Abstract:
An accessory module for a user terminal is disclosed that utilizes information broadcast from the GPS system to determine the user terminal&#39;s position on the earth. An improved electrical interface between the GPS accessory module and the user terminal is utilized that takes advantage of pre-existing electrical interfaces within the user terminal. The accessory module also includes a method and apparatus for managing its power consumption. A set of mechanical interfaces among the components of the GPS accessory module are disclosed for minimizing electrical path lengths, noise and crosstalk in the accessory module, and for providing for mechanical mounting of the components. A mechanical interface between the user terminal and the accessory module is also disclosed for coupling to an existing user terminal in place of that user terminal&#39;s removable battery pack. The invention further includes a method and apparatus for improving the accessory module&#39;s accuracy by providing position assistance data from a position reference server. The assistance data is provided to the accessory module by way of a transmission channel communication between the user terminal and the position reference server.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to radiotelephones or user terminals and, in particular, to an accessory module for providing location information for use by a radiotelephone or user terminal. 
     BACKGROUND OF THE INVENTION 
     The use of position information that is widely broadcast, for example, the Global Positioning System (GPS), for obtaining location data, i.e., a terrestrial position fix including latitude, longitude, and possibly elevation, is widespread and well known. Time may also be calculated from GPS data. It has been proposed that user terminals or wireless stations in modern wireless telecommunications systems include a capability to receive GPS information and to thereby calculate their position on the surface of the Earth. 
     It is known to include GPS functions in a battery power module for a cellular telephone. Reference in this regard can be had, by example, to U.S. Pat. No. 5,786,789, issued Jul. 28, 1998, entitled “GPS and Cellphone Unit Having Add-On Modules”, by J. Janky. In Janky, the electrical interface between the add-on module and the cell phone is implemented by UARTS communicating over two, unidirectional, serial lines. The electrical interface also utilizes the cell phone transmitter and receiver for transmitting GPS data from the add-on module to the cell phone. This electrical interface is not optimum for user terminals that are not adapted to receive information in these ways. A user terminal that does not have the requisite UARTS or serial lines available, or that does not have the capability to recognize information conveyed between UARTS, will not be capable of such communication. Also, user terminals that are not adapted to receive GPS data through their transmitter and receiver may not be able to operate with the GPS module disclosed in Jansky. 
     An accessory module that uses the same battery as the user terminal will consume power, and will thus negatively impact the talk and standby time of the user terminal. It is important that such an accessory module consume as little power as possible while performing its intended function(s), as well as when it is not performing its intended function(s). 
     The GPS system transmits two microwave carrier signals, a 1575.42 MHz carrier and a 1227.60 MHz carrier. These signals as received are attenuated (approximately −130 db). The mechanical placement of the accessory module components in relationship to each other is thus important in order to minimize signal length and to receive and amplify these signals, without introducing noise or crosstalk. The mechanical placement of the accessory module components is also important in that the accessory module should easily attach to the user terminal, and should also attach without interfering with the use of the terminal or with other accessories that may be attached. 
     For user terminals equipped with a GPS accessory module, a problem arises when the user terminal is out of view of the GPS satellite constellation. A server may be provided on the wireless network to receive position data from the user terminal, and based on additional information available, provide additional data to the user terminal for position determination. Reference in this regard can be had, by example, to allowed commonly assigned U.S. patent application Ser. No.: 09/547,089, filed Apr. 12, 2000, entitled “GPS Assistance Data Delivery Method and System”, by K. Pihl and H. Pirila. The disclosure of this patent application is incorporated by reference herein in its entirety insofar as it does not conflict with the teachings of the present invention. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     It is an object and advantage of this invention to provide an improved accessory module for a user terminal that utilizes information broadcast from the GPS system to determine the user terminal&#39;s position on the earth. 
     It is a further object and advantage of this invention to provide an improved electrical interface between the GPS accessory module and the user terminal. 
     It is a further object and advantage of this invention to provide a power management capability in the accessory module to reduce power consumption. 
     It is a further object and advantage of this invention to provide a mechanical interface between the components of the GPS accessory module, and also between the GPS accessory module and the user terminal. 
     It is another object and advantage of this invention to improve the accuracy of a GPS determined location by supplying additional data to a GPS accessory module from a position reference server on the wireless network that is accessible by the accessory module through the user terminal. 
     SUMMARY OF THE INVENTION 
     The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention. 
