CN101268643B - Apparatus and method for simultaneous testing of multiple orthogonal frequency division multiplexed transmitters with single vector signal analyzer - Google Patents
Apparatus and method for simultaneous testing of multiple orthogonal frequency division multiplexed transmitters with single vector signal analyzer Download PDFInfo
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Abstract
The invention provides an apparatus and method for simultaneous testing of multiple orthogonal frequency division multiplex (OFDM) signal. A vector signal analyzer (600) transforms multiplex signal that is received via a signal communication path and includes a plurality of OFDM signal for providing a plurality of transformed data signal, wherein, multiplex signal data source includes a remote signal source of a plurality of signal transmitting processes relatively, and includes a plurality of data groups, each data group includes respective parts of a plurality of preposing code data, and respective parts of a plurality of transmitting data, each respective parts of a plurality of transmitting data and each one of a plurality of data transmitting processes and respective parts of a plurality of known data relative to the signal communication path, and each one of a plurality of transformed data signal including respective parts of a plurality of data groups, and at least respective parts of receiving and processing a plurality of known data, a plurality of preposing code data, at least respective parts of a plurality of transmitting data for providing a plurality of detection data of error vector amplitude (EVM) associated with multiplex data signal.
Description
Related application
The application requires the U.S. Provisional Patent Application the 60/596th proposing on September 23rd, 2005, the priority of No. 444.
Technical field
The present invention relates to OFDM (OFDM, orthogonal frequencydivision multiplexing) test of transmitter, relate in particular to and utilize vector signal analyzer (VSA, vector signal analyzer) to test OFDM transmitter.
Background technology
As everyone knows, multiple-input and multiple-output (MIMO) communication system strengthens reliability and the signal volume of communication link with a plurality of transmitter and receivers.Conventionally by by each separately transmitter be connected with VSA, and repeat successively the measurement to each transmitter, complete the test of each transmitter.Alternately, another kind of method relates to and each transmitter is connected with its VSA and tests simultaneously.Therefore, first method only needs a VSA, but the more time of significant need, and second method needs a plurality of VSA systems, but the less time of significant need.
The traditional test of wireless device relates to active transmitter of each test.Even if equipment provides a plurality of transmitters, conventionally can not operate concurrently them yet.Yet people often attempt to improve data rate.In the past, this is by utilizing more complicated modulation and wider bandwidth to realize.These methods have been used individual transmitter, therefore, can utilize single input test instrument to measure.
Along with the introducing of MIMO technology, by allowing transmitter separately utilize identical transmission frequency and bandwidth to carry discrete information, with a plurality of parallel transmitters, improve the permission data rate in given bandwidth.In the normal operation period, system need to send reliably the mulitpath of parallel data stream in same band simultaneously.System depends on the advanced signal of separated different transmitted signals in required a plurality of receivers and processes.The data that receiver is separated and extraction is sent by a plurality of transmitters.Therefore, need a plurality of parallel receivers carry out the real MIMO signal of multianalysis, and can not re-use single input test instrument and carry out multianalysis transmitted signal.
This obtains the research and development (R & D) of the information of relevant equipment under test (DUT, device undertest) as much as possible for needs and tests especially true.Then, for production test, may not need so much information, because real test is in order to determine whether DUT is correctly assembled and whether all parts all work completely.Suppose that all critical pieces (for example, chip) all tested, and if hypothesis assembling be complete and correct, just confirm that the model machine of producing can correctly work, thus without understanding test plan in detail.
From the visual angle producing, the possible testing cost that people wish to cover completely required test is minimum.Production test generally include the examination and test of products and often prior product calibrate both.Between product alignment epoch, adjust the performance of equipment to meet desired properties.
The testing cost of optimizing in producing is included in the fastest possible testing time of assurance under reasonable price test request.Test MIMO transmitter shows, can utilize concurrent testing equipment, to test concurrently each transmitter.Compare with legacy equipment, this increases the testing time hardly, but will the cost of test equipment be doubled, and has therefore improved total testing cost.
Because modern test equipment provides much bigger signal handling capacity, really exist except only carrying out concurrently other option all tests.As mentioned above, may not measure aborning all parameters of DUT; Often can only measure the parameter that expection changes in production equipment.This comprises and identifies trouble unit and packing problem, and the performance calibration of transmitter is separately become to approach best ability.
Summary of the invention
According to the present invention, provide and utilized single VSA to test the apparatus and method from the signal of two or more OFDM transmitters simultaneously.
According to one embodiment of the present of invention, for test the vector signal analyzer of a plurality of OFDMs (OFDM) signal simultaneously, comprise:
Signal transformation part, for converting the composite data signal that receives and comprise a plurality of ofdm signals via signal communication paths, to the data-signal after a plurality of conversion is provided, wherein,
Described composite data signal is derived from the remote signal sources with a plurality of signal process of transmittings associated therewith, and comprises that a plurality of packets, each of a plurality of packets comprise the part separately of a plurality of preamble data and the part separately of a plurality of transmission data.
Each of a plurality of transmission data be relevant with signal communication paths the part separately corresponding to a plurality of given datas separately of part and a plurality of data transmission procedure separately, and
Each of data-signal after a plurality of conversion comprises the part separately of a plurality of packets; And
Signal Processing Element, for receiving and process the part at least separately of a plurality of given datas, a plurality of preamble data and the part at least separately of a plurality of transmission data, to a plurality of test datas of indicating the error vector magnitude (EVM, error vector magnitude) being associated with composite data signal are provided.
