CN103701749A - Method of obtaining underwater acoustic channel reciprocity by using compressed sensing - Google Patents
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Abstract
The invention discloses a method of obtaining underwater acoustic channel reciprocity by using compressed sensing and relates to underwater acoustic communication. The method is used for obtaining accurate channel parameters from OFDM (Orthogonal Frequency Division Multiplexing) received signals and ensuring the reciprocity of underwater acoustic channels. According to a compressed sensing theory, an OMP algorithm is used for reconstructing time domain impulse noise interference and wide single frequency noise interference, and eliminating the noise interference by observed quantity. For the time domain impulse noise interference, the time domain impulse noise interference is estimated by virtual subcarrier at a receiving end, is reconstructed by the OMP algorithm and is eliminated; the wide single frequency noise extracted at the receiving end has sparsity at a frequency domain, domain conversion is not needed, a measurement matrix is utilized, and the wide single frequency noise interference is reconstructed according to the OMP algorithm and is eliminated. The upper row and the lower row of underwater acoustic channels after the time domain impulse noise interference and the wide single frequency noise interference are eliminated are identical in channel states, namely, the underwater acoustic channels are provided with the reciprocity.
Description
Technical field
The present invention relates to underwater sound communication, especially relate to a kind of method of utilizing compressed sensing to obtain underwater acoustic channel reciprocity.
Background technology
Sound wave is unique information carrier that carries out remote transmission in subsurface communication, the development that deepens continuously along with ocean development in recent years, more and more higher for the transmittability of subsurface communication and the requirement of raising message capacity, however the channel of underwater sound communication makes the performance of communication system have significant limitation.Due to the complexity of underwater acoustic channel, there is the characteristics such as narrow bandwidth, strong multipath, strong noise, Space Time-frequency change at any time, seriously limited the performance of communication system.Need to there is the methods such as new modulation, coding, power control, more effectively be applied to fading channel.In recent years, there is Many researchers studying new technology for self-adaptively transmitting, these adaptive transmission schemes, are all by instantaneous monitoring channel condition, adjust modulation level, symbol rate, code check, transmit power level or with some aspects of these parameter correlations.In reality, in order to realize adaptive transmission method, channel condition information in transmitting procedure (CSI) must be known, receiver need to estimate channel condition information, and being transferred to transmitter by feedback channel, transmitter just can utilize these state informations to determine adaptive transmission method.Therefore, only, under the prerequisite of known feedback channel coefficient, could realize better adaptive transmission method.Because channel reciprocity can obtain by the channel condition information of up link the channel condition information of down link, the reciprocity that therefore obtains underwater acoustic channel has very important significance.
In TDD system, uplink downlink is used identical frequency spectrum, can think that up-downgoing channel has identical fading characteristic, therefore the channel status of up channel can be used as to the channel status of down channel, and up-downgoing channel has reciprocity.But in underwater sound communication, the reciprocity of TDD channel can be subject to the impact of many factors, thereby cause its forfeiture to a certain extent, concrete manifestation is exactly the channel status that the channel status of obtained up channel cannot characterize down channel, cause that in underwater sound communication, channel reciprocity is lost because have the following aspects:
(1) channel time-varying characteristics
In underwater sound communication environment, due to the random interface fluctuation of actual ocean, inhomogeneous medium, and the scattering effect that causes such as ocean temperature micro-structural, interior ripple, planktonic organism and bubble, make sound channel temporal evolution.During the time interval of twice observation large (be greater than channel coherence time), twice observed result just there will be larger difference before and after sound channel is carried out.In TDD system, sub-frame of uplink and descending sub frame are alternately to occur.At ascending-descending subframes, replace during this period of time in, during channel, become and will cause the channel status of descending sub frame to carry out accurate Characterization with the channel status of the up channel obtaining during sub-frame of uplink, thereby channel reciprocity is lost.Yet, can use the frequency pilot sign structure MMSE fallout predictor receiving to predict [1] to underwater acoustic channel, for the underwater acoustic channel in the time period, carry out Continuous Observation, the historical situation that a series of measured values of gained have become while just having reflected underwater acoustic channel; Based on these conception of history measured values, underwater acoustic channel state in following a period of time is compared to prediction accurately, thereby make the up channel condition information that sends preliminary treatment institute foundation reflect as far as possible exactly the channel status of current down link, the reciprocity loss of underwater acoustic channel is made up.