     A GPS accessory module for a user terminal is disclosed which includes an antenna for receiving GPS signals, circuitry for calculating location data from the GPS signals, and a communication unit. The communication unit is bi-directionally coupled to the calculating circuitry and manages communication between the circuitry and the user terminal. The communication unit includes an in-band modem for converting the calculated location data to a signal having a range of frequencies suitable for digitizing by a voice coder of the user terminal. 
     An energy management unit for the GPS accessory module is disclosed for controlling the power consumption of the module circuitry in response to information received from the user terminal. 
     A position reference unit in communication with said accessory is disclosed. The position reference unit includes circuitry for exchanging data with the communication unit and a position assistance task for providing assistance data to the said communication server. The position assistance data is used by the calculation circuitry for improving the calculation of the location data. The communication unit is further disclosed as including circuitry for initiating communication between the communication unit and the position reference unit through a wireless transmission channel. 
     The in-band modem of the communications unit is further disclosed as including circuitry for conveying a signal to the voice coder of the user terminal by an audio input signal and for receiving and demodulating another signal from an audio output of a voice decoder of the user terminal. 
     The GPS accessory module is further disclosed as including a connector coupled to a battery. The connector includes a power bus to convey power to both the accessory module and the user terminal, a signal for identifying the accessory module to the user terminal, and a signal which operates in two modes: as an input to the accessory module to cause a power up condition; and as an output to indicate battery temperature. 
     The GPS accessory is also disclosed as including a system connector which includes at least one digital data bus to convey control signals between the terminal and the accessory, and an analog signal bus to convey location data to the user terminal from the calculation circuitry. Both the battery connector and the system connector take advantage of pre-existing electrical interfaces within the user terminal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawings, wherein: 
     FIG. 1 is a block diagram of a wireless communications system utilizing the functions and embodiments disclosed herein. 
     FIG. 2 is an elevational view of a user terminal and further illustrates a wireless communication system and a service provider to which the user terminal is bi-directionally coupled through wireless RF links; 
     FIG. 3 is a block diagram of a user terminal that is suitable for practicing this invention. 
     FIG. 4 shows a block diagram of a GPS accessory module and its electrical connections to a user terminal 
     FIG. 5 is a block diagram of the preferred embodiment of the GPS accessory module. 
     FIG. 6 is an exploded view of a preferred embodiment of a GPS accessory module in accordance with the teachings of this invention. 
     FIG. 7 is a block diagram of a position reference server that is part of a wireless communication system to which a user terminal is bidirectionally coupled. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a system in accordance with the teachings of this invention. A user terminal  10  equipped with a GPS accessory module  15  receives position information from at least one satellite  20  which may be part of a GPS satellite constellation  25 . The user terminal communicates with a computing device  30  through a link  35 . The user terminal  10  further communicates with at least one base station  40 . The base station  40  provides the user terminal  10  with communication access to other user terminals  45 , and provides communication with at least one network  50 . The network  50  may include wireless networks, wired networks, and any other network available for providing communication with the user terminal  10 , including the PSTN. Through the network  50  the base station further provides the user terminal  10  with access to a position reference server  55 . The position reference server  55  receives position information from the user terminal  10  and utilizes that information to return further position data, referred to as position assistance data, to the user terminal  10 . 
     The satellites  20  and the satellite constellation are preferably part of what is generally known as the Global Positioning System or GPS. 
     Reference is made to FIGS. 2 and 3 for illustrating the user terminal  10  that is suitable for practicing this invention. The user terminal  10  may be, but is not limited to, a cellular telephone or a personal communicator. It should be understood that the user terminal  10  can be a vehicle mounted or a handheld device. 
     The user terminal  10  includes an antenna  112  for transmitting signals to and for receiving signals from the base station  40 . The base station  40  can be a part of a cellular network comprising a Base Station/Mobile Switching Center/Interworking function (BMI)  132  that includes a mobile switching center (MSC)  134 . The MSC  134  provides a connection to landline trunks when the user terminal  10  is involved in a call. Other wireless network facilities such as a Short Message Service Center (SMSC)  136  could also be provided. 
     The user terminal  10  includes a modulator (MOD)  114 A, a transmitter  114 , a receiver  116 , a demodulator (DEMOD)  116 A, and a controller  118  that provides signals to and receives signals from the transmitter  114  and receiver  116 , respectively. These signals include signaling information in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data. The particular type of air interface standard is not important to the operation of this invention, as the teachings of this invention apply generally to communications systems, including digital time division/multiple access (TDMA) systems (e.g., GSM, PDC) and code division/multiple access (CDMA) systems, as well as FDM systems such as frequency modulated (FM) systems (e.g., AMPS). 
