Patent Publication Number: US-7596366-B2

Title: System and method for controlling the power in a wireless client device

Description:
The present application is a continuation-in-part of parent application Ser. No. 10/412,179, filed Apr. 11, 2003, which is commonly owned and incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention in general relates to controlling the power in a wireless client device and, more particularly, to a system and method that controls the power within the device based on a discontinuous reception (DRX) parameter obtained from a wireless network. 
     BACKGROUND OF THE INVENTION 
     Telematics systems are being designed to deliver a wide spectrum of information and services via wireless links to vehicle-based subscribers. For instance, Telematics systems are being designed to allow remote service centers to control certain vehicle functions. A remote service center or remote device may be used to unlock or lock the vehicle&#39;s doors, to flash the vehicle&#39;s lights, to sound the horn, or to start the vehicle&#39;s engine. The remote service center may also be used to perform other functions such as theft tracking. 
     Some of these services must be capable of being performed when the vehicle&#39;s engine is turned off such as the unlocking of vehicle&#39;s doors and theft tracking. This requires that the Telematics system be powered so that it may monitor and receive commands and data. Today&#39;s Telematics systems, however, consume too much power to allow these systems to be continually powered on. The vehicle&#39;s battery must be protected from excessive drainage. 
     In the past, after the vehicle&#39;s engine is shut-off, the Telematics unit is powered for a fixed time period or cycled on and off for a fixed time period and then shut off completely to avoid draining the vehicle&#39;s battery. Current designs, however, typically only allow manufacturers to leave the system in a powered state for about forty-eight hours. A need exists for providing a Telematics system that can be powered for a much longer duration after the vehicle&#39;s engine is shut-off. 
     It is, therefore, desirable to provide a battery-powered client device that can operate for longer durations to overcome or minimize most, if not all, of the preceding problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a communication system according to one embodiment of the present invention; 
         FIG. 2  is a block diagram of a communication system according to another embodiment of the present invention; 
         FIG. 3  is a flow diagram of one method for controlling the power in a wireless client device; 
         FIG. 4  is a flow diagram of another method for controlling the power in a wireless client device; 
         FIG. 5  is a flow diagram of a further method for controlling the power in a wireless client device; 
         FIG. 6  is a flow diagram of yet another method for controlling the power in a wireless client device; 
         FIG. 7  is a flow diagram of yet another method for controlling the power in a wireless client device; and 
         FIG. 8  is a flow diagram detail of the establishing step of  FIG. 7 . 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     What is described is a system and method for controlling the power in a client device based on a discontinuous reception (DRX) parameter obtained from a wireless network. For purposes of illustration and description, an example of an application of a client device is described below in the context of a vehicle-based Telematics system. The present invention, however, is not limited to client devices in the form of vehicle-based Telematics systems but may also apply to other devices such as portable phones, personal digital assistances (PDAs), pagers, and the like. One of ordinary skill in the art having the benefit of this disclosure will realize that the devices and procedures described herein for controlling the power in a client device could be used in other applications. 
     To this end, in one embodiment, there is a client device comprising a network access device (NAD), a programmable timer, and a controller. The network access device receives messages over a communication channel and has a powered state and a power-off state. The programmable timer operates the network access device in a powered state. The controller is in communication with the programmable timer and is capable of providing a time period for operating the network access device in the powered state. The controller determines the time period based on a discontinuous reception parameter obtained from the network access device. 
     The controller may have a power-on state and a power-off state. The controller may switch from its power-on state to its power-off state after providing the time period to the programmable timer. The programmable timer may be a circuit that is separate from the controller or, alternatively, may be a timer or counter that is part of, or integral to, the controller. If the timer or counter were a part of the controller, the controller may then have a power-off state, a low-powered state, and a power-on state. The low-powered state would be a state where the circuitry of the programmable timer is provided with power but the power to the remaining circuitry of the controller would be in a sleep mode. 
     The network access device may simply include a transceiver or may include a transceiver and a controller. If another controller is used in the network access device, the network access device may be configured to monitor a voltage of a battery to determine whether the voltage of the battery is at or below a threshold. If the voltage is at or below the threshold, the network access device could switch itself to a power-off state. 
     The client device may further include, in an alternative embodiment, a current monitor that monitors an accumulated current drawn by the client device during the time period selected by the controller. The monitor may be configured to switch the client device to a power-off state if the accumulated current drawn by the client device meets or exceeds a predetermined threshold. Alternatively, the current monitor could monitor the accumulated current drawn by the network access device. 
     In another embodiment, the client device is embedded in a vehicle and comprises a network access device and a controller. The network access device has at least a powered state and a power-off state. The powered state allows the network access device to receive messages over a communication channel. The power-off state does not allow the network access device to receive messages over the communication channel. The controller determines a time period for the network access device. The time period defines the length of time that the network access device should be in the powered state after an ignition switch in the vehicle is turned off. The time period is based on a discontinuous reception parameter obtained from the network access device. 
