CN103034619A - Method and device for implementing FFT (Fast Fourier Transform) noncoherent integration - Google Patents
Method and device for implementing FFT (Fast Fourier Transform) noncoherent integration Download PDFInfo
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- CN103034619A CN103034619A CN2012105388419A CN201210538841A CN103034619A CN 103034619 A CN103034619 A CN 103034619A CN 2012105388419 A CN2012105388419 A CN 2012105388419A CN 201210538841 A CN201210538841 A CN 201210538841A CN 103034619 A CN103034619 A CN 103034619A
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Abstract
The invention discloses a method and a device for implementing FFT (Fast Fourier Transform) noncoherent integration. The method comprises the following steps of: carrying out FFT operation on an input signal, obtaining N pieces of data from each frame and carrying out modulus operation on each data; carrying out noncoherent integration on each data which is subjected to modulus operation in a shift registering manner; carrying out peak detection on the data which is subjected to noncoherent integration; and detecting the maximum frequency value of each frame of data and a frequency point corresponding to the maximum frequency value. According to the invention, the characteristic of FFT sequential value obtaining is utilized; noncoherent integration is carried out in a shift registering manner; the method and the device have simple logics and do not need to be additionally controlled; a small amount of resources are occupied; fussy time sequence control operation is not used; a processing speed is higher; and compared with a double-port RAM or an FIFO (First In First Out), the device is simple to operate.
Description
Technical field
The present invention relates to digital signal processing technique field, particularly relate to a kind of FFT(Fast Fourier Transform, Fast Fourier Transform (FFT)) implementation method and the device of incoherent accumulation.
Background technology
Fft algorithm is widely used in the fields such as radar system, image processing, communication system, Aero-Space.It is in order to reduce a kind of fast and effeciently algorithm of discrete Fourier transformation calculation times.
Discrete Fourier transformation (Discrete Fourier Transform, DFT) be a kind of important algorithm in the digital signal processing, can regard the conversion that continuous function consists of at time domain, frequency domain sampling as, but because the shortcoming that its calculated amount is large, operation time is long makes its usable range limited.Nineteen sixty-five, Cooley and Tukey propose fft algorithm, utilize periodicity and the symmetry of twiddle factor, the DFT of long sequence is decomposed into the more DFT of small point, thereby reduce the multiplication number of times, improve counting yield, this algorithm has just obtained very big concern once coming out, development a lot of relevant algorithms occurred rapidly.
Fourier transform just had been found that before more than 100 years and knows that already frequency-domain analysis is usually more superior than time-domain analysis, and is not only simple, and is easy to the Analysis of Complex signal.For example we receive one section gps signal, if it is carried out despreading (but not adding up), do not consider the impact of yard Doppler effect and noise etc., can obtain one section sine wave signal (residual frequency difference), it is carried out spectrum analysis (for example carrying out the FFT conversion), just can obtain the peak value spectral line; Because the signal bandwidth of this moment reduces, just can reduce its sampling rate with cumulative way, and then carry out spectrum analysis again.
Obtain the information of its frequency domain after the signal process FFT computing, the peak value of the meeting frequency of occurrences.If the signal to noise ratio (S/N ratio) of signal is very low, then must improve accordingly fft algorithm, before carrying out peak value detection judgement, take effective measures and improve signal to noise ratio (S/N ratio).The method of improving signal to noise ratio (S/N ratio) commonly used has coherent accumulation and two kinds of methods of incoherent accumulation.Coherent accumulation is exactly with the direct addition of the correlated results of adjacent periods, utilizes the correlativity of signal in integral time, the energy accumulation of signal is got up, and noise does not have the coherence within integral time, and cumulative process is equivalent to noise is averaged, and can significantly improve signal to noise ratio (S/N ratio) like this.But not coherent accumulation then is to add up after correlated results is asked mould square again, compares with coherent accumulation, has removed phase information, has only kept amplitude information, so also corresponding growth of noise power, needing increases accumulative frequency, just can obtain than satisfactory SN ratio.
When carrying out incoherent accumulation, the RAM module is carried out data storage, is very common storage mode, and is fairly simple, but needs the read-write of control RAM to enable, read address, write address, read data and write data, could control the read-write of data.FIFO(First In First Out, First Input First Output), be a kind of traditional data buffer, the instruction that is introduced into is finished first and is retired from office, and and then just carries out the second instruction.FIFO generally is used for the data transmission between the different clock-domains, and synchronization fifo is read clock and write clock is same clock, comes to occur simultaneously read-write operation on the clock edge temporarily.Asynchronous FIFO read-write clock is inconsistent, and is independent mutually.Generally in large capacity storage, be complementary in order to make storage speed and reading speed, adopt FIFO.
