Patent Publication Number: US-2015073706-A1

Title: Gps-assisted source and receiver location estimation

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This Application is a continuation of U.S. application Ser. No. 12/839,362, filed on Jul. 19, 2010 and entitled “GPS-ASSISTED SOURCE AND RECEIVER LOCATION ESTIMATION”, which Application claims benefit under 35 USC 119(e) of U.S. provisional application No. 61/226,629, filed on Jul. 17, 2009 and entitled “GPS-ASSISTED SOURCE AND RECEIVER LOCATION ESTIMATION,” the contents of which are incorporated herein by reference in their entirety. 
     The present application is related to U.S. application Ser. No. 12/830,245, filed Jul. 2, 2010, the content of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Traditional means of location estimation using a wireless receiver and known beacons, as is implemented in a traditional GPS system, require knowledge of the position of four or more beacons and the distance of the receiver from each beacon. Three beacons may be used if assumption about location on the earth&#39;s spherical surface is made. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an embodiment of the present invention, a mobile communication device includes, in part, a first wireless receiver adapted to determine, as it travels along a path, a multitude of positions of the mobile communication device using signals received from a primary positioning source, a second wireless receiver adapted to receive signals from one or more ambient wireless sources as the mobile communication device travels along the path, and a module adapted to use the multitude of determined positions of the mobile communication device and the received ambient wireless signals to estimate positions of the ambient sources. 
     In one embodiment, the mobile communication device includes an internal memory or database operative to store estimated positions and corresponding time references of the signals of the one or more ambient sources. In another embodiment, the mobile communication device includes a transceiver that accesses and stores or retrieves estimated positions of the one or more ambient sources and their corresponding time references in an external memory or database. In one embodiment, the primary positioning source includes satellite based communication sources. In one embodiment, an ambient source includes digital television, digital radio transmission, or cellular based stations. 
     In one embodiment, the mobile communication devices is further adapted to estimate differential distances to the ambient sources and apply a trilateration technique to the estimated differential distances to estimate distances to the ambient sources and to determine the position of the mobile communication device. In one embodiment, the positions of the ambient sources are estimated using markers carried by signals transmitted by the ambient sources. In one embodiment, the positions of the ambient sources are estimated using one or more fields disposed in the frames transmitted by the ambient sources. 
     In accordance with one embodiment of the present invention, an external database is accessible to a multitude of communication devices and is adapted to store estimated positions of a number of ambient sources as well as corresponding times of markers transmitted by the ambient sources. The external database is further adapted to receive and store updates to the estimated positions as the estimates are generated. The external database is further adapted to supply estimates of the positions of the ambient sources as well as corresponding times of markers transmitted by the ambient sources to any another communication device that can gain access to the database. Such access enables a mobile device that has no access to a primary positioning signal to estimate its position using data stored in the external database. 
     A method of estimating positions of a number of ambient wireless sources, in accordance with one embodiment of the present invention, includes in part, determining a multitude of positions of a mobile communication device using signals received from one or more primary positioning sources as the mobile communication device travels along a path, receiving signals from one or more ambient wireless sources as the mobile communication device travels along the path, and estimating positions of the ambient sources using the determined plurality of positions and the received ambient wireless signals. 
     In one embodiment, estimated positions and corresponding time references of the one or more ambient sources are stored in an internal memory or database. 
     In one embodiment, the primary positioning source includes satellite based communication sources. In one embodiment, ambient sources include digital television, digital radio transmission, or cellular based stations. 
     In one embodiment, the estimated differential distances to the ambient sources are applied to a trilateration technique to generate estimates of distances to the ambient sources. In one embodiment, the positions of the ambient sources are estimated using markers carried by signals transmitted by the ambient sources. In one embodiment, the positions of the ambient sources are estimated using one or more fields disposed in the frames transmitted by the ambient sources. The estimated positions of the ambient sources are used to estimate the position of the mobile communication device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a wireless receiver in communication with a primary positioning system, an ambient signal source, and internal an external databases, in accordance with one embodiment of the present invention. 
         FIG. 2  shows a number of frames transmitted by an ambient source and received by the receiver at a number of locations. 
         FIG. 3A  shows an exemplary DTV signal received by a DTV receiver in frequency domain and used to locate positions in accordance with one embodiment of the present invention. 
         FIG. 3B  shows the signal of  FIG. 3A  transformed into time domain and used to locate positions in accordance with one embodiment of the present invention. 