According to an alternative embodiment of the invention, the method for simultaneously testing a plurality of OFDMs (OFDM) signal comprises:
The composite data signal that conversion is received and comprised a plurality of ofdm signals by signal communication paths, to the data-signal after a plurality of conversion is provided, wherein,
Described composite data signal is derived from the remote signal sources with a plurality of signal process of transmittings associated therewith, and comprises that a plurality of packets, each of a plurality of packets comprise the part separately of a plurality of preamble data and the part separately of a plurality of transmission data,
Each of a plurality of transmission data be relevant with signal communication paths the part separately corresponding to a plurality of given datas separately of part and a plurality of data transmission procedure separately, and
Each of data-signal after a plurality of conversion comprises the part separately of a plurality of packets; And
Receive and process the part at least separately of a plurality of given datas, a plurality of preamble data and the part at least separately of a plurality of transmission data, to a plurality of test datas of indicating the error vector magnitude (EVM) being associated with composite data signal are provided.
Accompanying drawing explanation
Fig. 1 describes to be suitable for use in the signal graph according to the typical MIMO ofdm signal burst configuration in the method for one embodiment of the invention;
Fig. 2 describes to implement according to the calcspar of the receiver system of the method for one embodiment of the invention;
Fig. 3 is the calcspar of the receiver subsystem of Fig. 2;
Fig. 4 A and 4B are the calcspars of alternate embodiments of the interface/computer of depiction 2;
Fig. 5 is that describe will be according to the calcspar of a plurality of OFDM transmitters of one embodiment of the present of invention tests;
Fig. 5 A is the calcspar of an one exemplary embodiment in the process of transmitting stage of depiction 5;
Fig. 6 is described in to implement according to the calcspar of the process relating in the method for testing of various embodiment of the present invention;
Fig. 6 A and 6B they time domain and frequency domain in described to identify in Fig. 6 signals selected;
Fig. 7 is the calcspar of describing to characterize the technology of the non-linear behavior cause Signal Compression;
Fig. 8 A-8C is the calcspar of describing to implement test equipment configuration of the present invention;
Fig. 9 A-9B has described with figure the result that signal EVM measures;
Figure 10 A-10B has described the result of signal correlation measurement with figure;
Figure 11 A-11B has described CCDF curve with figure;
Figure 12 A-12B, 13A-13B, 14A-14C and 15A-15D with figure described variously not compress, compression and compound MIMO signal; And
Figure 16 describes to compare and measure the calcspar with the technology of reference signal according to one aspect of the present invention.
Embodiment
Describe with reference to the accompanying drawings one exemplary embodiment of the present invention in detail.Such description is intended to illustration the present invention, rather than limits the scope of the invention.Fully describing such embodiment in detail is in order to make those of ordinary skill in the art can implement the present invention, and can utilize some variants that do not depart from the spirit or scope of the present invention to implement other embodiment.
In disclosure full text, unless separately there is clear indication in context, should be understood that described circuit element separately can be odd number or plural number.For example, term " circuit " can comprise active and/or passive and connect or otherwise the single parts that are coupled or a plurality of parts (for example, becoming one or more integrated circuit (IC) chip), so that required function to be provided.In addition, term " signal " can refer to one or more electric currents, one or more voltage or data-signal.In accompanying drawing, identical or relevant element has identical or relevant letter, numeral or alphanumeric indicator.
According to method of testing of the present invention, for utilize single VSA to test two or more OFDM transmitters simultaneously, created condition.Such method has utilized typical MIMO OFDM transmitter in the beginning of burst,, during being convenient to the reliable reception of remainder and the preamble of demodulation of signal burst, sends the fact of its output signal with the burst with customizing messages.
With reference to Fig. 1, as shown in the figure, an example of the one group of signal using when testing two transmitters according to one embodiment of the present of invention comprises two signal bursts.In this example, three preambles have been used, each cyclic shift with itself (CS, cyclic shift).Except cyclic shift, the preamble of the second transmitter is identical with the preamble of the first transmitter.For example, preamble 1,2 and 3 cyclic shift are respectively 400,3100 and 1600 nanoseconds.But, should understand, other preamble that operates appointment for MIMO is also fine.
With reference to Fig. 2, an embodiment 200 who is applicable to implement system of the present invention comprises receiver 202, controller 204 and can comprise the interface 206 of computer.Input radio frequency (RF) signal 201 (as more discussed in detail below) by receiver 202 according to coming the control signal 205 of self-controller 204 to process.Gained sampled data vector 203 is offered to interface 206.If interface 206 comprises computer, can process in this locality sampled data vector 203.Otherwise, can sampled data vector 203 be transmitted to outer computer by for example network (such as Ethernet) interface 209 and be processed.Control data 207 are offered controller 204 or by outer computer, by interface 206, offered controller 204 such as what receive on network interfaces 209 by the inner computer of interface 206.
With reference to Fig. 3, an one exemplary embodiment 202a of receiver 202 comprises substantially as shown in the figure, the many traditional element that connect in a conventional manner.Input rf signal 201 by variable gain amplifier 302 according to coming the control signal 205a of self-controller 204 to amplify.In frequency mixer 306, utilize LO signal down-conversion gained signal 303, the one LO 304 that the first local oscillator (LO) 304 provides to be come the control signal 205b of self-controller 204 to control.Gained down-conversion signal 307 is by band pass filter 308 filtering.Utilize another variable gain amplifier 310 according to the control signal 205c that carrys out self-controller 204, the signal 309 after amplification filtering.
