Abstract:
A method for testing data packet reception characteristics, such as sensitivity and throughput, of a data packet signal transceiver. By monitoring responsive data packet signals returning from a device under test (DUT), it can be determined whether and when the DUT has successfully received valid data packets, received faulty data packets, received valid data packets in a faulty manner, or not received valid data packets. When any of such events are detected, the stimulus data packet signals can be provided in such a manner as to determine whether possible DUT reception problems are related to power level, duration or data rate of the stimulus data packet signals, or to circuitry within DUT without requiring external controls over or querying of the DUT.

Description:
BACKGROUND 
     The present invention relates to testing wireless transceivers, and in particular, to testing wireless data packet signal transceivers. 
     Many of today&#39;s electronic devices use wireless technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless technologies must adhere to various wireless technology standard specifications. 
     When designing such devices, engineers take extraordinary care to ensure that such devices will meet or exceed each of their included wireless technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless technology standard-based specifications. 
     For testing these devices following their manufacture and assembly, current wireless device test systems employ a subsystem for analyzing signals received from each device. Such subsystems typically include at least a vector signal analyzer (VSA) for analyzing signals produced by the device. The analyses performed by the VSA are generally programmable so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless technology standards with differing frequency ranges, bandwidths and signal modulation characteristics. 
     As part of the manufacturing of wireless communication devices, one significant component of product cost is manufacturing test cost. Typically, there is a direct correlation between the cost of test and the time required to perform such test. Thus, innovations that can shorten test time without compromising test accuracy or increasing capital equipment costs (e.g., increasing costs due to increasing sophistication of test equipment, or testers) are important and can provide significant cost savings, particularly in view of the large numbers of such devices being manufactured and tested. 
     Among others, one test often conducted involves testing the signal link between a device under test (DUT) and a tester when connected through a conductive signal path (typically in the form of a radio frequency (RF) transmission line (e.g., coaxial cable) having the characteristic impedance of the system) to a reference signal source to allow conveyance and communication of data packets between the reference device and the DUT. Such signal link tests are based on the number of data packets conveyed that are received by the DUT without error during a known or prescribed time interval. 
     Ordinarily, this type of test includes conveyance of data packets from the reference device to the DUT, which, in turn, responding with responsive data packets indicating whether a correct data packet has been received. The responsive data packets are typically in the form of a confirmation data packet, such as an acknowledgement (ACK) data packet. 
     However, absent additional circuitry or subsystems for capturing and retaining the data packets sent between the two devices (e.g., the reference data packets from the referenced device and the confirmation data packets from the DUT), it cannot be determined whether faulty packets were received due to faulty packets having been transmitted originally from the reference device, or correct packets had been received but received in a faulty manner by the DUT. 
     Accordingly, it would desirable to have a technique for capturing packets conveyed between the devices and for retaining those packets in response to which no confirmation packet is returned, or for which a confirmation packet is returned but after a prescribed time limit has been exceeded. 
     SUMMARY 
     In accordance with the presently claimed invention, a method is provided for testing data packet reception characteristics, such as sensitivity and throughput, of a data packet signal transceiver. By monitoring responsive data packet signals returning from a device under test (DUT), it can be determined whether and when the DUT has successfully received valid data packets, received faulty data packets, received valid data packets in a faulty manner, or not received valid data packets. When any of such events are detected, the stimulus data packet signals can be provided in such a manner as to determine whether possible DUT reception problems are related to power level, duration or data rate of the stimulus data packet signals, or to circuitry within DUT without requiring external controls over or querying of the DUT. 
