Abstract:
Method for testing a radio frequency (RF) data packet signal transceiver device under test (DUT) in which test data packets with varying power levels are transmitted to the DUT for testing the DUT while still ensuring that the DUT remains in receive (RX) mode and is prevented from searching for another data packet signal. Alternatively, in the event that the DUT becomes unresponsive due to searching for another data packet signal, multiple test data packets with sufficient signal power levels to ensure reception by the DUT are transmitted to the DUT to cause the DUT to cease searching for another data packet signal and return to RX mode.

Description:
BACKGROUND 
     The present invention relates to testing of a radio frequency (RF) data packet signal transceiver, and in particular, to testing a packet error rate (PER) of such a device. 
     Many of today&#39;s electronic devices use wireless signal 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 signal technologies must adhere to various wireless signal technology standard specifications. 
     When designing such wireless devices, engineers take extra care to ensure that such devices will meet or exceed each of their included wireless signal 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 signal technology standard-based specifications. 
     For testing these devices following their manufacture and assembly, current wireless device test systems typically employ testing subsystems for providing test signals to each device under test (DUT) and analyzing signals received from each DUT. Some subsystems (often referred to as “testers”) include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the DUT, and a vector signal analyzer (VSA) for analyzing signals produced by the DUT. The production of test signals by the VSG and signal analysis performed by the VSA are generally programmable (e.g., through use of an internal programmable controller or an external programmable controller such as a personal computer) so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless signal technology standards with differing frequency ranges, bandwidths and signal modulation characteristics. 
     In such devices, one measure of device receiver performance is packet error rate (PER). The PER is usually expressed as a percentage of the number of packets incorrectly received divided by the total number of packets that were sent and should have been received. When performing non-link testing of wireless devices, where received test data packet signals can be restricted to a single channel, PER testing is not compromised by attempts by the device to find a different wireless access point. However, when performing link testing, the test environment simulates actual operational behavior, including operation by the device where, when the power of the received data packet becomes too low, the device may start to search for a different access point, usually doing so at alternative frequencies or channels. 
     Hence, during link-based PER testing, where the receive data packet signal power is deliberately made low so as to test worst case performance, it is possible that the DUT may begin searching for a different access point, even as the tester continues to send test data packet signals while counting acknowledgement signals from the DUT (for computation of PER). Accordingly, the tester may interpret, as packet errors, the lack of acknowledgement packets from the DUT during the time that the DUT is searching for another access point, thereby computing a PER test result as being higher than it actually is. This potential problem becomes more significant as the signal power of the test data packets is reduced and approaches the minimum device receiver sensitivity level. 
     While it may be possible, during link-based PER testing, to prevent the DUT from initiating an access point search, such testing technique would not reflect normal driver operation. Accordingly, this would require modification of the DUT to include special drivers for purposes of PER testing. Therefore, it would be desirable to have a technique by which, from the perspective of the tester, it could be identified when access point searching has begun by the DUT, thereby enabling testing results during this time to be readily identifiable so they can be ignored, thereby allowing correct PER results to be obtained and reflect packet errors only occurring when no access point search is in progress. 
     SUMMARY 
     In accordance with the presently claimed invention, a method is provided for testing a radio frequency (RF) data packet signal transceiver device under test (DUT) in which test data packets with varying power levels are transmitted to the DUT for testing the DUT while still ensuring that the DUT remains in receive (RX) mode and is prevented from searching for another data packet signal. Alternatively, in the event that the DUT becomes unresponsive due to searching for another data packet signal, multiple test data packets with sufficient signal power levels to ensure reception by the DUT are transmitted to the DUT to cause the DUT to cease searching for another data packet signal and return to RX mode. 
