WO1995021386A1

WO1995021386A1 - Handheld gps/dgps receiver/computer

Info

Publication number: WO1995021386A1
Application number: PCT/US1995/001435
Authority: WO
Inventors: David R. Gildea; James M. Janky
Original assignee: Trimble Navigation
Priority date: 1994-02-02
Filing date: 1995-02-02
Publication date: 1995-08-10

Abstract

A handheld GPS/DGPS receiver/computer apparatus to receive Global Positioning System (GPS) signals having GPS information for determining a GPS-derived location, to receive a differential GPS (DGPS) radiowave signal having differential GPS (DGPS) information for correcting the GPS-derived location, and to display a differentially corrected GPS (DGPS) location. Five embodiments are disclosed. In a first embodiment, a GPS receiver, a DGPS receiver, and a display are built into a handheld apparatus. The GPS receiver is differential-ready to compute the DGPS location. In a second embodiment, a DGPS receiver is built onto a PCMCIA card that inserts into a PCMCIA computer. The PCMCIA computer includes the differential-ready GPS receiver. In a third embodiment, the differential-ready GPS receiver and the DGPS receiver are built onto PCMCIA cards. The PCMCIA computer passes the DGPS information from the DGPS receiver to the differential-ready GPS receiver. In a fourth embodiment, the GPS and DGPS receivers are built onto PCMCIA cards. The PCMCIA computer is differential-ready. In a fifth embodiment, a GPS frequency downconverter and the DGPS receiver are built onto PCMCIA cards. The PCMCIA computer processes the down converted GPS signal and is differential-ready to compute the DGPS location.

Description

HA DHELD GPS/DGPS RECEIVER/COMPUTER

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to Global Positioning System and more specifically to Global Positioning System and Differential Global Positioning System receivers.

Description of the Prior Art

Global Positioning System (GPS) is a navigation and position service offering worldwide 24 hour coverage. The GPS comprises GPS satellites to broadcast GPS satellite signals, control stations to monitor and control the satellites, and a GPS receiver. The GPS receiver demodulates the GPS satellite signals, decodes a pseudorange for each satellite that it receives, and calculates a GPS position and time of observation based upon these pseudoranges. A GPS antenna that is a part of the GPS receiver must be in line of sight with the satellites for the receiver to receive the GPS satellite signals.

GPS receivers are now used for many applications requiring accurate position and time. The inherent accuracy of the GPS position measured by a commercial GPS receiver is approximately 20 meters. However, the United States Government currently degrades the accuracy of GPS positions for commercial users with Selective Availability, SA. With SA the GPS position accuracy of a commercial GPS receiver is approximately 100 meters.

Differential Global Positioning System (DGPS) is a service for enhancing the accuracy of the GPS position. The' DGPS comprises the Global Positioning System together with a GPS reference station receiver situated at a known position. DGPS error correction information is derived by taking the difference between the measurements made by the GPS reference station and the expected measurement at the known position of the reference station. DGPS error correction information can be in the form of GPS satellite pseudorange offsets or GPS position offsets. If GPS position offsets are used the GPS satelhtes used in the calculation of the GPS position must be included as part of the DGPS error correction information. A processor in a "differential-ready" GPS receiver applies the DGPS error correction information to enhance the GPS position to an accuracy in the range of 10 meters to a few millimeters.

Two types of DGPS exist, postprocessed and realtime. In postprocessed systems the DGPS error correction information and a user's GPS position information are processed after the user has completed his application. In realtime systems the DGPS error correction information is transmitted to the GPS user in a DGPS radiowave signal and processed by a differential-ready GPS receiver as the application progresses. Realtime processing is desirable for many applications because the enhanced accuracy of DGPS is available to the GPS user while he is working in the field. Realtime broadcast of DGPS error correction information is available from many sources, both public and private, including Coast Guard RDF beacon and commercially operated FM broadcast subcarrier. The DGPS radiowave signal is an electromagnetic signal containing DGPS error correction information transmitted by the Coast Guard DGPS network, by FM broadcast subcarrier signals, by cellular telephone control signals, by cellular telephone on the voice, and by other suitable terrestrial and satellite systems. The DGPS radiowave signal may be modulated onto a radiowave carrier or subcarrier using frequency, phase, amplitude, single side band, digital, BPSK, QPSK, FSK, MSK, or any other modulation suitable for radiowave communications. A DGPS radiowave receiver is required to receive the DGPS radiowave signal containing the DGPS error correction information and pass the DGPS error corrections to the differential-ready GPS receiver. The DGPS error correction information may use the format o RTCM Special Committee 104 (SC104) messages as described in the RTC Recommended Standards for Differential Navstar GPS Service, Version 2. Type 1 and type 9 messages contains GPS satellite pseudorange error correction information. A total of 63 messages many of which are yet undefined are allowed within the standard. Data transfers use RS232 or

RS422, most significant bit first, asynchronous communication. A full duple receivers is called for in the standard but is not required for broadcast reception.

Many applications of GPS including mineral surveying, mapping, adding attributes or features to maps, finding sites on a map, vehicle navigation, marine navigation, field asset management, geographical information systems, and others require the enhanced accuracy that is available with DGPS. For instance, a 20 to 100 meter error could lead to unintentional trespassing, make the return to an underground asset difficult, or put a user on the wrong block while walking or driving in a city.

These apphcations require a computer to store and process data, retain databases, perform calculations, display information to a user, and take input from a user entry. For instance the user may need to store a map database, display a map, add attributes to features on the map, and store these attributes for geographical information. Or he may need to store and display locations or calculate range and bearing to another location.

These apphcations sometimes require that the equipment be carried about by an individual user. For instance, a utility field worker, insurance claims adjuster, rancher, prospector, and other outdoor workers will operate at least some of the time operate on foot. In apphcations such as marine navigation in which the eqmpment could be hard mounted, the navigator will often want to take his personal navigation equipment with him when he changes boats. In such apphcations cables and external connections are often a point of failure and equipment consisting of multiple packages is awkward to carry and takes time to assemble and disassemble. The fewest possible cables, external connections, and packages are desirable or required for efficient operation. A single, handheld package with no cables is highly desirable.

General purpose computers that use standard operating systems such as DOS or Windows are commercially available as handhelds using the names laptop, notebook, sub notebook, palmtop, penpad, and others. Specialized computers for GPS apphcations that use their own specialized operating systems, are commercially available in handheld form. Both general purpose and specialized computers use a variety of interfaces including Personal Computer Memory Card International Association (PCMCIA) and parallel or serial TTL level buses through which GPS capability can be integrated. The actual hardware containing the added GPS capability can be external as in the case of PCMCIA or internal as in the case of commercial, handheld GPS receivers.

