Patent Publication Number: US-6337975-B1

Title: System and method for power measurement in outdoor antenna units

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Appln claims benefit of Prov. No. 60/127,499 filed Apr. 2, 1999. 
    
    
     This application is related to commonly-owned applications, filed concurrently herewith, entitled “Power Output Control Of A Car Kit By A Coupled Wireless Device” having application serial number 09/387,143; “System And Method For Temperature Compensation Of External Antenna Units” having application serial number 09/387,138; and “System And Method For Constant Loop Gain In A Closed Loop Circuit” having application Serial No. 09/387,137, which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to mobile communication systems, and more particularly to a system and method for controlling transmitted output power of outdoor antenna units coupled to hand held wireless devices. The present invention is most applicable to wireless communication devices transmitting using code division multiple access (CDMA) modulation techniques where output power control is critical. 
     II. Related Art 
     Mobile telephone systems allow customers to establish communication links or place telephone calls from wireless devices such as portable or hand-held mobile phones. Calls initiated or received by wireless devices used in such systems are processed by a wireless communications network. One type of wireless network is a terrestrial cellular communication system communicating via a series of base stations and ground-based antennas that operate in the 800-1900 MHz range. Cellular communication systems limit the user to communication within a cell, which comprises a geographical service area to which the base station antennas can transmit. Users can move from cell to cell through known hand-off procedures that transfer calls from one cell to another. However, if no base station is within range of the mobile transmitter, such as in a rural area, a user cannot use the mobile telephone service. 
     Developments in mobile telephone system technology have led to wireless communication systems or networks that can transfer signals using a Low Earth Orbit (LEO) satellite system. The satellite systems can transmit and receive signals in rural areas as well as cities through the beams they project, and a user does not need to be within close range of a ground-based antenna. As a result, satellite communication systems are not limited to major cities as are cellular networks. In addition, each LEO satellite is capable of carrying a large number of user transmissions simultaneously. various satellite access schemes such as time division multiple access (TDMA) and code division multiple access (CDMA) allow concurrent access to LEO satellites by a large number of users. 
     The number of users that can be serviced by a wireless communication system, the system capacity, increases if the power output from each user&#39;s wireless device is decreased to the minimum power needed for quality transmission, and overhead or non-traffic messages or channel activity is reduced. This is the result of decreasing mutual interference between users, which is especially important in environments such as CDMA type communication systems. If one user&#39;s signal is too strong the quality of service for other users degrades due to increased interference. However, if the power of a user&#39;s signal becomes too low, the quality of service for that user becomes unacceptable. So, there is a desire to maintain as high a power level as possible to have higher quality service. 
     Thus, the number of users that may be provided service is increased by maintaining overhead power levels and each individual user&#39;s signals at the minimum levels needed for optimum performance. Therefore, the power output of wireless device transmissions are generally controlled using one or more power control methods to minimize interference and maximize communication link quality. Techniques for power control are discussed for example in U.S. Pat. No. 5,383,219, entitled “Fast Forward Link Power Control In A Code Division Multiple Access System,” issued Jan. 17, 1995; U.S. Pat. No. 5,396,516, entitled “Method And System For The Dynamic Modification Of Control Parameters In A Transmitter Power Control System,” issued Mar. 7, 1995; and U.S. Pat. No. 5,267,262, entitled “Transmitter Power Control System,” issued Nov. 30, 1993, which are incorporated herein by reference. In addition, also see U.S. patent application Ser. No. 09/164,384 filed Sep. 30, 1998 entitled “System And Method For Optimized Power Control”; and Ser. No. 08/908,528, filed Aug. 7, 1997, entitled “Method And Apparatus For Adaptive Closed Loop Power Using Open Loop Measurements,” which are incorporated herein by reference. The result is the communication system efficiently carries the substantially maximum number of individual user transmissions simultaneously. 
     Wireless devices, also referred to as user terminals, in current wireless communications systems may be any of several different types. One type is the portable unit, which is a hand-held device carried by the user and requires no external power source or antenna system. Another type is the mobile unit or station, which is typically fixed in a vehicle and operates like a desk type phone. A mobile unit has a separate unit (or “box”) that is mounted in the vehicle and contains most of the transmitting and receiving circuits or hardware. A hand-held unit such as a phone handset, containing a keypad, speaker and microphone, is connected by one or more cables, conductors, or connectors to the box. A cradle is provided for supporting the handset unit when it is not in operation or when it is being used in a “hands free” mode. The box in turn is connected by a cable to an externally mounted “outdoor” antenna unit, which transmits and receives signals via a satellite or terrestrial cellular communications system or a base station or gateway. 
     A third type of user terminal combines the features of both a portable unit and a mobile unit. This type uses a hand-held device that can be used as a standalone unit away from the vehicle, and can be connected to a vehicle mounted assembly sometimes called a “car kit,” for use in the vehicle. The car kit uses an external or outdoor unit (ODU) with an outdoor antenna to accommodate communications for the wireless device. A primary advantage of this combination unit or arrangement is that when the wireless device is used in the vehicle it can utilize additional power provided by the vehicle mounted electronics to establish a better and stronger communications link with satellite transceivers. It also allows conservation of internal battery power, drawing on vehicle provided power instead. 
     Satellite wireless telephone systems are particularly sensitive to outdoor or external antenna unit matching at the mobile unit due to potential path losses and a resulting difficulty in power control. The power output of the outdoor unit is calibrated against, or configured with, specific phone transmission circuits in mind. At present, a given car-kit is designed or calibrated in the factory to function with certain characteristics for phones with which it is to be connected. Once this designing or calibration (matching) takes place, the autonomous nature of phones and car kits is diminished because the phone is limited to being used with certain car kits or outdoor antenna units, such as specific models or manufacturers, having closely matched characteristics. This clearly sets certain constraints for mobile units or hand-held phones used with car kits in order to provide a closer match between the power output desired by the phone power control systems or methods, and the power actually being delivered by the outdoor unit. 
