Abstract:
A system and a method for activation of portable and mobile media player devices for wireless LAN services have been disclosed. In one embodiment, the system includes a server computer, a wireless transmitter to transmit a signal, and a portable device comprising a wireless receiver to receive the signal and a wireless transceiver to transition from a first state to a second state to perform content synchronization with the server computer in response to the signal, wherein the wireless transceiver consumes less power in the first state than in the second state. Other embodiments have been claimed and described.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/455,179, filed Mar. 17, 2003, entitled System and Method for Wakeup of Automotive Computer System for Wireless LAN Services; and No. 60/472,253, filed May 20, 2003, entitled System and Method for Wakeup of Automotive Computer System for Wireless LAN Services with Key Fob Actuation. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the field of wireless synchronization of content onto portable and mobile automotive media storage and playback devices.  
         BACKGROUND OF THE INVENTION  
         [0003]    Proliferation of high-speed wireless local area network (WLAN) access points combined with the availability of a wide variety of digital file-based content provides the opportunity for users to receive this content wirelessly at WLAN enabled media playback devices. These devices include portable devices specifically purposed for media playback such as portable MP3 or MPEG video players, Personal Digital Assistants (PDAs), laptop computers, GPS devices, and mobile automotive installed media players. Portable and mobile automotive media playback devices use either flash memory or hard disk drives to store the file-based content, and are battery powered. The file-based digital media available for transfer to portable or mobile automotive players includes for example navigation information (maps and street addresses) to be used in conjunction with GPS receivers, and entertainment content including audio (MP3, .wav, or other formats) and video (MPEG-2, MPEG-4, etc.) files.  
           [0004]    Currently, media playback devices such as those listed above typically receive new content when a user couples and activates such devices to a source of new content, such as a personal computer (PC). For example, the iPod®, provided by Apple Computer, Inc. of Cupertino, Calif., receives new digital audio files via a USB 2.0 connection to a Macintosh or Windows PC. The user may couple the iPod to the computer and activates synchronization using iTunes® media management software. Typically, the user activates the synchronization after they have manually acquired new audio content, either by purchasing the content from an online service or by encoding audio tracks from an audio Compact Disc (CD).  
           [0005]    One convenient system for transferring content to portable or mobile automotive player devices is to attach wireless LAN transceivers to the portable devices and execute synchronization automatically when the portable device is in range of the WLAN and when new content is available at a server coupled to the WLAN for synchronization. It would be convenient, for example, if a PDA could be left in a brief case and synchronization would occur automatically. Or, another convenient mode of operation would be provide the user with the capability to trigger the synchronization from the PC. Further convenience would be realized if a mobile automotive media playback device permanently installed in a car could synchronize wirelessly when in range of the WLAN and when new content is available to be transferred, and likewise when a user triggered the synchronization at the PC. However, current hardware and software designs for portable or mobile automotive media playback devices require the devices to be constantly attached to the WLAN for the above-described automatic or user-triggered synchronization to occur.  
           [0006]    A portable or mobile automotive device that is available on a wireless network for a substantially long period may require a significant portion of the electronics of the portable player device to be functioning. Although there are many digital wireless protocols, the 802.11 (802.11b, g, a) protocols have proliferated in the market and are very low in cost. Devices that use 802.11WLAN transceivers typically use an operating system with a Transmission Control Protocol/Internet Protocol (TCP/IP) software stack, therefore the processor and operating system must be fully functional for the TCP/IP software to function. For example, a mobile automotive device incorporating an ARM7 microprocessor running Linux, and an 802.11b WLAN transceiver uses more than 200 milliamps when active on the network. For battery-powered devices, this amount of energy usage would drain the battery after a short while.  
           [0007]    One solution for maintaining usable battery power in a portable player device would be to place the portable device in a docking/charging station. However, this is inconvenient for the user since they have to remember to place the portable device in the dock. And it would be expensive, if not cost prohibitive, to couple a mobile automotive media player to a constant source of AC power.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The present invention will be understood more filly from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.  
