Abstract:
An approach for synchronizing operation of a first communications terminal with operation of a second communications terminal involves establishing a communications link between the first communications terminal and the second communications terminal, the communications link being defined by a communication standard; and synchronizing a first clock coupled to the first communications terminal with a second clock coupled to the second communications terminal by receiving a time standard signal into the first communications terminal independently of the communication standard. This approach can be implemented using a first clock; a first communications terminal coupled to the first clock; a second clock; a second communications terminal coupled to the second clock; a communications link defined by a communication standard; and a transmitter transmitting a time standard signal independently of the communication standard to the first clock and setting the first clock in response to the time standard signal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the synchronization of a central station with a communications device, and more specifically, such synchronization wherein a communication standard through which the communications device communicates with base station infrastructure is not utilized to achieve such synchronization, but rather such synchronization is independent of the communication standard, whereby modification of the communication standard and the base station infrastructure is unnecessary in order to achieve such synchronization. 
     Recently, technologies have been developed wherein a remotely-located device such as an automobile, can be controlled from a central station through the use of a communications device, and an appropriate interface at the remotely-located device. In this way, features such as unlocking the doors of the automobile can be achieved from a central station, should the operator of the vehicle forget his/her keys in the automobile. One such system to implement this new technology is the ON-STAR System now available with automobiles made by General Motors. 
     Problematically, even communications devices such as hand-held portable cellular telephones, which are generally designed to be optimized for maximum battery life, draw too much current from an automobile&#39;s battery to be left operative for an extended period of time, such as a period of a day or more. Thus, it is highly desirable to deactivate the communications device most of the time, activating it only for brief periods during which it can monitor a communication channel for incoming pages, i.e. calls. 
     Problematically, during periods when the communications device is deactivated, and thus conserving battery life, incoming pages from base station infrastructure will be ignored. Thus, a mechanism must be employed to assure that at least some of such pages are initiated by the central station during periods when the communications device is active. 
     For example, one approach to assuring that pages destined for a particular mobile station are sent while such particular mobile station is active is to use the existing base station infrastructure and a communications standard associated therewith to synchronize operation of the central station and the mobile station. This can be done, for example, by defining a protocol for a control channel that directs the communications device as to when it should activate and deactivate. In such an arrangement, because the base station infrastructure is aware of the communications device&#39;s activate/deactivate cycling, having instructed the communications device as to when to activate and when to deactivate, the base station infrastructure can pass this information on to the central station and can assure that pages are sent only when the communications device is active. 
     Alternatively, the base station infrastructure may simply hold pages from the central station in a queue until the base station infrastructure determines that the communications device should be activated. 
     Unfortunately, these approaches require the establishment of a protocol for a control channel in the communication channel used by the base station infrastructure and the communications device so as to provide for methods of instructing the communications device as to the timing of its activate/deactivate cycling and to enable the base station infrastructure to communication this activate/deactivate cycling to the central station or to queue up pages until the communications device is to become activated. Problematically, the modification of existing protocols for the base station infrastructure requires modification of the communication standard employed, by the base station infrastructure, which presents both technical as well as political challenges. 
     The present invention advantageously addresses the above and other needs. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously addresses the needs above as well as other needs by providing a system and method for the synchronization of a central station with a communications device, and more specifically, such a system and method for synchronization wherein a communication standard through which the communications device communicates with base station infrastructure is not utilized to achieve such synchronization, but rather wherein a synchronization approach independent of the communication standard is employed, whereby modification of the communication standard and the base station infrastructure is unnecessary in order to achieve such synchronization. 
     In one embodiment, the present invention can be characterized as a method of synchronizing operation of a first communications terminal with operation of a second communications terminal involving establishing a communications link between the first communications terminal and the second communications terminal, the communications link being defined by a communication standard; and synchronizing a first clock coupled to the first communications terminal with a second clock coupled to the second communications terminal by receiving a time standard signal into the first communications terminal independently of the communication standard. 
     In another embodiment the present invention can be characterized as a system for synchronizing a first clock with a second clock employing the first clock; a first communications terminal coupled to the first clock; the second clock; a second communications terminal coupled to the second clock; a communications link defined by a communication standard; and a transmitter transmitting a time standard signal independently of the communication standard to the first clock and setting the first clock in response to the time standard signal. 