     In a further embodiment, there is a method in a client device that has a network access device, a programmable timer, and a controller. The method comprises the steps of: obtaining a discontinuous reception parameter from a network; determining a time period for operating the network access device in a powered state based on the obtained discontinuous reception parameter; sending the time period to the programmable timer; and operating the network access device in a powered state during the time period. The method may further include steps such as: monitoring a voltage of a battery during the time period to determine whether the voltage of the battery is at or below a predetermined threshold; and switching the network access device to a power-off state if the voltage of the battery is at or below the predetermined threshold. The method may also include steps such as: monitoring a current drawn by the network access device during the time period; determining an accumulated current drawn by the network access device; and switching the network access device to a power-off state if the accumulated current drawn by the network access device meets or exceeds a predetermined threshold. 
     Now, turning to the drawings,  FIG. 1  illustrates a block diagram of one embodiment of a communication system  20  for the present invention. Generally, the communication system  20  includes a client device  22  and a service center  24 . In one embodiment, the client device  22  is a Telematics device that is embedded in a vehicle. Although only one client device  22  and service center  24  are shown, the invention may include any number of these elements interoperating with each other. 
     An intermediate network  26  may be used for wireless communications between the client device  22  and the service center  24 . For instance, the network  26  could be one of several standard cellular communication networks, a satellite-based network, a public switched telecommunication network (PSTN), the Internet, an integrated services digital network (ISDN), and/or other communication networks. 
     A service provider may operate the service center  24  to provide Telematics applications and services to the client device  22 . For instance, the service center  24  may contain operators, content servers and content databases. The content servers for Telematics applications and services may include traffic servers, map servers, user profile servers, location information servers, and the like. The content databases for Telematics applications and services may include location information, user profiles, traffic content, map content, point-of-interest content, usage history, and the like. 
     In one embodiment, the client device  22  may generally comprise a network access device (NAD)  30  and a control unit  40 . In this embodiment, the network access device  30  includes at least a transceiver  32 , but may also include a controller  34 . The control unit  40  may include a controller  42 , a NAD power supply  44 , a main power supply  46 , and a programmable timer  48 . In  FIG. 1 , the client device  22  is shown as a single unit having a serial connection  36  between the network access device  30  and the controller  42  of the control unit  40 . Although shown as a single unit in  FIG. 1 , the network access device  30  may be a separate unit from the client device  22 . In particular, the network access device  30  may be part of a portable wireless communication device such as a phone, a personal digital assistant (PDA), a pager, and the like. An external interface could then be used to provide connectivity with the network access device  30 . 
     The transceiver  32  in the network access device  30  is used for transmitting uplink communications and receiving downlink communication to and from the network  26  and service center  24  over wireless communication link A. The wireless communication link A may use a wireless protocol such as a standard cellular network protocol such as Advanced Mobile Phone Service (AMPS), Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and the like. To transmit data in the cellular environment, different types of standard bearer services exist including, but not limited to, general packet radio service (GPRS), short message service (SMS), circuit switched data service (CSD), and high-speed circuit switched data service (HSCSD). In another embodiment, standard transmission control protocol/internet protocol (TCP/IP) may also be used as well as satellite communications. In a further embodiment, the transceiver  32  may be enabled using other wireless technologies such as Bluetooth™ technology. Bluetooth™ technology allows for the replacement of a wired connection by enabling devices to communicate with each other through a universal short-range radio link. A Bluetooth™ specification is available on the Internet from the Bluetooth Special Interest Group (SIG) at www.bluetooth.com. 
     The network access device  30  is provided power from a battery such as a vehicle&#39;s main battery  50 . A NAD power supply  44  may be connected between the network access device  30  and the vehicle&#39;s main battery  50 . The NAD power supply  44  is capable of converting the battery  50  voltage to the network access device  30  operating voltage. As will be described in more detail below, the power supply  44  may have an input  52  for disabling the power source to the network access device  30 . The power supply  44  may have another input  53  for switching the operating voltage of the network access device  30  from a normal operating voltage (such as 5 volts) to a relatively low operating voltage (such as 3 volts). 
     Generally, the power supply  44  may be disabled by components such as the programmable timer  48  (e.g., after expiration of a time period), the network access device  30  (e.g., after monitoring a low battery voltage), or by a current monitor  54  (e.g., after monitoring an excessive accumulated drawn current). With respect to the programmable timer  48 , the controller  42  in the control unit  40  provides the programmable timer  48  with information on when the power to the network access device  30  should be disabled. The programmable timer  48  may be a circuit that is separate from the controller  42  or, alternatively, the programmable timer  48  may be part of, or otherwise integral to, the controller  42 . The controller  42  receives a signal that the vehicle&#39;s ignition  56  has been turned off. In response, the controller  42  will then determine a time period for the programmable timer  48  to disable the power supply  44  to the network access device  30 . As will be explained in more detail below, in one embodiment, the time period is based on a discontinuous reception (DRX) parameter from the controller  34  in the network access device  30 . The network access device  30  receives the DRX parameter from the network  26 . 