     Another limitation on phone autonomy is that software in the phone makes assumptions that all antenna units, or those it expects to be coupled to, have similar design characteristics. Yet, in the actual marketplace it is not uncommon that a user may have more than one portable phone or have one that can be used both as a standalone unit and as a mobile phone when placed in a cradle mounted in a vehicle. Also, a user may commonly upgrade his or her phone as new models come on the market, and have more than one car-kit. Therefore, the mobile unit employed with a car kit may change permanently or on a transient basis, creating potential undesirable matching problems. 
     One goal of the present invention is to allow a variety of hand-held wireless devices to be used with a given vehicle mounted, or fixed, outdoor antenna unit or “car kit,” while maintaining a desired level of accuracy for the power output by the outdoor unit. Here, a given outdoor antenna unit is not calibrated against specific hand-held device characteristics in a factory, and hand held device software does not make any assumptions about antenna unit design characteristics. Instead, the antenna unit to which the hand held device is connected needs to inform the hand held device of its particular design characteristics. Yet, for improved or optimum performance, the outdoor antenna unit to which the hand-held wireless device is connected needs to inform the hand held device of its particular design characteristics. For example, the antenna unit power must be calibrated with the hand held device to which it is connected. 
     What is needed is a system and method for power control that provides design specification parameters (containing information about the antenna unit design characteristics) from the antenna unit to any hand held device to which the antenna unit is connected, while still allowing for an autonomous relationship between the hand held device and the antenna unit. The design specification parameters sent to the hand held device include information needed for the hand held device to operate in such a way as to optimize the performance of the antenna unit. 
     SUMMARY OF THE INVENTION 
     The present invention is a novel system and method for controlling transmit power in a hand held device. Multiple units for information signal transmission are utilized including: an antenna unit, a cradle, and any other units needed for transmission. With the present invention, transmit power is controlled by obtaining design specification parameters specific to the antenna unit and an output power measurement of the information signal transmitting from the antenna unit, also referred to as an outdoor unit. The outdoor unit design specification parameters are provided to the hand held device via a feedback loop to adjust the initial power of the information signal transmitting from the hand held device. Because the hand held device does not make any assumptions about the outdoor unit design characteristics, the present invention allows any hand held device to work with any outdoor unit by providing to the hand held device the design specification parameters of the outdoor unit. 
     The antenna unit of the present invention includes components for transmitting the information signal and components for obtaining an output power measurement of the information signal immediately prior to transmission. The hand held device comprises one or more transmit and receive components and a logic unit. The logic unit of the hand held device comprises a processor which processes software and a transmit power control. The software of the processor is initialized with the design specification parameters of the outdoor unit to operate the transmit power control in such a way as to optimize the performance of the outdoor unit. The hand held device interprets the output power measurement and adjusts the transmission power of the information signal accordingly. 
     The method of the present invention includes obtaining a digital output power measurement by the outdoor unit, modulating the digital power measurement, and transmitting the modulated measurement signal to the hand held device. The method of the present invention also includes receiving the modulated measurement signal by a cradle or hand held device, demodulating the measurement signal, and adjusting by the hand held device the transmit power of the information signal. 
     The system and method of the present invention allow control of the initial transmit power of the information signal from the hand held device in order to limit the output power of the signal transmitted from the hand held device to the power needed for high quality transmission. Efficient use of power by limiting the output power from the hand held device allows the maximum number of individual user transmissions to be carried by in a wireless communication system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, objects and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: 
     FIG. 1 is a block diagram of a mobile phone system according to a preferred embodiment of the present invention; 
     FIG. 2 is a flowchart illustrating an overview of the call process according to a preferred embodiment of the present invention; 
     FIG. 3 is a block diagram of a car kit according to a preferred embodiment of the present invention; 
     FIG. 4 is a block diagram of an ODU logic unit according to a preferred embodiment of the present invention; 
     FIG. 5 is a block diagram of a hand held logic unit according to a preferred embodiment of the present invention; 
     FIG. 6 is a flowchart illustrating the operation of connecting a hand held to a cradle according to a preferred embodiment of the present invention; 
     FIG. 7 is a flowchart illustrating the use of a car kit for placing a call according to a preferred embodiment of the present invention; 
     FIG. 8 is a flowchart illustrating the operation of obtaining a digital power measurement according to a preferred embodiment of the present invention; 
     FIG. 9 is a flowchart illustrating adjustment of transmit power by a hand held device according to a preferred embodiment of the present invention; 
     FIG. 10 is a diagram illustrating car kit communications protocol; and 
     FIG. 11 is a flowchart illustrating the operation of a processor processing software of the hand held logic unit according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With the system and method of the present invention, hand held wireless devices and antenna units remain autonomous because the hand held device does not make the assumption that all outdoor units have similar design characteristics. The present invention enables the antenna unit to provide its design specification parameters to the hand held device to inform it of the particular design characteristics of the antenna unit to which it is currently connected. With the present invention, transmit power is controlled in the hand held device. The transmit power is controlled by obtaining an output power measurement of an information signal transmitting from an outdoor unit and using the output power measurement to adjust the power of the transmitted information signal in the hand held device. 
     One embodiment of the present invention is in a car kit that comprises an external antenna unit, also referred to as an outdoor unit or ODU, that mounts to the exterior of a vehicle, such as the trunk or roof of a car or truck and a cradle. A hand held (holdable, portable) wireless device interfaces with the car kit to make and receive calls, or establish various communication links. The car kit operates in a wireless satellite communications system, preferably one that uses Low Earth Orbit (LEO) satellites. However, it would be apparent to one skilled in the relevant arts that other satellite systems, such as ones using Medium Earth Orbit (MEO) satellites, or geosynchronous (GEO) satellites, could also be used with this invention. The invention may also prove useful in some terrestrial communication systems where car kit power losses or differences unacceptably effect the control of output power. 