Summary of the invention
The technical problem to be solved in the present invention is implementation method and the device of the incoherent accumulation of a kind of FFT, adopts dual port RAM or FIFO to carry out the problem of incoherent accumulation complicated operation in order to solve prior art.
For solving the problems of the technologies described above, on the one hand, the invention provides the implementation method of the incoherent accumulation of a kind of FFT, comprising:
Input signal is carried out the FFT computing, and each frame obtains N data, and each data is asked mould;
The mode of asking each the data shift LD behind the mould is carried out incoherent accumulation;
Data after the incoherent accumulation are carried out peak value to be detected: detect the maximum frequently value of each frame data, with and the frequency of correspondence.
Further, ask mould to refer to each data is asked mould value square to each data.
Further, adopting the mode of shift LD to carry out incoherent accumulation specifically comprises:
Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.
Further, obtain data amount check after the number of register and each frame FFT computing identical.
On the other hand, the present invention also provides a kind of FFT implement device of incoherent accumulation, comprising:
Ask the mould module, be used for input signal is carried out the FFT computing, each frame obtains N data, and each data is asked mould;
Incoherent accumulation module is used for the mode of asking each the data shift LD behind the mould is carried out incoherent accumulation;
Peak detection block is used for that the data after the incoherent accumulation are carried out peak value and detects: detect the maximum frequently value of each frame data, with and the frequency of correspondence.
Further, the described mould module of asking asks mould to refer to each data is asked mould value square to each data.
Further, incoherent accumulation module specifically is used for:
Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.
Further, obtain data amount check after the number of register and each frame FFT computing identical.
Beneficial effect of the present invention is as follows:
The present invention utilizes FFT sequentially to go out several characteristics, adopts the shift LD mode to carry out non-coherent accumulation, and logic is simple, do not need extra control, take resource few, sequential control operation that need not be loaded down with trivial details, it is fast, obviously simple to operate than dual port RAM or FIFO that processing speed is wanted.
Description of drawings
Fig. 1 is the process flow diagram of the implementation method of the incoherent accumulation of a kind of FFT in the embodiment of the invention;
Fig. 2 is the incoherent accumulation hardware of a kind of FFT realization figure in the embodiment of the invention.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, does not limit the present invention.
The present invention adopts the mode of incoherent accumulation the FFT result of varying input signal to be added up detection peak.The present invention realizes the difference of the incoherent accumulation of FFT result, and the storage mode that is mainly reflected in the accumulation result is different, and traditional mode can be come it is controlled with dual port RAM or FIFO.
As shown in Figure 1, the embodiment of the invention relates to the implementation method of the incoherent accumulation of a kind of FFT, comprising:
Step S101 carries out the FFT computing to input signal, and each frame FFT result obtains N data, and each data is asked mould.
The embodiment of the invention obtains 256 data instances with the FFT computing of each frame and describes; But be not can only limit for this reason to count, the N value can be other numerical value.
Input signal is carried out the FFT computing, and the embodiment of the invention is carried out is 256 basic 2-FFT computing, and behind the given input signal, through the FFT computing, each the frame FFT result who obtains is 256 of its frequency domain frequently values.
Asking mould is to 256 of FFT result values frequently, asks modular arithmetic.Consider that the error ratio of evolution is larger when hardware is realized, so the embodiment of the invention is onlyed demand mould value square, be convenient to computing.
Step S102 carries out incoherent accumulation to the mode of asking the data shift LD behind the mould: be that FFT result to each frame adds up, when reseting port sets high (effectively low), cumulatively carry out always, when reseting port sets low, do not add up.Reseting port is controlled by the control side, for example, when carrying out incoherent accumulation, then reseting port is set high, and when incoherent accumulation was complete, reseting port set low.
The accumulation result storage: the embodiment of the invention adopts the mode of shift LD, and the FFT end value is stored.Obtain data amount check after the number of register and each frame FFT computing identical.Reg0, reg1, reg2 ...., reg255 is 256 registers that arrange, to the storage that is shifted of 256 frequency values.Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.For example, when depositing in the first frame first data, it is existed among the register reg0; When depositing the second data, deposit the data among the register reg0 in reg1 first, then, second data deposited among the register reg0, by that analogy, until 256 data are fully all deposited in 256 registers; When depositing first data of the second frame in, first with register reg0, reg1, reg2 ..., the data among the reg255 are shifted to the right successively, after data shift out among the reg255, and deposit register reg0 in after first data addition of the second frame, by that analogy, until all data deposited.That is to say 256 altogether of frame data, each data needs to ask successively mould, incoherent accumulation, and shift LD, after living through 256 clocks, the data of this frame all have been stored in 256 registers; After the next frame data come, carry out again 256 clocks after, accumulated value has just existed in these 256 registers, but this moment peak value to detect be the testing result that previous frame data (perhaps and in the past the accumulated value of frame data) are carried out.
