CN1582401A - Location of broadcast television signals using integrated services digital broadcasting terrestrial (ISDB-T) - Google Patents

Abstract

A method, apparatus, and computer-readable media for determining the position of a user terminal comprises receiving at the user terminal a digital television (DTV) broadcast signal from a DTV transmitter, wherein the DTV signal comprises an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal; determining a pseudo-range between the user terminal and the DTV transmitter based on a known component in the broadcast DTV signal; and determining a position of the user terminal based on the pseudo-range and a location of the DTV transmitter.

Description

Location of broadcast television signals using Integrated Services Digital Broadcasting Terrestrial (ISDB-T)

Cross References to Related Applications

This application is a continuation in part of the following U.S. patent application series: U.S. Patent Application No. 10/210,847, "Position Location Using Broadcast Digital Television Signals," filed July 31, 2002, by James J. Spilker, Jr. and Matthew Rabinowitz Positioning of Digital Television Signals)”; U.S. Patent Application No. 09/932,010, filed August 17, 2001, “Position Location using Terrestrial Digital Video Broadcast Television Signals” by Matthew Rabinowitz and James J. Spilker, Jr. Positioning of Broadcast Television Signals)”; U.S. Patent Application No. 10/209,578, “Time-Gated Noncoherent Delay Lock Loop Tracking of Digital Television Signals,” filed July 31, 2002, by James J. Spilker and Matthew Rabinowitz Time-Gated Non-Coherent Delay-Locked Loop); and U.S. Patent Application No. 10/159,478, filed May 31, 2002, by Matthew Rabinowitz and James J. Spilker, "Position Location using Positioning Signals Augmented by Broadcast Television Signals (using Positioning of global positioning signals supplemented by broadcast television signals)".

This application also claims the benefit of the following U.S. Provisional Patent Application: U.S. Patent Application No. 60/337,834, "Wireless Position Location Using the Japanese ISDB-T Digital TV Signals," filed November 9, 2001, by James J. Spilker -T Wireless Positioning of Digital Television Signals)"; No. 60/265,675 "System and Method for Navigation and/or Data Communication Using Satellite and/or Terrestrial Infrastructure (using Satellite and/or Subterranean Structures for Navigation and/or Data Communications)"; No. 60/281,270 "Use of the ETSI DVB Terrestrial Digital TV" by James J. Spilker, filed April 3, 2001 Broadcast Signals For High Accuracy Position Location in Mobile Radio Links (Use of ETSI DVB terrestrial digital television broadcasting signals for high-precision positioning in mobile radio links)"; No. 60 filed by James J. Spilker and Matthew Rabinowitz on April 3, 2001 /281,269 "An ATSC Standard DTV Channel For Low Data Rate Broadcast to Mobile Receivers"; by James J. Spilker and Matthew Rabinowitz, May 25, 2001 Application No. 60/293,812 "DTV Monitor System Unit (MSU)"; and 60/293,813, filed May 25, 2001, by James J. Spilker and Matthew Rabinowitz, " DTV Position Location Range And SNRPerformance (DTV positioning range and SNR performance)".

All of the foregoing are hereby incorporated by reference.

Background technique

The present invention relates generally to position determination, and more particularly to the use of digital television (DTV) signals for position determination.

Various technologies for two-dimensional latitude/longitude positioning systems using radio signals have existed for a long time. Ground-based systems such as Loran C and Omega, as well as satellite-based systems known as Transit, are widely used. Another satellite-based system that is gaining popularity is the Global Positioning System (GPS).

GPS was originally designed in 1974 and is widely used for positioning, navigation, surveying and time transfer. The GPS system is referenced to a constellation of 24 orbiting satellites in a subsynchronous 12-hour orbit. Each satellite carries a precise clock and transmits a pseudonoise signal that can be precisely tracked to determine pseudoranges. By tracking 4 or more satellites, people can determine the precise position in three-dimensional space around the world in real time. More details are provided in "Global Positioning System-Theory and Applications" by B.W. Parkinson and J.J. Spilker, Jr. (Volumes I and II, AIAA, Washington, DC, 1996) .

GPS revolutionized navigation and positioning technology. In some cases, however, GPS is not very effective. Since GPS signals are transmitted at relatively low power levels (less than 100 watts) and over large distances, the received signal strength is relatively weak (approximately 160 dBw when received by an omnidirectional antenna). The signal is therefore only marginally or not at all usable in the presence of obstacles or inside buildings.

A system has even been suggested that uses regular analog National Television Standards Committee (NTSC) television signals to determine location. This proposal is found in US Patent No. 5,510,801 (issued April 23, 1996), entitled "Location Determination System And Method Using Television Broadcast Signals." However, existing analog television signals contain horizontal and vertical sync pulses, which are intended for synchronization of relatively coarse TV scanning circuits. Additionally, in 2006 the US Federal Communications Commission (FCC) will consider shutting down NTSC transmitters and reallocating valuable spectrum so that it can be auctioned off for other purposes deemed more valuable.

Contents of the invention

In general, viewed from one aspect, the invention features a method, apparatus, and computer-readable medium for determining a location of a user terminal. It includes receiving, at a user terminal, a digital television (DTV) broadcast signal from a DTV transmitter, wherein the DTV signal includes an Integrated Services Digital Broadcast-Terrestrial (ISDB-T) signal; a pseudorange between the terminal and the transmitter; and determining the location of the user terminal based on the pseudorange and the location of the DTV transmitter.

Particular implementations may include one or more of the following features. Determining the location of the user terminal includes: adjusting the pseudorange based on a difference between a transmitter clock at the DTV transmitter and a known time reference; and determining the location of the user terminal based on the adjusted pseudorange and the location of the DTV transmitter s position. The known component is a kind of scattered pilot. Determining the location of the user terminal includes: determining an offset between a local time reference in the user terminal and a master time reference; and determining the location of the user terminal based on the pseudorange, the location of the DTV transmitter, and the offset. An embodiment includes utilizing the offset to determine a subsequent location of the user terminal. Determining the pseudorange includes: storing a portion of the DTV signal; and subsequently correlating the stored portion with a signal generated by the user terminal to generate the pseudorange. Determining the pseudorange includes, when receiving the DTV signal, correlating the DTV signal with a signal generated by a user terminal to generate the pseudorange. Determining the position of the user terminal includes: determining a general geographical area where the user terminal is located; and determining the position of the user terminal based on pseudoranges and the general geographical area. The general geographic area is the coverage area of an additional transmitter communicatively linked to the user terminal. Determining the location of the user terminal includes: determining the tropospheric propagation velocity in the vicinity of the user terminal; adjusting the pseudorange based on the tropospheric propagation velocity; and determining the location of the user terminal based on the adjusted pseudorange and the location of the DTV transmitter. Determining the location of the user terminal includes: adjusting pseudoranges based on ground elevation in the vicinity of the user terminal; and determining the location of the user terminal based on the adjusted pseudoranges and the location of the DTV transmitter. Embodiments include selecting the DTV signal from a plurality of DTV signals based on the identity of an additional transmitter communicatively linked to the user terminal and a stored table associating the additional transmitter with the DTV signal. Embodiments include: accepting a location input from a user; and selecting the DTV signal from a plurality of DTV signals based on the location input. Embodiments include: scanning the available DTV signals to combine a fingerprint of the location; and selecting, from the available DTV signals, a fingerprint for determining a pseudorange based on the fingerprint and a stored table of matching known fingerprints to known locations. DTV signal. Embodiments include using Receiver Autonomous Integrity Monitoring (RAIM) to check the integrity of pseudoranges based on one redundant pseudorange from the DTV transmitter.

In general, viewed from one aspect, the invention features a method, apparatus, and computer-readable medium for determining a location of a user terminal. It includes receiving at a user terminal a digital television (DTV) broadcast signal from a DTV transmitter, wherein the DTV signal includes a European Telecommunications Standards Institute (ETSI) Digital Video Broadcasting Terrestrial (ISDB-T) signal; determining based on the DTV broadcast signal a pseudorange between the user terminal and the transmitter; and communicating the pseudorange to a location server configured to determine the location of the user terminal based on the pseudorange and the location of the DTV transmitter.