         [0009]    [0009]FIG. 1 is an isometric view of one embodiment of a portable media player device.  
         [0010]    [0010]FIG. 2. shows one embodiment of a system for activation of portable media player devices for wireless LAN services.  
         [0011]    [0011]FIG. 3 shows one embodiment of a system for activation of portable media player devices for wireless LAN services.  
         [0012]    [0012]FIG. 4 shows one embodiment of a portable device.  
         [0013]    [0013]FIG. 5 shows one embodiment of the software components running on an exemplary server computer and an exemplary portable media player device.  
         [0014]    [0014]FIG. 6 shows one embodiment of a content selection graphical user interface.  
         [0015]    [0015]FIG. 7 shows one embodiment of a sync time settings graphical user interface.  
         [0016]    [0016]FIG. 8 is a flow chart of one embodiment of a process to automatically synchronize the content of a portable device with a server computer.  
         [0017]    [0017]FIG. 9 is a graph of the operational duty cycles of an exemplary RF pulse transmitter and RF pulse receiver subsystem.  
         [0018]    [0018]FIG. 10 shows one embodiment of a USB RF pulse transmitter.  
         [0019]    [0019]FIG. 11 shows one embodiment of a mobile automotive media playback device.  
         [0020]    [0020]FIG. 12 shows one embodiment of a mobile automotive media playback device in an exemplary automobile.  
         [0021]    [0021]FIG. 13 shows one embodiment of a key fob.  
     
    
     DETAILED DESCRIPTION  
       [0022]    A system and method for activation of portable and mobile media player devices for wireless LAN services is described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the present invention.  
         [0023]    In one embodiment, digital content synchronization of a portable or mobile automotive media playback device with a server computer is enabled automatically based on the availability of content, user specified synchronization times, or under the direct control of a user either at a server computer or when the user is within a predetermined signal range of the server computer and the portable or mobile automotive media playback device, without having the portable or mobile automotive media playback device to have communication established with a TCP/IP protocol network substantially constantly.  
         [0024]    In one embodiment, automatic synchronization of content is provided to a portable device when new content is present at a server computer and the portable device is in range. Furthermore, the portable device may not have to be placed in a docking station in order to have the content synchronized with the server computer. In one embodiment, synchronization of a new content is performed automatically when the device is brought within a predetermined range of the server computer. A user may activate synchronization while the user is at the server computer. Alternatively, the user may activate synchronization using a key fob activator when the user and portable device are within a predetermined RF range of the server computer. In one embodiment, synchronization of the portable device in an automobile and the server computer is activated while conserving portable device or automobile battery power.  
         [0025]    Some portions of the detailed descriptions which follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the tools used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.  
         [0026]    It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.  
         [0027]    The present invention also relates to apparatus for performing the operations described herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus.  
         [0028]    The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the processes. The required structure for a variety of these systems will appear from the description below. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein.  
         [0029]    A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (“ROM”); random access memory (“RAM”); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc.  
         [0030]    Overview  
         [0031]    In one embodiment, a portable automotive media player device, which may also be referred to as a mobile device, periodically receives and stores content files and a content database from a server computer. The main computer subsystem in the portable device may be powered down or be put into a low power state. The portable device may further include a separate low power RF pulse receiver subsystem. This RF pulse receiver subsystem may be powered and ready to receive a pulse from an RF pulse transmitter independent of the main computer subsystem. In one embodiment, the RF pulse transmitter is functionally coupled to the server computer and/or included in a fob carried by a user. RF pulse as described in this disclosure is defined as a modulated radio-frequency data packet transmission including a device address, command, and error detection information. A system control software application running on a server computer automatically, or under the control of the user, may acquire new digital content from various sources, such as, for example, Internet servers.  