     The controller  118  may include, or implement, a vocoder  130  for speech coding and decoding. It is understood that the controller  118  also includes other circuitry required for implementing the audio (speech path) and logic functions of the user terminal. By example, the controller  118  may be comprised of a digital signal processor device, a microprocessor device, and various analog to digital converters, digital to analog converters, and other support circuits. The control and signal processing functions of the user terminal are allocated between these devices according to their respective capabilities. 
     Access to the controller  118  and its functions maybe had through two bi-directional ports  140 ,  145 . Port  140  is hereinafter referred to as the MBUS. The MBUS  140  is a half-duplex, bi-directional, serial bus that provides communication among the functions of the controller  118 . The MBUS also provides communications between the functions of the user terminal  10  and accessories that may be a part of the user terminal  10 . The MBUS  140  is a multi-point or multi-drop bus, i.e., many functions can be connected to the MBUS  140  simultaneously. The MBUS is a USART (Universal Synchronous/Asynchronous Receiver Transmitter) type bus and thus provides both synchronous and asynchronous communications. A message server  135  in the controller  118  routes communications over the MBUS to their destinations. 
     Port  145  is hereinafter referred to as the FBUS and, in this embodiment, provides communication between the user terminal  10  and the external computing device  30 . The FBUS  145  is a full duplex, UART (Universal Asynchronous Receiver Transmitter) type bus. The FBUS comprises two signal lines, FBUS_Tx,  147  and FBUS_Rx  149 . 
     A user interface includes a conventional earphone or speaker  117  and an audio output  132  for driving an external speaker, or for providing audio output to accessories. The user interface further includes a conventional microphone  119  and an audio input  134  for receiving audio from an external microphone, or from accessories. In the case where the controller  118  includes the vocoder  130 , the audio output  132  is preferably an output of the voice decoder  137  of the vocoder  130 , and the audio input  134  is preferably an input to the voice coder  138  of the vocoder  130 . 
     The user interface also includes a display  120 , and a user input device, typically a keypad  122 , all of which are coupled to the controller  118 . The keypad  122  includes the conventional numeric ( 0 - 9 ) and related keys (#,*)  122   a,  and other keys  122   a  used for operating the user terminal  10 . These other keys  122   b  may include, by example, a SEND key, various menu scrolling and soft keys, and a PWR key. 
     The user terminal  10  also includes a battery enclosure  126 , which is preferably removable, for powering the various circuits that are required to operate the user terminal. The battery enclosure  126  preferably contains the GPS accessory module  15 . 
     The user terminal  10  also includes various memories, shown collectively as the memory  124 , wherein are stored a plurality of constants and variables that are used by the controller  118  during the operation of the user terminal. For example, the memory  124  stores the values of wireless system parameters and the number assignment module (NAM). An operating program for controlling the operation of controller  118  is also stored in the memory  124  (typically in a ROM device). The operating program in the memory  124  includes routines to present messages and message-related functions to the user on the display  120 , typically as various menu items. The memory  124  may also include a memory  124 B (FIG.  3 ), which could be a portion of memory  124 , for containing a program that includes routines for implementing the method disclosed herein. The program can provide menus to the user, and based on the user&#39;s menu selections, operates to provide user terminal position or location information. 
     One of the objects of this invention is to provide an improved electrical interface between the GPS accessory module and the user terminal  10 . In the presently preferred embodiment this is attained by providing communication between the GPS accessory module  15  and the user terminal  10  over the bi-directional MBUS  140 . As stated above, the GPS accessory module  15  receives position information from the satellite  20 . The user terminal  10  may utilize this information locally, or it may transmit it to the optionally connected computing device  30  by way of the FBUS  145 . The user terminal  10  may also transmit the position information externally to the position reference server  55  by way of a wireless communication. The user terminal  10  may further operate to receive position assistance data from the position reference server  55  and provide that data to the GPS accessory module  15 . The user terminal  10  may further operate to issue energy management commands to the GPS accessory module  15  in order to conserve power and extend operating time. 