     In accordance with an exemplary embodiment of the presently claimed invention, a method of testing a data packet signal transceiver includes: transmitting, via a radio frequency (RF) signal path having a controllable RF signal path attenuation, a test data packet signal including one or more test data packets for reception by a data packet signal transceiver device under test (DUT); receiving, from said DUT via said RF signal path, a response signal including one or more response data packets corresponding to one or more respective portions of said one or more test data packets; and following said reception of said one or more response data packets, performing one or more of transmitting, via said RF signal path with said increased RF signal path attenuation, said test data packet signal including another one or more test data packets for reception by said DUT, and increasing said RF signal path attenuation and transmitting, via said RF signal path with said increased RF signal path attenuation, said test data packet signal including another one or more test data packets for reception by said DUT. Further included, following a failure to receive within a prescribed time interval from said DUT at least another one or more response data packets corresponding to one or more respective portions of said another one or more test data packets, is performing one or more of retaining said one or more respective portions of said another one or more test data packets, and repeating said transmitting of said test data packet signal including another one or more test data packets for reception by said DUT. Such repeated transmitting includes one or more of maintaining a duration of at least one of said another one or more test data packets, maintaining a data rate of at least one of said another one or more test data packets, increasing a duration of at least one of said another one or more test data packets, and decreasing a data rate of at least one of said another one or more test data packets. 
     In accordance with another exemplary embodiment of the presently claimed invention, a method of testing a data packet signal transceiver includes: transmitting, during each one of a first plurality of time intervals via a radio frequency (RF) signal path having a controllable RF signal path attenuation, a test data packet signal including one or more test data packets for reception by a data packet signal transceiver device under test (DUT); awaiting reception from said DUT, during each one of a second plurality of time intervals via said RF signal path, a response signal including one or more response data packets corresponding to one or more respective portions of said one or more test data packets, wherein said first and second pluralities of time intervals are non-coincident; and preceding at least a later one of said first plurality of time intervals, performing one or more of maintaining said RF signal path attenuation, and increasing said RF signal path attenuation. Further included, following a failure, during a later one of said second plurality of time intervals following said later one of said first plurality of time intervals, to receive from said DUT at least one of said or more response data packets, is performing one or more of retaining at least a portion of said test data packet signal transmitted during said later one of said first plurality of time intervals, and repeating said transmitting of said test data packet signal including one or more test data packets for reception by said DUT. Such repeated transmitting includes one or more of maintaining a duration of at least one of said one or more test data packets, maintaining a data rate of at least one of said one or more test data packets, increasing a duration of at least one of said one or more test data packets, and decreasing a data rate of at least one of said one or more test data packets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a testing environment for testing data packet reception in accordance with exemplary embodiments of the presently claimed invention. 
         FIG. 2  depicts a testing environment for testing data packet reception in accordance with alternative exemplary embodiments of the presently claimed invention. 
         FIG. 3  is a signal diagram depicting conveyance of tested data packets and confirmation data packets as a result of successful reception of valid data packets by the DUT, and conveyance of tested data packets and late or no confirmation data packets due to reception of faulty data packets or reception in a faulty manner. 
         FIG. 4  depicts a signal timing diagram identifying signal parameters captured by the packet detection circuitry of  FIGS. 1 and 2 . 
         FIGS. 5 and 6  depict exemplary embodiments of the signal dividing or coupling circuitry of  FIGS. 1 and 2 . 
         FIG. 7  depicts exemplary alternative embodiments of a portion of the testing environments of  FIGS. 1 and 2 . 
         FIG. 8  is a signal diagram depicting exemplary conveyance of data packets and confirmation packets between the reference device and DUT in the testing environments of  FIGS. 1 and 2 . 
         FIG. 9  is a signal diagram depicting exemplary conveyance of data packets and confirmation packets before and after imposing signal attenuation upon the reference data packet signal. 
         FIG. 10  is a signal diagram depicting exemplary conveyance of data packets and confirmation packets before and after imposing signal attenuation upon the reference data packet signal and a decrease in the data rate of the reference data packet signal. 
         FIG. 11  is a signal diagram depicting exemplary conveyance of data packets and confirmation packets for testing data packet throughput in the testing environments of  FIGS. 1 and 2 . 