     FIG. 1 is a block diagram of an exemplary wireless mobile phone system  102 , in which the present invention may be used. Such communication systems are discussed in U.S. Pat. No. 4,901,307, issued Feb. 13, 1990, entitled “Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters;” U.S. Pat. No. 5,691,974, which issued Nov. 25, 1997, entitled “Method and Apparatus for Using Full Spectrum Transmitted Power in a Spread Spectrum Communication System for Tracking Individual Recipient Phase Time and Energy;” and U.S. patent application Ser. No. 09/120,859 filed Jul. 21, 1998, entitled “System And Method For Reducing Call Dropping Rates In A Multi-Beam Communication System,” all of which are assigned to the assignee of the present invention, and are incorporated herein by reference. 
     Mobile phone system  102  comprises one or more car kits  104 , hand-held wireless devices  110  and a wireless communications network  128  comprising equipment related to wireless communication service. Wireless device  110  is mounted in or coupled to a car kit  104 . Car kit  104  is mounted in a vehicle, such as an automobile or truck,  106 . Car kit  104  includes a cradle  108 , a cable  111 , an outdoor unit (ODU)  112 , and an ODU antenna  114 . Hand held device  110  can rest in or be removed from cradle  108 . It is anticipated and will be readily understood by those skilled in the art, that the “car kit” and ODU represent elements that can be used in non-vehicular arrangements as well, such as for fixed remote communication applications in or around structures where unit mobility is occasionally exploited or increased power is sometimes desired. 
     Connection of the elements of car kit  104  will next be illustrated. Cradle  108  is connected to ODU  112  by cable  111 . ODU  112  mounts to an exterior surface of vehicle  106 . Antenna  114  is attached to the top of ODU  112 . Hand held device  110  (HH) may rest within cradle  108 , whereby it is electrically connected to ODU  112  through cradle  108  directly, by inductive coupling, or via a wire connection in a well known manner. When a wire connection is used, hand held device  110  may be removed from its resting position within cradle  108  by a user to initiate or receive a call and still remain electrically connected to car kit  104 . In addition, hand held device  110  may be unplugged from cradle  108  and taken outside vehicle  106 , or other structure, for stand-alone use. In that event, hand held device  110  is electrically disconnected from car kit  104  and does not utilize any features that are incorporated in car kit  104 . 
     Cradle  108  remains within automobile  106  and ODU  112  remains fixed to vehicle  106 . Mobile phone system  102  transmits to and receives signals from an antenna  118  connected with a ground base station, hub, or gateway  120  via satellite  116  providing service for an area wireless device  110  is located in, in a manner known to persons skilled in the relevant arts, and disclosed in the patents referenced above. A gateway provides communication links for connecting a wireless device, also referred to as a user terminal, to other user terminals or users of other communication systems, such as a public switched telephone network. 
     Hand held device  110  constantly, or on a pre-selected periodic basis, adjusts the power of transmitted signals during a call or communication link using the power measurement of the present invention. Signal transmission between the mobile phone system  102  and a recipient  126  is illustrated in FIG. 2 which is a flowchart illustrating an overview of a call process. 
     Operation of the mobile phone system  102  includes sending information signals between hand held device  110  and a recipient device  126  via the components within the wireless communications network  128  (as described in reference to FIG. 1 above) in order to transmit information, such as a digitized representation of a voice. 
     The flowchart in FIG. 2 begins with step  206 . In step  206 , hand held device  110  is connected to cradle  108 . Hand held device  110  has two modes of operation, as a standalone unit and as a hand set plugged into cradle  108 . When hand held device  110  operates as a standalone unit, it transmits and receives via satellite  116  using a hand held antenna (not shown). When hand held device  110  is used within vehicle  106  and is connected to cradle  108 , it transmits and receives via ODU  112 . 
     In order to allow a variety of hand held devices  110  to work with any ODU  112  when hand held device  110  is connected to cradle  108 , ODU  112  sends information about its design specification parameters to hand held device  110  to inform hand held device  110  of the particular design characteristics of ODU  112 . The design specification parameters are passed to a processor in hand held device  110 , that makes no assumptions about ODU design characteristics before it receives the design specification parameters from ODU  112  itself. The process of how the processor, typically using software, in hand held device  110  utilizes the design specification parameters to adapt to the particular ODU  112  will be described later in reference to FIG.  11 . 
     Notification of the particular ODU  112  design characteristics allows hand held device  110  to ensure that the transmit power of the information signal does not exceed the design criteria of any of the components within ODU  112  thereby preventing damage to components of ODU  112 . It also allows more appropriate control over the output power of ODU  112  to achieve desired power levels. The initiation process provides hand held device  110  with the information it needs to limit the power of a transmit signal to that which will not damage ODU  112 , or to choose the appropriate power level. The choice of model and vendor of hand held device  110  may be independent of the choice of model and vendor of ODU  112 . The initiation process that occurs when hand held device  110  is plugged into cradle  108  is described in further detail with respect to FIG.  6 . 
     In step  208 , a caller initiates a call via hand held device  110 . A user initiates a call via hand held device  110  by entering digits into the keypad specifying a particular destination number and then entering send using the keypad. For example, a user may enter a destination number, also referred to as a telephone number, using the keypad of hand held device  110 . Destination numbers are numbers used by components of wireless communications network  128  to identify recipient network interface device  126 . 
     Call initiation proceeds with hand held device  110  transmitting an information signal to gateway  124 . The information signal includes information used to establish and terminate the call. Typically multiple information signals are sent. These signals follow standards established by the industry such as such as the well known IS-95 standard for wireless communication or other standards known to those skilled in the relevant art. Information signals also include digital representations of voice, data transmitted via personal computers, and digitized versions of the content on pages transmitted via facsimile. 
