Abstract:
Apparatus to determine the position of a user terminal, the apparatus having corresponding methods and computer-readable media, comprises: a receiver to receive, at the user terminal, a wireless NRSC-5 digital radio signal; and a pseudorange module to determine a pseudorange between the receiver and a transmitter of the NRSC-5 digital radio signal based on the NRSC-5 digital radio signal; wherein the position module determines the position of the user terminal based on the pseudorange and a location of the transmitter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/152,292 filed Feb. 13, 2009, the disclosure thereof incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present invention relates generally to position determination, and particularly to position determination with NRSC-5 digital radio signals. 
     BACKGROUND 
     There have long been methods of two-dimensional latitude/longitude position location systems using radio signals. In wide usage have been terrestrial systems such as Loran C and Omega, and a satellite-based system known as Transit. Another satellite-based system enjoying increased popularity is the Global Positioning System (GPS). 
     Initially devised in 1974, GPS is widely used for position location, navigation, survey, and time transfer. The GPS system is based on a constellation of 24 on-orbit satellites in sub-synchronous 12 hour orbits. Each satellite carries a precision clock and transmits a pseudo-noise signal, which can be precisely tracked to determine pseudo-range. By tracking 4 or more satellites, one can determine precise position in three dimensions in real time, world-wide. More details are provided in B. W. Parkinson and J. J. Spilker, Jr., Global Positioning System-Theory and Applications, Volumes I and II, AIAA, Washington, D.C. 1996. 
     GPS has revolutionized the technology of navigation and position location. However in some situations, GPS is less effective. Because the GPS signals are transmitted at relatively low power levels (less than 100 watts) and over great distances, the received signal strength is relatively weak (on the order of −160 dBw as received by an omni-directional antenna). Thus the signal is marginally useful or not useful at all in the presence of blockage or inside a building. 
     SUMMARY 
     In general, in one aspect, an embodiment features an apparatus to determine the position of a user terminal, comprising: a receiver to receive, at the user terminal, a wireless NRSC-5 digital radio signal; and a pseudorange module to determine a pseudorange between the receiver and a transmitter of the NRSC-5 digital radio signal based on the NRSC-5 digital radio signal; wherein the position module determines the position of the user terminal based on the pseudorange and a location of the transmitter. 
     Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise a correlator to correlate the NRSC-5 digital radio signal with a reference waveform; wherein the pseudorange module determines the pseudorange based on an output of the correlator. Some embodiments comprise a signal generator to generate the reference waveform. In some embodiments, the receiver receives control data; and the signal generator generates the reference waveform based on the control data. Some embodiments comprise a position module to determine the position of the user terminal based on the pseudorange and the location of the transmitter. In some embodiments, to determine the position of the user terminal, the position module determines an offset between a local time reference in the user terminal and a master time reference, and determines the position of the user terminal based on the pseudorange, the location of the transmitter, and the offset. Some embodiments comprise the user terminal comprising the apparatus. 
     In general, in one aspect, an embodiment features a method for determining the position of a user terminal, comprising: receiving, at the user terminal, a wireless NRSC-5 digital radio signal; and determining a pseudorange between the receiver and a transmitter of the NRSC-5 digital radio signal based on the NRSC-5 digital radio signal; wherein the position of the user terminal is determined based on the pseudorange and a location of the transmitter. 
     Embodiments of the method can include one or more of the following features. Some embodiments comprise correlating the NRSC-5 digital radio signal with a reference waveform; wherein the pseudorange is determined based on an output of the correlating. Some embodiments comprise generating the reference waveform. Some embodiments comprise receiving control data; and generating the reference waveform based on the control data. Some embodiments comprise determining the position of the user terminal based on the pseudorange and the location of the transmitter. In some embodiments, determining the position of the user terminal comprises: determining an offset between a local time reference in the user terminal and a master time reference; and determining the position of the user terminal based on the pseudorange, the location of the transmitter, and the offset. 
     In general, in one aspect, an embodiment features computer-readable media embodying instructions executable by a computer to perform a method comprising: determining a pseudorange between a receiver of a wireless NRSC-5 digital radio signal and a transmitter of the NRSC-5 digital radio signal based on the NRSC-5 digital radio signal; wherein the position of the user terminal is determined based on the pseudorange and a location of the transmitter. 
