CN101075816B - Method for inhibiting digital frequency-variable image - Google Patents
Method for inhibiting digital frequency-variable image Download PDFInfo
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- CN101075816B CN101075816B CN2006100826479A CN200610082647A CN101075816B CN 101075816 B CN101075816 B CN 101075816B CN 2006100826479 A CN2006100826479 A CN 2006100826479A CN 200610082647 A CN200610082647 A CN 200610082647A CN 101075816 B CN101075816 B CN 101075816B
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Abstract
The method uses computer to control the signal source and the spectrum analyzer. The computer is used to generate the test signals (including: frequency, amplitude, spread spectrum and scramble code; the generated test signals are downloaded to the signal source; the signal resource sends the test signals to the digital intermediate frequency board; the digital intermediate frequency board outputs the test signals to the spectrum analyzer; the computer reads out the amplitude at preset frequency point from the spectrum analyzer, and then according to a certain control policy, automatically modifies the parameters in the intermediate frequency board (including: I,Q channel gain of complex modulation, I,Q channel gain of quadrature modulation, DAC offset, fine adjustment gain, and rough adjustment gain) to form a negative feedback channel; gradually controlling the parameters in digital intermediate frequency board to minimize the amplitude of image frequency; when getting the optimal parameter, the obtained the optimal parameter is written into the initialized data in the digital intermediate frequency board.
Description
Technical field
The present invention relates to the software wireless electrical domain, relate in particular to the method that digital frequency-variable image suppresses.
Background technology
In order to solve the multi-mode that occurs in commercial and the military radio communication and the intercommunication interconnection problems between the multi-carrier signal, in May, 1992, Joe Mitola proposed the software radio notion first in the meeting of American National remote system.
Software radio (SDR) is the wireless device with reconfigurable hardware platform; Can stride multiple communication standard; It is representing the development trend of the nearly all radio electronics information system that comprises radio communication, and core concept is: 1) with A-D converter ADC and the as close as possible antenna of digital-to-analog converter DAC; 2) on abundant digitized basis, rely on software to define each item function of multi radio as far as possible to signal.Because have the performance of lower cost, greater flexibility and Geng Gao, software radio becomes the de facto standard of military affairs, public safety and commercial wireless domain rapidly.It is that it can carry out Base-Band Processing and digital intermediate frequency (IF) processing to multiple waveform that SDR becomes commercial popular one of the main reasons.The field that IF handles Digital Signal Processing expands to RF from base band.Support the ability of base band and IF process to increase system flexibility, reduced manufacturing cost simultaneously.
In present commercial signal communication system; Because various Primary Components; Particularly receive the restriction of A D C (A-D converter) and D S P (digital signal processor) development level; The digital intermediate frequency software radio is just becoming a kind of economy of desirable software radio, suitable compromise is selected, and it comprises Digital Up Convert and Digital Down Convert.
Communication system generally adopts super-heterodyne architecture in up-conversion at present, and Digital Up Convert is partly adopted in the intermediate frequency frequency conversion.In super-heterodyne architecture, generally be easy to generate mirror image and disturb.Produce mirror image for fear of the appearance of image frequency and disturb, adopt multistage (or single-stage) plural number and quadrature modulation to combine usually with the elimination image frequency.Wherein the complex modulation principle is as shown in Figure 1, supposes that the input of complex modulation is respectively real part a and imaginary part b, and then the real part of output is:
The imaginary part of output does
The principle of quadrature modulation is as shown in Figure 2, supposes that the input of quadrature modulation is respectively real part a and imaginary part b, then is output as:
When adopting one-level complex modulation and one-level quadrature modulation, the input of exactly output of complex modulation being received quadrature modulation, as shown in Figure 3.If be input as the form of A+i*B, so through being output as after complex modulation and the quadrature modulation:
When adopting two-stage complex modulation and one-level quadrature modulation, the input of exactly output of second level complex modulation being received quadrature modulation, as shown in Figure 4.If be input as the form of A+i*B, so through being output as after twice complex modulation and the quadrature modulation:
Can find out that output is not have image frequency through the theory after plural number and the quadrature modulation; But because the orthogonality of plural number and quadrature modulator itself; The layout of the finite word length effect of the inconsistency of IQ passage, digital quadrature device and DAC and simulation frequency conversion part, the influence of wiring often have mirror image and leak.