A PCMCIA interface is one method in which external hardware GPS may be integrated into a handheld computer that accepts cards built to the PCMCIA standard. The PCMCIA standard calls for a card approximately 85.6 mm by 54 mm with 68 electrical socket connections in two rows of 34 on each row on 1.27 mm centers to fit into a slot in a host computer or other electrical device. Three card types are used that have differing thicknesses, type I is approximately 3.3 mm, type II is approximately 5 mm, and type III is approximately 10 mm. Types I and π are described in the release 2.0 PCMCIA standard while type in is commonly known but is not contained within the version 2 standard. The PCMCIA bus comprises up to 26 address lines, up to 16 data lines, power at 3.3, 5, 12 volts, ground, enables, protects, ready/busy, interrupt request, IO, refresh, reset, register select, battery voltage detects, card detect, wait, audio digital wave form, and card status changed lines. Additional capabilities are available through lines that are reserved or undefined or by redefining existing lines. Not all lines will be used or supported by any one PCMCIA compatible host or card. Commercial, handheld GPS receivers are available on the open market from many manufacturers. These GPS receivers are specialized computers with integrated GPS hardware. General purpose computers have also been demonstrated that integrate GPS hardware internally.

Workers in other technical areas have developed some related technology. Urbish et al. in U.S. Patent No. 4,894,663 disclose a very thin radio housing having a printed circuit loop antenna mounted in a plane on an interior wall of the housing. The housing opens as a notebook would open, to disclose the antenna, a portion of the antenna electronics, and a portion of the antenna circuit located on a hinge that facilitates opening and closing the housing. The antenna, electronics, and housing are intended to serve as a credit card size pager signal receiver or other signal receiving system.

Mori et al. in U.S. Patent No. 4,935,745 disclose a credit card size radio receiver with slot antenna integrated as a part of the receiver housing. Three contiguous sides of the card housing serve together as the antenna. An RF frequency circuit (not shown) receives and processes the incoming radio signals and is carried by the housing. The apparatus is intended to serve as a credit card size page signal receiver.

Ushiyama et al. in U.S. Patent No. 5,054,120 disclose a credit card size radio page signal receiver with a portion of the receiver housing serving as an antenna. Top and bottom walls of the housing serve as a part of a loop antenna that can handle VHF signals. The antenna is not defined by any particular circuit integrated with the housing. Raubenheimer et al in U.S. Patent No. 5,059,970 disclose a handheld navigational aid, including a keyboard for data entry, a visual display and a loudspeaker for audible communication. The visual display presents a small map of a chosen region, and the map provides two cursors to indicate and determine the distance between two points on the map. An icon indicates the position of a chosen marine or airborne vessel on the map, and present position relative to a fixed point is visually displayed as distance/bearing or as latitude/longitude coordinates in a two dimensional representation. The apparatus contains a microprocessor and stored on board algorithms and mathematical equations for signal processing purposes and relies upon a resettable internal clock for certain display purposes. Input signals appear to be entered through the keyboard.

Yorimoto et al. in U.S. Patent No. 4,748,320 disclose an IC card having a CPU, EEPROM data memory and program memory, RAM, and an I/O port to receive processing instructions from, and pass processed information to, a separate card reader terminal to which the card may be connected. Data memory is divided into a plurality of sectors with different functions, and an internal error detection program detects whether any particular data memory address is defective.

Boston in U.S. Patent No. 4,766,293 discloses a foreign currency financial transaction IC card. The card contains a keypad for entry of the proposed foreign currency purchase and the cardholder's PIN, a plurality of special function key indicating the nature of the transaction, a numerical display of the transaction amount in the cardholder's "own" currency, a microprocessor, ROM program memory, RAM, EEPROM data memory, and a power supply. The card indicates whether the amount of the proposed purchase or other transaction exceeds the cardholder's credit limit at the time of each proposed transaction. This card is self-contained and does not interface with any card reader.

Aldous et al. in U.S. Patent No. 5,183,404 disclose systems for physical connection of communication cards to computers. The mechanical connection system improves the robustness of the standard PCMCIA connection.

Some related technology has been developed by workers in DGPS. Hatch in U.S. Patent 4,812,991 and Allison in U.S. Patent No. 5,148,179 disclose methods and apparatuses for accurately deteimining the relative positions of two or more radio signal receivers located on or above the earth's surface using the differences in measured pseudoranges from common satelhtes. One receiver remains fixed, while one or more are rovers.

Barnard in U.S. Patent No. 5,119,102 discloses a vehicle location system in which a mobile unit receives the GPS signals from the GPS satelhtes and then re-transmits a segment of the GPS signals to a base station. The base station receives the signals transmitted from the mobile units and also receives the GPS signals. The base station then calculates the location of the vehicles.

Mauney et al. in U.S. Patent No. 5,214,757 discloses an interactive transportable mapping system including a GPS receiver and a computer for creating maps or annotating existing map using a structured, geographical information system, GIS, database. Attributes related with a location may be entered in real-time and associated with the GIS database either in real-time or subsequently.

None of the prior art shows the possibility of integrating a DGPS receiver with a computer and differential-ready GPS receiver in a single or handheld package that is convenient for an individual to cany about for use in apphcations such as mineral surveying, mapping, adding attributes or features to maps, finding sites on a map, vehicle navigation, marine navigation, field asset management, and geographical information systems. In these mobile apphcations, it is inconvenient to lug about, assemble, and disassemble multiple boxes and cables. Further, cables and their connections are undesirable because they are prone to breakage. What is needed is an apparatus that combines a computer, a differential-ready GPS receiver, and a DGPS receiver in a single, handheld package.

SUMMARY OF THE PRESENT INVENTION

These needs are met by the invention which provides a handheld

GPS DGPS receiver/computer apparatus comprising a GPS antenna, positioned to receive GPS signals from one or more GPS satellites, with each signal being characteristic of a particular satellite source; a GPS frequency downconverter to down convert the primary frequency of the GPS signal to a selected lower frequency; a DGPS antenna to receive DGPS radiowave signals from a radiowave source of DGPS enor corrections; a DGPS radiowave receiver to demodulate and decode the DGPS radiowave signals passed from the DGPS radiowave antenna and to pass the DGPS error correction information to a "differential-ready" processing system; a key entry (optional) to allow a GPS user to send information to the processing system; a display to output information to the GPS user; and a power source to supply power to at least one of the elements of the apparatus. The differential-ready processing system includes a GPS processor that demodulates and decodes the selected lower frequency of the GPS signal to provide the GPS pseudoranges and/or GPS position and time of observation, and a computer processor that receives key entries (optional), operates an application, stores data, and issues outputs to a display. Either the GPS processor or the computer processor is differential-ready meaning that it can apply the DGPS error correction information to the GPS pseudoranges or to the GPS position and the satelhtes used in the GPS position in order to enhance the accuracy of the GPS position. A first embodiment of the apparatus includes a GPS antenna, a GPS frequency downconverter, a differential-ready processing system, a DGPS radiowave signal antenna, a DGPS radiowave receiver, a key entry, a display, and a power supply in a handheld package.

A second embodiment includes a GPS antenna, a GPS frequency downconverter, a differential-ready processing system, a key entry, a display, a PCMCIA interface, and a power supply in a host package; and a DGPS radiowave signal antenna, a DGPS radiowave receiver, and a PCMCIA interface in a PCMCIA card package.

A third embodiment includes a computer processor, a key entry, a display, two PCMCIA interfaces, and a power supply in a host package; a GPS antenna, a GPS frequency downconverter, a differential-ready GPS processor, and a PCMCIA interface in a PCMCIA card; and a DGPS radiowave signal antenna, a DGPS radiowave receiver, and a PCMCIA interface in a second PCMCIA card.