     Embodiments of the computer-readable media can include one or more of the following features. In some embodiments, the method further comprises: correlating the NRSC-5 digital radio signal with a reference waveform; wherein the pseudorange is determined based on an output of the correlating. In some embodiments, the method further comprises: generating the reference waveform. In some embodiments, the method further comprises: receiving control data; and generating the reference waveform based on the control data. In some embodiments, wherein the method further comprises: determining the position of the user terminal based on the pseudorange and the location of the transmitter. In some embodiments, determining the position of the user terminal comprises: determining an offset between a local time reference in the user terminal and a master time reference; and determining the position of the user terminal based on the pseudorange, the location of the transmitter, and the offset. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an example implementation for a user terminal according to some embodiments. 
         FIG. 2  shows a block diagram of the user terminal of  FIG. 1  according to some embodiments. 
         FIG. 3  shows a flowchart of a positioning process for the user terminal of  FIG. 2  according to some embodiments of the present disclosure. 
     
    
    
     The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
     DETAILED DESCRIPTION 
     As used herein, the terms “client” and “server” generally refer to an electronic device or mechanism. As used herein, the term “mechanism” refers to hardware, software, or any combination thereof. These terms are used to simplify the description that follows. The clients, servers, and mechanisms described herein can be implemented on any standard general-purpose computer, or can be implemented as specialized devices. 
     Embodiments of the present disclosure provide position determination using NRSC-5 digital radio signals. In the described embodiments, the position of a user terminal is determined with one or more wireless NRSC-5 digital radio signals. The NRSC-5 digital radio signal is described in “NRSC-5-B In-band/on-channel Digital Radio Broadcasting Standard,” April 2008, by the National Radio Systems Committee, also referred to herein as “the NRSC-5 standard.” The NRSC-5 digital radio signal is further described in “HD Radio Air Interface Design Description—Layer 1 FM” (NRSC-5-B reference document 1011s), also referred to herein as “the Layer 1 standard.” Unless otherwise noted, the present disclosure describes the NRSC-5 digital radio signal with reference to the Layer 1 standard. 
       FIG. 1  shows an example implementation  100  for a user terminal  102  according to some embodiments. Referring to  FIG. 1 , implementation  100  also includes a wireless base station  104 , transmitters  106 A-C, reference receivers  108 A-B, and a location server  110 . Although in the described embodiments, the elements of user terminal  102  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, the elements of user terminal  102  can be implemented in hardware, software, or combinations thereof. 
       FIG. 1  is used to illustrate various aspects of the invention but the invention is not limited to this implementation. For example, the phrase “user terminal” is meant to refer to any object capable of implementing the DTV position location described. Examples of user terminals include PDAs, mobile phones, cars and other vehicles, and any object which could include a chip or software implementing DTV position location. It is not intended to be limited to objects which are “terminals” or which are operated by “users.” 
     User terminal  102  receives wireless NRSC-5 digital radio signals  118 A-C from respective transmitters  106 A-C. When receiving NRSC-5 digital radio signals  118  from three or more transmitters  106 , user terminal  102  can determine its location without the use of other signals. When receiving fewer than three NRSC-5 digital radio signals  118 , user terminal  102  can use additional signals, such as GPS signals, broadcast television signals, and the like, to supplement the NRSC-5 digital radio signals  118  for position determination. 
     In some embodiments, user terminal  102  determines its location autonomously. In some embodiments, user terminal  102  determines its location independently, that is, using only the received signals and information stored on user terminal  102 . In other embodiments, user terminal  102  also employs information received from location server  110  to determine its position, as described below. 
     In other embodiments, user terminal  102  provides measurements of the received signals  118  to location server  110 , and location server  110  determines the position of user terminal  102 . Communication with location server  110  can be provided by base station  104 . For example, in some implementations, user terminal  102  is a wireless telephone and base station  104  is a wireless telephone base station. In some implementations, base station  104  is part of a mobile MAN (metropolitan area network) or WAN (wide area network). In some embodiments, reference receivers  108  at known locations receive the same wireless NRSC-5 digital radio signals as user terminal  102 , and send measurements of the signals to location server  110 . 
     The NRSC-5 digital radio signals contain a-priori known features that can be used for time-of-arrival (TOA) estimation. When TOA estimates are made for signals from a plurality of transmitters, and knowledge of the transmitter locations and timing is available, the location of user terminal  102  can be determined. 