(2) I/Q is uneven
I/Q branch road uneven [2,3] is that the non-ideal characteristic of device causes in communication equipment, and is present in up-conversion and down conversion system.In TDD system, even if channel is slow fading channel, the duration of a complete ascending-descending subframes, wireless channel remains unchanged, but due to the unbalanced existence of I/Q, also can make in up link to estimate to estimate on the channel status of the up channel that obtains and down link the not reciprocity of channel status of the down channel that obtains.The wide linearity of MMSE criterion (widely linear) the equalizer unbalanced compensating system of receiving end I/Q [4] that can achieve a butt joint.
(3) channel estimation errors
Channel estimation errors is apparent on the impact of channel reciprocity.Even the channel nonreciprocity that does not exist above-mentioned two factors (becoming during channel and I/Q imbalance) to cause, simple channel estimation errors also will cause the forfeiture of channel reciprocity.Therefore, well behaved channel estimation method is the effective ways that this reciprocity of compensation is lost.Now, can adopt compressed sensing (Compress Sensing) technology to carry out channel estimating [5] [6] [7] [8] to ofdm system.
(4) disturb asymmetric
In underwater acoustic channel, have active Noise Jamming and passive noise jamming, active noise comes from other ship in communication equipment and ocean, shows as significantly single-frequency noise and disturbs; Without source noise, being a kind of special jamming pattern, is that on naval vessel, various sound sources produce, and shows as impulse noise interference.And in transmitting procedure, noise jamming is different on the impact of uplink and downlink signals, this,, by causing the channel condition information that in TDD system, up-downgoing channel estimating obtains to lose reciprocity property, affects systematic function.If obtain the reciprocity of underwater acoustic channel, noise jamming must be removed.The way of the reciprocity loss due to this interference structure of current antagonism is asymmetric adopts closed-loop policy [9] substantially, at receiving terminal, carries out disturbance regime assessment and result feedback is arrived to transmitting terminal, thereby instruct transmitting terminal to use to prelist, code error is compensated.But due to the complexity of Underwater Acoustic Environment, the annoyance level that the signal of transmission is subject to is each time different, at transmitting terminal, signal is carried out to precoding and can not well eliminate noise jamming.Due to time domain impulse noise interference and significantly single-frequency noise disturb and all to there is sparse property, therefore the present invention proposes and utilize compressive sensing theory to eliminate impulse noise interference and the significantly impact of single-frequency noise interference in OFDM underwater sound communication system, to guarantee the reciprocity of underwater acoustic channel.
Compressive sensing theory is a kind of emerging sampling theory based on the sparse property of signal proposing in recent years.This theory is by the ADC(Analog-to-Digitial Conversion in traditional sampling process) conversion concept replace to AIC(Analog-to-Information Conversion) conversion concept, the sampling of signal is replaced to the sampling to information, under meeting some requirements, only rely on less sampled value to realize the reconstruct of signal [10] simultaneously.This theoretical breakthrough the restriction of nyquist sampling theorem to data sampling, be significant.Traditional sampling thheorem is separated and is carried out with compression the sampling of signal, conversion, and compressive sensing theory occurs in same step for sampling, the compressed encoding of signal, utilize the sparse property of signal, with the speed far below Nai Kuisi sample rate, signal is carried out the measurement coding of non-self-adapting.Measured value is not signal itself, but projection value from higher-dimension to low-dimensional, and from mathematical angle, each measured value is the composite function of each sample signal under traditional theory, and measured value has comprised a small amount of information of all sample signals.Decode procedure is not the simple inverse process of coding, but utilizing existing reconstructing method in signal Its Sparse Decomposition on probability meaning, to realize the Accurate Reconstruction of signal or the approximate reconstruct under certain error, the required measured value number of decoding is much smaller than the sample number under traditional theory.