A fourth embodiment includes a differential-ready computer processor, a key entry, a display, two PCMCIA interfaces, and a power supply in a host package; a GPS antenna, a GPS frequency downconverter,

GPS processor, and a PCMCIA interface in a PCMCIA card package; and a

DGPS radiowave signal antenna, a DGPS radiowave receiver, and a

PCMCIA interface in a second PCMCIA card package.

A fifth embodiment includes a differential-ready GPS/computer, a key entry, a display, two PCMCIA interfaces, and a power supply in a host package; a GPS antenna, a GPS frequency downconverter, and a PCMCIA interface in a PCMCIA card package; and a DGPS radiowave signal antenn a DGPS radiowave receiver, and a PCMCIA interface in a second PCMCIA card package. In embodiments 2, 3, 4, and 5 the PCMCIA card or cards insert into the host package to give the appearance and convenience of a single handhel package.

IN THE DRAWINGS

Figure 1 is a block diagram of a first embodiment of the present invention of a handheld GPS/DGPS receiver/computer;

Figure 2 is a block diagram of a second embodiment of the present invention of a handheld GPS/DGPS receiver/computer; Figure 3 is a block diagram of a third embodiment of the present invention of a handheld GPS/DGPS receiver/computer;

Figure 4 is a block diagram of a fourth embodiment of the present invention of a handheld GPS DGPS receiver/computer;

Figure 5 is a block diagram of a fifth embodiment of the present invention of a handheld GPS/DGPS receiver/computer;

Figure 6a is a front elevation view of the first embodiment described in

Figure 1;

Figure 6b is a right side sectional view of the first embodiment described in Figure 1 ;

Figure 7 is a perspective view of the second embodiment described in Figure 2; and

Figure 8 is a perspective view of the third, fourth, and fifth embodiments described in Figures 3, 4, and 5, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 illustrates a first embodiment of a handheld GPS/DGPS receiver/computer apparatus of the present invention referred to by the general reference number 10. The apparatus 10 includes a GPS antenna 13 positioned to receive GPS satellite signals from one or more GPS satellites, where each GPS satellite issues a distinct GPS satellite signal, and to issue a responsive conducted antenna output signal to a GPS frequency downconverter 14. Typically, the GPS antenna 13 includes a pre-amplifier to provide an amplified antenna output signal. Optionally, the GPS antenna 13 may be electrically connected to the GPS frequency downconverter 14 by a cable of up to 15 meters, thereby allowing the GPS antenna 13 to be housed in a second package and placed at a distance of the length of the cable from a first package containing the GPS frequency downconverter 14 and the other elements of the apparatus 10. The GPS frequency downconverter 14 down converts the frequency of the antenna output signal to a selected lower frequency and issues a GPS low frequency (LF) signal to a differential-ready processing system 15. A DGPS radiowave signal antenna 11 receives a DGPS radiowave signal, including DGPS error correction information, and issues a responsive DGPS antenna output signal to a DGPS radiowave receiver 12. Several sources of DGPS radiowave signals are available, including the United States Coast Guard RDF beacon signals and commercially operated FM broadcast subcarrier signals. The DGPS radiowave receiver 12 demodulates and decodes the DGPS antenna output signal and issues the DGPS error correction information in a DGPS data signal to the differential-ready processing system 15.

A display 17 receives a display signal including user output information from the differential-ready processing system 15 and provides a responsive display in a form that is visibly and/or audibly perceptible to a human user. In the preferred embodiment, the display 17 is a liquid crystal display (LCD) to display the user output information visually. A speaker may be used to display the user output information as sound. A key entry 19 receives user input information from a human user and issues a responsive user input signal to the differential-ready processing system 15. In the preferred embodiment, the key entry 19 is a key switch to provide the user input signal in response t a touch or a press by the user. Alternatively, the key entry 19 may be constructed of a touch screen on the display 17 or of an audio microphone. I some instances, the differential-ready processing system 15 may be programmed so that no key entry 19 is required.

The differential-ready processing system 15 includes a microprocessor and an electronic memory including program instructions for executing an application. The system 15 operates in a conventional manner to store and retrieve variable data, perform calculations, and input and output signals to other devices including the display 17, the key entry 19, and other processing systems according to the program instructions and variable data. The differential-ready processing system 15 includes a GPS processing capability for demodulating and decoding the GPS LF signal to provide GPS location information of the GPS satellite pseudoranges, GPS position, and time of observation and an application processing capability for receiving the user input signal, processing the user input information and the GPS location information according to an application program and issuing the display signal to the display 17. The GPS processing capability and the application processing capability may be implemented in a single microprocessor and an associated memory or in two separate microprocessors each with an associated memory. Where two microprocessors are used, either may perform the differential-ready capability of applying the DGPS error correction information to enhance the accuracy of the GPS position information. A power supply 18 supplies power to the GPS antenna 13, the GPS frequency downconverter 14, the DGPS radiowave antenna 11, the DGPS radiowave receiver 12, the display 17, and key entry 19, and the differential-ready processing system 15.

Figure 2 illustrates a second embodiment of a handheld GPS/DGPS receiver/computer apparatus of the present invention referred to by the general reference number 20. The apparatus 20 includes a host PCMCIA differential-ready GPS receiver/computer 20B and a DGPS PCMCIA card 20A. The DGPS PCMCIA card 20A inserts into a slot in the host PCMCIA differential-ready GPS receiver/computer 20B. The DGPS PCMCIA card 20A includes a DGPS radiowave signal antenna 21, a DGPS radiowave receiver 22, and a PCMCIA interface 23 A. The DGPS radiowave signal antenna 21 receives a DGPS radiowave signal, including DGPS error correction information, and issues a responsive DGPS antenna output signal to the DGPS radiowave receiver 22. The DGPS radiowave signal antenna 21 can be mounted on the DGPS PCMCIA card 20A or electrically connected to the DGPS PCMCIA card 20A through a cable and mounted elsewhere. Several sources of DGPS radiowave signals are available, including the United States Coast Guard RDF beacon signals and commercially operated FM broadcast subcarrier signals. The DGPS radiowave receiver 22 demodulates and decodes the DGPS antenna output signal and issues the DGPS error correction information in a data signal to the PCMCIA interface 23A. The PCMCIA interface 23A formats the data signal according to the PCMCIA standard as documented by the publication PCMCIA. Personal Computer Memory Card International Association. PC Card Standard. Release 2.0. published in September. 1991 by the Personal Computer Memory Card International Association, Sunnyvale, California, and issues a PCMCIA DGPS data signal to the host PCMCIA differential- ready GPS receiver/computer 20B. The PCMCIA interface 23 A may be included in the DGPS radiowave receiver 22.

The host PCMCIA differential-ready GPS receiver/computer 20B includes a GPS antenna 24 positioned to receive GPS satellite signals from one or more GPS satellites, where each GPS satellite issues a distinct GPS satellite signal, and to issue a responsive conducted antenna output signal to a GPS frequency downconverter 25. Typically, the GPS antenna 24 includes a pre-amplifier to provide an amplified antenna output signal. Optionally, the GPS antenna 24 may be electrically connected to the GPS frequency downconverter 25 by a cable of up to 15 meters, thereby allowing the GPS antenna 24 to be housed in a second package and placed at a distance of the length of the cable from a first package containing the GPS frequency downconverter 25 and the other elements of the host PCMCIA differential- ready GPS receiver/computer 20B. The GPS frequency downconverter 25 down converts the frequency of the antenna output signal to a selected lower frequency and issues a GPS low frequency (LF) signal to a differential-ready processing system 26. A PCMCIA interface 23B receives inputs from, and transmits outputs to, cards that conform to the PCMCIA standard. The PCMCIA interface 23B may be included in the differential-ready processing system 26.