     Call initiation continues with gateway  124  interpreting the information signal and responding. Gateway  124  contains the capability to analyze signals received from hand held device  110 , interpret the signals, and switch the call to other components within wireless communications system  128 . For example, if a caller wants to place a call to a recipient device  126 , say another user terminal or a wireline phone, using hand held device  110 , the caller inputs the destination number corresponding to recipient device  126 . The destination number is received by gateway  124  which determines the switching that is needed to complete the call to recipient network interface device  126 . Signaling proceeds until the call is initiated to recipient network interface device  126 . 
     In step  210 , the call proceeds until one of the parties terminates the call. Information signals sent during the call may contain a digitized voice, facsimile data, or any other data that may be transmitted via a communications network. Whether hand-held device  110  originates or responds to a call, during the call, hand held device  110  adjusts the transmit power of the information signals as the data rate changes, or as the path loss or signal attenuation changes, in accordance with known power control techniques or algorithms, as discussed above. In addition, hand held device  110  adjusts the transmit power to compensate for car kit  104  losses. Because the signal must transmit through cable  111  and ODU  112  before transmitting via ODU antenna  114 , losses result in a difference between the power of the initial transmit signal and the power output from ODU  112 . Hand held device  110  needs to know the difference between the output power from ODU  112  and the power of the initial transmitted signal in order to adjust the initial transmit power to achieve the desired power output from ODU  112 . The needed design specification parameters, which includes power measurement information, are provided to hand held device  110  via a power feedback loop. The process for providing the information is described in further detail with respect to FIG.  7 . 
     FIG. 3 is a block diagram of car kit  104 . Car kit  104  comprises components to transmit and receive via satellite  116  in order to communicate with gateway  120  or a wireless communications system. Car kit  104  interfaces with a hand held device  110  connected to cradle  108 . Cradle  108  is connected to outdoor unit  112  by cable  111 . ODU antenna  114  is connected to ODU  112 . 
     Hand held device  110  comprises hand held (HH) receive components  302  and HH transmit components  304 . In addition, in order to control power, hand held device  110  comprises a HH logic unit  308 . 
     Cradle  108  includes a duplexer  306 , a demodulator  310  and a power supply interface  326 . 
     Outdoor unit  112  comprises ODU power control components  328 . ODU power control components  328  include ODU transmit components  312 , a duplexer  322 , ODU receive components  324 , a power detector  314 , an analog-to-digital (A/D) converter  315 , a temperature detector  316 , an ODU logic unit  318 , a modulator  320 , and a power supply interface circuit  327 , to power active elements within ODU  112 . 
     The connection between hand held device  110  and cradle  108  will be described next. Logic unit  308  is connected to demodulator  310  in order to receive the power measurement from ODU  112 . Logic unit  308  is also connected to HH transmit components  304  in order to provide information for the adjustment of the transmit power of the signal. HH transmit components  304  are connected to duplexer  306  which provides connection to cable  111 . Duplexer  306  is also connected to HH receive components  302  so that HH receive components  302  can receive the signal from satellite  116  via cable  111  into hand held device  110 . Power supply interface  326  within cradle  108  is connected to the link between hand held device  110  and cable  111 . In addition, power supply interface  326  is connected to the vehicle battery (not shown) to provide a source of power for cradle  108  and/or outdoor unit  112 . 
     Cable  111  is connected to duplexer  322  within ODU  112 . Duplexer  322  is also connected to transmit components  312  and receive components  324  within ODU  112 . 
     The output of ODU transmit components  312  is connected to ODU antenna  114 . ODU power control components  328  are connected as a feedback loop from the output of transmit components  312  to cable  111 . 
     Within the ODU power control components feedback loop, power detector  314  is connected to the output of transmit components  312  to detect the power of the signal output from transmit components  312 . The output of power detector  314  is connected to ODU logic unit  318  (via A/D converter  315 ) so that detected power can be converted into a digital power measurement. Temperature detector  316  is connected to ODU logic unit  318  in order to provide a temperature measurement for improved estimation of the power. The output of ODU logic unit  318  is connected to the input of modulator  320  for modulation of the power measurement. The output of modulator  320  is connected to cable  111 . Thus, the signal is sent from modulator  320  back to cradle  108  via cable  111 . 
     In the alternative, temperature and power measurements can be maintained as analog values and transferred using known data modulation techniques for modulating measurement values on a carrier, such as is commonly used in modem communications over wireline links. The temperature and power measurement values are then recreated by demodulator  310 . Such techniques are well understood in the art. 
     Duplexer  322  in ODU  112  and duplexer  306  in cradle  108  allow connection between multiple circuits. The interfaces may be implemented using duplexers manufactured by Murata, such as Murata&#39;s duplexer model number DSY21R61C2R49BHB. In an alternate embodiment, car kit  104  includes a cellular link (not shown). In the alternate embodiment, triplexers are used in place of duplexers  322  and  306  in order to connect three links including the satellite transmit, satellite receive, and cellular links. The alternate embodiment, the circuit arrangement of which would be readily apparent to one skilled in the relevant arts, allows the mobile phone to be used in either a terrestrial cellular system or a satellite communications system. 
     Implementation of ODU power control components  328  will be described next. Power detector  314  may be implemented with a full-wave zero bias Schottky diode detector (ZBS) model number HSMS2852, manufactured by Hewlett Packard. In one embodiment of the present invention, the power detector design specifications include providing at least 25 db dynamic range, having power estimation errors of ±0.5 db from 27-35 dbm, a power estimation time of 1 millisecond, and operating at temperatures of −20° C. to +60° C. ambient. The output of power detector  314  is input to A/D converter  315  which uses a 16-bit single slope conversion and is recalibrated every second. A/D converter  315  is connected to ODU logic unit  318 . ODU logic unit  318  may be a microprocessor which runs at 13.125 MHz. 
