CN107896204A - A kind of OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator and compensation method based on FPGA - Google Patents
A kind of OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator and compensation method based on FPGA Download PDFInfo
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- CN107896204A CN107896204A CN201710941346.5A CN201710941346A CN107896204A CN 107896204 A CN107896204 A CN 107896204A CN 201710941346 A CN201710941346 A CN 201710941346A CN 107896204 A CN107896204 A CN 107896204A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/2659—Coarse or integer frequency offset determination and synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
- H04L27/2663—Coarse synchronisation, e.g. by correlation
Abstract
The invention discloses a kind of OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator based on FPGA and compensation method, by data preprocessing module, resampling module, multiple correlation module, N number of correlation maximum comparison module and carrier compensation module, totally 5 modules form, whole algorithm uses pipeline processing mode, saves substantial amounts of logical resource.The invention discloses the computational methods that complicated resampling is realized using linear interpolation principle, to reduce the FPGA implementation complexity of the amount of calculation of algorithm and algorithm.Invention additionally discloses the realization principle of streamline multiple correlation algorithm, FFT, IFFT and complex multiplication use the IP kernel that FPGA is carried, and use pipeline mode.The present invention can be difficult to the Doppler Compensation Algorithm of real-time implementation to low-power consumption DSP in real-time implementation underwater sound Modem, while it is integrated in acquisition control in monolithic FPGA, the design and debugging difficulty of signal-processing board are reduced, reduces signal-processing board area and power consumption.
Description
Technical field
It is mainly a kind of based on FPGA's the present invention relates to high speed OFDM underwater sound communication Modem real time signal processings field
OFDM underwater sound Modem time-frequency two-dimensionals search for Doppler compensator and compensation method.
Background technology
In recent years, OFDM technology had been obtained in field of underwater acoustic communication and had been widely applied, and this technology can solve well
The frequency selective fading problem caused by multipath effect, stretched yet with signal caused by serious Doppler frequency shift
With carrier frequency shift so that the receiving terminal of OFDM underwater sound communication systems generates more serious inter-sub-carrier interference.It is more general
Frequency displacement is strangled mainly as caused by the relative motion between emitter and receiver, the compound movement of water body itself, due to water
The frequency band of Acoustic channel is narrower, and it is more serious than terrestrial radio electromagnetic communication to result in influence of the Doppler frequency shift to underwater sound communication system
It is more.Underwater sound communication is usually broadband signal, and signal bandwidth is close with carrier frequency, and now, the influence of Doppler effect is not showed only as
Carrier frequency shift, include the stretching, extension or compression of signal.Therefore, how effectively to suppress or eliminate Doppler effect for
The influence of OFDM underwater sound communication systems turn into one it is important the problem of.
Underwater sound communication Modem FPGA is mainly used to carry out data acquisition both at home and abroad at present and signal source produces and control,
Signal processing algorithm is such as demodulated, matched filtering, Doppler effect correction, equilibria decoding complicated algorithm are completed on the DSP of low-power consumption,
Low-power consumption DSP often emphasizes low-power consumption, and to the algorithm process scarce capacity of complexity, sacrificed to reach real-time at signal
The partial properties of reason, the product for realizing underwater sound communication Modem data acquisition, control and signal transacting using monolithic FPGA are also located
In the pilot study stage, because FPGA is integrated with abundant configurable logical block resource, in addition to it is largely close towards calculating
Collect the Transmit-Receive Unit of the DSP unit of application, block RAM resources and high-speed communication, the signal processing tasks of complexity, institute can be carried out
To complete computationally intensive task on FPGA, Modem performance can be preferably played.
In OFDM underwater sounds Modem, while the search of time-frequency two-dimensional is carried out, the quantity of correlator is individual up to more than 2,000, low work(
The DSP of consumption is difficult to complete real-time operation, and FPGA can utilize the FFT IP kernels carried and multiplier to complete substantial amounts of phase in real time
Computing is closed, and Doppler effect correction can be completed at the appointed time according to the suitable structure of algorithms selection (parallel or flowing water),
So it is reasonable selection using FPGA schemes.
The content of the invention
It is an object of the invention to overcome the shortcomings of the prior art, and provide a kind of OFDM underwater sounds based on FPGA
Modem time-frequency two-dimensionals search for Doppler compensator and compensation method, and FPGA can be given full play to intensive using FPGA schemes
The advantage of algorithm real-time, it can realize the correlator real-time implementation of more than 2,000, and in computational efficiency and processing in real time
The performance of Doppler compensator in ability more in the past based on low-power consumption DSP is obviously improved.