     In general, discontinuous reception is a technique that allows a handset to power down significant amounts of its internal circuitry for a high percentage of time when it is in the idle mode. It also ensures that the handset is aware of when page requests for it may be transmitted. For instance, a handset that supports discontinuous reception will “sleep” during times that it knows that its paging requests will not be transmitted. When the handset enters a particular paging area, part of the registration process includes obtaining from a wireless network a parameter that tells the handset how often to “wake up” and process a page. A term called the discontinuous reception factor (or “DRX factor”) is used in GSM networks to notify handsets of the paging repetition rate within a particular area. The DRX factor is broadcast in the Broadcast Control Channel (BCCH). A lower value means that the paging message should be checked by the handsets at greater frequency intervals. This reduces the delay in setting up an incoming call but has the downside of draining the battery quicker. A higher value means that the paging messages should be checked by the handsets at less frequency intervals. This reduces the draining of the battery but has the downside of further delaying the setup of an incoming call. The present invention transfers the parameter from the controller  34  in the network access device  30  to the controller  42  in the control unit  40  so that the parameter may be advantageously used in other applications. 
     Moreover, the controller  42  can operate the network access device  30  in the powered state in at least two modes: a continuous power mode and a periodic power mode. In the continuous power mode, the circuitry for at least the receiving portion of the network access device  30  is continuously supplied with power from the battery  50  through the power supply  44 . In the periodic power mode, the circuitry for at least the receiving portion of the network access device  30  is periodically supplied with power from battery  50  through the power supply  44 . The controller  42  may set up the periodic power mode by determining an on/off duty cycle of the power supply  44 . The on/off duty is preferably based on the discontinuous reception parameter and sent to the programmable timer  48  for execution. The programmable timer  48  would then be programmed with the predetermined duty cycle to disable and enable the power supply  44  to the network access device  30 . 
     In another embodiment of the present invention, the power state of the network access device  30  is controlled with the assistance of a battery monitoring function in the controller  34  of the network access device  30 . This can be done as a backup feature to the timing scenario described above or as an independent method of controlling the power in a client device  22 . In one embodiment, the network access device  30  contains circuitry and software to monitor the voltage being drawn by the network access device  30  after the ignition  56  is shut-off. The network access device  30  would then be configured or otherwise programmed to disable itself from the battery  50  by sending a disable signal to the input  52  of the NAD power supply  44  if the voltage being monitored meets or exceeds a predetermined threshold. 
     In a further embodiment of the present invention, the powering state of the network access device  30  is controlled with the assistance of a current monitor  54 . This can be done as a backup feature to the timing scenario described above or as an independent method of controlling the power in a client device  22 . In one embodiment, the current monitor  54  is configured to monitor a current drawn by the client device  22  after the ignition  56  is shut-off. This may be accomplished with a sense resistor and a coulomb counter as described in more detail below. The sense resistor and coulomb counter could be used to monitor an accumulated current drawn by the client device  22  from the battery  50 . The current monitor  54  may disable the power by sending a disable signal to the input  52  of the power supply  44  through the programmable timer  48  if the accumulated current meets or exceeds a predetermined threshold. Alternatively, the current monitor  54  could monitor the accumulated current drawn by the network access device  30 . 
     The client device  22  also has a main power supply  46  that provides power to the controller  42  and other components. In some applications, the controller  42  may be electrically connected to a vehicle bus  72  and certain vehicle subsystems to help in the remote control of the vehicle. The vehicle bus  72  can include both vehicle electrical bus and a vehicle data bus. The vehicle subsystems may include an ignition system  56  or a door-locking system  74 . In the present invention, a connection to the ignition system  56  may be necessary for the determination of whether the vehicle&#39;s engine has been shut-off. After the engine is shut-off, any power consumed by the client device  22  would come from the vehicle&#39;s battery  50 . A connection to the door-locking system  74  is beneficial to unlock the doors of a vehicle when a user accidentally locks the keys in the vehicle. 
     The controller  42  can be configured to switch between two power states, a power-off state and a power-on state. In power-off state, the controller  42  consumes little or no power and is essentially in a sleep mode. In power-on state, the controller  42  can send and receive messages from the network access device  30  over serial connection  36 . The controller  42  may also send and receive messages and commands from other vehicle resources  56 ,  74 ,  78 . 
     Alternatively, the controller  42  can be configured to switch between three power states: a power-off state, a low-powered state, and a power-on state. This may be particularly important where the programmable timer  48  is part of, or integral to, the controller  42 . If the programmable timer  48  is a part of the controller  42 , the programmable timer  48  may be a real-time counter in the controller  42  that is capable of being programmed to wake the controller  42  at an end of the time period determined from the discontinuous reception parameter. In the low-powered state, only the real-time counter may be provided with power. The remaining circuitry in the controller  42  may be put in a sleep mode while the controller  42  is in the low-powered state. In the power-off state, the controller  42  consumes little or no power and all the circuitry is essentially in a sleep mode. In the power-on state, the controller  42  is fully powered and can send and receive messages from the network access device  30  over serial connection  36 . 