Particular implementations may include one or more of the following features. Determining the pseudorange includes: determining a time at which a known component of the DTV broadcast signal was transmitted from the DTV transmitter; determining a time at which the known component was received at the user terminal; and determining a difference between the time of transmission and the time of reception. The known component is a kind of scattered pilot. Determining the pseudorange includes: storing a portion of the DTV signal; and subsequently correlating the stored portion with a signal generated by the user terminal to generate the pseudorange. Determining the pseudorange includes, when receiving the DTV signal, correlating the DTV signal with a signal generated by a user terminal to generate the pseudorange.

In general, viewed from one aspect, the invention features a method, apparatus, and computer-readable medium for determining a location of a user terminal. It involves receiving pseudoranges from a user terminal determined between the user terminal and a DTV transmitter based on a DTV signal broadcast by the DTV transmitter, wherein the DTV signal includes European Telecommunications Standards Institute (ETSI) digital The video broadcasts a terrestrial (ISDB-T) signal, and wherein the pseudorange is determined based on a known component in the ISDB-T signal; and the location of the user terminal is determined based on the pseudorange and the location of the DTV transmitter.

Particular implementations may include one or more of the following features. Determining the location of the user terminal includes: adjusting the pseudorange based on a difference between a transmitter clock at the DTV transmitter and a known time reference; and determining the user terminal based on the adjusted pseudorange and the location of the DTV transmitter. The location of the terminal. The known component is a kind of scattered pilot. Determining the location of the user terminal includes: determining an offset between a local time reference in the user terminal and a master time reference; and determining the location of the user terminal based on the pseudorange, the location of the DTV transmitter, and the offset. An embodiment includes utilizing the offset to determine a subsequent location of the user terminal. Determining the location of the user terminal includes: determining a general geographic area where the user terminal is located; and determining the location of the user terminal based on the pseudorange and the general geographic area. The general geographic area is the coverage area of an additional transmitter communicatively linked to the user terminal. Determining the location of the user terminal includes: determining a tropospheric propagation velocity in the vicinity of the user terminal; adjusting the pseudorange based on the tropospheric propagation velocity; and determining the location of the user terminal based on the adjusted pseudorange and the location of the DTV transmitter. Determining the location of the user terminal includes: adjusting the pseudorange based on ground elevation in the vicinity of the user terminal; and determining the location of the user terminal based on the adjusted pseudorange and the location of the DTV transmitter.

Advantages that may be found in embodiments of the present invention include one or more of the following. Embodiments of the present invention can be used to locate cellular phones, wireless PDAs (Personal Digital Assistants), pagers, automobiles, OCDMA (Orthogonal Code Division Multiple Access) transmitters, and many other devices. Embodiments of the present invention utilize DTV signals with excellent coverage. The implementation of the present invention does not require any changes to the digital broadcast station.

DTV signals have the advantage of being 50dB more powerful than GPS and have substantially better geometry than satellite systems can provide, allowing positioning even in the presence of obstacles and indoors. DTV signals have roughly eight times the bandwidth of GPS, minimizing multipath effects. Processing requirements are minimal due to the high power and sparse frequency components of the DTV signal used for ranging. Embodiments of the present invention are applicable to cheaper, lower speed and lower power devices than required by GPS technology.

Compared to satellite systems such as GPS, the distance between a DTV transmitter and a user terminal changes very slowly. Therefore, DTV signals are not significantly affected by the Doppler effect. This allows pooling of signals over long periods of time, resulting in very efficient signal capture.

The frequency of the DTV signal is substantially lower than that of a conventional cellular telephone system, and thus has better propagation characteristics. For example, DTV signals are more diffracted than cellular signals and are therefore less affected by hills and have a larger horizon. Also, the signal has better propagation characteristics through buildings and cars. Additionally, embodiments of the present invention utilize a component of the ISDB-T signal which is continuous and constitutes a large ratio of the ISDB-T signal power.

Unlike terrestrial angle-of-arrival/time-of-arrival positioning systems for cellular phones, embodiments of the present invention require no changes to the hardware of the cellular base station and are capable of achieving a positioning accuracy of approximately 1 meter. Whether GSM (Global System for Mobile), AMPS (Advanced Mobile Phone Service), TDMA (Time Division Multiple Access), CDMA, etc., when the technology is used to locate a cellular phone, the technology is not dependent on the air interface. Large-band UHF (Ultra High Frequency) frequencies have been allocated to DTV transmitters. Thus, redundancy can be built into the system to prevent strong fading of particular frequencies due to absorption, multipath, and other attenuating effects.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be more apparent from the description and drawings, and from the claims.

Description of drawings

Figure 1 depicts one embodiment of the invention.

Figure 2 illustrates the operation of the embodiment.

Figure 3 depicts the geometry for positioning using three DTV transmitters.

Figure 4 depicts an implementation of a receiver to generate pseudorange measurements.

Figure 5 depicts a simplified example of a positioning calculation for a user terminal.

Figure 6 depicts the hilling effect on a fixed range circumference of a DTV transmitter located at the same height as the surrounding land.

Figure 7 shows some scattered pilots that are all transmitted simultaneously.

Figure 8 shows a coherent autocorrelation function.

Figure 9 depicts an embodiment of a monitoring unit.

Figure 10 illustrates one implementation for a software receiver.

Detailed ways

introduce

Digital television (DTV) is becoming increasingly popular. DTV first appeared in the United States in 1998. At the end of 2000, there were 167 stations broadcasting DTV signals over the air. As of February 28, 2001, the FCC had issued approximately 1,200 DTV construction permits. According to the FCC's goal, all TV transmissions will soon be digital, and then analog signals will be eliminated. By May 1, 2002, public broadcasting stations must be digital in order to maintain their licence. Private stations must be digital by May 1, 2003. It is expected that there will be more than 1600 DTV transmitters in the United States. Similar DTV systems are being implemented in other regions. The Japan Broadcasting Corporation (NHK) has specified a terrestrial DTV signal in Japan, referred to herein as an Integrated Services Digital Broadcasting Terrestrial (ISDB-T) signal. These new DTV signals allow multiple TV signals to be transmitted in the allocated 6MHz channels. These new ISDB-T DTV signals are completely different from analog NTSC TV signals and have completely new capabilities. The present inventors have realized that ISDB-T signals can be used for positioning and have developed techniques for such positioning. These techniques can be used in the immediate vicinity of ISDB-T DTV transmitters at distances far greater than typical TV reception distances. Because of the high power of the DTV signal, these techniques can even be used indoors with hand-held receivers, and thus offer a possible solution to the positioning needs of the Enhanced 911 (E911) system.

It will be apparent to those skilled in the relevant art that the techniques disclosed herein can be applied to other DTV signals that include known data sequences by simply modifying the correlators to accommodate the known sequences of data. These techniques can also be applied to other Orthogonal Frequency Division Multiplexing (OFDM) signals such as satellite radio signals.

In contrast to the digital pseudorange of GPS, DTV signals are received from transmitters only a few miles away, and those transmitters broadcast the signals with effective radiated powers as high as hundreds of kilowatts. Additionally, the DTV transmitter antenna has a significant antenna gain of about 14dB. Therefore, there is usually enough power to allow reception of DTV signals inside buildings.

As noted above, embodiments of the present invention utilize a component of the ISDB-T signal referred to as the "scattered pilot signal." The use of scattered pilot signals is advantageous for several reasons. First, it allows positioning indoors and at large distances from the DTV transmitter. Conventional DTV receivers utilize only one data signal at a time, and are therefore limited by the energy of a single signal over the distance from the DTV transmitter. In contrast, embodiments of the present invention utilize the energy of multiple scattered pilot signals simultaneously, thereby allowing operation at greater distances from the DTV transmitter than conventional DTV receivers. Additionally, scattered pilots are not data modulated. This is advantageous for two reasons. First, all the power in the scattered pilots is available for position determination; no power is dedicated to data. Second, scattered pilots can be observed over long periods of time without suffering from data modulation-induced degradation. Thus, the ability to track signals indoors over considerable distances from the DTV is greatly expanded. Furthermore, by using digital signal processing, these new tracking techniques can be implemented in a single semiconductor chip.