     FIG. 4 illustrates a block diagram of ODU logic unit  318 . ODU logic unit  318  comprises one or more processors and storage media. Within ODU logic unit  318  are: a multiplexer  402 , an analog-to-digital (A/D) converter  404 , a temperature look-up table  406 , a logarithmic transform table  410 , a power estimator  408 , calibration parameter tables  420 , and design specification parameter tables  422 . 
     ODU logic unit  318  comprises one or more processors that have the capability of processing computer software in the form of lines of executable code comprising commands from a computer programming language residing in a storage medium. The processors may comprise processing capability dispersed among one or more processing chips, application specific integrated circuits (ASICs), or any other hardware capable of processing computer software. In addition, ODU logic unit  318  includes a storage medium. 
     Storage medium, also referred to as memory, is any storage medium which includes long term memory, non volatile memory, removable memory such as floppy disk or any other memory that can be used to store computer code or information processed by computer software. The storage medium may be dispersed among one or more hardware storage medium components. In one embodiment of the present invention, ODU logic unit  318  is implemented with a microcomputer which runs at 13.125 MHz. The microcomputer is versatile and allows for future expansion. 
     Signals from power detector  314  and temperature detector  316  are input into multiplexer  402  within ODU logic unit  318 . The output of multiplexer  402  is connected to A/D converter  404  where the multiplexed temperature and power information is converted to digital format. The output of A/D converter  404  is connected to temperature look-up table  406  and logarithmic transformation table  410 . Temperature look-up table  406  and logarithmic transformation table  410  are connected to power estimator  408 . Power estimator  408  is connected to modulator  320  to send the estimated power to modulator  320  for modulation and transmission via cable  111 . The process of obtaining a digital power measurement will be described in further detail with respect to FIG.  8 . 
     Multiplexer  402  receives input from power detector  314  and temperature detector  316  and multiplexes the signals into one output signal. Multiplexing techniques such as those known to those skilled in the art are used to multiplex the signals. 
     The resulting multiplexed signal is sent from multiplexer  402  to A/D converter  404 . In a preferred embodiment, a 16 bit single slope A/D converter is used. However, those skilled in the art will readily recognize that the invention is not limited to a 16 bit A/D converter and that other such elements can be used within the teachings of tthe invention having other bit widths or slopes, as desired. The preferred implementation of A/D converter  404  is recalibrated every second using an internal bandgap reference. 
     Temperature look-up table  406  and logarithmic transformation table  410  are  256  level tables residing in memory. Temperature look-up table  406  converts an 8 bit voltage obtained from temperature detector  316  into an 8 bit temperature. Logarithmic transformation table  410  converts a 10 bit voltage into an 8 bit log (voltage). 
     Neither the look-up table  406  nor logarithmic transformation table  410  are limited to 256 levels. The voltage obtained from temperature detector  316  can be represented by a digital word length other than 8 bits. The logarithmic transformation table is not constrained to operate with a 10 bit word length, nor to provide an 8 bit log (voltage) output. The illustrated word lengths are for purposes of illustration and other word lengths can be used, depending on desired resolution, as will be clear to those skilled in the art. 
     Power estimator  408  receives the 8 bit temperature and the 8 bit log (voltage) and converts them into a 10 bit absolute power estimation (in dbm). The power estimation is determined by using voltage-temperature correlation equations shown below.                        P     i                 n            (       V   g     ,     T   g       )       =                  B   0     +       B   1          T   g       +       B   2          T   g   2       +       B   3          T   g   3       +   …   +       B   k          T   g   k       +                                  C     1   ,   1            V   g          T   g       +       C1     ,   2            V   g          T   g   2       +       C     1   ,   3            V   g          T   g   3       +   …   +       C     1   ,   k            V   g          T   g   k       +   …                                  +     C     m   ,   1              V   g   m          T   g       +       C     m   ,   2            V   g   m          T   g   2       +       C     m   ,   3            V   g   m          T   g   3       +   …   +       C     m   ,   k            V   g   m          T   g   k                       (   1   )                   [         1         V     g   ,   1             V     ,   1             V     ,   1             T   1         T       T           V     g   ,   1            T   1               V     g   ,   1          T             V     g   ,   1          T             1         V     g   ,   2             V     ,   1             V     ,   2             T   2         T       T           V     g   ,   2            T   2               V     g   ,   2          T             V     g   ,   2          T             1         V     g   ,   3             V     ,   3             V     ,   3             T   3         T       T           V     g   ,   3            T   3               V     g   ,   3          T             V     g   ,   3          T             1         V     g   ,   4             V     ,   4             V     ,   4             T   4         T       T           V     g   ,   4            T   4               V     g   ,   4          T             V     g   ,   4          T             1         V     g   ,   5             V     ,   5             V     ,   5             T   5         T       T           V     g   ,   5            T   5               V     g   ,   5          T             V     g   ,   5          T             ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮                                                                                                                                       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮           ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮       ⋮           1         V     g   ,   N             V     ,   N             V     ,   N             T   N         T       T           V     g   ,   N            T   N               V     g   ,   N          T             V     g   ,   N          T           ]          [           A   0               A   1               A   2               A   3               B   1               B   2               B   3               C   1               C   2               C   3           ]       =     [           P   1               P   2               P   3               P   4               P   5             ⋮                           ⋮           ⋮             P   N           ]             (   2   )                         
     Calibration coefficients are determined at the calibration temperature using the equation below. Calibration coefficients stored in calibration parameter tables  420  are used with the calibration temperature.                  [         1         V     g   ,   1               1         V     g   ,   2               1         V     g   ,   3               ⋮       ⋮           ⋮       ⋮           1         V     g   ,   N             ]     ·     [                                           A   0               A   1                                           ]       =     [           G   1               G   2               G   3             ⋮           ⋮             G   N           ]             (   3   )                         
     Design specification parameter tables  422  are connected to modulator  320  to provide design specification parameters to hand held device  110  during the initiation process that occurs when hand held device  110  is plugged into cradle  108 . The initiation process will be described in more detail with respect to FIG.  6 . 