     The controller  42  in the client device  22  has a processor  62  for processing algorithms and other data stored in memory  64 . The memory  64  may store operating software and variables that may be used in accordance with the present invention. For instance, as explained in more detail below, the memory  64  may store discontinuous reception parameters obtained from the network access device  30 . The network access device  30  may obtain these parameters from the network  26  at the time the network access device  30  registers the client device  22  in a networked area. The memory  64  could also store tables, formulas and other data for making certain determinations based on the stored discontinuous reception parameters. 
     Additionally, the memory  64  may also contain programs and algorithms to monitor and control the power in the client device  22 . In one embodiment, when the ignition  56  of the vehicle is turned off, the controller  42  configures the programmable timer  48  for a time period to operate the network access device  30  in a low-powered state. The controller  42  may then be instructed to enter into a power-off state. This has a significant benefit of reducing the power consumption of a client device  22  after the vehicle&#39;s engine has been shut-off. 
     The controller  42  may also be connected to a user interface  78 . The user interface  78  may include elements such as a display, a keyboard or keypad, one or more control buttons, indicator lights, one or more speakers, a microphone, and any other user interface type elements for Telematics applications and services. Optionally, the controller  42  may also be connected to a positioning unit (not shown). The positioning unit could be a system that determines the geographic location of the client device  22  or vehicle such as a global positioning system (GPS), a dead-reckoning system, and the like. 
       FIG. 2  shows an alternative embodiment of the client device  22 . In this embodiment, the functions of the controller  34  in the network access device  30  are transferred to the controller  42 . In effect, the network access device  30  serves only as a transceiver. This reduces the number of controllers in the system. It may also reduce the power consumed by the client device  22 . In particular, the network access device  30  in  FIG. 1  is the portion of the client device  22  that remains powered after the controller  42  provides a time period of operation to the programmable timer  48 . In the device of  FIG. 2 , the portion of the client device  22  that remains powered is transceiver  130 . In certain applications, it is contemplated that the power consumed by the transceiver  130  is less than the power required for the network access device  30 . 
     In the system shown in  FIG. 2 , the client device  22  may generally comprise a transceiver  130 , a controller  42 , a transceiver power supply  144 , a main power supply  46 , and a programmable timer  48 . Depending on the implementation, the client device  22  may have other components such as a current monitor  44  similar to that described above. 
     Here, the transceiver  130  is used for transmitting uplink communications and receiving downlink communication to and from the network  26  and service center  24  over wireless communication link A. The transceiver  130  is provided power from a battery such as a vehicle&#39;s main battery  50 . A transceiver power supply  144  may be connected between the transceiver  130  and the vehicle&#39;s main battery  50 . As will be described in more detail below, the power supply  144  may have an input  52  for disabling the power source to the transceiver  130 . 
     Generally, the transceiver power supply  144  may be disabled by components such as the programmable timer  48  (e.g., after expiration of a time period) or by a current monitor  54  (e.g., after monitoring an excessive accumulated drawn current). Depending on the implementation, the transceiver power supply  144  may be configured to be disabled by other components such as the controller  42 . However, it is preferred that the controller  42  be in the power-off state soon after the ignition  56  is shut-off. Similar to the above description, with respect to the programmable timer  48 , the controller  42  provides the programmable timer  48  with information on when the power to the transceiver  130  should be disabled. In particular, the controller  42  receives a signal that the vehicle&#39;s ignition  56  has been turned off. In response, the controller  42  will then set a time period for the programmable timer  48  to disable the transceiver power supply  144  to the transceiver  130 . As will be explained in more detail below, in one embodiment, the time period is based on a discontinuous reception (DRX) parameter from the network  26 . The time period may be determined at the time the ignition is shut-off or may be stored in memory  64  after receiving the discontinuous reception parameter from the network  26 . 
     Moreover, the controller  42  can operate the transceiver  130  in the powered state in at least two modes: a continuous power mode and a periodic power mode. In the continuous power mode, the circuitry for at least the receiving portion of the transceiver  130  is continuously supplied with power from the battery  50  through the transceiver power supply  144 . In the periodic power mode, the circuitry for at least the receiving portion of the transceiver  130  is periodically supplied with power from battery  50  through the transceiver power supply  144 . The controller  42  may set up the periodic power mode by determining an on/off duty cycle of the transceiver power supply  144 . The on/off duty is preferably based on the discontinuous reception parameter and sent to the programmable timer  48  for execution. The programmable timer  48  would then be programmed with the predetermined duty cycle to disable and enable the power supply  144  to the transceiver  130 . 