     FIG. 4 shows a block diagram of the GPS accessory module and its electrical connections to the user terminal  10 . GPS information from the satellites  20  (FIG. 1) is received by antenna  290  and conveyed to low noise amplifier circuit  300 . The output of low noise amplifier circuit  300  is coupled to a main printed circuit board  235  which contains the circuitry for implementing the position determining functions and logic functions of the GPS accessory module  15 . A flexible circuit board, referred to as a battery flex  210 , is used to transfer power from a battery  200  to the circuitry in the GPS accessory module  15 , as well as to the user terminal  10 . An additional flexible circuit board, referred to as a system flex  240 , conducts control signals and information between the user terminal  10  and the main printed circuit board  235 . 
     FIG. 5 shows a block diagram of the GPS accessory module  15  and the signals conducted by the system flex  240  and the battery flex  210  in greater detail. As was stated above, GPS information from the satellite  20  (FIG. 1) is received by antenna  290  and conveyed to low noise amplifier circuit  300 . The output of low noise amplifier circuit  300  is coupled to the main printed circuit board  235  which includes position calculation circuitry  310  and several servers  320 ,  340 ,  360 . The position calculation circuitry  310  calculates location information based on the GPS information received from the satellite  20  and/or received from the position reference server  55 . It is important to note that the position calculation circuitry  310  also includes circuitry required for implementing the position determining functions and logic functions of the GPS accessory module  15 . By example, the position calculation circuitry  310  may be comprised of a digital signal processor device, a microprocessor device, and various analog to digital converters, digital to analog converters, and other support circuits. By further example, the calculation circuitry  310  may also be comprised of a memory which may contain programs for performing some of the functions of the GPS accessory module  15 . The control, communication, and signal processing functions of the GPS accessory module  15  are allocated among these devices according to their respective capabilities. 
     The calculation circuitry  310  communicates with a data communications server  320 , an energy management server  340 , and a navigation server  360 . The data communications, energy management, and navigation servers  320 ,  340 ,  360  exchange information over the MBUS  140  with appropriate functions within the user terminal  10 . 
     In general, the data communication server  320  opens and closes communications paths among the navigation server  360 , the user terminal  10 , the position reference server  55  (FIG.  1 ), and/or the computing device  30  (FIG.  1 ). These communication paths are used to convey position information from the navigation server  360 , or position assistance data from the position reference server  55 . The communication server communicates with the user terminal  10  over the MBUS  140 . For communicating with the external computing device  30 , the data communication server  320  communicates using FBUS_Tx  147  and FBUS_Rx  149  signal paths. 
     The data communication server  320  includes a call controller  325  which issues commands to the user terminal  10  to open and close communication over a wireless transmission channel for communicating with the position reference server  55 . In a presently preferred embodiment, after the data communication server  320  has opened a transmission channel it utilizes an in-band modem  330  which sends and receives tones that are suitable for passing through the user terminal vocoder  130 . Due to typical user terminal vocoder bandwidth limitations, bit rates of approximately 150-4800 bit/s may be achieved. However, because of the relatively small amount of data to be exchanged, this relatively low bit rate is not a serious limitation to data transfer. The in-band modem  330  is suitable for data transfers over, for example, CDMA and AMPS transmission channels. 
     In accordance with an aspect of this invention, the in-band modem  330  exchanges signals with the vocoder  130  through the audio input  132  and audio output  134  of user terminal controller  118 . It can be appreciated that through the use of the in-band modem  330 , a traffic channel (voice channel) can be used to convey the data transfer. However, in other embodiments, the call controller may use other channels for communications, for example, control or packet data channels. 
     The navigation server  360  controls the location calculations of the control circuitry  310  and conveys position information to the communication server  320 . Alternatively, the navigation server  360  may receive position assistance data from the position reference server  55 , and cause the control circuitry  310  to include that data when performing location calculations. The position assistance data provided to the navigation server  360  may include, without limitation, the approximate position of the user terminal  10 , the exact time, satellite ephemeris data, almanac data, and differential corrections for subsequent position calculations. 
     The energy management server  340  monitors and controls the power consumption of the GPS accessory module  15 . On power up, the energy management server  340  sends a predefined hardware power consumption table to the user terminal  10  over the MBUS  140 . The table includes entries for various portions of the control circuitry  310 . During operation of the GPS accessory module  15 , the user terminal  10  may send a power state change request to the energy management server  340 . Upon receipt, and if the GPS accessory module  15  is in the requested state, the energy management server  340  will do nothing. Otherwise, the energy management server  340  coordinates a change in power consumption of the various portions of the control circuitry  310  in order to achieve the requested power state. Once the power change is successful, the energy management server  340  updates the hardware power consumption table and sends it to the user terminal  10 . If the power change was unsuccessful, the energy management server  340  sends a message to that effect to the user terminal  10 . 
