Abstract:
An assisted global positioning system (AGPS) for tracking a movable object of interest is disclosed. The system comprises a service center for calculating a tag location, a plurality of ground base stations, a plurality of beacons adapted to transmit individual ID data, and at least one GPS-based smart tag releasably affixed to the movable object. The system components are interconnected by means of one or more communication links. The service center is adapted for inquiring the tag and receiving a response from the tag constituting pseudo-ranges according to a predetermined protocol.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to an object tracking system and, more specifically, to a tracking system generating a GPS assisted data provided to an inquirable GPS smart tag attached to an object of interest. 
     BACKGROUND OF THE INVENTION 
     Global positioning systems (GPS) have become one of the most common tools used to determine an object&#39;s location accurately anywhere on the globe. Thus GPS has become a commonly used tool for navigation and for tracking fleets of vehicles, trucks, ships and airplanes. A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. The satellites are equipped with extremely accurate atomic clocks, and the receiver uses an internal crystal oscillator-based clock that is continually updated by using signals from the satellites. When distance to four satellites is measured simultaneously, the intersection of the four imaginary spheres determines the location of the receiver. Earth-based users can substitute the sphere of the planet for one satellite by using their altitude data. Typical measured position accuracy of GPS receivers is several meters. GPS receiver position measurement also has some limiting factors. The GPS receiver requires line-of-sight with at least four satellites. When the receiver is indoors or in an urban area, the signals received by a GPS receiver from the satellites are weak. Furthermore, some of the satellite data stream is broadcast at a very slow rate of 50 bits per second, thus taking several minutes for a conventional GPS receiver to download the required data from the satellites before computing its own location. 
     U.S. Pat. No. 6,700,533, which is incorporated herein by reference, discloses a system for tracking objects outdoors. Tags attached to objects such as trailers include GPS receivers. Tags transmit uncorrected position and satellite data to a base station, where differential corrections are applied, providing 2-5 meter accuracy of the position of the tag and object. Tags are on a low duty cycle. When a tag powers on, it receives accurate time and current satellite data from the base station, enabling the tags to acquire the satellite signal quickly and with minimum power consumption. When a tag is out of base station range, the tag periodically calculates and archives its position. The tag may also include Real Time Locating Systems technology, to enable tracking to continue when the tag moves indoors and becomes inaccessible to GPS satellite signals. 
     The normally asleep tag is preprogrammed to periodically wake up and receive satellite position data from the base station and acquire the satellite signals. Pseudo-range data calculated at the tag from the acquired satellite signals are transmitted to the base station. The aforesaid tag wakes up independently whether it is within the coverage zone of the base station and characteristics of the tag displacement. Unassisted search of the satellite signal is an energy-consuming process and reduces tag battery life. Providing an energy-saving protocol of tracking objects is hence a long-felt need. 
     SUMMARY OF THE INVENTION 
     It is the object of this invention to disclose an assisted GPS (AGPS) for tracking a movable object of interest. The system comprises at least one GPS-based smart tag releasably affixed to the movable object. The smart tag is interconnected to ground base stations and satellites by means of one or more communication links. The system further comprises a plurality of ground base stations and satellites which emit retrievable scheduled signals, a plurality of beacons adapted to transmit signals carrying individual ID data of the beacons, and, a service center adapted to provide the smart tag with an assisted data and calculating a location of the smart tag. The service center is adapted to communicate with the tag and obtaining a set of pseudo-ranges, calculated by a predetermined protocol of triangulation of the time delays of the signals received from the satellites. 
     In one embodiment of the invention, the service center of the system defined above is further adapted to receive a beacon ID data, determining an approximate tag location according to both (i) the received beacon ID and (ii) signal measurement data, and generating and transmitting assisted data related to the determined tag approximate location. 
     In another embodiment of the invention, the service center is adapted to inquire the tag and receiving a response from the tag constituting the pseudo-ranges according to a predetermined protocol. 