According to compressive sensing theory, sparse signal is not being lost under the required information state of reconstruct original signal, can be with the lower observation vector y ∈ R of dimension
mreplace the discrete series x ∈ R under traditional sampling
n, M is the points of measurement, N is that signal is counted, and M < N.
The essence of compression sampling is utilized an observing matrix Φ exactly, tries to achieve observation vector y ∈ R
m
y＝Φx＝ΦΨs＝Θs
Wherein, Θ=Φ Ψ, Φ and Ψ are irrelevant; Θ is the recovery matrix of M * N.X=Ψ s, s is the expansion coefficient of x on orthogonal basis Ψ.
List of references:
[1]Schafhuber?D,Matz?G.MMSE?and?Adaptive?Prediction?of?Time-Varying?Channels?for?OFDMSystems[J].IEEE?Transactions?on?Wireless?Communications,2005,4(2):593-602.[2]Liu?C.Impacts?of?I/Q?Imbalance?on?QPSK-OFDM?QAM?Detection[J].IEEE?Transactions?onConsumer?Electronics,1998,44(3):984-989.
[3]Valkama?M,Renfors?M,Koivunen?V.Advanced?Methods?for?I/Q?Imbalance?Compensation?inCommunication?Receivers[J].IEEE?Transactions?on?Signal?Processing,2001,49(10):2335-2344.
[4]Mattera?D,Paura?L,Sterle?F.MMSE?WL?Equalizer?in?Presence?of?Receiver?IQ?Imbalance[J].IEEE?Transactions?on?Signal?Processing,2008,56(4):1735-1740.
[5]Khojastepour?M?A,Gomadam?K,Wang?X.Pilot-Assisted?Channel?Estimation?for?MIMOOFDM?Systems?Using?Theory?of?Sparse?Signal?Recovery[C].IEEE?International?Conferenceon?Acoustics,Speech?and?Signal?Processing.IEEE,2009:2693-2696.
[6]Huang?J,Huang?J,Berger?C?R.Iterative?Sparse?Channel?Estimation?and?Decoding?forUnderwater?MIMO-OFDM[J].EURASIP?Journal?on?Advances?in?Signal?Processing,Volume2010,Article?ID:460379,11pages.
[7]Soltanolkotabi?M,Amini?A,Marvasti?F.OFDM?Channel?Estimation?Based?on?AdaptiveThresholdingfor?Sparse?Signal?Detection[C].17th?European?Signal?Processing?Conference.EUSIPCO,2009:1685-1689.
[8]Maechler?P,Greisen?P,Felber?N,et?al.Matching?Pursuit:Evaluation?and?Implementation?forLTE?Channel?Estimation[C].Proceedings?of2010IEEE?International?Symposium?on?Circuitsand?Systems.IEEE,2010:589-592.
[9]Cepeda?R,Fitton?M,Nix?A.The?Performance?of?Robust?Adaptive?Modulation?over?WirelessChannels?with?Non?Reciprocal?Interference[C].IEEE55th?Vehicular?Technology?Conference.IEEE,2002:1497-1501.
[10] Peng Yu, Sparse Channel Estimation Algorithm research [D] .2013. based on compressed sensing in ofdm system
[11]Cepeda?R,Fitton?M,Nix?A.The?Performance?of?Robust?Adaptive?Modulation?over?WirelessChannels?with?Non?Reciprocal?Interference[C].IEEE55th?Vehicular?Technology?Conference.IEEE,2002:1497-1501.
[12]Tolli?A,Cndreanu?M.Compensation?of?Interference?Non-Reciprocity?in?Adaptive?TDDMIMO-OFDM?Systems[C].15th?IEEE?International?Symposium?on?Personal,Indoor?andMobile?Radio?Communications.IEEE,2004:859-863.