         [0032]    In one embodiment, when new content has been acquired and is available at a server computer, the system control application triggers an RF pulse encoded for a predetermined portable device. If the portable device is within a predetermined range of the RF pulse, the RF pulse activates an RF pulse receiver circuit in the portable device, causing the portable device to power up and establish communication with the wireless network. The main computer system in the portable device may execute software instructions for content file transfers via the wireless network from the server computer. After the file transfer is complete, the main computer subsystem may be powered down until the next valid RF pulse transmission.  
         [0033]    In another embodiment, the user may trigger an RF pulse using the RF pulse generator in a key fob when the user is within a predetermined RF range of the portable device. In response to the RF pulse, the portable device may power up, establish communication with the wireless network, and transfer content via the network from the server computer if the portable device is within the predetermined range of the server computer. Thus content may be transferred automatically, periodically, and/or under the direct control of the user.  
         [0034]    Description of Hardware  
         [0035]    [0035]FIG. 1 shows a portable media storage and playback device  10  that includes a touch sensitive liquid crystal display (LCD)  16 , a stylus  20 , and function buttons  24  for interacting with a user interface that controls an operating system and software applications. FIG. 2 is a system diagram that shows a server computer  30  that is a personal computer that includes a hard disk drive  40  for storing content files  44  in one embodiment. A server computer  30  may be coupled to the Internet  18  via a broadband  42  Internet connection. Functionally coupled to server computer  30  is an RF pulse transmitter  14  that can activate a variety of devices for establishing communication with a wireless network, such as the portable device  10   a  and  10   b , and the mobile device  26 . In one embodiment, the RF pulse transmitter  14  includes a USB port. In other embodiments, the server computer  30  can be a set-top box or a dedicated home media server, each with a broadband Internet connection  42 . FIG. 3 is a system diagram showing that the server computer  30  is functionally coupled to a wireless LAN transceiver  34  to transfer digital content  44  to a variety of devices. A wired network, such as Ethernet, may couple the server  30  to a stationary device  22  for content  44  transfer if this physical layer is available. FIG. 2 and FIG. 3 show that the system may activate multiple portable media player devices. For example, the system may support multiple portable media storage and playback devices  10   a  and  10   b  and automobile-installed (mobile) media storage and playback devices  26 . A unique RF pulse code may be provided for each of the multiple portable and mobile devices.  
         [0036]    [0036]FIG. 4 shows a hardware block diagram of one embodiment of a portable device  10  that includes a main computer subsystem  46 , a low power RF pulse receiver computer subsystem  50 , and a power supply subsystem  54  that includes a voltage regulator  80  and a battery  84 . Main computer subsystem  46  includes a 1.8 inch hard disk drive  76 , a microprocessor  52 , a DRAM system memory  68 , a flash memory  64 , a digital-to-analog converter (DAC)  72 , and a wireless local area network (LAN) transceiver  58 . The microprocessor  52  may include a UART. The main computer system  46  may decode compressed audio files, such as MP3 files. In another embodiment, the portable device  10  may include one or more NAND flash memories as the mass memory storage medium. The WLAN transceiver  58  includes an 802.11b compliant transceiver. In other embodiments, the WLAN transceivers  58  operates according to alternative transmission formats, such as 802.11 g or 802.11a. In one embodiment, the microprocessor  52  includes an EP7312 ARM microprocessor manufactured by Cirrus Logic of Austin, Tex. In an alternative embodiment, the main computer subsystem  46  includes a microprocessor and/or a digital signal processing (DSP) functional unit to decode a variety of content file formats, such as audio files (MP3, WMA, .wav), digital image files (JPEG, TIFF, etc.), and video files (MPEG-2, MPEG-4, WMV, etc.).  