A display 28 receives user output information in a display signal from the differential-ready processing system 26 and displays the user output information for an application in a form that is visibly and/or audibly perceptible to a human user. In the preferred embodiment, the display 28 is a liquid crystal display (LCD) to display the user output information visually. A speaker may be used to display the user output information as sound. A key entry 101 receives user input information from a human user and issues a responsive user input signal to the differential-ready processing system 26. In the preferred embodiment, the key entry 101 is a key switch providing the user input signal in response to a touch or a press by the user. Alternatively, the key entry 19 may be constructed of a touch screen on the display 28 or of an audio microphone. In some instances, the differential-ready processing system 26 may be programmed so that no key entry 101 is required.

The differential-ready processing system 26, includes a microprocessor and an electronic memory including program instructions for executing an application. The system 26 operates in a conventional manner to store and retrieve variable data, perform calculations, and input and output signals to other devices including the display 28, the key entry 101, and other processing systems according to the program instructions and variable data. The differential-ready processing system 26 includes a GPS processing capability for demodulating and decoding the GPS LF signal to provide GPS location information of the GPS satellite pseudoranges, GPS position, and time of observation and an application processing capability for receiving the user input signal, processing the user input information and the GPS location information according to an application program and issuing the display signal to the display 28. The GPS processing capability and the computer processing capability may be implemented in a single microprocessor and an associated memory or in multiple separate microprocessors each with an associated memory. Where two microprocessors are used, either may perform the differential-ready capability of applyirς the DGPS error correction information to enhance the accuracy of the GPS position information. The PCMCIA interface 23B may be included in the differential- ready processing system 26. A power supply 29 supplies power to the GPS antenna 24, the GPS frequency downconverter 25, the DGPS PCMCIA card 20A, the PCMCIA interface 23B, the display 28, the key entry 101, and the differential-ready processing system 26.

Figure 3 illustrates a third embodiment of a handheld GPS/DGPS receiver/computer apparatus of the present invention referred to by the general reference number 30. The apparatus 30 includes a differential-ready GPS PCMCIA card 30B, a DGPS PCMCIA card 30A, and a host PCMCIA computer 30C. The differential-ready GPS PCMCIA card 30B and the DGPS PCMCIA card 30A insert into slots in the host PCMCIA computer 30C.

A DGPS PCMCIA card 30A includes a DGPS radiowave signal antenna 31, a DGPS radiowave receiver 32, and a PCMCIA interface 33 A. The DGPS radiowave signal antenna 31 receives a DGPS radiowave signal, including DGPS error correction information, and issues a responsive DGPS antenna output signal to the DGPS radiowave receiver 32. The DGPS radiowave signal antenna 31 can be mounted on the DGPS PCMCIA card 30A or electrically connected to the DGPS PCMCIA card 30A through a cable and mounted elsewhere. Several sources of DGPS radiowave signals are available, including the United States Coast Guard RDF beacon signals and commercially operated FM broadcast subcarrier signals. The DGPS radiowave receiver 32 demodulates and decodes the DGPS antenna output signal and issues the DGPS error correction information in a DGPS data signal to the PCMCIA interface 33A. The PCMCIA interface 33A formats the DGPS data signal according to the PCMCIA standard as documented by the publication PCMCIA. Personal Computer Memory Card International Association. PC Card Standard. Release 2.0. published in September. 1991 by the Personal Computer Memory Card International Association, Sunnyvale, California, and issues a PCMCIA DGPS data signal to the host PCMCIA computer 30C. The PCMCIA interface 33A may be included in the DGPS radiowave receiver 32.

The differential-ready GPS PCMCIA card 30B includes a PCMCIA interface 33B that receives inputs from, and transmits outputs to, hosts that conform to the PCMCIA standard, a GPS antenna 34 positioned to receive GPS satellite signals from one or more GPS satelhtes, where each GPS satellite issues a distinct GPS satellite signal, and to issue a responsive conducted antenna output signal to a GPS frequency downconverter 35. Typically, the GPS antenna 34 includes a pre-amphfier to amplify the antenna output signal. Optionally, the GPS antenna 34 may be electrically connected to the GPS frequency downconverter 35 by a cable of up to 15 meters, thereby allowing the GPS antenna 34 to be housed in a separate package and placed at a distance of the length of the cable from a PCMCIA card package containing the GPS frequency downconverter 35 and the other elements of the differential-ready GPS PCMCIA card 30B. The GPS frequency downconverter 35 down converts the frequency of the antenna output signal to a selected lower frequency and issues a GPS low frequency (LF) signal to a differential-ready GPS processor 36. The differential-ready GPS processor 36, includes a microprocessor and an electronic memory including program instructions and variable data. The processor 36 operates in a conventional manner to store and retrieve the variable data, perform calculations, and input and output signals to other devices and processing systems according to the program instructions and variable data. The differential-ready GPS processo 36 demodulates and decodes the GPS LF signal, calculates the GPS satellite pseudoranges, GPS position, and time of observation, receives DGPS error correction information through the PCMCIA interface 33B from the host PCMCIA computer 30C, applies DGPS error correction information to enhance the accuracy of the GPS position, and issues the enhanced GPS position in a DGPS location data signal through a PCMCIA interface 33B to the host PCMCIA computer 30C. The PCMCIA interface 33B may be included in the differential-ready GPS processor 36.

The host PCMCIA computer 30C includes two PCMCIA interfaces 33C and 33D to receive inputs from and transmit outputs to cards that conform to the PCMCIA standard. A computer processor 38 passes the DGPS error correction information from the DGPS PCMCIA card 30A to the differential-ready GPS PCMCIA card 30B and receives the enhanced GPS position back from the differential-ready GPS PCMCIA card 30B. A display

37 receives user output information in a display signal from the computer processor 38 and displays the user output information in a form that is visibly and/or audibly perceptible to a human user. In the preferred embodiment, the display 37 is a liquid crystal display (LCD) to display the user output information visually. A speaker may be used to display the user output information as sound. A key entry 103 receives user input information from a human user and issues a responsive user input signal to the computer processor 38. In the preferred embodiment, the key entry 103 is a key switch providing the user input signal in response to a touch or a press by the user. Alternatively, the key entry 103 may be constructed of a touch screen on the display 37 or of an audio microphone. In some instances, the computer processor 38 may be programmed so that no key entry 103 is required. The computer processor 38, includes a microprocessor and an electronic memory including program instructions for executing an application. The processor

38 operates in a conventional manner to store and retrieve variable data, perform calculations, and input and output signals to other devices including the display 37, the key entry 103, and other processing systems according to the program instructions and variable data. The PCMCIA interfaces 33 C and 33D may be included in the computer processor 38. A power supply 39 supplies power to the DGPS PCMCIA card 30A, the differential-ready GPS PCMCIA card 30B, the PCMCIA interfaces 33C and 33D, the display 37, the key entry 103, and the computer processor 38.