[13]Yomo?H,Reynisson?R?V.A?Power?Control?Method?for?Channel?Non-ReciprocityCompensation?in?Hybrid?Duplexing[C].IEEE17th?International?Symposium?on?Personal,Indoor?and?Mobile?Radio?Communications.IEEE,2006:1-5.
[14]Tolli?A,Codreanu?M,Juntti?M.Suppression?of?Non-reciprocal?Interference?in?AdaptiveCellular?Systems[C].IEEE61
stVehicular?Technology?Conference.IEEE,2005:1072-1076.
Summary of the invention
The object of the present invention is to provide a kind of method of utilizing compressed sensing to obtain underwater acoustic channel reciprocity.
Concrete steps of the present invention are as follows:
A. information source data are carried out to chnnel coding, QPSK modulation, goes here and there and changes, what become N-N_pilot-N_zeros sub-carrier formats needs secured transmission of payload data D, wherein N is the length of OFDM transmission system frame, and N_pilot is pilot length, the number that N_zeros is unloaded ripple;
B. produce subcarrier pilot data, the length that produces subcarrier pilot data is determined by OFDM transmission system frame structure, described pilot tone employing Comb Pilot, and Comb Pilot is for the channel estimating of receiving terminal, and unloaded ripple is used for eliminating time domain impulse noise interference;
C. pilot data, unloaded ripple and data to be transmitted structure are carried out to data pilot according to Comb Pilot form multiplexing, form OFDM transmitting data frame X;
D. OFDM transmitting data frame X is carried out to IFFT processing, add Cyclic Prefix to launch by sending module, the length that adds Cyclic Prefix is L, and the value of L is determined by actual channel condition;
E.OFDM receiving terminal is removed Cyclic Prefix by the signal receiving, and obtains receiving signal y, utilizes the time domain impulse noise interference that unloaded ripple is subject to it to estimate, and utilizes OMP algorithm to be reconstructed and to eliminate;
In step e, the detailed process that the described OMP of utilization algorithm is reconstructed can be:
Step 1: initialization, definition residual vector r, position vector P, makes r
0=y,
wherein
for empty set;
Step 2: iteration, suppose and carry out iteration the i time,
λ
i＝argmax|Θ
Tr
i-1|
In formula, i=1:K, K is iterations;
Step 3: upgrade P
i=[P
i-1, λ
i];
Step 4: solve;
In formula, Θ
ifor the row that extract from Θ, row number equal P
i;
Step 5: upgrade r
i=y-Θ
is
i;
Step 6: if i < is K, i=i+1, gets back to step 2 and be cycled to repeat; If i=K, stops iteration.
F. the signal of eliminating after time domain impulse noise interference is done to FFT processing, obtain Frame Y, and the significantly single-frequency noise extracting in Y is disturbed and eliminates, because the significantly single-frequency noise extracting has sparse property at frequency domain, do not need to carry out the conversion in territory, utilize observing matrix, according to above-mentioned OMP algorithm, can realize its reconstruct;
G. by eliminating signal data frame Y after single-frequency noise is significantly disturbed according to carrying out demultiplexing with the multiplexing identical method of transmitting terminal, the reception pilot data P' of corresponding OFDM and secured transmission of payload data D' are separated;
H. reception pilot data P' demultiplexing being obtained sends into channel estimation process device, by utilizing compressed sensing, obtains uplink channel estimation value H;
I. utilize the channel estimation value H obtaining to complete the data balancing on each sub-channels of OFDM, the secured transmission of payload data D' that is about to receive is divided by the channel estimation value H on correspondence position;
J. the valid data after equilibrium treatment are carried out to parallel-serial conversion, separate mediation channel decoding and process, the information source data that obtain finally recovering.