         FIG. 12  is a signal diagram depicting an exemplary timing relationship for the data packets, confirmation packets and signal attenuation imposed during operation of the testing environments of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is of example embodiments of the presently claimed invention with references to the accompanying drawings. Such description is intended to be illustrative and not limiting with respect to the scope of the present invention. Such embodiments are described in sufficient detail to enable one of ordinary skill in the art to practice the subject invention, and it will be understood that other embodiments may be practiced with some variations without departing from the spirit or scope of the subject invention. 
     Throughout the present disclosure, absent a clear indication to the contrary from the context, it will be understood that individual circuit elements as described may be singular or plural in number. For example, the terms “circuit” and “circuitry” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together (e.g., as one or more integrated circuit chips) to provide the described function. Additionally, the term “signal” may refer to one or more currents, one or more voltages, or a data signal. Within the drawings, like or related elements will have like or related alpha, numeric or alphanumeric designators. Further, while the present invention has been discussed in the context of implementations using discrete electronic circuitry (preferably in the form of one or more integrated circuit chips), the functions of any part of such circuitry may alternatively be implemented using one or more appropriately programmed processors, depending upon the signal frequencies or data rates to be processed. Moreover, to the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. 
     As discussed in more detail below, systems and methods for testing data packet reception in accordance with the presently claimed invention facilitate the controlling of capture and conditional retention of conveyed data packets to ensure that correctly received data packets can be captured but disregarded and not retained (e.g., not stored) while faulty and possibly faulty data packets are captured and retained for analysis. System test time is reduced since the capture and retention of faulty or possibly faulty data packets can be controlled and achieved simultaneously with the conveyance of data packets during normal testing. Further, system costs can be reduced by reducing the amount of data storage otherwise required if all data packets, including known good data packets and not just faulty or possibly data packets, were captured and retained for analysis. 
     Referring to  FIG. 1 , a testing environment  10  in accordance with exemplary embodiments of the presently claimed invention include a reference device  12 , a DUT  14 , a cabled signal connection  16 , one or more packet detection circuits  22   a ,  22   b , control logic  24  (e.g., a field programmable gate array), and one or more signal dividing or coupling circuits (e.g., resistive signal dividers or couplers)  32   a ,  32   b  (discussed in more detail below). The reference device  12  can be implemented using a known good device, such as a DUT which has already been tested and is known to operate in accordance with all prescribed operating standards and characteristics (or at least those prescribed operating characteristics necessary for current testing purposes). The cabled signal connection  16  preferably, though not necessarily, includes a signal attenuator  16   a , which can be variable in accordance with a control signal. In accordance with well-known testing techniques and operations, the reference device  12 , DUT  14 , control logic  24 , packet detectors  22   a ,  22   b  and signal attenuator  16   a  can be controlled by respective externally sourced control signals, as well as communicate to external subsystems via other control or data signals (not shown). For example, the reference device  12 , DUT  14 , control logic  24 , packet detectors  22   a ,  22   b  and signal attenuator  16   a  can each be controlled by one or more respective externally sourced control signals  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f  (e.g., from a personal computer controlling the test operations). Alternatively, or additionally, the reference device  12 , DUT  14 , packet detectors  22   a ,  22   b  and signal attenuator  16   a  can each be controlled by one or more respective control signals  31   a ,  31   b ,  31   d ,  31   e ,  31   f  provided by the control logic (e.g., under the direction of its externally sourced control signal(s)  11   c ). 
     The reference device  12  provides a data packet signal  13  for the DUT  14 , which, in turn, responds with its own data packet signal  15 . Such responsive data packet signal  15  is typically in the form of confirmation signals (e.g., ACK signals) indicating, or confirming, proper reception of valid data packets within the reference data packet signal  13 . 