     In accordance with one embodiment of the presently claimed invention, a method for testing a radio frequency (RF) data packet signal transceiver device under test (DUT) includes:
         transmitting, from a tester, a tester data packet signal including a plurality of tester data packets with alternating portions having corresponding intervals of mutually higher and lower nominal transmitted tester data packet signal powers as transmitted from the tester;   receiving, with the tester from a DUT, a DUT data packet signal including a plurality of DUT data packets with alternating portions related to respective ones of the alternating portions of the plurality of tester data packets, thereby defining
           a first ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having higher nominal transmitted tester data packet signal powers,   a second ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers, and   a ratio difference between the first and second ratios;   
           repeating the transmitting and receiving of the alternating portions of the pluralities of tester and DUT data packets; and   maintaining a cumulative count of the plurality of DUT data packets received by the tester and related to the portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers during at least one of
           the first ratio equals unity,   the first ratio remains substantially constant,   the first ratio is greater than the second ratio, or   the ratio difference is greater than a predetermined value.   
               

     In accordance with another embodiment of the presently claimed invention, a method for testing a radio frequency (RF) data packet signal transceiver device under test (DUT) includes:
         transmitting, from a tester, a tester data packet signal including a plurality of tester data packets with alternating portions having corresponding intervals of mutually higher and lower nominal transmitted tester data packet signal powers as transmitted from the tester;   receiving, with the tester from a DUT, a DUT data packet signal including a plurality of DUT data packets with alternating portions related to respective ones of the alternating portions of the plurality of tester data packets, thereby defining
           a first ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having higher nominal transmitted tester data packet signal powers,   a second ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers, and   a ratio difference between the first and second ratios;   
           repeating the transmitting and receiving of the alternating portions of the pluralities of tester and DUT data packets; and   maintaining a cumulative count of the plurality of DUT data packets received by the tester and related to the portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers until at least one of
           the first ratio becomes less than unity,   the first ratio becomes less than the second ratio, or   the ratio difference transcends a predetermined value.   
               

     In accordance with another embodiment of the presently claimed invention, a method for testing a radio frequency (RF) data packet signal transceiver device under test (DUT) includes:
         transmitting, from a tester, a tester data packet signal including a plurality of tester data packets with alternating portions having corresponding intervals of mutually higher and lower nominal transmitted tester data packet signal powers as transmitted from the tester;   receiving, with the tester from a DUT, a DUT data packet signal including a plurality of DUT data packets with alternating portions related to respective ones of the alternating portions of the plurality of tester data packets, thereby defining
           a first ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having higher nominal transmitted tester data packet signal powers,   a second ratio of the portion of the plurality of DUT data packets received by the tester and the related portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers, and   a ratio difference between the first and second ratios; and   
           repeating the transmitting and receiving of the alternating portions of the pluralities of tester and DUT data packets until at least one of
           the first ratio becomes less than unity,   the first ratio becomes less than the second ratio, or   the ratio difference transcends a predetermined value,   followed by ceasing the transmitting of the portion of the plurality of tester data packets having lower nominal transmitted tester data packet signal powers and repeating the transmitting of the portion of the plurality of tester data packets having higher nominal transmitted tester data packet signal powers.   
               

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a typical testing environment for a radio frequency (RF) data packet signal transceiver device under test (DUT) in a conductive, or wired, environment. 
         FIG. 2  depicts a typical testing environment for a radio frequency (RF) data packet signal transceiver device under test (DUT) in a radiative, or wireless, environment. 
         FIG. 3  depicts a PER test during which the DUT does not initiate an AP search. 
         FIG. 4  depicts an example of a PER test where reduced test data packet signal levels may have initiated an AP search by the DUT. 
         FIG. 5  depicts testing in accordance with one embodiment of the presently claimed invention. 
         FIG. 6  depicts PER testing in accordance with another embodiment of the presently claimed invention. 
         FIG. 7  depicts PER testing in accordance with another embodiment of the presently claimed invention. 
         FIG. 8  depicts PER testing in accordance with another embodiment of the presently claimed invention. 
     
    
    
     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. 
     Wireless devices, such as cellphones, smartphones, tablets, etc., make use of standards-based technologies (e.g., IEEE 802.11a/b/g/n/ac, 3GPP LTE, and Bluetooth). The standards that underlie these technologies are designed to provide reliable wireless connectivity and/or communications. The standards prescribe physical and higher-level specifications generally designed to be energy-efficient and to minimize interference among devices using the same or other technologies that are adjacent to or share the wireless spectrum. 
