PATENT DOCUMENT

Publication Number: US-9094840-B2
Application Number: US-201313738506-A
Country: US
Kind Code: B2

Title: Methods for testing receiver sensitivity of wireless electronic devices

Abstract:
A test system may include test equipment for testing the radio-frequency performance of wireless electronic devices. The test equipment may provide radio-frequency downlink signals to a wireless electronic device under test (DUT). The test equipment may perform a power sweep by stepping down the downlink signals in signal power level to test receiver sensitivity for the DUT. The DUT may gather measurement data from the downlink signals. The test equipment may retrieve measurement data from the DUT after downlink signal transmission has ended. The test equipment may identify a trigger in the retrieved measurement data to ensure that the data is synchronized with the power sweep in the transmitted downlink signals. The test equipment may identify path loss information associated with the test system. The test equipment may compute receiver sensitivity values for the DUT based on the path loss information and retrieved measurement data.

Claims:
What is claimed is: 
     
       1. A method of using a test system to test a device under test, comprising:
 with the test system, transmitting radio-frequency test signals at a plurality of power levels to the device under test, wherein the radio-frequency test signals include a test trigger signal having a test trigger duration; 
 with the test system, receiving test data from the device under test, wherein the test data includes a measured trigger signal having a measured trigger duration; 
 with the test system, determining whether the test data is synchronized with the test signals by comparing the measured trigger signal to the test trigger signal; 
 with the test system, computing a difference between the measured trigger duration and the test trigger duration; and 
 comparing the difference to a predetermined threshold to determine whether the test data is synchronized with the test signal. 
 
     
     
       2. The method defined in  claim 1 , wherein determining whether the test data is synchronized with the test signals comprises:
 comparing the measured trigger duration to the test trigger duration. 
 
     
     
       3. The method defined in  claim 1 , wherein the radio-frequency test signals further include a sensitivity power level sweep, and wherein the test trigger signal identifies a beginning of the sensitivity power level sweep. 
     
     
       4. The method defined in  claim 1 , further comprising:
 in response to determining that the test data is unsynchronized with the test signals, flagging the device under test as failing synchronization using the test system. 
 
     
     
       5. The method defined in  claim 1 , further comprising:
 in response to determining that the test data is synchronized with the test signals, identifying a receiver sensitivity for the device under test using the test data. 
 
     
     
       6. The method defined in  claim 1 , further comprising:
 with the test system, identifying a path loss power level associated with the device under test. 
 
     
     
       7. The method defined in  claim 6 , further comprising:
 in response to determining that the test data is synchronized with the test signals, computing a receiver sensitivity value for the device under test using the test data and the path loss power level. 
 
     
     
       8. A method of using a test system to test a device under test, comprising:
 with the test system, transmitting radio-frequency test signals at a plurality of power levels to the device under test, wherein the radio-frequency test signals include a test trigger signal; 
 with the test system, receiving test data from the device under test, wherein the test data includes a measured trigger signal; 
 with the test system, determining whether the test data is synchronized with the test signals by comparing the measured trigger signal to the test trigger signal; and 
 in response to determining that the test data is unsynchronized with the test signals, calibrating the test data by adding offset data to the test data so that the test data is synchronized with the test signals. 
 
     
     
       9. The method defined in  claim 8 , further comprising:
 in response to determining that the test data is unsynchronized with the test signals, flagging the device under test as failing synchronization using the test system, wherein flagging the device under test as failing synchronization further comprises calibrating the test data by adding the offset data to the test data so that the test data is synchronized with the test signals. 
 
     
     
