PATENT DOCUMENT

Publication Number: US-8054221-B1
Application Number: US-94681310-A
Country: US
Kind Code: B1

Title: Methods for testing satellite navigation system receivers in wireless electronic devices

Abstract:
A portable user device may provide Global Positioning System (GPS) services. The device may include a GPS receiver. The GPS receiver may provide accurate information about the current location of the device. A user may use the device to perform tasks. Certain tasks may generate excess heat or de-generate heat that causes the GPS receiver to perform unsatisfactorily. Methods are provided that can test GPS receiver performance during acquisition mode and during tracking mode. During testing, the GPS receiver may be given a predetermined amount of time to acquire a GPS fix. The GPS receiver may be tested repeatedly to acquire successive GPS fixes. After a desired number of tests are performed, a success rate may be calculated. If the success rate is satisfactory, the GPS receiver satisfies design criteria. If the success rate is not satisfactory, the GPS receiver may be reconfigured with new settings.

Claims:
1. A method of testing a device under test in a test system, wherein the device under test comprises a satellite navigation system receiver and wireless transceiver circuitry, the method comprising:
 with the test system, turning on the wireless transceiver circuitry to transmit radio-frequency signals at a desired output power level; and 
 while the wireless transceiver circuitry is transmitting radio-frequency signals at the desired output power level and while the satellite navigation system receiver is rising in temperature as a result of turning on the wireless transceiver circuitry and transmitting radio-frequency signals with the wireless transceiver circuitry, determining whether the satellite navigation system receiver has acquired a satellite navigation system fix. 
 
     
     
       2. The method defined in  claim 1 , wherein the wireless transceiver circuitry comprises cellular telephone transceiver circuitry and wherein turning on the wireless transceiver circuitry to transmit the radio-frequency signals comprises:
 directing the cellular telephone transceiver circuitry to transmit the radio-frequency signals. 
 
     
     
       3. The method defined in  claim 1 , wherein the wireless transceiver circuitry comprises a wireless local area network (WLAN) transceiver circuit and a Bluetooth transceiver circuit and wherein turning on the wireless transceiver circuitry to transmit the radio-frequency signals comprises:
 directing the wireless local area network transceiver circuit to transmit the radio-frequency signals; and 
 directing the Bluetooth transceiver circuit to transmit the radio-frequency signals. 
 
     
     
       4. The method defined in  claim 1 , wherein the wireless transceiver circuitry comprises a cellular telephone transceiver circuit, a wireless local area network (WLAN) transceiver circuit, and a Bluetooth transceiver circuit and wherein turning on the wireless transceiver circuitry to transmit the radio-frequency signals comprises:
 directing the cellular telephone transceiver circuit to transmit the radio-frequency signals; 
 directing the wireless local area network transceiver circuit to transmit the radio-frequency signals; and 
 directing the Bluetooth transceiver circuit to transmit the radio-frequency signals. 
 
     
     
       5. The method defined in  claim 1 , wherein turning on the wireless transceiver circuitry to transmit the radio-frequency signals at the desired output power level comprises:
 directing the wireless transceiver circuitry transmit the radio-frequency signals at a maximum output power level. 
 
     
     
       6. The method defined in  claim 1 , wherein the test system includes a test host and wherein turning on the wireless transceiver circuitry to transmit the radio-frequency signals comprises:
 with the test host, directing the wireless transceiver circuitry to transmit the radio-frequency signals at the desired output power level. 
 
     
     
       7. The method defined in  claim 1 , wherein the device under test further comprises storage and processing circuitry, the method further comprising:
 with the satellite navigation system receiver, calculating satellite navigation system information; and 
 storing the calculated satellite navigation information in the storage and processing circuitry. 
 
     
     
       8. The method defined in  claim 7 , further comprising:
 clearing the satellite navigation system information from the storage and processing circuitry prior to determining whether the satellite navigation system receiver has acquired the satellite navigation system fix. 
 
     
     
       9. The method defined in  claim 1 , wherein determining whether the satellite navigation system receiver has acquired the satellite navigation system fix comprises:
 determining whether the satellite navigation system receiver has acquired the satellite navigation system fix within a predetermined time period. 
 
     
     
       10. The method defined in  claim 1 , wherein the device under test includes a first crystal oscillator associated with the satellite navigation system receiver and a second crystal oscillator associated with the wireless transceiver circuitry, the method further comprising:
 loading the device under test with a test operating system, wherein the device under test lacks a graphical user interface when configured with the test operating system. 
 
     
     
       11. The method defined in  claim 1 , further comprising:
 turning off the wireless transceiver circuitry to prevent the wireless transceiver circuitry from transmitting radio-frequency signals; and 
 while the wireless transceiver circuitry is turned off and while the satellite navigation system receiver is falling in temperature as a result of turning off the wireless transceiver circuitry, determining whether the satellite navigation system receiver has acquired an additional satellite navigation system fix. 
 
     
     
       12. A method of testing a device under test in a test system, wherein the device under test includes a satellite navigation system receiver and wireless transceiver circuitry and wherein the test system includes a base station emulator, the method comprising:
 directing the base station emulator to wirelessly communicate with the wireless transceiver circuitry in the device under test; and 
 while the wireless transceiver circuitry is transmitting radio-frequency signals to wirelessly communicate with the base station emulator and while the satellite navigation system receiver is rising in temperature as a result of transmitting the radio-frequency signals with the wireless transceiver circuitry, determining whether the satellite navigation system receiver has acquired a satellite navigation system fix. 
 
     
     
       13. The method defined in  claim 12 , wherein the test system further includes a test host and wherein directing the base station emulator to wirelessly communicate with the wireless transceiver circuitry in the device under test comprises:
 with the test host, directing the base station emulator to wirelessly communicate with the wireless transceiver circuitry in the device under test. 
 
     
     
       14. The method defined in  claim 13 , further comprising:
 with the base station emulator, detecting the presence of the device under test, wherein the test host directs the base station emulator to communicate wirelessly with the device under test in response to detecting the presence of the device under test. 
 
     
     
       15. The method defined in  claim 12 , wherein the device under test further comprises storage and processing circuitry, the method further comprising:
 with the satellite navigation system receiver, calculating satellite navigation system information; and 
 storing the calculated satellite navigation information in the storage and processing circuitry. 
 