     Tests prescribed by these standards are meant to ensure that such devices are designed to conform to the standard-prescribed specifications, and that manufactured devices continue to conform to those prescribed specifications. Most devices are transceivers, containing at least one or more receivers and transmitters. Thus, the tests are intended to confirm whether the receivers and transmitters both conform. Tests of the receiver or receivers (RX tests) of a DUT typically involve a test system (tester) sending test packets to the receiver(s) and some way of determining how the DUT receiver(s) respond to those test packets. Transmitters of a DUT are tested by having them send packets to the test system, which then evaluates the physical characteristics of the signals sent by the DUT. 
     As discussed in more detail below, there is a power level at which a properly working receiver will reliably return an acknowledgement signal (ACK). During non-link testing, a signal sent at that power level to a DUT receiver will receive an acknowledgement data packet from the DUT. In a link-related test, a signal sent at that power level will also return an acknowledgement packet unless the packet as received by the DUT is defective (e.g., has a CRC error or is not otherwise correctly received) or, due to low test signal level, the DUT has begun a search for a different access point, e.g., at a different frequency. 
     In accordance with the presently claimed invention, it is this behavior of the DUT that is used to determine when a DUT has begun search for an access point. The tester can determine whether a PER test result is due to actual packet errors or, instead, due to the DUT having initiated an access point search, and, therefore, is not currently engaged in communications with the tester. If an elevated PER is due to initiation of an access point search, the tester is able to ignore questionable errors and thereby improve accuracy of PER test results. 
     As is well known, testing of a wireless DUT typically includes testing of the DUT receiving and transmitting subsystems. The tester sends a prescribed sequence of test data packet signals to the DUT, using different frequencies, power levels, or signal modulation types, or combinations of two or more of these, to determine whether the DUT receiving subsystem is operating properly. Similarly, the DUT will send DUT data packet signals at a variety of frequencies, power levels, or modulation types, or combinations of two or more of these, to determine if the DUT transmitting subsystem is operating properly. 
     One method for testing the receiver of a DUT is to send sequences of test data packet signals at different power levels while keeping track of the number of data packets transmitted and the number of successfully received responsive data packets at each power level. For example, if 100 packets are sent at a first power level P1 and 95 packets are correctly received, the packet error rate at power level P1 would be five per 100 (0.05 or 5%). 
     When a DUT is tested using non-link testing, i.e., sending signals directly to its receiver rather than establishing a prescribed link between test system and DUT, then the number of packet errors can be reliably attributed to a failure of correct data packet reception, since the DUT receiver is programmed to receive data packets only at the specified channel and/or frequency. However, in link-based testing, where the DUT performs essentially as it would under real life conditions, the DUT may begin searching for a different access point when its received signals approach a low power level limit prescribed by the underlying wireless signal standard for the DUT (e.g., IEEE 802.11x and implementation by the DUT of its firmware/MAC layer). 
     When a tester is sending test data packet signals to a DUT and the DUT is doing an access point search the DUT will not be sending responsive data packets to acknowledge receipt of the tester data packets, since the DUT is typically searching at a different frequency than that at which the intended tester data packets are being transmitted and, therefore, will not respond regardless of the power level(s) of the tester data packets. Under such conditions, the tester would normally count such lack of acknowledgement data packets as packet errors, thereby distorting PER test results. 
     Referring to  FIG. 1 , a typical testing environment  10   a  includes a tester  12  and a DUT  16 , with test data packet signals  21   t  and DUT data packet signals  21   d  exchanged as RF signals conveyed between the tester  12  and DUT  16  via a conductive signal path, typically in the form of co-axial RF cable  20   c  and RF signal connectors  20   tc,    20   dc.  As noted above, the tester typically includes a signal source  14   g  (e.g., a VSG) to provide the tester data packets for transmission (e.g., modulating and frequency up converting), and a signal analyzer  14   a  (e.g., a VSA) for receiving (e.g., frequency down converting and demodulating) and analyzing data packets received from the DUT  16  (via the shared RF signal connector  20   tc ). Also, as discussed above, the tester  12  and DUT  16  include preloaded information regarding predetermined test sequences, typically embodied in firmware  14   f  within the tester  12  and firmware  18   f  within the DUT  16 . As further noted above, the details within this firmware  14   f,    18   f  about the predetermined test flows typically requires some form of explicit synchronization between the tester  12  and DUT  16 , typically via the data packet signals  21   t,    21   d.    