     In a further embodiment the present invention can be characterized as a communications system having a communications transceiver; a controller coupled to the transceiver; a clock coupled to the controller, the controller powering on and powering off the communications transceiver in response to the clock; and a time standard receiver, independent of the communications transceiver, receiving a time standard signal and setting the clock in response to the time standard signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
     FIG. 1 is a functional block diagram of a communications device, interface, controlled system, GPS satellite array, base station infrastructure, public switched telephone network and central station employing a synchronization approach in accordance with one embodiment of the present invention; 
     FIG. 2 is a functional block diagram showing the central station, a public switched telephone network, and base station infrastructure in accordance with the embodiment of FIG. 1; 
     FIG. 3 shows a functional block diagram of the communications device and interface in accordance with the embodiment of FIG. 1; and 
     FIG. 4 is a state diagram showing the various states traversed by the communications device of FIG. 3 during operation in accordance with the synchronization approach of the embodiment of FIG.  1 . 
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the presently contemplated best mode of practicing the invention is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     Referring first to FIG. 1, a functional block diagram is shown of a system in accordance with one embodiment of the present invention. Shown are four (GPS) transmitter satellites  10 ,  12 ,  14 ,  16  forming a GPS array  18 . Also shown is a first GPS antenna  20  and first GPS receiver  22  coupled to a sleep controller  24 , which is coupled to a cellular transceiver  26  and cellular transceiver antenna  28 . The first GPS receiver  22 , sleep controller  24  and cellular transceiver together make up a communications device  21 . A base station antenna  30  that communicates with the cellular transceiver antenna  28  through a cellular communication channel  32  is coupled to a base station infrastructure  34 . The base station infrastructure  34  is coupled to a service center  36  via a public switched telephone network (PSTN)  38 . The service center  36  is, in turn, coupled to a second GPS receiver  40  and a second GPS antenna  42 . The service center  36  together with the second GPS receiver  40  make up a central station  35 . 
     The cellular transceiver  26  is coupled to an interface  72 , which is in turn coupled to controlled subsystems  73 , such as power door locks on an automobile. Through the interface  72 , the cellular transceiver  26  can be used to remotely control (by way of appropriate command signals from the central station  35 ) operation of, for example, the power door locks of the automobile. The interface  72  may be of the type now employed by General Motors in the OnStar system now available with some of it&#39;s automobiles. 
     In operation, normal cellular communications take place through the cellular communication channel  32  between the cellular transceiver antenna  28  and the base station antenna  30 . Such communications are in a manner well known in the art and preferably in accordance with the AMPS, NAMPS or other cellular or wireless communication standards. 
     The first GPS receiver  22  receives signals from the GPS array  18  via the first antenna  20  and a GPS spacelink  44 , including a time standard signal from which the GPS transceiver  22  is able to determine a time reference. The time standard signal is included in normal GPS transmissions and thus no modification to the GPS array  18  is required for use with the present invention. The time standard signal is passed to the sleep controller  24 , which algorithmatically determines an appropriate sleep schedule (i.e., activate/deactivate cycle) for the cellular transceiver  26 . For example, the sleep controller  24  may determine an activate/deactivate cycle for the cellular transceiver  26  as a function of the time standard signal from the GPS receiver  22  and of a station identification number (STID) assigned to the cellular transceiver  26 . For example, the sleep schedule for the cellular transceiver  26  may be one minute activated, followed by ten minutes deactivated, so as to define a ten minute cycle during which the cellular transceiver is activated for one minute and deactivated for nine minutes. Thus, for example, during each hour of operation the cellular transceiver may be activated from five minutes to six minutes passed the hour, fifteen minutes to sixteen minutes passed the hour, twenty-five minutes to twenty-six minutes passed the hour, thirty-five minutes to thirty-six minutes passed the hour, forty-five minutes to forty-six minutes passed the hour and fifty-five minutes to fifty-six minutes passed the hour. 