     
     
       16. The method defined in  claim 15 , further comprising:
 clearing the satellite navigation system information prior from the storage and processing circuitry to determining whether the satellite navigation system receiver has acquired the satellite navigation system fix. 
 
     
     
       17. The method defined in  claim 12 , wherein determining whether the satellite navigation system receiver has acquired the satellite navigation system fix comprises:
 determining whether the satellite navigation system receiver has acquired the satellite navigation system fix within a predetermined time period. 
 
     
     
       18. The method defined in  claim 12 , wherein the device under test includes a given crystal oscillator and wherein the satellite navigation system receiver and the wireless transceiver circuitry share the given crystal oscillator, the method further comprising:
 loading the device under test with a normal user operating system, wherein the device under test has a graphical user interface when configured with the normal user operating system. 
 
     
     
       19. The method defined in  claim 12 , wherein the device under test includes a given crystal oscillator and wherein the satellite navigation system receiver and the wireless transceiver circuitry share the given crystal oscillator, the method further comprising:
 loading the device under test with a test operating system, wherein the device under test lacks a graphical user interface when configured with the test operating system. 
 
     
     
       20. The method defined in  claim 12 , further comprising:
 directing the base station emulator to terminate wireless communication with the wireless transceiver circuitry in the device under test; and 
 while the wireless communication between the base station emulator and the wireless transceiver circuitry in the device under test is suspended and while the satellite navigation system receiver is rising in temperature as a result of terminating the wireless communication, determining whether the satellite navigation system receiver has acquired an additional satellite navigation system fix. 
 
     
     
       21. A method of testing a device under test in a test system, wherein the device under test includes a satellite navigation system receiver and wireless transceiver circuitry and wherein the test system includes a base station emulator, the method comprising:
 directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator; 
 while the wireless transceiver circuitry is transmitting radio-frequency signals to wirelessly communicate with the base station emulator and while the satellite navigation system receiver is rising in temperature as a result of transmitting the radio-frequency signals with the wireless transceiver circuitry, determining whether the satellite navigation system receiver has acquired a satellite navigation system fix. 
 
     
     
       22. The method defined in  claim 21 , wherein the test system further includes a test host and wherein directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator comprises:
 with the test host, directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator. 
 
     
     
       23. The method defined in  claim 21 , wherein the device under test further comprises storage and processing circuitry, the method further comprising:
 with the satellite navigation system receiver, calculating satellite navigation system information; and 
 storing the calculated satellite navigation information in the storage and processing circuitry. 
 
     
     
       24. The method defined in  claim 23 , further comprising:
 clearing the satellite navigation system information from the storage and processing circuitry prior to determining whether the satellite navigation system receiver has acquired the satellite navigation system fix. 
 
     
     
       25. The method defined in  claim 21 , wherein determining whether the satellite navigation system receiver has acquired the satellite navigation system fix comprises:
 determining whether the satellite navigation system receiver has acquired the satellite navigation system fix within a predetermined time period. 
 
     
     
       26. The method defined in  claim 21 , wherein the device under test includes a given crystal oscillator and wherein the satellite navigation system receiver and the wireless transceiver circuitry share the given crystal oscillator, the method further comprising:
 loading the device under test with a test operating system, wherein the device under test lacks a graphical user interface when configured with the test operating system. 
 
     
     
       27. The method defined in  claim 21 , further comprising:
 directing the wireless transceiver circuitry in the device under test to terminate wireless communication with the base station emulator; and 
 while the wireless communication between the base station emulator and the wireless transceiver circuitry in the device under test is suspended and while the satellite navigation system receiver is rising in temperature as a result of terminating the wireless communication, determining whether the satellite navigation system receiver has acquired an additional satellite navigation system fix. 
 
     
     
       28. The method defined in  claim 21 , wherein the wireless transceiver circuitry comprises cellular telephone transceiver circuitry and wherein directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator comprises:
 directing the cellular telephone transceiver circuitry to transmit the radio-frequency signals. 
 
     
     
       29. The method defined in  claim 21 , wherein the wireless transceiver circuitry comprises a wireless local area network (WLAN) transceiver circuit and a Bluetooth transceiver circuit and wherein directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator comprises:
 directing the wireless local area network transceiver circuit to transmit the radio-frequency signals; and 
 directing the Bluetooth transceiver circuit to transmit the radio-frequency signals. 
 
     
     
       30. The method defined in  claim 21 , wherein the wireless transceiver circuitry comprises a cellular telephone transceiver circuit, a wireless local area network (WLAN) transceiver circuit, and a Bluetooth transceiver circuit and wherein directing the wireless transceiver circuitry in the device under test to wirelessly communicate with the base station emulator comprises:
 directing the cellular telephone transceiver circuit to transmit the radio-frequency signals; 
 directing the wireless local area network transceiver circuit to transmit the radio-frequency signals; and 
 directing the Bluetooth transceiver circuit to transmit the radio-frequency signals.