         [0037]    In one embodiment, the low power RF pulse receiver computer subsystem  50  includes a microcontroller  48  coupled to microprocessor  52  via a communication link  28  so that control signals may be sent between the microcontroller  48  and the microprocessor  52 . The microcontroller  48  may include a microprocessor with an UART, a system memory, a number of programmable input/output ports, and an EPROM memory. In one embodiment, the aforementioned components reside on a single die. An RF pulse receiver circuit  56  is coupled to microcontroller  48  port. RF pulse receiver circuit includes the rfRXD0420 ASK receiver component, provided by Microchip of Chandler, Ariz. The communication link  28  may functionally couple the microcontroller  48  UART to the microprocessor  52  UART. In one embodiment, the communication link  28  uses RS-485 protocol. The programmable input/output port on the microcontroller  48  may be functionally coupled to the power supply subsystem  54  via a power enable link  92 .  
         [0038]    The microcontroller  48  may include a low cost PIC device, such as the PIC device made by Microchip Technology Inc., of Chandler, Ariz., which supports a low power mode. In one embodiment, the microcontroller  48  is programmed to power up at regular intervals to receive an RF pulse signal from the RF pulse receiver circuit  56  if an RF pulse transmission is sent from the RF pulse transmitter  14 . The microcontroller  48  may also be functionally coupled to the power supply sub-system  54  to activate the microprocessor  52  by enabling power to the microprocessor  52  and/or related components.  
         [0039]    An RF pulse receiver antenna  60 , operable to receive RF pulses from the RF pulse transmitter  14  may be coupled to the RF pulse receiver circuit  56 . The WLAN transceiver  58  may also include an antenna  88  used for 2.4 Ghz RF transmissions.  
         [0040]    Referring to FIG. 2, the RF pulse transmitter  14  is coupled to the server computer  30  via a USB port  36 . The RF pulse communications components, such as the components included in the RF pulse receiver  56  and the RF pulse transmitter  14 , may be commonly found in remote keyless entry systems, such as car alarm systems. Transmitter devices such as these may be legally permitted to broadcast for brief periods of time under Federal Communication Commission (FCC) Part  15  regulations.  
         [0041]    Description of Software—System Control Application  
         [0042]    Referring now to FIG. 5, a diagram shows software functions at server computer  30  and portable device  10 . In one embodiment, system control application  38  includes a software application running on server computer  30 . The system control application may include a number of sub-applications. The streaming service  100  provides communication, discovery, control logic, and streams via HTTP protocol to devices capable of receiving and decoding the associated digital media file streams, such as MP3 streams. Receiving and decoding streams is a service that is used by stationary device  22  and portable device  10  when portable device  10  is within range of the WLAN. The sync service application  96  may include communication, device discovery, scheduling of synchronization events, synchronization control, and logic for the transfer of digital media files  44  and other files via ftp to devices  10  and devices  26  with mass storage.  
         [0043]    The content database  32  is a relational database that relates a variety of parameters (database columns) pertaining to digital media files  44  stored on the server  30 , the hard disk drive  40 , or addresses to streams or downloadable files  12  on the Internet  18  servers.  
         [0044]    The content acquisition application  112  automatically acquires content  12  from the Internet  18  servers based on various parameters, such as user selection, availability of an item, and content refreshment policies specific to each content  12  item or content  12  service. Referring now to FIG. 6, a content selection graphical user interface  56  is shown. A user may select a content item  168  of interest from the content items list  172  and drag the content item  168  over to the content selection list  164 . Each content item  168  may be a graphical representation of a pointer to an audio file  12  on the Internet  18  server that is periodically updated. The update period policy value, a 24-hour time value, is provided by the content  12  provider. This policy value is stored in the content database  32  and is associated with the content item  168 . Other data related to the update function may be stored in the content database  32 , including the time and date of the last download, and the time and date that the content  44  was last synchronized with a specific device. For example, a news file  12  on Internet  18  server may be updated on an hourly basis. The content acquisition application  112  may manage the intelligent acquisition and caching of the Internet  18  content  12  for transference and/or synchronization with the viable portable  10  and the mobile player devices  26 .  