     The signal path  16 , e.g., a RF transmission line, is in electrical communication with the reference device  12  and DUT  14  via first  32   a  and second  32   b  signal connections which include the signal splitting or coupling circuitry. As discussed in more detail below, such circuitry provides a divided or coupled portion of the transmitted reference data packet signal  13   a  (and, if desired, the received responsive data packet signal  15   a ) as the input signal  17   a  to the first packet detector  22   a . Similarly, such circuitry provides a divided or coupled portion of the received referenced data packet signal  13   b  (and, if desired, the transmitted responsive data packet signal  15   b ) as the input signal  17   b  to the second packet detector  22   b . This circuitry also provides divided or coupled portions of these signals  13   b ,  15   b  as an input signal  19  for signal receiver and analysis circuitry  18 , e.g., a VSA. 
     As discussed in more detail below, the packet detectors  22   a ,  22   b  provide packet detection signals  23   a ,  23   b  to the control logic  24 . These packet detection signals  23   a ,  23   b  preferably provide information indicative of magnitude, e.g., power level, and start and end times of the reference  13  and responsive  15  data packet signals. For example, the first packet detector  22   a  can provide data packet magnitude and data packet start and end time information for the transmitted reference data packet signal  13   a  and received responsive data signal  15   a . Similarly, the second packet detector  22   b  can provide data packet magnitude and start and end time information for the received reference data packet signal  13   b  and transmitted responsive data packet signal  15   b . Also, the data packet magnitude information provided by the packet detectors  22   a ,  22   b  allows the type of signal being detected to be identified. For example, if the first packet detection signal  23   a  indicates a higher signal magnitude than that indicated by the second packet detection signal  23   b , that means that the transmitted  13   a  and received  13   b  reference data packet signals are being detected. Similarly, if the first packet detection signal  23   a  indicates a lower signal magnitude than that indicated by the second packet detection signal  23   b , that means that the transmitted  15   b  and received  15   a  responsive data packet signals are being detected. 
     Alternatively, a single packet detector can be used, e.g., either the first  22   a  or second  22   b  packet detector. By monitoring the detected signal magnitudes at either the first  32   a  or second  32   b  signal connection and comparing them to a predetermined threshold magnitude value, it can be determined whether the reference device signal  13  or DUT signal  15  is being detected. For example, due to the signal attenuator  16   a , detected signal magnitudes at the first signal connection  32   a  higher and lower than the threshold magnitude value correspond to the reference  13  and DUT  15  signals, respectively, and detected signal magnitudes at the second signal connection  32   ba  higher and lower than the threshold magnitude value correspond to the DUT  15  and reference  13  signals, respectively. 
     The packet detection signals  23   a ,  23   b  are processed by the control logic  24  to provide one or more commands, or control signals  25   a ,  25   b , for the signal receiver and analysis circuitry  18 . These commands can include “capture”  25   a  and “keep previous”  25   b  commands to inform the signal receiving and analysis system  18  that data packets currently being received should be captured (per the “capture” command  25   a ) and that previously received and captured data packets should be retained for analysis (per the “keep previous” command  25   b ). 
     Referring to  FIG. 2 , in accordance with alternative exemplary embodiments, the testing environment  10   a  can omit the first reference packet detector  22   a  ( FIG. 1 ). In such embodiment  10   a , the reference device  12   a  provides data packet information  13   c  (e.g., data packet magnitude and start and end time information for the transmitted reference data packet signal  13   a ) used by the control logic  24  to provide the “capture”  25   a  and “keep previous”  25   b  commands as discussed above. This also avoids a need for the first reference signal dividing or coupling circuitry  32   a  between the reference device  12   a  and signal path  16 . 
     Referring to  FIG. 3 , reference  13  and responsive  15  signals are depicted for different testing scenarios. In the first scenario  40   a , the DUT  14  ( FIGS. 1 and 2 ) receives the reference data packets  13   b . In this scenario  40   a , these data packets  13   b  are good, or valid, and are properly received and captured by the DUT  14 . Accordingly, within the prescribed time interval t 1 , the DUT  14  responds by transmitting confirmation data packets  15   b . Accordingly, the control logic  24  would provide appropriate “capture”  25   a  and “keep previous”  25   b  commands to inform the receiving and analysis circuitry  18  that valid data packets  13   b  were properly received and captured and need not be retained for analysis. 
