Abstract:
A method of checking messages from a network of communication sources includes initially testing the signal strength of a plurality of communication sources, storing the identity of the communication sources with the two strongest signals, and alternatively entering a sleep mode and a wake-up mode, the wake-up mode synchronized to the communication source with the strongest signal. The method further includes testing the signal strength of one additional communication source, switching synchronization to the additional communication source if said source presents a signal stronger than the signal of a stored communication source with the strongest signal, and replacing the identity of any stored communication source if an additional communication sources tested in sequence presents a signal stronger than the signal of said stored communication source.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of prior U.S. patent application Ser. No. 11/131,847 filed May 18, 2005, and claims the benefit of and priority to U.S. patent application Ser. No. 11/131,847 which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to vehicle recovery systems and, in particular, a vehicle locating unit of such a system with improved power management techniques. 
       BACKGROUND OF THE INVENTION 
       [0003]    The applicant&#39;s successful and popular vehicle recovery system sold under the trademark LoJack® includes a small electronic vehicle locating unit (VLU) with a transponder hidden within a vehicle, a private network of communication towers each with a remote transmitting unit (RTU), one or more law enforcement vehicles equipped with a vehicle tracking unit (VTU), and a network center with a database of customers who have purchased a VLU. The network center interfaces with the National Criminal Information Center. The entries of that database comprise the VIN number of the customer&#39;s vehicle and an identification code assigned to the customer&#39;s VLU. 
         [0004]    When a LoJack® product customer reports that her vehicle has been stolen, the VIN number of the vehicle is reported to a law enforcement center for entry into a database of stolen vehicles. The network center includes software that interfaces with the database of the law enforcement center to compare the VIN number of the stolen vehicle with the database of the network center which includes VIN numbers corresponding to VLU identification codes. When there is a match between a VIN number of a stolen vehicle and a VLU identification code, as would be the case when the stolen vehicle is equipped with a VLU, and when the center has acknowledged the vehicle has been stolen, the network center communicates with the RTUs of the various communication towers (currently there are 130 nationwide) and each tower transmits a message to activate the transponder of the particular VLU bearing the identification code. 
         [0005]    The transponder of the VLU in the stolen vehicle is thus activated and begins transmitting the unique VLU identification code. The VTU of any law enforcement vehicles proximate the stolen vehicle receive this VLU transponder code and, based on signal strength and directional information, the appropriate law enforcement vehicle can take active steps to recover the stolen vehicle. See, for example, U.S. Pat. Nos. 4,177,466; 4,818,988; 4,908,609; 5,704,008; 5,917,423; 6,229,988; 6,522,698; and 6,665,613 all incorporated herein by this reference. 
         [0006]    Since the VLU unit is powered by the vehicle&#39;s battery, power management techniques must be employed in the VLU to ensure the VLU does not drain the vehicle&#39;s battery. One prior technique employed by the applicant includes programming the VLU to “wake up” and check for messages from the communication towers only periodically, e.g., every 8 seconds for 0.2 seconds. The timing of the sleep and wake-up modes was synchronized to the transmission schedule of one communication tower. See U.S. Pat. No. 6,229,988. 
         [0007]    But, if the vehicle equipped with the VLU so programmed moves out of the transmission range of that tower, when the VLU wakes up, no signal will be received from that tower. According to prior methods, the VLU must wake up for a longer time in order to be sure to receive a tower transmission since the VLU has no memory of which time slot the tower is likely to transmit. This results in increased power consumption. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of this invention to provide a vehicle locating unit with improved power management technique. 
         [0009]    It is a further object of this invention to provide such a vehicle locating unit whose wake-up and sleep modes are synchronized to the communication source transmitting the strongest signal. 
         [0010]    It is a further object of this invention to provide such a vehicle locating unit which continuously updates its memory to store the identity of one or more communication towers with the strongest signals. 