In frequency mixer 314i, 314q, utilizing from the further down-conversion process down-conversion of quadrature LO signal 313i, 313q of the second LO 312 and signal 311, the two LO 312 of filtering is come the control signal 205d of self-controller 204 to control.Utilize low pass filter 316i, 316q filtering gained base band orthogonal signalling 315i, 315q (should easily understand, replace, can carry out single down-conversion, for example,, in the situation that input rf signal 201 is amplified by a variable gain amplifier 310 and the 2nd LO 312 provides orthogonal signalling 315i, 315q to be applicable to the frequency of low pass filter 316i, 316q).
Filtered signal 317i, 317q are the orthogonal data signals of analog form, and by analogue-to-digital converters (ADC) 318i, 318q, convert digital data signal 319i, 319q to, ADC 318i, 318q are come the control signal 205e of self-controller 204,205f to control.According to the control signal 205g that carrys out self-controller 204, these data-signals 319i, 319q are stored in memory 320, so that as in-phase data signal 321i and quadrature phase data-signal 321q.
With reference to Fig. 4 A, meet an embodiment 206a of 206 and comprise the computer that utilizes Survey Software 402 and control software 404 programmings.User's operation is undertaken by graphic user interface 406, and graphic user interface 406 is communicated by letter with control software 404 with Survey Software 402 with control information 405 by data message 403.
With reference to Fig. 4 B, when using outer computer, such computer 400 comprises interface 440, by this interface, Survey Software 402 and control software 404 by network be connected 209 and this locality connect 206 mutual.Exchange data information 441m and control information 441c between interface 440 and Survey Software 402 and control software 404.
With reference to Fig. 5, utilize according to the RF signal 201 of the method test of one embodiment of the invention is the combination from two or more (two in this example) transmitted signals of same quantity transmitter.In this example, the transmitting unit 500 that test comprises two signal sending systems.The data 501a sending, 501b are processed according to process of transmitting 502a, 502b.Gained signal 503a, 503b utilize amplifier 504a, 504b to amplify, and produce time domain data signal 505a, 505b, and time domain data signal 505a, 505b be through filter 506a, 506b filtering, time domain data signal 507a, 507b that generation will send.Filter 506a, 506b provide the simulation of linear distortion, for example, and the distortion of other form (, amplifier noise, nonlinear amplifier and frequency mixer distortion, I/Q is unbalance, phase noise etc.) is simulated by additive error signal 551a, the 551b introducing via signal combiner 552a, 552b.In signal combiner 554, be added gained signal 553a, 553b to produce RF signal 201.
With reference to Fig. 5 A, an one exemplary embodiment of process of transmitting 502a, 502b can be described below.By process 510, process input data 501a, 501b at first, wherein input data and be encoded, interweave, from serial conversion to parallel form and according to quadrature amplitude modulation (QAM), shine upon.According to invert fast fourier transformation (IFFT) 512, process orthogonal signalling U1 (k) 511i, the 511q of gained, then in transfer process 514, gained signal 513i, 513q are become to series form from parallel formal transformation.Gained serial signal 515i, 515q are added into Cyclic Prefix in next process 516, thereby produce orthogonal data signal 517i, the 517q that will send.
Preamble generator 518 produces quadrature preamble signal 519i, 519q.Data-signal 517i, 517q and preamble signal 519i, 519q are offered to signal router, and for example switch 520.According to control signal 521c, router five 20 is selected preamble signal 519i, 519q, then selects data-signal 517i, 517q.In being buffered in buffer amplifier 522i, 522q and in signal mixer 524i, 524q with quadrature switching signal 531i, 531q (as more discussed in detail below) mixing before, by digital-analog convertor (DAC) 532i, 532q, convert signals selected 521i, 521q to analog signal 533i, 533q, finally, in signal combiner 526, be added gained signal 525i, 525q to produce output signal 503a, 503b.
Local oscillation circuit 528 produces quadrature local oscillated signal 529i, 529q, in signal mixer 530i, 530q by quadrature local oscillated signal 529i, 529q and for orthogonal signalling 531a, the 531b mixing of the orthogonal unbalance in analog signal transmission path, thereby produce quadrature local oscillated signal 531i, 531q.The signal gain Gi of buffer amplifier 522i, 522q, Gq are for the amplitude imbalance of analogue orthogonal signal transmission path.
With reference to Fig. 6, according to one embodiment of the present of invention, Survey Software 402 carries out being expressed as many tests and the operation of process streams 600.Input sampled data vector 321i/321q is used in the many processes that comprise spectrum calculating 602, matched filtering detection 604 and frequency correction 606.Spectrum calculates 602 by for example the result of fast fourier transform (FFT) process being averaging, and the data 603 of the power spectrum that represents composite signal are provided.
Matched filtering testing process 604 is starting point, character boundary and the frequency error of input signal 321i/321q detection signal.Frequency error information 605a is offered to frequency correction process 606, and the starting point 605b of signal and character boundary 605c information are offered to parallel transfer process 608.
The nominal frequency of input signal 321i/321q is corrected according to frequency error information 605a in frequency correction process 606.Signal message 607 after correction converts parallel signal information by parallel transfer process 608 to according to the origin information 605b of signal and character boundary information 605c.