         [0045]    In one embodiment, the Internet time source application  116  is a service that acquires the latest correct time from the Internet  18  server to determine if the content  12  may be acquired from the Internet  18  server and to insure that the server computer  30  internal clock is accurate. For example, the Internet-based time source, such as the Network Time Protocol RFC-1305 (http://boulder.nist.gov/timefreq/service/its.htm), can be used as an accurate time source for the time-server service.  
         [0046]    In one embodiment, the graphical user interface (GUI) module  120  is the presentation layer application shown in FIG. 6 and FIG. 7. The GUI module  120  may functionally communicate with the set of functions contained in the system control application  38  to supply user inputs to the functions, to present system status and settings to the user, and to interact with and to modify the contents of the content database  32 . For example, graphical user interface module  120  may include media management functions, such as the ability to make and edit playlists.  
         [0047]    In one embodiment, the server computer  30  makes use of WLAN transceiver drivers  104  for delivering content to the portable device  10 . The system control application  38  uses RF pulse transmitter USB driver  108  to activate the USB RF pulse transmitter  14  with the RF pulse code that corresponds to the portable device  10  or the mobile device  26  to which the content  44  is to be synchronized. The system control application  38  may include a listing that associates a unique RF pulse code for each portable device  10  or mobile device  26  that is allowed to receive the content  44  from the server computer  30 .  
         [0048]    Description of Software—Portable Device  
         [0049]    In one embodiment, the portable device  10  includes a Linux operating system  124 , which may be stored in flash memory  64 , loaded into the DRAM system memory  68 , and executed on the microprocessor  52 , when the portable device  10  is powered on. FIG. 5 shows the software and/or firmware associated with the portable device  10 .  
         [0050]    The sync client application  128  may manage the discovery of and communication with the server  30 , file transfer utilizing file transfer protocol from the server  30 , and interface with the microcontroller  48  communication service  132 . During synchronization, the content files  44  may be transferred from the server  30  to portable device  10 . Microcontroller communication  132  includes the software service executing on the microprocessor  52  that handles communication with the microcontroller  48  via the RS-485 communication link  28 .  
         [0051]    In one embodiment, the playback control application  136  includes a set of software functions that enable the user control of the content files  44  stored on the hard disk drive  76 , and the associated compression and decompression operations. The playback control  136  may include presentation layer elements as well as control logic.  
         [0052]    In one embodiment, the sync budget manager  140  includes a set of software functions that determine the length of time that portable device  10  will execute content  44  synchronization with the server computer  30 . Based on the length of time, the sync budget manager  140  may determine the amount of power from the battery  54  that portable device  10  may expend on synchronization. The sync budget manager  140  may operate based on one or more parameters, such as the amount of recharge time.  
         [0053]    The microprocessor communication  148  function may handle communication between the microprocessor  52  and the microcontroller  48  over the RS-485 bus communication link  28 . The microprocessor communication  148  may send a synchronization message to the microprocessor  52  when the RF pulse receiver subsystem  50  has been activated in response to an RF pulse from the server computer  30 .  
         [0054]    In one embodiment, the RF pulse receiver  152  software runs on the microcontroller  48  and monitors the output of the RF pulse receiver circuit  56 . One embodiment of the RF pulse receiver  152  software is described in greater detail below.  
         [0055]    The power subsystem control  156  may enable and/or disable the power supply subsystem  54  via the power enable link  92 .  
         [0056]    Description of Operation  
         [0057]    In one embodiment, the main computer subsystem  46  in the portable device  10  powered down for the majority of the time. But the main computer subsystem  46  may be activated by the RF pulse receiver computer sub-system  50  to synchronize with the server  30 . A scheduling function is an aspect of one embodiment of the sync server application  96 . The sync server application  96  may activate the RF pulse transmitter  14 , at a predetermined time designated by the user, for powering up the main computer sub-system  46  to synchronize content and data  44 . The system control application  38  may include a user interface for setting a number of predetermined synchronization times.  