Description:
BACKGROUND 
     This invention relates to electronic devices and more particularly, to portable electronic devices with satellite navigation system capabilities. 
     Electronic devices use satellite navigation systems to support navigation functions. For example, an electronic device may use a satellite navigation system such as the Global Positioning System (GPS) to obtain position information, timing information, and other navigation information. The Global Positioning System includes satellites that orbit the Earth, Earth-based control and monitoring stations, and GPS receivers that are located within the electronic devices. GPS services may be provided on a continuous basis anywhere that is within range of the orbiting satellites. 
     A portable electronic device may include a GPS receiver. The GPS receiver may sometimes be referred to as a GPS unit. The GPS unit determines the current position (location) of the portable electronic device. During operation, the GPS unit may receive data streams from GPS satellites orbiting the Earth. Using a local clock, the GPS unit analyzes each data stream to make a transit time and distance estimation. 
     A method known as geometric trilateration may be used to determine the location of the GPS unit by analyzing the estimated distances of each of the satellites to the GPS unit. The accuracy of location measurements made using the GPS unit depends on accuracy of the local clock. The local clock is typically implemented using a crystal oscillator. If the output of the oscillator exhibits errors, the GPS receiver may not function as expected. 
     Some GPS units are housed in dedicated handheld devices. Other GPS units are used in more complex devices such as cellular telephones. Devices such as these may have components whose operations can adversely affect GPS performance. 
     As an example, a cellular telephone may include cellular telephone transceiver circuitry that is used to make telephone calls. The cellular telephone transceiver circuitry includes power amplifier circuitry that transmits radio-frequency (RF) signals to a nearby base station. If care is not taken, a rapid change in heat generated from the power amplifier circuitry may adversely affect the accuracy of the oscillator in the GPS unit, thereby resulting in degraded GPS performance. Acquiring a GPS location measurement when making a phone call may therefore be unacceptably slow. 
     Conventional arrangements for testing GPS receiver performance involve measuring the performance of the GPS unit while the power amplifier circuitry is placed in an active mode that constantly transmits radio-frequency signals. The performance of the GPS unit, however, may be most adversely affected when the thermal transient (i.e., the instantaneous change in heat generated by the cellular telephone transceiver circuitry) is maximized. Testing GPS performance using the conventional approach is not a rigorous test of GPS performance, because leaving the power amplifier circuitry in the active mode does not maximize thermal transient. 
     It would therefore be desirable to be able to provide ways of testing GPS receiver performance. 
     SUMMARY 
     An electronic device such as a portable user device may provide satellite navigation system services such as Global Positioning System (GPS) services. The user device may include a satellite navigation receiver such as a GPS receiver, storage and processing circuitry, cellular telephone transceiver circuitry (cellular radio), etc. The GPS receiver may provide information such as a current location of the user device. 
     In addition to providing the GPS services, the user device may be used perform various tasks. For example, the user device may be used to make telephone calls, browse the Internet, run gaming applications, take pictures, etc. Performing these tasks may produce thermal transient that momentarily raises the temperature of the GPS receiver. 
     If the GPS receiver suffers from rapid changes in temperature (e.g., if a high temperature gradient is produced on a printed circuit board on which GPS circuitry is mounted), the GPS receiver may not function properly. It may be desirable to test GPS receiver performance in the presence of such thermal transient (i.e., heat-inducing) activities. 
     A test system in which a device under test (DUT) is tested may include test equipment such as a base station emulator and a test host. The base station emulator and the DUT may be coupled to the test host during testing. 
     The DUT may be operable in an acquisition mode or a tracking mode. During acquisition mode testing, the GPS receiver may be given a time to fix (TTF) to acquire a GPS fix (lock) during activating or deactivating a heat-inducing activity (e.g., in response to turning on or turning off power amplifier circuitry at a specific duty cycle). GPS data may be cleared from the DUT before attempting another GPS acquisition. After a desired number of tests have been performed, an acquisition success rate may be calculated. If the acquisition success rate satisfies a predetermined threshold, the GPS receiver satisfies performance criteria, and the DUT is marked as a passing DUT. If the acquisition success rate is less than the predetermined threshold, the DUT is marked as a failing DUT. The GPS receiver may be reconfigured with new settings aimed to improve GPS performance (e.g., to increase the distance between the GPS receiver and the cellular radio, or provide better ground plane to dissipate heat, or adding thermal pad). 
     During tracking mode testing, the GPS receiver may be given time-to-fix (TTF), and the GPS receiver may be in hot start. The GPS receiver may initially be given a sufficient amount of time to acquire fixes to update its ephemeris without any thermal effect activities. Subsequently, the GPS receiver may continue to acquire a GPS fix during activating or deactivating a thermal effect activity. 
     GPS data need not be cleared from the DUT before attempting another GPS fix. After a desired number of tests have been performed, a tracking success rate may be calculated. If the tracking success rate is greater than a predetermined threshold, the GPS receiver satisfies performance criteria. If the tracking success rate is less than the predetermined threshold, the GPS receiver may be reconfigured with new settings. 
     Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of an illustrative test system in accordance with an embodiment of the present invention. 
         FIG. 3  is a graph illustrating how the temperature of a Global Positioning System (GPS) receiver may vary in time as thermal transient operations are performed during acquisition mode testing in accordance with an embodiment of the present invention. 
         FIG. 4  is a graph showing how the Global Positioning System receiver of  FIG. 3  may experience a temperature gradient that varies in time in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph illustrating how the temperature of a Global Positioning System receiver may vary in time as thermal transient operations are performed during tracking mode testing in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph showing how the Global Positioning System receiver of  FIG. 5  may experience a temperature gradient that varies in time in accordance with an embodiment of the present invention. 
         FIG. 7  is a flow chart of illustrative steps involved in non-signaling acquisition mode testing of Global Positioning System receiver performance in accordance with an embodiment of the present invention. 