     Design specification parameters are stored in the design specification parameter tables  422 . Design specification parameters are the design characteristics of ODU  112 . These design specification parameters inform hand held device  110  of limitations needed in the initial transmit power in order to avoid damaging ODU  112 . Design specification parameters often are characteristics of the power amplifier in the ODU  112  which is an expensive ODU component within transmit components  312 . Design specification parameters include, among others, maximum gain deviation, power detector minimum accurate power, power amplifier supply voltage, power amplifier hi/low bias versus frequency, maximum effective isotropic radiated power (EIRP) versus frequency, maximum effective isotropic radiated power (EIRP) backoff, and gain compression. 
     The calibration and design parameter, and other, tables can be conveniently implemented as a variety of memory storage devices such as ROM or RAM circuits. One type of implementation is an EEPROM circuit which allows programming and reprogramming of information without being volatile and subject to loss when the power is disconnected, as would happen in vehicular applications. Not all of the information needs to be stored in the same location. Since information may change over time, or be updated at a later date, it may be convenient to make some of the memory removable/replaceable, and possibly located separate from ODU Logic unit  318 . Therefore, a separate or additional memory  319  is shown I FIG. 3 for this purpose. 
     The advantage of supplying the design specification parameters of the ODU  112  to the hand held device  110  is that hand held device  110  makes no assumptions about ODU  112 . This allows for an individual hand held device  110  to be used with multiple ODUs  112 , where each ODU  112  has different design specifications. For example, the range of maximum output power for ODUs varies. An example of this range is from +10 dbm to +33 dbm. There may be certain circumstances where one output power is more desirable over another. Therefore, the present invention allows a single hand held device  110  to adaptively change its software in order to work with any ODU  112 . The initialization process of the software of hand held device  110  is discussed below in reference to FIG.  11 . 
     FIG. 5 is a block diagram of HH logic unit  308 . Logic unit  308  comprises one or more processors that may have the capability of processing computer software in the form of lines of executable code of a computer programming language residing in storage medium. Processors may actually constitute processing capability dispersed among one or more processing chips, application specific integrated circuits (ASICs), or any other hardware capable of processing computer software. In addition, logic unit  308  includes a storage medium. In one embodiment, logic unit  308  is implemented with an Intel 386 microcomputer. The Intel 386 microcomputer is capable of processing many tasks which is necessary for operation of hand held device  110 . 
     Within FIG. 5 is a processor  501  that processes software and a transmit power control  502 . Processor  501  is connected to ODU logic unit  318  and HH transmit power control element  502 . The software processed by processor  501  makes no assumptions about ODU  112  design characteristics until it receives the design specification parameters from ODU logic unit  318 . Processor  501  of the present invention, via software, utilizes the design specification parameters of ODU  112  to operate transmit power control  502  in such a way as to substantially optimize the performance of ODU  112 . 
     Transmit power control  502  is connected to HH transmit components  304 . The software in processor  501  is initialized by the power measurement and design specification parameters received by processor  501  from ODU logic unit  318 . Once the software in processor  501  is initialized with the design specification parameters, processor  501  controls transmit power control  502  to perform processing. Transmit power control  502  sends signals for controlling transmit power to transmit components  304 . The process for controlling power is described in further detail with respect to FIG.  7 . The execution of processor  501  with the software initialized with the design specification parameters operates to send appropriate limitations to transmit power control  502 . The process for initiating hand held device  110  is described in further detail with respect to FIG.  6 . 
     FIG. 6 is a detailed flowchart of step  206  illustrating the operation of providing hand held device  110  with information to establish initial transmit power when hand held device  110  is connected to cradle  108 . The design specification parameter tables  422  within ODU logic unit  318  contain the design specification parameters for ODU  112 . The design specification parameters are sent from ODU  112  to hand held device  110  when hand held device  110  is plugged into cradle  108 . This allows the selection of the model and vendor of hand held device  110  to be independent of ODU  112 . 
     The flowchart in FIG. 6 begins with step  603 . In step  603 , ODU  112  is in standby mode until cradle  108  initiates communication. In step  604 , cradle  108  detects hand held device  110  and cradle  108  sends a data send signal to ODU  112 . The data send signal indicates to ODU  112  that hand held device  110  is plugged into cradle  108  and is ready to receive the design specification parameters. 
     In step  606 , ODU  112  sends a message with a design specification parameter to cradle  108 . One design specification parameter is sent in response to a data send signal. The design specification parameter is any one of the design specification parameters that has not been already sent to hand held device  110  during this initiation process. Design specification parameters include maximum gain deviation, power detector minimum accurate power, power amplifier supply voltage, power amplifier hi/low bias versus frequency, maximum effective isotropic radiated power (EIRP) versus frequency, maximum EIRP backoff, gain compression, propagation delay between hand held device and unit transmit antenna, propagation delay between hand held device and unit receive antenna, transmit gain, and receive gain, and any other design specification parameter that hand held device  110  needs to know in order to establish an initial transmit power that will not damage any components in ODU  112 , or will be appropriate to produce desired power levels in the communication system (low interference, high quality). 
     In some embodiments the initial output power for hand held device  110  is set arbitrarily low, such that no other receiver is expected to receive the signal, this assures that the ODU is not overpowered by the output signal. The process of the invention then operates to achieve an important function of setting the output power to a desired (more useful) level as quickly as possible while conforming to any system constraints such as emission levels set by government agencies, or desired interference levels in the communication system. It is generally undesirable to have hand held device  110  or ODU  112  simply start at a very high power level even if that is ultimately what is chosen. 
     In step  608 , it is determined whether or not cradle  108  received the message. If, in step  608 , it is determined that cradle  108  did not receive the message, the processing of the method proceeds to step  610 . If it has been determined in step  608  that cradle  108  received the message, the method proceeds to step  612 . 
     In step  610 , cradle  108  responds to ODU  112  with a data send signal. This alerts ODU  112  to resend the design specification parameter that was sent. After step  610  is complete, processing flow returns to step  606 . 