Referring to FIG. 1, an example implementation 100 includes a user terminal 102 that communicates with a base station 104 via an air link. In one embodiment, user terminal 102 is a radiotelephone and base station 104 is a radiotelephone base station. In one embodiment, base station 104 is part of a mobile MAN (Metropolitan Area Network) or WAN (Wide Area Network).

Figure 1 is used to illustrate various aspects of the invention, but the invention is not limited to this embodiment. For example, the term "user terminal" means any object capable of enabling said DTV positioning. Examples of user terminals include PDAs, mobile phones, cars and other vehicles, and any object that may include a chip or software to enable DTV positioning. It is not intended to be limited to a "terminal" or an object operated by a "user".

Positioning performed by DTV location servers

FIG. 2 illustrates the operation of embodiment 100. As shown in FIG. User terminal 102 receives DTV signals from a plurality of DTV transmitters 106A and 106B through 106N (step 202).

The DTV channel used in positioning can be selected in various ways. In one embodiment, the DTV location server 110 tells the user terminal 102 the best DTV channel to monitor. In one embodiment, user terminal 102 exchanges messages with DTV location server 110 via base station 104 . In one embodiment, the user terminal 102 selects the DTV channel to monitor based on the identity of the base station 104 and a stored table associating base stations with DTV channels. In another embodiment, the user terminal 102 may accept location input from the user giving a general area indication, such as the nearest city name; and use this information to select a DTV channel for processing. In one embodiment, the user terminal 102 scans for available DTV channels to assemble a fingerprint for the location based on the power level of the available DTV channels. The user terminal 102 compares this fingerprint to a stored table that matches known fingerprints to known locations in order to select a DTV channel for processing. This selection is based on the power level of the DTV channel and the direction of arrival of each signal to minimize the Dilution of Precision (DOP) for position calculations.

User terminal 102 determines pseudoranges between user terminal 102 and each DTV transmitter 106 (step 204). Each pseudorange represents the time difference (or equivalent distance) between the time when a component of the DTV broadcast signal is transmitted from the transmitter 108 and the receiving time of the component at the user terminal 102, and the clock offset at the user terminal shift.

The user terminal 102 transmits the pseudoranges to the DTV location server 110 . In one embodiment, DTV location server 110 is implemented as a general purpose computer executing software designed to perform the operations described herein. In another embodiment, the DTV location server is implemented as an ASIC (Application Specific Integrated Circuit). In one embodiment, DTV location server 110 is implemented within base station 104 or near base station 104 .

DTV signals are also received by a plurality of monitoring units 108A through 108N. Each monitoring unit may be implemented as a small unit including a transceiver and a processor, and may be mounted at a suitable location such as a utility pole, DTV transmitter 106 or base station 104 . In one embodiment, the monitoring unit is implemented onboard a satellite.

For each DTV transmitter 106 from which the monitoring unit receives DTV signals, each monitoring unit 108 measures the time offset between the DTV transmitter's local clock and a reference clock. In one embodiment, the reference clock is derived from GPS signals. Using a reference clock allows determining a time offset for each DTV transmitter 106 when multiple monitoring units 108 are used, since each monitoring unit 108 is able to determine a time offset relative to the reference clock. Therefore, offsets in the local clock of the monitoring unit 108 do not affect these determinations.

In another embodiment, no external time reference is required. According to this embodiment, a single monitoring unit receives DTV signals from all of the same DTV transmitters as user terminal 102 . In fact, the local clocks of the individual monitoring units act as time references.

In one embodiment, each time offset is modeled as a fixed offset. In another embodiment, each time offset is modeled as a quadratic polynomial of the form, where the time offset can be described by a, b, c, T:

Offset = a+b(tT)+c(tT) ² (1)

In either embodiment, each measured time offset may be periodically transmitted to the DTV location server as part of the actual DTV broadcast data using the Internet, a secure modem connection, or the like. In one embodiment, a GPS receiver is used to determine the location of each monitoring unit 108 .

DTV location server 110 receives information from database 112 describing the phase center (ie, location) of each DTV transmitter 106 . In one embodiment, the phase center of each DTV transmitter 106 is measured by directly measuring the phase center using the monitoring unit 108 at various locations. One way of doing this is to use multiple time-synchronized monitoring units at some known locations. These units produce pseudorange measurements to a television transmitter at the same instant in time, and those measurements can be used to inverse-triangulate the position of the television transmitter's phase center. In another embodiment, the phase center of each DTV transmitter 106 is measured by measuring the antenna phase center. Once the phase center is determined, it is stored in the database 112 .

In one embodiment, DTV location server 110 receives weather information from weather server 114 describing the air temperature, barometric pressure, and humidity in the vicinity of user terminal 102 . Weather information is available from the Internet and other sources. Using methods such as those in B. Parkinson and J. Spilker, Jr., "Global Positioning System-Theory and Applications" (AIAA, Washington DC, 1996, Vol. 1, Ch. 17, J . Spilker, Jr. "On the Tropospheric Influence of GPS"), the DTV location server 110 determines the tropospheric propagation velocity from weather information.

DTV location server 110 may also receive information from base station 104 identifying the general geographic area of user terminal 102 . For example, the information may identify the cell or cell sector in which the cellular telephone is located. This information is used for ambiguity resolution, as described below.

The DTV location server 110 determines the location of the user terminal based on the pseudorange and location of each transmitter and the clock offset (step 206). FIG. 3 depicts the geometry for position determination using three DTV transmitters 106 . DTV transmitter 106A is located at location (x1, y1). The distance between user terminal 102 and DTV transmitter 106A is r1. DTV transmitter 106B is located at location (x2, y2). The distance between user terminal 102 and DTV transmitter 106B is r2. DTV transmitter 106N is located at location (x3, y3). The distance between user terminal 102 and DTV transmitter 106N is r3.

The DTV location server 110 may adjust the value of each pseudorange based on the tropospheric propagation velocity and the time offset of the corresponding DTV transmitter 106 . DTV location server 110 uses phase center information from database 112 to determine the location of each DTV transmitter 106 .

The user terminal 102 generates three or more pseudorange measurements in order to solve for three unknowns, namely: the location (x, y) of the user terminal 102 and the clock offset T. In other embodiments, the techniques disclosed herein are used to determine location in three dimensions (longitude, latitude, and altitude), and may include factors such as DTV transmitter altitude.

The above three pseudorange measurements pr1, pr2 and pr3 are given by:

pr1=r1+T (2)

pr2=r2+T (3)

pr3=r3+T (4)

These three distances can be expressed as:

... r1=|X-X1| (5)

... r2=|X-X2| (6)

... r3=|X-X3| (7)

Wherein X represents the two-dimensional vector position (x, y) of the user terminal, X1 represents the two-dimensional vector position (x1, y1) of the DTV transmitter 106A, X2 represents the two-dimensional vector position (x2, y2) of the DTV transmitter 106B, And X3 represents the two-dimensional vector position (x3, y3) of the DTV transmitter 106N. These relationships generate three equations for solving for the unknowns x, y and T. DTV location server 110 solves these equations according to conventional well-known methods. In one E911 application, the location of the user terminal 102 is communicated to the E911 location server 116 for distribution to the appropriate authority. In another application, the location is communicated to the user terminal 102 .