         FIG. 8  is a flow chart of illustrative steps involved in non-signaling tracking mode testing of Global Positioning System receiver performance with an embodiment of the present invention. 
         FIG. 9  is a flow chart of illustrative steps involved in signaling acquisition mode testing of Global Positioning System receiver performance in accordance with an embodiment of the present invention. 
         FIG. 10  is a flow chart of illustrative steps involved in signaling tracking mode testing of Global Positioning System receiver performance in accordance with an embodiment of the present invention. 
         FIG. 11  is a flow chart of illustrative steps involved in reduced-signaling acquisition mode testing of Global Positioning System receiver performance in accordance with an embodiment of the present invention. 
         FIG. 12  is a flow chart of illustrative steps involved in reduced-signaling tracking mode testing of Global Positioning System receiver performance in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates to techniques for testing the performance of Global Positioning System (GPS) receivers in electronic devices. Electronic devices such as portable electronic devices and other electronic equipment may provide GPS services. 
     An electronic device may include GPS circuitry that provides GPS capabilities. For example, the electronic device may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, a media player, etc. Electronic devices with GPS capabilities may provide a user with reliable positioning, navigation, and timing services (as examples). These GPS-based services may be used in navigation applications, games, applications with maps, and other location-based settings. 
     A schematic diagram of an electronic device such as electronic device  10  is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may include storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VoIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network (WLAN) protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     Circuitry  28  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, to support antenna diversity schemes and MIMO schemes or beam forming or other multi-antenna schemes, circuitry  28  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data, control which antenna structures within device  10  are being used to receive and process data. As an example, circuitry  28  may control which of two or more antennas is being used to receive incoming radio-frequency signals, may control which of two or more antennas is being used to transmit radio-frequency signals, may control the process of routing incoming data streams over two or more antennas in device  10  in parallel, etc. 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry  35  (e.g., for receiving satellite positioning signals at 1575 MHz) or GLONASS (e.g., for receiving satellite positioning signals at 1602 MHz), transceiver circuitry such as transceiver circuitry  36  and  38 , and antenna circuitry  40 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  36  may sometimes be referred to as wireless local area network (WLAN) transceiver circuitry (to support WiFi® communications) and Bluetooth® transceiver circuitry. Circuitry  34  may use cellular telephone transceiver circuitry (sometimes referred to as cellular radio)  38  for handling wireless communications in cellular telephone bands such as bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz or other cellular telephone bands of interest. 
     Examples of cellular telephone standards that may be supported by wireless circuitry  34  and device  10  include: the Global System for Mobile Communications (GSM) “2G” cellular telephone standard, the Evolution-Data Optimized (EVDO) cellular telephone standard, the “3G” Universal Mobile Telecommunications System (UMTS) cellular telephone standard, the “3G” Code Division Multiple Access 2000 (CDMA 2000) cellular telephone standard, and the “4G” Long Term Evolution (LTE) cellular telephone standard. Other cellular telephone standards may be used if desired. These cellular telephone standards are merely illustrative. 
     Wireless communications circuitry  34  may include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structure, patch antenna structures, inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link and another type of antenna may be used in forming a remote wireless link. 
     Wireless communications circuitry  34  may include an oscillator such as crystal oscillator  42 . Crystal oscillator  42  may provide a highly stable local clock that is used as a reference clock signal. As shown in  FIG. 1 , oscillator  42  may feed local clock signals to GPS receiver (unit)  35 , transceiver circuits  36 , cellular radio  38 , and other wireless circuits over path  44 . If desired, wireless communications circuitry  34  may include a plurality of oscillators  42 , where each of the plurality of oscillators  42  is used to generate a stable local clock signal for a respective transceiver circuit. 
     GPS receiver  35  may receive GPS signals from GPS satellites  12  as satellites  12  orbit the Earth. GPS receiver  35  may use the clock signals generated by oscillator  42  to calculate its position by precisely timing the signals that are being transmitted by GPS satellites  12 . For example, each GPS satellite  12  may continuously broadcast signals to GPS receiver  35 . The broadcasted signals may include information such as the time the signals were sent, relevant orbital information (e.g., the precise location of each satellite), and other related information. 
     GPS receiver  35  may receive the broadcasted GPS satellite information. GPS receiver  35  may analyze the times at which the signals are received. GPS receiver  35  may rely on crystal oscillator (local clock)  42  to make precise timing measurements on received signals. GPS receiver  35  may calculate the transit time for each received signal based on these timing measurements. The transit time of each message may be multiplied by the speed of light (e.g., the speed at which wireless signals propagate through air) to compute the distance between user device  10  and each corresponding GPS satellite  12 . 
     Geometric trilateration techniques may then be used to combine the computed distances with the GPS satellites&#39; current locations to determine the position (location) of GPS receiver  35 . GPS receiver  35  may feed GPS data to storage and processing circuitry  28 . The process of obtaining the current location of device  10  is sometimes referred to as obtaining a satellite navigation system fix (or GPS fix). In addition to determining the current location, GPS receiver  35  may provide time-to-fix (TTF) data (e.g., data indicating the amount of time it takes for receiver  35  to acquire an updated GPS fix). GPS receiver  35  may also be used to obtain other useful location information (e.g., to determine the altitude, direction, and speed of device  10 ). 
     As shown in  FIG. 1 , device  10  may communicate with a base station such as base transceiver station  14 . In particular, radio-frequency signals may be conveyed between cellular telephone transceiver circuitry (cellular radio)  38  and base station  14  during a phone call (as an example). Cellular radio  38  may rely on local clock signals generated by the same oscillator  42  used by GPS receiver  35  or by a separate oscillator  42  to process radio-frequency signals at desired frequencies during cellular transmission. 