     GPS signals from the GPS array  18 , including the time standard signal, are also transmitted via the GPS spacelink  44  to the second GPS antenna  42  and second GPS receiver  40 . Based on the station identification number for the cellular transceiver  26 , and a time standard signal from the second GPS receiver  40 , the service center  36  is able to determine periods during which the cellular transceiver  26  will be activated, and periods during which the cellular transceiver  26  will be deactivated. Advantageously, such determination is made completely independently of the cellular communication channel  32  between the cellular transceiver  26  and the base station infrastructure  34 , and furthermore, completely independently of the base station infrastructure  34 . 
     As a result of this cellular communication channel  32  and base station infrastructure  34  independence, the teachings of the present embodiment provide for synchronization the activate/deactivate cycle  36  of the cellular transceiver  26  with the initiation of transmissions via the cellular communication channel  32  by the service center  36  without a need to modify the cellular protocols utilized across the cellular communication channel  32  or otherwise involve the cellular communication channel  32  or the base station infrastructure  34 . 
     Various modifications such as are discussed hereinbelow may advantageously be made to the cellular transceiver  26  in order to operate in accordance with the teachings of the present embodiment, however, these modifications do not require alteration of the communication standards used over the cellular communication channel  32  or of the base station infrastructure  34 . Instead, an entirely independent and readily available channel, i.e., the GPS spacelink  44 , is utilized to synchronize the activate/deactivate cycles of the cellular transceiver  26  with the initiation of transmissions from the service center  36 . Advantageously, the GPS spacelink  44  is known to carry an accurate time standard built into its transmissions by the GPS array  18 . 
     Referring next to FIG. 2, shown is a block diagram of the central station  35 , the public switched telephone network  38  and the base station infrastructure  34 . The central station  35  is coupled to the base station infrastructure  34  via the public switch telephone network  38 . 
     Within the base station infrastructure  34 , the public switched telephone network  38  is coupled to a mobile telephone switching office  50 , which is in turn coupled to a cell site  52  and the base station antenna  30 . 
     Within the central station  35 , a private branch exchange  54  is connected to the public switched telephone network  38 , and to a modem  56 . The modem  56  is coupled to a workstation  58 , such as a microcomputer, a minicomputer, a mainframe, or a network of one or more such computers. Coupled to a workstation  58  is a database  60  of station identification numbers (STIDs) containing security information associated with each station identification number for verifying that persons wishing to access a particular cellular transceiver via the central station  35  is authorized to access to a particular cellular transceiver. Also shown is the second GPS receiver  40  and the second GPS antenna  42  for receiving GPS signals from a GPS array (not shown) and in particular for receiving the time standard signal therefrom. The time standard signal is passed along to the workstation  58  where the activate/deactivate cycling for a particular cellular transceiver to be accessed is algorithmatically determined. 
     Thus, the time standard signal used by the workstation is received entirely independently from signals that are transmitted and received via the cellular communication channel  32  utilized by the base station infrastructure  34  to communicate with the cellular transceiver. 
     Before the central station  35  initiates a communication with the cellular transceiver, the workstation  58  first accesses the database to recall a customer record. Within the customer record is the station identification number (STID) that identifies the cellular transceiver in, for example, a customer&#39;s vehicle. The customer record contains the customer&#39;s name and other identifying information and also contains a telephone number for the cellular transceiver. The workstation  58  then computes a time at which to access the mobile station based on the cellular transceiver&#39;s activate/deactivate cycle. This computation is based on a wakeup interval (T w ) and the station identification number of the cellular transceiver. Specifically, the time offset, T off =(STID AND OFFh) MOD T w  where “AND” is the Boolean “AND” function, and OFFh is a hexideamal notation for the number 255. For example, if the STID=1000, the T w =10 then STID AND OFFh=E8h, and T off =0 E8h MOV 10=2. 
     A next opportunity to access the cellular transceiver is defined as being T off  minutes after an access time period boundary. Specifically, if T w =10 then access time period boundaries fall on the hour, ten minutes after the hour, twenty minutes after the hour, thirty minutes the hour, forty minutes after the hour and fifty minutes after the hour. Thus, for the example, the vehicle access times would be at two, twelve, twenty-two, thirty-two, forty-two and fifty-two minutes after the hour (because T off  is 2.) The time offset algorithm is used to spread activation intervals, i.e., opportunities to access cellular transceivers within a population of such transceivers that all of the cellular transceivers are not active simultaneously. This helps to better utilize available bandwidth. 