       10. A method of using a test system to test a device under test, comprising:
 with the test system, transmitting radio-frequency test signals at a plurality of power levels to the device under test, wherein the radio-frequency test signals include a test trigger signal; 
 with the test system, receiving test data from the device under test, wherein the test data includes a measured trigger signal; 
 with the test system, determining whether the test data is synchronized with the test signals by comparing the measured trigger signal to the test trigger signal; and 
 in response to determining that the test data is synchronized with the test signals, identifying a receiver sensitivity for the device under test using the test data, wherein the test data includes error rate data, and identifying the receiver sensitivity comprises:
 comparing the error rate data to a predetermined threshold; and 
 identifying a power level in the plurality of power levels at which the device under test measures error rate data exceeding the predetermined threshold.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices having wireless communications circuitry. 
     Wireless electronic devices such as portable computers and cellular telephones are often provided with wireless communications circuitry. The wireless communications circuitry typically includes transceiver circuitry, antenna circuitry, and other radio-frequency circuitry that provides wireless communications capabilities. 
     The wireless communications circuitry is operable to receive radio-frequency signals. The wireless communications circuitry is tested in a test system to ensure adequate radio-frequency performance in response to receiving radio-frequency signals. The test system typically includes test equipment that provides radio-frequency downlink test signals to the wireless communications circuitry. Radio-frequency receive performance of the wireless communications circuitry is typically characterized by a performance metric such as receiver sensitivity. The wireless communications circuitry may fail to satisfy design criteria when the test equipment determines that the wireless communications circuitry has poor receiver sensitivity. 
     During conventional testing operations, radio-frequency data measured by the wireless communications circuitry is provided in real time to the test equipment, which adjusts signal power level of the radio-frequency downlink test signals based on the radio-frequency data. Performing test operations in this way may be time consuming and may lead to high manufacturing costs. 
     It would therefore be desirable to be able to provide improved test systems for testing wireless electronic devices. 
     SUMMARY 
     A wireless electronic device may include wireless communications circuitry. The wireless communications circuitry may include baseband circuitry, radio-frequency amplifier circuitry, radio-frequency transceiver circuitry, front-end circuitry, and antenna structures. The wireless communications circuitry may transmit and receive radio-frequency signals at a number of different frequencies. 
     A test system may be used to perform radio-frequency testing on a wireless electronic device to determine whether the wireless electronic device has adequate radio-frequency performance (e.g., adequate radio-frequency receive performance). Radio-frequency signals may be wirelessly conveyed between the test system and a wireless electronic device under test (DUT) at different frequencies. 
     During testing, a test system may transmit radio-frequency test signals to a DUT at a number of downlink signal power levels and at a selected frequency. The DUT may gather radio-frequency measurements such as radio-frequency performance information (e.g., error rate measurement data such as bit error rate, frame error rate, etc.) on the test signals without transmitting the performance information to the test system while the DUT is receiving the test signals from the test system. While receiving test signals, the DUT may run test software that identifies instructions for gathering the radio-frequency measurements. The test software may be stored on storage circuitry in the DUT prior to testing and may be disabled after testing. 
     The DUT may transmit radio-frequency uplink signals at a selected uplink power level to the test system while gathering performance information from the test signals. The DUT may compare gathered performance information to a predetermined threshold (e.g., error rate measurement value thresholds). If the DUT determines that the performance information exceeds the predetermined threshold, the DUT may reduce uplink power level. By reducing uplink power level, the DUT may instruct the test system to end transmission of the downlink test signals at the selected frequency (e.g., after a predetermined buffer time). The tester may, if desired, transmit additional test signals to the DUT at additional frequencies. Once no frequencies remain to be tested, the test system may retrieve the performance information from the DUT (e.g., the test system may retrieve test data gathered by the DUT from the test signals). 
     Downlink test signals provided by the test system to the DUT may include a trigger signal having a trigger duration. Some of the power levels with which the test signals are transmitted by the test system may form a sensitivity power level sweep (e.g., a sequence of monotonically decreasing downlink power level steps). The trigger signal may identify the beginning of the sensitivity power level sweep. The DUT may gather a measured trigger signal having a measured trigger duration from the test signals. The test system may compare the measured trigger duration to the trigger duration in the test signals to determine whether the measured performance information is synchronized with the corresponding test signals. 
     If the measured performance information is unsynchronized with the test signals, the DUT may be flagged as failing synchronization and, if desired, may be calibrated by adding offset data to the performance information (as an example). If the measured performance information is determined to be synchronized, the test system may identify receiver sensitivity for the DUT. The receiver sensitivity may, for example, be determined by identifying a power level in the sensitivity power level sweep at which the DUT measures performance information that exceeds the predetermined threshold. If desired, the test system may identify a path loss power level associated with the DUT. The test system may use the path loss power level to adjust the receiver sensitivity identified by the test system. The receiver sensitivity identified by the test system may be used to characterize the radio-frequency performance of the DUT. 
     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 wireless electronic device having wireless communications circuitry and test software in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of an illustrative test system including radio-frequency test equipment for testing a wireless electronic device using an over-the-air connection in accordance with an embodiment of the present invention. 
         FIG. 3  is a flow chart of illustrative steps for characterizing the radio-frequency performance of a wireless electronic device under test in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow chart of illustrative steps that may be performed by a wireless electronic device under test to gather measurement data in response to receiving downlink test signals from test equipment in accordance with an embodiment of the present invention. 
         FIG. 5  is a timing diagram illustrating the behavior of test signals that may be provided to a wireless electronic device for testing receiver sensitivity in accordance with an embodiment of the present invention. 
         FIG. 6  is a timing diagram illustrating error values that may be measured by a wireless electronic device under test in response to downlink test signals and illustrating the behavior of uplink test signals that may be provided to test equipment for indicating an excessive error value measurement in accordance with an embodiment of the invention. 
         FIG. 7  is a flow chart of illustrative steps that may be performed by test equipment to compute synchronized receiver sensitivity values after retrieving measurement data from a wireless electronic device in accordance with an embodiment of the present invention. 
         FIG. 8  is an illustrative graph showing how measurement data obtained by a wireless electronic device under test may be unsynchronized with respect to corresponding downlink test signals in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates generally to wireless communications, and more particularly, to systems and methods for testing wireless communications circuitry. 
     Electronic devices such as device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support long-range wireless communications such as communications in cellular telephone bands. Examples of long-range (cellular telephone) bands that may be handled by device  10  include the 800 MHz band, the 850 MHz band, the 900 MHz band, the 1800 MHz band, the 1900 MHz band, the 2100 MHz band, the 700 MHz band, and other bands. The long-range bands used by device  10  may include the so-called LTE (Long Term Evolution) bands. The LTE bands are numbered (e.g., 1, 2, 3, etc.) and are sometimes referred to as E-UTRA operating bands. 
     Long-range signals such as signals associated with satellite navigation bands may be received by the wireless communications circuitry of device  10 . For example, device  10  may use wireless circuitry to receive signals in the 1575 MHz band associated with Global Positioning System (GPS) communications, in the 1602 MHz band associated with Global Navigation Satellite System (GLONASS) communications, etc. Short-range wireless communications may also be supported by the wireless circuitry of device  10 . For example, device  10  may include wireless circuitry for handling local area network links such as WiFi® links at 2.4 GHz and 5 GHz, Bluetooth® links at 2.4 GHz, etc. In general, wireless communications circuitry in device  10  may support wireless communications in any suitable communications bands. 