         FIG. 4  shows a wireless receiver in communication with an ambient signal source and a databases, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with embodiments of the present invention, the position of a receiver traveling along a path is estimated using signals transmitted from digital radio or TV broadcasts, such as those conforming with DVB-T, DVB-H, ISDB-T, CMMB, MediaFLO, ATSC, DAB standards, signals transmitted from cellular phone systems, such as GSM, 3G, CDMA, W-CDMA, LTE, WiFi, WiMax, or the like, as well as any other sources of such signals that are synchronized to stable time bases and either do not know or do not broadcast their precise locations. All such signals are collectively referred to herein as ambient signals. Sources generating ambient signals are referred to as ambient sources. The positions estimated using ambient sources may be enhanced using signals transmitted from primary positioning systems such as the satellite based systems (e.g., GNSS, GPS). Signals transmitted by a satellite based system are collectively referred to as primary positioning signals. Sources generating primary positioning signals are referred to as primary positioning sources. 
     The following description of the exemplary embodiments of the present invention is provided with reference to an ambient signal transmitted from a DTV system and a primary positioning signal transmitted from a GNSS system. It is understood however that any other source of ambient signals and any other source of primary positioning signals may be used by embodiments of the present invention. 
     In accordance with embodiments of the present invention, a receiver establishes the positions of some or all of ambient sources whose signals are received by the receiver. The receiver subsequently uses positions of ambient sources (also referred to herein as ambient beacons or beacons) when the primary positioning system(s) becomes unavailable or is otherwise impaired. The positions of ambient beacons may be uploaded to a database or otherwise made accessible to other receivers within the range of the same ambient beacons to establish the receivers&#39; positions without any need for the primary signals. 
     A receiver system (alternatively referred to herein as receiver), in accordance with one embodiment of the present invention, includes, in part, a receiver and a network-accessible database which exchanges information with the receiver. The receiver has access to the database through one or more wireless or wireline networks. The receiver is adapted to concurrently receive primary positioning signals as well as ambient signals. Such a receiver performs the following operations in accordance with embodiments of the present invention. 
     Using the primary positioning signal (e.g. the GNSS signals), the receiver establishes data corresponding to the receiver&#39;s positions and the associated times that the receiver was present in each such position (due, for example, to the natural motion of the receiver). 
     Concurrently, since the receiver is also receiving ambient signals at each such position, the receiver also establishes time reference for each received ambient signal. Using this information, and as described further below, the receiver establishes the positions and corresponding time references associated with the ambient sources. The positions and corresponding time references of the ambient sources are uploaded to a database via one or more wireless or wireline networks or otherwise made available to other receiver systems. The positions and time references for the ambient sources may also be downloaded from the database or otherwise communicated to and used by a receiver which does not have access to a primary positioning source. Therefore, such a receiver despite not having access to primary positioning signals, is enabled in accordance with embodiments of the present invention, to estimate its position using only the ambient sources whose signals can be received by the receiver. 
     In the following description as well as in the Figures the following indexing convention is used. A quantity such as distance D, or receiver location LR, is typically indexed using two indices i and j, e.g. D ij  or LR ij . The first index i identifies the ambient source related to the quantity, and the second index j identifies the position of the receiver to the ambient source. For example, D 12  refers to the distance from ambient source  1  to the receiver position  2 . 
       FIG. 1  shows a receiver  100  that includes a primary positioning receiver  102  as well as an ambient signal receiver  104 . Primary positioning receiver  102 , that may be a GNSS receiver, enables receiver  100  to estimate its positions and obtain the associated times that the receiver is present in each such position as is travels along the path  140  using the GNSS signals received from GNSS system  250 . It is assumed herein that the estimated positions and the associated times obtained from the primary positioning receiver correspond substantially to the actual values of such positions and times. In one embodiment, receiver  100  has a database  106  that stores the positions and time values obtained using the primary positioning receiver  102  disposed in receiver  100 . In another embodiment, receiver  100  includes a transceiver  108  enabling receiver  100  to store the position and time values obtained using the primary positioning receiver  102  in an external database  170  via network  160 . Access to database  170  may be provided from network  160  using the Internet. Receiver  100  may operate in a number of different modes as described further below. 