With Fig. 5 is example, and clock frequency is 122.88MHz, and frequency point setting is 24.92MHz, thus intermediate frequency at 147.8MHz, the mirror image intermediate frequency is at 97.96Mhz.From figure, can see the image frequency that one-86.456dBm is arranged in the position of 97.96MHz.If the modulator of back level is a quadrature modulator, then this frequency must be used the filter filtering of back level, but because image frequency and output frequency are often nearer at interval, general RLC filter is difficult to obtain effect preferably.The method that addresses this problem at present generally has:
First kind method: adopt the customization SAW filter.
Second class methods: improve placement-and-routing's method, promptly improve the placement-and-routing of DAC and analog part, avoid occurring image frequency as much as possible.
The 3rd class methods: manual adjustment method analog parameter method, promptly manual adjustment influences the parameter of image frequency, to suppress the part image frequency.
In communication multi-carrier digital if system, it is more that customization SAW filter method adopts, but cost is higher, and the differential loss of SAW filter is big, and the back often need add amplifier, importantly can not be from addressing this problem in essence.
Improve placement-and-routing's method to the having relatively high expectations of the personnel of hardware PCB (Printed circuit board), and very big relation is arranged, can not guarantee the success rate of each placement-and-routing with experience.
The manual adjustment parametric method wastes time and energy very much, because influence the factor of mirror image a lot of is arranged, and the weight that influences the mirror image amplitude also differs, and artificial adjustment is difficult to obtain best effect, and time consumption is also very big.
Summary of the invention
The purpose of this invention is to provide a kind of method for inhibiting digital frequency-variable image, change the undesirable mirror image that causes owing to plural adjustment and quadrature modulation and modulus when it is suppressed at Digital Up Convert (DUC).
According to method for inhibiting digital frequency-variable image of the present invention; Comprise: step S101; Initialization system out gate limit value and adjustment threshold value, said adjustment threshold value comprise the adjustment threshold value 3 of fine tuning gain of adjustment threshold value 2 and analog to digital converter of coarse adjustment gain of adjustment threshold value 1, the analog to digital converter of the skew of analog to digital converter; Step S102 detects intermediate frequency output and makes an uproar at the end, detects the image frequency output amplitude; Step S103, the skew of adjustment analog to digital converter; Step S104 judges the skew of adjustment analog to digital converter and whether the mirror image that obtains suppresses less than adjustment threshold value 1, when less than adjustment threshold value 1; Get into step S105; When more than or equal to adjustment threshold value 1, then return step S103, continue the skew of adjustment analog to digital converter; Step S105 judges that mirror image suppresses when less than the out gate limit value, then to export the currency of each parameter whether less than the out gate limit value.
Preferably, said method also comprises: when mirror image among the step S105 suppresses more than or equal to the out gate limit value, then get into step S106;
Step S106, the coarse adjustment gain of adjustment analog to digital converter;
Step S107, whether the mirror image inhibition that judgement obtains in the coarse adjustment gain back of adjustment analog to digital converter is less than adjustment threshold value 2, when more than or equal to adjustment threshold value 2; Then return step S106; Continue the coarse adjustment gain of adjustment analog to digital converter, when less than adjustment threshold value 2, then get into step S108;
Step S108, judge that mirror image suppresses when less than the out gate limit value, then to export the currency of each parameter whether less than the out gate limit value.
Preferably, said method also comprises: when mirror image among the step S108 suppresses more than or equal to the out gate limit value, then get into step S109;
Step S109, the fine tuning gain of adjustment analog to digital converter;
Step S110, with above said method adjust quadrature modulation I road gain and adjustment quadrature modulation Q road gain successively;
Among the step S111, with above said method adjust complex modulation I road gain and adjustment complex modulation Q road gain successively;
Step S112 judges that the mirror image inhibition whether less than adjustment threshold value 3, when more than or equal to adjustment threshold value 3, turns back to step S109, proceeds adjustment, when less than adjustment threshold value 3, then exports current each parameter.