     In the second scenario  40   b , the reference data packets  13   b  are received by the DUT  14 . However, the responsive confirmation data packet  15   b  provided by the DUT  14  is transmitted after a time interval t 2  that exceeds the prescribed time interval between the end of the reference packet  13   b  and expected start of the responsive packet  15   b . Accordingly, the control logic  24  will interpret this as a situation where the reference data packet  13   b  is faulty or may be valid but was received or captured in a faulty manner and should be retained for analysis. Accordingly, the control logic  24  provides appropriate “capture”  25   a  and “keep previous”  25   b  commands for the signal receiving and analysis circuitry  18 . 
     In the third scenario  40   c , the reference data packet  13   b  is received by the DUT  14  but no confirmation data packet is provided in response. Following a timeout interval t 3 , another reference data packet  13   b  is received and, again, no responsive confirmation data packet  15  is returned. Accordingly, the control logic  24  interprets this situation as faulty or possibly faulty data packets having been received by the DUT  14 , and, therefore, provides appropriate “capture”  25   a  and “keep previous”  25   b  commands to the signal receiving and analysis circuitry  18  for retention of these data packets  13   b  for analysis. 
     For example, the “capture”  25   a  and “keep previous”  25   b  commands are asserted (e.g., “high”) during the reference packet  13   b  and remain asserted (meaning capture this packet  13   b ) until it is determined whether the reference packet  13   b  has been successfully received, as indicated by the timely transmission of the responsive packet  15   b . Hence, in the first scenario  40   a , the reference packet  13   b  has been successfully received, so the “keep previous” command  25   b  is de-asserted following the timely transmission of the responsive packet  15   b , and the “capture” command  25   a  is then also de-asserted, thereby indicating that the reference packet  13   b  need not be kept for analysis. However, in the second  40   b  and third  40   c  scenarios, the reference packet  13   b  has not been successfully received, as indicated by the late transmission or no transmission, respectively, of the responsive packet  15   b . Accordingly, the “keep previous” command  25   b  remains asserted until after the “capture” command  25   a  is de-aserted, thereby indicating that the reference packet  13   b  should be kept for analysis. 
     As will be readily appreciated by one skilled in the art, data packets transmitted as part of the DUT data packet signal  15  can be captured and retained for analysis as well. In other words, similar to the receive (RX) testing as discussed above for data packets  15   b  intended for reception by the DUT  14 , a similar procedure can be followed for transmit (TX) testing of the DUT  14 . For example, during transmission of data packet signals  15  by the DUT  14 , the “capture”  25   a  and “keep previous”  25   b  commands can be used to instruct the signal receiving and analysis circuitry  18  to capture retain for analysis those DUT data packets  15   b  for which their corresponding data packets  15   a  available for reception by the reference device  12  have been determined to be faulty or have otherwise not been successfully received by the reference device  12 . Such use of the “capture”  25   a  and “keep previous”  25   b  commands in this manner can be initiated or controlled in accordance with feedback data provided by the reference device  12  to the control logic  24  (e.g., via their mutual signal interface  31   a ). 
     Referring to  FIG. 4 , as discussed above, the packet detectors  22   a ,  22   b  ( FIGS. 1 and 2 ) provide packet detection signals  23   a ,  23   b  containing information about the magnitude  23   ap / 23   bp , start times  23   as / 23   bs  and end times  23   ae / 23   be  of the divided or coupled reference  13   a / 13   b  and responsive  15   a / 15   b  data packets. Such signal measurements can be done using voltage or power detection circuits, which are well known in the art. The data packet magnitude  23   ap / 23   bp  can be measured at a desired point in time during the time interval in which the peak signal level is expected, while the start  23   as / 23   bs  and end  23   ae / 23   be  times of the data packet signal can be measured as the divided or coupled signal  17   a / 17   b  transcends one or more predetermined signal thresholds defined between the expected minimum and maximum data packet signal levels. 
