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 . discussed in more detail below , a system and method are provided for forcing fewer transmitted and received packet data streams in a testing environment where a n × n mimo dut is mimo - linked to a n × n mimo reference device ( or , alternatively , to a tester configured to operate as a n × n mimo packet data signal transceiver ). once a n × n communication link has been established , the mimo dut will transmit data as packets parsed into n simultaneous parallel packet sets containing n data streams to the mimo reference device using all n transmitters and antenna ports . in accordance with well - known principles , successful reception of all n data streams of the n parallel packet sets by the mimo reference device will allow it to reconstruct the data . ( for purposes of the following discussion , a 3 × 3 system and testing sequence will be discussed , i . e ., where n = 3 . however , it will be readily understood by one skilled in the art that n can have other integer values .) to have the mimo dut revert to operation using fewer packet data streams , the link would need to be interrupted , the configuration changed and a new link established such that the system only supports two packet data streams . accordingly , if a 3 × 3 operation was to be changed to a two - stream operation , the data would be parsed into two data streams to be transmitted by the three dut transmitters ( or , alternatively , though less advantageous , two transmitters ). this allows the mimo reference device to reconstruct the data received from the dut transmitters . however , since the system is actually a 3 × 3 system ( for purposes of this example ), all three transmitters should be used to transmit the two packet data streams by using spatial mapping , in accordance with well - known techniques . as discussed in more detail below , in accordance with exemplary embodiments , the mimo dut is enabled to revert from an n × 3 to an n × 2 operation configuration without having to interrupt and then re - establish a new communication link , while still maintaining use of all dut transmitters . in accordance with exemplary embodiments , one of the packet data streams being transmitted by one of the dut transmitters is selectively corrupted ( discussed in more detailed below ) before being received by the mimo reference device . this corruption will cause the packet data stream to be unsuccessfully received and , therefore , deemed a failure , because the mimo reference device will be unable to reconstruct the data , since one of the packet data streams has been unsuccessfully received . as a result , the mimo reference device will not respond by transmitting confirmation data packets . subsequently , the dut again sends the packet data streams via all dut transmitters , and again one of the packet data streams is corrupted . accordingly , the mimo reference device will again be unable to reconstruct the data and , therefore , not respond with confirmation data packets . at this point , the dut , in accordance with standard protocol implemented by the applicable signal transmission standard , will revert to a reduced number of data streams , e . g ., to an n × 2 operation configuration , and now send the packet data streams parsed into fewer , e . g ., two rather than three , packet data streams via its n dut transmitters . the mimo reference device can now receive both packet data streams of uncorrupted data sent by fewer of the dut transmitters even when the third path is corrupted and respond accordingly with confirmation data packets . hence , the dut has effectively reverted from n × 3 to n × 2 operation without requiring an interruption and re - assertion , or re - establishment , of the communication link , and done so all while still using all n dut transmitters . as discussed in more detail below , in accordance with exemplary embodiments , a system and method are provided for testing a mimo dut using a compatible mimo reference device and an intervening set of controlled signal corruption circuits , one for each dut wireless signal path ( e . g ., one for each dut antenna port ). by communicating via a controller , which , in turn , controls the settings of the signal corruption circuits , a tester can cause one or more data packets being conveyed from the mimo dut to the mimo reference device to be corrupted , setting up the conditions , as described above , where the dut will revert to fewer packet data streams . ( signal corruption can be in virtually any form , so long as it causes the corrupted data packet to fail to conform to the signal communication standard or protocol while ensuring other parallel transmission packets can be received under which the dut is being tested . examples include signal power attenuation and partial packet attenuation .) the tester samples the data packets being transmitted by the mimo dut as received by it prior to the signal corruption . accordingly , the tester can detect and process uncorrupted data packets , while the mimo reference device will receive both corrupted and non - corrupted data packets . using selected data packet corruption where a latter portion of a data packet is corrupted ( partial packet attenuation ), rather than