     In step  612 , cradle  108  responds to ODU  112  with a data OK signal. The data OK signal indicates to ODU  112  that the design specification parameter was received by cradle  108 . 
     In step  614 , it is determined whether or not this is the final design specification parameter. If this is the final design specification parameter, processing proceeds to step  616 . If this is not the final design specification parameter, processing proceeds to step  606  to send the next design specification parameter. 
     In step  616 , ODU  112  goes back into standby mode. In step  618 , cradle  108  sends a message to hand held device  110  that ODU  112  design specification parameters have been acquired. The design specification parameters are used by logic unit  308  to determine limitations needed in the initial transmit power to ensure that components within ODU  112  are not damaged, or appropriate output power levels are achieved. In step  620 , hand held device  110  requests the first message from cradle  108 . 
     In step  622 , hand held device  110  sends a signal (via cradle  108 ) to turn on transmit components  312  in ODU  112 . Logic unit  308  sends a signal to turn on transmit components  312  within ODU  112  so that ODU  112  is ready for transmission of the information signal. HH transmit components  304  control the initial power of the transmit signal so that the signal that is sent does not exceed the power that can be accepted by ODU transmit components  312 . For example, ODU transmit components  312  include a power amplifier. The power amplifier is typically the most expensive component of ODU transmit components  312 . Thus, the present invention ensures that all signals sent to the power amplifier does not exceed the power that it can accept without being damaged. 
     Finally, in step  624 , ODU transmit components  312  are prepared for service. Transmit components  112  are activated or turned on and are ready to transmit the signal. 
     FIG. 7 is a flowchart illustrating the operation of step  208  of FIG. 2, namely the use of a car kit  104  to place or receive a call. Information passes to and from car kit  104  during progress of a call. First, a call is established, then the parties proceed to communicate information, and finally the call is terminated. Information signals containing the information needed for each of these phases of a call pass to and from car kit  104 . The transmit power of the information signals is controlled by hand held device  110  using a power measurement signal obtained from ODU power control components  328  within ODU  112 . 
     The flowchart in FIG. 7 begins with step  704 . In step  704 , HH transmit components  304  send the information signal to ODU  112  via cable  111 . If the information signal is the first information signal of a particular call, the initial power of the information signal has been determined by preliminary processing occurring in step  206  of FIG. 2 performed by HH logic unit  308  using information stored in ODU logic unit  318  (including the design specification parameters in design specification parameter tables  422 ). The preliminary processing is described in more detail above with respect to FIG.  6 . 
     Multiple information signals may be sent during the progress of a call which result in repeated processing of step  208 . That is, a call or communication link, meaning information signals, including access requests for the gateway, may be sent over a period of time and result in repeated adjustments of signal power. If an information signal is not the first information signal of a particular call, the power of the information signal has been determined by previous processing of step  708 . The information signal may include the following types of information: information to establish the call to a recipient, information to be sent from hand held device  110  to a recipient, such as a digitized version of someone&#39;s voice, data transmitted via personal computers, digitized versions of the content on pages transmitted via facsimile, and information to indicate that one of the parties has terminated the call. The information signal may also include information or signals needed to establish or terminate a call following 
     HH transmit components  304  send the information signal to ODU  112 . The signal is received by ODU transmit components  312  within ODU  112 . The circuitry within transmit components  312  needed to transmit the signal from vehicle  106  to satellite  116  resides in ODU  112 . 
     In step  706 , transmit components  312  in ODU  112  transmit the signal to satellite  116  via ODU antenna  114 . ODU antenna  114  is typically physically connected to the top of ODU  112  and contains the capability to transmit signals from vehicle  106  to satellite  116 . When satellite  116  receives the signal from ODU antenna  114 , satellite  116  sends the signal to antenna  118  where it is received and transferred to a recipient via gateway  120 . 
     In step  708 , ODU  112  provides an absolute power measurement to hand held device  110 . As the signal is sent from transmit components  312  to ODU  114 , power detector  314  obtains a measurement of the output power of the information signal. Power detector  314  is connected to the output of transmit components  312  to detect the output power. Because the power measurement is obtained immediately before the information signal is transmitted outside of car kit  104 , it provides an accurate assessment of the impact of circuitry within car kit  104  on the power of the information signal. The power measurement is sent back to hand held device  110  for adjustments in the initial (or subsequent) power of the transmitted signal allowing for accurate power control. Obtaining a digital power estimation will be described in further detail with respect to FIG.  8 . 
     In step  710 , the digital power measurement is modulated by modulator  320 . On off keying, half duplex modulation is used for modulation of the digital power measurement. Modulation of the digital power measurement is needed to transmit the power measurement from ODU  112  to cradle  108  via cable  111 . 
     In step  712 , the power measurement is transmitted to cradle  108 . The modulated power measurement output from modulator  320  is sent to cradle  108  via cable  111 . 
     In step  714 , the power measurement is demodulated in cradle  108 . Demodulator  310  in cradle  108  receives the modulated power measurement from ODU  112  via cable  111 . Demodulator  310  demodulates the signal using demodulation techniques well-known in the art. 
     In step  716 , cradle  108  sends the power measurement to hand held device  110 . Demodulator  310  within cradle  108  sends the power measurement to logic unit  308  within hand held device  110  via the connection between hand held device  110  and cradle  108 . 
     Finally, in step  718 , hand held device  110  adjusts the power of information signals being transmitted. Hand held device  110  provides adjustments needed to the initial transmitted power of the signal to compensate for losses, constraints, or limitations in the circuitry of car kit  104 . Adjustment by hand held device  110  of the power of transmitted information signals is described in further detail with respect to FIG.  9 . 
     FIG. 8 is a detailed flowchart of step  708 , illustrating the operation of obtaining the digital power measurement. The flowchart in FIG. 8 begins with step  804 . 