     Referring to  FIG. 2 , Referring to  FIG. 2 , an alternative testing environment  10   b  uses a wireless signal path  20   b  via which the test data packet signals  21   t  and DUT data packet signals  21   d  are communicated via respective antenna systems  20   ta,    20   da  of the tester  12  and DUT  16 . 
     Referring to  FIG. 3 , in a typical test (after a link between the tester  12  and DUT  16  has been established), the tester sends a test data packet signal  21   t  containing test data packets  23   t  to the DUT. Correct reception of a test data packet  23   t  by the DUT results in a responsive data packet  23   d  (e.g., an acknowledgement or ACK packet) transmitted by the DUT as part of its DUT data packet signal  21   d.  Similarly, the next test data packet results in another responsive data packet. However, the third test data packet results in no receipt of a responsive data packet  25 . Similarly, the eighth test data packet also results in no receipt of a responsive data packet. Accordingly, after eight tester data packets have been sent, six have been acknowledged and two have not. These two failures to receive responsive data packets can be reliably considered packet errors, thereby making the PER in this case two out of eight, or 0.25. 
     Referring to  FIG. 4 , the tester data packets  23   t  are now being transmitted at reduced data packet power levels. As discussed above, this could cause the DUT to initiate a search for another access point. Therefore, the failures of the third, fourth and fifth tester data packets to produce responsive data packets  27  may be due to actual packet errors, or, alternatively, may be due to engagement by the DUT in searching for another access point and, therefore, not receiving or responding to the transmitted tester data packets at reduced power levels. In the event of the tester counting these unacknowledged test data packets as packet errors, when they are actually due to the DUT distraction of searching for another access point, then the resulting PER will appear higher than it actually should be. 
     Referring to  FIG. 5 , in accordance with the presently claimed invention, uncertainties about PER test results due to possible access point searching by the DUT can be avoided. Instead of sending an unbroken sequence of test data packets, alternating sequences of higher powered test data packets  23   ta  and lower powered test data packets  23   tb  are transmitted, with confidence that the former should always produce a responsive data packet  23   da,  while the latter may not. Failure of the higher powered test data packet  23   ta  to be acknowledged by a responsive data packet  23   da  would indicate either a defective DUT or a DUT that has initiated an access point search. So long as the higher powered test data packets are acknowledged, any failure to acknowledge a lower powered test data packet can be counted reliably as a packet error. Furthermore, transmitting packets at high power will make a search for a new access point less likely as high power packets are received, thereby producing responsive data packets indicating a good connection. 
     Accordingly, as shown, a higher powered data packet  23   ta  produces an acknowledgement data packet  23   da.  The subsequent lower powered data packet  23   tb  also produces an acknowledgement data packet  23   db.  Continuing, the next higher powered data packet  23   tc  produces an acknowledgement data packet  23   dc.  Then, however, the next lower powered test data packet  23   td  fails to produce an acknowledgement data packet  23   dd.  The next higher powered test data packet  23   te  does produce an acknowledgement data packet  23   de.  As a result, it can be reliably concluded that of the two lower powered test data packets  23   tb,    23   td,  one such data packet  23   td  resulted in a packet error  23   dd.  Since all of the higher powered test data packets  23   ta,    23   tc,    23   te  did produce acknowledgement data packets  23   da,    23   dc,    23   de,  it can also be reliably concluded that the DUT was not searching for another access point and was responsive to all test data packets it managed to receive correctly. 
     Referring to  FIG. 6 , in accordance with another embodiment of the presently claimed invention, a higher powered test data packet  23   ta  produces an acknowledgement data packet  23   da,  and is then followed by a sequence of lower powered test data packets  29   t.  Of these four lower powered test data packets  29   t,  two are acknowledged and two are not, thereby producing only two responsive data packets  29   d.  After this sequence of lower powered test data packets  29   t  has been transmitted, a higher powered test data packet  23   tf  is transmitted and acknowledged  23   df.  This is indicative of the DUT remaining in receive mode (e.g., and not searching for another access point) and the PER test results for the sequence  29   t  of lower powered test data packets can be relied upon. 