     The accuracy of the position obtained by GPS receiver  35  is strongly dependent on the accuracy of crystal oscillator  42 . Even a small clock error in oscillator  42  may not be acceptable if precise GPS location data is desired within an allotted time limit. Small clock (frequency) errors may be magnified when multiplied by the speed of light (e.g., a very large number), resulting in a large positional error. 
     The accuracy of crystal oscillator  42  is generally acceptable during normal operating conditions (e.g., when device  10  is not running processor-intensive applications and is not using heat-producing components). The accuracy of GPS receiver  35  may, however, be adversely affected by heat-inducing operations on device  10 . For example, a sudden change in temperature (e.g., a high temperature gradient or low temperature gradient) produced as cellular radio  38  is enabled (or disabled) can result in a longer time-to-fix or missing fix. It may therefore be desirable to test GPS receiver performance in the presence of high/low-temperature-gradient-inducing activities. 
       FIG. 2  is a diagram showing a test system in which device  10  can be tested. Device  10  being tested may sometimes be referred to as a device under test (DUT). Test system  50  may include test equipment  52  that is used to test DUT  10 . Test equipment  52  may include base station emulator  54 , test host  56 , control circuitry, network circuitry, cabling, and other test equipment. Base station emulator  54  is a device that emulates the behavior of an actual base transceiver station. Base station emulator  54  may communicate with DUT  10  over a wireless path or over a wired connection in test system  50 . 
     Base station emulator  54  may be coupled to test host  56  (e.g., a personal computer) through line  58 . DUT  10  may be coupled to test host  56  through dotted line  60 . The connection represented by line  60  may be a Universal Serial Bus (USB) based connection, a Universal Asynchronous Receiver/Transmitter (UART) based connection, or other suitable types of connections. DUT  10  may transmit test data to test host  56  over line  60  or through base station emulator  54 . 
     GPS receiver  35  may be operable in an acquisition mode and a tracking mode. When GPS receiver  35  is turned on, GPS receiver  35  may retrieve GPS information stored on storage and processing circuitry  28 . GPS receiver  35  may calculate an updated location (fix) based on the retrieved GPS information. For example, a first scenario in which GPS receiver  35  is enabled to acquire a new GPS fix and storage circuitry  28  contains no previously calculated location data may be referred to as a “cold” start. A second scenario in which GPS receiver  35  is enabled to acquire a GPS lock and storage circuitry  28  contains previously calculated location data but no information indicating which satellites  12  were previously in view may be referred to as a “warm” start. A third scenario in which GPS receiver  35  is enabled to calculate a GPS lock and storage circuitry  28  contains previously calculated location data and information indicating which satellites  12  were previously in view may be referred to as a “hot” start. 
     DUT  10  may be tested while GPS receiver  35  is operating in the acquisition mode (e.g., for GPS factory cold start, cold start, or warm start) and in the tracking mode (e.g., for GPS hot start).  FIG. 3  is a graph showing how the temperature of GPS receiver  35  (T GPS ) may vary in time during acquisition mode testing of DUT  10 . At time to, DUT  10  is turned on. DUT  10  may be loaded with a test operating system (e.g., so that the behavior of DUT  10  may be directly controlled using test host  56 ). Storage and processing circuitry  28  may not include any previously calculated location data prior to time t 0 . 
     At time t 1 , T GPS  reaches normal operating temperature T 1 . The time it takes for DUT  10  to power up (e.g., the time period from time t 0  to t 1 ) may be referred to as boot-up time T BOOT . 
     At time t 2 , GPS receiver  35  may be turned on and DUT  10  may be directed to perform certain tasks that cause internal device circuitry (e.g., storage and processing circuitry  28 , cellular radio  28 , transceiver circuits  36 , etc.) to generate additional heat. For example, a user may want to make a telephone call, start a gaming application, launch a web browser, etc. Different tasks may vary in processing intensity and may cause the peripheral circuitry to generate different heat profiles. 
     Consider a scenario in which DUT  10  is directed to begin cellular transmission by turning on cellular radio  38  at time t 2 . Activating cellular transmission may involve turning on power amplifier circuitry in radio  38 . Turning on the power amplifier circuitry may cause temperature T GPS  to rise rapidly (see, e.g.,  FIG. 3 ). 
     This sudden change in T GPS  is illustrated in  FIG. 4 .  FIG. 4  is a graph showing the magnitude of the temperature gradient ∥δT GPS ∥ as a function of time. Temperature gradient is a measure of the instantaneous change in T GPs . The temperature gradient characteristic curve of  FIG. 4  can be calculated by taking the first derivative of the temperature curve of  FIG. 3  (as an example). As shown in  FIG. 4 , temperature gradient ∥δT GPS ∥ reaches a peak at gradient level G 1  after time t 2 . The ability of GPS receiver  35  to acquire a GPS fix may be adversely affected by such high temperature gradient levels. 
     At time t 3 , GPS receiver  35  may acquire a GPS fix (e.g., GPS receiver  35  may acquire an updated/current location of device  10 ). The time it takes for GPS receiver  35  to acquire the GPS fix in response to turning on radio circuitry  38  is indicated by time-to-fix TTF ON . At time t 4 , storage and processing circuit  28  may clear the recently acquired GPS data so that a successive GPS acquisition remains a cold start (e.g., to continue acquisition mode testing). At time t 4 , T GPS  may settle to temperature T 2  while temperature gradient ∥≡T GPS ∥ falls back down to a low value. 
     At time t 5 , the temperature-inducing task may be turned off (e.g., cellular radio  38  may be turned off). Similarly, turning off the power amplifier circuitry in radio  38  may cause temperature T GPS  to fall. As shown in  FIG. 4 , temperature gradient ∥≡T GPS ∥ reaches a peak at gradient level G 2  after time t 5 . Level G 2  may have the same value as G 1  or may be greater than G 1 . The ability of GPS receiver  35  to acquire a GPS fix may be adversely affected by such high temperature gradient levels. 
     At time t 6 , GPS receiver  35  may acquire a GPS fix. The time it takes for GPS receiver  35  to acquire the GPS fix in response to turning off radio circuitry  38  is indicated by time-to-fix TTF OFF . At time t 7 , storage and processing circuit  28  may clear the recently acquired GPS data so that a successive GPS acquisition remains a cold start. At time t 7 , temperature gradient ∥≡T GPS ∥ may fall back down to a low value. At time t 8 , cellular radio  38  may be turned on to continue testing GPS receiver  35  in the acquisition mode. 
     TTF ON  may be different than TTF OFF . The amount of heat generated when turning on cellular radio  38  may be different from the amount of heat de-generated when turning off cellular radio  38  (as an example). Also, when cellular radio  38  is on, the radio-frequency signals transmitted by the power amplifier circuitry may interfere with the operation of GPS receiver  35  to degrade TTF ON . 