Methods for projecting measurements at user terminals to a common moment in time are now described. Note: If the signal from the cellular base station or DTV transmitter 106 is used to stabilize or correct the clock of the user terminal 102, the projection of the above measurements is not required. When the user clock is not stabilized or corrected, the user clock offset can be viewed as a function of time T(t). For a small time interval A, the clock offset T(t) can be modeled with a constant and a first-order term. Right now:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Now we reconsider equations (2a)-(4a), treating clock offset as a function of time. Therefore, pseudorange measurements are also a function of time. For clarity, we assume that the distance remains substantially constant over the time interval Δ. The pseudorange measurements can then be described as:

pr1(t1)=r1+T(t1) (2b)

pr2(t2)=r2+T(t2) (3b)

prN(tN)＝rN+T(tN) (4b)

In one embodiment, user terminal 102 begins with another set of pseudorange measurements a period of time Δ after the initial set of measurements. These measurements can be described as:

$\mathrm{<span\; class="notranslate">\; pr</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; pr</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; prN</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; n</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>$

The user terminal 102 then projects all those pseudorange measurements to some common point in time, effectively canceling the effect of the first order term. For example, consider whether to use some common reference time t0. Applying equations (2b-4b) and (2c-4c) as follows directly states that we can project measurements to a common instant in time:

pr1(t0)＝pr1(t1)+[pr1(t1+Δ)-pr1(t1)](t0-t1)/Δ (2d)

pr2(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)

These projected pseudorange measurements are transmitted to a positioning server where they are used to solve for three unknowns x, y and T. NOTE: The projections in equations (2d-4d) are not exact and do not account for quadratic terms. But the result error is not significant. Those skilled in the art will recognize that quadratic and higher order terms can be computed by generating more than two pseudorange measurements for each shot. Also note: There are many other ways to implement the concept of projecting pseudorange measurements to the same moment in time. One approach, for example, is to implement a delay-locked loop, as described in J.J. Spilker, Jr., "Digital Communications by Satellite" (Prentice-Hall, Englewood Cliffs, NJ, 1977, 1995) and B.W. Parkinson with Those delay-locked loops described in "Global Positioning System-Theory and Application" by J.J. Spilker, Jr. (Vol. 1, AIAA, Washington, DC. 1996), both of which It is incorporated herein by reference. A separate tracking loop can be dedicated to each DTV transmitter 106 . These tracking rings are effectively inserted between pseudorange measurements. The state of each of these tracking loops is sampled at the same instant in time.

In another embodiment, instead of computing pseudoranges, user terminal 102 takes measurements of the DTV signal sufficient to compute pseudoranges (such as a segment of a correlator output) and then transmits these measurements to DTV location server 110 . The DTV location server 110 then calculates pseudoranges based on those measurements, and calculates a location based on the pseudoranges, as described above.

Positioning performed by the user terminal

In another embodiment, the location of the user terminal 102 is calculated by the user terminal 102 . In this embodiment, all necessary information is communicated to the user terminal 102 . Such information may be communicated to the user terminal by the DTV location server 110, the base station 104, the one or more DTV transmitters 106, or any combination thereof. User terminal 102 then measures pseudoranges and solves the simultaneous equations, as described above. This embodiment is now described.

User terminal 102 receives the time offset between each DTV transmitter's local clock and a reference clock. User terminal 102 also receives from database 112 information describing the phase center of each DTV transmitter 106 .

The user terminal 102 receives the tropospheric propagation velocity calculated by the DTV location server 110 . In another embodiment, the user terminal 102 receives weather information from a weather server 114 describing the air temperature, pressure and humidity in the vicinity of the user terminal 102 and uses conventional methods to determine the tropospheric propagation velocity from the weather information.

The user terminal 102 may also receive information from the base station 104 identifying the approximate geographic area of the user terminal 102 . For example, the information may identify the cell or cell sector in which the cellular telephone is located. This information is used for ambiguity resolution, as described below.

User terminal 102 receives DTV signals from multiple DTV transmitters 106 and determines pseudoranges between user terminal 102 and each DTV transmitter 106 . User terminal 102 then determines its position based on the pseudoranges and the phase centers of the transmitters.

In either of the embodiments described above, the location of the user terminal 102 can be determined using the two DTV transmitters and the offset T calculated during a previous fix only if the two DTV transmitters are available. The value of T can be stored or maintained according to conventional methods. Of course, since T is calculated in the past, this assumes that the local clock is sufficiently stable over time.

In one embodiment, the base station 104 determines the clock offset of the user terminal 102 . In this embodiment, only two DTV transmitters are required for position determination. The base station 104 communicates the clock offset T to the DTV location server 110, which then determines the location of the user terminal 102 from the pseudoranges calculated for each DTV transmitter.

In another embodiment, GPS is used to assist in positioning only when one or two DTV transmitters are available for positioning, and each GPS satellite is considered another transmitter in this positioning solution.

receiver structure

FIG. 4 depicts an embodiment of a receiver 400 used in generating pseudorange measurements. In one embodiment, receiver 400 is implemented within user terminal 102 . In another embodiment, receiver 400 is implemented within monitoring unit 108 .

In response to control signals provided by tuner controller 420, tuner 406, clocked by clock 416, tunes antenna 404 to DTV signal 402 in the region. In some embodiments, the tuner 406 also down converts the received DTV signal(s) to an intermediate frequency (IF). Mixers 408I and 408Q combine the carrier signal generated by carrier generator 418 with the tuned DTV signal to produce in-phase and quadrature DTV signals at intermediate frequency (IF) or baseband. In one embodiment, clock 416 runs at 27 MHz. These signals are each filtered by one of filters 410I and 410Q and digitized by one of analog-to-digital converters (A/D) 411I and 411Q, thereby generating signals m[tT] and q[tT], respectively. In an alternative embodiment, a single A/D converter with switches is used to alternately sample the in-phase and quadrature channels. Correlator 412I combines signal m[tT] with synchronization signal s[tT ^* ] and provides a correlation output to search controller 414 .

Delay locked loop 422 includes correlator 412Q, filter 424, numerically controlled oscillator (NCO) 426 clocked by clock 416, and synchronization signal generator 428 that generates a digital representation of the scattered pilot signal. The correlator 412Q combines the signal q[tT] with the synchronization signal s[tT ^* ] and causes the correlation output to be provided to the NCO 426 after being filtered by the filter 424 . The NCO 426 drives the sync generator 428 depending on the search controller 414 .

Control is provided by the search controller 414 during signal acquisition and by the NCO 426 during signal tracking after acquisition. Pseudoranges are obtained by sampling NCO 426.

Note: Only when the user needs to locate, the positioning operation of the user's mobile phone or other devices needs to be generated. For a user walking slowly, in a slow moving vehicle, or seated in a building or at the scene of an emergency, this positioning information only needs to be obtained occasionally. Therefore, batteries or other power sources can be small.

Of course, other aspects of the receiver 400 can be implemented using the concepts described above, for example by using a Fast Fourier Transform (FFT) method to process the received DTV signal. Alternatively, the sum of 9 chirp signals or the sum of all 117 chirp carriers can also be simply digitized and executed in a quasi-optimal manner.

Important to achieve this performance is the concept of correlating all stray pilots in parallel, or at least 9 stray pilots, in a single section. The wider bandwidth of the composite signal provides greater positioning accuracy. Timing accuracy is inversely proportional to bandwidth.

Other signals within the ISDB-T structure can also be used for positioning. For example, a wide-channel narrowing technique can be applied to consecutive pilot signals. However, techniques such as wide-channel pinching involve an inherent resolution of the cyclic ambiguity. Techniques for resolving such ambiguities are well known in the art.

User terminal local oscillators are often relatively poor in frequency stability. This instability affects two different receiver parameters. First, it induces a frequency offset in the receiver signal. Second, it slips the received bit pattern relative to the symbol rate of the reference clock. These two effects limit the integration time of the receiver and thus limit the processing gain of the receiver. The integration time can be increased by correcting the receiver reference clock. In one embodiment, a delay locked loop automatically corrects the receiver clock.

Enhanced positioning

Prior knowledge of cell site locations can be used to enhance positioning. This is conceptually illustrated in FIG. 5, which depicts a simplified example of a location calculation for a user terminal 102 receiving DTV signals from two separate DTV antennas 106A and 106B. For this simplified example, assume that the user's clock offset is known. Based on the distance measurements, a circle of constant extent 502A and 502B is drawn around each transmit antenna 106A and 106B, respectively. The location of the user terminal, including corrections to the user device clock offset, is at one of the intersections 904A and 904B of the two circles 902A and 902B. Note that the ambiguity problem is resolved because the base station 104 can determine in which sector 508 of its coverage area (ie, its coverage area) 506 a user device is located. Of course, if more than two DTV transmitters can be considered, the ambiguity problem can be resolved by taking the intersection of three circles. Because the sync code from the TV transmitter is actually repeating, there is a circular ambiguity problem determined by the repeat period of the TV sync code, which makes the distance ambiguity equal to the repeat period times the speed of light. This circular ambiguity problem can be resolved by the same technique described for the simplified example of Fig. 5 (which is the typical case) as long as the range ambiguity is large compared to the cell site size.