     As shown in  FIG. 1 , 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, 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, functions related to communications band selection during radio-frequency transmission and reception operations, software for testing the radio-frequency performance of device  10 , etc. To support interactions with external equipment (e.g., a radio-frequency base station, radio-frequency test equipment, etc.), 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 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, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, the “3G” Evolution-Data Optimized (EV-DO) protocol, the “4G” Long Term Evolution (LTE) protocol, MIMO (multiple input multiple output) protocols, antenna diversity protocols, etc. 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  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 devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  30  may include wireless communications circuitry  34  for communicating wirelessly with external equipment (e.g., a radio-frequency base station, radio-frequency test equipment, etc.). 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, transmission lines, 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 radio-frequency transceiver circuitry  38  for handling various radio-frequency communications bands. For example, circuitry  38  may handle the 2.4 GHz and 5 GHz communications bands for WiFi® (IEEE 802.11) communications, the 2.4 GHz communications band for Bluetooth® communications, cellular telephone bands such as at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz and/or the LTE bands and other bands (as examples). Circuitry  38  may handle voice data and non-voice data traffic. Transceiver circuitry  38  may include global positioning system (GPS) receiver equipment for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. 
     Wireless communications circuitry  34  may include one or more 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 structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, monopole antenna structures, dipole antenna structures, helical antenna structures, 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 Wi-Fi® wireless link antenna and another type of antenna may be used in forming a cellular wireless link antenna. During communication operations, transceiver circuitry  38  may be used to transmit radio-frequency signals at desired frequencies via antennas  40  (e.g., antennas  40  may transmit wireless signals having a desired frequency). 
     As shown in  FIG. 1 , wireless communications circuitry  34  may also include baseband processor  36 . Baseband processor  36  may include memory and processing circuits and may also be considered to form part of storage and processing circuitry  28  of device  10 . 
     Baseband processor  36  may be used to provide data to storage and processing circuitry  28 . Data that is conveyed to circuitry  28  from baseband processor  36  may include raw and processed data. Raw data may, for example, include downlink data received by antennas  40  (e.g., downlink test data transmitted by external test equipment). Processed data that is passed from baseband processor  36  to storage and processing circuitry  28  may include received (downlink) power level data (e.g., signal power levels of radio-frequency downlink signals received by antennas  40 ) and error data such frame error rate (FER) data, bit error rate (BER) data, block error rate (BLER) data, symbol error rate (SER) data, etc. Error data passed to circuitry  38  may be indicative of how well wireless communications circuitry  34  receives downlink signals. Baseband processor  36  may, for example, monitor and process raw data to generate radio-frequency error values (e.g., bit error rate values, block error rate values, symbol error rate values, etc.) and received power levels to be conveyed to storage and processing circuitry  28 . Baseband processor  26  may generate timing information to be conveyed to storage and processing circuitry  28 . Timing information generated by processor  26  may include time stamp values each corresponding to a respective error value and received power level generated by processor  26 . 
     During communications operations, non-idealities (e.g., amplifier noise, amplifier non-linearity, manufacturing variation, etc.) in wireless communications circuitry  34  may degrade the quality of received (downlink) radio-frequency signals. Degradation in signal quality may be greater for downlink signals received at a lower signal power level than for downlink signals received at a higher signal power level. For example, downlink signals received by circuitry  34  at insufficient signal power levels may have undesirable distortions or errors when received at transceiver circuitry  38 . 
     Radio-frequency test operations may be performed on wireless communications circuitry  34  (e.g., using external test equipment) to determine whether circuitry  34  has acceptable radio-frequency performance when receiving radio-frequency downlink signals. Radio-frequency performance of circuitry  34  may be characterized by a radio-frequency performance metric such as receiver sensitivity (sometimes referred to as receive sensitivity or downlink sensitivity). In general, any suitable performance metric associated with received radio-frequency signals may be used to characterize the radio-frequency performance of wireless communications circuitry  34  (e.g., signal to noise ratio, received signal strength indicator (RSSI) information, adjacent channel leakage ratio (ACLR) information, etc.). 
     If desired, error value data generated by baseband processor  36  during test operations may be used to determine whether wireless communications circuitry  34  satisfies a given performance metric. For example, bit error rate values generated by baseband processor  36  from received radio-frequency signals may be used to determine whether wireless communications circuitry  34  has acceptable receiver sensitivity. 
     Software for performing radio-frequency test operations on device  10  such as test software  26  may be provided (e.g., stored) on storage and processing circuitry  26 . Test software  26  may sometimes be referred to as a test operating system or a test application. Test software  26  may provide instructions for the operation of wireless communications circuitry  34  and storage and processing circuitry  28  during radio-frequency test operations. Test software  26  may, for example, instruct wireless communications circuitry  34  to gather measurements (sometimes referred to as measurement information) from radio-frequency downlink signals received from external test equipment. Measurement information gathered by circuitry  34  during testing may include received power levels, error values (e.g., bit error rate values), and corresponding time stamp values measured from received downlink test signals. 
     Measurement information gathered by wireless communications circuitry  34  may be stored in storage and processing circuitry  28  until completion of test operations. Once testing has been completed, external test equipment may retrieve and analyze measurement information from device  10  to characterize the radio-frequency performance of circuitry  34 . In this way, device  10  may perform test operations autonomously (e.g., wireless circuitry  34  may perform test operations without receiving test instructions from external test equipment and without transmitting measurement information to external test equipment during test operations). By performing test operations autonomously, excessive communication between external test equipment and device  10  during test operations may be avoided, thereby reducing testing time and increasing test efficiency. 
     Test software  26  may be stored on storage and processing circuitry  28  permanently or temporarily. For example, test software  26  may be loaded onto storage and processing circuitry  28  using external test equipment prior to test operations. If desired, test software  26  may be removed (e.g., deleted, disabled, placed in a hidden state, etc.) from storage and processing circuitry  28  after test operations have been completed. 
     As shown in  FIG. 2 , external test equipment such as radio-frequency test system  64  may be used to perform radio-frequency test operations on wireless communications circuitry in electronic devices such as device  10  (e.g., to ensure adequate radio-frequency performance of wireless communications circuitry  34 ). Each electronic device that is being tested using radio-frequency test system  64  may sometimes be referred to as a device under test (DUT)  10 ′. DUT  10 ′ may be, for example, a fully assembled electronic device such as an electronic device  10  or a partially assembled electronic device (e.g., DUT  10 ′ may include some or all of wireless circuitry  34  prior to completion of manufacturing). It may be desirable to test wireless communications circuitry  34  within partially assembled electronic devices so that wireless communications circuitry  34  can be more readily accessed during test operations (e.g., to test the performance of wireless communications circuitry  34  that have not yet been enclosed within a device housing). 
     As shown in  FIG. 2 , test system  64  may include test host  42  (e.g., a personal computer, laptop computer, tablet computer, handheld computing device, etc.), a test unit such as tester  44 , and a test enclosure structure such as test enclosure  56 . Test host  42  and/or tester  44  may include storage circuitry. Storage circuitry in test host  42  and tester  44  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), etc. 