Figure 4 illustrates a fourth embodiment of a handheld GPS/DGPS receiver/computer apparatus of the present invention refened to by the general reference number 40. The apparatus 40 includes a GPS PCMCIA card 40B, a DGPS PCMCIA card 40A, and a host PCMCIA differential- ready computer 40C. The GPS PCMCIA card 40B and the DGPS PCMCIA card 40A insert into slots in the host PCMCIA differential-ready computer 40C. The DGPS PCMCIA card 40A includes a DGPS radiowave signal antenna 41, a DGPS radiowave receiver 42, and a PCMCIA interface 43 A. The DGPS radiowave signal antenna 41 receives a DGPS radiowave signal, including DGPS error correction information, and issues a responsive DGPS antenna output signal to the DGPS radiowave receiver 42. The DGPS radiowave signal antenna 41 can be mounted on the DGPS PCMCIA card 40A or electrically connected to the DGPS PCMCIA card 40A through a cable and mounted elsewhere. Several sources of DGPS radiowave signals are available, including the United States Coast Guard RDF beacon signals and commercially operated FM broadcast subcarrier signals. The DGPS radiowave receiver 42 demodulates and decodes the DGPS antenna output signal and issues the DGPS error correction information in a DGPS data signal to the PCMCIA interface 43A. The PCMCIA interface 43A formats the DGPS data signal according to the PCMCIA standard as documented by the publication PCMCIA. Personal Computer Memory Card International Association. PC Card Standard. Release 2.0. published in September. 1991 by the Personal Computer Memory Card International Association, Sunnyvale, California, and issues a PCMCIA DGPS data signal to the host PCMCIA computer 40C. The PCMCIA interface 43A may be included in the DGPS radiowave receiver 42.

The GPS PCMCIA card 40B includes a PCMCIA interface 43B which receives inputs from, and transmits outputs to, hosts that conform to the PCMCIA standard, a GPS antenna 44 positioned to receive GPS satellite signals from one or more GPS satellites, where each GPS satellite issues a distinct GPS satellite signal, and to issue a responsive conducted antenna output signal to a GPS frequency downconverter 45. Typically, the GPS antenna 44 includes a pre-amplifier to amplify the antenna output signal. Optionally, the GPS antenna 44 may be electrically connected to the GPS frequency downconverter 45 by a cable of up to 15 meters, thereby allowing the GPS antenna 44 to be housed in a separate package and placed at a distance of the length of the cable from a PCMCIA card package containing the GPS frequency downconverter 45. The GPS frequency downconverter 45 down converts the frequency of the antenna output signal to a selected lower frequency and issues a GPS low frequency (LF) signal to a GPS processor 46. The GPS processor 46, includes a microprocessor and an electronic memory including program instructions and variable data. The processor 46 operates in a conventional manner to store and retrieve variable data, perform calculations, and input and output signals to other devices and processing systems according to the program instructions and variable data. The GPS processor 46 demodulates and decodes the GPS LF signal, calculates GPS location information of the GPS satelhte pseudoranges, the present position o the GPS antenna, and time of observation, and issues the GPS location information in a GPS location signal. The GPS location signal is formatted by the PCMCIA interface 43B according to the PCMCIA standard as documented by the publication PCMCIA. Personal Computer Memory Card International Association. PC Card Standard. Release 2.0. published in September. 1991 by the Personal Computer Memory Card International Association, Sunnyvale, California, and issued to the host PCMCIA differential-ready computer 40C. The PCMCIA interface 43B may be included in the GPS processor 46.

The host PCMCIA differential-ready computer 40C includes two PCMCIA interfaces 43C and 43D to receive inputs from, and transmit outputs to, cards that conform to the PCMCIA standard and a differential- ready computer processor 48. The differential-ready computer processor 48, includes a microprocessor and an electronic memory including program instructions and variable data. The processor 48 operates in a conventional manner to store and retrieve data for an application, perform calculations, and input and output signals to other devices and processing systems according to the program instructions and variable data. The differential-ready computer processor 48 receives the GPS satelhte pseudoranges, the GPS position, and the time of observation through PCMCIA interface 43 C from the GPS PCMCIA card 40B, receives the DGPS error correction information through the PCMCIA interface 43D from the DGPS PCMCIA card, applies the DGPS error correction information to enhance the accuracy of the GPS position or the GPS pseudoranges, and provides the enhanced GPS position as user output information in a display signal. A display 47 receives the display signal and displays the user output information in a form that is visibl and/or audibly perceptible to a human user. In the preferred embodiment, the display 47 is a liquid crystal display (LCD) to display the user output information visually. A speaker may be used to display the user output information as sound. A key entry 104 receives user input information from a human user and issues a responsive user input signal to the differential-ready computer processor 48. In the preferred embodiment, the key entry 104 is a key switch providing the user input signal in response to a touch or a press by the user. Alternatively, the key entry 104 may be constructed of a touch screen on the display 47 or of an audio microphone. In some instances, the differential-ready computer processor 48 may be programmed so that no key entry 104 is required. The PCMCIA interfaces 43C and 43D may be included in the differential-ready computer processor 48. A power supply 49 supplies operating power to the DGPS PCMCIA card 40A, the GPS PCMCIA card 40B, the PCMCIA interfaces 43C and 43D, the display 47, the key entry 104, and the differential-ready computer processor 48.

Figure 5 illustrates a fifth embodiment of a handheld GPS/DGPS receiver/computer apparatus of the present invention referred to by the general reference number 50. The apparatus 50 includes a GPS PCMCIA downconverter card 50B, a DGPS PCMCIA card 50A , and a host PCMCIA differential-ready GPS/computer 50C. The DGPS PCMCIA card 50A and GPS PCMCIA downconverter card 50B insert into slots in the host PCMCIA differential-ready GPS/computer 50C.

The DGPS PCMCIA card 50A includes a DGPS radiowave signal antenna 51, a DGPS radiowave receiver 52, and a PCMCIA interface 53A. The DGPS radiowave signal antenna 51 receives a DGPS radiowave signal, including DGPS error correction information, and issues a responsive DGPS antenna output signal to the DGPS radiowave receiver 52. The DGPS radiowave signal antenna 51 can be mounted on the DGPS PCMCIA card 50A or electrically connected to the DGPS PCMCIA card 50A through a cable and mounted elsewhere. Several sources of DGPS radiowave signals are available, including the United States Coast Guard RDF beacon signals and commercially operated FM broadcast subcarrier signals. The DGPS radiowave receiver 52 demodulates and decodes the DGPS antenna output signal and issues the DGPS enor correction information in a DGPS data signal to the PCMCIA interface 53A. The PCMCIA interface 53A formats the DGPS data signal according to the PCMCIA standard as documented by the publication PCMCIA. Personal Computer Memory Card International Association. PC Card Standard. Release 2.0. published in September. 1991 by the Personal Computer Memory Card International Association, Sunnyvale, California, and issues a PCMCIA DGPS data signal to the host PCMCIA computer 50C. The PCMCIA interface 53A may be included in the DGPS radiowave receiver 52.

