled to the antenna system for receiving the plurality of signals.

42. The receiver of claim 41 wherein the tunable bandpass filter comprises at least one filter selected from the group comprising a voltage controlled bandpass filter and a voltage controlled bandreject filter.

43. The receiver of claim 39 further comprising a third low pass filter coupled to the low noise amplifier for filtering the plurality of signals.

44. The receiver of claim 39 further comprising at least one automatic gain control coupled to the I/Q downconverter for adjusting the magnitudes of the I component and the Q component.

45. The receiver of claim 39 wherein the I/Q downconverter comprises a first mixer coupled to a local oscillator; and a 90 phase shifter having a shifter input and a shifter output, the shifter input coupled to the local oscillator and the shifter output coupled to a second mixer.

46. The receiver of claim 45 further comprising: a tunable bandpass filter having an adjustable passband, the tunable bandpass filter coupled to the antenna system for receiving the plurality of signals; a first low pass filter coupled to the low noise amplifier for filtering the plurality of signals; a plurality of low pass filters coupled to the I/Q downconverter for filtering the I component and the Q component; and at least one automatic gain control circuit coupled to the I/Q downconverter for adjusting the magnitudes of the I component and the Q component.

47. The receiver of claim 39 further comprising: a tunable bandpass filter having an adjustable passband, the tunable bandpass filter coupled to the antenna system for receiving the plurality of signals; a first low pass filter coupled to the low noise amplifier for filtering the plurality of signals; a plurality of low pass filters coupled to the I/Q downconverter for filtering the I component and the Q component; and at least one automatic gain control circuit coupled to the I/Q downconverter for adjusting the magnitudes of the I component and the Q component.

48. The receiver of claim 40 wherein the position information is a psuedo range.

49. The receiver of claim 40 wherein the position information is a user terminal location.

50. A receiver for processing television signals and GPS signals for position determination comprising: an antenna system for receiving a plurality of signals selected from the group comprising at least one television signal and at least one GPS signal, wherein the at least one television signal operates at a first frequency and the at least one GPS signal operates at a second frequency; a tunable bandpass filter having an adjustable passband, the tunable bandpass filter coupled to the antenna system for receiving the plurality of signals; a low noise amplifier coupled to the tunable bandpass filter for amplifying the plurality of signals; an I/Q downconverter coupled to the low noise amplifier for downconverting the plurality of signals to a third frequency and for generating an I component and a Q component for each of the plurality of signals, wherein the I/Q downconverter comprises a first mixer coupled to a local oscillator, and a 90 degree phase shifter having a shifter input and a shifter output, the shifter input coupled to the local oscillator and the shifter output coupled to a second mixer; a first low pass filter coupled to the I/Q downconverter for filtering the I component; a second low pass filter coupled to the I/Q downconverter for filtering the Q component; a first analog-to-digital converter coupled to the first low pass filter for digitizing the I component and generating a digitized I component; a second analog-to-digital converter coupled to the second low pass filter for digitizing the Q component and generating a digitized Q component; a processing component having a first processing input and a second processing input, the first processing input coupled to the first analog-to-digital converter for accepting the digitized I component, the second processing input coupled to the second analog-to-digital converter for accepting the digitized Q component, wherein the processing component converts the digitized I component and the digitized Q component into a position information.

51. The receiver of claim 50 wherein the position information is a psuedo range.

52. The receiver of claim 50 wherein the position information is a user terminal location.

53. A method for determining the position of a user terminal, comprising: receiving at the user terminal a plurality of broadcast television signals from a plurality of television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the plurality of television signal transmitters based on a known component of the plurality of broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; determining a second set of pseudo-ranges between the user terminal and the plurality of global positioning satellites based on the plurality of global positioning signals; and determining a position of the user terminal based on the first set and the second set of pseudo-ranges, a plurality of locations of the television signal transmitters, and a plurality of locations of the global positioning satellites.

54. The method of claim 53, wherein determining a position of the user terminal comprises: adjusting the first set of pseudo-ranges based on a difference between a transmitter clock at the plurality of broadcast television signals and a known time reference; adjusting the second set of pseudo-ranges based on a relative radial velocity between the plurality of global positioning satellites and the user terminal; and determining the position of the user terminal based on the adjusted first set and second set of pseudo-ranges, the plurality of locations of the television signal transmitters, and the plurality of locations of the global positioning satellites.

55. The method of claim 53, wherein the plurality of broadcast television signals are American Television Standards Committee (ATSC) digital television signals, and the known component in the plurality of broadcast television signals is a known digital sequence in the ATSC frame.