Said method uses in debugging and factory calibrated stage, obtains corresponding initiation parameter, when system start-up, loads automatically then.
Using method of the present invention can easily improve image frequency automatically suppresses.After image frequency suppresses, can carry out filtering with the lower RLC filter of cost.Because parameter is in the calibration data of the system that is stored in automatically, be written into automatically during each system initialization, suppress thereby need carry out mirror image when avoiding system's operation.
Description of drawings
Fig. 1 has provided the complex modulation theory diagram.
Fig. 2 has provided the quadrature modulation theory diagram.
Fig. 3 has provided one-level complex modulation and one-level quadrature modulation combination principle block diagram.
Fig. 4 has provided secondary complex modulation and one-level quadrature modulation combination principle block diagram.
Fig. 5 has provided image frequency (before suppressing) measured drawing;
Fig. 6 has provided digital intermediate frequency and has improved inhibition up-conversion image theory block diagram automatically;
Fig. 7 has provided the adjustment node that automatic improvement suppresses the up-conversion mirror image;
Fig. 8 has provided and has improved image frequency and suppress software flow pattern automatically;
Fig. 9 has provided image frequency (suppressing the back) measured drawing.
Embodiment
Describe the present invention in detail below in conjunction with accompanying drawing, but need to prove that given accompanying drawing and embodiment only are used to explain the present invention, the present invention is not limited to this.
At first pass through conscientious analysis and detailed test, find the principal element that influences the image frequency amplitude.In communication system; Owing to adopt digital if technology; Therefore frequency converter is inner with digital controlled oscillator (NCO) completion with analog to digital converter (DAC) in number respectively with quadrature modulation for complex modulation, so its orthogonality is bad and influence finite word length effect is less relatively but can not ignore; In addition, because antenna number is more and the pcb board area is limited, DAC placement-and-routing impacts bigger; The resistance precision prescribed of the configuration usefulness of DAC is very high, and the influence that the error between actual value and the required value causes is also bigger.
Method of the present invention adopts the amplitude that detects image frequency automatically, revises the methods such as parameter of digital intermediate frequency intralamellar part automatically.
Fig. 6 has provided the theory diagram of method of the present invention.As shown in Figure 6, method of the present invention adopts LabWindows (or LabView) language control signal source and spectrum analyzer through computer.The communication test signal (comprising frequency, amplitude, spreading code, scrambler etc.) that computer generation system needs downloads in the signal source then.Signal source sends to the communication test signal on the digital intermediate frequency plate, and the output of digital intermediate frequency plate is received in the spectrum analyzer, and computer reads the amplitude of predetermined frequency (image frequency) in the spectrum analyzer; Then according to certain control strategy; Automatically revise parameter (I, the Q channel gain that comprise complex modulation, the I of quadrature modulation, Q channel gain, the offset of DAC in the digital intermediate frequency plate; Fine Gain; Coarse Gain etc.), form a negative feedback channel, it is minimum that progressively the parameter of control figure IF board makes the amplitude of image frequency.
Fig. 7 has provided the adjustment node that automatic improvement suppresses the up-conversion mirror image.After obtaining optimum Control Parameter, write these parameters in the initialization data in the digital intermediate frequency plate.In the time of later on each system initialization, system reads in these parameters when carrying out initial configuration automatically, and is configured in the system.Because the radio frequency unit of this communication system has the factory calibrated link, therefore can improve the calculating that image frequency suppresses in this link, make it need not calculate specially again as a factory-calibrated step.
Because the parameter that will adjust is a lot, and weight differs.The parameter marshalling that method of the present invention will be controlled according to the big wisp of weight is controlled in order.At first adjust influencing the bigger parameter of image frequency amplitude weight; The error of the adjustment threshold value of inspection and setting; Automatically return during when error and to reset parameter greater than threshold value; Adjust repeatedly, as long as the output error of adjustment just gets into the modification loop of next stage parameter within error threshold value at the corresponding levels.If output error just withdraws from automatically, no longer carry out the parameter adjustment of back, in the initialization data with the parameter writing system within final requirement.