The purpose of the present invention is completed by following technical solution.During this OFDM underwater sound Modem based on FPGA
Frequency two-dimensional search Doppler compensator, mainly by data preprocessing module, resampling module, multiple correlation module, N number of complex correlator
Maximum comparison module and carrier compensation module composition；Whole algorithm uses pipeline processes, saves FPGA area.Its
In, data preprocessing module uses the RAM that FPGA is carried in a manner of read-write of rattling, and the data N of write-in is read with N times of speed
It is secondary；The method that resampling module uses linear interpolation, to reduce the complexity of amount of calculation and algorithm.In multiple correlation module
FFT and IFFT uses the IP kernel that FPGA is carried, and uses pipeline mode, and complex multiplier uses and carries IP kernel；Rationally choosing
The whole algorithm of Delay Guarantee of complex multiplier is taken to be run under higher clock frequency.N number of complex correlator maximum compares mould
Block deposits the maximum of currency multiple correlation by the way of register, is then compared with next batch data multiple correlation maximum
Compared with, deposit the position where maximum and maximum between the two, after the completion of multiple correlation, at the same find out multiple correlation maximum with
And the position of maximum.
This OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator used based on FPGA of the present invention
Compensation method, this method comprise the following steps：
(1) data of input, are subjected to data prediction, input data is read with more than N times input data rate circulation,
FPGA data read clock frequency is at least set to N times of input data rate, then with the clock frequency of N times of input data rate
Follow-up signal transacting is carried out, N is the number of complex correlator；
(2) resampling, is carried out to the data that high-speed is read, resampling uses linear interpolation algorithm；
(3), the data to resampling and the m-sequence being locally stored do multiple correlation；
(4), the maximum of more N number of correlator, Doppler time contraction-expansion factor a and carrier wave frequency deviation ε are estimated；
(5) carrier compensation, is carried out to a after estimation and ε, then carrying out data with the data of input is multiplied.
Beneficial effects of the present invention are：Time-frequency two-dimensional of the present invention search Doppler compensator can simultaneously estimating Doppler when
Between contraction-expansion factor a and carrier wave frequency deviation ε, using high clock frequency circulate read input data, follow-up signal transacting using it is high when
The processing of clock pipeline system, saves substantial amounts of logical resource.Data resampling is realized using linear interpolation method, is reduced
FPGA's realizes difficulty.
Brief description of the drawings
Fig. 1 is that OFDM underwater sound Modem time-frequency two-dimensional search Doppler compensator internal framework of the present invention based on FPGA shows
Meaning block diagram
Fig. 2 is resampling methods linear interpolation schematic block diagram in Fig. 1 of the present invention；
Fig. 3 is the schematic block diagram of complex correlator in Fig. 1 of the present invention.
Embodiment
Detailed introduction is done to the present invention below in conjunction with accompanying drawing：
As shown in figure 1, the OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator based on FPGA, by data in advance
Manage module, resampling module, multiple correlation module, N number of complex correlator maximum comparison module, carrier compensation module composition.
(1) in data preprocessing module, to be inputted more than N (operation times of correlator, about 2000 or more) times
Data rate reads input data, and then corresponding high clock frequency carries out follow-up signal transacting, and follow-up processing uses
Pipeline mode, save substantial amounts of logical resource.Reading and writing data takes the mode of two RAM ping-pong buffers read-writes to carry out, such as
Fruit input data rate is M, then repeats to read n times according to M*N clock rate, is sent into follow-up interpolation and relevant treatment.
(2) Fig. 2 show linear interpolation principle, and because resampling needs a large amount of computings, and algorithm is complicated, FPGA algorithms
Realize complex, can complete to receive the conversion of data sampling rate by the algorithm of linear interpolation, without carrying out resampling,
The amount of calculation of receiver can be greatlyd save.The principle of linear interpolation is as follows：
By NrIndividual over-sampling data are represented with vectorial Y：
Y=[y (1), y (2) ... y (n) ..., y (Nr)] (1)
Sampling instant in above formula corresponding to each discrete data is represented with vector T：
If the discrete data obtained after sample rate conversion is represented with vectorial Y'：
Y'=[y'(1), y'(2) ... y'(k) ..., y'(Ncp+N0)] (3)
If any data y'(k to be asked) corresponding to sampling instant be：Assuming that y'(k) it is in y (n)
Between y (n+1), t'(k) it is between x (n) and x (n+1), y (n) and y (n+1) sampling instant are：X (n) and x (n+1)
Then data y'(k) it is as follows by the estimation formula of linear interpolation：
Positive integer n meets following formula：
Pass through Interpolation Process above, it is possible to obtain the data Y' of sample rate conversion, remove above NcpIndividual sampled point
Data, remaining is exactly the useful OFDM symbol data for removing CP.