In one embodiment, instead of using the cell site to initially determine an approximate location, the user terminal 102 may accept input from the user giving a general indication of the area, such as the name of the nearest city or the like. In one embodiment, the user terminal 102 scans available DTV channels to assemble a fingerprint describing the location of the set of viewable channels. The user terminal 102 compares this fingerprint to a stored table that matches known fingerprints to known locations in order to identify the current approximate location of the user terminal 102 .

In one embodiment, the positioning calculation includes the effect of ground elevation. Thus, in terrain with hills and valleys, the circumference of the fixed range is distorted relative to the phase center of the DTV antenna 106 . FIG. 6 depicts the effect of a single hill 604 on a fixed range circumference 602 of a DTV transmitter 106 that is located at the same height as the surrounding ground.

The calculation of the user's position is readily performed by a simple computer having as its database a topographical map of the area which allows the calculation to include the effect of the user's height on the earth's surface (ie, the geoid). This calculation includes the distortion effect of a fixed range of circles as shown in FIG. 6 .

ISDB-T signal description

The ISDB-T signal is a composite Orthogonal Frequency Division Multiplexing (OFDM) signal that utilizes 1512 or 6048 separate carriers to carry 188 byte MPEG (Moving Picture Experts Group) packets. Most of these components carry the random-like data modulation of the video television signal and are less useful for precise tracking of low signal levels. Note: For our positioning purposes, user terminals may be in locations where the full information content of the ISDB-T signal is not available.

ISDB-T signal is a Band Segmented Transmission (BST) Orthogonal Frequency Division Multiplexing (OFDM) signal, which has the ability to transmit various video, voice and data services. Because it belongs to the OFDM system, it is resistant to multipath. The use of so-called band-segmented transmissions allows flexibility in the information being transmitted. Those segments have a bandwidth of 3000/7 = 428.5714286 kHz.

The ISDB-T signal contains a synchronous component which is very useful for positioning. The signal is available in both wideband and narrowband formats. The wideband format has a bandwidth of 5.6 MHz and is used for television and data. The narrowband format has a bandwidth of 430KHz and is used for lower bandwidth signals. The signal characteristics of the three modes of wideband format are listed in Table 1. The carrier frequency spacing is the reciprocal of the effective symbol duration. Coherent modulation segments have scattered pilots; differential coherent segments have continuous pilots. For each mode, the total number of segments is Ns=13=ns+nd. One of the three modes of the wideband format is described in this section of the description; however, the same concepts apply to all three modes.

Table 1 parameter 2K mode 8K mode Carrier number K 1705 6817 symbol duration 224 microseconds 896 microseconds Carrier spacing 4464Hz 1116Hz total pitch of the signal 7.61MHz 7.61MHz

The wideband signal consists of 13 OFDM segments, each containing 108 frequencies. The bandwidth of one OFDM segment in 108 carriers is 430 kHz. OFDM carriers are primarily modulated with video information in MPEG-2 format using quadrature amplitude modulation (QAM) modulation and powerful error correction coding. However, some frequencies are reserved within the 108 frequency groups for synchronization; these are the so-called scattered and continuous pilots. Some embodiments of the invention use continuous pilots for center frequency measurements. However, for high-accuracy position measurements, stray pilots are more useful.

ISDB-T signals provide a variety of modulation schemes, including: differential quadrature phase shift keying (DQPSK), quadrature phase shift keying (QPSK), 16QAM, 64QAM, and 1/2, 2/3, 3/4, 5/6 and 7/8 encoding rates for inner codes. These parameters can be chosen independently for each segment. For DQPSK with differential coherent modulation, the total data rate in wideband mode is only 3.651Mbps. For DQPSK modulation and 1/2 code rate, the narrowband single segment mode yields a data rate of 280.85kbps. For the 64QAM mode with an inner code rate of 7/8, the other modes are coherent and yield data rates up to 23.234Mbps.

Within each of the 13 OFDM segments, there are 36 scattered pilots. Thus, in each wideband DTV signal, there are a total of 468 scattered pilots for a total of 13 segments. Within an OFDM segment, the scattered pilots change frequency for each symbol. The number of such frequency hopping is 3 carriers. For one symbol in which the pattern repeats every 4 symbols, the same carrier is transmitted. Therefore, as shown in FIG. 7, there are some scattered pilots that are all transmitted at once. In Figure 7, the largest scattered pilot is 105.

As can be seen in Figure 7, the set of scattered pilots can be viewed as 9 scattered pilots each hopping 3 carriers per symbol. For a total of 117 scattered pilots, a good approximation is 9 "chirp" carriers for each of the 13 segments.

Although the bandwidth of these scattered pilots clearly has a linear component at a period rate of 4 symbols, it is essentially flat over the spectral footprint. However, because the symbol rate is relatively low, a 4-symbol period represents a very large distance. Therefore, the ambiguity problem caused by the signal is negligible and easy to solve.

The synthesized scattered pilot signal can be written as s[t] and represented in numerical form as used in U.S. Patent Application Serial No. 10/210,847 filed July 31, 2002 by James J. Spilker, Jr. and Matthew Rabinowitz The ATSC delay-locked loop described in "Position Location Using Broadcast Digital Television Signals" is the same as the pseudo-noise signal in the correlator. The exact form of the ISDB-T signal is different, but signal tracking can be performed in a similar manner using the reference signal s[t].

Also in "Digital Transmission Scheme for ISDB-T and Reception Characteristics of Digital Terrestrial Television Broadcasting in Japan" by S.Nakahara et al. (IEEE Transactions on Consumer Electronics, August , 1999) and ISDB-T signals are further described in "Transmission Scheme for the Terrestrial ISDB System (Transmission Scheme for the Terrestrial ISDB System)" (IEEE Transactions on Consumer Electronics, February, 1999) by M.Uehara et al.

Autocorrelation function for a single segment

The frequency spacing is 3 units, and a single segment of 108 carriers includes 36 scattered pilots. The transmitted sequence of tones is repeated every 105/3 = 35 symbols. Assuming a sampling rate of 1/400 symbol, the coherent autocorrelation function of this signal calculated for a single segment is shown in Figure 8. An autocorrelation width of a single segment of about 430 kHz can give a time resolution of about 1 microsecond. Using the full bandwidth of a signal with 13 segments and correlated over the entire frequency region, the autocorrelation peak is reduced by the same ratio of about 1000/13 = 77 nanoseconds or 77 feet. Pseudorange accuracies on the order of 5 meters or better are possible with sufficient signal-to-noise ratio and without multipath errors.

monitoring unit

FIG. 9 depicts an embodiment 900 of a monitoring unit 108 . Antenna 904 receives GPS signal 902 . The GPS time conversion unit 906 generates a master clock signal based on the GPS signal. To determine the offset of the DTV transmitter clock, an NCO (Numerically Controlled Oscillator) code sync timer 908A generates a master sync signal based on the master clock signal. The primary synchronization signal may include ISDB-T scattered pilots. In one embodiment, the NCO synchronization timers 908A in all monitoring units 108 are synchronized to the base date and time. In embodiments where a single monitoring unit 108 receives DTV signals from all of the DTV transmitters that are the same as user terminal 102, it is not necessary to synchronize monitoring unit 108 with any other monitoring unit in order to determine the location of user terminal 102. This synchronization is also unnecessary if all monitoring stations 108 or all DTV transmitters are synchronized to a common clock.

One DTV antenna 912 receives various DTV signals 910 . In another embodiment, multiple DTV antennas are used. An amplifier 914 amplifies the DTV signal. One or more DTV tuners 916A through 916N each tune to a DTV channel in the received DTV signal to generate a DTV channel signal. A plurality of NCO code synchronization timers 908B to 908M each receive a DTV channel signal. NCO code synchronization timers 908B to 908M each extract a channel synchronization signal from a DTV channel signal. The channel synchronization signal may include ISDB-T scattered pilots. In one embodiment, continuous pilot signals and symbol timing within the ISDB-T signal are used as an acquisition tool.