The GPS PCMCIA downconverter card 50B includes a PCMCIA interface 53B which receives inputs from, and transmits outputs to, hosts that conform to the PCMCIA standard, a GPS antenna 54 positioned to receive GPS satellite signals from one or more GPS satellites, where each GPS satellite issues a distinct GPS satellite signal, and to issue a responsive conducted antenna output signal to a GPS frequency downconverter 55. Typically, the GPS antenna 54 includes a pre-amphfier to provide an amplified antenna output signal. Optionally, the GPS antenna 54 may be electrically connected to the GPS frequency downconverter 55 by a cable, thereby allowing the GPS antenna 54 to be housed in a separate package and placed at a distance of the length of the cable from a PCMCIA card package containing the GPS frequency down converter 55. The GPS frequency downconverter 55 down converts the frequency of the antenna output signal to a selected lower frequency and issues a GPS low frequency (LF) signal through the PCMCIA interface 53B to a host PCMCIA differential-ready GPS/computer 50C. The PCMCIA interface 53B may be included in the GPS frequency downconverter 55.

The host PCMCIA differential-ready GPS receiver/computer 50C includes two PCMCIA interfaces 53C and 53D to receive inputs from, and transmit outputs to, cards that conform to the PCMCIA standard and a differential-ready GPS/computer processor 58. A display 57 receives user output information in a display signal from the differential-ready GPS/computer processor system 48 and displays the user output information for an application in a form that is visibly and or audibly perceptible to a human user. In the preferred embodiment, the display 57 is a liquid crystal display (LCD) to display the user output information visually. A speaker may be used to display the user output information as sound. A key entry 105 receives user input information from a human user and issues a responsive user input signal to the differential-ready GPS/computer processor 57. In the preferred embodiment, the key entry 105 is a key switch providing the user input signal in response to a touch or a press by the user. Alternatively, the key entry 105 may be constructed of a touch screen on the display 57 or of an audio microphone. In some instances, the differential-ready GPS/computer processor 57 may be programmed so that no key entry 105 is required. The differential-ready GPS/computer processor 58, includes a microprocessor and an electronic memory including program instructions and variable data for an application. The processor 58 operates in a conventional manner to store and retrieve the variable data, perform calculations, and input and output signals to other devices and processing systems according to the program instructions and variable data. The differential-ready GPS/computer processor 58 includes a GPS processing capability for demodulating and decoding the GPS LF signal and for calculating GPS location information of the GPS satelhte pseudoranges, GPS position, and time of observation. The differential-ready GPS/computer processor 58 receives the DGPS error correction information through the PCMCIA interface 43D from the DGPS PCMCIA card, applies the DGPS error correction information to enhance the accuracy of the GPS position, and provides the enhanced GPS position as user output information in a display signal. A display 47 receives the display signal and displays the user output information in a form that is visibly and/or audibly perceptible to a human user. The differential-ready GPS/computer processor 58 further includes a computer processing capability for receiving the user input signal, processing the user input information and the GPS location information according to program instructions and variable data for an application program and issuing application information in the display signal. The GPS processing capability and the computer processing capability may be implemented in a single microprocessor and its associated memory or in multiple separate microprocessors each with its associated memory. Where two microprocessors are used, either may perform the differential-ready capability of applying the DGPS error correction information to enhance the accuracy of the GPS position information. The PCMCIA interfaces 53C and 53D may be included in the differential-ready GPS computer processor 58. A power supply 49 supplies operating power t the DGPS PCMCIA card 50A, the GPS PCMCIA downconverter card 50B, the PCMCIA interfaces 53C and 53D, the display 57, the key entry 105, and the differential-ready GPS/computer processor 58. Figure 6a illustrates a front elevation of the apparatus 10. The apparatus 10 is enclosed in a housing 111 of a convenient shape and a size of 25 cm or less by 25 cm or less by 10 cm or less. In the preferred embodiment, the GPS antenna 13 is constructed as a "quadrifilar".

Alternatively, the GPS antenna 13 can be constructed as a dipole, turnstile, vertical whip, patch, quadrifilar, helix, micro strip, stripline, magnetic, or any other antenna type that is suitable for receipt of GPS signals. In the prefened embodiment, the DGPS radiowave signal antenna 11 is constructed as a "whip". Alternatively, the antenna 11 can be a dipole, turnstile, patch, quadrifilar, helix, micro strip, stripline, magnetic, or any other antenna that is suitable for receipt of radiowave signals in the band of the DGPS signals can also be used. The display 17 is shown as a "flat" display 17, such as an LCD or a plasma display. The key entry 19 is shown as a set of sixteen key switches.

Figure 6b illustrates a sectional right side view of the apparatus 10 showing the GPS antenna 13, the DGPS radiowave signal antenna 11, the display 17, and the key entry 19. The Figure 6b shows the housing 111 and the internal placements of the GPS frequency downconverter 14, the DGPS radiowave receiver 12, the differential-ready processing system 15, the display 17, the power supply 18, and the key entry 19.

Figure 7 illustrates a perspective view of the apparatus 20. The apparatus 20 is enclosed in a hinged housing 112 having an open position shown in the Figure 7 to allow the use of a large display 28 and key entry 101 and a closed position of a convenient shape and a size of 25 cm or less by 25 cm or less by 10 cm or less. The DGPS PCMCIA card 20A inserts into a slot in the host PCMCIA differential-ready GPS receiver/computer 20B to give the housing 112 the appearance and convenience of a single, handheld package. In the preferred embodiment, the GPS antenna 24 is constructed as a "patch", connected by a cable to the GPS frequency downconverter 25. Alternatively, the GPS antenna 24 can be constructed as a dipole, turnstile, vertical whip, patch, quadrifilar, helix, micro strip, stripline, magnetic, or other construction that is suitable for receipt of GPS signals. The DGPS radiowave signal antenna 21 is shown as a "whip" construction. Alternatively, the DGPS radiowave signal antenna can be a dipole, turnstile, patch, quadrifilar, helix, micro strip, stripline, magnetic, or any other antenna that is suitable for receipt of radiowave signals in the band of the DGPS signals.

Figure 8 illustrates a perspective view of the apparatus 40. (The perspective views of the apparatus 30 and the apparatus 50 as noted within parentheses are identical.) The apparatus 40 (30,50) is enclosed in a hinged housing 114 having an open position shown in the Figure 8 to allow the use a large display 47 (37,57) and key entry 104 (103,105) and a closed position of a convenient shape and a size of 25 cm or less by 25 cm or less by 10 cm or less. The DGPS PCMCIA card 40A (30A, 50A) and the GPS PCMCIA card 40B (30B, 50B) insert into a slot in the host 40C (30C, 50C) to give the housing 114 the appearance and convenience of a single, handheld package. In the preferred embodiment, the GPS antenna 44 (34, 54) is constructed as "patch". Alternatively, the GPS antenna 44 (34, 54) can be implemented as dipole, turnstile, vertical whip, patch, quadrifilar, helix, micro strip, stripline, magnetic, or any other antenna that is suitable for receipt of GPS signals. T DGPS radiowave signal antenna 41 (31, 51) shown as a "whip" type construction. Alternatively, the DGPS radiowave signal antenna 41 (31, 51) can be implemented as a dipole, turnstile, vertical whip, patch, quadrifilar, helix, micro strip, stripline, magnetic, or any other antenna that is suitable for receipt of radiowave signals in the band of the DGPS signals.

Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternatives and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

Claims

IN THE CLAIMS

1. A handheld GPS DGPS receiver/computer apparatus to receive GPS signals from one or more GPS satelhtes, where each GPS satelhte issues a distinct signal having information for determining a geographical GPS-based location, to receive a differential GPS (DGPS) radiowave signal having DGPS error correction information for correcting the GPS-based location, and to provide a differentially corrected GPS (DGPS) location to a user, the apparatus comprising: a GPS antenna to receive GPS satellite signals including GPS location information from one or more GPS satelhtes and to issue a GPS antenna output signal; a GPS frequency downconverter to receive the GPS antenna output signal and to issue this signal at a selected lower frequency as a GPS low frequency (LF) signal; a DGPS radiowave signal antenna to receive a DGPS radiowav signal including DGPS enor conection information from a DGPS radiowave source and to issue a DGPS antenna output signal; a DGPS radiowave receiver to process the DGPS antenna outp signal and to issue a DGPS data signal including the DGPS enor conection information; a differential-ready processing system to receive the GPS LF signal, to receive the DGPS data signal, to determine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in a user output signal; a display to receive the user output signal and to visually or audibly display the geographical DGPS location to a human user; and a power supply to supply operating power to at least one of the GPS antenna, the GPS frequency downconverter, the DGPS radiowave signal antenna, the DGPS radiowave receiver, the display, and the differential-ready processing system.

2. The apparatus of claim 1, further comprising a key entry to receive entries from the human user and issue these entries in a user input signal to the differential-ready processing system.

3. The apparatus of claim 1, wherein the differential-ready processing system comprises a first processor system to receive the GPS LF signal, to receive the DGPS data signal, to determine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue data indicative of the DGPS location in a DGPS location signal, and a second processor system to receive the DGPS location signal and to issue the DGPS location in the user output signal.

4. The apparatus of claim 1, wherein the differential-ready processing system comprises a first processor system to receive the GPS LF signal, to determine GPS location information including the time of observation and at least one of (i) the GPS satellite pseudoranges to the GPS antenna and (ii) the present position of the GPS antenna, and to issue the GPS location information in a GPS location signal, and a second processor system to receive the GPS location signal, to receive the DGPS data signal, to determine the DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in the user output signal.

5. The apparatus of claim 1, wherein the differential-ready processing system includes program instructions and variable data for at least one of: (i) storing a map database, (ii) displaying a map, (in) adding attribute features to a map, and (iv) calculating a range and a bearing from the DGPS location to another location.

6. The apparatus of claim 1, further comprising a cable to electrically connect the GPS antenna to the GPS frequency downconverter and to allow the GPS antenna to be placed away from the GPS frequency downconverter by the length of the cable.

7. The apparatus of claim 1, further comprising a cable to electrically connect the DGPS radiowave signal antenna to the DGPS radiowave receiver and to allow the DGPS radiowave signal antenna to be placed away from the DGPS radiowave receiver by the length of the cable.

8. A handheld GPS/DGPS receiver/computer apparatus to receive GPS signals from one or more GPS satelhtes, where each GPS satelhte issues a distinct signal having information for determining a geographical GPS-based location, to receive a differential GPS (DGPS) radiowave signal having DGPS enor conection information for conecting the GPS-based location, and to provide a differentially conected GPS (DGPS) location to a user, the apparatus comprising: a DGPS PCMCIA card constructed to be compatible with a PCMCIA standard established by the Personal Computer Memory Card International Association, the DGPS PCMCIA card comprising: a DGPS radiowave signal antenna to receive a DGPS radiowave signal including DGPS enor conection information from a DGPS radiowave source and to issue a DGPS antenna output signal; and a DGPS radiowave receiver, including a PCMCIA interface, to process the DGPS antenna output signal and to issue the DGPS enor conection information in a DGPS data signal in a format according to the PCMCIA standard; and a host PCMCIA differential-ready GPS receiver/computer constructed to accept one or more PCMCIA cards constructed according to the PCMCIA standard, the host PCMCIA differential-ready GPS receiver/computer comprising: a GPS antenna to receive GPS satelhte signals including GPS location information from one or more GPS satellites and to issue a GPS antenna output signal; a GPS frequency downconverter to receive the GPS antenna output signal and to issue this signal at a selected lower frequency as a GPS low frequency (LF) signal; a differential-ready processing system to receive the GPS LF signal, to receive the PCMCIA-formatted DGPS data signal, to determine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in a user output signal; a display to receive the user output signal and to visually or audibly display the geographical DGPS location to a human user; and a power supply to supply operating power to at least one of the DGPS PCMCIA card, the GPS antenna, the GPS frequency downconverter, the display, and the differential-ready processing system.

9. The apparatus of claim 8, wherein the host PCMCIA differential-ready GPS receiver/computer further comprises a key entry to receive entries from the human user and issue these entries in a user input signal to the differential ready processing system.

10. The apparatus of claim 8, wherein the differential-ready processing system comprises a first processor system to receive the GPS LF signal, to receive the DGPS data signal, to determine a geographic DGPS location fro the GPS location information and the DGPS enor conection information, and to issue data indicative of the DGPS location in a DGPS location signal, and second processor system to receive the DGPS location signal and to issue the DGPS location in the user output signal.

11. The apparatus of claim 8, wherein the differential-ready processing system comprises a first processor system to receive the GPS LF signal, to determine GPS location information including the time of observation and at least one of (i) the GPS satellite pseudoranges to the GPS antenna and (ii) th present position of the GPS antenna, and to issue the GPS location information in a GPS location signal, and a second processor system to receive the GPS location signal, to receive the DGPS data signal, to determine the DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in the user output signal.

12. The apparatus of claim 8, wherein the differential-ready processing system includes program instructions and variable data for at least one of: (i) storing a map database, (ii) displaying a map, (iii) adding attribute features to a map, and (iv) calculating a range and a bearing from the DGPS location to another location.

13. The apparatus of claim 8, further comprising a cable to electrically connect the GPS antenna to the GPS frequency downconverter and to allow the GPS antenna to be placed away from the GPS frequency downconverter by the length of the cable.

14. The apparatus of claim 8, further comprising a cable to electrically connect the DGPS radiowave signal antenna to the DGPS radiowave receiver and to allow the DGPS radiowave signal antenna to be placed away from the DGPS radiowave receiver by the length of the cable.