     Signal paths FBUS_Tx  147 , FBUS_Rx  149 , audio input  134 , audio input  132 , and MBUS  140  are coupled from the GPS accessory  15  through the user terminal  10  by a system connector  225 . This system connector  225  may be a standard connector that can be used for other functions as well, and is thus not specially designed or adapted for use with only the GPS accessory module  15 . It should be understood that system connector  225  is not limited to coupling only the aforementioned signal paths but may include any signal paths that may be coupled between the GPS accessory module  15  and the user terminal  10 . 
     Battery interface signals are coupled from the GPS accessory  15  to the user terminal  10  through battery connector  220 . The battery interface signals include VBAT  380 , BTEMP  385 , and BSI  390 , which will now be explained. A battery  200  provides operating power to the GPS accessory module  15 . The battery  200  also provides power to the user terminal  10  through the conductor VBAT  380 . BTEMP  385  is a signal that serves two functions. The controller  118  may force BTEMP to a voltage level which causes the GPS accessory module  15  to power up and begin operating. BTEMP also serves as an output from the GPS accessory  15  to the user terminal  10  indicating the temperature of the battery  200 . BSI  390  is used by the controller  118  to identify the accessory. In a preferred embodiment, the controller interrogates the BSI  390  function to identify a battery size. Upon identification of a particular battery size assigned to the GPS accessory module, the controller  118  then concludes that the GPS accessory module  15  is coupled to the user terminal  10 . It should be understood that battery connector  220  is not limited to coupling only the aforementioned battery interface signal paths but may include any signal paths that may be coupled between the GPS accessory module  15  and the user terminal  10 . As stated for the system connector  25 , the battery connector  220  may also be a standard connector that can be used for other functions as well, and is thus not specially designed or adapted for use with only the GPS accessory module  15 . 
     The mechanical components and assembly of the GPS accessory module will now be described. FIG. 6 shows an exploded view of the GPS accessory module  15  as embodied in the battery enclosure  126 . 
     The battery  200 , also shown in FIG. 5, is provided for supplying power to the GPS accessory module  15  and to the user terminal  10 . The battery  200  may be user replaceable. 
     A bracket assembly  205  retains the battery  200  and provides a mounting platform for modules of the GPS accessory module  15 . A battery flex  210  mounts to the bracket assembly  205  and an opening  215  allows the battery connector  220 , also shown in FIG. 5, to contact the battery  200 . The battery flex  210  is used to transfer power from the battery  200  to the GPS accessory module  15  and to the user terminal  10  simultaneously. The battery flex is preferably soldered to a main printed circuit board  235  and then reinforced using an epoxy bond for strain relief. The system connector  225  also shown in FIG. 5, mounts to the bracket assembly  205  and an opening  230  allows the system connector  225  to contact the user terminal  10 . A system flex wiring board conducts signals between the user terminal  10  and the main printed circuit board  235  through the system connector  225 . 
     A bottom shield assembly is partitioned into two parts. A bottom RF shield portion  245  shields the RF portion of the bottom side of the main printed circuit board  235 . A bottom baseband shield portion  250  shields the baseband portion of the bottom side of the main printed circuit board  235 . Alternatively, two separate shield assemblies could be used. 
     The main printed circuit board  235  is preferably a double sided,  6  layer, printed circuit board. The main printed circuit board  235  is located and supported by two tabs on the bracket assembly  205  which slide into slots on the main printed circuit board  235 . 
     A battery latch  255  is used to retain the GPS accessory module  15  to the user terminal  10 . A latch spring  260  is assembled under the latch to provide a return force to hold the battery latch  255  in place. 
     A top shield assembly is partitioned into two parts. A top RF shield assembly portion  265  includes a frame and a removable lid for troubleshooting and is located in close proximity to the RF section of the top side of the main printed circuit board  235 . A top baseband shield portion  270  is located in close proximity to the baseband section of the top side of the main printed circuit board  235 . Alternatively, two separate shield assemblies could be used. 
     A low noise amplifier flex wiring board, also referred to as an LNA flex  275 , is located adjacent to the top RF shield portion  265  and the top baseband shield portion  270 . The LNA flex  275  is preferably soldered to the main PCB and then reinforced using an epoxy bond for strain relief. The LNA flex  275  includes a low noise amplifier shield, also referred to as an LNA shield  280 . The LNA shield  280  may, in the same manner as the other shields, be constructed as one piece. All of the various shields could be constructed using an electrically conductive nickel-silver material. 