     The NRSC-5 digital radio signal is an OFDM-type signal, composed of a large number of adjacent narrowband subcarriers, also referred to herein simply as “subcarriers.” Some of these subcarriers are reserved as reference subcarriers, described for example in Sections 11.2.3 and 12.2.2 in the Layer 1 standard. Each transmitter uses these reference subcarriers to transmit identity and configuration information associated with the transmitter. Each reference subcarrier is modulated with a data sequence that is synchronous with the OFDM symbol rate and repeats with a period of 0.092864 seconds. The reference subcarriers are depicted, for example, in FIGS. 5-5 and 5-6 of the Layer 1 standard. 
     Because the data modulated onto the reference subcarriers are periodic, synchronous with the OFDM symbols and can be known a priori, the specific combined waveform of the reference subcarriers can be computed a priori. Once computed, this reference waveform can be used as a matched filter to estimate the TOA of the start of the reference data period of the NRSC-5 digital radio signal. TOA estimates from a plurality of transmitters can be used to calculate the position of user terminal  102 . The specific technique used for this calculation is selected based upon the manner in which the NRSC-5 transmitter network is operated, that is, upon whether the network is synchronized. 
     In a synchronized network, the transmitters are synchronized to a common clock, and start transmission of their reference subcarriers simultaneously. In this synchronized network, the TOA estimates and the known transmitter positions can be used to calculate both the position of user terminal  102  and the time-of-reception using a standard time-difference-of-arrival-plus-bias geolocation algorithm. Because the transmitter positions and reference carrier data change infrequently, this information can be stored in user terminal  102 , allowing autonomous operation that requires no other supporting elements. 
     In an unsynchronized network, the transmitters are operated independently. In this case, one or more reference receivers  108  are used to estimate the time-of-transmission (TOT) of the reference subcarrier sequence for each transmitter, and to express those TOT estimates in terms of a common clock, such as UTC or GPS. The TOA estimates of user terminal  102 , the TOT estimates of reference receiver(s)  108 , and positions of transmitters  106  can be used to calculate the position of user terminal  102  and TOR using a standard TOA-plus-bias or TOA geolocation algorithm. In this positioning technique, user terminal  102  is given frequent updates of the data obtained by reference receiver(s)  108 . This data can be passed to user terminal  102 , for example, by base station  104 , by the NRSC-5 digital radio signals  118 , or the like. 
       FIG. 2  shows a block diagram of user terminal  102  of  FIG. 1  according to some embodiments. Referring to  FIG. 2 , user terminal  102  includes a receiver  202  to receive wireless NRSC-5 digital radio signals  118 , a pseudorange module  204  to determine pseudoranges  212  based on the received NRSC-5 digital radio signals  118 , and a position module  206  to determine the position  214  of user terminal  102  based on the pseudoranges  212  and locations of the transmitters  106  of the signals  118 . User terminal  102  includes also a signal generator  208  to generate a reference waveform  216  and a correlator  210  to correlate the received NRSC-5 digital radio signals  118  with the reference waveform  216 . In some embodiments, the reference waveform  216  is provisioned with user terminal  102 . In other embodiments, signal generator  208  generates reference waveform  216  based on control data  218  received by user terminal  102 . For example, control data  218  can be generated by location server  110  based on measurements of signals  118  made by reference receivers  108 . 
       FIG. 3  shows a flowchart of a positioning process  300  for user terminal  102  of  FIG. 2  according to some embodiments of the present disclosure. Although in the described embodiments, the elements of process  300  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of process  300  can be executed in a different order, concurrently, and the like. 
     Referring to  FIG. 3 , at  302 , receiver  202  of user terminal  102  receives a wireless NRSC-5 digital radio signal  118 . At  304 , signal generator  208  generates reference waveform  216  based on control data  218 . Control data  218  can be provisioned in user terminal  102 , passed to user terminal  10  by location server  110 , or the like. Signal  118  has multiple service modes, which can employ different numbers of reference subcarriers. Signal generator  208  can employ all available subcarriers in generating reference waveform  216 . 