     As shown in  FIG. 3 , the test time allotted for GPS receiver to acquire a fix in response to enabling a heat-inducing task (e.g., from time t 2  to t 5 ) and in response to disable the heat-inducing task (e.g., from time t 5  to t 8 ) may, for example, be 20 seconds. GPS receiver  35  may or may not be able to acquire a GPS fix during this allotted time period. If desired, the allotted (predetermined) time period during acquisition mode testing may be less than 20 seconds or more than 20 seconds. 
     GPS receiver  35  may include an automatic frequency correction (AFC) circuit to help compensate for sudden changes in temperature. Even with the help of the AFC circuit, the ability of GPS receiver  35  to accurately acquire a GPS lock in the presence of high temperature-gradient-inducing activities may vary because of process, voltage, and temperature variations. As a result, some GPS receivers may be more robust than others. The more robust GPS receivers may be capable of acquiring a GPS fix during the predetermined time period, whereas the less robust GPS receivers may fail to acquire a GPS fix during the predetermined time period. 
     DUT  10  may also be tested while GPS receiver  35  is operating in the tracking mode (e.g., for GPS hot starts).  FIG. 5  is a graph showing how T GPS  may vary in time during tracking mode testing of DUT  10 . At time t 0 , DUT  10  is turned on. After boot-up time T BOOT , T GPS  may reach normal operating temperature T 1  (at time t 1 ). At time t 1 , GPS receiver  35  may be turned on to acquire new GPS fixes. Storage and processing circuitry  28  does not include any previously calculated location data prior to time t 0 . 
     At time t 2 , GPS receiver  35  may acquire a GPS acquisition fix. The time it takes for GPS receiver  35  to acquire the new GPS following start-up (e.g., cold start) may sometimes be referred to as acquisition time-to-fix TTF ACQ . TTF ACQ  may be 15 seconds (as an example). GPS receiver  35  may be given sufficient time to acquire this initial GPS fix. During the duration between t 2  and t 3 , GPS receiver  35  may acquire several tracking fixes to ensure that the DUT may have the update ephemeris. 
     At time t 3 , DUT  10  may be directed to perform certain tasks that cause internal device circuitry to generate additional heat. For example, consider a scenario in which DUT  10  is directed to begin cellular transmission by turning on cellular radio  38 . Activating cellular transmission may involve turning on power amplifier circuitry in circuitry  38 . Turning on the power amplifier circuitry may cause temperature T GPS  to rise rapidly (see, e.g.,  FIG. 5 ). This sudden change in T GPS  is illustrated in the temperature gradient plot of  FIG. 6 . 
     While T GPS  is rising, GPS receiver  35  may acquire a first GPS fix (e.g., GPS receiver  35  may acquire an updated/current location of device  10 ) at time t 4 . The time it takes for GPS receiver  35  to acquire the first GPS fix during turning on radio circuitry  38  is indicated by time-to-fix TTF TRK . TTF TRK  may be less than TTF ACQ , because the time-to-fix based on a hot start is significantly shorter than the time-to-fix based on a cold start. TTF TRK  may be as short as 1.5 sec (as an example). At time t 4 , T GPS  may continue to rise, because not much time has passed since turning on the power amplifier circuitry (e.g., temperature gradient ∥δT GPS ∥ stays high after t 4 ). 
     While T GPS  continues to rise, GPS receiver may acquire a second GPS fix (at time t 5 ). The time it takes for GPS receiver  35  to acquire the second fix following acquisition of the first GPS fix is indicated by time-to-fix TTF′ TRK . TTF′ TRK  may be less than TTF TRK , greater than TTF TRK , or approximately equal to TTF TRK . 
     As shown in this example, GPS receiver  35  is capable of acquiring two GPS fixes within a predetermined allotted time period (e.g., four seconds). It may be desirable to test the ability of GPS receiver  35  to acquiring multiple GPS fixes during the allotted time period. The predetermined allotted time period may at least two seconds, at least 4 seconds, at least eight seconds, etc. 
     At time t 6 , the temperature-inducing task may be disabled (e.g., cellular radio  38  may be turned off). Turning off the power amplifier circuitry in radio  38  may cause temperature T GPS  to fall. As shown in  FIG. 6 , temperature gradient ∥δT GPS ∥ reaches a peak gradient level at time t 6 ′ in response to turning off the power amplifier circuitry in radio  38 . The ability of GPS receiver  35  to acquire a GPS fix may be adversely affected by such high temperature gradient levels. 
     While T GPS  is falling, GPS receiver  35  may acquire a first GPS fix (at time t 7 ). The time it takes for GPS receiver  35  to acquire the first GPS fix during the process of turning off radio circuitry  38  is indicated by time-to-fix TTF TRK . At time t 7 , T GPS  may continue to fall, because not much time has passed since turning off the power amplifier circuitry (e.g., temperature gradient ∥δT GPS ∥ stays high after t 7 ). While T GPS  continues to fall, GPS receiver may acquire a second GPS fix (at time t 8 ). The time it takes for GPS receiver  35  to acquire the second fix following acquisition of the first GPS fix is indicated by time-to-fix TTF′ TRK . TTF′ TRK  may be less than TTF TRK , greater than TTF TRK , or approximately equal to TTF TRK . At time t 9 , cellular radio  38  may be turned on to continue testing GPS receiver  35  in the tracking mode. 
       FIG. 5  illustrates a scenario in which GPS receiver  35  is capable of obtaining at least two GPS tracking fixes within the allotted time period. As shown in  FIG. 5 , the test time allotted for GPS receiver to acquire a fix in response to enabling a heat-inducing task (e.g., from time t 3  to t 6 ) and in response to disable the heat-inducing task (e.g., from time t 6  to t 9 ) may, for example, be four seconds. GPS receiver  35  may or may not be able to acquire multiple GPS fixes during this predetermined allotted time period. The allotted time period for GPS receiver  35  to obtain a GPS fix during tracking mode testing may be significantly shorter than the allotted time period for GPS receiver  35  to obtain a GPS fix during acquisition mode testing. If desired, the predetermined time period for tracking mode testing may be less than four seconds or more than four seconds. 
     The timing diagrams of  FIGS. 3-6  are merely illustrative. The heat experienced by GPS receiver  35  during acquisition mode and during tracking mode may have any suitable temperature profile. 
     Different types of test arrangements may be used during testing of DUT  10 . In one suitable arrangement, DUT  10  may be tested using a “non-signaling” test arrangement. The non-signaling test approach may be suitable for testing DUT  10  that includes a first oscillator  42  for cellular circuitry and a second oscillator  42  for GPS circuitry (as an example). The non-signaling test may involve configuring DUT  10  with a test operating system and directing radio circuitry  38  to broadcast radio-frequency signals at a maximum output power level without establishing a protocol-based wireless connection with base station emulator  54  (e.g., base station emulator may not be used during non-signaling testing). 
       FIG. 7  shows steps involved in acquisition mode testing of DUT  10  using the non-signaling arrangement. At step  70 , DUT  10  (e.g., a DUT with a crystal for cellular radio and another crystal for GPS circuitry) is powered on. 
     At step  72 , cellular radio circuitry  38  may be toggled on or off (e.g., the power amplifier circuitry may be configured to transmit RF signals at maximum output power level or may be turned completely off). 