Step S103, the data after the incoherent accumulation are carried out peak value detect: each frame data is detected, detects its maximum frequently value, with and the frequency of correspondence, analyze by frequency spectrum.But be the result who postpones a frame at this moment, what detect specifically is the maximal value of the accumulated value of upper frame data and former frame data.The embodiment of the invention only relates to the maximum frequently detection of value, does not relate to spectrum analysis, therefore, no longer describes about spectrum analysis.
In addition, the invention still further relates to a kind of implement device of realizing the incoherent accumulation of FFT of said method, comprising:
Ask the mould module, be used for input signal is carried out the FFT computing, each frame obtains N data, and each data is asked mould;
Incoherent accumulation module is used for the mode of asking each the data shift LD behind the mould is carried out incoherent accumulation;
Peak detection block is used for that the data after the incoherent accumulation are carried out peak value and detects: detect the maximum frequently value of each frame data, with and the frequency of correspondence.
Wherein, the described mould module of asking asks mould to refer to each data is asked mould value square to each data.
Wherein, incoherent accumulation module specifically is used for:
Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.
Wherein, obtain data amount check after the number of register and each frame FFT computing identical.As can be seen from the above-described embodiment, the present invention utilizes FFT sequentially to go out several characteristics, adopt the shift LD mode to carry out non-coherent accumulation, logic is simple, do not need extra control, take resource few, sequential control operation that need not be loaded down with trivial details, it is fast, obviously simple to operate than dual port RAM or FIFO that processing speed is wanted.
Although be the example purpose, the preferred embodiments of the present invention are disclosed, it also is possible those skilled in the art will recognize various improvement, increase and replacement, therefore, scope of the present invention should be not limited to above-described embodiment.
Claims (8)
1. the implementation method of the incoherent accumulation of FFT is characterized in that, comprising:
Input signal is carried out the FFT computing, and each frame obtains N data, and each data is asked mould;
The mode of asking each the data shift LD behind the mould is carried out incoherent accumulation;
Data after the incoherent accumulation are carried out peak value to be detected: detect the maximum frequently value of each frame data, with and the frequency of correspondence.
2. the implementation method of the incoherent accumulation of FFT as claimed in claim 1 is characterized in that, asks mould to refer to each data is asked mould value square to each data.
3. the implementation method of the incoherent accumulation of FFT as claimed in claim 1 or 2 is characterized in that, the mode of employing shift LD is carried out incoherent accumulation and specifically comprised:
Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.
4. the implementation method of the incoherent accumulation of FFT as claimed in claim 3 is characterized in that, obtains data amount check after the number of register and each frame FFT computing identical.
5. the implement device of the incoherent accumulation of FFT is characterized in that, comprising:
Ask the mould module, be used for input signal is carried out the FFT computing, each frame obtains N data, and each data is asked mould;
Incoherent accumulation module is used for the mode of asking each the data shift LD behind the mould is carried out incoherent accumulation;
Peak detection block is used for that the data after the incoherent accumulation are carried out peak value and detects: detect the maximum frequently value of each frame data, with and the frequency of correspondence.
6. the implement device of the incoherent accumulation of FFT as claimed in claim 5 is characterized in that, the described mould module of asking asks mould to refer to each data is asked mould value square to each data.
7. such as the implement device of claim 5 or the incoherent accumulation of 6 described FFT, it is characterized in that, incoherent accumulation module specifically is used for:
Each data is once deposited at each clock, when next number certificate deposits in, the data integral body that deposits register in is shifted to the right, there are data to shift out if be positioned at the register of low order end, then with these data and the current data addition that will deposit in, deposit in the register of high order end; Do not have data to shift out if be positioned at the register of low order end, then the current data that will deposit in are deposited in the register of high order end.
8. the implement device of the incoherent accumulation of FFT as claimed in claim 7 is characterized in that, obtains data amount check after the number of register and each frame FFT computing identical.
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| CN101261318A (en) * | 2008-04-03 | 2008-09-10 | 北京航空航天大学 | High dynamic state spread-spectrum precise distance measurement receiving machine |
| CN102053250A (en) * | 2010-12-29 | 2011-05-11 | 成都国星通信有限公司 | Two-directional pseudo code parallel search system and realization method thereof |
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| CN101261318A (en) * | 2008-04-03 | 2008-09-10 | 北京航空航天大学 | High dynamic state spread-spectrum precise distance measurement receiving machine |
| CN102053250A (en) * | 2010-12-29 | 2011-05-11 | 成都国星通信有限公司 | Two-directional pseudo code parallel search system and realization method thereof |
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