     Subsequently, another set of four lower powered test data packets  31   t  are transmitted and produce another responsive data packet sequence  31   d  in which only partial acknowledgement occurs. Another higher powered test data packet  23   tk  is then transmitted, but produces no responsive data packet  23   dk.  This failure to produce a responsive data packet is indicative of the DUT no longer being in receive mode, at least not at the current signal frequency and/or channel but instead possibly being in search of another access point. Accordingly, any PER test results attributable to this partial sequence of responsive data packets  31   d  may be ignored in its entirety. Alternatively, only the missing responsive data packets may be ignored for purposes of the PER test. 
     Referring to  FIG. 7 , in accordance with another embodiment of the presently claimed invention, a higher powered test data packet  23   ta  is transmitted and acknowledged  23   da.  Then, four lower powered test data packets  23   tb  are transmitted with two acknowledged and two resulting in no responsive data packets  31   d.  The subsequent higher powered test data packet  23   tf  also produces no responsive data packet  23   df.  Hence, similar to the preceding example, the apparent packet errors indicated by these results may be ignored, since the DUT may have been distracted by searching for another access point. However, after the higher powered test data packet  23   tf  has been transmitted and produces no responsive data packet  23   df,  the tester is prompted to repeat sending only higher powered test data packets  23   tg  until one such data packet  23   tj  does produce a responsive data packet  23   dj.  Following receipt of this responsive data packet  23   dj,  the tester then resumes sending a sequence  33   t  of lower powered test data packets and maintains a count of responsive data packets  33   d  received and return. Then, since the subsequent higher powered test data packet  23   to  produces a responsive data packet  23   do,  this sequence of lower powered test data packets  33   t  and the resulting one missing acknowledgement among the responsive data packets  33   d  are deemed reliable for purposes of the PER test. (As will be readily appreciated, the use of four lower powered test data packets in this example is merely exemplary. Such sequences of lower powered test data packets can include more or fewer packets as desired or needed.) 
     Referring to  FIG. 8 , in accordance with further exemplary embodiments, increased efficiencies may be realized by not transmitting higher powered test data packets  23   ta  at a predefined or set interval N (e.g., where one out of every N+1 data packets is not used for purposes of PER testing, even if no packet error occurs), but instead, initiating higher powered test data packets based on the number of missing responsive test data packets. For example, as shown here, if three consecutive lower powered test data packets  23   tb  are not acknowledged, the tester assumes that the DUT may no longer be receiving and, therefore, transmit a higher powered test data packet  23   tg  which produces a responsive data packet  23   dg  indicating that the DUT is, in fact, still receiving. 
     Accordingly, transmission of lower powered test data packets  23   th  resumes until a new interval  35   d  during which no responsive data packets are received. Another higher powered test data packet  23   tm  is then transmitted but produces no responsive data packet, so the tester continues to transmit higher powered test data packets  23   tm  until a responsive data packet  23   dm  is finally received. Transmission of higher powered test data packets  23   tm  not producing responsive data packets, however, should not be of such a duration that the DUT has time to scan for a new access point and still return to the current frequency and/or channel. Such a scenario can be rendered unlikely, however, since the tester controls the frequency of the generated test data packets. 
     It will be readily appreciated that the power levels of the test data packets need not have the same power level. Further, it may be advantageous to transmit test data packets at a power level expected to produce a PER of 50%, since such power level will typically result in responsive data packets returned for every other test data packet, thereby providing more rapid determination of receiver sensitivity. (Such technique is described in more detail in U.S. patent application Ser. No. 13/959,354, the disclosure of which is incorporated herein by reference.) 
     Additionally, this method can also be applied to a non-link test to determine if a DUT is suddenly unresponsive. Such method allows the tester to force an early exit from testing when a DUT stops operating (e.g., due to software issues). One benefit realized from this is reduced test time due to the early test exit instead of waiting for the full test run or a time out condition. 
     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.