     When the workstation  58  determines that the next opportunity to access a particular cellular transceiver is about to arrive, it dials the cellular transceiver&#39;s telephone number using the modem  56 . The dialing is started just prior to the activation interval to allow for network cut through delays, i.e., delays involved in passing the call through the private branch exchange  54 , the public switched telephone network  38 , the mobile telephone switching office  50  and the cell site  52 . The call arrives via the cellular communication channel  32  to the cellular transceiver just after the cellular transceiver is activated. The call is automatically answered by the cellular transceiver and data exchange via the cellular communication channel  32  can then ensue. 
     Referring next to FIG. 3, a block diagram is shown of a communications device and interface useable with the present embodiment of the present invention. Shown is the first GPS receiver  22  and the first GPS antenna  20  coupled via a first data bus to a processor  70 . The processor  70  is also coupled via a second data bus to an interface  72 , which may be used to control various functions of, for example, a vehicle, such as locking and unlocking a vehicle&#39;s doors. A time of day clock  74  and an application specific integrated circuit (ASIC)  76  are also coupled to the processor  70  via a third data bus. The application specific integrated circuit  74  serves as an interface between the processor  70  and the cellular transceiver  26 , which is coupled to the cellular communication channel  32  via the cellular antenna  28 . The time of day clock  76  receives the time standard signal from the GPS receiver  22  via the processor  70 , and controls a power and reset control unit  78 . The power and reset control unit  78  determines when power is applied to the cellular transceiver  26 , i.e., when the cellular transceiver  26  is activated, and when power is not applied to the cellular transceiver  26 , i.e., when the cellular transceiver is deactivated. Note that modification in the cellular transceiver&#39;s programming is needed in environments where a power off de-registration is called for, so that discontinuous operation does not result in de-registration every time the cellular transceiver is deactivated by the power and reset control unit  78 . Such modification can easily be achieved by the skilled artisan. 
     The cellular transceiver  26  maintains communications with the central station  35  even when, for example, a vehicle&#39;s engine is turned off. During this time, power consumption of the cellular transceiver  26  becomes a critical parameter because available battery current is limited to the extent that a certain amount of battery current must be maintained in order to start the vehicle. To permit operation over an extended period of time, the concept of discontinuous receive is utilized in accordance with the present embodiment, allowing the cellular transceiver to be powered down for periods of time, powering on only briefly to monitor for incoming communications, i.e., pages. As described above, for example, the cellular transceiver  26  may power down for nine minutes and power up for one minute in a repeating cycle, allowing for improved power savings over continuous operation. In order to allow for the use of the concept of discontinuous receive, the cellular transceiver  26  is synchronized with central station  35  so that the cellular transceiver  26  is activated when the central station  35  expects it to be activated. Thus, in accordance with the present embodiment, synchronization is accomplished by having the cellular transceiver read an accurate time of day via the GPS receiver  22 , and simultaneously having the central station  35  read this same time of day via a separate GPS receiver  40 . The time of day information from the GPS receiver is used to program the time of day clock  76  within the communications device  21 . 
     When the communications device  21  commences discontinuous receive operation it sets the time of day clock  76  to awaken the cellular transceiver  26  at a specific time, and then powers down the cellular transceiver  26 . When the specific time arrives, the cellular transceiver  26  is powered back on long enough to monitor for incoming communications from the central station  35 , and at the completion of a prescribed period, if no incoming communication is detected, the communications device  21  repeats the power down cycle. 
     Heretofore, discontinuous receive operation typically required that synchronization be built into control channel protocol operating between the cellular transceiver  26  and the base station infrastructure  34 . By directly synchronizing the cellular transceiver  26  and the central station  35  (thus effectively bypassing the cellular communication channel  32  and the base station infrastructure  34  for purposes of synchronization) a need to deviate from standard cellular or other control protocols is eliminated. 