     Tester  44  may include, for example, a radio communications analyzer, spectrum analyzer, vector network analyzer, power sensor, or any other components suitable for performing radio-frequency test operations on DUT  10 ′. Tester  44  may be operated directly or via computer control (e.g., when tester  44  receives commands from test host  42 ). When operated directly, a user may control tester  44  by supplying commands directly to tester  44  using a user input interface of tester  44 . For example, a user may press buttons in a control panel on tester  44  while viewing information that is displayed on a display in test unit  44 . In computer controlled configurations, test host  42  (e.g., software running autonomously or semi-autonomously on test host  42 ) may communicate with tester  44  by sending and receiving control signals and data over path  46 . Test host  42  and tester  44  may collectively be considered as test equipment  48 . Test equipment  48  may be a computer, test station, or other suitable system that performs the functions of test host  42  and tester  44  (e.g., the functionality of test host  42  and tester  44  may be implemented on one or more computers, test stations, etc.). 
     During testing, at least one DUT  10 ′ may be placed within test enclosure  56 . Test enclosure  56  may be a shielded enclosure (e.g., a shielded test box) for use in providing radio-frequency isolation from external sources of radiation, interference, and noise so that DUT  10 ′ is tested in a controlled environment. Test enclosure  56  may, for example, be a transverse electromagnetic (TEM) cell. Test enclosure  56  may have a cubic structure (six planar walls), a rectangular prism-like structure (six rectangular walls), a pyramid structure (four triangular walls with a rectangular base), or any other desired structures. 
     If desired, the interior of test enclosure  56  may be lined with radio-frequency absorption material such as rubberized foam configured to minimize reflections of wireless signals. Test enclosure  56  may include wireless structures  54  in its interior for communicating with DUT  10 ′ using wireless radio-frequency signals. Wireless structures  54  may sometimes be referred to herein as test antennas  54 . Test antenna  54  may, as an example, be a microstrip antenna, microstrip patch antenna, inverted-F antenna, loop antenna, dipole antenna, monopole antenna, planar inverted-F antenna, slot antenna, notch antenna, hybrid antenna, or any other desired antenna structure. During test operations, wireless radio-frequency signals that are transmitted from DUT  10 ′ to antennas  54  (e.g., in the direction of arrow  60 ) may sometimes be referred to as uplink test signals. Wireless signals that are transmitted from antennas  54  to DUT  10 ′ during test operations (e.g., in the direction of arrow  62 ) may sometimes be referred to as downlink test signals. 
     DUT  10 ′ may be optionally coupled to test host  42  via path  50 . Path  50  may be, for example, a wired path such as a Universal Serial Bus (USB) cable, a Universal Asynchronous Receiver/Transmitter (UART) cable, or other types of cabling (e.g., bus  218  may be a USB-based connection, a UART-based connection, or other types of connections). Connected in this way, test host  42  may provide software such as test software  26  to be stored on storage and processing circuitry  28  of DUT  10 ′ prior to testing (see  FIG. 1 ) and may receive measurement information from DUT  10 ′ upon completion of testing. 
     Test antenna  54  may be coupled to tester  44  via radio-frequency cable  52  (e.g., a coaxial cable or any other desired radio-frequency transmission line structure). Test antenna  54  and radio-frequency cable  52  may be used during test operations to perform over-the-air (wireless) testing on DUT  10 ′. For example, radio-frequency uplink and downlink test signals may be conveyed between DUT  10 ′ and tester  44  via test antenna  54  and radio-frequency cable  52 . 
     During test operations, tester  44  may generate and transmit downlink test signals for DUT  10 ′ (e.g., via cable  52  and antenna  54 ). Downlink test signals may, if desired, include a sequence of digital bits (e.g., a data stream of digital bits). Tester  44  may generate downlink test signals at different transmit frequencies. For example, tester  44  may generate downlink test signals at a first frequency during a first time period and may generate downlink test signals at a second frequency during a second time period. In another suitable arrangement, tester  44  may generate and transmit downlink test signals in different frequency channels (e.g., different ranges of transmit frequencies). 
     Tester  44  may generate downlink test signals at different signal power levels (e.g., at different output power levels of tester  44 ). Output power levels at which downlink test signals are generated by tester  44  may sometimes be referred to as downlink power levels. If desired, tester  44  may sequentially generate downlink test signals at different downlink power levels. For example, tester  44  may generate downlink test signals at a first downlink power level during a first time period and at a second downlink power level during a second time period. Downlink test signals may, if desired, be stepped up or down in downlink power level to test receiver sensitivity of DUT  10 ′ (e.g., the minimum downlink power level for which DUT  10 ′ can still receive corresponding downlink test signals properly). The process by which downlink test signals are stepped down in downlink power level by tester  44  to test for receiver sensitivity may sometimes be referred to herein as a “sensitivity sweep” or “power sweep.” 
     Tester  44  may generate downlink test signals having a so-called “trigger” signal that identifies the beginning of a corresponding power sweep. The trigger may, for example, include of an increase or decrease in downlink power level (e.g., an increase or decrease in power by a known power level) for a predetermined trigger duration prior to the beginning of a power sweep. The trigger may be used after the completion of downlink test signal transmission (e.g., during analysis of measurement information using test equipment  48 ) to ensure proper synchronization between measurement data gathered by DUT  10 ′ during downlink signal transmission and information associated with the corresponding downlink test signals generated by tester  44  (e.g., a test sequence with which the corresponding downlink signals are generated by tester  44 ). 
     DUT  10 ′ may perform desired radio-frequency measurements on the downlink test signals received from tester  44 . For example, DUT  10 ′ may measure downlink power levels, error values (e.g., bit error rate values), and time stamp values for the received downlink test signals. Downlink power levels, error values, and time stamp values gathered by DUT  10 ′ from received downlink test signals may sometimes be referred to herein as measured downlink power levels, measured error values, and measured time stamp values, respectively. Measured downlink power levels, measured error values, and measured time stamp values may sometimes be referred to collectively as measurement data. Measured time stamp values may each correspond to a respective measured error value and measured downlink power level (e.g., DUT  10 ′ may record a time stamp value to indicate a time at which each corresponding error value and downlink power level is measured). In this way, DUT  10 ′ may record measured downlink power levels and measured error values as a function of time for downlink test signals received at DUT  10 ′ (e.g., DUT  10 ′ may record a sequence with which downlink test signals are received at different measured downlink power levels). 
     Test equipment  48  may record information associated with generated downlink test signals such as downlink power levels at which downlink test signals are transmitted to DUT  10 ′. Test equipment  48  may store time stamp values associated with the downlink test signals (sometimes referred to herein as tester time stamp values). Tester time stamp values may be indicative of the times at which downlink test signals are transmitted at given downlink power levels. In this way, test equipment  48  may record downlink power levels transmitted to DUT  10 ′ as a function of time (e.g., tester  44  may record a sequence with which downlink test signals are transmitted at selected downlink power levels). This information may be used after completion of downlink test signal transmission to ensure proper synchronization between the transmitted downlink test signals and the corresponding measurement data obtained by DUT  10 ′ (e.g., by comparing the duration of a trigger signal measured by DUT  10 ′ to the duration of a corresponding trigger signal in the downlink test signals generated by tester  44 ). Due to various non-idealities in DUT  10 ′ (e.g., manufacturing variations, timing circuitry variations, etc.), measurement data may sometimes be unsynchronized with respect to the corresponding downlink test data (e.g., measured time stamp values may not match tester time stamp values recorded by tester  44  during testing). Proper synchronization may ensure reliable measurement of receiver sensitivity for DUT  10 ′. 