     In another embodiment of the present invention, the power state of the transceiver  130  is controlled with the assistance of a current monitor  54 . This can be done as a backup feature to the timing scenario described above or as an independent method of controlling the power in a client device  22 . In one embodiment, the current monitor  54  is configured to monitor a current drawn by the client device  22  after the ignition  56  is shut-off. This may be accomplished with a sense resistor and a coulomb counter as described in more detail below. The sense resistor and coulomb counter could be used to monitor an accumulated current drawn by the client device  22  from the battery  50 . The current monitor  54  may disable the power by sending a disable signal to the input  52  of the transceiver power supply  144  through the programmable timer  48  if the accumulated current meets or exceeds a predetermined threshold. Alternatively, the current monitor  54  could monitor the accumulated current drawn by the transceiver  130 . 
     In above embodiments, the client device  22  includes at least one controller  42  having a processor  62  that implements software stored in the memory  64 . Certain functions of the client device  22  may be implemented in hardware.  FIG. 3  illustrates one embodiment of a method according to the present invention. The method begins at decision block  102  where a determination is made whether a triggering event has occurred, such as whether the ignition  56  of the vehicle has been turned off. This determination may be made by the controller  42  during a monitoring process of the ignition system  56 . If the ignition  56  has not been turned off, then the process waits at decision block  102  until the ignition  56  has been turned off. When the ignition  56  has been turned off, the process continues to block  104 . 
     At process block  104 , the controller  42  obtains a discontinuous reception (DRX) parameter. If the client device  22  uses a GSM network protocol, this DRX parameter may range in value between 2-9. The DRX parameter may be obtained and stored in memory  64  of the client device  22  when the device registers itself with a network  26  in a particular geographic area. A lower value means that the paging messages should be checked by the client device  22  at greater frequency intervals. This reduces the delay in setting up an incoming call but has the downside of draining the battery quicker. A higher value means that the paging messages should be checked by the client device at less frequency intervals. This reduces the draining of the battery but has the downside of further delaying the setup of an incoming call. 
     At process block  106 , the controller  42  uses the DRX parameter to determine a time period for switching the network access device  30  (or transceiver  130 ) to a power-off state. Hereinafter, for purposes of illustration, the references to the network access device  30  should also be viewed to include transceiver  130 , unless otherwise noted. In any event, in one embodiment, the determination of a timer period may be done by using a look-up table  108 . A sample look-up table  108  is provided in  FIG. 3 . The exact values of the time period will depend on the amount of current drawn by the network access device  30 ,  130  at each level of discontinuous reception. In other words, the exact values for the time periods at each level of discontinuous reception is implementation specific and depends on design details of the network access device  30 ,  130  and other circuitry in the client device  22  as well as operator preferences. Alternative to the look-up table  108 , the controller  42  could obtain the time period through a formula or other algorithm based on the factors mentioned previously. In any event, the time period should relate to a conservative period of time that the network access device  30 ,  130  could remain powered while keeping the battery  50  above a level that the engine of the vehicle may still be started. After the controller  42  determines an adequate time period, based on the DRX parameter, the process then continues to block  110 . 
     At process block  110 , the controller  42  will set the programmable timer  48  so that it is capable of disabling the power to the network access device  30 ,  130  at the expiration of the time period determined in block  106 . The process then proceeds to block  112 . 
     At process block  112 , the controller  42  will then set itself to a power-off state. In the power-off state, the controller  42  consumes little or no power and is essentially in a sleep mode. It should be noted that the time period (determined by the controller  42 ) is processed or otherwise executed by the programmable timer  48 . The advantage of using a programmable timer  48  is that it consumes less power than continuing to supply power to the controller  42 . The ability to power down the controller  42  at this point significantly reduces the power that may be drawn from the battery  50 . 
     At decision block  114 , the programmable timer  48  will wait for the expiration of the time period that was determined by the controller  42 . When the time period expires, the process may proceed to block  116  where the network access device  30 ,  130  is set to a power-off state. Sending a disable signal to the input  52  of the power supply  44 ,  144  can switch the network access device  30 ,  130  into a power-off state. In the power-off state, the network access device  30 ,  130  is not capable of sending or receiving wireless communications over wireless link A. In effect, at this point, the engine of the vehicle would need to be turned back on before the client device  22  could be powered. Alternatively, other triggers, such as a door handle being pulled up, could wake up the client device  22 . 
     While the client device  22  is in the state of waiting for the time period to expire or end, the network access device  30 ,  130  will be checking for any incoming paging messages from external transmission sources such as the network  26  or other wireless devices. It should be understood that if the client device  22  receives a page during the time period, a signal or interrupt will be sent to the controller  42  so it will wake-up and process the incoming paging message. 