56. The method of claim 55, wherein the known digital sequence is a synchronization code.

57. The method of claim 56, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

58. The method of claim 56, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

59. The method of claim 53, wherein the plurality of broadcast television signals are European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signals.

60. The method of claim 59, wherein the known component in the plurality of broadcast television signals is a scattered pilot carrier.

61. The method of claim 53, wherein the plurality of broadcast television signals are Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signals.

62. The method of claim 53, wherein the plurality of broadcast television signals are analog television signals.

63. The method of claim 62, wherein the known component in the plurality of broadcast television signals is selected from the group comprising: a horizontal synchronization pulse; a horizontal blanking pulse; a horizontal blanking pulse and a horizontal synchronization pulse; a ghost canceling reference signal; and a vertical interval test signal.

64. The method of claim 53 further comprising: adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

65. The method of claim 64 wherein the first common time instant is the same as the second common time instant.

66. The method of claim 53 further comprising a delay-locked loop adjusting the first set of pseudo ranges to a first common time instant; and the delay-locked loop adjusting the second set of pseudo ranges to a second common time instant.

67. A method for determining the position of a user terminal, comprising: receiving at the user terminal a plurality of broadcast television signals from a plurality of television signal transmitters; determining a first set of pseudo-ranges between the user terminal and the plurality of television signal transmitters based on a known component of the plurality of broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; determining a second set of pseudo-ranges between the user terminal and the plurality of global positioning satellites based on the plurality of global positioning signals; and transmitting the first set and second set of pseudo ranges to a location server configured to determine a position of the user terminal based on the first set and second set of pseudo-ranges, a plurality of locations of the television signal transmitters, and a plurality of locations of the global positioning satellites.

68. The method of claim 67, wherein the plurality of broadcast television signals are American Television Standards Committee (ATSC) digital television signals, and the known component in the plurality of broadcast television signals is a known digital sequence in the ATSC frame.

69. The method of claim 68, wherein the known digital sequence is a synchronization code.

70. The method of claim 69, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

71. The method of claim 69, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

72. The method of claim 67, wherein the plurality of broadcast television signals are European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signals.

73. The method of claim 72, wherein the known component in the plurality of broadcast television signals is a scattered pilot carrier.

74. The method of claim 67, wherein the plurality of broadcast television signals are Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signals.

75. The method of claim 67, wherein the plurality of broadcast television signals are analog television signals.

76. The method of claim 75, wherein the known component in the plurality of broadcast television signals is selected from the group comprising: a horizontal synchronization pulse; a horizontal blanking pulse; a horizontal blanking pulse and a horizontal synchronization pulse; a ghost canceling reference signal; and a vertical interval test signal.

77. The method of claim 67 further comprising: adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

78. The method of claim 77 wherein the first common time instant is the same as the second common time instant.

79. The method of claim 67 further comprising: a delay-locked loop adjusting the first set of pseudo ranges to a first common time instant; and the delay-locked loop adjusting the second set of pseudo ranges to a second common time instant.

80. A method for determining the position of a user terminal, comprising: receiving a first set of pseudo-ranges from the user terminal, the first set of pseudo-ranges determined between the user terminal and the plurality of television signal transmitters based on a known component of a plurality of broadcast television signals transmitted by the plurality of television signal transmitters; receiving a second set of pseudo-ranges from the user terminal, the second set of pseudo-ranges determined between the user terminal and a plurality of global positioning satellites based on a plurality of global positioning signals transmitted by the plurality of global positioning satellites; and determining a position of the user terminal based on the first set and second set of pseudo-ranges, a plurality of locations of the television signal transmitters, and a plurality of locations of the global positioning satellites.

81. The method of claim 80, wherein determining a position of the user terminal comprises: adjusting the first set of pseudo-ranges based on a difference between a transmitter clock at the plurality of broadcast television signals and a known time reference; adjusting the second set of pseudo-ranges based on a relative radial velocity between the plurality of global positioning satellites and the user terminal; and determining the position of the user terminal based on the adjusted first set and second set of pseudo-ranges, the plurality of locations of the television signal transmitters, and the plurality of locations of the global positioning satellites.

82. The method of claim 80, wherein the plurality of broadcast television signals are American Television Standards Committee (ATSC) digital television signals, and the known component in the plurality of broadcast television signals is a known digital sequence in the ATSC frame.

83. The method of claim 82, wherein the known digital sequence is a synchronization code.

84. The method of claim 83, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

85. The method of claim 83, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

86. The method of claim 80, wherein the plurality of broadcast television signals are European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signals.

87. The method of claim 86, wherein the known component in the plurality of broadcast television signals is a scattered pilot carrier.

88. The method of claim 80, wherein the plurality of broadcast television signals are Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signals.