         [0058]    [0058]FIG. 7 shows one embodiment of the sync settings graphical user interface (GUI)  62  of the system control application  38  running on the server computer  30 . The sync settings graphical user interface  62  may include three synchronization time input fields and sync time setting fields  176   a, b , and c. The sync server application  96  may send the time values entered in the sync time setting fields  176   a, b , and c to a timer application, such as Windows OS timer service. Windows OS timer service may send a message to the sync server application  96  when the system time equals one of the sync time settings in the fields  176   a, b , or c. When the sync server application  96  receives the response from Windows OS timer service, the sync server application  96  activates the RF pulse transmitter  14  to send an encoded message onto the airwaves. If the RF pulse receiver circuit  56  receives the encoded message, the encoded message may be interpreted by the RF pulse receiver firmware  152  on the microcontroller  48 . The sync settings graphical user interface  62  may include a manual activation button  180  for the user to activate an immediate synchronization using the same process described herein. When the manual activation button  180  is selected, sync server application  96  causes the RF pulse transmitter  14  to send an RF pulse to a corresponding portable device  10  or mobile device  26  according to an RF pulse code. In one embodiment, the RF pulse code is encrypted by the RF pulse transmitter driver  108 , and decrypted by the RF pulse receiver subsystem  50 . The encryption and decryption may use public key/private key encryption technology.  
         [0059]    [0059]FIG. 8 is a flow chart showing one embodiment of a process by which the RF pulse triggered synchronization occurs. The microcontroller  48  may be programmed to continuously cycle between a full power mode and a low power mode. In one embodiment, the microcontroller  48  enters full power mode (processing block  184 ). Microcontroller  48  and related components (e.g., power supply  54 ) may use approximately 15 mA of power. In state  196  low power mode, microcontroller  48  and related sub-system components may use approximately 10 μA of power.  
         [0060]    [0060]FIG. 9 is a graph of a duty cycle that shows that microcontroller  48  is in full power mode 5% of the time. This duty cycle provides for low total power usage by portable device  10  when portable device  10  is not being operated. In low power mode, microcontroller  48  is simply counting time and monitoring other inputs, until it changes to full power mode.  
         [0061]    Referring again to FIG. 8, while in full power mode, the microcontroller  48  waits to receive an RF pulse message on a port that is coupled to the RF pulse receiver circuit  56 , shown in FIG. 4 (the processing block  188 ). When the system control application  38  receives a message from Windows OS timer service, the system control application  38  activates RF pulse transmitter  14  by sending an activation message to the RF pulse transmitter PC driver  108 , which activates the RF pulse transmitter  14  hardware.  
         [0062]    When RF pulse transmission is received, the microcontroller  48  enables the power supply subsystem  54  to provide power to the microprocessor  52  and the main computer subsystem  46  (processing block  192 ). After microprocessor  52  is booted, the microcontroller  48  may send a message via the communication link  28  to the microprocessor  52  (processing block  204 ) instructing the microprocessor  52  to activate the wireless LAN transceiver  58  and to establish communication with the system control application  38  on the server computer  30  to synchronize content and data  44  (processing block  208 ). The portable device  10  synchronizes content with the system control application  38  (processing block  210 ). After synchronization is complete, the microprocessor  52  may send a message to the microcontroller  48  (processing block  216 ) informing the microcontroller  48  that the microprocessor  52  and the main computer subsystem  46  is powering down (processing block  220 ). The microcontroller  48  then enters low power mode (processing block  196 ) and waits for 950 milliseconds (processing block  200 ) before resuming the power mode cycle. If an RF pulse is transmitted by the server computer  30  and there is no response from portable device  10  after a predetermined time interval (for example, after 2 minutes), the RF pulse is transmitted again until the corresponding portable device  10  or mobile device  26  responds and synchronization of content  44  is executed. In one embodiment, the RF pulse is transmitted every 5 minutes until there is a response.  