     Control data  218 , also referred to as system control channel (SCCH) data, is sent on the reference carriers of the wireless NRSC-5 digital radio signal  118 , as defined in Section 6 and Table 6-1 of the Layer 1 standard. Section 11.2 defines the process by which the control data parameters are formatted into a 32-bit word called the “reference subcarrier control data sequence.” There are two formats for this control data sequence. The primary format is shown in FIG. 11-2 of the L1 standard, while the secondary format is shown in FIG. 11-3. Each NRSC-5 digital radio signal is transmitted in one of a plurality of service modes. The primary format is present in all service modes. The secondary format is present only in service modes that are not used in conjunction with conventional analog radio service. 
     Reference subcarriers 0-14 and 45-60 carry the primary reference subcarrier system control data sequence, which is the same on every one of those subcarriers with the exception of a 2-bit field that is a function of the reference subcarrier number defined by Table 11-3 of the L1 standard. Reference subcarriers 15-44 carry the secondary reference subcarrier system control data sequence, which is the same on every one of those subcarriers with the exception of a 2-bit field that is a function of reference subcarrier number defined by Table 11-3 of the L1 standard. In current systems, the secondary subcarriers do not appear because that spectrum is used for conventional analog radio service. 
     These control data sequences are differentially encoded and modulated onto their respective reference subcarriers. Every OFDM symbol of the total signal carries one bit of the primary control data sequence and (if present) one bit of the secondary control data sequence. Each bit (if present) appears in multiple copies on multiple reference subcarriers. The entire 32-bit control data sequence is transmitted over a period of 32 OFDM symbols. This period of 32 OFDM symbols is an “L1 Block Duration,” as defined in Section 3.5 of the L1 standard, and has a duration of 0.09288 seconds, meaning that the reference carrier waveform repeats with a frequency of 10.7666 Hz. 
     Referring again to  FIGS. 2 and 3 , at  306 , correlator  210  correlates the received signal  118  with reference waveform  216 . For example, reference waveform  216  can be used as a matched filter to process received NRSC-5 digital radio signal  118 . 
     In any of the service modes, the reference subcarriers account for about 5.5% of the total energy in signal  118 , meaning that it has a natural SINR (Signal to Interference-plus-Noise Ratio) of −12.6 dB. Each subcarrier has a bandwidth of 363.4 Hz, and in the most commonly expected service modes, there will be 20-30 reference subcarriers giving a total bandwidth of 7.2-10.9 kHz and a time-bandwidth product of 28-30 dB over every L1 block and 38-40 dB over one second. 
     The data modulated upon the reference subcarriers includes a 4-bit block counter that increments in every L1 block (every 0.09288 seconds). This block counter repeats in a 16-block 1.4861-second cycle. Therefore user terminal  102  can assume any valid value of the block counter, and try the resulting matched filter in 16 different positions. Once user terminal  102  is synchronized to the block counter, signal generator  208  can generate matching reference waveforms  216  in a predictable manner by generating a local copy of the block counter. 
     The reference carrier data waveform has a period of 32 OFDM symbols, or 0.092864 seconds. There are 20-30 reference subcarriers in NRSC-5 digital radio signal  118 , depending on the service mode. Each subcarrier has a bandwidth of 363.4 Hz, given a total reference waveform bandwidth of 7,268-10,902 Hz. The period and total bandwidth together give a time-bandwidth product of 675-1012, corresponding to 28-30 dB of processing gain for a full-period matched filter. 
     Referring again to  FIGS. 2 and 3 , at  308 , pseudorange module  204  determines a pseudorange  212  between user terminal  102  and the transmitter  106  of the received signal  118  based on signal  118 . That is, pseudorange module  204  determines pseudorange  212  based on an output of correlator  210 . For example, pseudorange module  204  can include a peak detector to detect a time offset corresponding to a maximum correlation result. 
     Then at  310 , position module  206  determines the position  214  of user terminal  102  based on pseudorange  212  and the location of the respective transmitter  106 . The identity of the transmitter  106  is included in the data modulated upon the reference subcarriers, and so can be obtained from signal  118 . In most cases the local time reference of user terminal  102  has some offset from the master time reference used. In such cases, position module  206  determines the position  214  of user terminal  102  based on that offset. The reference data period of 0.092864 corresponds to an ambiguity distance of roughly 16,000 miles. Because this distance is much greater than the expected reception range for signal  118 , no special provisions are required for resolving these ambiguities. 
     Embodiments of the disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments of the disclosure can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the disclosure can be performed by a programmable processor executing a program of instructions to perform functions of the disclosure by operating on input data and generating output. The disclosure can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     A number of implementations of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.