89. The method of claim 80, wherein the plurality of broadcast television signals are analog television signals.

90. The method of claim 89, wherein the known component in the plurality of broadcast television signals is selected from the group comprising: a horizontal synchronization pulse; a horizontal blanking pulse; a horizontal blanking pulse and a horizontal synchronization pulse; a ghost canceling reference signal; and a vertical interval test signal.

91. The method of claim 80 further comprising: adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

92. The method of claim 91 wherein the first common time instant is the same as the second common time instant.

93. The method of claim 80 further comprising a delay-locked loop adjusting the first set of pseudo ranges to a first common time instant; and the delay-locked loop adjusting the second set of pseudo ranges to a second common time instant.

94. A method for determining the position of a user terminal, comprising: receiving at the user terminal a plurality of broadcast television signals from a plurality of television signal transmitters; a location server determining a first set of pseudo-ranges between the user terminal and the plurality of television signal transmitters based on a known component of the plurality of broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; the location server determining a second set of pseudo-ranges between the user terminal and the plurality of global positioning satellites based on the plurality of global positioning signals; and the location server determining a position of the user terminal based on the first set and second set of pseudo-ranges, a plurality of locations of the television signal transmitters, and a plurality of locations of the global positioning satellites.

95. The method of claim 94, wherein the plurality of broadcast television signals are American Television Standards Committee (ATSC) digital television signals, and the known component in the plurality of broadcast television signals is a known digital sequence in the ATSC frame.

96. The method of claim 95, wherein the known digital sequence is a synchronization code.

97. The method of claim 96, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

98. The method of claim 96, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

99. The method of claim 94, wherein the plurality of broadcast television signals are European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signals.

100. The method of claim 99, wherein the known component in the plurality of broadcast television signals is a scattered pilot carrier.

101. The method of claim 94, wherein the plurality of broadcast television signals are Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signals.

102. The method of claim 94, wherein the plurality of broadcast television signals are analog television signals.

103. The method of claim 102, wherein the known component in the plurality of broadcast television signals is selected from the group comprising: a horizontal synchronization pulse; a horizontal blanking pulse; a horizontal blanking pulse and a horizontal synchronization pulse; a ghost canceling reference signal; and a vertical interval test signal.

104. The method of claim 94 further comprising: adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

105. The method of claim 104 wherein the first common time instant is the same as the second common time instant.

106. The method of claim 94 further comprising: a delay-locked loop adjusting the first set of pseudo ranges to a first common time instant; and the delay-locked loop adjusting the second set of pseudo ranges to a second common time instant.

107. A method for determining the position of a user terminal, comprising: receiving at the user terminal a plurality of broadcast television signals from a plurality of television signal transmitters; the user terminal determining a first set of pseudo-ranges between the user terminal and the plurality of television signal transmitters based on a known component of the plurality of broadcast television signals; receiving at the user terminal a plurality of global positioning signals from a plurality of global positioning satellites; the user terminal determining a second set of pseudo-ranges between the user terminal and the plurality of global positioning satellites based on the plurality of global positioning signals; and the user terminal determining a position of the user terminal based on the first set and second set of pseudo-ranges, a plurality of locations of the television signal transmitters, and a plurality of locations of the global positioning satellites.

108. The method of claim 107, wherein the plurality of broadcast television signals are American Television Standards Committee (ATSC) digital television signals, and the known component in the plurality of broadcast television signals is a known digital sequence in the ATSC frame.

109. The method of claim 108, wherein the known digital sequence is a synchronization code.

110. The method of claim 109, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

111. The method of claim 109, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

112. The method of claim 107, wherein the plurality of broadcast television signals are European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting-Terrestrial (DVB-T) signals.

113. The method of claim 112, wherein the known component in the plurality of broadcast television signals is a scattered pilot carrier.

114. The method of claim 107, wherein the plurality of broadcast television signals are Japanese Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signals.

115. The method of claim 107, wherein the plurality of broadcast television signals are analog television signals.

116. The method of claim 115, wherein the known component in the plurality of broadcast television signals is selected from the group comprising: a horizontal synchronization pulse; a horizontal blanking pulse; a horizontal blanking pulse and a horizontal synchronization pulse; a ghost canceling reference signal; and a vertical interval test signal.

117. The method of claim 107 further comprising: adjusting the first set of pseudo ranges to a first common time instant; and adjusting the second set of pseudo ranges to a second common time instant.

118. The method of claim 117 wherein the first common time instant is the same as the second common time instant.

119. The method of claim 107 further comprising: a delay-locked loop adjusting the first set of pseudo ranges to a first common time instant; and the delay-locked loop adjusting the second set of pseudo ranges to a second common time instant.