     Tester  44  may perform a series of power sweeps at different frequencies while testing receiver sensitivity for DUT  10 ′. After performing the series of power sweeps, test host  42  may retrieve the measurement data from DUT  10 ′ and extract portions of the measurement data that correspond to each power sweep performed by tester  44  (e.g., portions of the measurement data each corresponding to power sweeps at respective test frequencies). Each portion of the measurement data may be further divided into groups of measurement data. Each group in a given portion of measurement data may correspond to a respective step in the associated power sweep performed by tester  44 . The measurement data (e.g., each group of measurement data) may be considered to be synchronized with a given power sweep in the downlink test signals if the measured time stamp values between the beginning of the trigger signal and the end of the power sweep is consistent with a predetermined value such as the corresponding tester time stamp values associated with the downlink test signals generated by tester  44 . In another suitable arrangement, each group of measurement data may be considered to be synchronized if the trigger duration measured by DUT  10 ′ is consistent with a predetermined value such as the corresponding trigger duration generated by tester  44  in the downlink test signals. 
     Measured downlink power levels may exhibit an offset with respect to the corresponding downlink power levels generated at tester  44 . For example, measured downlink power levels may be offset with respect to corresponding downlink power levels generated at tester  44  due to radio-frequency path loss in test system  64 . 
     Radio-frequency path loss can be defined as the attenuation in power as wireless signals propagate through a particular medium. Test system  64  may experience run-to-run measurement variation due to variations in over-the-air (OTA) path loss (e.g., path loss associated with the propagation of radio-frequency signals as they propagate through air, path loss associated with the behavior of test antennas  54  during wireless transmission, etc.). Test system  64  may experience run-to-run measurement variation with respect to other test systems due to OTA path loss and radio-frequency cable path loss associated with cable  52 . It may therefore be desirable to characterize test system path loss in order to take variations associated with path loss into account when determining the receiver sensitivity of DUT  10 ′. 
     The OTA path loss and radio-frequency cable path loss in a given test system  64  is typically unique, because it is challenging to manufacture test equipment that are exactly identical to one another and to configure each test system  64  with an identical spatial arrangement. OTA path loss may, for example, be sensitive to the location of test antenna  54 , the placement of DUT  10 ′ within test enclosure  56 , the transmit frequency of tester  44  and DUT  10 ′, etc. Test system  64  may account for path loss when determining receiver sensitivity for DUT  10 ′ (e.g., to determine receiver sensitivity values for DUT  10 ′ that are independent of the test system). 
     During test operations, DUT  10 ′ may generate and transmit uplink test signals for tester  44  (e.g., via cable  52  and antenna  54 ). If desired, DUT  10 ′ may generate uplink test signals having different signal power levels. Signal power levels with which uplink test signals are generated may sometimes be referred to as uplink power levels. As an example, DUT  10 ′ may generate uplink test signals at a first uplink power level during a first time period and at a second uplink power level during a second time period. 
     Software  26  that is stored on storage and processing circuitry  28  may instruct DUT  10 ′ to gather measurement data (e.g., measured power levels, measured error values, and measured time stamp values) from received downlink test signals and may instruct DUT  10 ′ to transmit uplink test signals at selected uplink power levels to tester  44 . Measurement data gathered by DUT  10 ′ may be maintained in storage and processing circuitry  28  until completion of testing (e.g., measurement data may be stored as an array of data in storage and processing circuitry  28 ). 
     Tester  44  may perform desired radio-frequency measurements on uplink test signals received from DUT  10 ′. For example, tester  44  may measure uplink power levels of received uplink test signals. During test operations, DUT  10 ′ may adjust uplink power level to signal that DUT  10 ′ has gathered enough measurement data to determine receiver sensitivity. For example, once a sufficient amount of measurement data has been gathered, DUT  10 ′ may reduce uplink power level to signify the end of a power sweep cycle so that test system  64  can prepare another power sweep cycle (e.g., a power sweep cycle at a different test frequency). This is merely illustrative. If desired, DUT  10 ′ may completely shut down uplink transmission or may increase uplink power level to signify the end of a current power sweep cycle. 
     Once test operations have been completed (e.g., once tester  44  has ceased transmitting downlink test signals), DUT  10 ′ may provide measurement data to test host  42  via path  50 . In another suitable arrangement, DUT  10 ′ may wirelessly provide measurement data to test host  42  via antennas  54  and cable  52 . Test host  42  may subsequently process the received measurement data to characterize the radio-frequency performance of DUT  10 ′ (e.g., by determining receiver sensitivity for DUT  10 ′). 
       FIG. 3  shows a flow chart of illustrative steps that may be performed by a test system such as test system  64  to test the radio-frequency performance of DUT  10 ′. The steps of  FIG. 3  may be performed to ensure adequate receiver sensitivity of DUT  10 ′. 
     At step  70 , test host  42  may provide test software such as test software  26  to DUT  10 ′. Test software  26  may be stored on storage and processing circuitry  28  of DUT  10 ′. Test software  26  may, for example, be conveyed from test host  42  to DUT  10 ′ over path  50  (see  FIG. 2 ). In another suitable arrangement, test software  26  may be wirelessly provided to DUT  10 ′ over cable  52  and test antenna  4 . In yet another suitable arrangement, test software  26  may be provided to DUT  10 ′ by a test station operator. 
     At step  72 , test host  42  may select a frequency at which to transmit downlink test signals to DUT  10 ′ (sometimes referred to as a test frequency). The selected test frequency may, for example, be a frequency in a communications band such as a cellular band, GPS band, Wi-Fi® band, or any other desired communications band implemented by DUT  10 ′ during radio-frequency communications. 
     At step  74 , tester  44  transmits downlink test signals (downlink test data) to DUT  10 ′ at the selected test frequency and with desired downlink power levels. For example, tester  44  may step down the downlink test signals in downlink power level for testing receiver sensitivity of DUT  10 ′ (e.g., tester  44  may perform a power sweep using the transmitted downlink test signals). Tester  44  may transmit downlink test signals having a trigger prior to the power sweep (e.g., a trigger that identifies the beginning of the power sweep). 
     Tester  44  may receive uplink test signals from DUT  10 ′ while transmitting downlink test signals to DUT  10 ′. Tester  44  may measure uplink power levels of the received uplink test signals. Tester  44  may monitor received uplink test signals for uplink power level adjustments performed by DUT  10 ′. 
     At step  76 , tester  44  may identify a change in uplink power level (e.g., a change in uplink power level due to an uplink power level adjustment performed by DUT  10 ′). For example, tester  44  may identify a decrease in uplink signal power level. Tester  44  may subsequently end downlink test signal transmission at the selected test frequency. If desired, tester  44  may continue to step down downlink test signals in downlink power level after identifying a decrease in uplink signal transmission and prior to ending downlink test signal transmission. For example, tester  44  may continue to step down the downlink test signals for a selected buffer time. The buffer time may be selected to allow tester  44  to verify that DUT  10 ′ has properly decreased uplink power level (e.g., to ensure that a decrease in uplink power level provided by DUT  10 ′ is not due to a temporary error or glitch). As another example, tester  44  may continue to step down the downlink test signals for a selected number of additional downlink power levels. If there are additional frequencies to be tested, processing may loop back to step  72  via path  78  to transmit downlink test signals to DUT  10 ′ at the additional test frequencies. 
     If no frequencies remain to be tested, processing may proceed to step  82 , as indicated by path  80 . At step  82 , test host  42  may retrieve measurement data gathered by DUT  10 ′. Test host  42  may analyze the retrieved measurement data to determine receiver sensitivity values for DUT  10 ′ at each of the tested frequencies. For example, test host  42  may use measured error values, measured power levels, and measured time stamp values gathered by DUT  10 ′ to determine receiver sensitivity values. Receiver sensitivity values may be determined from the last measured downlink power level that is greater than a downlink power level at which DUT  10 ′ measures excessively high error values (e.g., the lowest downlink power level associated with acceptable downlink signal reception at DUT  10 ′). During analysis, test host  42  may ensure proper synchronization between retrieved measurement data and downlink test signals transmitted by tester  44 . If desired, test host  42  may determine path loss information for DUT  10 ′. Test host  42  may adjust receiver sensitivity values using the path loss information to generate adjusted receiver sensitivity values that are independent of the particular test system  64  that is used. 