(3) Fig. 3 show multiple correlation principle, the data after the resampling of input data position, due in OFDM transmission signals, m
Sequence is to be blended in one piece according to certain mode with information, and Doppler's estimation is to make relevant treatment using m-sequence, so
Need to take out m-sequence according to corresponding position before mixing to the data after resampling, then place related to the m-sequence work to prestore
Reason.
Multiple correlation uses frequency domain algorithm, i.e., first first carries out FFT to the data after resampling, is then multiplied by copy signal
Spectrum H (ω), then be reduced into discretely-timed signal with IFFT, its formula is as follows：
Xcorr (i, n)=IFFT [Y (i, ω) × H*(ω)]=IFFT [FFT (y (i, n)) × conj (FFT (h (n)))] (8)
Copy vector is generally pre-stored in FPGA ROM, so multiple correlation only needs a plural FFT, a multiplier
With an IFFT it is achieved that plural FFT and IFFT realize that pipeline mode allows defeated using the pipeline organization of IP kernel
Enter data continuous processing, complex multiplier carries IP using FPGA, and it inputs two complex vector located real and imaginary parts and clock frequency
Rate, exports the real and imaginary parts of product, and input and output digit and delayed clock number can be controlled flexibly.
(4) because algorithm uses pipeline processing mode, maximum compares in FPGA is deposited by the way of register
The maximum of currency multiple correlation, then compared with next batch data multiple correlation maximum, deposit maximum between the two
Position where value and maximum, after the completion of multiple correlation, while the position of multiple correlation maximum and maximum is found out, then solved
Calculate a and ε.
(5) Doppler effect correction is carried out according to formula (9) and formula (10) to the original rate data of input using a and ε obtained
The signal companding phenomenon as caused by Doppler effect has tentatively been eliminated by resampling, i.e., has tentatively eliminated width
An identical frequency shift (FS) item also be present in band Doppler frequency shift, all subcarriersIfIt is referred to as narrow
Band Doppler shift, only further eliminates influence of this frequency deviation to reception signal, ofdm signal can just pass through
FFT is demodulated.
Wherein, T is usedsThe unguarded interval cycle of OFDM symbol is represented, then carrier frequency separation is Δ f=1/Ts, provided with Ns
Individual subcarrier, then the frequency of k-th of subcarrier be：fk=fc+ k Δ f, k=0,1 ..., Ns- 1, wherein fcFor the center of carrier wave
Frequency, in an OFDM symbol TsComplex information symbol that is interior, representing to be transmitted on k-th of subcarrier with d [k], wherein Ap(t) table
Show the amplitude of path signal, τp(t) time delay in path, p represent multipath number.
It is understood that it will be understood by those skilled in the art that technical scheme and inventive concept are subject to
The protection domain of appended claims of the invention should all be belonged to replacement or change.
Claims (2)
- A kind of 1. OFDM underwater sound Modem time-frequency two-dimensionals search Doppler compensator based on FPGA, it is characterised in that：Mainly by counting Data preprocess module, resampling module, multiple correlation module, N number of complex correlator maximum comparison module and carrier compensation module group Into；Wherein, data preprocessing module uses the RAM that FPGA is carried in a manner of read-write of rattling, and the number of write-in is read with N times of speed According to n times；The method that resampling module uses linear interpolation, what FFT and IFFT in multiple correlation module were carried using FPGA IP kernel, and pipeline mode is used, complex multiplier uses and carries IP kernel；N number of complex correlator maximum comparison module uses The mode of register deposits the maximum of currency multiple correlation, then compared with next batch data multiple correlation maximum, posts Deposit the position where maximum and maximum between the two, after the completion of multiple correlation, while find out multiple correlation maximum and most The position being worth greatly.
- It is 2. a kind of using the OFDM underwater sound Modem time-frequency two-dimensionals search Doppler effect correction based on FPGA as claimed in claim 1 The compensation method of device, it is characterised in that：This method comprises the following steps：(1) data of input, are subjected to data prediction, input data, FPGA are read with more than N times input data rate circulation Data read clock frequency be at least set to N times of input data rate, then carried out with the clock frequency of N times of input data rate Follow-up signal transacting, N are the number of complex correlator；(2) resampling, is carried out to the data that high-speed is read, resampling uses linear interpolation algorithm；(3), the data to resampling and the m-sequence being locally stored do multiple correlation；(4), the maximum of more N number of correlator, Doppler time contraction-expansion factor a and carrier wave frequency deviation ε are estimated；(5) carrier compensation, is carried out to a after estimation and ε, then carrying out data with the data of input is multiplied.
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