A plurality of adders 918A through 918N each generate a clock offset between the master sync signal and a channel sync signal. Processor 920 formats and transmits the resulting data to DTV location server 110 . In one embodiment, for each DTV channel measured, the data includes the identification number of the DTV transmitter, the DTV channel number, the antenna phase center of the DTV transmitter, and the clock offset. This data can be communicated by any of a variety of means including airlinks and the Internet. In one embodiment, the data is broadcast in idle MPEG packets on the DTV channel itself. The clock offset for each channel can also be modeled as a function of time.

software receiver

A radical way to mitigate multipath effects is to sample the entire autocorrelation function instead of only early and late sampling as in a hardware setup. Multipath effects can be mitigated by selecting the earliest correlation peak.

Where the position can be calculated with a short delay, a simple approach is to use a software receiver that samples the filtered signal sequence and then processes the samples in firmware on a digital signal processor.

Figure 10 illustrates one embodiment 1000 of a software receiver. Antenna 1002 receives DTV signals. Antenna 1002 may be a magnetic dipole antenna or any other type of antenna capable of receiving DTV signals. Bandpass filter 1004 passes the entire DTV signal spectrum to LNA 1006. In one embodiment, filter 1004 is a tunable bandpass filter that, under the control of digital signal processor (DSP) 1014, transmits the frequency spectrum of a particular DTV channel.

A low noise amplifier (LNA) 1006 amplifies and transmits the selected signal to a DTV channel selector 1008 . The DTV channel selector 1008 under the control of the processor 1014 selects a particular DTV channel and the selected channel signal is filtered and down converted from UHF (Ultra High Frequency) to IF (Intermediate Frequency) according to conventional methods. Amplifier (AMP) 1010 amplifies the selected IF channel signal. This amplifier can use automatic gain control (AGC) in order to improve the dynamic range of the architecture. Analog-to-digital converter and sampler (A/D) 1012 generates digital samples Ssamp(t) of the DTV channel signal and transmits these samples to DSP 1014.

Now, the processing of DTV channel signals by DSP 1014 is described with respect to a non-coherent software receiver. Assume a standard offset frequency for downconverting the sampled signal. If this signal is down converted to baseband, the standard offset is 0 Hz. This process generates a complete autocorrelation function based on the sampled signal s _samp (t). There are a number of techniques for this process to be performed more efficiently, such as using a low duty cycle reference signal. Let T _i be the period of sampling data. ω _in be the standard offset of the sampled incident signal, and let ω _offset be the maximum possible offset frequency due to Doppler shift and oscillator frequency shift. This processing executes the pseudocode listed below.

· _Rmax = 0

Generate a composite coded signal

s _code (t)＝C _i (t)+jC _q (t)

where C _i is a function describing the in-phase baseband signal and C _q is a function describing the quadrature baseband signal.

• Compute F(s _code )*, where F is the Fourier transform operator and * is the conjugate operator.

·For ω=ω _in -ω _offset to ω _in +ω _offset the step size is

Generate a composite mixed frequency signal

s _mix (t)=cos(ωt)+jsin(ωt), t=[0...T _i ]

Combine the incident signal s(t) and the mixed signal s _mix (t)

s _comb = s _samp (t) s _mix (t)

· Calculation of correlation functions

R(τ)＝F ^-1 {F(s _code )*F(s _comb )}

·If max _τ |R(τ)|＞R _max , R _max ←max _τ |R(τ)|, R _store (τ)＝R(τ), then

·Next ω

的一半。产生最大Ti相关输出的时间偏移τ被用作伪距。After exiting from this process, R _store (τ) will store the correlation between the incident sampled signal s _samp (t) and the composite coded signal s _code (t). R _sotre (τ) can be further refined by searching on a smaller step size of ω. The initial step size of ω must be smaller than the Nyquist rate

half of. The time offset τ that produces the largest Ti correlation output is used as the pseudorange.

alternative implementation

The invention can be implemented in the form of digital electronic circuitry or in the form of computer hardware, firmware, software or a combination thereof. The apparatus of the present invention can be implemented in a computer program product, and the computer program product can be substantially contained in a machine-readable storage device and executed by a programmable processor; and each method step of the present invention can be implemented by a programmable processor. A processor is programmed to execute program instructions to perform functions of the invention by operating on input data and generating output. Advantageously, the invention can be implemented in the form of one or more computer programs executable on a programmable system comprising at least one programmable processor coupled for A data storage system, at least one input device, and at least one output device receive data and instructions, and transmit data and instructions to the same data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level or object-oriented programming language, or in assembly or machine language, if desired. And in any case, the language may be a compiled or translated 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 random access memory. Typically, 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 embodying substantially computer program instructions and data include all forms of non-volatile memory including, for example: semiconductor memory devices such as EPROM, EEPROM and flash memory devices; such as internal hard disks and removable magnetic disks; disks such as; magneto-optical disks; and CD-ROM disks. All of the above can be supplemented or combined with ASIC (Application Specific Integrated Circuit).

Several embodiments of the invention have been described above. It should be understood, however, that various modifications may be made without departing from the spirit and scope of the invention.

For example, although one method is described for tracking ISDB-T signals, it should be clear that there are a variety of methods of tracking these signals using various forms of conventional delay-locked loops and by using various types of matching filters to track these signals.

Although embodiments of the invention are discussed with reference to 8 MHz signals, the embodiments may be applied with signals of other bandwidths. Additionally, implementations of the present invention can use a subset of the ISDB-T signal bandwidth. For example, one embodiment of the present invention achieves satisfactory results using only 6 MHz of an 8 MHz ISDB-T signal. Embodiments of the present invention can be extended to take advantage of future improvements to the ISDB-T signal.

Embodiments of the present invention take advantage of the fact that DTV signals have high power and can also be tracked by capturing signal bursts or using a low duty factor reference signal (not utilizing all of the incident signal energy). For example, one embodiment uses a time-gated delay-locked loop (DLL), such as described in J.J. Spilker, Jr., "Digital Communications by Satellite" (Prentice-Hall, Englewood Cliffs NJ, 1977, Chapter 18-6) disclosed in. Other implementations use other variants of DLLs, including coherent, non-coherent, and quasi-coherent DLLs, as described in J.J. Spilker, Jr., "Digital Communications by Satellite" (Prentice-Hall, Englewood Cliffs NJ, 1977, Chapter 18) and B.Parkinson and J.Spilker, Jr. "Global Positioning System-Theory and Applications" (AIAA, Washington, DC, 1996, Vol. 1, No. 17 Chapter, J. Spilker Jr, "Principles of Signal Tracing Fundamentals"). Other implementations use various types of matched filters, such as recirculating matched filters.

In some embodiments, DTV location server 110 uses redundant signals available at the system level, such as pseudoranges that may be obtained from DTV transmitters, to perform additional checks to validate each DTV channel and pseudorange, and to identify erroneous DTV The pseudorange of the channel. One such technique is conventional Receiver Autonomous Integrity Monitoring (RAIM).

Another embodiment of the present invention combines the DTV ranging signals described above with other forms of signals from which pseudoranges can be calculated. For example, in U.S. Patent Application No. 10/159,478 "Position Location using Global Positioning Signals Augmented by Broadcast Television Signals" filed May 31, 2002 by Matthew Rabinowitz and James J. Spilker )" describes the combined use of DTV and GPS satellite signals, the contents of which are incorporated herein by reference. Additionally, for a combined location solution, the DTV signal can be combined with a cellular base station signal or a digital radio signal, or any other signal that includes a synchronization code.

Accordingly, other implementations are within the scope of the following claims.

Claims (87)

1. a kind of method for determining user terminal location, comprising:

DTV (DTV) broadcast singal from a DTV transmitter is received at the user terminal, wherein the DTV signal includes integrated service Digital Broadcasting Terrestrial (ISDB-T) signal；

The pseudorange between the user terminal and the transmitter is determined based on a known components in the broadcasts DTV signals；With

The position of the user terminal is determined based on the position of the pseudorange and the DTV transmitter.

2. the method according to claim 1, wherein determining that the position of the user terminal includes:

The pseudorange is adjusted based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

3. the method according to claim 1, wherein the known components are scattered pilots.