     In another embodiment of the invention, the smart tag comprises (a) a GPS receiver adapted to receive signals broadcasted by a plurality of GPS satellites and calculating a plurality of pseudo-ranges from the tag to the satellites by processing the signals; and, (b) an RF transceiver adapted to (i) measure a signal transmitted by the beacon; (ii) extract the beacon ID data from the signal; (iii) receive the assisted data, (iv) transmit said calculated pseudo-ranges; and (v) retransmit the beacon ID and signal measurement data. 
     In another embodiment of the invention, the RF transceiver comprises circuits adapted to measure beacon signal parameters selected from the group consisting of a received signal strength indicator and a phase delay, or a combination thereof. 
     In another embodiment of the invention, the ground base station comprises (a) an RF-transceiver adapted to retransmit the assisted data to the smart tag and receiving the calculated pseudo-ranges, beacon ID and signal measurement data from the smart tag; and an Ethernet interface adapted to retransmit the pseudo-ranges, the beacon ID and signal measurement data to the service center. 
     In another embodiment of the invention, the communication link between the tag and the ground base station is wireless. 
     In another embodiment of the invention, the system comprises smart tags selected from the group consisting of optical radiation tags, RF triangulation tags, gate crossing detection tags, or any combination thereof. 
     In another embodiment of the invention, the smart tag further comprises at least one element selected from a group consisting of microcontroller unit, a motion sensor, and a plurality of I/O lines. 
     In another embodiment of the invention, a method for tracking a location of a smart tag comprises the steps of: measuring a signal of a nearest beacon device and deriving an ID and signal measurements data from said signal; transferring said ID and signal measurement data to said service center; determining an approximate location of said tag; calculating assisted data according to the approximate tag location; transmitting assisted data according to tag approximate location; searching satellite-broadcasted signal according to said assisted data; receiving satellite-broadcasted signals; calculating pseudo-ranges from said smart tag to said satellites; transferring said pseudo-ranges from said smart tag via a ground base station to a service center; and calculating a tag location. 
     In another embodiment of the invention, the method further comprises the steps of (i) waking up said smart tag in a cold standby condition prior to receiving ID and signal measurement data of a nearest beacon device; and (ii), restoring said smart tag to a cold standby condition after transferring said pseudo-ranges from said smart tag via a ground base station to a service center. 
     In another embodiment of the invention, the step of calculating the location of the tag is performed by triangulating the pseudo-ranges. 
     In another embodiment of the invention, the step of downloading assisted data comprises downloading almanac, ephemeris, transmission frequency, and encoding data. 
     In another embodiment of the invention, the step of determining an approximate location of the tag is performed according to the beacon location. 
     In another embodiment of the invention, the step of determining an approximate location of the tag is performed by triangulating the smart tag position using beacon signal measurement data. 
     In another embodiment of the invention, the step of measuring the beacon signal comprises measuring a received signal strength indicator and a phase delay or any combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The object and the advantages of various embodiments of the invention will become apparent from the following description when read in conjunction with the accompanying drawings, wherein 
         FIG. 1  is a schematic diagram of an AGPS tracking system according to an embodiment of the invention; 
         FIG. 2  is a block diagram of the smart tag shown in  FIG. 1 ; 
         FIG. 3  is a block diagram of the ground base station shown in  FIG. 1 ; 
         FIG. 4  is a block diagram of the beacon device shown in  FIG. 1 ; and 
         FIG. 5  is a flow chart of a method for using the AGPS tracking system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following description is provided alongside all chapters of the present invention, so as to enable any person skilled in the art to make use of said invention and sets forth the best modes contemplated by the inventor of carrying out this invention. Various modifications however, will remain apparent to those skilled in the art, since the generic principles of the present invention have been defined specifically to provide a wireless communication system for tracking assets and methods thereof. 