         [0063]    [0063]FIG. 10 shows a block diagram of one embodiment of the RF pulse transmitter  14 . In one embodiment, the RF pulse transmitter  14  is a USB device that includes an 8-bit RF pulse microcontroller  224 , such as the RFPIC12C509AG microcontroller, manufactured by Microchip Technology, Inc. of Chandler, Ariz., and includes an RF transmitter functional unit. A USB device transceiver chip  228  may be functionally coupled to the RF pulse microcontroller  224  to enable the device to be coupled to the USB port of the server computer  30  and to provide power to the RF pulse transmitter  14 . The RF pulse microcontroller  224  may also include an antenna  232 .  
         [0064]    Referring again to FIG. 9, the timing of the microcontroller  48  low power/full power duty cycle is approximately 5%, that is, the microcontroller  48  is powered up and able to receive the RF pulse transmission for approximately 50 ms out of every one second. FIG. 9 also shows that the system control application  38  may repeatedly activate the RF pulse transmitter  14  for a total of about 1.5 seconds. During this time, the encoded message carried by the RF pulse may be repeated approximately 100 times and therefore, the length of the actual encoded message is approximately 15 milliseconds. Since, the encoded activation message is repeated over a substantially longer period than the inactive (low power) period of the microcontroller  48 , the microcontroller  48  may become active to receive the encoded message during some part of the RF pulse activation message interval.  
         [0065]    Alternative Embodiment—Wide Area Network  
         [0066]    In another embodiment, the RF pulse transmission system can be implemented using a Wide Area Network pager system. A pager network receiver may be coupled to the microcontroller  48 , in place of, or in addition to, the RF pulse receiver circuit  56 . The system control application  38  on the server  30  includes a link to the Internet  18 . The system control application  38  may send an XML message using HTTP to a server on the Internet. The server may re-package the message for broadcasting on the pager network. To trigger synchronization, a pager message with the specific pager serial number of the associated pager receiver in the portable device  10  is sent and the message is broadcast. The pager receiver in the car receives the message and activation of the microprocessor  52  follows as described herein. The Wide Area Network approach can also be implemented using the mobile cellular phone network. A mobile cellular phone transceiver integral to the automobile includes an input into the microcontroller  48  for triggering a low power subsystem, which in turn activates the main computer subsystem  46 .  
         [0067]    In another embodiment, the automobile includes a GPS system that provides location information via the mobile cellular connection to the server computer. This information is used to determine if content synchronization is possible, i.e., whether the mobile automotive media player device is within range of a viable WLAN.  
         [0068]    Alternative Embodiment—Microprocessor with Low Power Mode  
         [0069]    In another embodiment, the portable device includes a microprocessor operable at a clock speed lower than a standard operating clock speed (required for media decoding) to conserver power. The microprocessor may shut down various subsystems, such as the USB port, the internal registers, and/or other input/output subsystems. In one embodiment, the internal registers that receive the activation signal from the RF pulse receiver circuit are active. The portable device may not include a micocontroller.  
         [0070]    Alternative Embodiment—Mobile Automotive Application  
         [0071]    Referring now to FIG. 11 and FIG. 12, one embodiment of a mobile automotive playback device  26  that can be installed in an automobile is shown. A processor module  74  includes the main computer subsystem  90  and a low power RF pulse receiver subsystem  94 , as well as a removable hard disk drive cartridge  78  on which the content  44  is stored. A user interface controller  50  is coupled to processor module  74  via a 485-bus communication link  284  and includes a backlit liquid-crystal display  52  and a plurality of buttons  240  that allow the user to control playback. In one embodiment, placement of the mobile playback device  26  into an automobile is schematically similar to systems incorporating multi-CD changers that are typically located in the trunk. Processor module  74  may be located in the trunk or underneath a seat, and controller  70  should be located in a DIN-shaped slot or may be surface mounted within the reach of the driver or passengers. FIG. 12 shows that power supply subsystem  98  is coupled to the car battery so that power is supplied to mobile automotive media player device  26  when the car ignition is turned off.  