4. the method according to claim 1, wherein determining that the position of the user terminal includes:

Determine the offset between the local time reference and a main time reference in the user terminal；With

The position of the user terminal is determined based on the pseudorange, the position of the DTV transmitter and the offset.

5. method according to claim 4, further comprises:

The follow-up location of the user terminal is determined using the offset.

6. the method according to claim 1, wherein determining that pseudorange includes:

Store a part of the DTV signal；And

Then keep stored part related to the signal generated by the user terminal to generate the pseudorange.

7. the method according to claim 1, wherein determining that pseudorange includes:

When receiving the DTV signal, keep the DTV signal related to the signal generated by the user terminal to generate the pseudorange.

8. the method according to claim 1, wherein determining that the position of the user terminal includes:

Determine locating for the user terminal substantially geographic area；And

The position of the user terminal is determined based on the pseudorange and the substantially geographic area.

9. method according to claim 8, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

10. the method according to claim 1, wherein determining that the position of the user terminal includes:

Determine the tropospheric propagation velocity near the user terminal in area；

The pseudorange is adjusted based on the tropospheric propagation velocity；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

11. the method according to claim 1, wherein determining that the position of the user terminal includes:

The pseudorange is adjusted based on the ground elevation near the user terminal in area；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

12. the method according to claim 1 further comprises:

Based on the identity for an additional transmitters for being communicably linked to the user terminal, and make additional transmitters storage table relevant to the DTV signal, the DTV signal is selected from multiple DTV signals.

13. the method according to claim 1 further comprises:

Receive position input from the user；With

It is inputted based on the position to select the DTV signal from multiple DTV signals.

14. the method according to claim 1 further comprises:

Available DTV signal is scanned to combine the fingerprint of the position；And

Based on the fingerprint, and the storage table for making known fingerprint and known location match, the DTV signal for determining the pseudorange is selected from the available DTV signal.

15. the method according to claim 1 further comprises:

Using receiver autonomous integrity monitoring (RAIM), to check the integrity of the pseudorange based on the redundancy pseudorange from the DTV transmitter.

16. a kind of method for determining user terminal location, comprising:

DTV (DTV) broadcast singal from a DTV transmitter is received at the user terminal, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal；

The pseudorange between the user terminal and the transmitter is determined based on the DTV broadcast singal；With

The pseudorange is transmitted to a location server, which is configured for determining the position of the user terminal based on the position of the pseudorange and the DTV transmitter.

17. method according to claim 16, wherein determining that pseudorange includes:

Determine the time that a known components of the DTV broadcast singal emit from the DTV transmitter；

Determine receiving time of the known components at the user terminal；With

Determine the difference between the launch time and receiving time.

18. method according to claim 16, wherein the known components are scattered pilots.

19. method according to claim 16, wherein determining that pseudorange includes:

Store a part of the DTV signal；And

Then keep stored part related to the signal generated by the user terminal to generate the pseudorange.

20. method according to claim 16, wherein determining that pseudorange includes:

When receiving the DTV signal, keep the DTV signal related to the signal generated by the user terminal to generate the pseudorange.

21. a kind of method for determining user terminal location, comprising:

Pseudorange is received from user terminal, the pseudorange is determined between the user terminal and a DTV transmitter, based on the DTV signal that the DTV transmitter is broadcasted, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal, and wherein the pseudorange is determined based on a known components in the ISDB-T signal；And

The position of the user terminal is determined based on the position of the pseudorange and the DTV transmitter.

22. method according to claim 21, wherein determining that the position of the user terminal includes:

The pseudorange is adjusted based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

23. method according to claim 21, wherein the known components are scattered pilots.

24. method according to claim 21, wherein determining that the position of the user terminal includes:

Determine the offset between the local time reference and a main time reference in the user terminal；With

The position of the user terminal is determined based on the pseudorange, the position of the DTV transmitter and the offset.

25. method according to claim 24, further comprises:

The follow-up location of the user terminal is determined using the offset.

26. method according to claim 21, wherein determining that the position of the user terminal includes:

Determine locating for the user terminal substantially geographic area；And

The position of the user terminal is determined based on the pseudorange and the substantially geographic area.

27. method according to claim 26, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

28. method according to claim 21, wherein determining that the position of user terminal includes:

Determine the tropospheric propagation velocity near the user terminal in area；

The pseudorange is adjusted based on the tropospheric propagation velocity；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

29. method according to claim 21, wherein determining that the position of the user terminal includes:

The pseudorange is adjusted based on the ground elevation near the user terminal in area；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

30. a kind of equipment for determining user terminal location, comprising:

Device, for receiving DTV (DTV) broadcast singal from a DTV transmitter at the user terminal, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal；

Device, for determining the pseudorange between the user terminal and the transmitter based on a known components in the DTV broadcast singal；With

Device, for determining the position of the user terminal based on the position of the pseudorange and the DTV transmitter.

31. equipment according to claim 30, wherein being used to determine that the device of the user terminal location to include:

Device, for adjusting the pseudorange based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

32. according to the equipment of claim 31, wherein the known components are scattered pilots.

33. equipment according to claim 30, wherein being used to determine that the device of the user terminal location to include:

Device, for determining the offset between local time reference and a main time reference in the user terminal；With

Device, for determining the position of the user terminal based on the position of the pseudorange, the DTV transmitter and the offset.

34. further comprising according to the equipment of claim 33:

Device, for determining the follow-up location of the user terminal using the offset.

35. equipment according to claim 30, wherein being used to determine that the device of pseudorange to include:

Device, for storing a part of the DTV signal；With

Device generates the pseudorange for then making stored part related to the signal generated by the user terminal.

36. equipment according to claim 30, wherein being used to determine that the device of pseudorange to include:

Device generates the pseudorange for when receiving the DTV signal, making the DTV signal related to the signal generated by the user terminal.

37. equipment according to claim 30, wherein being used to determine that the device of the user terminal location to include:

Device, for determining locating for the user terminal substantially geographic area；With

Device, for determining the position of the user terminal based on the pseudorange and the substantially geographic area.

38. according to the equipment of claim 37, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

39. equipment according to claim 30, wherein being used to determine that the device of the user terminal location to include:

Device, for determining the tropospheric propagation velocity near the user terminal in area；

Device, for adjusting the pseudorange based on the tropospheric propagation velocity；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

40. equipment according to claim 30, wherein being used to determine that the device of the user terminal location to include:

Device, for adjusting each pseudorange based on the ground elevation near the user terminal in area；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

41. equipment according to claim 30, further comprises:

Device for the identity based on an additional transmitters for being communicably linked to the user terminal and makes additional transmitters storage table relevant to the DTV signal, the DTV signal is selected from multiple DTV signals.

42. equipment according to claim 30, further comprises:

Device, for receiving position input from the user；With

Device selects the DTV signal for inputting based on the position from multiple DTV signals.

43. equipment according to claim 30, further comprises:

Device combines the fingerprint of the position for scanning available DTV signal；With

Device is used to be based on the fingerprint, and the storage table for making known fingerprint and known location match, and the DTV broadcast singal for determining the pseudorange is selected from the available DTV signal.

44. equipment according to claim 30, further comprises:

Device, for using receiver autonomous integrity monitoring (RAIM), to check the integrity of the pseudorange based on the redundancy pseudorange from the DTV transmitter.

45. a kind of equipment for determining user terminal location, comprising:

Device, for receiving DTV (DTV) broadcast singal from a DTV transmitter at the user terminal, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal；

Device, for determining the pseudorange between the user terminal and the transmitter based on a known components in the DTV broadcast singal；With

Device, for the pseudorange to be transmitted to a location server, which is configured for determining the position of the user terminal based on the position of the pseudorange and the DTV transmitter.

46. according to the equipment of claim 45, wherein being used to determine that the device of pseudorange to include:

Device, the time emitted for determining a known components of the DTV broadcast singal from the DTV transmitter；

Device, for determining receiving time of the known components at the user terminal；With

Device, for determining the difference between the launch time and receiving time.

47. according to the equipment of claim 45, wherein the component is scattered pilot.