     At step  74 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within an allotted (predetermined) acquisition time period (e.g., a 20 second time period). At step  76 , DUT  10  may determine whether a new GPS fix has been acquired during the allotted time. Data indicating whether or not a GPS fix has been acquired may be stored on test host  56 . 
     At step  78 , GPS location data stored on storage and processing circuitry  28  may be cleared to continue acquisition mode testing. Processing may loop back to step  72  to perform additional test iterations, as indicated by path  80 . 
     After a sufficient number of test iterations, an acquisition success rate may be calculated using test host  56 . The acquisition success rate may be defined as the ratio (or percentage) of the number of successful GPS fixes acquired within the predetermined time period to the total number of test iterations. For example, consider a scenario in which 77 test iterations are performed. According to the 3GPP TS 34.171 specification, if a user desires a 95% acquisition success rate, all 77 fixes will have to be acquired to satisfy pass criteria. 
     If the acquisition success rate is satisfactory, GPS receiver  35  satisfies design criteria and DUT  10  is marked as a passing DUT (step  82 ). If the acquisition success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria (step  84 ). If desired, DUT  10  may be configured with new design settings (e.g., the distance between cellular radio circuitry  38  and GPS receiver circuitry  35  may be increased to reduce the interference between circuitry  38  and  35  and to further isolate GPS circuitry  35  from the heat generated by circuitry  38 ). 
     The steps of  FIG. 7  are merely illustrative. If desired, WiFi® and Bluetooth® transceiver circuits  36  may be toggled on or off at step  72  while cellular radio circuitry  38  remains off during the entirety of the acquisition mode testing. Enabling and disabling transceiver circuits  36  may generate rapid changes in T GPS  to introduce stress that negatively impacts the performance of GPS receiver  35 . If desired, radio circuitry  38  and transceiver circuitry  36  may simultaneously be toggled on or off at step  72  during acquisition mode testing. For example, circuitry  36  and  38  may both be turned on at time t 2  and may both be turned off at time t 5  (see, e.g., timing diagram of  FIGS. 3 and 4 ). 
       FIG. 8  shows steps involved in tracking mode testing of DUT  10  using the non-signaling arrangement. At step  90 , DUT  10  (e.g., a DUT with a crystal for cellular radio and another crystal for GPS circuitry) is powered on. At step  92 , DUT  10  may be given sufficient time to acquire a GPS fix, while the cellular radio may be turn off. At step  94 , cellular radio circuitry  38  may be toggled on or off (e.g., the power amplifier circuitry may be configured to transmit RF signals at maximum output power level or may be turned completely off). 
     At step  96 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within an allotted tracking time period (e.g., a four seconds time period). At step  98 , DUT  10  may determine whether at least two GPS fixes have been acquired during the allotted time. Data indicating whether or not multiple GPS fixes have been acquired may be stored on test host  56 . 
     GPS location data stored on storage and processing circuitry  28  need not be cleared for tracking mode testing. Processing may loop back to step  94  to perform additional test iterations, as indicated by path  100 . 
     After a sufficient number of test iterations, a tracking success rate may be calculated using test host  56 . If the tracking success rate is satisfactory, GPS receiver  35  satisfies design criteria and DUT  10  is marked as a passing DUT (step  102 ). If tracking success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria, and DUT  10  may be configured with new design settings aimed to improve GPS performance (step  104 ). 
     The steps of  FIG. 8  are merely illustrative. If desired, WiFi® and Bluetooth® transceiver circuits  36  may be toggled on or off at step  94  while cellular radio circuitry  38  remains off during the entirety of the tracking mode testing. Enabling and disabling transceiver circuits  36  may generate rapid changes in T GPS  to introduce stress that negatively impacts the performance of GPS receiver  35 . If desired, radio circuitry  38  and transceiver circuitry  36  may simultaneously be toggled on or off at step  94  during tracking mode testing. For example, circuitry  36  and  38  may both be turned on at time t 3  and may both be turned off at time t 6  (see, e.g., timing diagram of  FIGS. 5 and 6 ). 
     In another suitable arrangement, DUT  10  may be tested using a “signaling” test arrangement. The signaling test approach may be suitable for testing DUT  10  that includes a shared oscillator  42  for cellular circuitry and GPS circuitry (as an example). The signaling test may involve configuring DUT with a normal user operating system (e.g., DUT  10  may be loaded with default user applications, graphical user interface, etc.). If desired, DUT  10  may be configured in the test mode described in connection with  FIGS. 7 and 8 . 
       FIG. 9  shows steps involved in acquisition mode testing of DUT  10  using the signaling arrangement. At step  110 , DUT  10  (e.g., a DUT with a shared crystal for cellular radio and for GPS circuitry) is powered on. At step  112 , DUT  10  automatically registers with base station emulator  54  (e.g., DUT  10  notifies base station emulator  54  of its presence). 
     At step  114 , test host  56  may direct base station emulator  54  to engage/disengage with DUT  10 . When base station emulator  54  is engaged with DUT  10 , cellular radio  38  is in an active mode (e.g., cellular radio  38  is actively transmitting radio-frequency signals to base station emulator  54  over a protocol-based wireless connection). When base station emulator  54  is disengaged with DUT  10 , cellular radio  38  is in a sleep mode. 
     At step  116 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within an allotted acquisition time period (e.g., a 20 second time period). At step  118 , DUT  10  may determine whether a new GPS fix has been acquired during the allotted time. Data indicating whether or not a GPS fix has been acquired may be stored on test host  56 . 
     At step  120 , GPS location data stored on storage and processing circuitry  28  may be cleared to continue acquisition mode testing. Processing may loop back to step  114  to perform additional test iterations, as indicated by path  122 . 
     After a sufficient number of test iterations, an acquisition success rate may be calculated using test host  56 . If the acquisition success rate is satisfactory, GPS receiver  35  satisfies design criteria, and DUT  10  is marked as a passing DUT (step  124 ). If acquisition success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria, and DUT  10  may be reconfigured with new design settings (step  126 ). 
       FIG. 10  shows steps involved in tracking mode testing of DUT  10  using the signaling arrangement. DUT  10  may be configured in normal user mode or test mode. At step  130 , DUT  10  (e.g., a DUT with a shared crystal for cellular radio and for GPS circuitry) is powered on. At step  132 , DUT  10  automatically registers with base station emulator  54 . At step  134 , DUT  10  may be given sufficient time to acquire a GPS fix. 