     At step  84 , test host  42  may compare adjusted receiver sensitivity values to predetermined receiver sensitivity thresholds. In response to determining that the receiver sensitivity value for one or more test frequencies is greater than a corresponding receiver sensitivity threshold, test host  42  may determine that DUT  10 ′ fails testing. In other words, if DUT  10 ′ has excessively high receiver sensitivity values (i.e., poor receiver sensitivity), test host  42  may identify that DUT  10 ′ has insufficient radio-frequency receiver performance (e.g., DUT  10 ′ may have degraded signal reception due to excessive non-idealities in wireless communications circuitry  34 ). 
     Devices under test that fail testing may be scrapped or, if desired, may be reworked. If desired, test frequencies corresponding to excessively high receiver sensitivity values may be flagged for subsequent analysis. In response to determining that the receiver sensitivity values each satisfy corresponding receiver sensitivity thresholds (e.g., that the receiver sensitivity values are each less than a corresponding receiver sensitivity threshold), test host  42  may determine that DUT  10 ′ passes testing. In this way, test equipment  48  may ensure that DUT  10 ′ has sufficient radio-frequency receive performance. 
     If desired, DUT  10 ′ may be identified as having unacceptable radio-frequency receive performance if the receiver sensitivity value for any desired number of test frequencies exceeds a corresponding receiver sensitivity threshold. For example, DUT  10 ′ may be characterized as having insufficient radio-frequency receive performance if the receiver sensitivity value at one or more test frequencies fails to satisfy the corresponding receiver sensitivity threshold. Determining whether DUT  10 ′ passes or fails testing may sometimes be referred to as performing pass-fail operations. 
       FIG. 4  shows a flow chart of illustrative steps that may be performed by a wireless electronic device under test such as DUT  10 ′ during radio-frequency test operations. The steps of  FIG. 4  may be performed to determine radio-frequency receive performance for DUT  10 ′. 
     At step  170 , DUT  10 ′ receives test software  26  from test host  42 . Test software  26  received from test host  42  may be stored (e.g., installed) on storage and processing circuitry  28 . Test software  26  may instruct DUT  10 ′ to perform radio-frequency test operations. For example, the steps of  FIG. 4  may be performed by DUT  10 ′ in response to test instructions provided by test software  26  (e.g., DUT  10 ′ may perform test operations without receiving further test instructions from test equipment  48 ). 
     At step  172 , DUT  10 ′ may begin receiving downlink test signals (e.g., downlink test data) from tester  44 . At step  174 , DUT  10 ′ may begin transmitting uplink test signals to tester  44  at a selected uplink power level. Uplink test signals transmitted by DUT  10 ′ may, for example, be transmitted at a maximum output power level of wireless communications circuitry  34 , at a minimum output power level of wireless communications circuitry  34 , or any other suitable uplink power level. In another suitable arrangement, DUT  10 ′ may begin transmitting uplink test signals prior to beginning to receive downlink test signals from tester  44  (i.e., DUT  10 ′ may, if desired, perform step  174  prior to step  172 ). DUT  10 ′ may transmit uplink test signals and receive downlink test signals simultaneously. 
     At step  176 , DUT  10 ′ may perform radio-frequency measurements on downlink test signals received from tester  44 . For example, DUT  10 ′ may gather measurement data including measured downlink power levels, measured error values, and measured time stamp values from received downlink test signals. Measurement data gathered by DUT  10 ′ may be stored in storage and processing circuitry  28  until completion of testing. 
     While gathering measurement data from downlink test signals, DUT  10 ′ may compare measured error values to error value thresholds (e.g., DUT  10 ′ may compare error values that have already been measured to error value thresholds while gathering additional measured error values). For example, DUT  10 ′ may compare measured bit error rate (BER) values for received downlink test signals to a bit error rate threshold. When the measured error values exceed the error value threshold, processing may proceed to step  178 . The threshold error value may be determined, for example, from carrier-imposed requirements, regulatory requirements, manufacturing requirements, design requirements, or any other suitable standards for the radio-frequency performance of DUT  10 ′. 
     At step  178 , DUT  10 ′ may reduce the uplink power level provided to tester  44 . For example, DUT  10 ′ may reduce uplink power level to half of the maximum output power level of circuitry  34 , to a minimum output power level of circuitry  34 , or to any other suitable power level that is less than the uplink power level transmitted at steps  174  and  176 . By reducing the uplink power level, DUT  10 ′ may signify to tester  44  that DUT  10 ′ has measured excessive error values (e.g., error values that are greater than the error value threshold). In this way, DUT  10 ′ may produce a trigger that instructs tester  44  to end a current power sweep and to begin an additional power sweep (e.g., an additional power sweep at a different test frequency). 
       FIG. 5  is an illustrative graph showing how downlink test signals may be provided at different downlink power levels to DUT  10 ′ to determine receiver sensitivity of DUT  10 ′ in accordance with an embodiment of the present invention. Curve  88  illustrates downlink power levels over time generated by tester  44  at a selected frequency. Times T 0 , T 1 , T 2 , etc. may, for example, be tester time stamp values stored in test equipment  48 . Curve  88  may, for example, be obtained by performing step  74  of  FIG. 3 . 
     Between times T A  and T 1 , tester  44  may provide downlink test data to DUT  10 ′ at downlink power level P 0 . The duration between times T A  and T 1  may be selected to ensure that DUT  10 ′ and tester  44  are able to establish a reliable wireless connection (e.g., to ensure that DUT  10 ′ and tester  44  are communicating at the same test frequency). At time T 1 , tester  44  may increase downlink power level by trigger size ΔP T  to power level P 0 +ΔP T . Tester  44  may generate downlink power level P 0 +ΔP T  between times T 1  and T 2  to form trigger  180  having a trigger duration ΔT TR . Downlink power level P 0  may be any suitable output power level that allows DUT  10 ′ to detect trigger  180 . Trigger duration ΔT TR  may be any suitable duration that is detectable by DUT  10 ′ upon measurement of the downlink test data associated with curve  88 . For example, trigger duration ΔT TR  may be chosen so that DUT  10 ′ has sufficient time to detect an increase in downlink signal power by trigger size ΔP T . 
     Between times T 2  and T 3 , tester  44  may step down downlink power level by initialization step size ΔP S . In the example of  FIG. 4 , tester  44  decreases downlink power level by initialization step size ΔP S  three times to sweep initialization power level P 1  at time T 3 . The duration between times T 3  and T 2  may sometimes be referred to as sweep initialize duration ΔT TS . By stepping down downlink power level between times T 2  and T 3 , tester  44  may ensure that DUT  10 ′ properly receives the downlink test signals associated with curve  88  (e.g., to ensure that DUT  10 ′ maintains a wireless connection with tester  44 ). A reliable wireless connection between DUT  10 ′ and tester  44  may sometimes be lost or “dropped” in a scenario where downlink power is not suitably stepped down between times T 2  and T 3 . For example, if tester  44  transmits downlink test signals at 40 dBm at time T 2  and steps down once to a downlink power level of −40 dBm at time T 3 , DUT  10 ′ may lose connection with the downlink test signals provided by tester  44  (e.g., due to insufficient response time in wireless circuitry  34 , etc.). 
     At time T 3 , tester  44  may perform a power (sensitivity) sweep for DUT  10 ′. For example, tester  44  may step down downlink power level by sweep step size ΔP W  between times T 3  and T 8  to provide a number of discrete downlink power levels each for step duration ΔT SW . In the example of  FIG. 5 , tester  44  may decrease downlink power level by step size ΔP W  to power level P 2  at time T 4 . After step duration ΔT SW  (e.g., at time T 5 ), tester  44  may decrease downlink power level by step size ΔP W  to power level P 3 . After an additional step duration ΔT SW  (e.g., at time T 7 ), tester  44  may decrease downlink power level by step size ΔP W  to power level P 4 . This process may be repeated until time T 8 . 
     At time T 8 , tester  44  may reset downlink power to downlink power level P 0 . At time T 9 , tester  44  may end transmission of downlink test signals at the selected frequency. If desired, this process may be repeated to provide downlink test signals to DUT  10 ′ at other transmit frequencies (e.g., as shown by path  78  of  FIG. 3 ). The time duration between times T 8  and T 9  may sometimes be referred to as handover time ΔT H . Handover time ΔT H  may be selected to allow sufficient time for DUT  10 ′ to begin receiving downlink test signals at a subsequent test frequency. 
     For example, DUT  10 ′ may measure an increase in downlink power level to downlink power level P 0 , after which DUT  10 ′ will have time duration ΔT H  to begin receiving downlink test signals at the subsequent test frequency (e.g., tester  44  may begin transmitting downlink test signals at the subsequent frequency at time T 9 ). DUT  10 ′ may begin searching for downlink test signals at the additional frequency at time T 8 . Once a reliable connection between DUT  10 ′ and tester  44  has been established at the additional frequency, this process may be repeated to test DUT  10 ′ at additional frequencies. 