In ofdm system in step b, adopt Comb Pilot, can effectively reduce the quantity of pilot tone, thereby improve the availability of frequency spectrum of system.At receiving terminal, can utilize compressed sensing to carry out channel estimating, reduce underwater acoustic channel evaluated error, to guarantee the reciprocity of underwater acoustic channel simultaneously.
In transmitting data frame in step c, there is free carrier wave, at receiving terminal, can utilize unloaded ripple, time domain impulse noise interference is estimated, thereby can, based on orthogonal matching pursuit (OMP) algorithm, utilize observed quantity paired pulses noise jamming to eliminate.
In step e according to compressive sensing theory, utilize OMP algorithm that time domain impulse noise interference is reconstructed and is eliminated.
In step f, first extract significantly single-frequency noise and disturb, recycling compressed sensing is reconstructed and eliminates.
In step f, single-frequency noise is disturbed and is had sparse property at frequency domain, does not need to carry out the conversion in territory, utilizes observing matrix, according to OMP algorithm, can realize its reconstruct.
After elimination time domain impulse noise interference and significantly single-frequency noise are disturbed, strengthened the robustness of system, improved precision of channel estimation, guaranteed that the channel condition information that up-downgoing channel estimating obtains has reciprocity property, makes underwater acoustic channel have reciprocity.
In step g by pilot tone with send after data separating, based on compressive sensing theory, utilize OMP algorithm to carry out channel estimating, improve precision of channel estimation, thereby the reciprocity property that guarantees the channel condition information that up-downgoing channel estimating obtains, makes underwater acoustic channel have reciprocity.
In step I, according to the channel estimation value that utilizes compressed sensing to obtain, carry out channel equalization, eliminate I/Q asymmetric, guarantee the reciprocity property of the channel condition information that up-downgoing channel estimating obtains, make underwater acoustic channel there is reciprocity.
The present invention utilizes compressive sensing theory to eliminate impulse noise interference and the significantly impact of single-frequency noise interference in OFDM underwater sound communication system.At impulse noise interference with when significantly single-frequency noise is disturbed reconstruct, adopt orthogonal matching pursuit (OMP) algorithm, utilize the observed quantity of receiving terminal to eliminate noise jamming.Elimination impulse noise interference and significantly single-frequency noise are disturbed the Different Effects that uplink and downlink signals is produced, and guarantee the reciprocity property of the channel condition information that up-downgoing channel estimating obtains, and make underwater acoustic channel have reciprocity.
The present invention utilizes compressive sensing theory to eliminate impulse noise interference and the significantly impact of single-frequency noise interference in OFDM underwater sound communication system, thereby guarantees the reciprocity of underwater acoustic channel.The present invention is according to compressive sensing theory, adopt orthogonal matching pursuit (OMP) algorithm to time domain impulse noise interference and significantly single-frequency noise interference be reconstructed, utilize observed quantity to eliminate it.Elimination impulse noise interference and significantly single-frequency noise are disturbed the Different Effects that uplink and downlink signals is produced, and guarantee the reciprocity property of the channel condition information that up-downgoing channel estimating obtains, and make underwater acoustic channel have reciprocity.
The invention provides impulse noise interference and the scheme of single-frequency noise interference significantly eliminated in underwater acoustic channel, design a kind of interference asymmetry problem that solves sending and receiving end in OFDM underwater sound communication system, with above-mentioned channel prediction method, equalization methods and utilize compression sensing method to carry out channel estimating one to be used from and to determine uplink downlink communication channel characteristics, guarantee the reciprocity of underwater acoustic channel.
The present invention obtains accurate channel parameter for receiving signal from OFDM, guarantee the reciprocity of underwater acoustic channel, according to compressive sensing theory, use OMP algorithm to time domain impulse noise interference and significantly single-frequency noise interference be reconstructed, utilize observed quantity to eliminate it.For time domain impulse noise interference, at the unloaded ripple of receiving terminal utilization, it is estimated, and utilize OMP algorithm to be reconstructed and to eliminate.And the significantly single-frequency noise that receiving terminal extracts has sparse property at frequency domain, do not need to carry out the conversion in territory, utilize observing matrix, according to OMP algorithm, realize its reconstruct and eliminate.Up-downgoing underwater acoustic channel after elimination time domain impulse noise interference and significantly single-frequency noise are disturbed has identical channel status, and underwater acoustic channel has reciprocity.