         [0011]    The subject invention results from the realization that a more effective power management subsystem for a VLU is configured to alternately enter sleep and wake-up modes, to synchronize the wake-up mode to the communication source (e.g., tower) transmitting the strongest signal, and to test the signal strength of at least one additional communication source in sequence. 
         [0012]    The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
         [0013]    The subject invention features a vehicle locating unit with improved power management. A receiver receives a signal from a network of communication sources and a signal strength monitoring subsystem determines which of the communication sources are transmitting the strongest signals. The power management subsystem is responsive to the signal strength monitoring subsystem and is configured to: alternatively enter sleep and wake-up modes, synchronize the wake-up mode to the communication source transmitting the strongest signal, and test the signal strength of at least one additional communication source according to a predefined sequence. 
         [0014]    Typically, the power management subsystem is configured to test and store the identity of two communication sources with the two strongest signals, switch to synchronization with any communication source having a signal stronger than the strongest signal of the two stored communication sources, and store the identity of any communication source with a signal stronger than the signal of any previously stored communication source. 
         [0015]    In one embodiment, there are n (e.g., eight) communication sources each transmitting a signal at a different time every n seconds. Preferably, the power management system is configured to include a start-up mode wherein all communication sources are tested. In one preferred embodiment, the power management subsystem is implemented in a microcontroller which is configured to power down the receiver during the sleep mode and to power up the receiver during the wake-up mode. One example of a signal strength monitoring subsystem includes a demodulation circuit embodied in a transceiver. 
         [0016]    A method of checking messages from a network of communication sources in accordance with this invention includes initially testing the signal strength of a plurality of communication sources, storing the identity of the communication sources with the two strongest signals, alternatively entering a sleep mode and a wake-up mode, the wake-up mode synchronized to the communication source with the strongest signal, testing the signal strength of one additional communication source, switching synchronization to the additional communication source if said source presents a signal stronger than the signal of the stored communication source with the strongest signal, and replacing the identity of any stored communication source if an additional communication source tested in sequence presents a signal stronger than the signal of said stored communication source. 
         [0017]    For VLUs and other electronic receivers which receive a signal from a network of communication sources, a signal strength monitoring subsystem determines which of the communication sources are transmitting the strongest signals. A power management subsystem is responsive to the signal strength monitoring subsystem and is configured to: alternatively enter sleep and wake-up modes, synchronize the wake-up mode to the communication source transmitting the strongest signal, and test the signal strength of at least one additional communication source to ensure the wake-up mode is synchronized to the communication source transmitting the strongest signal. 
         [0018]    One embodiment features a vehicle locating unit power management system comprising a memory, and a controller configured to alternatively output sleep and wake-up mode signals, store in said memory the identity of at least a first communication source presenting the strongest signal, test the signal strength of at least one different communication source during the wake-up mode, synchronize the wake-up mode to the communication source identified in said memory, and update the memory to store the identity of a different communication source presenting a signal stronger than the first communication source. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0020]      FIG. 1  is a schematic block diagram showing the primary components associated with a vehicle recovery system in accordance with the subject invention; 
           [0021]      FIG. 2  is a block diagram showing the primary components associated with a vehicle locating unit in accordance with the subject invention; 
           [0022]      FIG. 3  is a flow chart depicting the primary steps associated with one example of the programming of the microcontroller of the vehicle locating unit shown in  FIG. 2  as it relates to power management; and 
           [0023]      FIG. 4  is a schematic timing diagram showing a time slot synchronization pattern for an example of a communication network including eight communication towers. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0025]    As discussed in the background section above, the applicant&#39;s successful and popular vehicle recovery system sold under the trademark LoJack® includes a small electronic vehicle locating unit (VLU)  10 ,  FIG. 1 , with a transponder  12  hidden within a vehicle  14 , a private network of communication towers  16  each with a remote transmitting unit (RTU)  18 , one or more law enforcement vehicles  20  equipped with a vehicle tracking unit (VTU)  22 , and network center  24 . 