For example, in the present invention, each is adjusted threshold value (but be not limited only to these values, can require to be provided with based on real system) can be as shown in table 1 be set respectively:
Table 1
| Threshold | Threshold value | 1 | Threshold value 2 | Threshold value 3 | The out gate limit value |
| Numerical value (dB) | 8 | 5 | 3.5 | 2 |
Above-mentioned threshold value 1,2,3 is represented the Offset to physical quantity DAC respectively, the threshold value that DAC Coarse Gain and DAC Fine Gain set.
After whole system of the present invention (comprising computer, signal source, IF board and spectrum analyzer) starts, start software, set the threshold value (concrete threshold value is seen top table 1) of adjustment, generate test data then.Put into signal source to test data, obtain the range value of mirror image frequency at the delivery outlet of the DAC of digital intermediate frequency plate automatically.Judge whether this range value needs to suppress, and suppresses like needs, then at first adjusts the skew (Offset) of DAC; After the mirror image of adjustment Offset acquisition suppresses to reach the threshold value of setting; Get into coarse adjustment gain (Coarse Gain) stage of adjustment DAC, analogize in proper order, finish up to adjustment.
DAC Offset; The adjustment strategy of DAC Coarse Gain and DAC Fine Gain (fine tuning gain) is at first to adopt heuristic, reduces parameter value to be adjusted earlier, reads the range value of spectrum analyzer mirror image frequency; If reduce; Explain that the direction initialization of waiting to adjust parameter is correct, big if range value becomes, then to adjustment in the other direction.The gain of quadrature modulation I road (Gain) and Q road Gain; And the adjustment strategy of the I road Gain of complex modulation and Q road Gain is earlier fixing one road Gain (like the Q road), adjusts the Gain (like the I road) on another road, and is minimum up to the mirror image amplitude of output; Fixing then this road Gain; A road the Gain that adjustment is corresponding, repeated multiple times (advising getting final product for 2 times) is to reach best effect.
Fig. 8 has provided parameter and has adjusted software flow pattern automatically.As shown in Figure 8, at step S101, initialization system out gate limit value and adjustment threshold value, said adjustment threshold value comprises the adjustment threshold value 1 of the Offset of DAC, the adjustment threshold value 2 of DAC Coarse Gain and the adjustment threshold value 3 of DAC Fine Gain.In step S102, detect intermediate frequency output and make an uproar at the end, detect the image frequency output amplitude.At step S103, the Offset of adjustment DAC is in step S104; Whether the mirror image inhibition of judging the Offset of adjustment DAC and obtaining is less than adjustment threshold value 1; When less than adjustment threshold value 1, get into step S105, when the time more than or equal to adjustment threshold value 1; Then return step S103, continue the Offset of adjustment DAC.At step S105, judge that mirror image suppresses when less than the out gate limit value, then to export the currency of each parameter whether less than the out gate limit value, when more than or equal to the out gate limit value, then get into step S106.In step S106, the Coarse Gain of adjustment DAC.In step S107, judge that whether the mirror image inhibition that behind the Coarse Gain of adjustment DAC, obtains is less than adjustment threshold value 2, when more than or equal to adjustment threshold value 2; Then return step S106, continue the Coarse Gain of adjustment DAC, when the time less than adjustment threshold value 2; Then get into step S108, judge that mirror image suppresses whether less than the out gate limit value, when less than the out gate limit value; Then export the currency of each parameter, when more than or equal to the out gate limit value, then get into step S109.At step S109, the Fine Gain of adjustment DAC.In step S110, with above said method adjust quadrature modulation I road Gain and adjustment quadrature modulation Q road Gain successively.In step S111, with above said method adjust complex modulation I road Gain and adjustment complex modulation Q road Gain successively.Then, in step S112, judge that the mirror image inhibition whether less than adjustment threshold value 3, when more than or equal to adjustment threshold value 3, turns back to step S109, proceed adjustment, when less than adjustment threshold value 3, then export current each parameter.