     In accordance with the current invention, the preferred technical solution constitutes precisely tracking a plurality of GPS smart tags affixed to the movable objects of interest. The GPS smart tags are wirelessly linked to a service center via a plurality of ground stations covering a tracking area. Additionally, a plurality of beacon devices is disposed in the aforesaid tracking area. The beacon devices are adapted to RF transmit their ID data to the smart tags situated within the beacon service area. Each smart tag situated in the coverage zone of the base station is initialized under command of a service center. One method for determining the location of the smart tag comprises the following steps: (i) determining an approximate location of the smart tag by identifying the nearest beacon device or by triangulating the smart tag position using beacon signal measurements and (ii) determining a precise location of the smart tag by means of an Assisted GPS (AGPS) technology. 
     The system, which is known as Assisted GPS or AGPS, uses a wireless network to provide the GPS receiver with data, thereby assisting it to acquire the satellite&#39;s signal. In a preferred embodiment of the invention, the system provides Ephemeris data to the GPS receiver, which improves the time-to-first-fix (TTFF). The data provided to the GPS receiver can be either the Ephemeris data for visible satellites or, more helpfully the code phase and Doppler ranges over which the GPS device has to search, i.e. ‘acquisition assistance’. This technique improves the TTFF by many orders of magnitude, thus minimizing energy consumption. AGPS is also used to improve the sensitivity of the GPS device, thus improving the performance within buildings. By providing so called ‘sensitivity assistance’ (based roughly on the estimated position of the GPS receiver) to the GPS device, it is able to better correlate the signal being received from the satellite when the signal is low in strength. 
     Being provided with assisted data, the smart tag receives satellite-broadcasted signals and calculates pseudo-ranges from the tag to the satellites. After transferring data, the smart tag is restored to a cold standby condition. The calculated pseudo-range data is transferred to the service center adapted to determine a smart tag location. 
     The term ‘Assisted GPS’ (AGPS) relates to a configuration consisting of a GPS server and plurality of simple mobile GPS receivers connected via a communication link. The mobile GPS receivers are assisted by the GPS server providing data and processing power for position measurement. 
     The term ‘GPS smart tag’ relates to tags consisting of a GPS receiver, limited processing power and an interface to a dedicated wireless communication link. 
     The term ‘Almanac’ relates to coarse time information and status information about the satellites included in the primary navigation signal broadcasted by a satellite. 
     The term ‘Ephemeris’ relates to information that allows the receiver to calculate the position of the satellite. 
     The term ‘Assisted data’ relates to data generated by the service center and provided to the GPS smart tag for shortening Time To First Fix (“Acquisition Assistance”) and increasing sensitivity (“Sensitivity Assistance”). The aforesaid data comprises at least one element selected from the group consisting of almanac, ephemeris, code phase, and Doppler ranges characterizing the satellite-broadcasted signal. 
     The term ‘Pseudo-range’ relates to the range of each of the satellites used by a GPS receiver and is calculated by the time delay of signals received from each satellite. The pseudo-range values are further used to calculate the GPS receiver position by triangulation. 
     The term ‘pseudo random’ relates to numbers that are generated digitally and approximate the properties of random numbers. 
     The term ‘Radio frequency (RF) beacon’ relates to a radio transmitter transmitting identification data within an area of the transmitter antenna. 
     The term ‘Central processing server’ relates to a central processing platform recording location data obtained from all the system smart tags in the database. 
     The term ‘Application server’ relates to a user interface platform. 
     The term ‘Application interface’ (API) relates to user interface software running on the central processing server and the application server. 
     The term ‘System console’ relates to a terminal usable for operating the system. 
     The term ‘IP’ is the acronym of internet protocol. 
     The term ‘MCU’ is an acronym for a microcontroller unit. 
     The term ‘Receive Signal Strength Indicator’ refers to a circuit to measure the strength of an incoming signal. The basic circuit is designed to pick an RF signal and to generate an output equivalent to the signal strength. 