Utilize FFT process 610 to process parallel signal information 609, to produce the frequency domain information Y1 (k) corresponding with initial data transmitted signal 201
*+ Y2 (k)
*611.This information 611 is offered to preamble processing procedure 612 (discussing as follows).In addition, additive process 616 is further processed this information 611 by deducting broadcast reference signal information 615 (discussing as follows), to produce the error signal in the frequency domain 617 being present in initial data transmitted signal 201.
Preamble processing procedure 612 is that filtering 506aa, 506ba (discussing as follows) produce control signal 613a, 613b.In addition, it also produces each data 613c, the I that represents each transmitter of power level and the unbalance data between Q data-signal (for example,, as phase place and the amplitude discussed for Fig. 5 A) and the spectrum flatness of each data transmitted signal (amplitude of each the OFDM carrier wave in data transmitted signal 553a, 553b) of representative data transmitted signal 553a, 553b above.
For test purpose, the initial data that tested transmitting system 500 sends is known, and provides as given data 501aa, 501ba, for repetition process of transmitting 502aa, the 502ba in Survey Software 402.Gained repeats frequency domain data signal U1 (k)
*503aa, U2 (k)
*503ba controls data 613a, 613b filtering by the filtering 506aa, the 506ba that are intended to imitate original filter 506a, the 506b of transmitting system 500 according to filtering.In anabolic process 614, be added gained filtering data S1 (k)
*507aa, S2 (k)
*507ba to produce the desirable transmitted signal 615 of reconstruct, deducts the desirable transmitted signal 615 of this reconstruct, to produce composite error signal E1 (k) from receive signal 611
*+ E2 (k)
*617.Utilize normalized form, can from this composite error signal 617, calculate EVM.
Should easily understand, given data 501aa, 501ba may for example, be processed by the scrambler (, in process of transmitting 502a, 502b) of initial state the unknown in transmitting unit 500.In receiver 600, can utilize the data of retrieving from input signal 321i/321q are solved to such uncertainty with the process that all possible scrambler initial state is associated.
According to discussion above, as the signal measurement being depicted in Fig. 6 can be summarized as follows: by for example matched filter, for preamble, detect beginning and the character boundary of input signal.The output of matched filter is used for to sending out signals carrier frequency shift, in time domain, can from this signal(-) carrier frequency skew, calculate and apply suitable frequency correction and (should easily understand, other well-known technology also can be for reaching this object, for example, power envelope detects or auto-correlation).
Utilize fast fourier transform (FFT) to process the remainder of input signal, for example, be connected on preamble data below, each FFT output represents a symbol.For each FFT output with N value, the subset N1 of these values represents the OFDM of inclusion information (OFDM) signal carrier.Conventionally, value N is that 2 power and N1 are approximately equal to N-10.MIMO preamble structure for M transmitter allows to set up M the equation for each the OFDM carrier wave N1 that is present in transmitted signal Y1 (k), Y2 (k) with M unknown number.Each carrier wave that to solve these equations be transmission among these signals Y1 (k), Y2 (k) provides the estimated value of amplitude and phase response H1, H2.Amplitude response H1, H2 by filter determine channel flatness, and determine power level by being added the power of each carrier wave in transmitted signal Y1 (k), Y2 (k), and to calculate I/Q unbalance by assessing relevance between near the positive negative carrier of each centre frequency of transmitted signal Y1 (k), Y2 (k).
Because the content of preamble is in advance known, and because input preamble has different cyclic shifts, for each carrier signal, can the separated signal from various transmitters.For different multiple-input and multiple-output (MIMO), realize, can use different preambles, such preamble is designed at least basic quadrature.If initial data is known, owing to can utilizing matched filter to derive scrambler setting, can allow scrambling ground operate transmitters 500, and, if scrambler setting is known, can derive required reference signal.
As result above, can set up the power level from each carrier signal of each transmitter, can therefrom determine the available power from each transmitter, and spectrum flatness, the i.e. uniformity of signal power on whole frequency spectrum.The power of each carrier signal of each transmitter and phase place are the indications of the channel response of each transmitter as simulated in filtering 506aa, 506ba.
By comparing these separated transmitter signals, the quadrature (I/Q) that can derive each transmitter is unbalance.
If picture in test condition (as mentioned above, take into account the uncertainty of scrambler) lower expect such, data content is known, can, by the output of FFT process is compared with the desirable FFT output after application channel correction, carry out error of calculation vector magnitude (EVM).The calculating of phase noise can similarly be carried out.By FFT output is averaging, power spectrum that can calculation combination signal.
Can determine relative timing according to the output peak of matched filter 60.