     Referring to  FIG. 5 , the signal dividing or coupling circuitry  32   a / 32   b  ( FIGS. 1 and 2 ) can be implemented using signal dividers/adders  52   a ,  52   b ,  52   c ,  52   d , interconnected substantially as shown. In accordance with well-known principles, power-divided portions of the referenced data packets  13   ad / 13   bd  and responsive data packets  15   ad / 15   bd  provided by the two in-line dividers/adders  52   a ,  52   b  become the power-divided data packet signals  17   a / 17   b  provided to the packet detectors  22   a / 22   b . In the case of the second signal divider or coupler  32   b , an additional shunt divider/adder  52   d  conveys power-divided portions of the reference  13   ad / 13   bd  and responsive  15   ad / 15   bd  data packets to the signal receiving and analysis circuitry  18 . (As noted above, these can be implemented as simple resistive signal dividers, which are well known in the art.) 
     Referring to  FIG. 6 , in accordance with another exemplary embodiment, in-line signal couplers  54   a / 54   b  can be used instead of divider/adder circuits  52   a ,  52   b  ( FIG. 5 ). In this embodiment, coupled portions of the reference  13   ac / 13   bc  and responsive  15   ac / 15   bc  data packets are provided via signal combiners  56   c ,  56   d  as the input signals  17   a / 17   b  to the packet detectors  22   a ,  22   b  and the input signal  19  to the signal receiving and analysis circuitry  18 . 
     Referring to  FIG. 7 , in accordance with exemplary alternative embodiments, the second connection, between the cabled signal path  16  and DUT  14 , can include a wireless connection  26  via which the reference  13  and responsive  15  signals can be conveyed via radiated electromagnetic waves  27   a ,  27   b  between antennas  26   a ,  26   b  connected to the cabled signal path  16  and DUT  14 . In such an embodiment, the signal path  19  to the signal receiver and analysis circuitry  18  can be implemented as a signal path  19   a  connected at the cabled signal path  16  side and an additional signal path  19   b  connected at the DUT  14  side of the wireless signal connection  26 . This would ensure reliable reception and capturing of data and confirmation packets originating from the reference device  12  and DUT  14  for analysis, as discussed above. In accordance with well-known techniques, the captured packets can be stored in memory  28  contained within, connected to, or otherwise associated with the signal receiver and analysis circuitry  18 . 
     Referring to  FIG. 8 , in accordance with additional exemplary embodiments and as discussed in more detail below, the reference signal  13  and responsive signal  15  can include reference data packets  13   b  and confirmation packets  15   b , respectively. Alternatively, the DUT  14  can transmit a signal  15  containing data packets  15   b  to which the reference device  12  responds by transmitting a responsive signal  13  containing responsive, e.g., confirmation, packets  13   b , in accordance with well-known techniques. 
     Referring to  FIG. 9 , as discussed above, testing of the DUT  14  includes providing it with test data packet signals  13   b  via the signal path  16  with controllable (e.g., incrementally increased and decreased) signal attenuation  16   a . For example, as depicted here, the first two test data packets  13   b  are presented at a nominal signal power, following which, successive data packets  13   ba  are attenuated. For purposes of this example, the attenuation is sufficient to result in unsuccessful reception of the data packets  13   ba  by the DUT  14 . Accordingly, the DUT responds with confirmation packets  15   b  following successful reception of the earlier data packets  13   b , but, due to its unsuccessful reception of the attenuated data packets  13   ba , no responsive confirmation packets are returned during the time intervals  35   b  in which they would be expected by the reference device  12 . 