     In an alternative embodiment, the process further includes decision block  118 . At decision block  118 , during the time period, the network access device  30  may be configured to perform a battery monitoring function. In one embodiment, the battery monitoring function may reside in the controller  34  of the network access device  30 . The controller  34  could monitor a voltage drawn from the battery  50  by the network access device  30 . This may be done through an analog to digital converter at power input  38 . The controller  34  may then compare the voltage drawn from the battery  50  to a predetermined threshold. The threshold should have some relation to a minimum voltage required by the battery  50  to start the engine of the vehicle. In this embodiment, if the battery  50  is at or below the predetermined threshold, then the network access device  30  would not wait for the full time period to switch the network access device  30  to the power-off state. Instead, the process would proceed to block  116  where the controller  34  sends a disable signal to input  52  of the power supply  44 . If the battery  50  is stable, the process may return to decision block  114  for a continued determination of whether the time period has expired. In effect, decision block  118  advantageously serves as a backup process to protect excessive drainage of the battery  50 . 
     In another embodiment, decision block  118  may be done with the use of a current monitor  54 . The current monitor  54  would measure and monitor an accumulated current drawn from the battery  50 . This accumulated total provides the current-time product, in units such as milliamp-hours, of the current drawn by the client device  22  from the battery  50 . The accumulated current could then be compared to a predetermined threshold. The threshold should have some relation to the minimum energy required by the battery  50  to start the engine of the vehicle. This could be provided by the manufacturer of the vehicle. In this embodiment, if the accumulated current drawn from the battery  50  meets or exceed the predetermined threshold, then the network access device would be switched to a power-off state before the expiration of the time period. 
     In the alternative case where the current monitor  54  is monitoring an accumulated current drawn by the network access device  22 , the monitor  54  may be positioned on the other side of the power supply  44 ,  144 . In that case, the threshold should take into account any efficiency improvements caused by using a switching power supply  44 ,  144  to convert the battery voltage to the network access device  30 ,  130  operating voltage. Again, if the accumulated current drawn from the battery  50  meets or exceed the predetermined threshold, then the network access device would be switched to a power-off state before the expiration of the time period. This may be accomplished by the current monitor  54  sending a disable signal to input  52  of the power supply  44 . 
     The following example is provided for purposes of illustration. For purposes of this example, it is assumed that the criteria for a particular design is 4 mA current drawn from the battery over a period of 4 weeks. It is assumed that the battery voltage is set to 12 volts and the network access device  30 ,  130  is set to 3 volts. If the switching power supply  44 ,  144  has 100% efficiency, the following relations (1)-(3) applies:
 
Po=Pi  (1)
 
 Vo×Io=Vi×Ii   (2)
 
 Io=Ii× ( Vi/Vo )  (3)
 
     where Po is the power output and Pi is the power input of the power supply  44 ,  144 ; Vo is the voltage output and Vi is the voltage input of the power supply  44 ,  144 ; Io is the current input and Io is the current output of the power supply  44 ,  144 . 
     However, in reality, the use of power supply  44 ,  144  will not result in 100% efficiency. Accordingly, the power supply efficiency (eff) should be accounted for as shown in relation (4):
 
 Io=Ii× ( Vi/Vo )× eff   (4)
 
     If the power supply  44 ,  144  were 75% efficient at the current levels used by the network access device  30 ,  130  when idle, this would yield a total allowable draw of 12 mA for 4 weeks or 8064 milliamp hours. Other factors such as current drawn by the monitor  54  and any other bias currents should be considered to subtract off this number. The result can be used to determine a predetermined threshold. 
     In one embodiment, the monitor  54  may include components such as a sense resistor and a counter. The counter may be a coulomb counter. When the car ignition  56  is turned off, the counter is cleared. The counter would then count up at a rate proportional to the current passing through the sense resistor. The counter could be compared to the predetermined threshold. When the counter meets or exceeds the threshold, the monitor  54  may generate an alarm or send a disable signal to the power supply  44 ,  144 . 
     In a further embodiment, the process further includes decision block  119 . At decision block  119 , during the time period, the network access device  30 ,  130  may be configured to wake up controller  42  upon a change in the value for the discontinuous reception parameter. If no change is detected, then the process may go back to determining whether the first time period has expired. However, when the network access device detects a change in value, the controller  42  is awakened and processing continues back at process block  104 . A new discontinuous reception parameter is obtained at block  104  and then used in process block  106  to calculate or determine a new time period or timeout value. The calculation or determination of the new timeout value may take into account the amount of time the network access device was operating at the previous value for the discontinuous reception parameter. In a system where the value of the discontinuous reception parameter is expected to change multiple times during the time period, the controller  42  could maintain a running estimate of total milliamp-hours consumed based on the amount of time spent at each discontinuous reception level. Then the new timeout value could be calculated based on the total allowable milliamp-hours, the new discontinuous reception level, and the expected current draw for the new discontinuous reception level obtained from look-up table  108 . 