     In another suitable arrangement, DUT  10 ′ may begin searching for downlink test signals at the additional frequency at time T 6 . Time T 6  may be a time at which DUT  10 ′ measures an error value that is above a predetermined error value threshold (e.g., the time at which DUT  10 ′ reduces uplink power level to instruct tester  44  to prepare for testing at the additional frequency). Tester  44  may begin transmitting downlink test signals at the additional frequency at time T 8  (e.g., tester  44  may continue to perform a power sweep for buffer duration ΔT B  after time T 6  before providing downlink power level P 0  at the additional test frequency at time T 8 ). DUT  10 ′ may then have a time period given by handover duration ΔT H  to detect and reliably receive downlink test signals at the additional frequency. The duration between times T 1  and T 8  may sometimes be referred to as test duration ΔT T . Test duration ΔT T  may include trigger duration ΔT TR , sweep initialization duration ΔT TS , and the duration of the sensitivity sweep. 
       FIG. 6  is an illustrative graph showing how uplink test signals may be transmitted by DUT  10 ′ to tester  44  in response to receiving downlink test signals and in response to error value measurements gathered by DUT  10 ′. Curve  90  illustrates uplink power levels transmitted by DUT  10 ′ over time. Curve  90  may, for example, be obtained by performing steps  174 - 178  of  FIG. 4 . 
     Curve  92  illustrates measured error values gathered by DUT  10 ′ from received downlink test signals over time. Curve  92  may, for example, be obtained by performing step  176  of  FIG. 4 . The uplink test signals associated with curve  90  may be used to instruct tester  44  to end downlink test signal transmission after excessive error values (e.g., error values associated with curve  92 ) are measured. 
     Before time T 0 , DUT  10 ′ may transmit uplink test signals to tester  44  at uplink power level P A . If desired, uplink power level P A  may be a minimum power level of wireless communications circuitry  34 . At time T 0 , DUT  10 ′ may increase uplink power level to power level P B . If desired, power level P B  may be a maximum power level of wireless communications circuitry  34 . 
     Before time T 3 , DUT  10 ′ may measure error value E 0  from the received downlink test signals. Error value E 0  may, for example, be negligible because downlink power level P 0  transmitted by tester  44  at time T 0  is sufficiently high. Between times T 3  and T 8 , DUT  10 ′ may measure error values in response to the sensitivity sweep in the downlink test data. In the example of  FIG. 6 , DUT  10 ′ measures error value E 1  from received downlink test signals between times T 3  and T 4  (e.g., during a first step of the sensitivity sweep performed by tester  44  in which a downlink power level P 1  is generated as shown in  FIG. 5 ). DUT  10 ′ measures error value E 2  from received downlink test signals between times T 4  and T 5  (e.g., during a second step of the sensitivity sweep in which a downlink power level P 2  is generated). DUT  10 ′ may measure error value E 3  from received downlink test signals between times T 6  and T 7  (e.g., during a third step of the sensitivity sweep in which a downlink power level P 3  is generated). DUT  10 ′ may determine that error value E 3  is greater than threshold error value E TH . In other words, DUT  10 ′ may measure an excessively high error value from downlink test signals generated at power level P 3 . In this example, downlink power level P 3  may be insufficient for downlink signal reception by DUT  10 ′ (e.g., receiving downlink test signals at or below downlink power level P 3  may cause wireless circuitry  34  to measure excessively high error values). 
     In response to determining that error value E 3  is greater than threshold E TH , DUT  10 ′ may reduce uplink power level by margin ΔP AB  (e.g., at time T 6 ). If desired, margin ΔP AB  may be equal to the difference between maximum output power level P B  and minimum output power level P B . In general, margin ΔP AB  may be any desired decrease in uplink power level that can be detected by tester  44  (e.g., margin ΔP AB  may be larger than any inherent variation in uplink power level due to instability of wireless communications circuitry  34 , thermal noise, measurement tolerance in tester  44 , etc.). 
     In this way, DUT  10 ′ may indicate to tester  44  that DUT  10 ′ has measured excessive error values in response to the downlink test data. Tester  44  may continue to step down downlink power levels and DUT  10 ′ may continue to gather measurement data for a selected buffer time (e.g., between times T 7  and T 8 ). The duration between times T 7  and T 8  may sometimes be referred to as buffer duration ΔT B  (see, e.g.,  FIG. 5 ). 
     In another suitable arrangement, DUT  10 ′ may measure multiple error values for each step of the sensitivity sweep. In this scenario, error values E 0 , E 1 , E 2 , and E 3  may each be average error values that are computed by DUT  10 ′ for all measured error values in each corresponding sensitivity sweep step. If desired, step duration ΔT SW  may be selected to allow DUT  10 ′ to measure a sufficient number of error values for each step in the sensitivity sweep (e.g., a sufficient number of error values necessary to compute reliable average error values, etc.). For example, if DUT  10 ′ is configured to measure each error value in 1 ms and 100 measured error values are desired for each step of the sensitivity sweep, tester  44  may generate downlink test signals having step durations of 100 ms (100*1). 
     When measurement data is analyzed by test host  42  (e.g., while performing step  82  of  FIG. 3 ), the downlink power level preceding a level at which DUT  10 ′ measures an error value that exceeds the threshold error value may be used to determine a receiver sensitivity value of DUT  10 ′ (e.g., the downlink power level associated with the last adequately received downlink test signals may be used to determine a receiver sensitivity value). In the example of  FIGS. 5 and 6 , downlink power level P 2  (i.e., the downlink power level corresponding to error value E 2 ) may be used to determine a receiver sensitivity value. This process may be repeated between times T 10  and T 11  to test DUT  10 ′ at other frequencies (e.g., in response to downlink test signals provided by tester  44  at different test frequencies). 
       FIG. 7  shows a flow chart of illustrative steps that may be performed by test host  42  to determine reliable receiver sensitivity values for DUT  10 ′ using measurement data gathered by DUT  10 ′. The steps of  FIG. 7  may, for example, be performed as part of step  82  of  FIG. 3 . The steps of  FIG. 7  may be performed by test host  42  after retrieving measurement data gathered by DUT  10 ′ during test operations. 
     Tester  42  may ensure proper synchronization between measurement data retrieved from DUT  10 ′ and the corresponding test sequence (e.g., the corresponding downlink test signals). The measurement data (e.g., each group of measurement data associated with a respective power level step) retrieved from DUT  10 ′ may be considered to be synchronized with a power sweep in the downlink test signals if a measured time duration between the beginning of trigger signal  180  and the end of the power sweep is consistent with a predetermined time period such as the time period between times T 1  and T 8  in the downlink test signals (see, e.g.,  FIG. 5 ). In another suitable arrangement, each group of measurement data may be considered to be synchronized if the measured time duration between the rising edge and falling edge of trigger signal  180  is consistent with a predetermined time period such as the time period between times T 1  and T 2  in the downlink test signals. 
     At step  270 , test host  42  may identify measurement data gathered by DUT  10 ′ in response to trigger  180  in the downlink test signals transmitted by tester  44  (sometimes referred to as test trigger  180 ). For example, test host  42  may identify a set of measured time stamp values, a corresponding set of measured downlink power levels, and a corresponding set of measured error values gathered in response to test trigger  180 . Measurement data gathered by DUT  10 ′ in response to test trigger  180  may sometimes be referred to collectively as measured trigger  180 ′. Test host  42  may identify measured trigger  180 ′ by searching the measurement data for an increase in measured downlink power level by trigger size ΔP T . Test host  42  may subsequently search for a decrease in measured downlink power level by initialization step size ΔP S . 
     Measured time stamp values corresponding to measured trigger  180 ′ may exhibit a measured trigger duration ΔT TR ′. At step  272 , test host  42  may compare measured trigger duration ΔT TR ′ with trigger duration ΔT TR  to ensure proper synchronization between the retrieved measurement data and the downlink test signals. In a scenario where measured trigger duration ΔT TR ′ substantially matches trigger duration ΔT TR , the measurement data may be identified as being properly synchronized with the downlink test signals. If measured trigger duration ΔT TR ′ does not sufficiently match trigger duration ΔT TR , then the measurement data may be identified as being unsynchronized with the downlink test signals. Proper synchronization may allow test host  42  to determine reliable sensitivity values for DUT  10 ′. 
       FIG. 8  is an illustrative graph showing how retrieved measurement data (e.g., measured trigger  180 ′) may be unsynchronized with corresponding downlink test signals (e.g., test trigger  180 ). Curve  88  illustrates downlink power levels generated by tester  44  to form test trigger  180  (e.g., as shown in  FIG. 5 ). Curve  88  may, for example, be stored in test equipment  48  during downlink test signal transmission for comparison with measurement data after test operations. 