Accompanying drawing explanation
Fig. 1 is for being used the uplink OFDM of the inventive method to transmit and receive working-flow schematic diagram.
Fig. 2 is the schematic diagram of assurance underwater acoustic channel reciprocity of the present invention.
Fig. 3 is the simulation result that the embodiment of the present invention is eliminated time domain impulse noise interference.Wherein a line represents to contain time domain impulse noise interference in signal, and receiving terminal does not carry out the simulation result of impulse noise interference elimination; B line is illustrated in the simulation result after receiving terminal is eliminated time domain impulse noise interference; C line represents that signal is not subject to the simulation result of time domain impulse noise interference impact.
Fig. 4 is that the embodiment of the present invention is eliminated the simulation result that significantly single-frequency noise is disturbed.Wherein a line represents that in signal, containing significantly single-frequency noise disturbs, and receiving terminal does not carry out the simulation result of noise jamming elimination; B line is illustrated in receiving terminal single-frequency noise is significantly disturbed to the simulation result after eliminating; C line represents that signal is not subject to the significantly simulation result of single-frequency noise interference effect.
Embodiment
The present invention is further illustrated in connection with accompanying drawing for following examples.
Referring to Fig. 1 and 2, take up link as example, the specific implementation step that the embodiment of the present invention obtains underwater acoustic channel reciprocity method is as follows:
(1) information source data are carried out to chnnel coding, QPSK modulation, goes here and there and changes, what become N-N_pilot-N_zeros sub-carrier formats needs secured transmission of payload data D, and wherein, N is the length of OFDM transmission system frame, N_pilot is pilot length, the number that N_zeros is unloaded ripple;
(2) produce subcarrier pilot data, the length that produces pilot data is decided by OFDM transmission system frame structure, and what the present invention adopted is Comb Pilot.Pilot length is N_pilot=256, and unloaded ripple number is N_zeros=96, and an OFDM frame length is N=1024.Pilot tone is for the channel estimating of receiving terminal, and unloaded ripple is used for eliminating time domain impulse noise interference;
(3) pilot data and data to be transmitted structure are carried out to data pilot according to Comb Pilot form multiplexing, form OFDM transmitting data frame X;
(4) OFDM transmitting data frame X is carried out to N=1024 point IFFT and process, add Cyclic Prefix to launch by sending module.The length that adds Cyclic Prefix is L, and the value of L is decided by actual channel condition, and the present invention gets counting as N/4 of L, is 256;
(5) OFDM receiving terminal is removed Cyclic Prefix by the signal receiving, and obtaining length is the reception signal y of N=1024, utilizes the time domain impulse noise interference that unloaded ripple is subject to it to estimate, and utilizes OMP algorithm to be reconstructed and to eliminate.Concrete OMP algorithm restructuring procedure is as follows:
Step 1: initialization, definition residual vector r, position vector P, makes r
0=
y,
wherein
for empty set.
Step 2: iteration, suppose and carry out iteration the i time,
λ
i＝argmax|Θ
Tr
i-1|
In formula, i=1:K, K is iterations.
Step 3: upgrade P
i=[P
i-1, λ
i]
Step 4: solve
In formula, Θ
ifor the row that extract from Θ, row number equal P
i.
Step 5: upgrade r
i=y-Θ
is
i
Step 6: if i < is K, i=i+1, gets back to step 2 and be cycled to repeat; If i=K, stops iteration.