     Ambient Source Localization 
     In this mode of operation, receiver  100  receives signals from both primary positioning sources as well as ambient sources. Receiver  100  uses the signals transmitted from the primary positioning source  250  to establish its position along a multitude of points while traversing path  140 . Since receiver  100  is also in the range of one or more ambient sources, such as ambient source  1 , as receiver  100  traverses along path  140 , it receives from ambient source  1  signal AS 1i  at location LR 1i , at time TR 1i , where i is an integer varying from 1 to N. Receiver  100  then uses the position data obtained from the primary positioning source to determine the position of ambient source  1 , as described further below. Receiver  100  uses the same technique to determine the position of any other source of ambient signals. It is understood that the signals from the primary positioning source and the ambient source need not be received simultaneously so long as receiver  100  has a time base which is relatively stable over short time intervals (such as a few seconds), as is widely available in consumer products today. 
     To determine the position of ambient sources, the ambient sources are assumed to transmit their signals with markers MM 1i  (e.g., frame boundaries or any characteristics that occur in known locations within the frame) whose time intervals are known in advance in a predictable manner, as is the case with frame boundaries in many transmission protocols.  FIG. 2  shows a number of frames transmitted by ambient source  1  as received by receiver  100 . To determine the position of ambient source  1 , receiver  100  is adapted to perform the following operations. 
     Referring to  FIG. 2 , frame boundary MM 11  of signal AS 11  transmitted by ambient source  1  is shown as being received by receiver  100  at time TR 11 . Receiver  100  associates time TR 11  with position L 11 . Time TR 12′  is the expected reception time of frame boundary MM 12  if receiver  100  were to remain stationary at position L 11 . Likewise, receiver  100  associates time TR 1i  at which signal AS 1i  is received with position L 1i , where index i identifies the position of the receiver. But since receiver  100  is assumed to be moving, it receives frame MM 12  at time TR 12  at position LR 12 . The difference between times TR 12  and TR 12′ , i.e., (TR 12 -TR 12′ ) is shown in  FIG. 2  as DT 12 . The product of DT 12  and the speed of light in air represents the difference between D 12  and D 11 , designated herein as DD 121 . In general, for differential distance DD ijk , index i corresponds to the ambient source, and indices j and k correspond to positions of the receiver. It is understood that frames MM 11 , MM 11+1  . . . are not actually received at position LR 12  and are only shown to indicate their relative expected reception times by receiver  100  at that location. Frames that are not received by receiver  100  and are only included to aid in understanding embodiments of the present invention are shown using diagonally hashed lines. 
     In a similar manner, for ambient source  1 , the difference between D 1j  and D 1k  may be calculated to determine the differential distances DD 1jk . These differential distances and their associated locations LR 1j  and LR 1k  are subsequently used by well-known trilateration techniques to establish an estimate of the position (LT 1 ) of ambient source  1 . It is understood that with more data points, estimated position LT 1  may be improved through filtering and other known noise reduction techniques. In a similar manner, the position LTi of any number of ambient sources may be obtained. 
     One example of an ambient source suitable for use in accordance with embodiments of the present invention is the GSM system in conformity with which a cellular base station transmits frames of data in regular, precisely-timed intervals. The frame boundaries of GSM signals may be used as markers. Another example is the DTV broadcast system in conformity with which digital data is broadcast in frames which are frequently synchronized to a system clock to implement what is commonly referred to as single-frequency networks (SFN). Broadcast towers of an SFN system covering a region transmit data in a synchronous fashion. The absolute time TTAi of transmission of the markers MMij can also be determined. 
     Once the position LT, of an ambient source i is estimated by a receiver, as described above, the receiver may store the position information in either or both databases  106  and  170 , depending, for example, on their availability. Such information includes, among other things, the identity of the ambient source i, the position LTi of ambient source i, the absolute time TTAi associated with its marker MMij, time of upload of the data, confidence level, and any other statistics of the estimated data and ambient source, such as average offset of the ambient source. 
     Use of Ambient Sources to Establish Position 
     In this mode of operation, receiver  100  detects and identifies ambient sources that are in its vicinity and whose signals are received by receiver  100 . Receiver  100  retrieves the associated data and statistics for such ambient sources from its own database  106  or an external database  170 , depending on their availability. The reception of signals from the ambient sources need not be simultaneous as long as receiver  100  maintains a time base which is relatively stable over short time intervals, as is widely available in mobile devices. With this information retrieved from such a database, receiver  100  may extract the difference in distances among the different ambient sources it is receiving signals from, and using the knowledge of their positions, trilaterates to determine the position of receiver  100 , even in the absence of a GNSS signal or an accurate time estimate.  FIG. 4  shows a receiver  100  that estimates its position using signals received only from ambient source  300  and external database  170 . 