       FIG. 4  illustrates another embodiment of a method according to the present invention. The method is similar to the one described in  FIG. 3  but with the additional process blocks  120  and  122 . In particular, after the controller  42  determines a time period for leaving the network access device  30 ,  130  in a powered state, the process continues to block  120 . At block  120 , the controller  42  further determines an on/off duty cycle of the power supply  44  for the network access device  30 ,  130 . The benefit of this step in the process is that client device  22  will consume less power than when the network access device  30 ,  130  is a continuous powered state. In particular, a different look-up table  124  or other algorithm or formula may be used that factors in the network access device  30 ,  130  operating in a periodic power mode. In the periodic power mode, the circuitry for at least the receiving portion of the network access device  30 ,  130  is periodically supplied with power from battery  50  through the power supply  32 . The controller  42  may set this up in process block  122  after the determination of an on/off duty cycle for the power supply  44 . The on/off duty cycle is preferably based on the discontinuous reception (DRX) parameter and supplied to the programmable timer  48 . After the controller  42  sets the on/off duty cycle of the power supply, the process may then continue back to process block  112  where the controller  42  is set to a power-off state as described in more detail above. 
       FIG. 5  illustrates another embodiment of a method according to the present invention. The method is similar to the ones described in  FIGS. 3 and 4  but with the additional process block  132 . In particular, after the controller  42  obtains the discontinuous reception parameter, the controller  42  will then determine a time period for leaving the network access device in a powered state after the ignition is shut-off. Process block  132  is different from  106  in that it further considers different voltage levels that the network access device  30 ,  130  may operate. In particular, the network access device  30 ,  130  will consume significantly lower power if operated in a low voltage level. For instance, in some applications during normal operation when the ignition is on, a network access device  30 ,  130  may operate at about 5 volts in order to achieve the required output power. When monitoring paging messages, the network access device  30 ,  130  may be capable of being operated at a lower voltage level such as 3 volts. This will significantly increase the value of the time period that the network access device  30 ,  130  may be powered. The switching from a normal operating voltage to a relatively low operating voltage may be done through input  53 . In the preferred embodiment, when the ignition is turned off and the unit is not transmitting, the voltage for the network access device  30 ,  130  would be set to the lower voltage level. 
     As a result, the process block  132  may use a look-up table  134 , formula or other algorithms that takes into account whether the network access device  30 ,  130  is operating at a lower than normal voltage level. The process would then continue to process block  120  where the controller  42  determines an on/off duty cycle. Again, as mentioned above, the on/off duty cycle is preferably based on the discontinuous reception parameter and supplied to the programmable timer  48  for execution. 
       FIG. 6  illustrates another embodiment of a method according to the present invention. The method is similar to the one described in  FIG. 3  but with the additional decision block  140 . In particular, during the time period, the network access device  30  may be configured to make a determination whether wireless coverage is still being provided to the client device  22 . This may occur if the client device  22  (or vehicle) resides in an area of very poor or no coverage. In this case, it may not be desirable to further drain the battery  50  when the client device  22  could not receive communications. Accordingly, in this embodiment, if there is no wireless coverage, then the network access device  30  would not wait for the full time period to switch the network access device  30  to the power-off state. Instead, the process would proceed to block  116  where the network access device  30  sends a disable signal to input  52  of the power supply  44 . In determining whether wireless coverage exists, a fixed length of time should be considered in the evaluation. It would not be beneficial to shut-off the network access device  30  if there is just a temporary, intermittent lack of wireless coverage. In any event, if the battery  50  is stable, the process may return to decision block  114  for a continued determination of whether the time period has expired. In effect, decision block  140  advantageously serves as a backup process to protect excessive drainage of the battery  50 . 
     It would be beneficial to provide this additional out-of-coverage functionality, without additional hardware in either the Telematics controller or the NAD controller. Therefore, the present invention also envisions using an existing Ring Indicator, RI (shown as  11  in  FIGS. 1 and 2 ) to indicate an out-of-coverage condition (step  140  in  FIG. 6 ). In particular, an existing Ring Indication (RI) from the NAD  30  or WAN transceiver  130  (hereinafter transceiver) will have its function expanded to include an indication when the transceiver is out of wireless coverage. 
     Currently, the ring indication gives the Telematics controller  42  an indication of an incoming call or incoming Short Messaging Service (SMS) message. If the controller  42  is sleeping, the ring indication will wake the controller  42  up to full operating mode. In accordance with the present invention, once awake the controller  42  can then poll and/or monitor the transceiver device over the serial bus  36  to determine the reason that it was awakening: incoming call, incoming SMS message, or out of wireless coverage. If the reason is out of wireless coverage then the controller  42  will turn off the transceiver  30 ,  130  so that the increase in current drain needed by the transceiver to search for a new network does not completely drain the car battery. 
     In practice, since the out-of-coverage indication as defined in this scenario is only needed when the controller  42  is off and not when it is on, this functionally can be turned on and off with a communication command from the controller on the serial bus  36 . In other words, when the controller  42  is on and fully operational, the out-of-wireless coverage indication on the RI is not needed. 
     In review, the above described solution simply wakes up the controller when the transceiver goes out-of-coverage for any amount of time. The controller can then decide what action to perform. The wireless coverage indication from the transceiver can be a dedicated pin or a solicited or unsolicited status message on a serial interface to the controller. 