     In step  804 , power is detected. The power is detected by power detector  314  at the output of ODU transmit components  312  immediately before the signal is transmitted by ODU antenna  114 . 
     In step  806 , the temperature is detected. Temperature detector  316  detects the temperature within ODU  112  using temperature detection techniques well-known in the art. Temperature is detected because the performance of many power detector models, including the Schottky power detector, varies based on temperature. 
     In step  808 , the power and temperature signals are multiplexed. The power and temperature signals are multiplexed by multiplexer  402  in order to provide one multiplexed signal to A/D converter  404 . 
     In step  810 , the multiplexed power and temperature signals are converted to digital signals. A/D converter  404  converts the multiplexed signal comprising the power and temperature measurements to digital format. 
     In step  812 , the temperature measurement is converted from an 8-bit voltage value to an 8-bit temperature value. The input of temperature look-up table  406  is an 8-bit voltage  411  received from A/D converter  404 . In the present embodiment, processing of the temperature look-up table  406  results in an 8-bit temperature. However, the process is not limited to nor dependent upon using 8-bit values or data words. The various digital systems or processing techniques illustrated herein do not depend on using digital words or data values of the specific lengths given herein. These digital values or words are given by way of example only, and the technique can be implemented using digital values with other data resolutions, that is, longer or shorter words, within the teachings of the invention, as desired. 
     In step  814 , the power measurement is converted from an 8-bit voltage to an 8-bit log. In addition to sending an 8-bit voltage, A/D converter  404  sends a 10-bit voltage to the logarithmic transformation table  410 . Processing of logarithmic transformation table  410  results in an 8-bit log voltage. 
     Finally, in step  816 , a resulting estimated power is determined that is a 10-bit power estimation. Both the 8-bit temperature from temperature look-up table  406  and the 8-bit log voltage from logarithmic transformation table  410  are received and processed by power estimator  408 . Power estimator  408  uses the 8-bit temperature and 8-bit log and produces the 10-bit power estimation. The 10-bit power estimation is formatted according to the protocol shown m FIG.  10  and sent to modulator  320 . 
     FIG. 9 is a detailed flowchart of step  718 , illustrating the operation of adjusting the transmit power by hand held device  110 . The flowchart in FIG. 9 begins with step  904 . 
     In step  904 , logic unit  308  receives the demodulated power measurement. 
     In step  906 , hand held device  110  determines whether or not an adjustment in transmit power is needed. An adjustment in power may be needed because hand held device  110  needs to vary the power in conjunction with maintaining a desired communication link quality or signal strength, and/or because the output power from ODU  112  is different from the power of the signal transmitted from hand held device  110 . Often adjustments are needed both to change the desired power and compensate for error or differences in the transmission via ODU  112 . The power of the signals transmitted from hand held device  110  varies based on the data rate of the information. Varying data rate occurs when variable rate vocoders, specialized equipment, or other known input devices are used for creating the information signal. 
     Logic unit  308  compares the current initial transmit power to the power measurement received from ODU  112 . A calculation of difference of the power measurement received from ODU  112  subtracted from the current initial transmit power from HH transmit components  304  provides an error measurement. A calculation is then made using the error measurement and the desired next power to be transmitted from transmit components  304 . 
     If an adjustment in transmit power is needed, the processing proceeds to step  908 . If an adjustment in transmit power is not needed, the processing flow of FIG. 9 is completed. 
     In step  908 , transmit components  304  adjust the power of the transmitted signal. 
     FIG. 10 illustrates car kit communications protocol  1002 . FIG. 10 provides the timing of design specification parameter, power, and temperature data sent from ODU  112  to cradle  108  according to one embodiment of the present invention. The packet length for sending parameter data  1004  is longer and supports error checking. The packet length for sending power data  1006  is shorter and faster but has parity for primitive error detection. 
     In addition, the timing for sending data  1008  from cradle  108  to ODU  112  is illustrated. Messages are not required to be sent from cradle  108  to ODU  112  for operation of the present invention. However, in one embodiment of the present invention, messages are sent in order to assist in ODU  112  communication. In order to send messages from cradle  108  to ODU  112 , cradle  108  has a modulator (not shown) and ODU  112  has a demodulator (not shown). On off keying type modulation is typically used for transmission from cradle  108  to ODU  112 . 
     Data send and data OK messages sent from cradle  108  to ODU  112  inform ODU  112  that it should send design specification parameter data and acknowledge that design specification parameter data has been sent. If a checksum error occurs when design specification parameter data is being transmitted, cradle  108  retransmits the previous design specification parameter. A transmit components on/off message indicates that transmit components  312  are to turn on or off, respectively. Alternatively, the message may be a power amplifier on/off message indicating that a power amplifier within transmit components  312  should be turned on or off. A bias hi/lo message indicates to ODU  112  that a power amplifier should be switched to high/low bias depending on emission (signal strength) requirements, or desired constraints. Each message is repeated at least twice in succession to be recognized and provide rudimentary error checking. Other numbers of repetitive transfers could be used, as well as pre-selected spacing between transfers. 
     The process of how processor  501  in hand held device  110  utilizes the design specification parameters to adapt to the particular ODU  112  is now described in reference to FIG.  11 . The flowchart in FIG. 11 begins with step  1104 . In step  1104 , processor  501  accepts the first design specification parameter from ODU  112  via cradle  108  as described above in reference to FIG.  6 . An example communications protocol for the design specification parameters was described above in reference to FIG.  10 . In step  1106 , processor  501  assigns, generally using software, the value of the design specification parameter that was passed to a corresponding software variable. 
     In step  1108 , it is determined whether or not this is the final design specification parameter. If this is the final design specification parameter, the processing flow of FIG. 11 ends. If this is not the final design specification parameter, processing proceeds to step  1104  to receive the next design specification parameter. This continues until processor  501  has received all of the design specification parameters and the variables have all been initialized to a value. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.