     Assisted Location 
     In this mode of operation, receiver  100  uses the information it retrieves from its own database  106  or an external database  170  about one or more ambient sources to compute the positions of such sources and further to improve the accuracy or the acquisition time of the signals received from the primary positioning source. Accordingly, in this mode the ambient sources are treated as additional primary sources. This information is delivered to a standard positioning engine which trilaterates the position of receiver  100 . For example, relatively few base stations may be within the range of receiver  100 . In such cases, the receiver may supplement the data received from the primary positioning source with data retrieved from internal database  106  or external database  170  to enable the positioning engine to improve the accuracy of the estimated position of the receiver. 
     Database Functions 
     In addition to receiving and storing the position, absolute transmission time of the markers, upload time and confidence (certainty) estimates from the receiver and subsequently permitting retrieval of this information, the database may also track information such as the relative stability of each ambient source over time (e.g. offsets or drifts). It may compute a more accurate estimate of the ambient source information using an ensemble of information obtained from a large number of receivers about these ambient sources. 
     Enhancements 
     The receiver may be enhanced to obtain more accurate estimates of the time of arrival of markers MMi.  FIG. 3A  shows a DTV signal received by a DTV receiver in the frequency domain.  FIG. 3B  shows the signal of  FIG. 3A  transformed into time domain in accordance with an embodiment of the present invention. The DTV receiver uses OFDM modulation and pilot tones PTi or training sequences, as defined by the DTV standards, to demodulate the DTV signal. The pilot tones PTi in the frequency domain may be used by the receiver to obtain a time-domain estimate of the channel impulse response  225  (shown in  FIG. 3B ) using an inverse FFT. 
     Referring to  FIG. 3B , because of channel impairments such as multipath, the receiver may receive the ambient signal in a direct path at time P 1  as well as echoes at P 2  and P 3 . The receiver may use the pilot tones PTi, or training sequences commonly available in wireless transmission standards, to estimate the channel and extract P 1  from the total signal, thereby obtaining a more accurate estimate for precise first time of arrival of markers MMij. 
     The DTV receiver system may be optimized for the purpose of location estimation, as described further below. The receiver may perform averaging, filtering and other noise-reduction techniques on the pilot tones PTi or training sequences to reduce the effective bandwidth of the receiver and thereby significantly increase its sensitivity. In the DTV standard, this involves averaging over the continuous and scattered pilot tones to sense transmission towers that are much farther than conventional TV reception ranges. 
     In a CMMB system, the signals present at the beginning of each frame includes two consecutive known symbols which can be used to obtain very long-distance, accurate estimates of differential distance among transmission towers. Furthermore, the receiver may switch frequencies and receive other DTV channels to obtain relative distance information at other frequencies to improve the estimation of the relative distance. This has the benefit of providing the system with a diverse range of signal sources, some of which may be stronger and more easily received. 
     The databases uses in accordance with embodiments of the present invention provide a number of other advantages, as described further below. A multitude of receivers may share access to the same external database, thereby building up a shared source of information regarding ambient sources. This allows users to benefit from collective knowledge of the positions of ambient sources without determining them independently. It also allows the accuracy and validity of the shared database to be checked and improved by data from a large number of users. 
     The sharing and further improvements of such a database enables receivers which do not have a built-in primary positioning receiver to determine their positions using other ambient source signals that they can receive to determine their positions accurately. The database can also be used to obtain statistical information concerning the positions of users of such a shared database and system at any given time. This information can be extremely valuable for the purposes of marketing, planning, or emergency services. 
     Furthermore, the timing and position information about ambient sources which are not adequately stable may be stored and updated in the shared database when the database is updated by a sufficient number of users. So long as the timing information about the less stable sources is updated with sufficient frequency to keep the accumulated timing error within bounds acceptable to a particular application, users within range of such less stable sources can use them as ambient signal sources for positioning purposes. 
     The above embodiments of the present invention are illustrative and not limiting. Various alternatives and equivalents are possible. The invention is not limited by the type or the number of primary positioning systems. The invention is not limited by the type or the number ambient sources. The invention is not limited by the rate used to transfer the data. The invention is not limited by the type of integrated circuit in which the present disclosure may be disposed. Nor is the disclosure limited to any specific type of process technology, e.g., CMOS, Bipolar, or 
     BICMOS that may be used to manufacture the present disclosure. Other additions, subtractions or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.