(6) signal of eliminating after time domain impulse noise interference is done to N=1024 point FFT processing, obtain Frame Y, and the significantly single-frequency noise extracting in Y is disturbed and eliminates.Because the significantly single-frequency noise extracting has sparse property at frequency domain, do not need to carry out the conversion in territory, utilize observing matrix, according to above-mentioned OMP algorithm, can realize its reconstruct;
(7) by eliminating signal data frame Y after single-frequency noise is significantly disturbed according to carrying out demultiplexing with the multiplexing identical method of transmitting terminal, the reception pilot data P' of corresponding OFDM and secured transmission of payload data D' are separated;
(8) reception pilot data P' demultiplexing being obtained sends into channel estimation process device, by utilizing compressed sensing, obtains uplink channel estimation value H;
(9) utilize the channel estimation value H obtaining to complete the data balancing on each sub-channels of OFDM, the secured transmission of payload data D' that is about to receive is divided by the channel estimation value H on correspondence position;
(10) valid data after equilibrium treatment are carried out to parallel-serial conversion, separate mediation channel decoding and process, the information source data that obtain finally recovering.
According to the method described above, eliminate time domain impulse noise interference and uplink channel estimation value H that significantly single-frequency noise obtains after disturbing and be equal to the down channel estimated value H' that eliminates time domain impulse noise interference and significantly obtain after single-frequency noise interference, make underwater acoustic channel there is reciprocity.
Because underwater acoustic channel is quite complicated, the noise jamming that signal is subject to is along with marine environment and ship disturb and constantly change.Therefore the present invention compares with list of references of the prior art [11] [12] [13] [14], the embodiment of the present invention is by eliminating noise jamming (as shown in Figure 1) in sending and receiving end, to guarantee that the channel estimation value of up link can, for the channel estimating of down link, guarantee the reciprocity of underwater acoustic channel.
Figure 1 shows that and use the up link OFDM of the inventive method to transmit and receive working-flow schematic diagram.As shown in Figure 1, transmitting terminal carries out chnnel coding by information source data, and QPSK modulation, goes here and there and change, and the data to be transmitted obtaining and pilot data carry out data-reusing processing by dressing form, then data are sent into IFFT unit, then are added Cyclic Prefix.After underwater acoustic channel, receiving terminal removes the signal receiving to Cyclic Prefix and eliminates time domain impulsive noise and process, carry out again FFT and eliminate significantly single-frequency noise and process, the data that obtain carry out obtaining respectively pilot tone and valid data after data pilot demultiplexing, utilize compressed sensing to process pilot data, obtain corresponding underwater acoustic channel estimated parameter, and utilize channel estimating parameter to carry out channel equalization to the valid data that receive, and then through parallel-serial conversion, solution mediation channel decoding, process respectively the information source data that are finally restored.And after elimination noise jamming, utilize the uplink channel estimation value that compressed sensing obtains can be for the channel estimating of down link.
Figure 2 shows that the schematic diagram of assurance underwater acoustic channel reciprocity of the present invention.As shown in Figure 2, in order to obtain the underwater acoustic channel that uplink downlink is equal, at uplink downlink, all utilize compressive sensing theory to carry out noise jamming elimination.
Figure 3 shows that the system emulation figure of time domain impulse noise interference elimination when unlike signal noise ratio.Black line represents to contain time domain impulse noise interference in signal, and receiving terminal does not carry out the simulation result of impulse noise interference elimination; Blue line is illustrated in the simulation result after receiving terminal is eliminated time domain impulse noise interference; Red line represents that signal is not subject to the impact of time domain impulse noise interference.As seen from Figure 3, from 2dB, the method that the present invention proposes can obtain very large performance gain.Fig. 3 shows based on compressed sensing, utilizes OMP algorithm can effectively eliminate time domain impulse noise interference, and systematic function is greatly improved, and has improved receiving terminal precision of channel estimation.