With reference to Fig. 6 A and 6B, by by frequency domain data signal U1 (k)
*503aa is as an example, and the time domain between signal and frequency domain relation can be described below.With reference to Fig. 6 A, signal U1 (k) is column vector sequence, and each column vector has N FFT unit, and every row represent the symbol dividing into groups in frequency domain.For example, for IEEE 802.11a/g signal, quantity N normally 64, and 64 yuan of vector inputs are carried out to IFFT and FFT functions.Signal U1 (k) is the column vector of k symbol in grouping.With reference to Fig. 6 B, signal u1 (t) is the time-domain signal (length of preamble disproportionate) corresponding with U1 (k).For example, frequency domain vector U1 (2) is corresponding to the time-domain signal u1 (t) on following time interval t:
T
0+T
CP+2.T
s＜t＜T
0+3.T
s
Frequency-region signal U1 (k) can be by deriving from time-domain signal u1 (t) as follows:
U1(k)＝FFT(u1(t)·e
-jωt)
Wherein: t=mT
sa-kT
s+ T
0+ T
cP
ω=2 π f
c, f
cit is the frequency of local oscillated signal 529i, 529q
T
sathe sampling clock frequency of=1/ digital-analog convertor
T
s=symbol duration, comprises Cyclic Prefix
T
0the starting point of first symbol after=preamble
T
cPthe duration of=Cyclic Prefix
K=symbolic number
M=hits (for example,, for IEEE802.11a/g, m=0:63)
As mentioned above, can test concurrently MIMO transmitter, wherein, for example, by power combiner, combine the output of transmitter separately, so that composite signal feed-in can be carried out in the single tester of real signal analysis.By utilizing advanced signal Processing Algorithm, can utilize composite signal to extract many each autoregressive parameters for transmitter separately.The data of this analysis based on known transmission and the standing part of MIMO packet (for example, data packet header).This ability is extremely beneficial to production system, because it allows only to utilize single tester concurrent testing MIMO transmitting system, thereby provides fast test speed and low cost, has therefore met the minimum requirement that may produce cost.
A kind of test of hope is to measure be used in the compression separately of the different transmitters in mimo system and quality metric is assigned to each transmitter.When transmitter compression transmitted signal, this has reduced the quality of signal, and this difference that can be expressed as transmitted signal and ideal signal by EVM has great tolerance.For ofdm signal, the EVM that EVM is expressed as to the planisphere of each carrier wave and for example IEEE.11a/g standard requires the difference between described ideal constellation.By compression level, be to measure CCDF (CCDF with sending separately a kind of method that chain is associated, complementary cumulative distribution function), CCDF is well-known characteristic (this method will more discuss in detail below).
With reference to Fig. 7, another kind of method is to characterize the non-linear behavior that causes compression.Output x (t) from the non-linear element such as power amplifier can be expressed as follows with its input signal y (t):
x(t)＝a
1 *y(t)+a
3 *y
3(t)+a
5 *y
5(t)+...
Wherein, a
3and a
5it is the non linear coefficient of determining the power of the 3rd and the 5th rank response.Can be always from the compression property of each transmitter of composite signal, i.e. coefficient a
3and a
5in, derive the signal quality about each transmitter of its EVM.
By IFFT process 702a, 704a, 704b separately, often next symbol ground transforms to time domain by the local generated ideal transmitter signal 507aa of the composite error signal in frequency domain 617, first and the second local generated ideal transmitter signal 507ba.According to the 3rd rank (706a) and the 5th rank (708a) non-linear process, process the first transmitter time-domain signal 705a.By result 707a, 709a and composite error signal 703e
1(t)
*+ e
2(t)
*be associated.The first correlator output 711a
13the estimated value for the a3 item of the first transmitter of each symbol, and the second correlator output 711b
15the a for the first transmitter of each symbol
5the estimated value of item.Similarly, the 3rd correlator output 711c
23the a for the second transmitter of each symbol
3the estimated value of item, and the 4th correlator output 711d
25the a for the second transmitter of each symbol
5the estimated value of item.EVM computational process 712 is averaging these estimated values to grouping, mean estimates is used for to addressing look-up table, to determine the poor 713a of expection EVM and EVM estimated value 713b, the 713c based on compression between transmitter.
With reference to Fig. 8 A, test configurations 800a comprises for example, DUT 802, signal combiner 806, VSA 808 and computer 810 with a plurality of (, two) transmitter 804a, 804b.Computer 810 comprises and moves by interface 813 provides/receives the DUT of instruction and data control software 812 and mutually and by another interface 815 control software 814 and analysis software 816 with the VSA of VSA808 swap data and instruction to/from DUT 802.
With reference to Fig. 8 B, in alternative test configurations 800b, switch 820a, 820b are inserted between transmitter 804a, 804b and signal combiner 806, and are subject to control from the instruction of the VSA in computer 810 and switch control software 814b.
With reference to Fig. 8 C, in alternative test configurations 800c, signal combiner 806 is removed, and directly measures each transmitter output 805a, 805b by its VSA 808a, 808b.
Referring again to Fig. 8 A, according to a kind of test configurations, when changing the compression of the second transmitter 804b, with constant output signal 805a, compress to operate the first transmitter 804a, thereby produce the EVM of 32dB.Utilize single VSA 808 to measure the EVM of the second transmitter 804b.In order to obtain EVM benchmark, utilize the VSA808 being only connected with the second transmitter 804b, that is, do not add the signal 805a of the first transmitter 804a, directly measure the EVM from the second transmitter 804b.
With reference to Fig. 9 A and 9B, can compare the EVM of two kinds of measurements.Trunnion axis illustrates the EVM of the second transmitter 804b when utilizing reference software to analyze.Vertical axis illustrates the error (YidBWei unit) of EVM when using duplex measurement technology.For this fc-specific test FC being intended to for IEEE802.a/g system, because the limit accepted of peak data rate is-25dB, so interested especially EVM scope is between-24 to-27dB.Fig. 9 A is configured to situation about sending with equal power (before compression) exemplified with two transmitters, and Fig. 9 B is in than the situation on the level of high 1 decibel of the second transmitter 804b exemplified with the first transmitter 804a.In interested scope, error presents little positively biased, and Fig. 9 A has the error range of +/-1dB, and Fig. 9 B has the error range of +/-1.5dB.These tests are for only having the relatively short grouping of 24 symbols to carry out.The length that increases grouping will improve precision.