attenuating the signal as a whole , the process is more robust since this will minimize the possibility of an attenuated signal nonetheless being received due to leakage through the corresponding receive channel of the mimo reference device which , due to the attenuation of the incoming signal , has increased its receive signal gain in an attempt to receive the attenuated signal . it is important that the system monitor the duration of the packets transmitted to determine the number of streams being used by the dut 20 . for example , the dut 20 could switch from three streams directly to one stream , which would also result in a confirmation packet being generated . however , this would result in a longer packet being generated by the dut 20 ( as the data from three streams is now contained in one stream ). different strategies to force the correct number of streams can be identified by those persons skilled in the art . further advantages include a reduction in test time by enabling the tester to test all possible packet data streams without interruption or re - establishment of the mimo communication link and verification that the dut 20 can negotiate to the environment in which only two of the three transmitted packets are possible to be successfully received . additionally , where the wireless signal protocol being tested provides for a reduction or ratcheting down of the data rate when a data packet fails to prompt a responsive acknowledgement data packet , more ( e . g ., all ) of the possible packet data rates prescribed by the underlying signal standard or protocol can be automatically tested . referring to fig1 , a test environment 10 in accordance with exemplary embodiments provides for testing a mimo dut 20 ( discussed herein below as a 3 × 3 mimo dut , though other n × n or n × m configurations can be similarly tested .) communicating with a reference mimo device 30 while the packet data signal streams are monitored and detected by a tester 40 . ( it will be readily appreciated by one skilled in the art that , as an alternative , the reference mimo device 30 can be included as part of the tester 40 , or be implemented as another tester configured to operate as a compatible mimo device .) also included is signal corruption circuitry 50 , which includes signal corruption circuits 52 a , 52 b , 52 c , which selectively corrupt the respective packet data streams transmitted by the dut 20 ( e . g ., attenuate latter portions of data packets within the respective packet data streams ) in accordance with control signals 55 a , 55 b , 55 c provided by control circuitry 54 ( e . g ., a field programmable gate array ). the control circuitry 54 , in turn , communicates with the tester 40 via a command , control and data signal interface 41 . the mimo dut 20 and reference mimo device 30 communicate their respective packet data dreams and acknowledgement data packets via the signal corruption circuitry 50 , signal splitters or dividers 42 a , 42 b , 42 c , and signal paths 21 , 51 , 31 . the signal paths 21 , 51 , 31 , are typically conductive signal paths in the form of rf cables , where the cables 21 connecting the mimo dut 20 and signal splitters 42 a , 42 b , 42 c are connected to the antenna ports 22 a , 22 b , 22 c of the mimo dut 20 . in accordance with well - known principles and techniques , the signal splitters or dividers 42 a , 42 b , 42 c ( various implementations of which are well known in the art ) split or divide ( in terms of signal magnitude or power ) the packet data signal streams transmitted by the mimo dut 20 during testing . these divided packet data signal streams 43 a , 43 b , 43 c are received and monitored by the tester 40 during testing for determining whether the mimo dut 20 is transmitting packet data signals in accordance with the prescribed signal standard or protocol . alternatively , if it is only desired or necessary to monitor data packet throughput using the reference mimo device 30 , the tester 40 can be omitted . as depicted here for this example , the mimo dut 20 is a 3 × 3 dut . initially , the dut 20 is configured for full mimo ( i . e ., 3 × 3 ) operation . accordingly , three packet data streams are transmitted by the dut transmitters ( not shown , but known to be within the dut 20 ) for reception by the reference mimo device 30 via their respective signal splitters 42 a , 42 b , 42 c , signal corruption circuits 52 a , 52 b , 52 c , and signal paths 21 , 51 , 31 , as well as reception by the tester 40 . with no corruption applied , the packet data streams are conveyed from the dut 20 to the reference device 30 fully intact . however , if as a data packet is transmitted it later becomes sufficiently corrupted ( e . g ., attenuated ) as it is received by the reference device 30 , then one or more packet data signal streams containing such selectively corrupted data packets will be unsuccessfully received by the reference device 30 . this will prevent the reference device 39 from being able to reconstruct the data from the non - corrupted data packets , and , as a result , not respond with a corresponding confirmation , or acknowledgement , data packet ( or parallel confirmation packets ). it should be noted that because the packet was not attenuated initially , i . e ., during the beginning of the data packet conveyance , the corresponding receiver circuit within the mimo reference device 30 will maintain a signal gain that will remain substantially constant during the remainder of the data packet , thereby limiting the possibility of reception of the corrupted data packet due to an increased signal gain caused by the gain control circuitry of the receiver circuit that would automatically increase signal gain if the packet data signal stream were attenuated from the outset . referring to fig2 , a system and method such as described above for reducing mimo signal streams without interrupting or otherwise altering initial mimo communication link conditions can be better understood . the mimo reference to device 30 transmits a set of data packets 33 ( e . g ., “ ping ” packets , though other types of packets can be used as well ) from its three signal transmitter subsystems ( not shown though known to be within the reference mimo device 30 ). such packets 33 are conveyed to the dut 20 via the signal paths 21 , 51 , 31 , signal splitters 42 a , 42 b , 42 c , and signal corruptions circuits 52 a , 52 b , 52 c , where the latter are set by their control circuitry 54 to not yet introduce any disabling signal corruption . in response , the dut 20 transmits one or more confirmation data packets 23 from its respective transmitter subsystems . with a communication link now established between the dut 20 and reference device 30 , the dut 20 follows up with response data packets 35 a ( having packet durations similar to those of the initial packets 33 ) containing three respective data streams : s 1 , s 2 and s 3 ; s 1 ′, s 2 ′ and s 3 ′ ; and s 1 ″, s 2 ″ and s 3 ″. ordinarily , the reference device 30 would receive the three packet data streams and be able to reconstruct the data . however , prior to these data streams being received by the reference device 30 , one of the packet streams , e . g ., the packet arriving at the first , or top , signal port 31 a of the reference device 30 , is corrupted ( e . g ., attenuated ) as shown . as discussed above , during a first portion , or time interval , 36 aa of the data packet , it remains non - corrupted . however , during a latter portion 36 ba , corruption is applied by the corresponding signal corruption circuit 52 a . as a result , the reference device 30 cannot reconstruct the data and , accordingly , does not respond to the dut 20 by transmitting confirmation packets . the dut 20 can continue to respond by re - transmitting the same data packets 35 b ( since the previous packets were not successfully received ) now having a reduced data rate , though still using three packet data streams . however , as before , the first packet data stream is corrupted during a latter portion 36 bb following an initial portion 36 ab during which no corruption is applied so as to cause the receiver circuitry to maintain its initial nominal signal gain . as a result , again , the reference device 30 cannot reconstruct the data and does not respond with confirmation packets . accordingly , as shown , the dut 20 continues to transmit , this time with another set of response data packets 35 c . however , the dut 20 has now reverted to a two - stream operation configuration using a decided data rate ( which can be equal , higher or lower than the previous three - stream operation ), with the data now parsed into two signal streams for continued transmission via all three dut transmission paths : s 1 and s 2 ; s 1 ′ and s 2 ′; s 1 ″ and s 2 ″. as a result , despite one of the data packets being corrupted ( i . e ., the data packet containing the first signal stream s 1 and s 2 ) the reference device 30 now receives two packets with the two parsed streams ( s 1 ′ and s 2 ′, and s 1 ″ and s 2 ″), which are now sufficient to allow the reference device 30 to reconstruct the data . accordingly , it responds by sending confirmation packets 25 . referring to fig3 , as discussed above , during an initial interval 36 a of the data packet to be corrupted , the applied , or induced , corruption is disabled ( or at least significantly decreased ). subsequently , during a later time interval 36 b , corruption is enabled ( or at least significantly increased ). referring to fig4 , as an exemplary embodiment , the signal corruption circuits 52 can be implanted as controllable signal attenuator circuitry 52 r , various forms of which are well known in the art , to cause the packet data stream to have an insufficient power level for successful reception . referring to fig5 , in accordance with another exemplary embodiment , the portions 21 of the signal paths between the dut 20 and signal splitters 42 a , 42 b , 42 c can be implemented as wireless signal paths 21 w , in which antennas 22 aa , 22 ba , 22 ca connected to the dut 20 communicate with antennas 22 ab , 22 bb , 22 cb connected to the signal splitters 42 a , 42 b , 42 c to convey the packet data streams . such a cable - free interface for the dut 20 would be have the advantage of operating the dut 20 in a more realistic manner and avoid the need to physically connect and disconnect test cables to and from the dut 20 . various other modifications and alternations 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 .