48. according to the equipment of claim 45, wherein determining that the device of pseudorange includes:

Device, for storing a part of the DTV signal；With

Device generates the pseudorange for then making stored part related to the signal generated by the user terminal.

49. according to the equipment of claim 45, wherein being used to determine that the device of pseudorange to include:

Device, for keeping the DTV signal related to the signal generated by the user terminal to generate the pseudorange when DTV receives signal.

50. a kind of equipment for determining user terminal location, comprising:

Device, for receiving pseudorange from user terminal, the pseudorange is determined between the user terminal and a DTV transmitter, based on the DTV signal that the DTV transmitter is broadcasted, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal, and wherein the pseudorange is determined based on a known components in the DTV signal；With

Device, for determining the position of the user terminal based on the position of the pseudorange and the DTV transmitter.

51. according to the equipment of claim 50, wherein being used to determine that the device of the user terminal location to include:

Device, for adjusting the pseudorange based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

52. according to the equipment of claim 50, wherein the known components are scattered pilots.

53. according to the equipment of claim 50, wherein being used to determine that the device of the user terminal location to include:

Device, for determining the offset between local time reference and a main time reference in the user terminal；With

Device, for determining the position of the user terminal based on the position of the pseudorange, the DTV transmitter and the offset.

54. further comprising according to the equipment of claim 53:

Device, for determining the follow-up location of the user terminal using the offset.

55. according to the equipment of claim 50, wherein being used to determine that the device of the user terminal location to include:

Device, for determining locating for the user terminal substantially geographic area；With

Device, for determining the position of the user terminal based on the pseudorange and the substantially geographic area.

56. according to the equipment of claim 55, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

57. according to the equipment of claim 50, wherein being used to determine that the device of the user terminal location to include:

Device, for determining the tropospheric propagation velocity near the user terminal in area；

Device, for adjusting the pseudorange based on the tropospheric propagation velocity；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

58. according to the equipment of claim 50, wherein being used to determine that the device of the user terminal location to include:

Device, for adjusting the pseudorange based on the ground elevation near the user terminal in area；With

Device, for determining the position of the user terminal based on the position of the pseudorange adjusted and the DTV transmitter.

59. a kind of be substantially stored on computer-readable medium for determining the computer program product of user terminal location comprising can operational order use so that programmable processor:

DTV (DTV) broadcast singal from a DTV transmitter is received at the user terminal, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal；

The pseudorange between the user terminal and the transmitter is determined based on a known components in the broadcasts DTV signals；With

The position of the user terminal is determined based on the position of the pseudorange and the DTV transmitter.

60. according to the computer program product of claim 59, wherein with so that programmable processor determine the user terminal location can operational order include can operational order use so that programmable processor:

The pseudorange is adjusted based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

61. according to the computer program product of claim 59, wherein the known components are scattered pilots.

62. according to the computer program product of claim 59, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine the offset between the local time reference and a main time reference in the user terminal；With

The position of the user terminal is determined based on the pseudorange, the position of the DTV transmitter and the offset.

63. according to the computer program product of claim 62, further comprise can operational order use so that programmable processor:

The follow-up location of the user terminal is determined using the offset.

64. according to the computer program product of claim 59, wherein with so that programmable processor determine pseudorange can operational order include can operational order use so that programmable processor:

Store a part of the DTV signal；And

Make stored part related to the signal generated by the user terminal then to generate the pseudorange.

65. according to the computer program product of claim 59, wherein with so that programmable processor determine pseudorange can operational order include can operational order use so that programmable processor:

When receiving the DTV signal, keep the DTV signal related to the signal generated by the user terminal to generate the pseudorange.

66. according to the computer program product of claim 59, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine locating for the user terminal substantially geographic area；And

The position of the user terminal is determined based on the pseudorange and the substantially geographic area.

67. according to the computer program product of claim 66, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

68. according to the computer program product of claim 59, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine the tropospheric propagation velocity near the user terminal in area；

The pseudorange is adjusted based on the tropospheric propagation velocity；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

69. according to the computer program product of claim 59, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

The pseudorange is adjusted based on the ground elevation near the user terminal in area；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

70. according to the computer program product of claim 59, further comprise can operational order use so that programmable processor:

Based on the identity for an additional transmitters for being communicably linked to the user terminal, and make additional transmitters storage table relevant to the DTV signal, the DTV signal is selected from multiple DTV signals.

71. according to the computer program product of claim 59, further comprise can operational order use so that programmable processor:

Receive position input from the user；With

It is inputted based on the position and selects the DTV signal from multiple DTV signals.

72. according to the computer program product of claim 59, further comprise can operational order use so that programmable processor:

Available DTV signal is scanned to combine the fingerprint of the position；And

Based on the fingerprint, and the storage table for making known fingerprint and known location match, the DTV broadcast singal for determining the pseudorange is selected from the available DTV signal.

73. according to the computer program product of claim 59, further comprise can operational order use so that programmable processor:

Using receiver autonomous integrity monitoring (RAIM), to check the integrity of the pseudorange based on the redundancy pseudorange from the DTV transmitter.

74. a kind of be substantially stored on computer-readable medium for determining the computer program product of user terminal location comprising can operational order use so that programmable processor:

DTV (DTV) broadcast singal from a DTV transmitter is received at the user terminal, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal；

The pseudorange between the user terminal and the transmitter is determined based on a known components in the broadcasts DTV signals；With

The pseudorange is transmitted to a location server, which is configured for determining the position of the user terminal based on the position of the pseudorange and the DTV transmitter.

75. according to the computer program product of claim 74, wherein with so that programmable processor determine pseudorange can operational order include can operational order use so that programmable processor:

Determine the time that the one-component of the DTV broadcast singal emits from the DTV transmitter；

Determine receiving time of the known components at the user terminal；With

Determine the difference between the launch time and receiving time.

76. according to the computer program product of claim 74, wherein the component is scattered pilot.

77. according to the computer program product of claim 74, wherein with so that programmable processor determine pseudorange can operational order include can operational order use so that programmable processor:

Store a part of the DTV signal；And

Then keep stored part related to the signal generated by the user terminal to generate the pseudorange.

78. according to the computer program product of claim 74, wherein with so that programmable processor determine pseudorange can operational order include can operational order use so that programmable processor:

When receiving the DTV signal, keep the DTV signal related to the signal generated by the user terminal to generate the pseudorange.

79. a kind of be substantially stored on computer-readable medium for determining the computer program product of user terminal location comprising can operational order use so that programmable processor:

Pseudorange is received from user terminal, the pseudorange is determined between the user terminal and a DTV transmitter, based on the DTV signal that the DTV transmitter is broadcasted, wherein the DTV signal includes ETSI European Telecommunications Standards Institute (ETSI) digital video broadcast terrestrial (ISDB-T) signal, and wherein the pseudorange is determined based on a known components in the DTV signal；And

The position of the user terminal is determined based on the position of the pseudorange and the DTV transmitter.

80. according to the computer program product of claim 79, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

The pseudorange is adjusted based on the difference between the transmitter clock and a known time benchmark at the DTV transmitter；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

81. according to the computer program product of claim 79, wherein the known components are scattered pilots.

82. according to the computer program product of claim 79, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine the offset between the local time reference and a main time reference in the user terminal；With

The position of the user terminal is determined based on the pseudorange, the position of the DTV transmitter and the offset.

83. according to the computer program product of claim 82, further comprise can operational order use so that programmable processor:

The follow-up location of the user terminal is determined using the offset.

84. according to the computer program product of claim 79, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine locating for the user terminal substantially geographic area；And

The position of the user terminal is determined based on the pseudorange and the substantially geographic area.

85. according to the computer program product of claim 84, wherein the roughly reason region is the area coverage for being communicably linked to an additional transmitters of the user terminal.

86. according to the computer program product of claim 79, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

Determine the tropospheric propagation velocity near the user terminal in area；

The pseudorange is adjusted based on the tropospheric propagation velocity；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

87. according to the computer program product of claim 79, wherein with so that programmable processor determine user terminal location can operational order include can operational order use so that programmable processor:

The pseudorange is adjusted based on the ground elevation near the user terminal in area；With

The position of the user terminal is determined based on the position of the pseudorange adjusted and the DTV transmitter.

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