     Advantageously, the teachings of the present invention are not limited in application to either systems that utilize the global positioning system (GPS) to establish a time standard, or that utilize cellular telephone technologies as their communications topology. Certainly the present invention has application in newly introduced technologies such as the Personal Communications System (PCS) or satellite telephony. Similarly an earth-based time standard may be used, including the employment of very accurate clocks, such as Cs clocks, that are factory synchronized with the central station. Thus, the present invention can properly be characterized as involving the synchronization of two communications systems independently of the particular communications protocol or standard employed. 
     Thus, for example, consistent with the present invention, the cellular communication channel described above could be used to effect synchronization consistently with the present invention so long as the cellular standards employed were not involved in the synchronization, i.e., the synchronization occurred via communications from the central station to the communications device of which the base station infrastructure was “unaware”, i.e., for which the base station performed no function or analysis outside those functions and analysis dictated by the cellular standard employed. Specifically, the base station infrastructure performs no functions or analysis other than those normally performed for the transmission and reception of data or voice signals. 
     Thus, for example, synchronization could be effected consistently with the present invention via a modem-to-modem communication carried by the communications channel  32  between a modem at the central station and a modem at the communications device with such modem-to-modem communication occurring independently of the base station infrastructure  35  other than as a mode of data or audio transmission. 
     Referring next to FIG. 4, a state diagram is shown of states traversed by the communications device  21  during operation in accordance with the present embodiment. 
     Once the time of day clock alarm time is programmed, the communications device  21  exits a VCU monitor state (State  1000 ) and powers down all circuits in the cellular transceiver  26  or even all circuits in the communications device  21  except the time of day clock  76  and other essential low power circuits, thus entering a VCU sleep state (State  1002 ). When the time of day clock  76  determines that a period of time during which the cellular transceiver  26  is to stay deactivated has expired, the cellular transceiver  26  powers up into a VCU resume state (State  1004 ), and monitors the cellular communication channel for a prescribed wakeup period, such as one minute, using normal minimal current draw standby techniques. After the prescribed awake period has expired, the communications device  21  reprograms the time of day clock  76  for a subsequent wakeup period and again powers down into the VCU sleep state (State  1002 ). This cycle repeats over a prescribed time period as defined by the total amount of current that can be drawn from, for example, a vehicle&#39;s battery without jeopardizing its ability to restart the vehicle, after which the communications device  21  ceases discontinuous receive activity the VCU sleep state (State  1002 ). If battery power is completely removed from the communications device  21 , it enters a VCU unpowered state (State  1006 ) until battery power is restored, e.g., until the vehicle&#39;s ignition is started. 
     If, while the cellular transceiver  26  is powered up into the VCU resume state (State  1004 ), bus activity is detected by the application specific integrated circuit  74  and processor  70 , an incoming call is similarly detected or a power key on the cellular transceiver is depressed, the communications device enters a VCU wakeup delay state (State  1008 ) during which the communications device  21  waits for devices with which it shows a data bus to power up. Next, following a wakeup delay, the communications device  21  enters the VCU awake state (State  1010 ) where normal powered operation of the cellular transceiver continues until the application specific integrated circuit  71  and processor  70  detect no bus activity for a timeout period or detect that no cellular telephone call is in progress. When the timeout period expires without any detected bus activity and when a detection is made that there is no call in progress, the communications device  21  returns to the VCU monitor state (State  1000 ). 
     If, on the other hand, the power key is depressed or the vehicle&#39;s ignition is turned on while the communication device  21  is in the VCU awake state (State  1010 ), the communications device is put into a VCU on state (State  1012 ) until the power key is depressed again (to turn the cellular transceiver off) or the ignition is turned off while there is no call in progress, at which time the communications device  21  returns to the VCU awake state (State  1010 ). 
     In this way, the present embodiment provides for discontinuous operation of the communications device  21  synchronously with the central station  35  from which transmissions are from time-to-time initiated without a need to revise or even involve the communications standard employed by the base station infrastructure  34  and cellular communication channel  32  in the synchronization of the communications device  21  with the central station  35 . In the embodiment described above, it is unnecessary even to involve the base station infrastructure  34  or cellular communication channel  32  in the synchronization of the communications device with the central station. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.