Figure 4 shows that significantly single-frequency noise is disturbed the system emulation figure of eliminating when unlike signal noise ratio.Black line represents that in signal, containing significantly single-frequency noise disturbs, and receiving terminal does not carry out significantly single-frequency noise and disturbs the simulation result of eliminating; Blue line is illustrated in receiving terminal single-frequency noise is significantly disturbed to the simulation result after eliminating; Red line represents that signal is not subject to the impact that significantly single-frequency noise is disturbed.As seen from Figure 4, eliminating system bit error rate after single-frequency noise is significantly disturbed is in close proximity to and does not add the system bit error rate that significantly single-frequency noise is disturbed.Fig. 4 shows that method that the present invention proposes can effectively eliminate significantly single-frequency noise and disturb equally, improved the precision of channel estimation of receiving terminal, guaranteed that the channel condition information that up-downgoing channel estimating obtains has reciprocity property, makes underwater acoustic channel have reciprocity.
Claims (2)
1. utilize compressed sensing to obtain a method for underwater acoustic channel reciprocity, it is characterized in that concrete steps are as follows:
A. information source data are carried out to chnnel coding, QPSK modulation, goes here and there and changes, what become N-N_pilot-N_zeros sub-carrier formats needs secured transmission of payload data D, wherein N is the length of OFDM transmission system frame, and N_pilot is pilot length, the number that N_zeros is unloaded ripple;
B. produce subcarrier pilot data, the length that produces subcarrier pilot data is determined by OFDM transmission system frame structure, described pilot tone employing Comb Pilot, and Comb Pilot is for the channel estimating of receiving terminal, and unloaded ripple is used for eliminating time domain impulse noise interference;
C. pilot data, unloaded ripple and data to be transmitted structure are carried out to data pilot according to Comb Pilot form multiplexing, form OFDM transmitting data frame X;
D. OFDM transmitting data frame X is carried out to IFFT processing, add Cyclic Prefix to launch by sending module, the length that adds Cyclic Prefix is L, and the value of L is determined by actual channel condition;
E.OFDM receiving terminal is removed Cyclic Prefix by the signal receiving, and obtains receiving signal y, utilizes the time domain impulse noise interference that unloaded ripple is subject to it to estimate, and utilizes OMP algorithm to be reconstructed and to eliminate;
F. the signal of eliminating after time domain impulse noise interference is done to FFT processing, obtain Frame Y, and the significantly single-frequency noise extracting in Y is disturbed and eliminates, because the significantly single-frequency noise extracting has sparse property at frequency domain, do not need to carry out the conversion in territory, utilize observing matrix, according to above-mentioned OMP algorithm, can realize its reconstruct;
G. by eliminating signal data frame Y after single-frequency noise is significantly disturbed according to carrying out demultiplexing with the multiplexing identical method of transmitting terminal, the reception pilot data P' of corresponding OFDM and secured transmission of payload data D' are separated;
H. reception pilot data P' demultiplexing being obtained sends into channel estimation process device, by utilizing compressed sensing, obtains uplink channel estimation value H;
I. utilize the channel estimation value H obtaining to complete the data balancing on each sub-channels of OFDM, the secured transmission of payload data D' that is about to receive is divided by the channel estimation value H on correspondence position;
J. the valid data after equilibrium treatment are carried out to parallel-serial conversion, separate mediation channel decoding and process, the information source data that obtain finally recovering.
2. a kind of method of utilizing compressed sensing to obtain underwater acoustic channel reciprocity as claimed in claim 1, is characterized in that in step e, and the detailed process that the described OMP of utilization algorithm is reconstructed is:
Step 1: initialization, definition residual vector r, position vector P, makes r
0=y,
wherein
for empty set;
Step 2: iteration, suppose and carry out iteration the i time,
λ
i＝argmax|Θ
Tr
i-1|
In formula, i=1:K, K is iterations;
Step 3: upgrade P
i=[P
i-1, λ
i];
Step 4: solve;
In formula, Θ
ifor the row that extract from Θ, row number equal P
i;
Step 5: upgrade r
i=y-Θ
is
i;
Step 6: if i < is K, i=i+1, gets back to step 2 and be cycled to repeat; If i=K, stops iteration.
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