     Reference is now made to  FIG. 1 , schematically illustrating a block diagram of an AGPS smart tag system  100  according to an exemplary embodiment of the invention. As seen in  FIG. 1 , the system  100  comprises a service center  16 , a ground base station  18 , a beacon  32 , and a smart tag  14  adapted to releasably affix to an object of interest  12 . The ground base station  18  is connected to the service center  16  via IP network  30 . The service center  16  further comprises a central processing server  24 , a customer application server  26  connected to the central processing server  24  via a application programming interface  25 , and stationary GPS receiver  22  furnished with an antenna  20 . The receiver  22  and the smart tag  14  are adapted for to receive signals broadcasted by satellites  10   a  . . .  10   d  via wireless communication channels  40  and  42 , respectively. The ground base station  18  is adapted to wirelessly RF-communicate with the smart tag  14  via a channel  44 . The stationary GPS receiver  22  furnished with the antenna  20  is adapted for search and receive signals broadcasted by the satellites available for receiving. As seen in  FIG. 1 , the beacon device  32  has a service zone  34 . 
     In accordance with the current invention, the smart tag  14  affixed to an object of interest  12  is situated in the service zone  34  of the beacon device  32 . The smart tag  14  is woken up by either itself when sensing predefined events (such as motion or time elapsed) or a command sent from the service center  16 . Being woken up, for example, by the service center  16 , the smart tag  14  receives a signal from the beacon device  32  via wireless communication channel  46 . The aforesaid signal carries ID data of this specific beacon  32 . The smart tag  14  measures parameters of the beacon signal and derives the beacon ID data. Further the beacon  32  retransmits the received beacon ID and signal measurement data to the service center  16 . The beacon ID data enables the service center  16  to determine an approximate location of the smart tag  14  and provide the smart tag  14  with assisted data. The aforesaid data is generated according to satellite-broadcasted signals receivable by the stationary reference GPS receiver  22 . 
     As said above, providing the smart tag  14  with assisted data enables the system  100  to reduce energy consumption due to shortening TTFF (acquisition assistance) and more reliable reception (sensitivity assistance) that is very important in indoor conditions. 
     The smart tag  14  performs signal search according to the received assisted data, receives satellite-broadcasted signals and calculates pseudo-ranges from the tag  14  to the available satellites  10   a ,  10   b ,  10   c , and  10   d . The calculated pseudo-ranges are transmitted to the service center  16  for further processing. The central processing server  24  is adapted to calculate a location of the smart tag  14  by means of triangulating the obtained pseudo-ranges. 
     Reduced power consumption comes about because the smart tag  14  is in standby condition and is woken up for a short time on demand. 
     Reference is now is made to  FIG. 2 , presenting a block diagram of the AGPS smart tag  14 . The aforesaid smart tag comprises an AGPS receiver  50 , an RF-transceiver  52 , a data bus  54 , a microcontroller unit  56 , a motion sensor  58 , a battery  60 , and I/O port  62 . 
     As said above, the AGPS smart tag  14  is in standby condition by default. The tag is woken up by either itself when sensing predefined events (such as motion or time elapsed) or a command sent from the service center  16  via the wireless RF-communication channel  44 . The transceiver  52  receives a signal from the beacon device  32  via wireless communication channel  46 . The aforesaid signal carries ID data of the specific beacon  32 . The microcontroller  56  measures signal parameters and derives the beacon ID data. Optionally, a received signal strength indicator and a phase delay or any combination thereof are measured by microcontroller  56 . 
     Further, the transceiver  52  retransmits the received beacon ID and signal measurement data to the service center  16 . The beacon ID data enables the service center  16  (not shown) to determine an approximate location of the smart tag  14 , generate the assisted data, and provide the smart tag  14  with the approximate location and the assisted data. 