Fig. 9 has provided through the result after the mirror image inhibition of the inventive method.From Fig. 9, can be clearly seen that, through after this method, the mirror image of system from Fig. 5-86.456dBm successfully be suppressed to Fig. 9-96.047dBm, successfully reduced 10dBm, proved the correct and validity of this method.
Foregoing is not to be used for limiting embodiment of the present invention, and all modification and change or combinations of carrying out according to the main inventive concept of this method all should belong to protection range of the presently claimed invention.
Claims (4)
1. a method for inhibiting digital frequency-variable image is characterized in that, comprising:
Step S101; Initialization system out gate limit value and adjustment threshold value, said adjustment threshold value comprise the adjustment threshold value 3 of fine tuning gain of adjustment threshold value 2 and analog to digital converter of coarse adjustment gain of adjustment threshold value 1, the analog to digital converter of the skew of analog to digital converter;
Step S102 detects intermediate frequency output and makes an uproar at the end, detects the image frequency output amplitude;
Step S103, the skew of adjustment analog to digital converter;
Step S104 judges the skew of adjustment analog to digital converter and whether the mirror image that obtains suppresses less than adjustment threshold value 1, when less than adjustment threshold value 1; Get into step S105; When more than or equal to adjustment threshold value 1, then return step S103, continue the skew of adjustment analog to digital converter;
Step S105 judges that mirror image suppresses when less than the out gate limit value, then to export the currency of each parameter whether less than the out gate limit value.
2. method according to claim 1 is characterized in that, said method also comprises: when mirror image among the step S105 suppresses more than or equal to the out gate limit value, then get into step S106;
Step S106, the coarse adjustment gain of adjustment analog to digital converter;
Step S107, whether the mirror image inhibition that judgement obtains in the coarse adjustment gain back of adjustment analog to digital converter is less than adjustment threshold value 2, when more than or equal to adjustment threshold value 2; Then return step S106; Continue the coarse adjustment gain of adjustment analog to digital converter, when less than adjustment threshold value 2, then get into step S108;
Step S108, judge that mirror image suppresses when less than the out gate limit value, then to export the currency of each parameter whether less than the out gate limit value.
3. method according to claim 2 is characterized in that, said method also comprises: when mirror image among the step S108 suppresses more than or equal to the out gate limit value, then get into step S109;
Step S109, the fine tuning gain of adjustment analog to digital converter;
Step S110, with above said method adjust quadrature modulation I road gain and adjustment quadrature modulation Q road gain successively;
Among the step S111, with above said method adjust complex modulation I road gain and adjustment complex modulation Q road gain successively;
Step S112 judges that the mirror image inhibition whether less than adjustment threshold value 3, when more than or equal to adjustment threshold value 3, turns back to step S109, proceeds adjustment, when less than adjustment threshold value 3, then exports current each parameter.
4. method according to claim 1 is characterized in that, said method is used in debugging and factory calibrated stage, obtains corresponding initiation parameter, when system start-up, loads automatically then.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1244315A (en) * | 1997-09-25 | 2000-02-09 | 皇家菲利浦电子有限公司 | Improvements in or relating to phase receivers |
| US6330290B1 (en) * | 1998-09-25 | 2001-12-11 | Lucent Technologies, Inc. | Digital I/Q imbalance compensation |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1244315A (en) * | 1997-09-25 | 2000-02-09 | 皇家菲利浦电子有限公司 | Improvements in or relating to phase receivers |
| US6330290B1 (en) * | 1998-09-25 | 2001-12-11 | Lucent Technologies, Inc. | Digital I/Q imbalance compensation |
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Effective date of registration: 20151030 Address after: 200233 Shanghai, Xuhui District Jiang Road, No. 41, building 333 Patentee after: Datang Mobile Communication Equipment Co., Ltd., Shanghai Patentee after: Datang Mobile Communication Equipment Co., Ltd. Address before: 100083 Haidian District, Xueyuan Road, No. 29, Patentee before: Datang Mobile Communication Equipment Co., Ltd. |