     As will be readily appreciated by one skilled in the art, the level of signal attenuation  16   a  (as well as data related to the corresponding power level of the test data packet signal  13 ) can be noted and stored, e.g., within the control logic  24 , at the onset of the failures to receive responsive confirmation packets  15   b . For example, following transmission of the first attenuated data packet  13   ba  and the first responsive time interval  35   b  during which no responsive confirmation packet  15   b  is received, the signal attenuation and/or signal  13  power level can be recorded as the reference device  12  begins re-transmission of the test data packets  13   ba  for which no confirmation packets  15   b  were received. 
     Referring to  FIG. 10 , alternatively, following transmission of the first attenuated data packet  13   ba  resulting in no reception of a confirmation packet during the responsive time interval  35   b , the reference device  12  can initiate a reduction in the data rate of the transmitted data packets  13   b  (e.g., in accordance with the operating protocol of the reference device  12  and DUT  14 ). If the amount of data being transmitted remains unchanged, this results in a data packet  13  bar having a longer packet duration. This longer packet duration can be detected by the control logic  24  (based on the start and end times of the data packet  13  bar as measured by one or more of the packet detectors  22   a ,  22   b , as discussed above), and would be recognized as corresponding to a reduction in the data rate within such data packet  13  bar. In some instances, this can result in successful reception of the data packet  13  bar and the transmission of a responsive confirmation packet  15   b  accordingly. Such combination of a failure to receive a confirmation packet and a subsequent reception of a confirmation packet  15   b  in response to a subsequent data packet  13  bar having a reduced data rate could be interpreted as indicative of the onset of the sensitivity limit (e.g., the “knee point”) of the DUT  14 . 
     Referring to  FIG. 11 , in accordance with another exemplary embodiment, data throughput of the DUT  14  can be tested with little or no interaction with the DUT other than exchanges of data packets and responsive confirmation packets. For purposes of this example, four data packets  13   b  are sent by the reference device  12  to the DUT  14 . However, only three of the data packets  13   b  evoke responsive confirmation packets  15   b . In this example, the second transmitted test data packet  13   bd  was somehow deemed a defective data packet or otherwise unsuccessfully received by the DUT  14 . Accordingly, during the response time interval  35   b , no confirmation packet  15   b  is returned. As a result, within the time interval as shown, the number of data bits successfully transferred from the reference device  12  to the DUT  14  would be equal to those contained within the three successfully received data packets  13   b  corresponding to the three responsive confirmation packets  15   b . By knowing the number of bits within each data packet  13   b , a number of detected packets sent within the known time interval, and the number of detected confirmation packets  15   b  corresponding to those successfully transmitted data packets  13   b , the data throughput in bits per second can be determined, e.g., computed by the control logic  24 . 
     Alternatively, one could also measure the time it takes to transmit a predetermined number (n) of good data packets and from that derive the same throughput metric. Defective or otherwise unsuccessfully received data packets  13   bd  would produce no confirmation packet  15   b  during the response time interval  35   b . Accordingly, the bits contained in such defective, or otherwise unsuccessfully received, packets would not be considered as successfully transferred and would not contribute to the total number of transferred bits. They would simply cause the data transfer time interval to be longer, and thereby reduce the measured throughput. 
     Referring to  FIG. 12 , to ensure maximum likelihood of receiving the response signal  15  transmitted by the DUT  14  following increases in attenuation  16   a  of the signal path  16  for the incident test signal  13 , such attenuation  16   a  can be decreased during the time intervals in which responsive confirmation packets  15   b  are expected. For example, as discussed above, the RF test signal  13  attenuation  16   a  is increased during transmission of the test data packets  13   b . However, as noted, to help ensure that responsive confirmation packets  15   b  evoked from the DUT  14  are successfully received by the reference device  12 , the attenuation  16   a  can be decreased. Accordingly, the time intervals during which the test signal attenuation is higher and lower are non-coincident. For example, the test signal attenuation is higher  36   a  during a time interval at least coextensive with the duration of the test data packets  13   b , while the time interval  36   b  during which the signal path attenuation  16   a  is lower is at least coextensive with the time interval during which a response data packet  15   b  is expected. 
     Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and the spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.