15. A handheld GPS/DGPS receiver/computer apparatus to receive GPS signals from one or more GPS satellites, where each GPS satellite issues a distinct signal having information for deteraiining a geographical GPS-based location, to receive a differential GPS (DGPS) radiowave signal having DGPS enor conection information for conecting the GPS-based location, and to provide a differentially conected GPS (DGPS) location to a user, the apparatus comprising: a DGPS PCMCIA card constructed to be compatible with a PCMCIA standard established by the Personal Computer Memory Card International Association, the DGPS PCMCIA card comprising: a DGPS radiowave signal antenna to receive a DGPS radiowave signal including DGPS enor conection information from a DGPS radiowave source and to issue a DGPS antenna output signal; and a DGPS radiowave receiver, including a PCMCIA interface, to process the DGPS antenna output signal and to issue the DGPS enor conection information in a DGPS data signal in a format according to the PCMCIA standard; a differential-ready GPS PCMCIA card constructed to be compatible with a PCMCIA standard comprising: a GPS antenna to receive GPS satellite signals including GPS location information from one or more GPS satelhtes and to issue a GPS antenna output signal; a GPS frequency downconverter to receive the GPS antenna output signal and to issue this signal at a selected lower frequency as a GPS low frequency (LF) signal; and a differential-ready GPS processor, including a PCMCIA interface, to receive the GPS LF signal, to receive the PCMCIA-formatted DGPS data signal, to determine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in a DGPS location data signal; and a host PCMCIA computer constructed to accept two or more PCMCI cards, the host PCMCIA computer comprising: a computer processor, including two PCMCIA interfaces, to pass the PCMCIA-formatted DGPS data signal from the DGPS PCMCIA card to the differential-ready GPS PCMCIA card, to receive the PCMCIA- formatted DGPS location signal, and to issue the DGPS location in a user output signal; a display to receive the user output signal and to visually or audibly display the geographical DGPS location to a human user; and a power supply to supply operating power to at least one of the DGPS PCMCIA card, the differential-ready GPS PCMCIA card, the display, and the computer processor.

16. The apparatus of claim 15, wherein the host PCMCIA computer further comprises a key entry to receive entries from the human user and issue these entries in a user input signal to the computer processor.

17. The apparatus of claim 15, further comprising a cable to electrically connect the GPS antenna to the GPS frequency downconverter and to allow the GPS antenna to be placed away from the GPS frequency downconverter by the length of the cable.

18. The apparatus of claim 15, further comprising a cable to electrically connect the DGPS radiowave signal antenna to the DGPS radiowave receiver and to allow the DGPS radiowave signal antenna to be placed away from the DGPS radiowave receiver by the length of the cable.

19. A handheld GPS/DGPS receiver/computer apparatus to receive GPS signals from one or more GPS satelhtes, where each GPS satellite issues a distinct signal having information for deterrnining a geographical GPS-based location, to receive a differential GPS (DGPS) radiowave signal having DGPS enor conection information for conecting the GPS-based location, and to provide a differentially conected GPS (DGPS) location to a user, the apparatus comprising: a DGPS PCMCIA card constructed to be compatible with a PCMCIA standard established by the Personal Computer Memory Card International Association, the DGPS PCMCIA card comprising: a DGPS radiowave signal antenna to receive a DGPS radiowave signal including DGPS enor conection information from a DGPS radiowave source and to issue a DGPS antenna output signal; and a DGPS radiowave receiver, including a PCMCIA interface, to process the DGPS antenna output signal and to issue the DGPS enor conection information in a DGPS data signal in a format according to the PCMCIA standard; a GPS PCMCIA card constructed to be compatible with a PCMCIA standard comprising: a GPS antenna to receive GPS satellite signals including GPS location information from one or more GPS satelhtes and to issue a GPS antenna output signal; a GPS frequency downconverter to receive the GPS antenna output signal and to issue this signal at a selected lower frequency as a GPS low frequency (LF) signal; and a GPS processor, including a PCMCIA interface, to receive the GPS LF signal, to determine GPS location information including the time of observation and at least one of (i) the GPS satelhte pseudoranges to the GS antenna and (ii) the present position of the GPS antenna, and to issue the GPS location infor r: ation in a GPS location signal formatted according to the PCMCIA standard; and a host PCMCIA differential-ready computer constructed to accept two or more PCMCIA cards, the host differential-ready PCMCIA computer comprising: a differential-ready computer processor, including at least two PCMCIA interfaces, to receive the PCMCIA-formatted DGPS data signal, to receive the PCMCIA-formatted GPS location signal, to deterrnine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in a user output signal; a display to receive the user output signal and to visually or audibly display the geographical DGPS location to a human user; and a power supply to supply operating power to at least one of the DGPS PCMCIA card, the GPS PCMCIA card, the display and the differential-ready computer processor.

20. The apparatus of claim 19, wherein the host PCMCIA differential-ready computer further comprises a key entry to receive entries from the human user and issue these entries in a user input signal to the differential-ready computer processor.

21. The apparatus of claim 19, further comprising a cable to electrically connect the GPS antenna to the GPS frequency downconverter and to allow the GPS antenna to be placed away from the GPS frequency downconverter by the length of the cable.

22. The apparatus of claim 19, further comprising a cable to electrically connect the DGPS radiowave signal antenna to the DGPS radiowave receiver and to allow the DGPS radiowave signal antenna to be placed away from the DGPS radiowave receiver by the length of the cable.

23. A handheld GPS/DGPS receiver/computer apparatus to receive GPS signals from one or more GPS satelhtes, where each GPS satelhte issues a distinct signal having information for determining a geographical GPS-based location, to receive a differential GPS (DGPS) radiowave signal having DGPS enor conection information for conecting the GPS-based location, and to provide a differentially conected GPS (DGPS) location to a user, the apparatus comprising: a DGPS PCMCIA card constructed to be compatible with a PCMCIA standard established by the Personal Computer Memory Card International Association, the DGPS PCMCIA card comprising: a DGPS radiowave signal antenna to receive a DGPS radiowave signal including DGPS enor conection information from a DGPS radiowave source and to issue a DGPS antenna output signal; and a DGPS radiowave receiver, including a PCMCIA interface, to process the DGPS antenna output signal and to issue the DGPS enor conection information in a DGPS data signal in a format according to the PCMCIA standard; a GPS PCMCIA downconverter card constructed to be compatible with a PCMCIA standard comprising: a GPS antenna to receive GPS satellite signals including GPS location information from one or more GPS satellites and to issue a GPS antenna output signal; and a GPS frequency downconverter, including a PCMCIA interfac to receive the GPS antenna output signal and to issue this signal at a selected lower frequency as a GPS low frequency (LF) signal formatted according to the PCMCIA standard; and a host PCMCIA differential-ready GPS/computer constructed to accept one or more PCMCIA cards according to the PCMCIA standard, the host PCMCIA differential-ready GPS/computer comprising: a differential-ready GPS/computer processor to receive the PCMCIA-formatted GPS LF signal, to receive the PCMCIA-formatted DGPS data signal, to determine a geographic DGPS location from the GPS location information and the DGPS enor conection information, and to issue the DGPS location in a user output signal; a display to receive the user output signal and to visually or audibly display the geographical DGPS location to a human user; and a power source to supply operating power to at least one of the DGPS PCMCIA card, the GPS PCMCIA downconverter card, the display, and the differential-ready GPS/computer processor.

24. The apparatus of claim 23, wherein the host PCMCIA differential GPS/computer further comprises a key entry to receive entries from the human user and issue these entries in a user input signal to the differential- ready GPS/computer processor.

25. The apparatus of claim 23, further comprising a cable to electrically connect the GPS antenna to the GPS frequency downconverter and to allow the GPS antenna to be placed away from the GPS frequency downconverter by the length of the cable.

26. The apparatus of claim 23, further comprising a cable to electrically connect the DGPS radiowave signal antenna to the DGPS radiowave receiver and to allow the DGPS radiowave signal antenna to be placed away from the DGPS radiowave receiver by the length of the cable.