     Curve  202  illustrates measured downlink power levels retrieved by test host  42  from DUT  10 ′. Times T 1 ′ and T 2 ′ may, for example, be measured time stamp values gathered by DUT  10 ′. Curve  202  may be obtained by DUT  10 ′ from received downlink test signals (e.g., from downlink test signals associated with curve  88  of  FIG. 5 ). Curve  202  may be compared to curve  88  (e.g., while performing step  272  of  FIG. 7 ) to determine whether the measurement data is properly synchronized with the downlink test data. 
     In the example of  FIG. 8 , test host  42  may identify power trigger  180 ′ between measured time stamp values T 1 ′ and T 2 ′ having trigger duration ΔT TR ′ (e.g., by searching the measurement data for an increase in measured downlink power level by trigger size ΔP T , etc.). Test host  42  may determine that the measurement data is unsynchronized with the corresponding downlink test signals because measured trigger duration ΔT TR ′ is less than trigger duration ΔT TR . In another suitable arrangement, measurement data may be considered unsynchronized with corresponding downlink test signals when the difference between measured trigger duration ΔT TR ′ and trigger duration ΔT TR  exceeds a predetermined threshold. In this arrangement, test host  42  may compute a difference between measured trigger duration ΔT TR ′ and trigger duration ΔT TR  (e.g., ΔT TR ′−ΔT TR ). Test host  42  may subsequently compare the difference value to a predetermined threshold. 
     If test host  42  measures excessive variation between the measured trigger duration ΔT TR ′ and trigger duration ΔT TR , processing may proceed to step  276  via path  274 . At step  276 , test equipment  48  may flag DUT  10 ′ as failing synchronization. At optional step  278 , test equipment  48  may calibrate the retrieved measurement data to ensure proper synchronization with the corresponding downlink test signals. For example, an offset may be provided to the measured time stamp values to ensure proper synchronization with the corresponding downlink test signals (e.g., offset data may be added to the test data to ensure proper synchronization). Processing may subsequently proceed to step  272  to use ensure that the calibrated measurement data is properly synchronized. By ensuring proper synchronization, test host  42  can determine receiver sensitivity values for DUT  10 ′ using the downlink power levels transmitted by tester  44  and measured downlink power levels gathered by DUT  10 ′. 
     If measurement data is properly synchronized with the corresponding downlink test data, processing may proceed to step  284  via path  282 . At step  284 , test host  42  may identify measurement data associated with the sensitivity sweep performed by tester  44  (e.g., measurement data gathered by DUT  10 ′ from downlink test signals between times T 3  and T 8  as shown in  FIG. 5 ). Measurement data associated with the sensitivity sweep may sometimes be referred to herein as sensitivity sweep data and may include measured power levels, measured error values, and measured time stamp values gathered by DUT  10 ′ during the sensitivity sweep. Test host  42  may identify sensitivity sweep data by, for example, searching for retrieved measurement data having a measured time stamp value that is greater than time T 3 . 
     At step  286 , test host  42  may partition sensitivity sweep measurement data into groups corresponding to each downlink power level of the sensitivity sweep (e.g., a first group corresponding to downlink power level P 1  between times T 3  and T 4 , a second group corresponding to downlink power level P 2  between times T 4  and T 5 , etc.). Test host  42  may, if desired, partition the sensitivity sweep measurement data using step duration ΔT SW . For example, test host  42  may organize measured downlink power levels and measured error values having measured time stamp values within duration ΔT SW  after time T 3  into the first group, within duration ΔT SW  after time T 4  into the second group, etc. Test host  42  may, if desired, compute an average measured downlink power level for each sensitivity sweep group. 
     At step  288 , test host  42  may compare measured error values in each sensitivity sweep group to an error value threshold such as threshold error value E TH  as shown in  FIG. 6 . If one or more measured error values in a given sensitivity sweep group exceed threshold error value E TH , the downlink power level associated with the immediately preceding sensitivity sweep group may be recorded as an unadjusted receiver sensitivity level (e.g., the last measured power level that satisfies the error value threshold may be identified as the unadjusted receiver sensitivity). This process may be repeated to determine unadjusted receiver sensitivity values for all frequencies tested. 
     In another suitable arrangement, test host  42  may compute an average measured error value for each group. For example, test host  42  may compute a first average error value E 1  for the first sensitivity sweep group of measurement data between times T 3  and T 4  (e.g., as shown in  FIG. 6 ), may compute a second average error value E 2  for the second sensitivity sweep group between times T 4  and T 5 , etc. If the average error value in a given sensitivity sweep group exceeds error threshold value E TH , the average power level of the immediately preceding group may be identified as the unadjusted receiver level. 
     At step  290 , test host  42  may identify path loss information for the measurement data. Path loss power may be determined, for example, by comparing measured downlink power level at time T 0  to the corresponding downlink power generated by tester  44 . In the example of  FIG. 8 , tester  44  generates downlink test signals having downlink power level P 0 , whereas DUT  10 ′ measures downlink power level P 0 ′ at time T 0 . Test host  42  may determine that measured downlink power level P 0 ′ is less than downlink power level P 0  by path loss margin P PL . Path loss margin P PL  may, for example, result from over-the-air and radio-frequency cable path loss in test system  64 . 
     At step  292 , test host  42  may compute an adjusted receiver sensitivity level for DUT  10 ′ using path loss margin P PL  and the unadjusted receiver sensitivity value. For example, test host  42  may add the path loss power P PL  to the unadjusted receiver sensitivity value to obtain an adjusted receiver sensitivity value. Adjusted receiver sensitivity values computed by test host  42  may be independent of test system  64  and the placement of DUT  10 ′ within test system  64  during test operations. This process may be performed to compute adjusted receiver sensitivity values for all frequencies tested. The adjusted receiver sensitivity values may be used to characterize the radio-frequency performance of DUT  10 ′ (e.g., by performing step  84  of  FIG. 3 ). 
       FIGS. 4-8  are merely illustrative. If desired, tester  44  may step down downlink test signals in downlink power level during the sensitivity sweep any desired number of times. For example, tester  44  may step down the downlink power level ten times, twenty times, etc. Similarly, DUT  10 ′ may measure a number of error values each corresponding to each step of the downlink power sweep. If desired, tester  44  may produce trigger  180  by decreasing downlink power level by trigger size ΔP T . In this scenario, test host  42  may search for the measurement data for a decrease in measured downlink power level by trigger size ΔP T  when identifying measured trigger  180 ′. If desired, tester  44  may step down the downlink test signals during the sensitivity sweep using different step durations ΔT SW  (e.g., tester  44  may produce downlink power level P 2  for a first step duration, may produce downlink power level P 3  for a second step duration that is longer than the first step duration, etc.). Similarly, different step sizes ΔP W  may be used for each sensitivity sweep step (e.g., tester  44  may decrease downlink power level by a first margin at time T 3 , by a second margin at time T 4  that is greater than the first margin, etc.). 
     Measurement data gathered by DUT  10 ′ may include any desired radio-frequency measurements performed by DUT  10 ′ in response to receiving downlink test signals. For example, measurement data may include RSSI information, ACLR information, signal to noise ratio information, etc. The measurement data may include any suitable information gathered by DUT  10 ′ for determining receiver sensitivity of DUT  10 ′. 
     If desired, test duration ΔT T  may be used to ensure proper synchronization between the measurement data and corresponding downlink test signals. In this scenario, test host  42  may determine that the downlink test signals are unsynchronized with the measurement data if test duration ΔT T  in the downlink test signals does not suitably match the corresponding test duration in the measured time stamp values. In another suitable arrangement, both test duration ΔT T  and test trigger  180  may be used to determine whether the measurement data retrieved by test host  42  is synchronized (e.g., the measurement data may be unsynchronized if one of the trigger time or the test time does not match between the measured time stamp values and the tester time stamp values). 
     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. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20130110
Publication Date: 20150728
Grant Date: 20150728
Priority Date: 20130110
Inventors: LIU SONG
TAKEYA TOMOKI
SYED ADIL
VENKATARAMAN VISHWANATH
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/29", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/29", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/00", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 51061305