         [0026]    When a LoJack® product customer reports that her vehicle has been stolen, the VIN number of the vehicle is reported to law enforcement center  26  for entry into database  28  of stolen vehicles. Network center  24  includes software that interfaces with database  28  of law enforcement center  26  to compare the VIN number of the stolen vehicle with database  30  of network center  24  which includes VIN numbers corresponding to VLU identification codes. When there is a match between a VIN number of a stolen vehicle and a VLU identification code, as would be the case when stolen vehicle  14  is equipped with VLU  10 , network center  24  communicates with the RTUs  18  of the various communication towers  16  and each tower transmits a message to activate transponder  12  of VLU  10  bearing the particular identification code. 
         [0027]    Transponder  12  of VLU  10  in stolen vehicle  14 , once activated, begins transmitting a unique VLU identification code. VTU  22  of law enforcement vehicle  20  proximate stolen vehicle  14  receives this VLU transponder code and, based on signal strength and directional information, the appropriate law enforcement vehicle can take active steps to recover stolen vehicle  14 . 
         [0028]    VLU  10 ′,  FIG. 2 , in accordance with the subject invention includes transceiver  40  or, in another example, a receiver without transmission capabilities. Signal strength monitoring subsystem  42 , in one embodiment, is a demodulator circuit on a chip within transceiver  40  and outputs a signal identifying and characterizing the signal strength of all signals received by transceiver  40  via antenna  44  from the communication network and one or more communication towers  16 ,  FIG. 1 . 
         [0029]    Microcontroller  46 ,  FIG. 2 , (e.g., a Texas Instrument microcontroller model No. MSP430) receives the output of subsystem  42 , is programmed to evaluate the signal strength of all signals received by transceiver  40 , and is also programmed to alternatively cause transceiver  40  to enter sleep and wake-up modes to save battery power by outputting a signal to power supply unit circuitry  48  in accordance with the flow-chart of  FIG. 3 . Memory  47 ,  FIG. 2 , is shown separate from controller  47  but many microcontrollers, as is known by those skilled in the art, have internal memories including the controller example above. 
         [0030]    In the following example, there are eight communication sources or LoJack® towers A-H,  FIG. 4 , transmitting signals to VLU  10 ′,  FIG. 2 . Each transmits a synchronization signal at a different time t 0 -t 7  each eight seconds and possibly a message (in the case of a reportedly stolen vehicle) in which instance microcontroller  46 ,  FIG. 2  would activate transponder  12 . 
         [0031]    But, transceiver  40 , if continuously left on to check for such a message, would more quickly drain the battery of the vehicle. According to the subject invention, microcontroller  46  at start-up, step  60 ,  FIG. 3 , tests the signal strength of towers A-H by analyzing the output of signal strength monitoring subsystem  42 . In this test mode, the signal strength of each tower is noted and if any signal carries a message, the message is acted upon. 
         [0032]    The identity of the two strongest tower signals is stored in memory  47 ,  FIG. 2 , step  62 ,  FIG. 3 , and the wake-up mode is then synchronized, step  64 , to the strongest of these two signals. Next, the sleep mode is entered and when the wake-up mode is activated in synchronization with the communication tower presenting the strongest signal, the signal strength of the two previously stored towers is tested as is the signal strength of one additional communication tower, in sequence. 