With reference to Figure 10 A and 10B, the EVM of each transmitter 804a, 804b can be subject to the impact in other harmful source.By relatively send the interrelation level of chain from difference, can monitor the compression of each transmitter.Ratio (=10 using trunnion axis as the 3rd rank incidence coefficient
*log
10(average (
13)/average (
23))) function, and using vertical axis the EVM between transmitter 804a, 804b poor, Figure 10 A is exemplified with transmitter output signal 805a, 805b (not being non-linear) equal situation on power before compression, and Figure 10 B is in than the situation on the level of high 1 decibel of the second transmitter 804b exemplified with the first transmitter 804a.
The another kind of test of wishing is to measure the compression separately that is used in the different transmitters in mimo system.At the high signal of peak-to-average force ratio, for example, in ofdm signal, often with the form of CCDF, measure compression, and the important information that can help to examine transmitter performance is provided.In well-designed system, transmitted signal power is adjusted in certain compression level, make to meet transmission quality requirement.Reduce output signal power and will make power supply power consumption increase, but improve power, will make system become darker output signal compression, thereby make to send on the point of the transmission quality limitations that Quality Down may be differed to systematic function.
With reference to Figure 11 A, the typical CCDF curve representation signal of IEEE 802.11a/g (OFDM) transmitter has the probability of X-dB or higher instantaneous power with respect to average power.Curve 1102 represents the measurement CCDF of typical well-designed transmitter, and the theoretical CCDF that curve 1104 represents while there is no Signal Compression.With respect to the skew of average power, on trunnion axis, and probability is on vertical axis.The end points 1106 of compression CCDF curve can represent compression level, because it has pointed out the compression degree at the top of input signal.In this example, output signal is with respect to the compressed about 3dB of theory signal.This point 1106 may have some to change with the grouping of short data more because relatively low owing to reaching the probability of this summit level, packet content (compression) may not can follower theory curve 1104 accurately.Therefore,, although this point 1106 is usually used to visually identify compression, should only be counted as the indication of compression.
CCDF is the relative simple function that can derive separately.Problem is, in producing equipment, people find the signal with the high compression for example being caused by bad circuit block conventionally.In single-shot transmitter system, people can easily identify the compression (Figure 11 A) that higher curvature is the indication of compression.Signal can present the peak power up to 10dB with respect to absolute power, but the transmitter of measuring output may only illustrate the summit of about 7dB; Therefore, transmitter is compressed to about 7dB by top.Because these peak levels are relatively rare, such compression generally can not affect transmitter performance to being enough to prevent that the normal performance tolerance limit of basis and error correction from recovering to send data.If two transmitters show identical compression, this is also like this for mimo system.
But, with the mimo system of imperfection transmitter, may produce compressed signal and non-compressed signal, thereby present different signal transfer characteristics.If as for multithread MIMO signal, signal peak is uncorrelated, may be difficult to measure compression by observing composite signal.If two signals demonstrate not compression, absolute peak is by than the high 3dB of the peak value of each signal.But RMS power is high 3dB also, therefore the peak to average of maximum 10dB is held.If a signal demonstrates not compression, and another has demonstrated some compressions, for example, 7dB peak-peak as above (CCDF will stop at 7dB), when two signals of combination, CCDF will demonstrate summit and reduce about 1.3dB (for equal rms signal power).If compression increases to 5dB, compound CCDF is by the 1.8dB compression only illustrating with respect to theory signal, if be further reduced to 3dB summit, CCDF is by the 2.2dB showing with respect to theory signal.Conventionally, compression by the performance limitations of transmitter to the summit scope between 6.5dB and 7dB, if there is fault in one of two transmitters, the whole mimo system imperfection that becomes.
With reference to Figure 11 B, Figure 11 B shows the comparison between the CCDF curve compound and CCDF separately of dual transmitter MIMO signal.Curve 1108 is theoretical curves of MIMO ofdm signal, and curve 1110 is compound (combination) CCDF.The curve of the not compression input of one of two MIMO transmitters is almost identical with theoretical curve 1108.Curve 1112 is about another MIMO transmitter, and pointed out the obvious compression that approaches with best alignment transmitter.Therefrom can know and find out, utilize and provide considerably less information to the CCDF measurement of composite signal.People almost can not distinguish composite signal and theory signal, and one of transmitter are compressed to the maximum for better systems simultaneously.Therefore it is impossible that the single traditional instrument that, utilization can be measured CCDF as production test equipment is usually desirable is measured CCDF fully.But CCDF is the hope analysis tool that usually can help to improve production test speed, because it is simple analysis and the important insight compound to signal is provided.
By measuring composite signal EVM, can identify other contributor to compound EVM, then, also by understanding compression property, can determine that whether EVM contribution is similar for unlike signal transmission path, or whether a kind of effect of signal transmission path arranges compound EVM.