     At step  136 , test host  56  may direct base station emulator  54  to engage/disengage with DUT  10 . At step  138 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within an allotted tracking time period (e.g., a four seconds time period). At step  140 , DUT  10  may determine whether at least two new GPS fixes have been acquired during the allotted time. Data indicating whether or not multiple GPS fixes have been acquired may be stored on test host  56 . 
     GPS location data stored on storage and processing circuitry  28  need not be cleared for tracking mode testing. Processing may loop back to step  136  to perform additional test iterations, as indicated by path  142 . 
     After a sufficient number of test iterations, a tracking success rate may be calculated using test host  56 . If the tracking success rate is satisfactory, GPS receiver  35  satisfies design criteria and DUT  10  is marked as a passing DUT (step  144 ). If tracking success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria, and DUT  10  may be configured with new design settings aimed to improve GPS performance (step  146 ). 
     In another suitable arrangement, DUT  10  may be tested using a “reduced-signaling” test arrangement. The reduced-signaling test approach may be suitable for testing DUT  10  that includes a shared oscillator  42  for cellular circuitry and GPS circuitry (as an example). The reduced-signaling test may involve configuring DUT  10  with a test operating system (e.g., the behavior of DUT  10  may be directly controlled using test host  56 ). Start-up time T BOOT  of DUT  10  with the test operating system may be shorter than T BOOT  of DUT  10  loaded with the normal user operating system. Testing DUT  10  using this approach may be referred to as reduced-signal testing, because DUT  10  only responds to commands received over path  60  from test host  56  (e.g., DUT  10  only transmits radio-frequency signals in response to test host commands). 
       FIG. 11  shows steps involved in acquisition mode testing of DUT  10  using the reduced-signaling arrangement. At step  150 , DUT  10  (e.g., a DUT with a shared crystal for cellular radio and for GPS circuitry) is powered on. At step  152 , test host  56  directs DUT  10  to register with base station emulator  54  (e.g., a protocol-based connection is established between DUT  10  and base station emulator  54 ). 
     At step  154 , test host  56  may direct DUT  10  to engage/disengage with base station emulator  54 . For example, DUT  10  may be directed to make a telephone call to engage base station emulator  54 . DUT  10  may be directed to end a telephone call to disengaged base station emulator  54 . 
     At step  156 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within an allotted acquisition time period (e.g., a 20 second time period). At step  158 , DUT  10  may determine whether a new GPS fix has been acquired during the allotted time. Data indicating whether or not a GPS fix has been acquired may be stored on test host  56 . 
     At step  160 , GPS location data stored on storage and processing circuitry  28  may be cleared to continue acquisition mode testing. Processing may loop back to step  154  to perform additional test iterations, as indicated by path  162 . 
     After a sufficient number of test iterations, an acquisition success rate may be calculated using test host  56 . If the acquisition success rate is satisfactory, GPS receiver  35  satisfies design criteria and DUT  10  is marked as a passing DUT (step  164 ). If acquisition success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria, and DUT  10  may be configured with new design settings (step  166 ). 
     The steps of  FIG. 11  are merely illustrative. If desired, test host  56  may direct DUT  10  to engage or disengage with a short-range network emulator (e.g., WiFi® and Bluetooth® transceiver circuits  36  may be toggled on or off at step  154  while cellular radio circuitry  38  remains off during the entirety of the acquisition mode testing). For example, test system  50  may include a network-access-point emulator that can communicate with the WiFi® circuitry in DUT  10  and a mobile device emulator that can communicate with the Bluetooth® circuitry in DUT  10  during testing. Enabling and disabling transceiver circuits  36  may generate rapid changes in T GPS  to introduce stress that negatively impacts the performance of GPS receiver  35 . If desired, radio circuitry  38  and transceiver circuitry  36  may simultaneously be toggled on or off at step  154  during acquisition mode testing. For example, circuitry  36  and  38  may both be turned on at time t 2  and may both be turned off at time t 5  (see, e.g., timing diagram of  FIGS. 3 and 4 ). 
       FIG. 12  shows steps involved in tracking mode testing of DUT  10  using the reduced-signaling arrangement. At step  168 , DUT  10  (e.g., a DUT with a shared crystal for cellular radio and for GPS circuitry) is powered on. At step  170 , DUT  10  may be directed to register with base station emulator  54 . At step  172 , DUT  10  may be given sufficient time to acquire a GPS fix. 
     At step  174 , test host  56  may direct DUT  10  to engage/disengage with base station emulator  54 . At step  176 , a timer may be started to allow GPS receiver  35  to acquire a GPS fix within the allotted tracking time period (e.g., a four seconds time period). At step  178 , DUT  10  may determine whether at least two new GPS fixes have been acquired during the allotted time. Data indicating whether or not multiple GPS fixes have been acquired may be stored on test host  56 . 
     GPS location data stored on storage and processing circuitry  28  need not be cleared for tracking mode testing. Processing may loop back to step  174  to perform additional test iterations, as indicated by path  180 . 
     After a sufficient number of test iterations, a tracking success rate may be calculated using test host  56 . If the tracking success rate is satisfactory, GPS receiver  35  satisfies design criteria and DUT  10  is marked as a passing DUT (step  182 ). If tracking success rate is not satisfactory, GPS receiver  35  fails to satisfy design criteria, and DUT  10  may be configured with new design settings aimed to improve GPS performance (step  184 ). 
     The steps of  FIG. 12  are merely illustrative. If desired, test host  56  may direct DUT  10  to engage or disengage with a short-range network emulator (e.g., WiFi® and Bluetooth® transceiver circuits  36  may be toggled on or off at step  174  while cellular radio circuitry  38  remains off during the entirety of the tracking mode testing). Enabling and disabling transceiver circuits  36  may generate rapid changes in T GPS  to introduce stress that negatively impacts the performance of GPS receiver  35 . If desired, radio circuitry  38  and transceiver circuitry  36  may simultaneously be toggled on or off at step  174  during tracking mode testing. For example, circuitry  36  and  38  may both be turned on at time t 3  and may both be turned off at time t 6  (see, e.g., timing diagram of  FIGS. 5 and 6 ). 
     Steps shown in  FIGS. 7-12  are merely illustrative. These validation techniques may be used to test GPS receiver performance during product design and during production testing. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20101115
Publication Date: 20111108
Grant Date: 20111108
Priority Date: 20101115
Inventors: LUONG ANH
KONG DANIEL C.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01S19/23", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S19/23", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44882518