     However, it is undesirable to have the transceiver wakeup the controller should it momentarily go out-of-coverage for a short period of time. For example, the controller could wait a programmable amount of time to see if the transceiver goes back into wireless coverage. If the transceiver went back into wireless coverage then the controller could keep the transceiver on and put itself back into a low power mode. If the transceiver did not go back into coverage over this programmable amount of time then the controller could turn off the transceiver and then put itself back into a low power mode. It is anticipated that when the vehicle is turned off there may be times when the transceiver momentarily goes out of wireless coverage. For example, this could be due to momentary interfering signals, poor network coverage, momentary network outages, and momentary interference from obstacles. Therefore, it is preferred that the transceiver  30 ,  130  wait a predetermined time interval before it activates the RI line to wakeup the controller  42 . Similarly, the controller can immediately receive the out-of-coverage indication from the transceiver and then wait the predetermined time interval before acting. This time interval can be dynamically varied to suit conditions. 
     As an example, suppose in a given system that the unit occasionally goes out-of-coverage for twenty to thirty seconds at a time over the course of a day. In this case, the increased current drain during this twenty to thirty second period is acceptable to the system and it would not be required to wake up the controller  42 . Thus, when the vehicle&#39;s ignition is turned off the controller  42  would enable this RI signal on the transceiver and program the transceiver to only activate the RI line when the transceiver has been out of network coverage for a programmable amount of time. In this particular example, it would be programmed for a time period greater than approximately one minute. When the ignition to the vehicle is turned back on and the controller  42  is fully powered on, this out-of-coverage indication on the RI line is no longer needed and the controller  42  could send a command to the transceiver  30 ,  130  to disable the ring indication. 
     In an alternative embodiment, instead of being awakened by the RI, the controller  42  could be awakened by any activity on the serial port from the transceiver  30 ,  130 . In this approach, when the transceiver detects an out-of-coverage condition, or receives an incoming call, or receives an incoming SMS message, then the transceiver would send a message on the serial line to the controller  42 . Activity on the serial line would cause the controller  42  to wakeup. 
     Optionally, out-of-coverage functionality can take into account existing network search algorithms embedded in current transceiver products. As an example, when a wireless transceiver first goes out-of-coverage the transceiver may look for a new network continuously for a few seconds (consuming full power). Then, if a network still is not found, the transceiver may intermittently look for a new network and go to a lower power state between searches. If a suitable network is still not found, the transceiver can search less often and sleep more often over time, thereby saving power by lengthening the intervals between turn-on periods over time. Thus, there are logical breaks in the search algorithm that affect the current drain thresholds. For example, continuously searching equates to a high current drain, periodically searching equates to a medium current drain, and infrequently searching equates to a low current drain. In this example, the transceiver  30 ,  130  could be programmed to provide an indication when changing search periods or changing to a specific search period. 
     Referring to  FIG. 7 , the present invention also includes a method for power control in a client device, such as a Telematics device in a vehicle, having a network access device and a controller. In a first step  102 , the method detects  102  whether the ignition is on or off. In a next step, upon ignition turn-off, the method includes obtaining  104  a discontinuous reception parameter from a network. A next step includes determining  106  time periods for operating the network access device (transceiver) in a powered state based on the obtained discontinuous reception parameter. A next step includes operating  107  the network access device in a powered state during the time period. A next step includes establishing  140  whether wireless coverage exists for the network access device, the network access device being switched to the power-off state  116  if it is established that no wireless coverage exists for the network access device. 
       FIG. 8  shows more detail in regards to the establishing step  140  of  FIG. 7 . In particular, when the establishing step indicates that there is no wireless coverage, this step  140  includes a substep  146  of indicating an out-of-coverage condition to the controller. A next substep can include powering  148  the controller upon the indication of the out-of-coverage condition. Preferably, the establishing step includes waiting  142  a predetermined amount of time to see if the transceiver goes back into wireless coverage. If coverage is not re-established  144 , the controller can be notified. 
     Preferably, the enabling step  105  includes programming the network access device to only indicate an out-of-coverage condition when the network access device has been out-of-coverage for a predetermined amount of time. More preferably, and referring to  FIG. 7 , the method includes the further steps of turning on the ignition  102  of the vehicle, powering  101  the controller, and disabling  103  the indication for out-of-coverage conditions, wherein the method returns to monitoring for ignition turn-off  102 . 
     What has been described is a system and method for controlling the power in a wireless client device. The system and method protects the battery that powers the client device from being excessively drained. This is especially important in Telematics applications and services after the ignition of a vehicle is shut-off. Additionally, the system and method advantageously extends the operational period that Telematics applications and services may be offered after the ignition of the vehicle is shut-off. The above description of the present invention is intended to be exemplary only and is not intended to limit the scope of any patent issuing from this application. The present invention is intended to be limited only by the broad scope of the following claims.