         [0072]    [0072]FIG. 2 shows one embodiment of the mobile automotive media player  26  operable to receive content  44  from the server computer  30  as shown in the preferred embodiment. In one embodiment, the mobile automotive media player  26  is integrated into an automobile with an existing conventional car stereo.  
         [0073]    Referring now to FIG. 12, the processor module  74  includes a microprocessor  248 , flash memory  252 , dynamic random access memory (DRAM)  256 , a power supply sub-system  98 , a digital-to-analog converter (DAC)  260 , a USB host controller  292 , and a 20 gigabyte hard disk drive cartridge  78 . A USB 802.11b wireless LAN transceiver  82  is coupled to processor module  74  via a USB port.  
         [0074]    In one embodiment, the output of DAC  260  is plugged into line level inputs  288  in the existing car stereo system head unit. The DAC  260  may convert decompressed digital audio to an analog signal at line levels. In one embodiment, the existing car stereo system provides the ability to switch to an auxiliary source. In another embodiment, the analog audio signal that is output from processor module  74  is input into the automobile audio system by being plugged into an FM antenna tap. The analog output from DAC  260  is modulated by an FM modulator. This type of connection into existing car stereos may be found in after-market CD changer installations.  
         [0075]    Alternative Embodiment—Integrated Head Unit  
         [0076]    In an alternative embodiment, the control interface is integrated into the head unit, which may be installed in the automobile at a factory. The processor module  74  is installed in a different location, such as underneath a seat or in the trunk.  
         [0077]    In another embodiment, the processor module  74  includes the main computer subsystem  90 . The factory head unit enclosure includes the low power RF pulse receiver subsystem  94 , which is located in the dash. In one embodiment, the factory head unit includes a Compact Flash slot into which a Compact Flash wireless LAN card may be inserted to provide wireless access. In another embodiment, the wireless LAN transceiver may be located elsewhere, such as in the headliner of the car, and may be functionally coupled to the main computer subsystem via a USB port.  
         [0078]    The mass storage memory for mobile automotive media player may include flash memories. In one embodiment, all the flash memories are non-removable. Alternatively, some of the flash memories are removable. Alternatively, all partially removable, or totally removable.  
         [0079]    In an alternative embodiment, a mobile automotive media player is provided that can support transfer and presentation of video content such as MPEG-2 or MPEG-4 video files. The video content may be downloaded to the mobile automobile media player where the video content maybe decoded and displayed. In one embodiment, the mobile automobile media player includes a high-resolution graphics LCD. Furthermore, the user can receive information, such as driving directions, maps, or movies, using the mobile automobile media player.  
         [0080]    Alternative Embodiment—RF Wakeup Subsystem in Key Fob  
         [0081]    In some embodiments, the RF communication subsystem described above may be triggered by an RF pulse from a key fob. The key fob may include electronic circuitries and a power supply (e.g., a battery). Furthermore, the key fobs may be used with car alarms or keyless entry systems. FIG. 13 shows one embodiment of an RF pulse key fob  86  with an RF pulse transmitter. The key fob  86  may include a emergency mode button  308 , a lock/unlock button  312 , and a trunk open button  316 . The key fob  86  may further include a button  320  for triggering wireless synchronization  320 . In one embodiment, the RF pulse transmitter produces an RF pulse that includes the RF pulse message. When the RF pulse receiver subsystem  94  receives the pulse, synchronization may be triggered as described above. Alternatively, the RF pulse transmitter may be implemented in a car alarm remote/keyless remote entry control housing that does not include a car key.