With reference to Figure 12 A and 12B, not the compressed format (Figure 12 B) of the desirable not time samples of compressed signal (Figure 12 A) and same time sample relatively not affecting the peak larger peak value of also decaying with the similar CCDF characteristic of curve 1102 of Figure 11 A and compression and be greater than the fact compared with small leak disclosing in time domain.
With reference to Figure 13 A and 13B, for the composite signal of two MIMO signals, result when Figure 13 A has described that two signals do not compress, and Figure 13 B described one of two signals be compressed to as be depicted in Figure 11 A 1102 in level time result.Therefrom can find out, in some cases, can see compression, and in other cases, signal continue to present whole summit.As expected, the peak value of compressed signal (Figure 13 B) is less, but not with benchmark not compressed signal (Figure 13 A) be relatively difficult for identifying compression.
With reference to Figure 14 A-14C, two difference transmitted signals (Figure 14 A and 14B) produce composite signal (Figure 14 C), wherein can find out, in some cases, a signal domination summit, in other cases, another signal accounts for mainly, and in other situation, two signals reach peak value simultaneously, thereby make the peak value of composite signal higher.
With reference to Figure 15 A-15D, identical difference transmitted signal (Figure 15 A and 15B) has produced another composite signal (Figure 15 C), but a Signal Compression (Figure 15 A) and another signal does not compress (Figure 15 B).In order not compare with there is no Signal Compression, also produced another composite signal (Figure 15 D).
As mentioned above, if the data that send via MIMO signal are known, can estimate desirable composite signal and therefrom estimate EVM.This procedure extraction receives signal, in frequency with on the time, it is aimed at ideal basis calibration signal, and it is compared with reference signal, the signal of extraction and reference signal respectively be depicted in those class signals in Figure 15 C and 15D seemingly.From seeing signal measurement separately, there are two reference signals separately, therefore, also there is signal separately.Therefore, can identify the different peak maximums of two signals, and how associated with compound (combination) signal they are.Utilize this knowledge, can at one of signal as main contributions person, on power, arrange another point analysis composite signal, at this point, desirable composite signal can be compared with actual measured signal, and can determine the compression of main signal.
With reference to Figure 16, substantially as shown in the figure, obtain measuring-signal and an example of circuit 1600 that it is compared with reference signal comprises: signal envelope testing circuit 1602,1614a, 1614b; IIFT circuit 1612a, 1612b; Threshold value comparison circuit 1616a, 1616b; Switching circuit 1604a, 1604b; Power calculation circuit 1606a, 1606b; With histogram calculation circuit 1608a, 1608b.Detected envelope input sampled data vector signal 321i/321q, and make they can be used for as determined in control signal 1617a, 1617b switch (discussing as follows).The power level of switching signal 1605a, 1605b utilizes gained signal power data 1607a, 1607b to determine, gained signal power data 1607a, 1607b are for calculating the CCDF curve of each transmitter.
By they IFFT process 1612a, 1612b separately, the local generated ideal transmitter signal 507aa, the 507ba that are in frequency domain are transformed to time domain.Detect the envelope of transmitter time-domain signal 1613a, 1613b, and with threshold separately, to determine the low-power point of transmitter signal.As mentioned above, gained control signal 1617a, 1617b are for switch or enable the envelope of the composite signal envelope 1603 of detection.
Alternative technology comprises that utilization iterates means and other mutation of the actual derivation of the CCDF curve of transmitter separately, all technology all based on the comparison unlike signal to know the relative power of signal, the basic means of then result being compared with the compound CCDF curve of measurement.
Various other modifications and changes of structure of the present invention and method of operation are apparent for the person of ordinary skill of the art, and they do not depart from scope and spirit of the present invention.Although the present invention is described in conjunction with certain preferred embodiment, should be understood that desired invention should exceedingly not be confined to such specific embodiment.Appending claims is intended to define scope of the present invention, thereby is encompassed in structure and method within the scope of equivalent of these claims and they.
Claims (8)
1. for testing a vector signal analyzer for OFDM (OFDM) signal of a plurality of whiles, comprise:
Signal transformation part, receives and the composite data signal of the time domain of the ofdm signal that comprises a plurality of whiles for converting via signal communication paths, to the data-signal after a plurality of conversion of frequency domain is provided, wherein,
Described composite data signal is derived from the remote signal sources with a plurality of signal process of transmittings associated therewith, and comprises that a plurality of packets, each of a plurality of packets comprise the part separately of a plurality of preamble data and the part separately of a plurality of transmission data,
The part separately of relevant with described signal communication paths a plurality of given datas corresponding to time domain separately of part and described a plurality of signal process of transmittings separately described in each of described a plurality of transmission data, and
Each of data-signal after described a plurality of conversion comprises the frequency domain representation of part separately of described a plurality of packets; And
Signal Processing Element, for receive and process described a plurality of given data, frequency domain described a plurality of preamble data at least described in separately part and described a plurality of transmission data of frequency domain at least described in part separately, to a plurality of test datas of the frequency domain of indicating the error vector magnitude (EVM) being associated with described composite data signal are provided
Wherein, described signal transformation part comprises:
Signal detecting part, for detection of a plurality of characteristics of described composite data signal, to a plurality of control data corresponding with time started of one separately of the frequency of described composite data signal, described a plurality of packets and the character boundary of the data in described a plurality of packet are provided;
Signal frequency correcting unit, for respond a part for described a plurality of control data by proofreading and correct the frequency of described composite data signal, to the corresponding data signal with expectation nominal frequency is provided;
Signal conversion part, for converting described corresponding data signal to a plurality of parallel data signals; And
Fast fourier transform (FFT) parts, for converting described a plurality of parallel data signal, to the data-signal after described a plurality of conversion is provided, and
Wherein, described Signal Processing Element comprises:
Preamble processing unit, for the treatment of described a plurality of preamble data at least described in part separately, at least a plurality of control data are provided;
Data processor, for by processing described a plurality of given data according to described a plurality of signal process of transmittings, responds described a plurality of control data, to a plurality of reconstruction signals are provided; And
Signal plus parts, for being added data-signal and the described a plurality of reconstruction signal after described a plurality of conversion, to described a plurality of test data is provided.