     A ground plane flex  285  is provided for the purpose of increasing the size of a ground plane on which a GPS antenna  290  is mounted. The ground plane flex  285  may be constructed as a single layer of metal or metalization, and may further be constructed in such a way as to increase the circular polarization of the GPS antenna  290 . The GPS antenna  290  can be a patch antenna which has been designed in shape to fit within the GPS accessory module  15  and designed in frequency for receiving the GPS signals. The GPS antenna  290  has further been designed to resonate at an appropriate frequency for receiving GPS signals when assembled with the components of the GPS module  15 . The GPS antenna  290  is preferably constructed of a metal, such as aluminum, that is deposited onto a dielectric substrate, such as a ceramic substrate. 
     The battery enclosure  126  is provided to enclose the GPS accessory module  15 . The enclosure  126  may be ultrasonically welded to the bracket assembly  205  to form the enclosure for the GPS accessory module  15 . The battery enclosure  126  is shaped to be form and fit compatible with a user terminal battery pack and as such defines a shape that does not interfere with existing accessories for the user terminal  10 . 
     Turning to FIG. 7, the functions of the position reference server  55  are now described. The purpose of the position reference server  55  is to receive calculated location information from the GPS accessory module  15  (FIG. 5) and to provide position assistance data to the GPS accessory module  15 . The position reference server  55  includes at least one application program  400 , communication protocols  410 , map software  420 , a position assistance task  440 , and a modem  460 . Communications from the GPS accessory module through the user terminal  10  are received by the modem  460 . The communication protocols  400  control the reception of incoming calls. The data rate for the information transferred during the call is decided by the user terminal  10 . The application program  400  routes the data to the correct task within the position reference server  55 . The map software  420  receives calculated location information from the GPS accessory module  15  and displays the location information on a graphical map. The position assistance task  440  also receives the calculated location information from the GPS accessory module and calculates position assistance data to be used by the GPS accessory module  15  to improve the accuracy of the calculated location information in the event that the GPS accessory module  15  is unable to receive accurate position information from the satellite  20  (FIG.  1 ). The position assistance task  440  may use additional information to provide the assistance data including, without limitation, the number of satellites, satellite identification, satellite ephemeris data, the reference time, the location of the serving base station  40 , and other calculations about the location, direction, and speed of the user terminal. Once the assistance data has been determined it is sent back to the GPS accessory module using the modem  460 . As was stated above, the position assistance data provided to the GPS accessory module  15  may include, without limitation, approximate position of the user terminal  10 , exact time, the satellite ephemeris data, and differential corrections for subsequent position calculations. 
     Returning to FIG. 1, the computing device  30  receives the calculated location information from the GPS accessory module  15  through link  35 . Computing device  30  preferably includes a mapping program which utilizes the location information to display the current location graphically. The computing device may also be capable of providing other information to the user, including directions to other locations, distances between different locations, etc. 
     The computing device  30  may be a laptop computer, a personal organizer, or any type of computing device appropriate for use with user terminal  10  or the GPS accessory module  15 . 
     In a further embodiment, the GPS accessory module  15  may also be coupled with a vehicle installed user terminal  10 , and could aid in providing a navigation system for the vehicle. In such an embodiment, the FBUS  145  could be connected to a data processor on-board the vehicle. 
     In a further embodiment, the GPS accessory module  15  may be incorporated into a PCMCIA card, plugged into the computer device  30 , and may communicate with the position reference server  55  through a wireless modem present in the computing device  30  or in the PCMCIA card. In this case, there may be no requirement for the user terminal  10 . 
     It should be understood that while the presently preferred embodiment of the GPS accessory module  15  has been described as comprising having three servers, the communication server  320 , the energy management server  340 , and the navigation server  360 , the invention is not limited to any particular number of servers, or to the use of discrete servers at all. 
     It should also be understood that this invention is not limited to receiving position information from the GPS system. In another embodiment, the user terminal may receive position information from any system, terrestrial or non terrestrial, that transmits position information that the GPS accessory module  15  is capable of receiving. 
     It should also be understood that the connection between the user terminal  10  and the external computing device  30  is not limited to the FBUS  145 , but may include any bidirectional digital interface suitable for conveying the appropriate signals between the user terminal  10  and the external computing device  30 . 
     It should be further understood that the antenna  290  is not limited to a patch antenna but may include an omni-directional, linear, or helical configuration. 
     Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.