     Being provided with assisted data, the AGPS receiver  50  searches and receives the satellite-broadcasted signals. The pseudo-random waveform received by GPS receiver  50  is compared with an internally generated version of the same code with delay control, until both waveforms are synchronized. The obtained delay of internal pseudo-random form corresponding to the waveform synchronization defines the travel time of the GPS signal from the satellite to the receiver  50 . The obtained delay values are provided via the data bus  54  to the microcontroller unit  56 . The delay values (pseudo-ranges) further are transferred to the service center  16  via an RF-communication link  44  for calculating the smart tag location. Thereafter, the smart tag  14  restores to the standby condition. 
     The smart tag  14  is a mobile battery-powered device. Therefore, it is important that the suggested mode of short-time sessions of pseudo-range measurements secures a long battery service life. The smart tag  14  further comprises a motion sensor  58  enabling the service center to assist tracking the smart tag  14  outside the service area. I/O port  62  provides a connection of peripheral devices (not shown) to the smart tag  14  and two-way data interchange between the aforesaid device and the service center  16 . 
     Reference is now made to  FIG. 3 , schematically illustrating a block diagram of the architecture of the ground base station  18 . The aforesaid base station  18  is a ground communication unit communicating with the plurality of mobile smart tags via wireless communication links. 
     The base station  18  comprises four independent RF transceiver modules  70   a ,  70   b ,  70   e , and  70   d  (rack transceiver) operating simultaneously. The rack transceiver is required for supporting the frequency diversity mode of operation, providing the required capabilities for withstanding external interferences. Microcontroller units  72   a ,  72   b ,  72   c , and  72   d  perform management of the data stream in transceivers  70   a ,  70   b ,  70   e , and  70   d , respectively. 
     A central microcontroller unit  74  is responsible for activating and controlling internal operational logic of the base station  18 . A serial port  76  connects peripheral devices to the base station  18 . As seen in  FIG. 4 , the base station  18  further comprises Ethernet chipset  78  for connecting to the Ethernet  30 . The base station  18  is controlled by central processing server  24  via the Ethernet connection  30 . 
     Reference is now made to  FIG. 4 , presenting a block diagram of the AC/DC ( 84 )-powered beacon device  32  comprising an RF-transceiver  80  capable of transmitting beacon device ID data at the predetermined frequency and time. The beacon device  32  is furnished with an attenuator  82  and the serial or USB port  76  enabling the service center to change over the air a level of emitted power and configuring and maintaining the beacon device  32 , respectively. 
     Reference is now made to  FIG. 5 , showing a flowchart of a method  300  for using a preferred embodiment of an AGPS system for tracking an object of interest, according to the invention. In step  200 , an AGPS system is provided having a smart tag. The smart tag is woken up at step  210 . The aforesaid smart tag measures RF-signals of the nearest beacon devices in-view and derives signal ID data of the nearest beacon device at step  220 . The smart tag then retransmits signal measurement and ID data to the service center (step  230 ). The service center determines an approximate location of the smart tag (step  240 ) and generates and transmits the assisted data (step  250 ). As stated above, the assisted data provides both acquisition and sensitivity assistance. Stated another way, using the assisted data shortens TTFF and increases reliability of the objects location in indoor conditions. 
     The smart tag receives the satellite-broadcasted signals at the further step  260  according the assisted data. 
     Calculating the pseudo-ranges at step  270  is based on the obtained satellite signals. The calculated pseudo-ranges are transferred to the service center at the step  280 . Restoring the smart tag to the cold standby condition at the step  290  secures reduced power consumption and enhances battery life. Calculating the tag location at the step  310  ends the flowchart  300 . The obtained result provides coordinates characterizing the smart tag location. 
     Thus, in accordance with the current invention, the reduction of power consumption is attained due to initializing the smart tag by the service center during determining the smart tag location and restoring the aforesaid tag to the cold standby condition after transmitting the pseudo-ranges. 
     The preliminary determination of the approximate tag location using the beacon devices enables the service center to provide improved GPS assistance by means of transmitting more precise satellite data to the smart tag.