2. vector signal analyzer according to claim 1, wherein, described preamble processing unit be further used for processing described a plurality of preamble data at least described in part separately, to a plurality of additional datas of one or more signal transfer characteristics of the ofdm signal of described a plurality of whiles of indication are provided.
3. vector signal analyzer according to claim 2, wherein, described one or more signal transfer characteristics comprise one or more in the unbalance and spectrum flatness of each power level, the orthogonal signalling of ofdm signal of described a plurality of whiles.
4. vector signal analyzer according to claim 1, further comprise signal spectra analysis component, for analyzing one or more spectral properties of described composite data signal, at least one a plurality of spectrum data of the described one or more spectral properties of indication are provided.
5. for testing a method for OFDM (OFDM) signal of a plurality of whiles, comprise:
Conversion receives via signal communication paths and the composite data signal of the time domain of the ofdm signal that comprises a plurality of whiles, to the data-signal after a plurality of conversion of frequency domain is provided, wherein,
Described composite data signal is derived from the remote signal sources with a plurality of signal process of transmittings associated therewith, and comprises that a plurality of packets, each of a plurality of packets comprise the part separately of a plurality of preamble data and the part separately of a plurality of transmission data,
The part separately of relevant with described signal communication paths a plurality of given datas corresponding to time domain separately of part and described a plurality of signal process of transmittings separately described in each of described a plurality of transmission data, and
Each of data-signal after described a plurality of conversion comprises the frequency domain representation of part separately of described a plurality of packets; And
Receive and process described a plurality of given data, frequency domain described a plurality of preamble data at least described in separately part and frequency domain described a plurality of transmission data at least described in part separately, to a plurality of test datas of the frequency domain of indicating the error vector magnitude (EVM) being associated with described composite data signal are provided
Wherein, described conversion comprises:
Detect a plurality of characteristics of described composite data signal, to a plurality of control data corresponding with time started of one separately of the frequency of described composite data signal, described a plurality of packets and the character boundary of the data in described a plurality of packet are provided;
By proofreading and correct the frequency of described composite data signal, respond a part for described a plurality of control data, to the corresponding data signal with expectation nominal frequency is provided;
Convert described corresponding data signal to a plurality of parallel data signals; And
According to fast fourier transform (FFT), convert described a plurality of parallel data signal, to the data-signal after described a plurality of conversion is provided,
And wherein, described reception and pack processing contain:
Process described a plurality of preamble data at least described in part separately, at least a plurality of control data are provided;
By processing described a plurality of given data according to described a plurality of signal process of transmittings, respond described a plurality of control data, to a plurality of reconstruction signals are provided; And
Be added data-signal and described a plurality of reconstruction signal after described a plurality of conversion, to described a plurality of test data is provided.
6. method according to claim 5, wherein, described processing further comprises: process described a plurality of preamble data at least described in part separately, to a plurality of additional datas of one or more signal transfer characteristics of the ofdm signal of described a plurality of whiles of indication are provided.
7. method according to claim 6, wherein, described one or more signal transfer characteristics comprise one or more in the unbalance and spectrum flatness of each power level, the orthogonal signalling of ofdm signal of described a plurality of whiles.
8. method according to claim 5, further comprises: analyze one or more spectral properties of described composite data signal, at least one a plurality of spectrum data of the described one or more spectral properties of indication are provided.
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| US11/533,971 US7822130B2 (en) | 2005-09-23 | 2006-09-21 | Apparatus and method for simultaneous testing of multiple orthogonal frequency division multiplexed transmitters with single vector signal analyzer |
| US11/533,971 | 2006-09-21 | ||
| PCT/US2006/036995 WO2007038279A2 (en) | 2005-09-23 | 2006-09-22 | Apparatus and method for simultaneous testing of multiple orthogonal frequency division multiplexed transmitters with single vector signal analyzer |
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| US8780745B2 (en) * | 2011-01-31 | 2014-07-15 | Intel Mobile Communications GmbH | Communication terminal, communication device, method for measuring a signal and method for requesting a measurement |
| US9002290B2 (en) * | 2012-05-09 | 2015-04-07 | Litepoint Corporation | System and method for testing a radio frequency (RF) multiple-input-multiple-output (MIMO) device under test (DUT) |
| US8774745B2 (en) * | 2012-12-10 | 2014-07-08 | Qualcomm Incorporated | Reconfigurable receiver circuits for test signal generation |
| US10104621B2 (en) * | 2015-12-17 | 2018-10-16 | Texas Instruments Incorporated | Power efficient packet detection |
| CN107809404B (en) * | 2016-09-09 | 2021-09-03 | 中兴通讯股份有限公司 | Method and device for estimating symbol offset |
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