         [0033]    As an example, suppose towers A and B,  FIG. 4 , are transmitting the strongest signals by virtue of their proximity to VLU  10 ,  FIG. 2 . If tower A&#39;s signal is assumed to be stronger than tower B&#39;s signal, the wake-up mode synchronization is in accordance with tower A&#39;s signal. Thus, in each cycle, (typical wake up times are 8 sec. apart), controller  46  would power up transceiver  40  by signaling power supply unit circuit  48  at time t 0 ,  FIG. 4 , and sleep between times t 1 -t 7 , steps  66 - 68 . At the next wake-up time, the signal strength of the two previously stored towers (A and B) is tested for strength as is the signal strength of the next tower according to a predefined sequence which, in this example, is tower C, step  70 . In this way, if at any time due to movement of the vehicle a different tower in the sequence A-H presents a stronger signal than a) the tower upon which controller  46  synchronizes the wake-up mode or b) the stored identity of the tower with the second strongest signal, the identity of the new tower is stored in memory  47 ,  FIG. 2 , steps  72 - 74 ,  FIG. 3 , and synchronization to the tower with the strongest signal is ensured at step  64 . 
         [0034]    Suppose, however, that tower C does not present a stronger signal than either towers A or B and that the wake up and sleep modes are still synchronized to tower A in step  66 . At steps  68  and  70  towers A, B, and now D are tested and if tower D&#39;s signal strength is not stronger than either tower A or B and once again the sleep mode is entered, step  66 . Upon entering the wake-up mode at step  68 , still synchronized to tower A, the signal strength of towers A, B, and now E is checked, step  70 . 
         [0035]    Now, if the signal strength of tower E is stronger than the signal strength of tower B, but not tower A, the identity of tower E is stored in memory  47 ,  FIG. 2  at step  74 ,  FIG. 3 , replacing tower B. But at step  64  the wake-up mode is still synchronized to the strongest tower, namely tower A at steps  64 - 68 . 
         [0036]    So, next, the signal strengths of towers A, E, and F are tested, step  70 ; and suppose at step  72  the signal strength of tower F is stronger than tower A and E but tower A is still stronger than tower E. Now, synchronization will be according to tower F at step  64  and at step  70 , towers F, A, and G are tested, and so on. 
         [0037]    In another example, imagine towers C and D initially present the strongest first and second signals to the VLU. The wake up mode is initially synchronized to tower C and the identity of towers C and D are stored in memory. After the first sleep mode, the signal strength of towers C, D, and E are tested, and next towers C, D, and F, and then towers C, D, and G, and then towers C, D, and H, and so on—one additional tower during each subsequent wake-up mode. If during this wake-up/sleep mode cycle, towers C and D remain the strongest two towers, synchronization remains with tower C and the memory continues to store the identity of towers C and D. If during the next cycle, when tower A is tested and is found to present a signal stronger than tower D but not C, the memory is updated to store the identity of towers C and A, synchronization continues according to tower C&#39;s transmission schedule, and during each subsequent wake-up mode the signal strength of towers C, A, and B; C, A, and D; C, A, and E; C, A, and F . . . and so on is tested. 
         [0038]    In this way, the identity of the towers which transmit the two strongest signals is always stored and controller  46 ,  FIG. 2  in sequence checks another tower in the wake-up mode to maintain in storage  47 ,  FIG. 2 , the identity of the two towers emitting the strongest signals. Also, controller  46  ensures the wake-up mode is synchronized to only the tower emitting the strongest signal. Power is conserved but now in a way which ensures no communication message from any tower in the network is missed. To enter the sleep mode, microcontroller  46  sends a signal to power supply unit  48  which then powers down transceiver  40 . To enter the wake-up mode, microcontroller  46  sends a signal to power supply unit  48  which then again provides power to transceiver  40  so that it can receive signals via antenna  44 . 
         [0039]    The example presented above in reference to  FIGS. 3-4  assumes eight towers in a given region, continuous storage of the two strongest tower signals, and testing of an additional tower in a specific sequence, but this is an example only and not a limitation of the subject invention: any number and combination of towers and storage of tower combinations can be used. The example above also assumes that the power management method of the subject invention applies to a VLU of a vehicle recovery system but the invention hereof may find applicability to battery powered electronic devices other than VLUs. 
         [0040]    Thus, although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. Moreover, the words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Also, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims. 
         [0041]    In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.